Phase relations and Gibbs energies of spinel phases and solid solutions in the system Mg-Rh-O

Energy Technology Data Exchange (ETDEWEB)

Jacob, K.T., E-mail: katob@materials.iisc.ernet.in [Department of Materials Engineering, Indian Institute of Science, Bangalore 560 012 (India); Prusty, Debadutta [Department of Materials Engineering, Indian Institute of Science, Bangalore 560 012 (India); Kale, G.M. [Institute for Materials Research, University of Leeds, Leeds, LS2 9JT (United Kingdom)

2012-02-05

Highlights: Black-Right-Pointing-Pointer Refinement of phase diagram for the system Mg-Rh-O and thermodynamic data for spinel compounds MgRh{sub 2}O{sub 4} and Mg{sub 2}RhO{sub 4} is presented. Black-Right-Pointing-Pointer A solid-state electrochemical cell is used for thermodynamic measurement. Black-Right-Pointing-Pointer An advanced design of the solid-state electrochemical cell incorporating buffer electrodes is deployed to minimize polarization of working electrode. Black-Right-Pointing-Pointer Regular solution model for the spinel solid solution MgRh{sub 2}O{sub 4} - Mg{sub 2}RhO{sub 4} based on ideal mixing of cations on the octahedral site is proposed. Black-Right-Pointing-Pointer Factors responsible for stabilization of tetravalent rhodium in spinel compounds are identified. - Abstract: Pure stoichiometric MgRh{sub 2}O{sub 4} could not be prepared by solid state reaction from an equimolar mixture of MgO and Rh{sub 2}O{sub 3} in air. The spinel phase formed always contained excess of Mg and traces of Rh or Rh{sub 2}O{sub 3}. The spinel phase can be considered as a solid solution of Mg{sub 2}RhO{sub 4} in MgRh{sub 2}O{sub 4}. The compositions of the spinel solid solution in equilibrium with different phases in the ternary system Mg-Rh-O were determined by electron probe microanalysis. The oxygen potential established by the equilibrium between Rh + MgO + Mg{sub 1+x}Rh{sub 2-x}O{sub 4} was measured as a function of temperature using a solid-state cell incorporating yttria-stabilized zirconia as an electrolyte and pure oxygen at 0.1 MPa as the reference electrode. To avoid polarization of the working electrode during the measurements, an improved design of the cell with a buffer electrode was used. The standard Gibbs energies of formation of MgRh{sub 2}O{sub 4} and Mg{sub 2}RhO{sub 4} were deduced from the measured electromotive force (e.m.f.) by invoking a model for the spinel solid solution. The parameters of the model were optimized using the measured

Spinel-structured surface layers for facile Li ion transport and improved chemical stability of lithium manganese oxide spinel

Energy Technology Data Exchange (ETDEWEB)

Lee, Hae Ri [Center for Energy Convergence Research, Korea Institute of Science Technology, Hwarang-ro 14-gil 5, Seongbuk-gu, Seoul 136-791 (Korea, Republic of); Department of Chemical and Biological Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul 136-701 (Korea, Republic of); Seo, Hyo Ree; Lee, Boeun; Cho, Byung Won [Center for Energy Convergence Research, Korea Institute of Science Technology, Hwarang-ro 14-gil 5, Seongbuk-gu, Seoul 136-791 (Korea, Republic of); Lee, Kwan-Young [Department of Chemical and Biological Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul 136-701 (Korea, Republic of); Oh, Si Hyoung, E-mail: sho74@kist.re.kr [Center for Energy Convergence Research, Korea Institute of Science Technology, Hwarang-ro 14-gil 5, Seongbuk-gu, Seoul 136-791 (Korea, Republic of)

2017-01-15

Graphical abstract: Strategically-designed spinel-structured nano-scale surface layer, LiM{sub x}Mn{sup IV}{sub 1−x}O{sub 4}, featuring a high Li{sup +} ion conductivity and a good chemical stability was applied on Al-doped LiMn{sub 2}O{sub 4} spinel for the drastic improvement of the electrochemical performance at the elevated temperature as a promising cathode material for lithium rechargeable batteries. - Highlights: • Spinel-structured surface layer with a high Li-ion conductivity and a good chemical stability was prepared. • Simple wet process was developed to apply nano-scale surface layer on aluminum doped lithium manganese oxide spinel. • The properties of nano-scale surface layer were characterized by analytical tools including GITT, HR-TEM and XAS. • Materials with surface coating layer exhibit an excellent electrochemical performance at the elevated temperature. - Abstract: Li-ion conducting spinel-structured oxide layer with a manganese oxidation state close to being tetravalent was prepared on aluminum-doped lithium manganese oxide spinel for improving the electrochemical performances at the elevated temperatures. This nanoscale surface layer provides a good ionic conduction path for lithium ion transport to the core and also serves as an excellent chemical barrier for protecting the high-capacity core material from manganese dissolution into the electrolyte. In this work, a simple wet process was employed to prepare thin LiAlMnO{sub 4} and LiMg{sub 0.5}Mn{sub 1.5}O{sub 4} layers on the surface of LiAl{sub 0.1}Mn{sub 1.9}O{sub 4}. X-ray absorption studies revealed an oxidation state close to tetravalent manganese on the surface layer of coated materials. Materials with these surface coating layers exhibited excellent capacity retentions superior to the bare material, without undermining the lithium ion transport characteristics and the high rate performances.

Spinel Li2CoTi3O8 nanometer obtained for application as pigment

International Nuclear Information System (INIS)

Costa de Camara, M. S.; Alves Pimentel, L.; Longo, E.; Nobrega Azevedo, L. da; Araujo Melo, D. M. de

2016-01-01

Pigments are used in ceramics, cosmetics, inks, and other applications widely materials. To this must be single and easily reproducible. Moreover, the pigments obtained in the nanoscale are more stable, reproducible and highlight color in small amounts compared with those obtained in micrometer scale. The mixed oxides with spinel structures AB 2 O 4 have important applications, including: pigments, refractories, catalytic and electronic ceramics. In this context, the aim of this work was the preparation of powder Li 2 CoTi 3 O 8 spinel phase with nanometer particle size of the polymeric precursor method (Pechini) and characterization by means of thermal analysis (TG/DTA) X-ray diffraction (XRD), refined by the Rietveld method, BET, transmission electron microscopy (TEM), Raman and colorimetric coordinates. The pigment was obtained by heat treatment of 400 degree centigrade to 1000 degree centigrade after pyrolysis at 300 degree centigrade/1 h for removing the organic material. Li 2 CoTi 3 O 8 desired spinel phase was obtained from 500 degree centigrade, and presenting stability nanometer to about 1.300 degree centigrade. Spinel green phase introduced at temperatures in the range of 400 degree centigrade and 500 degree centigrade, and 600 degree centigrade at temperatures between blue and 1000 degree centigrade. (Author)

A new high-pressure phase of Fe2SiO4 and the relationship between spin and structural transitions

Science.gov (United States)

Yamanaka, T.; Kyono, A.; Nakamoto, Y.; Kharlamova, S. A.; Struzhkin, V. V.; Gramsch, S.; Mao, H.; Hemley, R. J.

2013-12-01

Structure transformation of Fe2SiO4 Angle-dispersive powder x-ray diffraction was carried out at beam line 16-BMD APS. Structure of a new high-pressure phase of I-Fe2SiO4 spinel was determined by Rietveld profile fitting of x-ray diffraction data up to 64GPa at ambient temperature. A structural transition from the cubic spinel to the new structure was observed at 34GPa. Diffraction patterns taken at 44.6GPa and 54.6GPa indicate a two-phase mixture of spinel and new high-pressure phase. Reversible transition from I-Fe2SiO4 to spinel was confirmed. Laser heating experiment at 1500K proved the decomposition of Fe2SiO4 spinel to two oxides of FeO and SiO2. Spin transition X-ray emission measurements of Fe2SiO4 were carried out up to 65GPa at ambient temperature at beam line 16-IDD APS. The spin transition exerts an influence to Fe2SiO4 spinel structure and triggers two distinct curves of the lattice constant in the spinel phase. Although the compression curve of the spinel is discontinuous at approximately 20 GPa, Fe Kβ emission measurements show that the transition from a high spin (HS) to an intermediate spin (IS) state begins at 17GPa in the spinel phase. The IS electronic state is gradually enhanced with pressure, which results in an isostructural phase transition. HS-to-LS transition of iron bearing spinels starts from 15.6GPa in Fe3O4 and 19.6GPa in Fe2TiO4. The transition is more capable due to Fe2+ in the octahedral site. The extremely shortened octahedral bonds result in a distortion of 6-fold cation site. New structure of Fe2SiO4 Monte Carlo method was applied to find candidates for the high-pressure phase using the diffraction intensities with fixed lattice constants determined by DICVOL. Rietveld profile fitting was then performed using the initial model. The new structure is a body centered orthorhombic phase (I-Fe2SiO4) with space group Imma and Z=4, with two crystallographically distinct FeO6 octahedra. Silicon exists in six-fold coordination in I-Fe2Si

Synthesis and characterization of advanced high capacity cathode active nanomaterials with three integrated spinel-layered phases for Li-ion batteries

Energy Technology Data Exchange (ETDEWEB)

Bulut, Emrah, E-mail: ebulut@sakarya.edu.tr [Department of Chemistry, Sakarya University, 54187 Serdivan, Sakarya (Turkey); Can, Mustafa, E-mail: mstfacan@gmail.com [Vocational School of Arifiye, Sakarya University, 54580 Arifiye, Sakarya (Turkey); Özacar, Mahmut, E-mail: nmozacart@hotmail.com [Department of Chemistry, Sakarya University, 54187 Serdivan, Sakarya (Turkey); Akbulut, Hatem, E-mail: akbulut@Sakarya.edu.tr [Department of Metallurgical and Materials Engineering, Sakarya University, 54187 Serdivan, Sakarya (Turkey)

2016-06-15

Mesoporous cathode active materials that included undoped and separated Cu{sup 2+} and Co{sup 3+} doped spinels were prepared. The “doped spinel-Layered-Li-rich spinel” composite nanoparticles within the three integrated phased (LiM{sub 0,02}Mn{sub 1,98}O{sub 4}–Li{sub 2}MnO{sub 3}–Li{sub 1,27}Mn{sub 1,73}O{sub 4}; where M is Cu{sup 2+} and Co{sup 3+}) were synthesized by a microwave assisted hydrothermal synthesis. These materials were investigated with X-Ray powder Diffraction spectroscopy (XRD), Scanning Electron Microscopy (SEM and FE-SEM), High Resolution Transmission Electron Microscopy (HR-TEM), galvanostatic cycling at 0.1C and 0.5C rates, Cyclic Voltammetry (CV), and Electrochemical Impedance Spectroscopy (EIS). The effects of the calcination temperature and the partial substitution of Mn{sup 3+} in the spinel by Cu{sup 2+} and Co{sup 3+}, and onto the spinel structure were investigated with XRD. The lattice parameters of the spinel structured compounds were calculated from the XRD data using the Williamson-Hall equation. However, the morphological changes, which depended on the calcination temperature, were examined by SEM, FE-SEM and HRTEM. Furthermore, the two other phases which were different from LiM{sub 0,02}Mn{sub 1,98}O{sub 4} had a great impact on the electrochemical performance over the potential range of the 3–5 V. At the 0.1C rate, the first discharge capacities of undoped and Cu{sup 2+}, Co{sup 3+} doped materials were 577, 285, 560 mAh/g respectively. After 50 cycles at 0.5C rate, we achieved 96.2%; 52.5%; 95.4% capacity retention for the undoped and Cu{sup 2+}, Co{sup 3+} doped materials respectively. - Highlights: • Mesoporous cathode active nanomaterials with three integrated phase were synthesized. • The materials were characterized structurally by XRD, FE-SEM, HR-TEM. • Integrated phases provide an additional 400 mAh/g discharge capacity at low rate. • Higher specific capacities than literature values were achieved at 0

Single-crystalline MgAl2O4 spinel nanotubes using a reactive and removable MgO nanowire template

International Nuclear Information System (INIS)

Fan Hongjin; Knez, Mato; Scholz, Roland; Nielsch, Kornelius; Pippel, Eckhard; Hesse, Dietrich; Goesele, Ulrich; Zacharias, Margit

2006-01-01

Using MgO nanowires as a reactive template, we fabricated for the first time single-crystal MgAl 2 O 4 spinel nanotubes through an interfacial solid-state reaction of MgO-Al 2 O 3 core-shell nanowires. Single-crystal MgO nanowires are coated with a conformal thin layer of amorphous Al 2 O 3 via atomic layer deposition. Subsequent annealing at 700 deg. C activates the interfacial reaction between MgO and Al 2 O 3 , transforming the alumina shell into a spinel shell. Finally, after etching away the remaining MgO core in ammonia sulfuric solution, MgAl 2 O 4 spinel nanotubes are obtained. As a transition from conventional planar spinel layers via thin-film interface reactions, our result might open a window for the fabrication of a wide variety of MgO-based spinel one-dimensional nanostructures

Effects of synthetic parameters on structure and electrochemical performance of spinel lithium manganese oxide by citric acid-assisted sol-gel method

International Nuclear Information System (INIS)

Yi Tingfeng; Dai Changsong; Gao Kun; Hu Xinguo

2006-01-01

The spinel lithium manganese oxide cathode materials were prepared by citric acid-assisted sol-gel method at 623-1073 K in air. The effects of pH value, raw material, synthesis temperature and time on structure and electrochemical performance of spinel lithium manganese oxide are investigated by X-ray diffraction (XRD), scanning electronic microscope (SEM) and cyclic voltammetry (CV). XRD data results strongly suggest that the synthesis temperature is the dominating factors of the formation of spinel phase, and spinel lithium manganese oxide powder with various crystallites size can be obtained by controlling the sintering time. CV shows that spinel lithium manganese oxide powder formed about 973 K presents the best electrochemical performance with well separated two peaks and the highest peak current. Charge-discharge test indicates that spinel lithium manganese oxide powders calcined at higher temperatures have high discharge capacity and capacity loss, and sintered at lower temperatures has low discharge capacity and high capacity retention

Effects of synthetic parameters on structure and electrochemical performance of spinel lithium manganese oxide by citric acid-assisted sol-gel method

Energy Technology Data Exchange (ETDEWEB)

Yi Tingfeng [Department of Applied Chemistry, Harbin Institute of Technology, Harbin 150001 (China)]. E-mail: tfyihit@hit.edu.cn; Dai Changsong [Department of Applied Chemistry, Harbin Institute of Technology, Harbin 150001 (China); Gao Kun [Department of Applied Chemistry, Harbin Institute of Technology, Harbin 150001 (China); Hu Xinguo [Department of Applied Chemistry, Harbin Institute of Technology, Harbin 150001 (China)

2006-11-30

The spinel lithium manganese oxide cathode materials were prepared by citric acid-assisted sol-gel method at 623-1073 K in air. The effects of pH value, raw material, synthesis temperature and time on structure and electrochemical performance of spinel lithium manganese oxide are investigated by X-ray diffraction (XRD), scanning electronic microscope (SEM) and cyclic voltammetry (CV). XRD data results strongly suggest that the synthesis temperature is the dominating factors of the formation of spinel phase, and spinel lithium manganese oxide powder with various crystallites size can be obtained by controlling the sintering time. CV shows that spinel lithium manganese oxide powder formed about 973 K presents the best electrochemical performance with well separated two peaks and the highest peak current. Charge-discharge test indicates that spinel lithium manganese oxide powders calcined at higher temperatures have high discharge capacity and capacity loss, and sintered at lower temperatures has low discharge capacity and high capacity retention.

Low Temperature Synthesis of Magnesium Aluminate Spinel

International Nuclear Information System (INIS)

Lebedovskaya, E.G.; Gabelkov, S.V.; Litvinenko, L.M.; Logvinkov, D.S.; Mironova, A.G.; Odejchuk, M.A.; Poltavtsev, N.S.; Tarasov, R.V.

2006-01-01

The low-temperature synthesis of magnesium-aluminum spinel is carried out by a method of thermal decomposition in combined precipitated hydrates. The fine material of magnesium-aluminium spinel with average size of coherent dispersion's area 4...5 nanometers is obtained. Magnesium-aluminum spinel and initial hydrates were investigated by methods of the differential thermal analysis, the x-ray phase analysis and measurements of weight loss during the dehydration and thermal decomposition. It is established that synthesis of magnesium-aluminum spinel occurs at temperature 300 degree C by method of the x-ray phase analysis

Low-temperature synthesis of single-phase Co7Sb2O12

International Nuclear Information System (INIS)

Brito, M.S.L.; Escote, M.T.; Santos, C.O.P.; Lisboa-Filho, P.N.; Leite, E.R.; Oliveira, J.B.L.; Gama, L.; Longo, E.

2004-01-01

Polycrystalline Co 7 Sb 2 O 12 compounds have been synthesized by a chemical route, which is based on a modified polymeric precursor method. In order to study the physical properties of the samples, X-ray diffraction (XRD), thermal analyses (TG and DSC), infrared spectroscopy (IR), specific surface area (BET), and magnetization measurements were performed on these materials. Characterization through XRD revealed that the samples are single-phase after a heat-treatment at 1100 deg. C for 2 h, while the X-ray patterns of the samples heat-treated at lower temperatures revealed the presence of additional Bragg reflections belonging to the Co 6 Sb 2 O 6 phase. These data were analyzed by means of Rietveld refinement and further analyze showed that Co 7 Sb 2 O 12 displays an inverse spinel crystalline structure. In this structure, the Co 2+ ions occupy the eight tetrahedral positions, and the sixteen octahedral positions are randomly occupied by the Sb 5+ and Co 2+ ions. IR studies disclosed two strong absorption bands, ν 1 and ν 2 , in the expected spectral range for a spinel-type binary oxide with space group Fd3m. Exploratory studies concerning the magnetic properties indicated that this sample presents a spin-glass transition at T f ∼ 64 K

Structure and electromagnetic properties of NiZn spinel ferrite with nano-sized ZnAl{sub 2}O{sub 4} additions

Energy Technology Data Exchange (ETDEWEB)

Zheng, Zongliang, E-mail: zzlma@163.com; Zhang, Huaiwu; Yang, Qinghui; Jia, Lijun

2015-11-05

In this study, nanocrystalline ZnAl{sub 2}O{sub 4} (ZA) (x = 0–20 wt%) were introduced into Ni{sub 0.4}Zn{sub 0.6}Fe{sub 2}O{sub 4} ferrite (NZ) by a solid-state reaction method combining a sol–gel auto-combustion method. The effects of ZA addition on the crystalline phase formation, microstructures, magnetic and dielectric properties were systematically investigated. X-ray diffraction and scanning electron microscope results reveal that the added ZA can fully solve into the NZ to form a ceramic with single-phase cubic spinel structure, and the grain size decreases obviously as x > 5 wt%. Meanwhile, the magnetic and dielectric properties exhibit significantly dependent on the ZA addition content. With the increasing addition level of ZA from 0 to 20 wt%, the initial permeability μ{sub i} is found increased initially and then decreased with the maximum 679 at x = 0.5 wt%. For the samples with x ≤ 5 wt%, permittivity ε′ is relatively higher at low frequencies (ε′ = 91–138 at 1 MHz) and dielectric loss tan δ{sub ε} shows distinct peak behavior. When x reaches 10 wt%, however, the ε′ and tan δ{sub ε} show very stable spectra from 1 MHz to 1 GHz. - Highlights: • Various amount of nanocrystalline ZnAl{sub 2}O{sub 4} (ZA) were introduced into NiZn ferrite. • NiZn ferrite can form single-phase spinel ceramic materials with ZA additives. • ZA has significant effects on magnetic and dielectric properties of the ceramics. • It provides a new method for fabricating NiZn ferrite with tunable properties.

Ferromagnetic-phase transition in the spinel-type CuCr2Te4

International Nuclear Information System (INIS)

Suzuyama, Takeshi; Awaka, Junji; Yamamoto, Hiroki; Ebisu, Shuji; Ito, Masakazu; Suzuki, Takashi; Nakama, Takao; Yagasaki, Katsuma; Nagata, Shoichi

2006-01-01

Ferromagnetic-phase transition in spinel-type CuCr 2 Te 4 has been clearly observed. CuCr 2 Te 4 is a telluride-spinel with the lattice constant a=11.134A, which has been synthesized successfully. The heat capacity exhibits a sharp peak due to the ferromagnetic-phase transition with the Curie temperature T C =326K. This value of T C corresponds exactly to that of the negative peak of dM/dT in low field of 1.0Oe. The magnetic susceptibility shows the Curie-Weiss behavior between 380 and 650K with the effective magnetic moment μ eff =4.14μ B /Cr-ion and the Weiss constant θ=+357K. The low temperature magnetization indicates the spin-wave excitations, where the existence of first term of Bloch T 3/2 law and the next T 5/2 term are verified experimentally. This spin-wave excitation is detected up to approximately 250K which is a fairly high temperature

Inhomogeneous magnetic phase in Co–Al–O spinel nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Sato, K., E-mail: sato.koichi@nims.go.jp [National Institute for Materials Science, 2-1-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Naka, T., E-mail: naka.takashi@nims.go.jp [National Institute for Materials Science, 2-1-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Nakane, T. [National Institute for Materials Science, 2-1-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Rangappa, D. [International Advanced Research Centre for Powder Metallurgy and New Materials, Balapur PO, Hyderabad 500-005 (India); Takami, S. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan); Ohara, S. [Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Adschiri, T. [WPI, Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577 (Japan)

2014-01-15

We report on the crystallographic structure and magnetism of 5-nm Co–Al–O spinel nanocrystals synthesized under supercritical hydrothermal conditions. Structural examination using powder X-ray diffraction and chemical analysis showed the composition of the sample to be Co{sub 0.47}Al{sub 2.36}O{sub 4} rather than the stoichiometric composition of CoAl{sub 2}O{sub 4}. The site occupancy of Co on the A-site forming the diamond lattice was 0.47, which is slightly larger than the site percolation limit. Magnetization measurements showed that magnetic clusters emerged below 40 K. At temperatures below 40 K, a Griffiths-phase-like inhomogeneous state appeared in the sample in which magnetic clusters and paramagnetic spins coexisted. The dc-paramagnetic and ac-susceptibilities exhibited an anomaly below 7 K. - Highlights: • The synthesized sample had an Al-rich structure described by Co{sub 0.47}Al{sub 2.36}O{sub 4}. • The site occupancy of Co at the A-site is larger than the site percolation limit of the A-site. • The non-linearity of the magnetization appeared at T<40 K. • The paramagnetic component showed a peak at 7 K. • An inhomogeneous state is established in our Co–Al oxide nanocrystals.

Unique atom hyper-kagome order in Na4Ir3O8 and in low-symmetry spinel modifications.

Science.gov (United States)

Talanov, V M; Shirokov, V B; Talanov, M V

2015-05-01

Group-theoretical and thermodynamic methods of the Landau theory of phase transitions are used to investigate the hyper-kagome atomic order in structures of ordered spinels and a spinel-like Na4Ir3O8 crystal. The formation of an atom hyper-kagome sublattice in Na4Ir3O8 is described theoretically on the basis of the archetype (hypothetical parent structure/phase) concept. The archetype structure of Na4Ir3O8 has a spinel-like structure (space group Fd\\bar 3m) and composition [Na1/2Ir3/2](16d)[Na3/2](16c)O(32e)4. The critical order parameter which induces hypothetical phase transition has been stated. It is shown that the derived structure of Na4Ir3O8 is formed as a result of the displacements of Na, Ir and O atoms, and ordering of Na, Ir and O atoms, ordering dxy, dxz, dyz orbitals as well. Ordering of all atoms takes place according to the type 1:3. Ir and Na atoms form an intriguing atom order: a network of corner-shared Ir triangles called a hyper-kagome lattice. The Ir atoms form nanoclusters which are named decagons. The existence of hyper-kagome lattices in six types of ordered spinel structures is predicted theoretically. The structure mechanisms of the formation of the predicted hyper-kagome atom order in some ordered spinel phases are established. For a number of cases typical diagrams of possible crystal phase states are built in the framework of the Landau theory of phase transitions. Thermodynamical conditions of hyper-kagome order formation are discussed by means of these diagrams. The proposed theory is in accordance with experimental data.

Distribution of solute atoms in β- and spinel Si6-zAlzOzN8-z by Al K-edge x-ray absorption near-edge structure

International Nuclear Information System (INIS)

Tatsumi, Kazuyoshi; Mizoguchi, Teruyasu; Yoshioka, Satoru; Tanaka, Isao; Yamamoto, Tomoyuki; Suga, Takeo; Sekine, Toshimori

2005-01-01

Local environments of solutes in β- and spinel Si 6-z Al z O z N 8-z are investigated by means of Al K x-ray absorption near-edge structure. The experimental spectra are found to be the same throughout the wide solubility range. This suggests that the local environments of Al are independent of the solute concentration. First-principles band-structure calculations are systematically made to interpret the experimental spectra. Effect of a core hole was included into the calculation. Theoretical spectra were obtained using variety of different model structures constructed by a set of plane-wave pseudopotentials calculations in our previous study [K. Tatsumi, I. Tanaka, H. Adachi, and M. Yoshiya, Phys. Rev. B 66, 165210 (2002)]. The numbers of models were 51 and 45 for both β and spinel, respectively. They are classified and averaged according to the local atomic structure of Al solutes. The combination of experimental spectra and theoretical results can unambiguously lead to the conclusion that Al atoms are preferentially coordinated by O atoms in both β and spinel phases. This is consistent with the conclusion obtained by the first-principles total-energy calculations. In the spinel phase, Al atoms are found to be located preferentially at the octahedral cationic site. This agrees with the conclusion in a recent report on the nuclear magnetic resonance experiment

Melt growth of zinc aluminate spinel single crystal by the micro-pulling down method under atmospheric pressure

Science.gov (United States)

Kamada, K.; Shoji, Y.; Yamaji, A.; Kurosawa, S.; Yokota, Yuui; Ohashi, Y.; Kim, Kyoung Jin; Ivanov, M.; Kochurikhin, V. V.; Yoshikawa, A.

2018-06-01

ZnAl2O4 crystals were grown using few starting compositions with various ZnO:AlO3/2 ratio using an Ir wire seed and Ir + Re crucible under ordinary pressure with Ar + 2%O2 atmosphere by the radiofrequency heating μ-PD furnace. The ZnAl2O4 spinel single crystal with 4 mm diameter could be successfully grown by the μ-PD method by optimization of starting melt composition considering with Zinc oxide evaporation. During 10 min of growth under normal pressure the formation of ZnAl2O4 single phase observed even at high vapor pressure of ZnO. The transmittance spectra and X-ray locking curve were measured for evaluating of grown ZnAl2O4 crystals quality.

High energy density layered-spinel hybrid cathodes for lithium ion rechargeable batteries

Energy Technology Data Exchange (ETDEWEB)

Basu, S., E-mail: sbasumajumder@yahoo.com [Department of Physics, Indian Institute of Technology Kharagpur, Kharagpur 721 302 (India); Dahiya, P.P.; Akhtar, Mainul [Materials Science Center, Indian Institute of Technology Kharagpur, Kharagpur 721 302 (India); Ray, S.K. [Department of Physics, Indian Institute of Technology Kharagpur, Kharagpur 721 302 (India); Chang, J.K. [Institute of Materials Science and Engineering, National Central University, Taiwan (China); Majumder, S.B. [Materials Science Center, Indian Institute of Technology Kharagpur, Kharagpur 721 302 (India)

2016-11-15

Highlights: • Structural integration of layered domains in spinel matrix of the composite particles. • Highest discharge capacity (275 mAh g{sup −1}) in composite with 30.0 mole% Li{sub 2}MnO{sub 3}. • Reasonably good rate capability of layered-spinel composite cathode. • Capacity fading with cycling is related to cubic to tetragonal structural phase transition. - Abstract: High energy density Li{sub 2}MnO{sub 3} (layered)–LiMn{sub 1.5}Ni{sub 0.5}O{sub 4} (spinel) composite cathodes have been synthesized using auto-combustion route. Rietveld refinements together with the analyses of high resolution transmission electron micrographs confirm the structural integration of Li{sub 2}MnO{sub 3} nano-domains into the LiMn{sub 1.5}Ni{sub 0.5}O{sub 4} matrix of the composite cathodes. The discharge capacity of the composite cathodes are due to the intercalation of Li{sup +} ion in the tetrahedral (8a) and octahedral (16c) sites of the spinel component and also the insertion of Li{sup +} in the freshly prepared MnO{sub 2} lattice, formed after Li{sub 2}O extraction from the Li{sub 2}MnO{sub 3} domains. The capacity fading of the composite cathodes are explained to be due to the layered to spinel transition of the Li{sub 2}MnO{sub 3} component and Li{sup +} insertion into the octahedral site of the spinel lattices which trigger cubic to tetragonal phase transition resulting volume expansion which eventually retard the Li{sup +} intercalation with cycling.

Sol-gel synthesis and characterization of single-phase Ni ferrite nanoparticles dispersed in SiO2 matrix

International Nuclear Information System (INIS)

Nadeem, K.; Traussnig, T.; Letofsky-Papst, I.; Krenn, H.; Brossmann, U.; Wuerschum, R.

2010-01-01

Nanoparticles of NiFe 2 O 4 dispersed in SiO 2 (25 wt%) matrix were synthesized by sol-gel method using tetraethyl orthosilicate (TEOS), as a precursor for SiO 2 . The sol-gel method for nanocomposites normally provides multi-phase nanoparticles. We investigated by a synopsis of different analysis methods, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and SQUID-magnetometry, how the various chemical phases are transformed to a single-phase spinel structure during the various stages of annealing from 300 to 900 o C. We have developed a full phase diagram of chemical phases as a function of annealing temperature. The average particle size lies in the range 16-27 nm. The chemical phases formed below 900 o C are NiFe, NiO, γ-Fe 2 O 3 , α-Fe 2 O 3 , and NiFe 2 O 4 , respectively. The role of the TEOS prepared SiO 2 matrix is to restrict the particle size in a small range in order to rule out particle size effects. In the mid-infrared, a shift of the vibrational Fe-O bond is observed from 568 to 586 cm -1 for annealing between 500 and 700 o C which indicates an increasing NiFe 2 O 4 phase formation. A systematic study of coercivity field (ranging from 32 to 200 Oe) and saturation magnetic moment (ranging from 12.2 to 32.1 emu/g) for differently annealed samples supports our findings about the evolution of single-phase NiFe 2 O 4 at 900 o C. The opposite trend of saturation magnetic moment and coercivity with respect to annealing temperature clearly separates the different phases of metallic, antiferromagnetic, and finally single-phase spinel NiFe 2 O 4 .

Restitic or not? Insights from trace element content and crystal - Structure of spinels in African mantle xenoliths

Science.gov (United States)

Lenaz, Davide; Musco, Maria Elena; Petrelli, Maurizio; Caldeira, Rita; De Min, Angelo; Marzoli, Andrea; Mata, Joao; Perugini, Diego; Princivalle, Francesco; Boumehdi, Moulay Ahmed; Bensaid, Idris Ali Ahmadi; Youbi, Nasrrddine

2017-05-01

The lithospheric architecture of Africa consists of several Archean cratons and smaller cratonic fragments, stitched together and flanked by polycyclic fold belts. Here we investigate the structure and chemistry of spinels from lithospheric mantle xenoliths from distinct tectonic settings, i.e. from the Saharan metacraton in Libya (Waw-En-Namus) which could show archaic chemical features, Cameroon (Barombi Koto and Nyos Lakes) where the Sub Continental Lithospheric Mantle was modified during the Pan-African event and fluxed by asthenospheric melts of the Tertiary Cameroon Volcanic Line and Morocco (Tafraoute, Bou-Ibalrhatene maars) in the Middle Atlas where different metasomatic events have been recorded. From a structural point of view it is to notice that the Libyan spinels can be divided into two groups having different oxygen positional parameter (u > 0.2632 and u Morocco spinels show a Tc in the range 630-760 °C. About 150 different spinels have been studied for their trace element content and it can be seen that many of them are related to Cr content, while Zn and Co are not and clearly distinguish the occurrences. Differences in the trace element chemistry, in the structural parameters and in the intracrystalline closure temperatures suggest that a different history should be considered for Cameroon, Morocco and LB I and LB II spinels. Even if it was not considered for this purpose, we tentatively used the Fe2 +/Fe3 + vs. TiO2 diagram that discriminate between peridotitic and the so-called "magmatic" spinels, i.e. spinel crystallized from melts. LB I and LB II spinels plot in the peridotitic field while Cameroon and Morocco spinels fall in the magmatic one. Consequently, the xenoliths sampled from a probably juvenile SCLM at the edge of the most important lithospheric roots (i.e. Cameroon and Morocco) apparently have spinels possibly fractionated in situ from percolating melts and do not represent a real spinel-peridotite facies. On the contrary mantle

High-pressure behaviour of selenium-based spinels and related structures - an experimental and theoretical study

International Nuclear Information System (INIS)

Waskowska, A; Gerward, L; Olsen, J Staun; Feliz, M; Llusar, R; Gracia, L; Marques, M; Recio, J M

2004-01-01

The high-pressure structural behaviour of the cubic spinel CdCr 2 Se 4 (space group Fd3barm) and tetragonal CdGa 2 Se 4 (I4bar) has been investigated experimentally and theoretically in order to understand the large difference in compressibility between the two selenides. The experimental values of the bulk modulus for these compounds are 101(2) and 48(2) GPa, respectively. These values compare well with 92 and 44 GPa obtained from first-principles calculations based on the density functional theory formalism. The observed difference in compressibility between the cubic and tetragonal structures can be understood in terms of polyhedral analysis. In a hypothetical cubic spinel structure Fd3barm), the calculated bulk modulus for CdGa 2 Se 4 is 85 GPa. This value together with the experimental and theoretical results for CdCr 2 Se 4 suggest that the selenium-based cubic spinels should have a bulk modulus about 100 GPa, which is half the value found for the oxide spinels

Cation disorder in high-dose, neutron-irradiated spinel

International Nuclear Information System (INIS)

Sickafus, K.E.; Larson, A.C.; Yu, N.; Nastasi, M.; Hollenberg, G.W.; Garner, F.A.; Bradt, R.C.

1994-08-01

The objective of this effort is to determine whether MgAl 2 O 4 spinel is a suitable ceramic for fusion applications. Here, the crystal structures of MgAl 2 O 4 spinel single crystals irradiated to high neutron fluences [>5·10 26 n/m 2 (E n > 0.1 MeV)] were examined by neutron diffraction. Crystal structure refinement of the highest dose sample indicated that the average scattering strength of the tetrahedral crystal sites decreased by ∼ 20% while increasing by ∼ 8% on octahedral sites. Since the neutron scattering length for Mg is considerably larger than for Al, this results is consistent with site exchange between Mg 2+ ions on tetrahedral sites and Al 3+ ions on octahedral sites. Least-squares refinements also indicated that, in all irradiated samples, at least 35% of Mg 2+ and Al 3+ ions in the crystal experienced disordering replacements. This retained dpa on the cation sublattices is the largest retained damage ever measured in an irradiated spinel material

Detoxification and immobilization of chromite ore processing residue in spinel-based glass-ceramic

Energy Technology Data Exchange (ETDEWEB)

Liao, Chang-Zhong [Guangdong Key Laboratory of Agricultural Environment Pollution Integrated Control, Guangdong Institute of Eco-Environmental and Soil Sciences, Guangzhou 510650 (China); Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong Special Administrative Region (China); Tang, Yuanyuan [School of Environmental Science and Engineering, South University of Science and Technology of China, Shenzhen 518055 (China); Lee, Po-Heng [Department of Civil & Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong Special Administrative Region (China); Liu, Chengshuai, E-mail: csliu@soil.gd.cn [Guangdong Key Laboratory of Agricultural Environment Pollution Integrated Control, Guangdong Institute of Eco-Environmental and Soil Sciences, Guangzhou 510650 (China); State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550009 (China); Shih, Kaimin, E-mail: kshih@hku.hk [Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong Special Administrative Region (China); Li, Fangbai [Guangdong Key Laboratory of Agricultural Environment Pollution Integrated Control, Guangdong Institute of Eco-Environmental and Soil Sciences, Guangzhou 510650 (China)

2017-01-05

Graphical abstract: Schematic illustration of detoxification and immobilization of chromite ore processing residue in spinel-based glass-ceramic matrix. All Cr(VI) species is reduced to Cr(III) and most chromium contents are incorporated into spinel structure where the residual chromium are resided in the glass networks. - Highlights: • COPR was detoxified and immobilized in a spinel-based glass-ceramic matrix. • Cr-rich crystalline phase was determined to be MgCr{sub 1.32}Fe{sub 0.19}Al{sub 0.49}O{sub 4} spinel. • The partitioning ratio of Cr into spinel in the glass-ceramic can be up to 77%. • No Cr(VI) was observed after conversion of COPR into a glass-ceramic. • TCLP results demonstrate the superiority of the final product in immobilizing Cr. - Abstract: A promising strategy for the detoxification and immobilization of chromite ore processing residue (COPR) in a spinel-based glass-ceramic matrix is reported in this study. In the search for a more chemically durable matrix for COPR, the most critical crystalline phase for Cr immobilization was found to be a spinel solid solution with a chemical composition of MgCr{sub 1.32}Fe{sub 0.19}Al{sub 0.49}O{sub 4}. Using Rietveld quantitative X-ray diffraction analysis, we identified this final product is with the phases of spinel (3.5 wt.%), diopside (5.2 wt.%), and some amorphous contents (91.2 wt.%). The partitioning ratio of Cr reveals that about 77% of the Cr was incorporated into the more chemically durable spinel phase. The results of Cr K-edge X-ray absorption near-edge spectroscopy show that no Cr(VI) was observed after conversion of COPR into a glass-ceramic, which indicates successful detoxification of Cr(VI) into Cr(III) in the COPR-incorporated glass-ceramic. The leaching performances of Cr{sub 2}O{sub 3} and COPR-incorporated glass-ceramic were compared with a prolonged acid-leaching test, and the results demonstrate the superiority of the COPR-incorporated glass-ceramic matrix in the

Detoxification and immobilization of chromite ore processing residue in spinel-based glass-ceramic

International Nuclear Information System (INIS)

Liao, Chang-Zhong; Tang, Yuanyuan; Lee, Po-Heng; Liu, Chengshuai; Shih, Kaimin; Li, Fangbai

2017-01-01

Graphical abstract: Schematic illustration of detoxification and immobilization of chromite ore processing residue in spinel-based glass-ceramic matrix. All Cr(VI) species is reduced to Cr(III) and most chromium contents are incorporated into spinel structure where the residual chromium are resided in the glass networks. - Highlights: • COPR was detoxified and immobilized in a spinel-based glass-ceramic matrix. • Cr-rich crystalline phase was determined to be MgCr 1.32 Fe 0.19 Al 0.49 O 4 spinel. • The partitioning ratio of Cr into spinel in the glass-ceramic can be up to 77%. • No Cr(VI) was observed after conversion of COPR into a glass-ceramic. • TCLP results demonstrate the superiority of the final product in immobilizing Cr. - Abstract: A promising strategy for the detoxification and immobilization of chromite ore processing residue (COPR) in a spinel-based glass-ceramic matrix is reported in this study. In the search for a more chemically durable matrix for COPR, the most critical crystalline phase for Cr immobilization was found to be a spinel solid solution with a chemical composition of MgCr 1.32 Fe 0.19 Al 0.49 O 4 . Using Rietveld quantitative X-ray diffraction analysis, we identified this final product is with the phases of spinel (3.5 wt.%), diopside (5.2 wt.%), and some amorphous contents (91.2 wt.%). The partitioning ratio of Cr reveals that about 77% of the Cr was incorporated into the more chemically durable spinel phase. The results of Cr K-edge X-ray absorption near-edge spectroscopy show that no Cr(VI) was observed after conversion of COPR into a glass-ceramic, which indicates successful detoxification of Cr(VI) into Cr(III) in the COPR-incorporated glass-ceramic. The leaching performances of Cr 2 O 3 and COPR-incorporated glass-ceramic were compared with a prolonged acid-leaching test, and the results demonstrate the superiority of the COPR-incorporated glass-ceramic matrix in the immobilization of Cr. The overall results suggest that

Thermal decomposition of chromite spinel with chlorite admixture

Energy Technology Data Exchange (ETDEWEB)

Sanchez-Ramos, S. [Department of Analytical Chemistry, Faculty of Chemistry, University of Valencia, C/Doctor Moliner 50, 46100-Burjassot, Valencia (Spain); Escuela Superior de Ceramica, C/Ceramista A. Blat 22, 46940 Manises, Valencia (Spain); Domenech-Carbo, A. [Department of Analytical Chemistry, Faculty of Chemistry, University of Valencia, C/Doctor Moliner 50, 46100-Burjassot, Valencia (Spain); Gimeno-Adelantado, J.V. [Department of Analytical Chemistry, Faculty of Chemistry, University of Valencia, C/Doctor Moliner 50, 46100-Burjassot, Valencia (Spain)], E-mail: jose.v.gimeno@uv.es; Peris-Vicente, J.; Valle-Algarra, F.M. [Department of Analytical Chemistry, Faculty of Chemistry, University of Valencia, C/Doctor Moliner 50, 46100-Burjassot, Valencia (Spain)

2008-09-30

The behaviour of minerals in a South African chromite ore during the increasing of the temperature has been studied. Firstly, the changes produced during the ignition process have been examined by means of thermal and differential analysis (TGA-DTA) until 1200 deg. C. The characterization of the initial mineral and those obtained after heating at several temperatures in room atmosphere has been performed by X-ray diffraction (XRD). Moreover, voltammetric analyses have allowed to determine the variation of the iron oxidation degree in the studied materials. Light microscopy was applied to find more information about the different phases by their colour. During the heating, a wide range of complex exothermic and endothermic transformations take place. Decomposition compounds were identified, which were produced by heat decomposition, loss of structural water, element substitutions and oxygen absorptions and desorptions, caused mainly by the variation of the iron oxidation degree. The spinels of the chromite ore decompose in other spinels, with a partial change of the iron oxidation degree. From nearly 800 deg. C, chrome oxide (Cr{sub 2}O{sub 3}) comes off from the chromite forming another phase, and almost at 1000 deg. C, a slow decrease of weight was detected, caused among others to the formation of a magnetite phase. Simultaneously, the silicates undergo strong modifications, including decompositions and incorporation of iron (II) in their structure and producing other silicates stable at high temperatures, which modify the behaviour of the pure spinels. Moreover, at 1200 deg. C these silicates decompose to cristobalite (SiO{sub 2})

A comparison between the irradiation damage response of spinel and zirconia due to Xe ion bombardment

International Nuclear Information System (INIS)

Sickafus, K.E.; Wetteland, C.J.; Baker, N.P.; Yu Ning; Devanathan, R.; Nastasi, M.; Bordes, N.

1998-01-01

The mechanical properties of Xe-implanted spinel and cubic zirconia surfaces, as determined by nano-indentation measurements, are distinct and the differences can be related to their microstructures. Upon Xe 2+ ion irradiation to high dose at cryogenic temperature (120 K), the Young's modulus of irradiated spinel falls dramatically until the modulus is only about 3/4 the un-irradiated value. The maximum modulus occurs concurrent with the formation of a metastable crystalline phase of spinel. The subsequent elastic softening at higher Xe 2+ doses is an indication of the onset of amorphization of the spinel. Xe-implanted zirconia surfaces behave differently, in all cases showing almost no change in elastic modulus with increasing Xe 2+ ion dose. This is consistent with microstructural observations of Xe-implanted zirconia crystals which, unlike spinel, show no change in crystal structure with increasing ion dose. The hardness of both spinel and zirconia increases slightly for low Xe 2+ ion doses. At higher doses, zirconia shows little change in hardness, while the hardness of the implanted spinel falls by more than a factor of two. The initial increase in hardness of both spinel and zirconia is consistent with point defect accumulation and the precipitation of small interstitial clusters, while the drop in hardness of spinel at high Xe 2+ ion doses is due to the formation of an amorphous phase. (orig.)

Solid-liquid phase equilibria of Fe-Cr-Al alloys and spinels

Science.gov (United States)

McMurray, J. W.; Hu, R.; Ushakov, S. V.; Shin, D.; Pint, B. A.; Terrani, K. A.; Navrotsky, A.

2017-08-01

Ferritic FeCrAl alloys are candidate accident tolerant cladding materials. There is a paucity of data concerning the melting behavior for FeCrAl and its oxides. Analysis tools have therefore had to utilize assumptions for simulations using FeCrAl cladding. The focus of this study is to examine in some detail the solid-liquid phase equilibria of FeCrAl alloys and spinels with the aim of improving the accuracy of severe accident scenario computational studies.

Order-disorder transition in the complex lithium spinel Li2CoTi3O8

International Nuclear Information System (INIS)

Reeves, Nik; Pasero, Denis; West, Anthony R.

2007-01-01

Li 2 CoTi 3 O 8 has an ordered Li 2 BB' 3 O 8 spinel structure, space group P4 3 32, at room temperature with 3:1 ordering of Ti and Li on the octahedral sites, and Li, Co disordered over the tetrahedral site. Rietveld refinement of variable temperature neutron powder diffraction data has shown an order-disorder phase transition in Li 2 CoTi 3 O 8 which commences at ∼500 deg. C with Li and Co mixing on the tetrahedral and 4-fold octahedral sites and is complete at a first order structural discontinuity at ∼915 deg. C. The fraction of Ti on the 12-fold octahedral site exhibits a small decrease with increasing temperature, which may suggest that the disordering involves all three cations. Above 930 deg. C, the structure, space group Fd3-barm, has Li, Co and Ti sharing a single-octahedral site and Li, Co sharing a tetrahedral site, although Co still exhibits a preference for tetrahedral coordination. A labelling scheme for ordered and partially ordered 3:1 spinels is devised which focuses on the occupancy of the Li,B cations. - Graphical abstract: Rietveld refinement of variable temperature neutron powder diffraction data shows an order-disorder phase transition in Li 2 CoTi 3 O 8 commencing at ∼500 deg. C with Li,Co mixing on tetrahedral and octahedral sites. This becomes complete at a first-order structural discontinuity at ∼915 deg. C. Above 930 deg. C, the structure, space group Fd3-barm, has Li, Co and Ti sharing a single-octahedral site and Li, Co sharing a tetrahedral site

Ferri-magnetic order in Mn induced spinel Co3-xMnxO4 (0.1≤x≤1.0) ceramic compositions

Science.gov (United States)

Meena, P. L.; Sreenivas, K.; Singh, M. R.; Kumar, Ashok; Singh, S. P.; Kumar, Ravi

2016-04-01

We report structural and magnetic properties of spinel Co3-xMnxO4 (x=0.1-1.0) synthesized by solid state reaction technique. Rietveld refinement analysis of X-ray diffraction (XRD) data, revealed the formation of polycrystalline single phase Co3-xMnxO4 without any significant structural change in cubic crystal symmetry with Mn substitution, except change in lattice parameter. Temperature dependent magnetization data show changes in magnetic ordering temperature, indicating formation of antiferromagnetic (AFM) and ferrimagnetic (FM) phase at low Mn concentration (x≤0.3) and well-defined FM phase at high Mn concentration (x≥0.5). The isothermal magnetization records established an AFM/FM mixed phase for composition ranging 0.10.5.

Investigation of spinel-related and orthorhombic LiMNO2 cathodes for rechargeable lithium batteries

CSIR Research Space (South Africa)

Gummow, RJ

1994-05-01

Full Text Available ~ and with carbon at 600~ have been evaluated in rechargeable lithium cells. The cathodes which initially have a composition close to LiMnO2 contain structures related to the lithiated-spinel phase Li2\\[Mn2104 and/or orthorhombic Li... the cathode structure to yield an "over-discharged" state which is possible, for example, with a Lix\\[Mn2104 spinel cathode. 7 Lix\\[Mn2\\]O4 operates at approximately 4 V vs. lithium over the range 0 < x -< 1 and has a...

Transparent magnesium aluminate spinel: a prospective biomaterial for esthetic orthodontic brackets.

Science.gov (United States)

Krishnan, Manu; Tiwari, Brijesh; Seema, Saraswathy; Kalra, Namitha; Biswas, Papiya; Rajeswari, Kotikalapudi; Suresh, Madireddy Buchi; Johnson, Roy; Gokhale, Nitin M; Iyer, Satish R; Londhe, Sanjay; Arora, Vimal; Tripathi, Rajendra P

2014-11-01

Adult orthodontics is recently gaining popularity due to its importance in esthetics, oral and general health. However, none of the currently available alumina or zirconia based ceramic orthodontic brackets meet the esthetic demands of adult patients. Inherent hexagonal lattice structure and associated birefringence limits the visible light transmission in polycrystalline alumina and make them appear white and non transparent. Hence focus of the present study was to assess the feasibility of using magnesium aluminate (MgAl2O4) spinel; a member of the transparent ceramic family for esthetic orthodontic brackets. Transparent spinel specimens were developed from commercially available white spinel powder through colloidal shaping followed by pressureless sintering and hot isostatic pressing at optimum conditions of temperature and pressure. Samples were characterized for chemical composition, phases, density, hardness, flexural strength, fracture toughness and optical transmission. Biocompatibility was evaluated with in-vitro cell line experiments for cytotoxicity, apoptosis and genotoxicity. Results showed that transparent spinel samples had requisite physico-chemical, mechanical, optical and excellent biocompatibility for fabricating orthodontic brackets. Transparent spinel developed through this method demonstrated its possibility as a prospective biomaterial for developing esthetic orthodontic brackets.

Thermal expansion of spinel-type Si3N4

DEFF Research Database (Denmark)

Paszkowics, W.; Minkikayev, R.; Piszora, P.

2004-01-01

The lattice parameter and thermal expansion coefficient (TEC) for the spinel-type Si3N4 phase prepared under high-pressure and high-temperature conditions are determined for 14 K......The lattice parameter and thermal expansion coefficient (TEC) for the spinel-type Si3N4 phase prepared under high-pressure and high-temperature conditions are determined for 14 K...

Synthesis on spinel behaviour under irradiation

International Nuclear Information System (INIS)

Chauvin, N.; Dodane, C.; Noirot, J.; Konings, R.J.M.; Matzke, H.J.; Wiss, T.; Conrad, R.

2001-01-01

The spinel MgAl 2 O 4 is one of the materials able to be used in reactor for the transmutation of the minor actinides stemming from the back-end of the fuel cycle. It has been studied under irradiation since many years. Indeed, one of the first uses considered is to be employed as material for fusion reactors. Otherwise, it was shown that spinel presents nuclear and physico-chemical properties suitable for an utilization as nuclear inert matrix that loaded with an actinide phase constitutes a target devoted to the heterogeneous recycling in reactor. In order to improve the knowledge on spinel behaviour under irradiation, an assessment of the former studies must be done. The objective of this paper is to gather all the results of the spinel irradiations and to take out synthetic conclusion on the opportunity to use this material for the transmutation programme. (author)

Ferri-magnetic order in Mn induced spinel Co_3_−_xMn_xO_4 (0.1≤x≤1.0) ceramic compositions

International Nuclear Information System (INIS)

Meena, P.L.; Sreenivas, K.; Singh, M.R.; Kumar, Ashok; Singh, S.P.; Kumar, Ravi

2016-01-01

We report structural and magnetic properties of spinel Co_3_−_xMn_xO_4 (x=0.1–1.0) synthesized by solid state reaction technique. Rietveld refinement analysis of X-ray diffraction (XRD) data, revealed the formation of polycrystalline single phase Co_3_−_xMn_xO_4 without any significant structural change in cubic crystal symmetry with Mn substitution, except change in lattice parameter. Temperature dependent magnetization data show changes in magnetic ordering temperature, indicating formation of antiferromagnetic (AFM) and ferrimagnetic (FM) phase at low Mn concentration (x≤0.3) and well-defined FM phase at high Mn concentration (x≥0.5). The isothermal magnetization records established an AFM/FM mixed phase for composition ranging 0.1 0.5. - Highlights: • Synthesis of single phase polycrystalline Co_3_−_xMn_xO_4 ceramic. • Change in magnetic ordering with varying Mn concentration. • The complex spin distribution is contributing to FM ordering with higher Mn.

EPR, mu-Raman and Crystallographic properties of spinel type ZnCr{sub 2}O{sub 4}

Energy Technology Data Exchange (ETDEWEB)

Vargas-Hernandez, C; Almanza, O; Jurado, J F, E-mail: cvargash@unal.edu.c [Universidad Nacional de Colombia, Manizales-Colombia Laboratorio de Propiedades Opticas de Materiales-POM (Colombia)

2009-05-01

Structural, vibrational and electron paramagnetic resonance (EPR) analysis for compound ZnCr{sub 2}O{sub 4} are shown in this work. These types of materials are used in technological applications as humidity sensors and piezoelectric devices. The compound was obtained by mean of solid state reaction technique from binary precursors ZnO and Cr{sub 2}O{sub 3}. After three thermal treatments the sample structure was monitoring using X ray diffraction (XRD), the spinel cubic phase has been indexed within O{sup 7}{sub h}(Fd3m) spatial group. It is observed normal spinel phase. Micro-Raman analysis revealed bands for normal vibration modes of Zn and Cr atoms in tetrahedral and octahedral environments formed by oxygen atoms at approximately 400 and 900 cm{sup -1}, respectively. Bands around 941 cm{sup -1} are associated possibly to vacancies in the tetrahedral and octahedral sites due to interaction between Zn and Cr ions. EPR signal from 150 to 300 K isothermals indicates a transition between inverse spinel to normal spinel type in a central field around 3350 G. A signal at approximately 3400 G corresponding to the C'r{sup +3} in tetrahedral sites is observed near the central field.

Micro-XANES measurements on experimental spinels and the oxidation state of vanadium in coexisting spinel and silicate melt

International Nuclear Information System (INIS)

Righter, K.; Sutton, S.R.; Newville, M.; Le, L.; Schwandt, C.S.

2006-01-01

We show that experimental spinels coexisting with silicate melt always have lower valence vanadium, and that spinels typically have 3+, whereas the coexisting melt has 4+ or 5+. Implications of these results for planetary basalts will be discussed. Spinel can be a significant host phase for V which has multiple oxidation states V 2+ , V 3+ , V 4+ or V 5+ at oxygen fugacities relevant to natural systems. The magnitude of D(V) spinel/melt is known to be a function of composition, temperature and fO 2 , but the uncertainty of the oxidation state under the range of natural conditions has made elusive a thorough understanding of D(V) spinel/melt. For example, V 3+ is likely to be stable in spinels, based on exchange with Al in experiments in the CaO-MgO-Al 2 O 3 -SiO 2 system. On the other hand, it has been argued that V 4+ will be stable across the range of natural oxygen fugacities in nature. In order to build on our previous work in more oxidized systems, we have carried out experiments at relatively reducing conditions from the FMQ buffer to 2 log fO 2 units below the IW buffer. These spinel-melt pairs, where V is present in the spinel at natural levels (∼300 ppm V), were analyzed using an electron microprobe at NASA-JSC and mi-cro-XANES at the Advanced Photon Source at Argonne National Laboratory. The new results will be used together with previous results to understand the valence of V in spinel-melt systems across 12 orders of magnitude of oxygen fugacity, and with application to natural systems.

Spinel versus layered structures for lithium cobalt oxide synthesized at 400-degrees-c

CSIR Research Space (South Africa)

Gummow, RJ

1993-03-01

Full Text Available -type structure) give comparable fits to the data. This structural anomaly is discussed in terms of the refinements and electrochemical data obtained when lithium is extracted from LiCoO2 in non-aqueous cells at room temperature. A spinel-related model for LixCoO2...

A series of spinel phase cathode materials prepared by a simple hydrothermal process for rechargeable lithium batteries

International Nuclear Information System (INIS)

Liang Yanyu; Bao Shujuan; Li Hulin

2006-01-01

A series of spinel-structured materials have been prepared by a simple hydrothermal procedure in an aqueous medium. The new synthetic method is time and energy saving i.e., no further thermal treatment and extended grinding. The main experimental process involved the insertion of lithium into electrolytic manganese dioxide with glucose as a mild reductant in an autoclave. Both the hydrothermal temperature and the presence of glucose play the critical roles in determining the final spinel integrity. Particular electrochemical performance has also been systematically explored, and the results show that Al 3+ , F - co-substituted spinels have the best combination of initial capacity and capacity retention among all these samples, exhibited the initial capacity of 115 mAh/g and maintained more than 90% of the initial value at the 50th cycle. - Graphical abstract: It is a SEM image of the spinel LiMn 2 O 4 , which was prepared by this novel hydrothermal procedure. It illustrates that reasonable-crystallized spinel oxide has occurred through the special hydrothermal process and the average particle size declined to about 1 μm. This homogeneous grain size distribution provides an important morphological basis for the reversibility and accessibility of lithium ion insertion/extraction reactions

Spinel LiMn 2 O 4 Nanorods as Lithium Ion Battery Cathodes

KAUST Repository

Kim, Do Kyung

2008-11-12

Spinel LiMn 2O 4 is a low-cost, environmentally friendly, and highly abundant material for Li-ion battery cathodes. Here, we report the hydrothermal synthesis of single-crystalline β-MnO 2 nanorods and their chemical conversion into free-standing single-crystalline LiMn 2O 4 nanorods using a simple solid-state reaction. The LiMn 2O 4 nanorods have an average diameter of 130 nm and length of 1.2 μm. Galvanostatic battery testing showed that LiMn 2O 4 nanorods have a high charge storage capacity at high power rates compared with commercially available powders. More than 85% of the initial charge storage capacity was maintained for over 100 cycles. The structural transformation studies showed that the Li ions intercalated into the cubic phase of the LiMn 2O 4 with a small change of lattice parameter, followed by the coexistence of two nearly identical cubic phases in the potential range of 3.5 to 4.3V. © 2008 American Chemical Society.

Spinel LiMn 2 O 4 Nanorods as Lithium Ion Battery Cathodes

KAUST Repository

Kim, Do Kyung; Muralidharan, P.; Lee, Hyun-Wook; Ruffo, Riccardo; Yang, Yuan; Chan, Candace K.; Peng, Hailin; Huggins, Robert A.; Cui, Yi

2008-01-01

Spinel LiMn 2O 4 is a low-cost, environmentally friendly, and highly abundant material for Li-ion battery cathodes. Here, we report the hydrothermal synthesis of single-crystalline β-MnO 2 nanorods and their chemical conversion into free-standing single-crystalline LiMn 2O 4 nanorods using a simple solid-state reaction. The LiMn 2O 4 nanorods have an average diameter of 130 nm and length of 1.2 μm. Galvanostatic battery testing showed that LiMn 2O 4 nanorods have a high charge storage capacity at high power rates compared with commercially available powders. More than 85% of the initial charge storage capacity was maintained for over 100 cycles. The structural transformation studies showed that the Li ions intercalated into the cubic phase of the LiMn 2O 4 with a small change of lattice parameter, followed by the coexistence of two nearly identical cubic phases in the potential range of 3.5 to 4.3V. © 2008 American Chemical Society.

A series of spinel phase cathode materials prepared by a simple hydrothermal process for rechargeable lithium batteries

Science.gov (United States)

Liang, Yan-Yu; Bao, Shu-Juan; Li, Hu-Lin

2006-07-01

A series of spinel-structured materials have been prepared by a simple hydrothermal procedure in an aqueous medium. The new synthetic method is time and energy saving i.e., no further thermal treatment and extended grinding. The main experimental process involved the insertion of lithium into electrolytic manganese dioxide with glucose as a mild reductant in an autoclave. Both the hydrothermal temperature and the presence of glucose play the critical roles in determining the final spinel integrity. Particular electrochemical performance has also been systematically explored, and the results show that Al 3+, F - co-substituted spinels have the best combination of initial capacity and capacity retention among all these samples, exhibited the initial capacity of 115 mAh/g and maintained more than 90% of the initial value at the 50th cycle.

Elucidation of structural, vibrational and dielectric properties of transition metal (Co2+) doped spinel Mg-Zn chromites

Science.gov (United States)

Choudhary, Pankaj; Varshney, Dinesh

2018-05-01

Co2+ doped Mg-Zn spinel chromite compositions Mg0.5Zn0.5-xCoxCr2O4 (0.0 ≤ x ≤ 0.5) have been synthesized by the high-temperature solid state method. Synchrotron and X-ray diffraction (XRD) studies show single-phase crystalline nature. The structural analysis is validated by Rietveld refinement confirms the cubic structure with space group Fd3m. Crystallite size is estimated from Synchrotron XRD which was found to be 30-34 nm. Energy dispersive analysis confirms stoichiometric Mg0.5Zn0.5-xCoxCr2O4 composition. Average crystallite size distribution is estimated from imaging software (Image - J) of SEM is in the range of 100-250 nm. Raman spectroscopy reveals four active phonon modes, and a pronounced red shift is due to enhanced Co2+ concentration. Increased Co2+ concentration in Mg-Zn chromites shows a prominent narrowing of band gap from 3.46 to 2.97 eV. The dielectric response is attributed to the interfacial polarization, and the electrical modulus study supports non-Debye type of dielectric relaxation. Ohmic junctions (minimum potential drop) at electrode interface are active at lower levels of doping (x transformer applications at high frequencies.

The effect of Cr substitution on the structural, electronic and magnetic properties of pulsed laser deposited NiFe_2O_4 thin films

International Nuclear Information System (INIS)

Panwar, Kalpana; Tiwari, Shailja; Bapna, Komal; Heda, N.L.; Choudhary, R.J.; Phase, D.M.; Ahuja, B.L.

2017-01-01

We have studied the structural, electronic and magnetic properties of pulsed laser deposited thin films of Ni_1_−_xCr_xFe_2O_4 (x=0.02 and 0.05) on Si (111) and Si (100) substrates. The films reveal single phase, polycrystalline structure with larger grain size on Si (111) substrate than that on Si (100) substrate. Contrary to the expected inverse spinel structure, x-ray photoemission (XPS) studies reveal the mixed spinel structure. XPS results suggest that Ni and Fe ions exist in 2+ and 3+ states, respectively, and they exist in tetrahedral as well as octahedral sites. The deviation from the inverse spinel leads to modified magnetic properties. It is observed that saturation magnetization drastically drops compared to the expected saturation value for inverse spinel structure. Strain in the films and lattice distortion produced by the Cr doping also appear to influence the magnetic properties. - Highlights: • Thin films of Ni_1_−_xCr_xFe_2O_4 are grown on Si(111) and Si(100) substrates. • Films on Si(111) substrate are better crystalline than those on Si(100). • XRD and FTIR results confirm the single phase growth of the films. • Cationic distribution deviates from inverse spinel structure, as revealed by XPS. • Saturation magnetization is larger on Si(100) but lower than the bulk value.

Spinel Li{sub 2}CoTi{sub 3}O{sub 8} nanometer obtained for application as pigment; Espinela Li{sub 2}CoTi{sub 3}O{sub 8} nanometrica obtenida para aplicacion como pigmento

Energy Technology Data Exchange (ETDEWEB)

Costa de Camara, M. S.; Alves Pimentel, L.; Longo, E.; Nobrega Azevedo, L. da; Araujo Melo, D. M. de

2016-05-01

Pigments are used in ceramics, cosmetics, inks, and other applications widely materials. To this must be single and easily reproducible. Moreover, the pigments obtained in the nanoscale are more stable, reproducible and highlight color in small amounts compared with those obtained in micrometer scale. The mixed oxides with spinel structures AB{sub 2}O{sub 4} have important applications, including: pigments, refractories, catalytic and electronic ceramics. In this context, the aim of this work was the preparation of powder Li{sub 2}CoTi{sub 3}O{sub 8} spinel phase with nanometer particle size of the polymeric precursor method (Pechini) and characterization by means of thermal analysis (TG/DTA) X-ray diffraction (XRD), refined by the Rietveld method, BET, transmission electron microscopy (TEM), Raman and colorimetric coordinates. The pigment was obtained by heat treatment of 400 degree centigrade to 1000 degree centigrade after pyrolysis at 300 degree centigrade/1 h for removing the organic material. Li{sub 2}CoTi{sub 3}O{sub 8} desired spinel phase was obtained from 500 degree centigrade, and presenting stability nanometer to about 1.300 degree centigrade. Spinel green phase introduced at temperatures in the range of 400 degree centigrade and 500 degree centigrade, and 600 degree centigrade at temperatures between blue and 1000 degree centigrade. (Author)

In Situ Measurements of the Post-Spinel and Post-Garnet Phase Boundaries in Pyrolite at 17-32 GPa and 1500-2400 K

Science.gov (United States)

Ye, Y.; Gu, C.; Shim, S. H.; Prakapenka, V.; Meng, Y.

2014-12-01

Recent seismic studies have revealed complex structures near 660-km depth. In order to understand the effects of composition and temperature, we measured the depth and Clapeyron slope of the post-spinel and post-garnet boundaries at the pressure-temperature conditions of 600-700 km depths in pyrolitic compositions: (1) MgO-Al2O3-SiO2 (MAS) and (2) CaO-MgO-Al2O3-SiO2-FeO (CMASF). Glass starting materials were mixed with either gold or platinum powder (10 wt%) for laser coupling and internal pressure scale. Cold compressed foils of the mixtures were loaded in the diamond-anvil cell together with Ar or KCl for thermal insulation and pressure transmission. X-ray diffraction patterns were measured for the samples in the diamond-anvil cell at in situ high pressure and high temperature combined with double side laser heating at beamlines 13-IDD (GSECARS) and 16-IDB (HPCAT) in the Advanced Photon Source. Within 5 to 8 minutes of heating, stable crystalline phase assemblages were formed and persisted with further heating for 20 to 30 minutes. A total of 160 heating cycles were conducted at different pressures and temperatures, providing tight constrains on the phase boundaries. Our data show that the post-spinel transition occurs at 23.6-24.5 GPa and 1850 K with a Clapeyron slope of -2.5(4) MPa/K if the Pt pressure scales are used, consistent with the seismic observation of the 660 discontinuity. The post-garnet boundary occurs at 24.2-27.5 GPa and 1900 - 2450 K. We found that the Clapeyron slope of the post-garnet transition increases with Fe: from 2.4 MPa/K for MAS to 6.2 MPa/K for CMASF. Below 1900 K, garnet disappears near the post-spinel boundary within the resolution of our measurements. Our new data supports the notion that the 660 discontinuity is dominated by the post-spinel phase transition below 1900 K while dominated by the post-garnet phase transition above 1900 K. However, our data indicate much larger Clapeyron slope of the post-garnet transition, suggesting

Studying magnetic structure of Bi doped Co2MnO4 cubic spinel by neutron diffraction

International Nuclear Information System (INIS)

Rajeevan, N.E.; Kaushik, S.D.; Kumar, Ravi

2016-01-01

In present work, we studied effect of Bi doped spinel Bi x Co 2-x MnO 4 (x = 0, 0.05, 0.10, 0.15 and 0.20) samples on their crystal as well as magnetic structure by employing neutron diffraction of wavelength 1.48 A using focusing crystal diffractometer of UGC-DAECSR Mumbai Centre at Dhruva, Trombay, Mumbai, India. The analysis of the neutron diffraction using Fullprof program reveals that crystal structure due to Bi doping remains intact and all the samples have been formed in the cubic spinel structure with Fd3m (space group no. 227). The lattice parameter shows the positive thermal expansion upon Bi doping across the temperature range. In order to understand the implication on the spin structure and magnetism in the detail, temperature dependent neutron diffraction study is carried out on some of the samples (x = 0, 0.1) in the series. The ND pattern of x = 0.1 at 2.9K is shown. The experimental finding in terms of modified magnetic structure upon Bi doping are discussed which are understood in terms of variation in the ferroelectric properties, bond lengths and their effect on the CoO 6 polyhedra. Furthermore, Bi substitution in Co 2 MnO 4 spinel brings in the balance of structural distortion, which affects both ferrimagnetism and ferroelectricity

Synthesis and structural characterization of defect spinels in the Lithium-Manganese-Oxide system

CSIR Research Space (South Africa)

Thackeray, MM

1993-10-01

Full Text Available Lithium-manganese-oxides prepared at moderate temperatures are under investigation as insertion electrodes for rechargeable lithium batteries. The structures of two defect-spinel compounds synthesised by the reaction of MnCO3 and Li2CO3 at 400...

Synthesis and structural characterization of defect spinels in the lithium-manganese-oxide system

CSIR Research Space (South Africa)

Thackeray, MM

1993-10-01

Full Text Available Lithium-manganese-oxides prepared at moderate temperatures are under investigation as insertion electrodes for rechargeable lithium batteries. The structures of two defect-spinel compounds synthesized by the reaction of MnCO3 and Li2CO3 at 400°C...

Synthesis and characterization of inverse spinels, intercalation materials for Li-ion batteries

NARCIS (Netherlands)

Van Landschoot, N.

2006-01-01

Chapter 2 describes the solid-state synthesis of LiNiVO4 and LiCoVO4. The materials are prepared at 800C and are phase pure, as shown by X-ray diffraction and have the inverse spinel structure. Due to the solid-state synthesis the particle size is quite large and the particle size distribution is

Observation and manipulation of magnetic domains in sol gel derived thin films of spinel ferrites

Science.gov (United States)

Datar, Ashwini A.; Mathe, Vikas L.

2017-12-01

Thin films of spinel ferrites, namely zinc substituted nickel, cobalt ferrite, and manganese substituted cobalt ferrite, were synthesized using sol-gel derived spin-coating techniques. The films were characterized using x-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and Raman spectroscopy techniques for the analysis of structural, morphological and vibrational band transition properties, which confirm the spinel phase formation of the films. The magnetic force microscopy (MFM) technique was used to observe the magnetic domain structure present in the synthesized films. Further, the films were subjected to an external DC magnetic field of 2 kG to orient the magnetic domains and analyzed using an ex situ MFM technique.

Dating exhumed peridotite with spinel (U-Th)/He chronometry

Science.gov (United States)

Cooperdock, Emily H. G.; Stockli, Daniel F.

2018-05-01

The timing of cooling and exhumation of mantle peridotites in oceanic and continental settings has been challenging to determine using traditional geo- and thermochronometric techniques. Hence, the timing of the exhumation of mantle rocks to the Earth's surface at mid-ocean ridges, rifted and passive continental margins, and within continental volcanic and orogenic systems has remained largely elusive or only loosely constrained by relative age bracketing. Magmatic spinel [(Mg, Fe)(Al,Cr)2O4] is a ubiquitous primary mineral phase in mantle peridotites and is often the only primary mineral phase to survive surface weathering and serpentinization. This work explores spinel (U-Th)/He thermochronology as a novel tool to directly date the exhumation and cooling history of spinel-bearing mantle peridotite. Samples were chosen from a range of tectonic and petrologic settings, including a mid-ocean ridge abyssal peridotite (ODP Leg 209), an orogenic tectonic sliver of sub-continental mantle (Lherz massif, France), and a volcanic-rock hosted mantle xenolith (Green Knobs, NM). Spinel grains were selected based on grain size and morphology, screened for internal homogeneity using X-ray computed tomography, and air abraded to eliminate effects of alpha ejection/implantation. These case studies yield spinel He age results that are reproducible and generally in good agreement with independent age constraints. For ODP Leg 209, a spinel He age of 1.1 ± 0.3 Ma (2 SE) (n = 8) is consistent with independent U-Pb and magnetic anomaly ages for the exhumation of oceanic crust by detachment faulting along this segment of the slow-spreading ridge. Spinel from the Lherz massif yield He ages from 60-70 Ma (n = 3), which correspond well with independent thermochronometric constraints for cooling associated with Pyrenean collisional exhumation. Spinel from a mantle xenolith within a previously undated kimberlite diatreme at Green Knobs, New Mexico, generate a reproducible mean He age of 11

The effect of dolomite type and Al2O3 content on the phase composition in aluminous cements containing spinel

Directory of Open Access Journals (Sweden)

R. Naghizadeh

2011-06-01

Full Text Available In this paper, the effect of dolomite type and Al2O3 content on the phase composition in aluminous cements containing MA spinel is investigated. For this reason, the raw and calcined dolomites are used as raw materials along with calcined alumina in the preparation of the cement. Then, different compositions are prepared at 1350°C using the sintering method and their mineralogical compositions are investigated using the diffractometric technique. Also, their microstructures arre evaluated. The results indicate that raw materials used have great effect on the type and amount of formed phases in cement composition. Independently of the dolomite type used, a mixed phase product consisting of spinel accompanied by CA and CA2 is obtained. The content of CA phase in the cement composition is decreased with increasing of Al2O3 in the raw materials composition. On the other hand, the content of CA2 phase is increased with the addition of Al2O3. In addition, the results show that the formation of C12A7 is favored by use of calcined dolomite.

Structural, electronic and magnetic properties of partially inverse spinel CoFe2O4: a first-principles study

International Nuclear Information System (INIS)

Hou, Y H; Liu, Z W; Yu, H Y; Zhong, X C; Qiu, W Q; Zeng, D C; Wen, L S; Zhao, Y J

2010-01-01

Partially inverse spinel CoFe 2 O 4 , which may be prepared through various heat treatments, differs remarkably from the ideal inverse spinel in many properties. The structure of partially inverse spinel CoFe 2 O 4 as well as its electronic and magnetic properties through a systemic theoretical calculation of (Co 1-x Fe x ) Tet (Co x Fe 2-x ) Oct O 4 (x = 0, 0.25, 0.5, 0.75 and 1.0) have been investigated by the generalized gradient approximation (GGA) + U approach. It is found that the Co and Fe ions prefer their high spin configurations with higher spin moments at octahedral sites in all the studied cases, in line with experimental observations. The Co ions at the octahedral sites favour being far away from each other in the partial inverse spinels, which also show half metallicity at certain inversion degrees.

The effect of Cr substitution on the structural, electronic and magnetic properties of pulsed laser deposited NiFe{sub 2}O{sub 4} thin films

Energy Technology Data Exchange (ETDEWEB)

Panwar, Kalpana [Department of Physics, Govt. Women Engineering College, Ajmer, 305002 India (India); Department of Pure and Applied Physics, University of Kota, Kota, 324010 India (India); Tiwari, Shailja, E-mail: tiwari_shailja@rediffmail.com [Department of Physics, Govt. Women Engineering College, Ajmer, 305002 India (India); Bapna, Komal [Department of Physics, M. L. Sukhadia University, Udaipur, 313001 India (India); Heda, N.L. [Department of Pure and Applied Physics, University of Kota, Kota, 324010 India (India); Choudhary, R.J.; Phase, D.M. [UGC-DAE Consortium for Scientific Research, University Campus, Indore, 452001 India (India); Ahuja, B.L. [Department of Physics, M. L. Sukhadia University, Udaipur, 313001 India (India)

2017-01-01

We have studied the structural, electronic and magnetic properties of pulsed laser deposited thin films of Ni{sub 1−x}Cr{sub x}Fe{sub 2}O{sub 4} (x=0.02 and 0.05) on Si (111) and Si (100) substrates. The films reveal single phase, polycrystalline structure with larger grain size on Si (111) substrate than that on Si (100) substrate. Contrary to the expected inverse spinel structure, x-ray photoemission (XPS) studies reveal the mixed spinel structure. XPS results suggest that Ni and Fe ions exist in 2+ and 3+ states, respectively, and they exist in tetrahedral as well as octahedral sites. The deviation from the inverse spinel leads to modified magnetic properties. It is observed that saturation magnetization drastically drops compared to the expected saturation value for inverse spinel structure. Strain in the films and lattice distortion produced by the Cr doping also appear to influence the magnetic properties. - Highlights: • Thin films of Ni{sub 1−x}Cr{sub x}Fe{sub 2}O{sub 4} are grown on Si(111) and Si(100) substrates. • Films on Si(111) substrate are better crystalline than those on Si(100). • XRD and FTIR results confirm the single phase growth of the films. • Cationic distribution deviates from inverse spinel structure, as revealed by XPS. • Saturation magnetization is larger on Si(100) but lower than the bulk value.

Magnetic behavior of the oxide spinels:

Indian Academy of Sciences (India)

Magnetic behavior of the oxide spinels: Li0.5Fe2.5−2xAlxCrxO4. U N TRIVEDI, K B MODI and H H JOSHI. Department of Physics, Saurashtra University, Rajkot 360 005, India. Abstract. In order to study the effect of substitution of Fe3+ by Al3+ and Cr3+ in Li0.5Fe2.5O4 on its structural and magnetic properties, the spinel ...

Ferri-magnetic order in Mn induced spinel Co{sub 3−x}Mn{sub x}O{sub 4} (0.1≤x≤1.0) ceramic compositions

Energy Technology Data Exchange (ETDEWEB)

Meena, P.L., E-mail: plmeena@gmail.com [Department of Physics, Deen Dayal Upadhyaya College (University of Delhi), Shivaji Marg, Karampura, New Delhi 110015 (India); Sreenivas, K. [Department of Physics and Astrophysics, University of Delhi, North Campus, Delhi 110007 (India); Singh, M.R. [Technical Physics and Prototype Engineering Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra 400085 (India); Kumar, Ashok; Singh, S.P. [National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110012 (India); Kumar, Ravi [Beant College of Engineering and Technology, Gurdaspur, Punjab 143521 (India)

2016-04-01

We report structural and magnetic properties of spinel Co{sub 3−x}Mn{sub x}O{sub 4} (x=0.1–1.0) synthesized by solid state reaction technique. Rietveld refinement analysis of X-ray diffraction (XRD) data, revealed the formation of polycrystalline single phase Co{sub 3−x}Mn{sub x}O{sub 4} without any significant structural change in cubic crystal symmetry with Mn substitution, except change in lattice parameter. Temperature dependent magnetization data show changes in magnetic ordering temperature, indicating formation of antiferromagnetic (AFM) and ferrimagnetic (FM) phase at low Mn concentration (x≤0.3) and well-defined FM phase at high Mn concentration (x≥0.5). The isothermal magnetization records established an AFM/FM mixed phase for composition ranging 0.1phase above x>0.5. - Highlights: • Synthesis of single phase polycrystalline Co{sub 3−x}Mn{sub x}O{sub 4} ceramic. • Change in magnetic ordering with varying Mn concentration. • The complex spin distribution is contributing to FM ordering with higher Mn.

Effect of annealing time on structural and magnetic properties of ...

Indian Academy of Sciences (India)

We studied the effects on the structural and magnetic properties of Fe3O4 thin films. The films have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). XRD studies showed pure single phase spinel cubic structure of Fe3O4 with a preferential [111] ...

Study of structural phase transformation and hysteresis behavior of inverse-spinel α-ferrite nanoparticles synthesized by co-precipitation method

Science.gov (United States)

Dabagh, Shadab; Chaudhary, Kashif; Haider, Zuhaib; Ali, Jalil

2018-03-01

Substitution of cobalt (Co2+) ions in cobalt ferrite (CoFe2O4) with copper (Cu2+) and aluminum (Al3+) ions allows variations in their electric and magnetic properties which can be optimized for specific applications. In this article, synthesis of inverse-spinel Co1-xCuxFe2-xAlxO4 (0.0 ≤ x ≤ 0.8) nanoparticles by substituting Cu2+ and Al3+ ions in CoFe2O4 via co-precipitation method is reported. By controlling copper and aluminum (Cu-Al) substituent ratio, the magnetic moment and coercivity of synthesized cobalt ferrite nanoparticles is optimized. The role of substituents on the structure, particle size, morphology, and magnetic properties of nano-crystalline ferrite is investigated. The Co1-xCuxFe2-xAlxO4 (0.0 ≤ x≤ 0.8) nanoparticles with crystallite size in the range of 23.1-26.5 nm are observed, 26.5 nm for x = 0.0-23.1 nm for x = 0.8. The inverse-spinel structure of synthesized Co1-xCuxFe2-xAlxO4 (0.0 ≤ x ≤ 0.8) nano-particles is confirmed by characteristic vibrational bands at tetrahedral and octahedral sites using Fourier transform infrared spectroscopy. A decreases in coercive field and magnetic moment is observed as Cu-Al contents are increased (x = 0.0-0.8). The positive anisotropy of synthesized particles Co1-xCuxFe2-xAlxO4 (0.0 ≤ x ≤ 0.8) is obtained in the range 1.96 × 105 J/m3 for x = 0.0 to 0.29 × 105 J/m3 for x = 0.8.

Thermobarometry for spinel lherzolite xenoliths in alkali basalts

Science.gov (United States)

Ozawa, Kazuhito; Youbi, Nasrrddine; Boumehdi, Moulay Ahmed; Nagahara, Hiroko

2016-04-01

Application of geothermobarometers to peridotite xenoliths has been providing very useful information on thermal and chemical structure of lithospheric or asthenospheric mantle at the time of almost instantaneous sampling by the host magmas, based on which various thermal (e.g., McKenzie et al., 2005), chemical (e.g., Griffin et al., 2003), and rheological (e.g., Ave Lallemant et al., 1980) models of lithosphere have been constructed. Geothermobarometry for garnet or plagioclase-bearing lithologies provide accurate pressure estimation, but this is not the case for the spinel peridotites, which are frequently sampled from Phanerozoic provinces in various tectonic environments (Nixon and Davies, 1987). There are several geobarometers proposed for spinel lherzolite, such as single pyroxene geothermobarometer (Mercier, 1980) and geothermobarometer based on Ca exchange between olivine and clinopyroxene (Köhler and Brey, 1990), but they have essential problems and it is usually believed that appropriated barometers do not exist for spinel lherzolites (O'Reilly et al., 1997; Medaris et al., 1999). It is thus imperative to develop reliable barometry for spinel peridotite xenoliths. We have developed barometry for spinel peridotite xenoliths by exploiting small differences in pressure dependence in relevant reactions, whose calibration was made through careful evaluation of volume changes of the reactions. This is augmented with higher levels of care in application of barometer by choosing mineral domains and their chemical components that are in equilibrium as close as possible. This is necessary because such barometry is very sensitive to changes in chemical composition induced by transient state of the system possibly owing to pressure and temperature changes as well as chemical modification, forming chemical heterogeneity or zoning frequently reported from various mantle xenoliths (Smith, 1999). Thus very carful treatment of heterogeneity, which might be trivial for

Structural and magnetic properties of Co substituted Li{sub 0.5}Fe{sub 2.5}O{sub 4}

Energy Technology Data Exchange (ETDEWEB)

Patil, R.P., E-mail: raj_rbm_raj@yahoo.co.in [Department of Chemistry, M.H. Shinde Mahavidyalaya, Tisangi 416206, MH (India); Patil, S.B. [Department of Physics, Krantisinh Nana Patil College Walwa, Sangli 416313, MH (India); Jadhav, B.V. [Department of Chemistry, Changu Kana Thakur Arts, Commerce and Science College, New Panvel 400035, MH (India); Delekar, S.D.; Hankare, P.P. [Department of Chemistry, Shivaji University, Kolhapur 416004, MH (India)

2016-03-01

Nanocrystalline Li{sub 0.5}Fe{sub 2.5−x}Co{sub x}O{sub 4} (2.5≥x≥0) system was prepared by sol–gel route. Formation of single phase cubic spinel structure for all the compositions was confirmed from their X-ray diffraction studies. These ferrite samples existed as homogenous and uniform grains as observed from Scanning Electron Microscopy technique. The magnetic studies indicated that, the ferrimagnetic behavior decreases with Cobalt substitution. In general, the substitution of cobalt plays an important role in changing the structural and magnetic properties of these ferrites. - Highlights: • Novel Co doped Li{sub 0.5}Fe{sub 2.5}O{sub 4} system. • Sol–gel method synthesized Co–Lithium ferrites. • Single Phase Cubic spinel structure. • Homogenous and uniform grain size of samples. • Ferrimagnetic behavior for all the samples.

Nickel stabilization efficiency of aluminate and ferrite spinels and their leaching behavior.

Science.gov (United States)

Shih, Kaimin; White, Tim; Leckie, James O

2006-09-01

Stabilization efficiencies of spinel-based construction ceramics incorporating simulated nickel-laden waste sludge were evaluated and the leaching behavior of products investigated. To simulate the process of immobilization, nickel oxide was mixed alternatively with gamma-alumina, kaolinite, and hematite. These tailoring precursors are commonly used to prepare construction ceramics in the building industry. After sintering from 600 to 1480 degrees C at 3 h, the nickel aluminate spinel (NiAl204) and the nickel ferrite spinel (NiFe204) crystallized with the ferrite spinel formation commencing about 200-300 degrees C lower than for the aluminate spinel. All the precursors showed high nickel incorporation efficiencies when sintered at temperatures greater than 1250 degrees C. Prolonged leach tests (up to 26 days) of product phases were carried out using a pH 2.9 acetic acid solution, and the spinel products were invariably superior to nickel oxide for immobilization over longer leaching periods. The leaching behavior of NiAl2O4 was consistent with congruent dissolution without significant reprecipitation, but for NiFe2O4, ferric hydroxide precipitation was evident. The major leaching reaction of sintered kaolinite-based products was the dissolution of cristobalite rather than NiAl2O4. This study demonstrated the feasibility of transforming nickel-laden sludge into spinel phases with the use of readily available and inexpensive ceramic raw materials, and the successful reduction of metal mobility under acidic environments.

X-ray diffraction at high pressure and high/low temperatures using synchrotron radiation. Applications in the study of spinel structures

International Nuclear Information System (INIS)

Gerward, L.; Jiang, J.Z.; Olsen, J.S.; Recio, J.M.; Wakowska, A.

2004-01-01

High-pressure x-ray diffraction made a quantum leap in the 1960's with the advent of the diamond-anvil cell. This ingenious device, where two opposing diamond faces apply pressure to a tiny sample, made it possible to replicate the pressure near the core of the Earth by turning a thumbscrew. Multianvil cells, such as the Japanese MAX80 press, were developed for combined high-pressure and high-temperature studies. The availability n at about the same time n of dedicated synchrotron radiation sources of hard x-rays was another big step forward. Since then, the white-beam energy-dispersive method has been the workhorse for high pressure, high-temperature x-ray diffraction, although it is now gradually being replaced by high-resolution monochromatic methods based on the image plate, the CCD camera or other electronic area detectors. The first part of the paper is a review of high-pressure x-ray diffraction (HPXRD), covering roughly the last three decades. Physical parameters, such as the bulk modulus, the compressibility and the equation of state, are defined. The diamond-anvil cell, the multianvil press and other high-pressure devices are described, as well as synchrotron radiation sources and recording techniques. Examples are drawn from current experimental and theoretical research on crystal structures of the spinel type. Accurate structural parameters have been determined at ambient conditions and at low temperatures using single-crystal diffraction and four-circle diffractometers. The uniform high-pressure behavior of the oxide spinels has been investigated in detail and compared with the corresponding behavior of selenium-based spinels. The synthesis of advanced novel materials is exemplified in the case of the cubic spinel Si 3 N 4 . This and other nitrogen spinels, which have a bulk modulus of about 300 GPa modulated by the actual cation, are opening a road towards superhard materials. The paper finishes off with an outlook into the future, where new

Structural and magnetic studies of Cr doped nickel ferrite thin films

International Nuclear Information System (INIS)

Panwar, Kalpana; Heda, N. L.; Tiwari, Shailja; Bapna, Komal; Ahuja, B. L.; Choudhary, R. J.; Phase, D. M.

2016-01-01

We have studied the structural and magnetic properties of Cr doped nickel ferrite thin films deposited on Si (100) and Si (111) using pulsed laser deposition technique. The films were deposited under vacuum and substrate temperature was kept at 700°C. X-ray diffraction analysis revealed that films on both substrates have single phase cubic spinel structure. However, the film grown on Si (111) shows better crystalline behavior. Fourier transform infrared spectroscopy suggests that films on both substrates have mixed spinel structure. These films show magnetic hysteresis behavior and magnetization value of film on Si (100) is larger than that on Si (111). It turns out that structural and magnetic properties of these two films are correlated.

Structural, magnetic and electrical properties of nickel doped Mn-Zn spinel ferrite synthesized by sol-gel method

Energy Technology Data Exchange (ETDEWEB)

Jalaiah, K., E-mail: kjalu4u@gmail.com [Department of Physics, Andhra University, Visakhapatnam 530003 (India); Vijaya Babu, K. [Advanced Analytical Laboratory, Andhra University, Visakhapatnam 530003 (India)

2017-02-01

Manganese ferrites (MnFe{sub 2}O{sub 4}) have been of great interest for their remarkable and soft-magnetic properties (low coercivity, moderate saturation magnetization) accompanied by good chemical stability and mechanical hardness. X-ray diffraction analysis confirmed the presence of single phase cubic spinel ferrite with space group Fm3m for all prepared samples. Structural parameters such as lattice constant, crystallite size were calculated from the studies of X-ray diffraction. The morphological analysis of all the compounds is studied using scanning electron microscope. The magnetic properties were measured using electron spin resonance (ESR) and vibrating sample magnetometer (VSM). The results obtained showed the formation of manganese ferrites with an average particle size are in good agreement with previous results and displayed good magnetic properties. The dielectric and impedance properties are studied over a frequency range 20 Hz–1 MHz at room temperature. - Highlights: • We prepared Mn{sub 0.85}Zn{sub 0.15}Ni{sub x}Fe{sub 2}O{sub 4} (x=0.03, 0.06, 0.09, 0.12 and 0.15) nano-ferrite materials by using sol-gel method. • All the compounds characterized by XRD, SEM, VSM, ESR and dielectric studies. • We get lower coercivity values. • We get good results from ESR spectra.

Multifunctional thick-film structures based on spinel ceramics for environment sensors

International Nuclear Information System (INIS)

Vakiv, M; Hadzaman, I; Klym, H; Shpotyuk, O; Brunner, M

2011-01-01

Temperature sensitive thick films based on spinel-type NiMn 2 O 4 -CuMn 2 O 4 -MnCo 2 O 4 manganites with p- and p + -types of electrical conductivity and their multilayer p + -p structures were studied. These thick-film elements possess good electrophysical characteristics before and after long-term ageing test at 170 deg. C. It is shown that degradation processes connected with diffusion of metallic Ag into film grain boundaries occur in one-layer p-and p + -conductive films. Some part of the p + -p structures were of high stability, the relative electrical drift being no more than 1 %.

Method of microbially producing metal gallate spinel nano-objects, and compositions produced thereby

Science.gov (United States)

Duty, Chad E.; Jellison, Jr., Gerald E.; Love, Lonnie J.; Moon, Ji Won; Phelps, Tommy J.; Ivanov, Ilia N.; Kim, Jongsu; Park, Jehong; Lauf, Robert

2018-01-16

A method of forming a metal gallate spinel structure that includes mixing a divalent metal-containing salt and a gallium-containing salt in solution with fermentative or thermophilic bacteria. In the process, the bacteria nucleate metal gallate spinel nano-objects from the divalent metal-containing salt and the gallium-containing salt without requiring reduction of a metal in the solution. The metal gallate spinel structures, as well as light-emitting structures in which they are incorporated, are also described.

Obtainment the reverse phase spinel [Zn2+0,5Fe3+0,5](Ni2+0,5Fe3+ 1,5)O4 by the method combustion reaction: the form of assessment heating

International Nuclear Information System (INIS)

Silva, M.C.; Costa, A.C.F.; Coutinho, J.P.; Silva, A.T.C.; Freitas, N.L.

2011-01-01

This paper aims to synthesize the inverse spinel phase of by combustion reaction method and to evaluate how [Zn 2+ 0,5Fe 3+ 0,5](Ni 2+ 0,5Fe 3+ 1,5)O 4 the heat source influences the structural and morphological this phase. The forms of heating were muffle oven and ceramic plate with built-in resistance and aniline as reducing agent. Comparisons were made between temperature, reaction time and physical changes undergone by the material during the combustion carried out in two warm-up. The material was characterized by XRD, SEM, and textural analysis. Based on the results showed that the spinel phase was successfully obtained, were found traces of the phases ZnO and Fe2O3. The Most crystallite size and higher reaction temperature were presented by the material produced in the plate. As for surface area and pore volume, the highest values were achieved by the material synthesized in the oven. The agglomerates were presented in the form of skeins made of pre-sintered particles. (author)

Chemical, structural, and electrochemical characterization of 5 V spinel and complex layered oxide cathodes of lithium ion batteries

Science.gov (United States)

Tiruvannamalai Annamalai, Arun Kumar

2007-12-01

Lithium ion batteries have revolutionized the portable electronics market since their commercialization first by Sony Corporation in 1990. They are also being intensively pursued for electric and hybrid electric vehicle applications. Commercial lithium ion cells are currently made largely with the layered LiCoO 2 cathode. However, only 50% of the theoretical capacity of LiCoO 2 can be utilized in practical cells due to the chemical and structural instabilities at deep charge as well as safety concerns. These drawbacks together with the high cost and toxicity of Co have created enormous interest in alternative cathodes. In this regard, spinel LiMn2O4 has been investigated widely as Mn is inexpensive and environmentally benign. However, LiMn 2O4 exhibits severe capacity fade on cycling, particularly at elevated temperatures. With an aim to overcome the capacity fading problems, several cationic substitutions to give LiMn2-yMyO 4 (M = Cr, Fe, Co, Ni, and Cu) have been pursued in the literature. Among the cation-substituted systems, LiMn1.5Ni0.5O 4 has become attractive as it shows a high capacity of ˜ 130 mAh/g (theoretical capacity: 147 mAh/g) at around 4.7 V. With an aim to improve the electrochemical performance of the 5 V LiMn 1.5Ni0.5O4 spinel oxide, various cation-substituted LiMn1.5-yNi0.5-zMy+zO4 (M = Li, Mg, Fe, Co, and Zn) spinel oxides have been investigated by chemical lithium extraction. The cation-substituted LiMn1.5-yNi0.5-zM y+zO4 spinel oxides exhibit better cyclability and rate capability in the 5 V region compared to the unsubstituted LiMn1.5Ni 0.5O4 cathodes although the degree of manganese dissolution does not vary significantly. The better electrochemical properties of LiMn 1.5-yNi0.5-zMy+zO4 are found to be due to a smaller lattice parameter difference among the three cubic phases formed during the charge-discharge process. In addition, while the spinel Li1-xMn1.58Ni0.42O4 was chemically stable, the spinel Li1-xCo2O4 was found to exhibit both

Ceramic compositions based on nano forsterite/nano magnesium aluminate spinel powders

International Nuclear Information System (INIS)

Khattab, R.M.; Wahsh, M.M.S.; Khalil, N.M.

2015-01-01

According to the wide applications in the field of chemical and engineering industries, forsterite (Mg_2SiO_4)/spinel (MgAl_2O_4) ceramic compositions were the matter of interest of several research works during the last three decades. This work aims at preparation and characterization of improved ceramic bodies based on forsterite and spinel nano powders through controlling the forsterite and spinel contents in the prepared mixes. These prepared ceramic compositions have been investigated through measuring the densification parameters, cold crushing strength as well as volume resistively. Nano spinel was added from 0 to 30 mass% on expense of nano forsterite matrix and fired at 1550 °C for 2 h. The phase composition of the fired samples was examined using x-ray diffraction (XRD) technique. The microstructure of some selected samples was shown using scanning electron microscope (SEM). A pronounced improvement in the sintering, mechanical properties and volume resistively were achieved with increasing of nano spinel addition up to 15 mass%. This is due to the improvement in the matrix of the prepared forsterite/spinel bodies as a result of well distribution of spinel in the forsterite matrix as depicted by SEM analysis. - Highlights: • Ceramic compositions based on nano forsterite/nano-MgAl_2O_4 spinel were synthesized. • CCS was improved (333.78 MPa) through 15 mass% of nano-MgAl_2O_4 spinel addition. • Volume resistivity was enhanced to 203*10"1"3 Ohm cm with 15 mass% of spinel addition. • Beyond 15 mass% spinel, CCS and volume resistivity were decreased.

Preparation of Layered-Spinel Microsphere/Reduced Graphene Oxide Cathode Materials for Ultrafast Charge-Discharge Lithium-Ion Batteries.

Science.gov (United States)

Luo, Dong; Fang, Shaohua; Yang, Li; Hirano, Shin-Ichi

2017-12-22

Although Li-rich layered oxides (LLOs) have the highest capacity of any cathodes used, the rate capability of LLOs falls short of meeting the requirements of electric vehicles and smart grids. Herein, a layered-spinel microsphere/reduced graphene oxide heterostructured cathode (LS@rGO) is prepared in situ. This cathode is composed of a spinel phase, two layered structures, and a small amount of reduced graphene oxide (1.08 wt % of carbon). The assembly delivers a considerable charge capacity (145 mA h g -1 ) at an ultrahigh charge- discharge rate of 60 C (12 A g -1 ). The rate capability of LS@rGO is influenced by the introduced spinel phase and rGO. X-ray absorption and X-ray photoelectron spectroscopy data indicate that Cr ions move from octahedral lattice sites to tetrahedral lattice sites, and that Mn ions do not participate in the oxidation reaction during the initial charge process. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structure and single-phase regime of boron carbides

International Nuclear Information System (INIS)

Emin, D.

1988-01-01

The boron carbides are composed of twelve-atom icosahedral clusters which are linked by direct covalent bonds and through three-atom intericosahedral chains. The boron carbides are known to exist as a single phase with carbon concentrations from about 8 to about 20 at. %. This range of carbon concentrations is made possible by the substitution of boron and carbon atoms for one another within both the icosahedra and intericosahedral chains. The most widely accepted structural model for B 4 C (the boron carbide with nominally 20% carbon) has B/sub 11/C icosahedra with C-B-C intericosahedral chains. Here, the free energy of the boron carbides is studied as a function of carbon concentration by considering the effects of replacing carbon atoms within B 4 C with boron atoms. It is concluded that entropic and energetic considerations both favor the replacement of carbon atoms with boron atoms within the intericosahedral chains, C-B-C→C-B-B. Once the carbon concentration is so low that the vast majority of the chains are C-B-B chains, near B/sub 13/C 2 , subsequent substitutions of carbon atoms with boron atoms occur within the icosahedra, B/sub 11/C→B/sub 12/. Maxima of the free energy occur at the most ordered compositions: B 4 C,B/sub 13/C 2 ,B/sub 14/C. This structural model, determined by studying the free energy, agrees with that previously suggested by analysis of electronic and thermal transport data. These considerations also provide an explanation for the wide single-phase regime found for boron carbides

Inverse spinel transition metal oxides for lithium-ion storage with different discharge/charge conversion mechanisms

International Nuclear Information System (INIS)

Wang, Jiawei; Ren, Yurong; Huang, Xiaobing; Ding, Jianning

2016-01-01

Highlights: • Inverse spinel structure relieves the irreversible phase transition of electrodes. • Anodes with the same structure show different discharge/charge conversion mechanisms. • High reversible capacity confirms the potential feasibility of composites. - Abstract: Inverse spinel transition metal oxides (Fe 3 O 4 , MnFe 2 O 4 , Fe 3 O 4 /reduced graphene oxide and MnFe 2 O 4 /reduced graphene oxide) are prepared by a facile ethylene-glycol-assisted hydrothermal method. The stability of inverse spinel structure and the high specific surface area of nanoscale provide transition metal oxides with high specific capacity. And the surface modification with reduced graphene oxide improves the poor conductivity of pristine transition metal oxides. Pristine Fe 3 O 4 and MnFe 2 O 4 deliver the high initial discharge capacity of 1137.1 and 1088.9 mAh g −1 , respectively. Fe 3 O 4 /reduced graphene oxide and MnFe 2 O 4 /reduced graphene oxide get the reversible capacity of 645.8 and 720 mAh g −1 , respectively, even after 55 cycles. The different discharge/charge conversion mechanisms make them different capacity stability. The great electrochemical performances of composites offer electrodes with suitable characteristics for high-performance energy storage application.

Multifunctional thick-film structures based on spinel ceramics for environment sensors

Energy Technology Data Exchange (ETDEWEB)

Vakiv, M; Hadzaman, I; Klym, H; Shpotyuk, O [Institute of Materials of SRC ' Carat' , 202 Stryjska str., Lviv, 79031 (Ukraine); Brunner, M, E-mail: shpotyuk@novas.lviv.ua, E-mail: klymha@yahoo.com [Fachhochschule Koeln/University of Applied Sciences, 2 Betzdorfer str., Koeln, 50679 (Germany)

2011-04-01

Temperature sensitive thick films based on spinel-type NiMn{sub 2}O{sub 4}-CuMn{sub 2}O{sub 4}-MnCo{sub 2}O{sub 4} manganites with p- and p{sup +}-types of electrical conductivity and their multilayer p{sup +}-p structures were studied. These thick-film elements possess good electrophysical characteristics before and after long-term ageing test at 170 deg. C. It is shown that degradation processes connected with diffusion of metallic Ag into film grain boundaries occur in one-layer p-and p{sup +}-conductive films. Some part of the p{sup +}-p structures were of high stability, the relative electrical drift being no more than 1 %.

Structural, vibrational and thermal characterization of phase transformation in L-histidinium bromide monohydrate single crystals

Energy Technology Data Exchange (ETDEWEB)

Moura, G.M. [Universidade Federal do Maranhão, CCSST, Imperatriz, MA, 65900-410 (Brazil); Universidade Federal do Sul e Sudeste do Pará, ICEN, Marabá, PA 68505-080 (Brazil); Carvalho, J.O. [Universidade Federal do Maranhão, CCSST, Imperatriz, MA, 65900-410 (Brazil); Instituto Federal do Tocantins, Araguaína, TO, 77.826-170 (Brazil); Silva, M.C.D.; Façanha Filho, P.F. [Universidade Federal do Maranhão, CCSST, Imperatriz, MA, 65900-410 (Brazil); Santos, A.O. dos, E-mail: adenilson1@gmail.com [Universidade Federal do Maranhão, CCSST, Imperatriz, MA, 65900-410 (Brazil)

2015-09-01

L-Histidinium bromide monohydrate (LHBr) single crystal is a nonlinear optical material. In this work the high temperature phase transformation and the thermal stability of single crystals of LHBr was investigated by X-ray diffraction, thermogravimetric analysis, differential thermal analysis, differential scanning calorimetry and Raman spectroscopy. The results showed the LHBr phase transformation of orthorhombic (P2{sub 1}2{sub 1}2{sub 1}) to monoclinic system (P 1 2 1) at 120 °C, with the lattice parameters a = 12.162(1) Å, b = 16.821(2) Å, c = 19.477(2) Å and β = 108.56(2)°. These techniques are complementary and confirm the structural phase transformation due to loss water of crystallization. - Highlights: • -histidinium bromide single crystal was grown by slow evaporation technique. • X-ray diffraction characterize the high-temperature phase transformation. • The structural phase transformation occur due to loss of water of crystallization. • The LHBr thermal expansion coefficients exhibit an anisotropic behavior.

Magnetic, hyperthermic and structural properties of zn substituted CaFe2O4 powders

Science.gov (United States)

Kheradmand, Abbas; Vahidi, Omid; Masoudpanah, S. M.

2018-03-01

In the present study, we have synthesized single phase Ca1 - x Zn x Fe2O4 powders by hydrothermal method. The cation distribution between the tetrahedral and octahedral sites in the spinel structure and the magnetic properties as a function of the zinc substitution have been investigated by X-ray diffraction (XRD), infrared spectroscopy and vibrating sample magnetometer methods. The obtained XRD pattern indicated that the synthesized particles had single phase cubic spinel structure with no impurity. The magnetic measurements showed that the saturation magnetization increased from 83 to 98 emu/g with the addition of zinc due to the decrease of inversity. The particle size observed by electron microscopy decreased from 1.38 to 0.97 µm with the increase of zinc addition. The Ca0.7Zn0.3Fe2O4 powders exhibited appropriate heating capability for hyperthermia applications with the maximum AC heating temperature of 20 °C and specific loss power of 9.29 W/g.

Structural, impedance and Mössbauer studies of magnesium ferrite synthesized via sol–gel auto-combustion process

Directory of Open Access Journals (Sweden)

Shahid Khan Durrani

2017-12-01

Full Text Available Crystalline magnesium ferrite (MgFe2O4 spinel oxide powder was synthesized by nitrate–citrate sol–gel auto-combustion process with stoichiometric composition of metal nitrate salts, urea and citric acid. The study was focused on the modification of synthesis conditions and effect of these modified conditions on the structural and electrical properties of synthesized MgFe2O4 ceramic materials. Phase composition, crystallinity, structure and surface morphology were studied by X-ray diffraction, FTIR and SEM. Pure single phase MgFe2O4 spinel ferrite was obtained after calcination at 850 °C. Rietveld refinement of XRD result confirmed the single cubic phase spinel oxide with the lattice constant of a = 8.3931 Å and Fd3m symmetry. UV–visible absorption study of calcined powder revealed an optical band gap of 2.17 eV. SEM images of sintered specimens (1050–1450 °C showed that the grain size increased with the increase in sintering temperature. From the impedance results of the sintered MgFe2O4 specimens, it was found that the resistance of grain, grain boundary and electrode effect decreased with an increase in sintering temperature and associated grain growth. In the intermediate frequency region lowering of impedance and dielectric values was observed due to the decrease in grain boundary areas. Mössbauer studies indicated that magnesium ferrite had a mixed spinel structure in calcined and sintered samples, however, the well refined single phase MgFe2O4 was observed due to well developed high crystalline structure at 1350 °C and 1450 °C. Keywords: Sol–gel auto-combustion, Magnesium ferrite, X-ray diffraction, SEM, Mössbauer spectroscopy, Impedance spectroscopy

Ab initio calculation of the electronic structure and spectroscopic properties of spinel γ-Sn3N4

International Nuclear Information System (INIS)

Ching, W. Y.; Rulis, Paul

2006-01-01

The electronic structure and physical properties of γ-Sn 3 N 4 in the spinel structure are investigated by first-principles calculations. The calculated band structure, electronic bonding, and optical properties are compared with two well-studied spinel nitrides γ-Si 3 N 4 and γ-Ge 3 N 4 . γ-Sn 3 N 4 is a semiconductor with a direct band gap of 1.40 eV and an attractive small electron effective mass of 0.17. Its optical properties are different from that of γ-Si 3 N 4 and γ-Ge 3 N 4 because of the difference in the conduction band minimum. The Sn K, Sn L 3 , Sn M 5 , and N K edges of the x-ray-absorption near-edge structure spectra in γ-Sn 3 N 4 are calculated using a supercell approach and are found to be rich in structures. These spectra are discussed in the context of the electronic structure of the unoccupied conduction band in the presence of the electron core-hole interaction. These calculated spectra can be used for the characterization of this novel compound

Identification of Spinel Iron Oxide Nanoparticles by 57Fe NMR

Directory of Open Access Journals (Sweden)

SangGap Lee

2011-12-01

Full Text Available We have synthesized and studied monodisperse iron oxide nanoparticles of smaller than 10 nm to identify between the two spinel phases, magnetite and maghemite. It is shown that 57Fe NMR spectroscopy is a promising tool for distinguishing between the two phases.

Structure of spinel at high temperature using in-situ XANES study at the Al and Mg K-edge

Energy Technology Data Exchange (ETDEWEB)

Ligny, D de [Universite Claude Bernard Lyon 1, LPCML, 69622 Villeurbanne (France); Neuville, D R [Physique des Mineraux et Magmas, Geochimie-Cosmochimie, CNRS-IPGP, 4 place Jussieu, 75005 Paris (France); Flank, A-M; Lagarde, P, E-mail: deligny@pcml.univ-lyon1.f [Synchrotron SOLEIL, L' Orme des Merisiers, Saint Aubin, 91192 France (France)

2009-11-15

We present structural information obtained on spinel at high temperature (298-2400 K) using in situ XANES at the Mg and Al K-edge. Spinel, {sup [4]}(Al{sub x},Mg{sub 1-x}){sup [6]}(Al{sub 2-x},Mg{sub x})O{sub 4}, with increasing temperature, show a substitution of Mg by Al and Al by Mg in their respective sites. This substitution corresponds to an inversion of the Mg and Al sites. Furthermore, both experiments at the Al and Mg K-edges are in good agreement with XANES calculation made using FDMNES code.

On the combination of molecular replacement and single-wavelength anomalous diffraction phasing for automated structure determination

International Nuclear Information System (INIS)

Panjikar, Santosh; Parthasarathy, Venkataraman; Lamzin, Victor S.; Weiss, Manfred S.; Tucker, Paul A.

2009-01-01

The combination of molecular replacement and single-wavelength anomalous diffraction improves the performance of automated structure determination with Auto-Rickshaw. A combination of molecular replacement and single-wavelength anomalous diffraction phasing has been incorporated into the automated structure-determination platform Auto-Rickshaw. The complete MRSAD procedure includes molecular replacement, model refinement, experimental phasing, phase improvement and automated model building. The improvement over the standard SAD or MR approaches is illustrated by ten test cases taken from the JCSG diffraction data-set database. Poor MR or SAD phases with phase errors larger than 70° can be improved using the described procedure and a large fraction of the model can be determined in a purely automatic manner from X-ray data extending to better than 2.6 Å resolution

Sodium storage capability of spinel Li4Mn5O12

International Nuclear Information System (INIS)

Zhang, Jiaolong; Wang, Wenhui; Li, Yingshun; Yu, Denis Y.W.

2015-01-01

Highlights: • Electrochemical behavior of spinel Li 4 Mn 5 O 12 is examined in Na-ion battery. • A capacity of 120.7 mAh g −1 is obtained during the first sodiation process. • Na storage performance is found to be strongly dependent on particle size. • Ion-exchange between Li ions and Na ions occurs in Li 4 Mn 5 O 12 structure upon cycling. • Loss of crystallinity with cycling, leading to capacity fading. - Abstract: Spinel Li 4 Mn 5 O 12 , a well-known 3 V Li-ion battery (LIB) material with excellent cycling stability and good rate capability, is examined as Na-ion battery (NIB) cathode for the first time. Electrochemical studies clearly show that Na ions can be reversibly inserted into and extracted from the three-dimensional spinel structure. However, unlike in LIB, the available capacity in NIB is strongly dependent on the particle size and current rate due to the sluggish Na-ion transport in solid phase. Cycle performance of Li 4 Mn 5 O 12 in NIB is also inferior to that in LIB. Ex-situ X-ray diffraction study indicates a gradual loss of crystallinity with cycling, and that the crystal lattice undergoes an irreversible expansion during the initial 20 cycles. Inductively coupled plasma spectroscopy shows a decrease of Li/Mn ratio in Li 4 Mn 5 O 12 with cycling. The results suggest that Li ions are removed from the material during the charging process. The charge-discharge mechanism is also discussed in the paper.

The effect of Y2O3 addition on thermal shock behavior of magnesium aluminate spinel

Directory of Open Access Journals (Sweden)

Pošarac Milica

2009-01-01

Full Text Available The effect of yttria additive on the thermal shock behavior of magnesium aluminate spinel has been investigated. As a starting material we used spinel (MgAl2O4 obtained by the modified glycine nitrate procedure (MGNP. Sintered products were characterized in terms of phase analysis, densities, thermal shock, monitoring the damaged surface area in the refractory specimen during thermal shock and ultrasonic determination of the Dynamic Young modulus of elasticity. It was found that a new phase between yttria and alumina is formed, which improved thermal shock properties of the spinel refractories. Also densification of samples is enhanced by yttria addition.

Rapid synthesis of monodispersed highly porous spinel nickel cobaltite (NiCo{sub 2}O{sub 4}) electrode material for supercapacitors

Energy Technology Data Exchange (ETDEWEB)

Naveen, A. Nirmalesh, E-mail: nirmalesh.naveen@gmail.com; Selladurai, S. [Ionics Laboratory, Department of Physics, Anna University, Chennai-600025 (India)

2015-06-24

Monodispersed highly porous spinel nickel cobaltite electrode material was successfully synthesized in a short time using combustion technique. Single phase cubic nature of the spinel nickel cobaltite with average crystallite size of 24 nm was determined from X-ray diffraction study. Functional groups present in the compound were determined from FTIR study and it further confirms the spinel formation. FESEM images reveal the porous nature of the prepared material and uniform size distribution of the particles. Electrochemical evaluation was performed using Cyclic Voltammetry (CV) technique, Chronopotentiometry (CP) and Electrochemical Impedance Spectroscopy (EIS). Results reveal the typical pseudocapacitive behaviour of the material. Maximum capacitance of 754 F/g was calculated at the scan rate of 5 mV/s, high capacitance was due to the unique porous morphology of the electrode. Nyquist plot depicts the low resistance and good electrical conductivity of nickel cobaltite. It has been found that nickel cobaltite prepared by this typical method will be a potential electrode material for supercapcitor application.

Dynamics Assessment of Advanced Single-Phase PLL Structures

DEFF Research Database (Denmark)

Golestan, Saeed; Monfarad, Mohammad; Freijedo, Francisco D.

2013-01-01

Recently, several advanced phase locked loop (PLL) techniques have been proposed for single-phase applications. Among these, the Park-PLL, and the second order generalized integrator (SOGI) based PLL are very attractive, owing to their simple digital implementation, low computational burden...

Microstructure, crystal structure and electrical properties of Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics obtained at different sintering conditions

International Nuclear Information System (INIS)

Bodak, O.; Akselrud, L.; Demchenko, P.; Kotur, B.; Mrooz, O.; Hadzaman, I.; Shpotyuk, O.; Aldinger, F.; Seifert, H.; Volkov, S.; Pekhnyo, V.

2002-01-01

Details of the formation of Cu 0.1 Ni 0.8 Co 0.2 Mn 1.9 O 4 ceramics under different sintering conditions have been studied by optical microscopy, scanning electron microscopy (SEM), electron probe and energy dispersive spectroscopy (EDX) microanalyses, X-ray diffraction (XRD) and electrical resistivity measurements. Microstructure studies of samples sintered at 1170 deg. C for 1 h indicated the presence of a secondary phase besides the main spinel phase with modified composition. XRD measurements showed that the spinel phase exhibits a tetragonally distorted spinel structure (space group I4 1 /amd, a=5.9410(5) A, c=8.4196(15) A). The secondary phase (solid solution based on NiO) crystallizes with the NaCl-type structure (space group Fm3-bar m, a=4.1872(3) A). The content of the secondary phase in ceramics is 10.61 mass%. For NiMn 2 O 4 ceramics, prepared under the same sintering conditions, the decomposition with Ni 1-x Mn x O solid solution (NaCl-type structure) and spinel phase formation have been observed. The tetragonal modification of the spinel phase for NiMn 2 O 4 ceramics is more preferable (space group I4 1 /amd, a=5.9764(5) A, c=8.4201(8) A). The distribution of atoms in the structure has been proposed for both ceramics. According to XRD results the Cu 0.1 Ni 0.8 Co 0.2 Mn 1.9 O 4 ceramic samples, sintered at 920 deg. C for 8 h (program 1), at 920 deg. C for 8 h and at 750 deg. C for 24 h (program 2), at 920 deg. C for 8 h, at 1200 deg. C for 1 h and at 920 deg. C for 24 h (program 3) and at 920 deg. C for 8 h, at 1200 deg. C for 1 h, at 920 deg. C for 24 h and at 750 deg. C for 48 h (program 4), contain a single phase with the cubic spinel structure (space group Fd3-bar m). Small residuals of the secondary phase for the ceramics, prepared via programs 3 and 4, have been observed by SEM investigations. The structure transformations of the spinel phase for Cu 0.1 Ni 0.8 Co 0.2 Mn 1.9 O 4 ceramics sintered at 1170 deg. C are attributed to a Jahn

Exploring Lithium-Cobalt-Nickel Oxide Spinel Electrodes for ≥3.5 V Li-Ion Cells

Energy Technology Data Exchange (ETDEWEB)

Lee, Eungje; Blauwkamp, Joel; Castro, Fernando C.; Wu, Jinsong; Dravid, Vinayak P.; Yan, Pengfei; Wang, Chongmin; Kim, Soo; Wolverton, Christopher; Benedek, Roy; Dogan, Fulya; Park, Joong Sun; Croy, Jason R.; Thackeray, Michael M.

2016-10-19

Recent reports have indicated that a manganese oxide spinel component, when embedded in a relatively small concentration in layered xLi2MnO3(1-x)LiMO2 (M=Ni, Mn, Co) electrode systems, can act as a stabilizer that increases their capacity, rate capability, cycle life, and first-cycle efficiency. These findings prompted us to explore the possibility of exploiting lithiated cobalt oxide spinel stabilizers by taking advantage of (1) the low mobility of cobalt ions relative to manganese and nickel ions in close-packed oxides and (2) their higher potential (~3.6 V vs. Li0) relative to manganese oxide spinels (~2.9 V vs. Li0) for the spinel-to-lithiated spinel electrochemical reaction. In particular, we have revisited the structural and electrochemical properties of lithiated spinels in the LiCo1-xNixO2 (0x0.2) system, first reported almost 25 years ago, by means of high-resolution (synchrotron) X-ray diffraction, transmission electron microscopy, nuclear magnetic resonance spectroscopy, electrochemical cell tests, and theoretical calculations. The results provide a deeper understanding of the complexity of intergrown layered/lithiated spinel LiCo1-xNixO2 structures, when prepared in air between 400 and 800 C, and the impact of structural variations on their electrochemical behavior. These structures, when used in low concentration, offer the possibility of improving the cycling stability, energy, and power of high energy (≥3.5 V) lithium-ion cells.

Cation distribution in spinels and its effect on activity pick-up and passivation behaviour

International Nuclear Information System (INIS)

Subramanian, H.; Velmurugan, S.; Narasimhan, S.V.

2000-01-01

Spinels are found to be the major corrosion products in the primary heat transport system or nuclear reactors. These corrosion products are activated in the core and are picked up on the deposited corrosion product oxides, which lead to the radiation field buildup on out of core surfaces. In order to mitigate this phenomenon, it is extremely important to understand the structural changes that take place in a spinel in the primary heat transport system. Most of the spinels found in reactor systems are mixed spinels. Cation distribution in tetrahedral and octahedral sites of these spinels, which is temperature dependent, will affect the pickup of active metal ions from solution into these spinels. Distribution of cations in simple spinels was estimated by minimising the Gibbs energy change for the migration of ions between tetrahedral and octahedral sites, based on the assumption that it is the configurational entropy change for the process that dominates the distribution. Cation distribution for mixed spinels was also calculated using the same method. Energy demand for the exchange of an aqueous ion with these spinels has been estimated. (author)

Irradiation effects and behaviour of fission products in zirconia and spinel

International Nuclear Information System (INIS)

Gentils, A.

2003-10-01

Crystalline oxides, such as zirconia (ZrO 2 ) and spinel (MgAl 2 O 4 ), are promising inert matrices for the transmutation of plutonium and minor actinides. This work deals with the study of the physico-chemical properties of these matrices, more specifically their behaviour under irradiation and their capacity to retain fission products. Irradiations at low energy and incorporation of stable analogs of fission products (Cs, I, Xe) into yttria-stabilized zirconia and magnesium-aluminate spinel single crystals were performed by using the ion implanter IRMA (CSNSM-Orsay). Irradiations at high energy were made on several heavy ion accelerators (GANIL-Caen, ISL-Berlin, HIL-Warsaw). The damage induced by irradiation and the release of fission products were monitored by in situ Rutherford Backscattering Spectrometry experiments. Transmission electron microscopy was also used in order to determine the nature of the damage induced by irradiation. The results show that irradiation of ZrO 2 and MgAl 2 O 4 with heavy ions (about hundred keV and about hundred MeV) induces a huge structural damage in crystalline matrices. Total disorder (amorphization) is however never reached in zirconia, contrary to what is observed in the case of spinel. The results also emphasize the essential role played by the concentration of implanted species on their retention capacity. A dramatic release of fission products was observed when the concentration exceeds a threshold of a few atomic percent. Irradiation of implanted samples with medium-energy noble-gas ions leads to an enhancement of the fission product release. The exfoliation of spinel crystals implanted at high concentration of Cs ions is observed after a thermal treatment at high temperature. (author)

Magnetic structure and phase diagram of the frustrated spinel Cd{sub 1-x}Zn{sub x}Cr{sub 2}Se{sub 4}

Energy Technology Data Exchange (ETDEWEB)

Loudghiri, E. [Laboratoire de Physique des Materiaux, Faculte des Sciences, Universite Mohammed V, B.P. 1014 Rabat (Morocco); Belayachi, A. [Laboratoire de Physique des Materiaux, Faculte des Sciences, Universite Mohammed V, B.P. 1014 Rabat (Morocco)], E-mail: belayach@fsr.ac.ma; Nogues, M. [Laboratoire de Magnetisme et d' Optique de l' Universite de Versailles (URA 1531), Batiment, Fermat, 45 Avenue des Etats Unis, 78035 Versailles Cedex (France); Taibi, M. [Laboratoire de Physico-Chimie des Materiaux associe a l' AUF (LAF 502), Ecole Normale, Superieure Takadoum, B.P. 5118 Rabat (Morocco); Cruz, M.M.; Godinho, M. [Dept. Fisica/CFMC-UL, Fac. Ciencias, Universidade de Lisboa, Campo Grande, Ed.C8, 1749-016 Lisbon (Portugal)

2008-03-15

In attempt to characterise the magnetic ordering in the whole composition range of the Cd{sub 1-x}Zn{sub x}Cr{sub 2}Se{sub 4} system, various magnetic measurements were performed on both crystalline and polycrystalline samples with 0{<=}x{<=}1. The magnetic properties of the system are typical of a ferromagnet below x=0.4 and of a complex antiferromagnet one above x=0.6. In this work the intermediate region was carefully studied. The variations of both M(T) and {chi}{sub ac} at low fields suggest that transitions from ferromagnetic to Gabay-Toulouse ferromagnetic-spin-glass mixed phase at low temperature occur in the range 0.41{<=}x{<=}0.58. The high-temperature susceptibility measurements show that for the whole concentration range the system obeys Curie-Weiss laws. The results can be explained by the coexistence of competing interactions (ferromagnetic between nearest neighbours and antiferromagnetic between higher order neighbours) and disorder due to the random substitution between zinc and cadmium ions in the tetrahedral sites of the spinel lattice. An experimental magnetic phase diagram of the system is established.

Microstructure, crystal structure and electrical properties of Cu{sub 0.1}Ni{sub 0.8}Co{sub 0.2}Mn{sub 1.9}O{sub 4} ceramics obtained at different sintering conditions

Energy Technology Data Exchange (ETDEWEB)

Bodak, O.; Akselrud, L.; Demchenko, P.; Kotur, B.; Mrooz, O.; Hadzaman, I.; Shpotyuk, O.; Aldinger, F.; Seifert, H.; Volkov, S.; Pekhnyo, V

2002-12-16

Details of the formation of Cu{sub 0.1}Ni{sub 0.8}Co{sub 0.2}Mn{sub 1.9}O{sub 4} ceramics under different sintering conditions have been studied by optical microscopy, scanning electron microscopy (SEM), electron probe and energy dispersive spectroscopy (EDX) microanalyses, X-ray diffraction (XRD) and electrical resistivity measurements. Microstructure studies of samples sintered at 1170 deg. C for 1 h indicated the presence of a secondary phase besides the main spinel phase with modified composition. XRD measurements showed that the spinel phase exhibits a tetragonally distorted spinel structure (space group I4{sub 1}/amd, a=5.9410(5) A, c=8.4196(15) A). The secondary phase (solid solution based on NiO) crystallizes with the NaCl-type structure (space group Fm3-bar m, a=4.1872(3) A). The content of the secondary phase in ceramics is 10.61 mass%. For NiMn{sub 2}O{sub 4} ceramics, prepared under the same sintering conditions, the decomposition with Ni{sub 1-x}Mn{sub x}O solid solution (NaCl-type structure) and spinel phase formation have been observed. The tetragonal modification of the spinel phase for NiMn{sub 2}O{sub 4} ceramics is more preferable (space group I4{sub 1}/amd, a=5.9764(5) A, c=8.4201(8) A). The distribution of atoms in the structure has been proposed for both ceramics. According to XRD results the Cu{sub 0.1}Ni{sub 0.8}Co{sub 0.2}Mn{sub 1.9}O{sub 4} ceramic samples, sintered at 920 deg. C for 8 h (program 1), at 920 deg. C for 8 h and at 750 deg. C for 24 h (program 2), at 920 deg. C for 8 h, at 1200 deg. C for 1 h and at 920 deg. C for 24 h (program 3) and at 920 deg. C for 8 h, at 1200 deg. C for 1 h, at 920 deg. C for 24 h and at 750 deg. C for 48 h (program 4), contain a single phase with the cubic spinel structure (space group Fd3-bar m). Small residuals of the secondary phase for the ceramics, prepared via programs 3 and 4, have been observed by SEM investigations. The structure transformations of the spinel phase for Cu{sub 0.1}Ni{sub 0.8}Co

Photocatalytic degradation of methylene blue on magnetically separable MgFe2O4 under visible light irradiation

KAUST Repository

Shahid, Muhammad; Jingling, Liu; Ali, Zahid; Shakir, Imran; Warsi, Muhammad Farooq; Parveen, Riffat; Nadeem, Muhammad Tahir

2013-01-01

A magnetically separable single-phase MgFe2O4 photocatalyst with a spinel crystal structure was synthesized by using the solid-state reaction method. The formation of spinel structure is confirmed by X-ray diffraction and Fourier transform infrared

Accelerated safety analyses - structural analyses Phase I - structural sensitivity evaluation of single- and double-shell waste storage tanks

International Nuclear Information System (INIS)

Becker, D.L.

1994-11-01

Accelerated Safety Analyses - Phase I (ASA-Phase I) have been conducted to assess the appropriateness of existing tank farm operational controls and/or limits as now stipulated in the Operational Safety Requirements (OSRs) and Operating Specification Documents, and to establish a technical basis for the waste tank operating safety envelope. Structural sensitivity analyses were performed to assess the response of the different waste tank configurations to variations in loading conditions, uncertainties in loading parameters, and uncertainties in material characteristics. Extensive documentation of the sensitivity analyses conducted and results obtained are provided in the detailed ASA-Phase I report, Structural Sensitivity Evaluation of Single- and Double-Shell Waste Tanks for Accelerated Safety Analysis - Phase I. This document provides a summary of the accelerated safety analyses sensitivity evaluations and the resulting findings

The Effects of Oxygen Partial Pressure on Liquidus Temperature of a High-Level Waste Glass with Spinel as the Primary Phase

International Nuclear Information System (INIS)

Izak, Pavel; Hrma, Pavel R.; Wilson, Benjamin K.; Vienna, John D.

2000-01-01

The redox state of iron affects spinal crystallization in vitrified high-level waste (HLW) glass. Simulated HLW glass with spinel as the primary crystalline phase field was heat treated at constant temperatures within the interval from 850 C to 1300 C under varying atmospheres with oxygen partial pressure, Po2, ranging from 1x10-16 kPa (pure CO) to 101 kPa (pure O2). Liquidus temperature (TL) of glass increased with decreasing Po2 up to Po2 > 3 x 10-9 kPa. At Po2 < 3 x 10-9 kPa, Ni-Fe alloy precipitated from the glass, and TL decreased. Samples were analyzed with optical microscope and scanning electron microscope. The mass fraction of spinel in glass was determined using quantitative X-ray diffraction. Spinel composition was investigated with energy disperse spectroscopy. Ferrous-ferric equilibrium at TL was calculated in a HLW glass as a function of temperature and Po2, based on the previous studies by Schreiber. TL/FeO over the interval 0.0063 < gFeO < 0.051 (1x10-2 kPa < Po2 < 3x10-9 kPa) was estimated from calculated ferrous-ferric equilibrium at TL as 1835 C

Towards a lattice-matching solid-state battery: synthesis of a new class of lithium-ion conductors with the spinel structure.

Science.gov (United States)

Rosciano, Fabio; Pescarmona, Paolo P; Houthoofd, Kristof; Persoons, Andre; Bottke, Patrick; Wilkening, Martin

2013-04-28

Lithium ion batteries have conquered most of the portable electronics market and are now on the verge of deployment in large scale applications. To be competitive in the automotive and stationary sectors, however, they must be improved in the fields of safety and energy density (W h L(-1)). Solid-state batteries with a ceramic electrolyte offer the necessary advantages to significantly improve the current state-of-the-art technology. The major limit towards realizing a practical solid-state lithium-ion battery lies in the lack of viable ceramic ionic conductors. Only a few candidate materials are available, each carrying a difficult balance between advantages and drawbacks. Here we introduce a new class of possible solid-state lithium-ion conductors with the spinel structure. Such compounds could be coupled with spinel-type electrode materials to obtain a "lattice matching" solid device where low interfacial resistance could be achieved. Powders were prepared by wet chemistry, their structure was studied by means of diffraction techniques and magic angle spinning NMR, and Li(+) self-diffusion was estimated by static NMR line shape measurements. Profound differences in the Li(+) diffusion properties were observed depending on the composition, lithium content and cationic distribution. Local Li(+) hopping in the spinel materials is accompanied by a low activation energy of circa 0.35 eV being comparable with that of, e.g., LLZO-type garnets, which represent the current benchmark in this field. We propose these novel materials as a building block for a lattice-matching all-spinel solid-state battery with low interfacial resistance.

Electronic, optical and transport properties of {alpha}-, {beta}- and {gamma}-phases of spinel indium sulphide: An ab initio study

Energy Technology Data Exchange (ETDEWEB)

Sharma, Yamini, E-mail: sharma.yamini62@gmail.com [Department of Physics, Feroze Gandhi College, Rae Bareli 229001, U.P. (India); Srivastava, Pankaj [Department of Physics, Feroze Gandhi College, Rae Bareli 229001, U.P. (India)

2012-08-15

Spinel indium sulphide exists in three phases. The tetragonal {beta}-phase transforms to the cubic {alpha}-phase at 420 Degree-Sign C which further transforms to the trigonal {gamma}-phase at 754 Degree-Sign C. Due to wide energy bandgap, the phases of indium sulphide have possibilities of applications in photo-electrochemical solar cell devices as a replacement of toxic CdS. The electronic, optical and transport properties of the three phases have therefore been investigated using full potential linear augmented plane wave (FP-LAPW) + local orbitals (lo) scheme, in the framework of density functional theory (DFT) with generalized gradient approximation (GGA) for the purpose of exchange-correlation energy functional. We present the structure, energy bands and density of states (DOS) for {alpha}-, {beta}- and {gamma}-phases. The partial density of states (PDOS) of {beta}-In{sub 2}S{sub 3} is in good agreement with experiment and earlier ab initio calculations. To obtain the fundamental characteristics of these phases we have analysed their linear optical properties such as the dynamic dielectric function in the energy range of 0-15 eV. From the dynamic dielectric function it is seen that there is no directional anisotropy for {alpha}-phase since the longitudinal and transverse components are almost identical, however the {beta} and {gamma}-phases show birefringence. The optical absorption profiles clearly indicate that {beta}-phase has possibility of greater multiple direct and indirect interband transitions in the visible regions compared to the other phases. To study the existence of interesting thermoelectric properties, transport properties like electrical and thermal conductivities, Seebeck and Hall coefficients etc. are also calculated. Good agreements are found with the available experimental results. -- Highlights: Black-Right-Pointing-Pointer The electronic properties of phases of In{sub 2}S{sub 3} have been investigated. Black-Right-Pointing-Pointer The

Cation-substituted spinel oxide and oxyfluoride cathodes for lithium ion batteries

Science.gov (United States)

Manthiram, Arumugam; Choi, Wonchang

2010-05-18

The present invention includes compositions and methods of making cation-substituted and fluorine-substituted spinel cathode compositions by firing a LiMn2-y-zLiyMzO4 oxide with NH4HF2 at low temperatures of between about 300 and 700.degree. C. for 2 to 8 hours and a .eta. of more than 0 and less than about 0.50, mixed two-phase compositions consisting of a spinel cathode and a layered oxide cathode, and coupling them with unmodified or surface modified graphite anodes in lithium ion cells.

Syndeformation Chrome Spinels Inclusions in the Plastically Deformed Olivine Aggregates (Kraka Ophiolites, the Southern Urals

Directory of Open Access Journals (Sweden)

D. E. Saveliev

2015-12-01

Full Text Available This article presents the results of structural, petrographic, mineralogical and chemical studies of dunite veinlets in spinel peridotite from the Kraka ophiolites. It is demonstrated that plastic deformation of polycrystalline olivine, which form dunite, was accompanied by precipitation of impurities (aluminum and chrome as newly formed chrome spinels. The thinnest acicular inclusions of 0.3-0.5 micron thick are aligned in olivine grains along [010] axis. Bigger elongated irregular chrome spinel grains usually occur along grain and sub-grain olivine boundaries, and, occasionally, inside the grains along [100] axis. Alteration from the fine xenomorphic grains of chrome spinels to the bigger idiomorphic crystals was observed. Analogically to dynamic ageing (dispersion hardening in metals, the structural and chemical alterations in dunites are interpreted as deformation induced segregation of impurities. It is suggested that the euhedral chrome spinel grains typical for ophiolitic dunites were formed by coalescence and spheroidization. This process may be a key factor in the formation of ophiolitic chrome ore deposits.

Direct observation of cation distributions of ideal inverse spinel CoFe2O4 nanofibres and correlated magnetic properties

KAUST Repository

Zeng, Xue

2017-04-25

Low-dimensional spinel ferrites have recently attracted increasing attention because their tunable magnetic properties make them attractive candidates as spin-filtering tunnel barriers in spintronic devices and as magnetic components in artificial multiferroic heterostructures. Although we know that the distribution of cations (Fe3+ and Co2+) in a spinel structure governs its magnetic properties, their distribution in the so-called ideal inverse spinel structure of a ferrite, CoFe2O4, has not yet been imaged with sub-ångstrom resolution. In this work, we fill this gap in evidence by reporting a direct observation of the distribution of cations in an ideal inverse spinel structure of CoFe2O4 nanofibres using aberration-corrected transmission electron microscopy (TEM). The ordering of Co2+ and Fe3+ at the octahedral sites imaged along either [001], [011] or [-112] orientation was identified as 1 : 1, in accordance with the ideal inverse spinel structure. The saturation magnetisation calculated based on the crystal structure as determined from the TEM image is in good agreement with that measured experimentally on the spinel CoFe2O4 nanofibres, further confirming results from TEM.

Cr diffusion in MgAl2O4 synthetic spinels: preliminary results

Science.gov (United States)

Freda, C.; Celata, B.; Andreozzi, G.; Perinelli, C.; Misiti, V.

2012-04-01

Chromian spinel is an accessory phase common in crustal and mantle rocks, including peridotites, gabbros and basalts. Spinel, it has been identified as one of the most effective, sensible, and versatile petrogenetic indicator in mafic and ultramafic rock systems due to the strict interdependence between its physico-chemical properties (chemical composition, cation configuration etc.) and genetic conditions (temperature, pressure, and chemical characteristics of the system). In particular, studies on intra- and inter-crystalline Mg-Fe2+, Cr-Al exchange demonstrated the close relationship between spinel composition and both degree of partial melting and equilibrium temperature of spinel-peridotites. Moreover, studies focused on the chemical zoning of Mg-Fe2+ and/or Cr-Al components in spinel have been used, combined with a diffusion model, to provide quantitative information on peridotites and gabbros pressure-temperature paths and on deformation mechanisms. Although these potentials, most of the experimental studies have been performed on spinels hosting a limited content of divalent iron (sensu stricto, MgAl2O4), whereas the scarce studies on Cr-Al inter-diffusion coefficient have been performed at 3-7 GPa as pressure boundary condition. In order to contribute to the understanding of processes occurring in the lithospheric mantle, we have initiated an experimental research project aiming at determining the Cr-Al inter-diffusion in spinel at 2 GPa pressure and temperature ranging from 1100 to 1250 °C. The experiments were performed in a end-loaded piston cylinder by using a 19 mm assembly and graphite-Pt double capsules. As starting materials we used synthetic Mg-Al spinel (200-300 μm in size) and Cr2O3 powder. Microanalyses of experimental charge were performed on polished carbon-coated mounts by electronic microprobe. Line elemental analyses were made perpendicular to the contact surface between Cr2O3 powder and spinel, at interval of 2 μm. By processing these

Effect of d-block element Co{sup 2+} substitution on structural, Mössbauer and dielectric properties of spinel copper ferrites

Energy Technology Data Exchange (ETDEWEB)

Dar, M.A.; Varshney, Dinesh, E-mail: vdinesh33@rediffmail.com

2017-08-15

Highlights: • Tetragonal (I41/amd) to cubic (Fd3m) phase change is observed in Cu{sub 1−x}Co{sub x}Fe{sub 2}O{sub 4}. • Raman studies reveal 2 (5) optical active modes in CuFe{sub 2}O{sub 4} and 5 (5) at room temperature. • Transmission Mössbauer spectroscopy discerns two sets of six-line hyperfine patterns. • The dielectric constant increases is maximum for Co{sup 2+}x = 0.1 composition. • ac conductivity is constant (low frequency) and increases abruptly (high frequency). - Abstract: The present work focuses on the influence of replacement of d-block element Cu{sup 2+} ion by Co{sup 2+} in Cu-spinel ferrites [Cu{sub 1−x}Co{sub x}Fe{sub 2}O{sub 4} (x = 0.0, 0.1, 0.2, 0.4, 0.6, and 1.0)] on the structural, vibrational and dielectric properties as synthesized by Solid-state reaction route. A structural transition from tetragonal (space group I41/amd)) to cubic (space group Fd3m) phase is observed due to introduction of cobalt. Cubic spinel- type structure at room temperature of Cu{sub 1−x}Co{sub x}Fe{sub 2}O{sub 4} (0.4 ≤ x ≤ 1.0) is confirmed by Rietveld – refined X-ray powder diffraction patterns. Raman spectroscopic studies reveal 2 (5) optical active modes in CuFe{sub 2}O{sub 4} (CoFe{sub 2}O{sub 4}) at room temperature. Transmission Mössbauer spectroscopy of Cu{sub 1−x}Co{sub x}Fe{sub 2}O{sub 4} (x = 0.0, 0.2 and 0.6) shows two sets of six-line hyperfine patterns for all the three samples, indicating the presence of Fe in both A and B sites. Identification of sites is accomplished by evidence from hyperfine distribution and isomer-shift data. Dielectric constant and dielectric loss tangent measured in the frequency range from 1 KHz to 1 MHz at room temperature are found to be decreasing with the increase in frequency.

Microfluidic Manufacturing of Polymeric Nanoparticles: Comparing Flow Control of Multiscale Structure in Single-Phase Staggered Herringbone and Two-Phase Reactors.

Science.gov (United States)

Xu, Zheqi; Lu, Changhai; Riordon, Jason; Sinton, David; Moffitt, Matthew G

2016-12-06

We compare the microfluidic manufacturing of polycaprolactone-block-poly(ethylene oxide) (PCL-b-PEO) nanoparticles (NPs) in a single-phase staggered herringbone (SHB) mixer and in a two-phase gas-liquid segmented mixer. NPs generated from two different copolymer compositions in both reactors and at three different flow rates, along with NPs generated using a conventional bulk method, are compared with respect to morphologies, dimensions, and internal crystallinities. Our work, the first direct comparison between alternate microfluidic NP synthesis methods, shows three key findings: (i) NP morphologies and dimensions produced in the bulk are different from those produced in a microfluidic mixer, whereas NP crystallinities produced in the bulk and in the SHB mixer are similar; (ii) NP morphologies, dimensions, and crystallinities produced in the single-phase SHB and two-phase mixers at the lowest flow rate are similar; and (iii) NP morphologies, dimensions, and crystallinities change with flow rate in the two-phase mixer but not in the single-phase SHB mixer. These findings provide new insights into the relative roles of mixing and shear in the formation and flow-directed processing of polymeric NPs in microfluidics, informing future reactor designs for manufacturing NPs of low polydispersity and controlled multiscale structure and function.

Ab initio investigation of the thermodynamics of cation distribution and of the electronic and magnetic structures in the LiMn2O4 spinel

Science.gov (United States)

Santos-Carballal, David; Ngoepe, Phuti E.; de Leeuw, Nora H.

2018-02-01

The spinel-structured lithium manganese oxide (LiMn2O4 ) is a material currently used as cathode for secondary lithium-ion batteries, but whose properties are not yet fully understood. Here, we report a computational investigation of the inversion thermodynamics and electronic behavior of LiMn2O4 derived from spin-polarized density functional theory calculations with a Hubbard Hamiltonian and long-range dispersion corrections (DFT+U-D3). Based on the analysis of the configurational free energy, we have elucidated a partially inverse equilibrium cation distribution for the LiMn2O4 spinel. This equilibrium degree of inversion is rationalized in terms of the crystal field stabilization effects and the difference between the size of the cations. We compare the atomic charges with the oxidation numbers for each degree of inversion. We found segregation of the Mn charge once these ions occupy the tetrahedral and octahedral sites of the spinel. We have obtained the atomic projections of the electronic band structure and density of states, showing that the normal LiMn2O4 has half-metallic properties, while the fully inverse spinel is an insulator. This material is in the ferrimagnetic state for the inverse and partially inverse cation arrangement. The optimized lattice and oxygen parameters, as well as the equilibrium degree of inversion, are in agreement with the available experimental data. The partial equilibrium degree of inversion is important in the interpretation of the lithium ion migration and surface properties of the LiMn2O4 spinel.

Mechanism of γ-irradiation induced phase transformations in nanocrystalline Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} ceramics

Energy Technology Data Exchange (ETDEWEB)

Jagadeesha Angadi, V. [Department of Physics, Bangalore University, Bangalore, Karnataka 560056 (India); Anupama, A.V.; Choudhary, Harish K.; Kumar, R. [Materials Research Centre, Indian Institute of Science, Bangalore, 560012 (India); Somashekarappa, H.M. [Center for Application of Radioisotopes and Radiation Technology, Mangalore University, Mangalore 574199 (India); Mallappa, M. [Department of Chemistry, Government Science College, Bangalore 560001 (India); Rudraswamy, B. [Department of Physics, Bangalore University, Bangalore, Karnataka 560056 (India); Sahoo, B., E-mail: bsahoo@mrc.iisc.ernet.in [Materials Research Centre, Indian Institute of Science, Bangalore, 560012 (India)

2017-02-15

The structural, infrared absorption and magnetic property transformations in nanocrystalline Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} samples irradiated with different doses (0, 15, 25 and 50 kGy) of γ-irradiation were investigated in this work and a mechanism of phase transformation/decomposition is provided based on the metastable nature of the Mn-atoms in the spinel lattice. The nano-powder sample was prepared by solution combustion route and the pellets of the sample were exposed to γ-radiation. Up to a dose of 25 kGy of γ-radiation, the sample retained the single phase cubic spinel (Fd-3m) structure, but the disorder in the sample increased. On irradiating the sample with 50 kGy γ-radiation, the spinel phase decomposed into new stable phases such as α-Fe{sub 2}O{sub 3} and ZnFe{sub 2}O{sub 4} phases along with amorphous MnO phase, leading to a change in the surface morphology of the sample. Along with the structural transformations the magnetic properties deteriorated due to breakage of the ferrimagnetic order with higher doses of γ-irradiation. Our results are important for the understanding of the stability, durability and performance of the Mn-Zn ferrite based devices used in space applications. - Graphical abstract: The nanocrystalline Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} ceramic sample transforms to crystalline α-Fe{sub 2}O{sub 3} and ZnFe{sub 2}O{sub 4} phases (and amorphous MnO phase) at a γ-irradiation dose of 50 kGy, as MnO goes out of the spinel lattice. The high energy γ-irradiation causes structural damage to the nanomaterials leading to change in morphology of the sample as seen in the SEM images. - Highlights: • Mn atoms are more unstable in the Mn-Zn ferrite spinel lattice than Zn-atoms. • Displacement of Mn atoms by γ-radiation from the lattice renders phase transformation. • In Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4}, Mn-ferrite cell transforms to crystalline α-Fe{sub 2}O{sub 3} and amorphous MnO. • The stable ZnFe{sub 2}O

Thermodynamic Modelling of Fe-Cr-Ni-Spinel Formation at the Light-Water Reactor Conditions

International Nuclear Information System (INIS)

Kurepin, V. A.; Kulik, D. A.; Hitpold, A.; Nicolet, M.

2002-03-01

In the light water reactors (LWR), the neutron activation and transport of corrosion products is of concern in the context of minimizing the radiation doses received by the personnel during maintenance works. A practically useful model for transport and deposition of the stainless steel corrosion products in LWR can only be based on an improved understanding of chemical processes, in particular, on the attainment of equilibrium in this hydrothermal system, which can be described by means of a thermodynamic solid-solution -aqueous-solution (SSAS) model. In this contribution, a new thermodynamic model for a Fe-Cr-Ni multi-component spinel solid solutions was developed that considers thermodynamic consequences of cation interactions in both spinel sub-Iattices. The obtained standard thermodynamic properties of two ferrite and two chromite end-members and their mixing parameters at 90 bar pressure and 290 *c temperature predict a large miscibility gap between (Fe,Ni) chromite and (Fe,Ni) ferrite phases. Together with the SUPCRT92-98 thermo- dynamic database for aqueous species, the 'spinel' thermodynamic dataset was applied to modeling oxidation of austenitic stainless steel in hydrothermal water at 290*C and 90 bar using the Gibbs energy minimization (GEM) algorithm, implemented in the GEMS-PSI code. Firstly, the equilibrium compositions of steel oxidation products were modelIed as function of oxygen fugacity .fO 2 by incremental additions of O 2 in H 2 O-free system Cr-Fe- Ni-O. Secondly, oxidation of corrosion products in the Fe-Cr-Ni-O-H aquatic system was modelIed at different initial solid/water ratios. It is demonstrated that in the transition region from hydrogen regime to oxygen regime, the most significant changes in composition of two spinel-oxide phases (chromite and ferrite) and hematite must take place. Under more reduced conditions, the Fe-rich ferrite (magnetite) and Ni-poor chromite phases co-exist at equilibrium with a metal Ni phase, maintaining

Thermodynamic Modelling of Fe-Cr-Ni-Spinel Formation at the Light-Water Reactor Conditions

Energy Technology Data Exchange (ETDEWEB)

Kurepin, V.A.; Kulik, D.A.; Hitpold, A.; Nicolet, M

2002-03-01

In the light water reactors (LWR), the neutron activation and transport of corrosion products is of concern in the context of minimizing the radiation doses received by the personnel during maintenance works. A practically useful model for transport and deposition of the stainless steel corrosion products in LWR can only be based on an improved understanding of chemical processes, in particular, on the attainment of equilibrium in this hydrothermal system, which can be described by means of a thermodynamic solid-solution -aqueous-solution (SSAS) model. In this contribution, a new thermodynamic model for a Fe-Cr-Ni multi-component spinel solid solutions was developed that considers thermodynamic consequences of cation interactions in both spinel sub-Iattices. The obtained standard thermodynamic properties of two ferrite and two chromite end-members and their mixing parameters at 90 bar pressure and 290 *c temperature predict a large miscibility gap between (Fe,Ni) chromite and (Fe,Ni) ferrite phases. Together with the SUPCRT92-98 thermo- dynamic database for aqueous species, the 'spinel' thermodynamic dataset was applied to modeling oxidation of austenitic stainless steel in hydrothermal water at 290*C and 90 bar using the Gibbs energy minimization (GEM) algorithm, implemented in the GEMS-PSI code. Firstly, the equilibrium compositions of steel oxidation products were modelIed as function of oxygen fugacity .fO{sub 2} by incremental additions of O{sub 2} in H{sub 2}O-free system Cr-Fe- Ni-O. Secondly, oxidation of corrosion products in the Fe-Cr-Ni-O-H aquatic system was modelIed at different initial solid/water ratios. It is demonstrated that in the transition region from hydrogen regime to oxygen regime, the most significant changes in composition of two spinel-oxide phases (chromite and ferrite) and hematite must take place. Under more reduced conditions, the Fe-rich ferrite (magnetite) and Ni-poor chromite phases co-exist at equilibrium with a metal Ni

Comparative Study of Optical and Magneto-Optical Properties of Normal, Disordered and Inverse Spinel Type Oxides

OpenAIRE

Zviagin, Vitaly; Richter, Peter; Böntgen, Tammo; Lorenz, Michael; Ziese, Michael; Zahn, Dietrich R. T.; Salvan, Georgeta; Grundmann, Marius; Schmidt-Grund, Rüdiger

2015-01-01

Co$_3$O$_4$, ZnFe$_2$O$_4$, CoFe$_2$O$_4$, ZnCo$_2$O$_4$, and Fe$_3$O$_4$ thin films were fabricated by pulsed laser deposition at high and low temperatures resulting in crystalline single-phase normal, inverse, as well as disordered spinel oxide thin films with smooth surface morphology. The dielectric function, determined by spectroscopic ellipsometry in a wide spectral range from 0.5 eV to 8.5 eV, is compared with the magneto-optical response of the dielectric tensor, investigated by magne...

Single-Phase PLLs

DEFF Research Database (Denmark)

Golestan, Saeed; Guerrero, Josep M.; Quintero, Juan Carlos Vasquez

2017-01-01

Single-phase phase-locked loops (PLLs) are popular for the synchronization and control of single-phase gridconnected converters. They are also widely used for monitoring and diagnostic purposes in the power and energy areas. In recent years, a large number of single-phase PLLs with different stru......-PLLs). The members of each category are then described and their pros and cons are discussed. This work provides a deep insight into characteristics of different single-phase PLLs and, therefore, can be considered as a reference for researchers and engineers....

Origin of the low compressibility in hard nitride spinels

DEFF Research Database (Denmark)

Mori-Sánchez, P.; Marqués, M.; Beltrán, A.

2003-01-01

A microscopic investigation of first-principles electron densities of gamma-A(3)N(4) (A:C,Si,Ge) spinels reveals a clear relationship between the compressibility and the chemical bonding of these materials. Three striking findings emanate from this analysis: (i) the chemical graph is governed...... by a network of highly directional strong bonds with covalent character in gamma-C3N4 and different degrees of ionic polarization in gamma-Si3N4 and gamma-Ge3N4, (ii) nitrogen is the lowest compressible atom controlling the trend in the bulk modulus of the solids, and (iii) the group-IV counterions show strong...... site dependent compressibilities enhancing the difficulty in the synthesis of the spinel phases of these nitrides....

Magnetic phase diagrams of the spinels AB2xGa2-2xO4 (A = Zn, Co; B = Al, Cr) systems

International Nuclear Information System (INIS)

Hamedoun, M.; Masrour, R.; Bouslykhane, K.; Hourmatallah, A.; Benzakour, N.

2008-01-01

The magnetic properties of the spinels CoAl 2x Ga 2-2x O 4 and ZnCr 2x Ga 2-2x O 4 systems in the range 0 ≤ x ≤ 1 have been studied by mean field theory and high-temperature series expansions. By using the first theory, we have evaluated the nearest neighbour and the next-neighbour super-exchange interaction J 1 (x) and J 2 (x), respectively, for the first systems in the range 0 ≤ x ≤ 1 and J 1 (x = 1), J 2 (x = 1) for the second system. The intra-planar and the inter-planar interactions are deduced. The corresponding classical exchange energy for magnetic structure is obtained for the first system. The second theory have been applied in the spinels CoAl 2x Ga 2-2x O 4 and ZnCr 2x Ga 2-2x O 4 systems, combined with the Pade approximants method, we have obtained the magnetic phase diagrams (T N versus dilution x) in the range 0 ≤ x ≤ 1. The obtained theoretical results are in agreement with experimental ones obtained by magnetic measurements and Moessbauer spectroscopy. The threshold percolation in the second system is x p ∼ 0.4. The critical exponents associated with the magnetic susceptibility (γ) and the correlation lengths (ν) are deduced in the range 0 ≤ x ≤ 1

Crystal growth and magnetic properties of spinel (Co,Mn)3O4

Science.gov (United States)

Kang, Sun Hee; Kim, Ill Won; Jeong, Yoon Hee; Koo, Tae Yeong

2012-04-01

Single crystals of cubic and tetragonal spinel Co3-xMnxO4 (x=1.0 and 1.5) were successfully grown using a solvent evaporation method with PbF2 flux. Single crystals in octahedral shape with a size of about 4 mm on edge were obtained from 100 cm3 Pt crucibles. Ferrimagnetic transitions were detected at 170 K and 160 K from the measurements of temperature dependent magnetization and specific heat of Co2MnO4 and Co1.5Mn1.5O4, respectively. Low temperature field-dependent magnetization curves give a strong indication of the non-collinear spin structure, offering an insulating Co3-xMnxO4 system as a possible candidate for examining the multiferroicity.

The role of praseodymium substituted ions on electrical and magnetic properties of Mg spinel ferrites

Energy Technology Data Exchange (ETDEWEB)

Farid, Muhammad Tahir, E-mail: tahirfaridbzu@gmail.com; Ahmad, Ishtiaq; Kanwal, Muddassara; Murtaza, Ghulam; Ali, Irshad; Khan, Sajjad Ahmad

2017-04-15

Spinel ferrites with composition MgPr{sub y}Fe{sub 2−y}O{sub 4} (y=0.0, 0.025, 0.05, 0.075, 0.10) were successfully synthesized using sol-gel auto-combustion technique. The structural prisoperties of a prepared sintered powder were characterized with the help of X-ray Diffraction (XRD) and then also by using Scanning electron microscopy (SEM). Electrical measurements demonstrate that resistivity and activation energy increases with the Praseodymium substitution while dc resistivity decreases with the rise of temperature showing the semiconductor nature of the synthesized ferrites. Remanence and the saturation magnetization (M{sub s}) decrease while coercivity (H{sub c}) also increases with the increase in praseodymium contents. Anisotropic constant is observed to exhibit similar behavior as H{sub C}. The above mentioned parameters suggest that the synthesized samples are favorable for microwave absorbing purposes. - Highlights: • Magnesium based spinel ferrites were successfully synthesized by sol-gel method. • The spinel phase has been observed in all samples. • The dc resistivity are found to increase with increasing Pr content • The samples with high resistivity have high values of activation energy. • The Ms Decreases with increasing Pr contents while Hc increases.

The behavior of mineral inclusions during host decomposition. A SEM-STEM study of rutile inclusions at a natural propagating corundum-spinel interface.

Science.gov (United States)

Baldwin, Lisa; Li, Chen; Habler, Gerlinde; Abart, Rainer

2017-04-01

When two neighbor phases are not in chemical equilibrium, they may react and produce a reaction rim at their interface, separating the mutually incompatible phases. At constant P-T-X conditions, such a reaction will continue until one of the reactants is completely consumed. Reaction rim growth involves transfer of chemical components across the growing rim by long-range diffusion and localized interface reactions on either side of the growing rim. Consequently, the thickness of the reaction rim will be a function of time. Yet, in order to quantify and interpret such corona structures and to define a reaction rate law, the kinetics and mechanism of rim formation must be well constrained. In particular, the coupling between long-range diffusion, and interface reaction must be known. In this contribution we focus on potential complexities associated with interface reactions. Many natural minerals contain inclusions of other phases, which in turn may influence the reaction interface propagation kinetics during host phase decomposition (Ashby et al. 1969), as a propagating reaction interface dissipates more free energy when bypassing a mineral inclusion, resulting in a locally decelerated reaction rate. Here, we report results of a SEM-STEM study of the interface between natural rutile-bearing corundum and a polycrystalline ferromagnesio-aluminate spinel that grew topotactically with respect to the corundum precursor as a consequence of its reaction with FeO and MgO from basaltic melt. Electron Backscatter Diffraction (EBSD) crystal orientation imaging revealed that the spinel rim is polycrystalline and exhibits (111) twinning that is parallel to the corundum (0001) plane. The rutile inclusions in corundum are elongated perpendicular to the corundum [0001] axis and are randomly oriented in the (0001) plane. Furthermore, they follow an oscillatory grain size distribution zonation with grain sizes being either a few tens of nanometers, or about 500 to 800 nanometers in

Spinel + quartz-bearing ultrahigh-temperature granulites from Xumayao, Inner Mongolia Suture Zone, North China Craton: Petrology, phase equilibria and counterclockwise p-T path

Directory of Open Access Journals (Sweden)

Huatian Zhang

2012-09-01

Our phase equilibria modeling indicates two main stages during the metamorphic evolution of these rocks: 1 near-isobaric cooling from 975 °C to 875 °C around 8 kbar, represented by the formation of garnet porphyroblasts from spinel and quartz; and 2 cooling and decompression from 850 °C, 8 kbar to below 750 °C, 6.5 kbar, represented by the break-down of garnet. The spinel + quartz assemblage is considered to have been stable at peak metamorphism, formed through the break-down of cordierite, indicating a near isothermal compression process. Our study confirms the regional extent of UHT metamorphism within the IMSZ associated with the Paleoproterozoic subduction-collision process.

Effect of MgCl2 addition on the sintering behavior of MgAl2O4 spinel and formation of nano-particles

Directory of Open Access Journals (Sweden)

Mohammadi F.

2014-01-01

Full Text Available In this paper, the effect of MgCl2 addition on the sintering behavior of MgAl2O4 spinel produced via oxide mixture method was investigated. For this reason, the stoichiometric mixture of magnesite and calcined alumina as raw materials was calcined at 1100°C. The calcined mixture was milled, pressed and then, fired at 1300 and 1500°C after addition of various amounts of MgCl2. Besides, the physical properties, phase composition and microstructure of fired samples were investigated. The results showed that MgCl2 addition has great effect on the densification and particle size of spinel. Besides, MgCl2 addition increases the amount of spinel phase at all firing temperatures. Due to the decomposition of MgCl2 and then formation of ultra-fine MgO particles, the nano-sized spinel is formed on the surface of the larger spinel particles.

Rietveld structure refinement and elastic properties of MgAlxCrxFe2-2xO4 spinel ferrites

Science.gov (United States)

Thummer, K. P.; Tanna, Ashish R.; Joshi, Hiren H.

2017-05-01

MgAlxCrxFe2-2xO4 (x = 0.1, 03 & 0.6) ferrites are synthesized by solid state reaction method. The Rietveld refinement of X-ray diffraction (XRD) data confirms the cubic spinel structure with Fd3m space group. The Fourier Transform Infrared Transmission Spectroscopy (FTIR) is employed to study elastic properties of present systems at 300K. The force constants for tetrahedral (A) and octahedral (B) sites of the spinel lattice are determined by infrared spectral and X-ray diffraction analysis. The elastic constants like bulk modulus, rigidity modulus, Young's modulus, Poisson's ratio and Debye temperature are determined. The vibrational frequency of both the interstitial sites increases as Al-Cr content increases hence the force constant and elastic moduli for all the samples are found to increase for the present ferrite system.

Kinetic model for quartz and spinel dissolution during melting of high-level-waste glass batch

International Nuclear Information System (INIS)

Pokorny, Richard; Rice, Jarrett A.; Crum, Jarrod V.; Schweiger, Michael J.; Hrma, Pavel

2013-01-01

The dissolution of quartz particles and the growth and dissolution of crystalline phases during the conversion of batch to glass potentially affects both the glass melting process and product quality. Crystals of spinel exiting the cold cap to molten glass below can be troublesome during the vitrification of iron-containing high-level wastes. To estimate the distribution of quartz and spinel fractions within the cold cap, we used kinetic models that relate fractions of these phases to temperature and heating rate. Fitting the model equations to data showed that the heating rate, apart from affecting quartz and spinel behavior directly, also affects them indirectly via concurrent processes, such as the formation and motion of bubbles. Because of these indirect effects, it was necessary to allow one kinetic parameter (the pre-exponential factor) to vary with the heating rate. The resulting kinetic equations are sufficiently simple for the detailed modeling of batch-to-glass conversion as it occurs in glass melters. The estimated fractions and sizes of quartz and spinel particles as they leave the cold cap, determined in this study, will provide the source terms needed for modeling the behavior of these solid particles within the flow of molten glass in the melter

Effect of Feed Melting, Temperature History and Minor Component Addition on Spinel Crystallization in High-Level Waste Glass

International Nuclear Information System (INIS)

Izak, Pavel; Hrma, Pavel R.; Arey, Bruce W.; Plaisted, Trevor J.

2001-01-01

This study was undertaken to help design mathematical models for high-level waste (HLW) glass melter that simulate spinel behavior in molten glass. Spinel, (Fe,Ni,Mn) (Fe,Cr)2O4, is the primary solid phase that precipitates from HLW glasses containing Fe and Ni in sufficient concentrations. Spinel crystallization affects the anticipated cost and risk of HLW vitrification. To study melting reactions, we used simulated HLW feed, prepared with co-precipitated Fe, Ni, Cr, and Mn hydroxides. Feed samples were heated up at a temperature-increase rate (4C/min) close to that which the feed experiences in the HLW glass melter. The decomposition, melting, and dissolution of feed components (such as nitrates, carbonates, and silica) and the formation of intermediate crystalline phases (spinel, sodalite (Na8(AlSiO4)6(NO2)2), and Zr-containing minerals) were characterized using evolved gas analysis, volume-expansion measurement, optical microscope, scanning electron microscope, thermogravimetric analysis, differential scanning calorimetry, and X-ray diffraction. Nitrates and quartz, the major feed components, converted to a glass-forming melt by 880C. A chromium-free spinel formed in the nitrate melt starting from 520C and Sodalite, a transient product of corundum dissolution, appeared above 600C and eventually dissolved in glass. To investigate the effects of temperature history and minor components (Ru,Ag, and Cu) on the dissolution and growth of spinel crystals, samples were heated up to temperatures above liquidus temperature (TL), then subjected to different temperature histories, and analyzed. The results show that spinel mass fraction, crystals composition, and crystal size depend on the chemical and physical makeup of the feed and temperature history

Facile and efficient one-pot solvothermal and microwave-assisted synthesis of stable colloidal solutions of MFe2O4 spinel magnetic nanoparticles

International Nuclear Information System (INIS)

Solano, Eduardo; Perez-Mirabet, Leonardo; Martinez-Julian, Fernando; Guzmán, Roger; Arbiol, Jordi; Puig, Teresa; Obradors, Xavier; Yañez, Ramón; Pomar, Alberto; Ricart, Susagna; Ros, Josep

2012-01-01

Well-defined synthesis conditions of high quality MFe 2 O 4 (M = Mn, Fe, Co, Ni, Zn, and Cu) spinel ferrite magnetic nanoparticles, with diameters below 10 nm, have been described based on facile and efficient one-pot solvothermal or microwave-assisted heating procedures. Both methods are reproducible and scalable and allow forming concentrated stable colloidal solutions in polar solvents, but microwave-assisted heating allows reducing 15 times the required annealing time and leads to an enhanced monodispersity of the nanoparticles. Non-agglomerated nanoparticles dispersions have been achieved using a simple one-pot approach where a single compound, triethyleneglycol, behaves at the same time as solvent and capping ligand. A narrow nanoparticle size distribution and high quality crystallinity have been achieved through selected nucleation and growth conditions. High resolution transmission electron microscopy images and electron energy loss spectroscopy analysis confirm the expected structure and composition and show that similar crystal faceting has been formed in both synthetic approaches. The spinel nanoparticles behave as ferrimagnets with a high saturation magnetization and are superparamagnetic at room temperature. The influence of synthesis route on phase purity and unconventional magnetic properties is discussed in some particular cases such as CuFe 2 O 4 , CoFe 2 O 4 , and ZnFe 2 O 4 .

Structural characterization and electrochemical behaviour of Li{sub (4−x)/3}Ti{sub (5−2x)/3}Mn{sub x}O{sub 4} solid solution with spinel-structure

Energy Technology Data Exchange (ETDEWEB)

Martín, P., E-mail: pmartinp@quim.ucm.es; López, M.L.; Pico, C.; Veiga, M.L.

2013-07-15

A series of new oxides Li{sub (4−x)/3}Ti{sub (5−2x)/3}Mn{sub x}O{sub 4} (0.1 ≤ x ≤ 0.9) have been synthesized by solid state reactions and characterized by thermal analysis and X-ray and neutron diffraction. In all phases, Li{sup +} cations mainly occupy tetrahedral sites and transition metals cations are located on the octahedral ones. These phases show a structural disorder–order transition associated to the proportion of manganese in the samples and to its oxidation state. All these factors have a marked influence on the electrochemical properties and the phase x = 0.1 shows the best characteristics to be used as anode in a solid state battery. - Highlights: • Lithium spinels anodes in batteries. • Influence of Ti/Mn ratio in the electrochemical behaviour. • Li{sub 1.3}Ti{sub 1.6}Mn{sub 0.1}O{sub 4}: a promising zero-strain material. • Influence of disorder–order transitions on the physical properties.

Control of Single-Stage Single-Phase PV inverter

DEFF Research Database (Denmark)

Ciobotaru, Mihai; Teodorescu, Remus; Blaabjerg, Frede

2005-01-01

In this paper the issue of control strategies for single-stage photovoltaic (PV) inverter is addressed. Two different current controllers have been implemented and an experimental comparison between them has been made. A complete control structure for the single-phase PV system is also presented......-forward; - and the grid current controller implemented in two different ways, using the classical proportional integral (PI) and the novel proportional resonant (PR) controllers. The control strategy was tested experimentally on 1.5 kW PV inverter....

Dynamics of Mantle Plume Controlled by both Post-spinel and Post-garnet Phase Transitions

Science.gov (United States)

Liu, H.; Leng, W.

2017-12-01

Mineralogical studies indicate that two major phase transitions occur near 660 km depth in the Earth's pyrolitic mantle: the ringwoodite (Rw) to perovskite (Pv) + magnesiowüstite (Mw) and majorite (Mj) to perovskite (Pv) phase transitions. Seismological results also show a complicated phase boundary structure for plume regions at this depth, including broad pulse, double reflections and depressed 660 km discontinuity beneath hot regions etc… These observations have been attributed to the co-existence of these two phase transformations. However, previous geodynamical modeling mainly focused on the effects of Rw-Pv+Mw phase transition on the plume dynamics and largely neglected the effects of Mj-Pv phase transition. Here we develop a 3-D regional spherical geodynamic model to study the influence of the combination of Rw - Pv+Mw and Mj - Pv phase transitions on plume dynamics, including the topography fluctuation of 660 km discontinuity, plume shape and penetration capability of plume. Our results show that (1) a double phase boundary occurs at the hot center area of plume while for other regions with relatively lower temperature the phase boundary is single and flat, which respectively corresponds to the double reflections in the seismic observations and a high velocity prism-like structure at the top of 660 km discontinuity; (2) a large amount of low temperature plume materials could be trapped to form a complex trapezoid overlying the 660 km depth; (3) Mj - Pv phase change strongly enhances the plume penetration capability at 660 km depth, which significantly increases the plume mass flux due to the increased plume radius, but significantly reduces plume heat flux due to the decreased plume temperature in the upper mantle. Our model results provide new enlightenments for better constraining seismic structure and mineral reactions at 660 km phase boundaries.

Influence of graphite contamination on the optical properties of transparent spinel obtained by spark plasma sintering

International Nuclear Information System (INIS)

Bernard-Granger, G.; Benameur, N.; Guizard, C.; Nygren, M.

2009-01-01

The optical properties of transparent spinel sintered by spark plasma sintering have been investigated for incident electromagnetic radiations with wavelengths in the range 0.2-2 μm. It is shown that residual porosities and second-phase graphite particles have a strong influence on the in-line transmittance. Because of the graphite particles, the in-line transmittance measured does not approach that of monocrystalline spinel for wavelengths above 1 μm

Amplification of the discharge current density of lithium-ion batteries with spinel phase Li(PtAu)0.02Mn1.98O4 nano-materials

CSIR Research Space (South Africa)

Ross, N

2014-05-01

Full Text Available -ion batteries (LIB) was synthesized by incorporation of the Pt-Au (1:1) nanoparticles onto the spinel phase LiMn(sub2)O(sub4). Ultra-low scan rate (0.01 mV (sups-1)) cyclic voltammetry of the cathode material in 1 M LiPF(sub6) (in 1:1 EC:DMC), showed four sets...

Direct observation of cation distributions of ideal inverse spinel CoFe2O4 nanofibres and correlated magnetic properties

KAUST Repository

Zeng, Xue; Zhang, Junwei; Zhu, Shimeng; Deng, Xia; Ma, Hongbin; Zhang, Junli; Zhang, Qiang; Li, Peng; Xue, Desheng; Mellors, Nigel J; Zhang, Xixiang; Peng, Yong

2017-01-01

multiferroic heterostructures. Although we know that the distribution of cations (Fe3+ and Co2+) in a spinel structure governs its magnetic properties, their distribution in the so-called ideal inverse spinel structure of a ferrite, CoFe2O4, has not yet been

Investigations on structural, vibrational and dielectric properties of nanosized Cu doped Mg-Zn ferrites

Energy Technology Data Exchange (ETDEWEB)

Yadav, Anand [School of Physics, Vigyan Bhavan, Devi Ahilya University, Khandwa Road Campus, Indore 452001 (India); Department of Physics, MEDICAPS Institute of Science and Technology, Pithampur 453331 (India); Rajpoot, Rambabu; Dar, M. A.; Varshney, Dinesh, E-mail: vdinesh33@rediffmail.com, E-mail: anand.212@gmail.com [School of Physics, Vigyan Bhavan, Devi Ahilya University, Khandwa Road Campus, Indore 452001 (India)

2016-05-23

Transition metal Cu{sup 2+} doped Mg-Zn ferrite [Mg{sub 0.5}Zn{sub 0.5-x}Cu{sub x}Fe{sub 2}O{sub 4} (0.0 ≤ x ≤ 0.5)] were prepared by sol gel auto combustion (SGAC) method to probe the structural, vibrational and electrical properties. X-ray diffraction (XRD) pattern reveals a single-phase cubic spinel structure without the presence of any secondary phase corresponding to other structure. The average particle size of the parent Mg{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} is found to be ~29.8 nm and is found to increase with Cu{sup 2+} doping. Progressive reduction in lattice parameter of Mg{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} has been observed due to difference in ionic radii of cations with improved Cu doping. Spinel cubic structure is further confirmed by Raman spectroscopy. Small shift in Raman modes towards higher wave number has been observed in doped Mg-Zn ferrites. The permittivity and dielectric loss decreases at lower doping and increases at higher order doping of Cu{sup 2+}.

Electron spin transition causing structure transformations of earth's interiors under high pressure

Science.gov (United States)

Yamanaka, T.; Kyono, A.; Kharlamova, S.; Alp, E.; Bi, W.; Mao, H.

2012-12-01

To elucidate the correlation between structure transitions and spin state is one of the crucial problems for understanding the geophysical properties of earth interiors under high pressure. High-pressure studies of iron bearing spinels attract extensive attention in order to understand strong electronic correlation such as the charge transfer, electron hopping, electron high-low spin transition, Jahn-Teller distortion and charge disproponation in the lower mantle or subduction zone [1]. Experiment Structure transitions of Fe3-xSixO4, Fe3-xTixO4 Fe3-xCrxO4 spinel solid solution have been investigated at high pressure up to 60 GPa by single crystal and powder diffraction studies using synchrotron radiation with diamond anvil cell. X-ray emission experiment (XES) at high pressure proved the spin transition of Fe-Kβ from high spin (HS) to intermediate spin state (IS) or low spin state (LS). Mössbauer experiment and Raman spectra study have been also conducted for deformation analysis of Fe site and confirmation of the configuration change of Fe atoms. Jahn-Teller effect A cubic-to-tetragonal transition under pressure was induced by Jahn-Teller effect of IVFe2+ (3d6) in the tetrahedral site of Fe2TiO4 and FeCr2O4, providing the transformation from 43m (Td) to 42m (D2d). Tetragonal phase is formed by the degeneracy of e orbital of Fe2+ ion. Their c/a ratios are c/adisordered in the M2 site. At pressures above 53 GPa, Fe2TiO4 structure further transforms to Pmma. This structure change results in the order-disorder transition [2]. New structure of Fe2SiO4 The spin transition exerts an influence to Fe2SiO4 spinel structure and triggers two distinct curves of the lattice constant in the spinel phase. The reversible structure transition from cubic to pseudo-rhombohedral phase was observed at about 45 GPa. This transition is induced by the 20% shrinkage of ionic radius of VIFe2+at the low sin state. Laser heating experiment at 1500 K has confirmed the decomposition from the

Atomic-deficient nanostructurization in water-sorption alumomagnesium spinel ceramics MgAl2O4

Science.gov (United States)

Ingram, A.

2018-02-01

Atomic-deficient nanostructurization in alumomagnesium MgAl2O4 ceramics sintered at 1100-1400 °C caused by water sorption are studied employing positron annihilation lifetime spectroscopy. Detected PAL spectra are reconstructed from unconstrained x4-term decomposition, and further transformed to x3-term form to be applicable for analysis with x3-x2-CDA (coupling decomposition algorithm). It is proved that water-immersion processes reduce positronium (Ps) decaying in large-size holes of ceramics (1.70-1.84 nm in radius) at the expense of enhanced trapping in tiny ( 0.2 nm in radius) Ps-traps. The water sorption is shown to be more pronounced in structurally imperfect ceramics sintered at T s = 1100-1200 °C due to irreversible transformations between constituting phases, while reversible physical-sorption processes are dominated in structurally uniform ceramics composed of main spinel phase.

Chromian spinel-rich black sands from eastern shoreline of ...

Indian Academy of Sciences (India)

Chromian spinel; detrital sand; ophiolites; Andaman Island; India. J. Earth Syst. .... (olivine: ol) inclusion; (e) peridotitic spinel with extensive fracturing; and (f) heavily altered rim of a peridotitic spinel. ..... The authors acknowledge the financial.

Phase evaluation of Li{sup +} substituted CoFe{sub 2}O{sub 4} nanoparticles, their characterizations and magnetic properties

Energy Technology Data Exchange (ETDEWEB)

Kadam, R.H. [Materials Science Research Lab, Shrikrishna Mahavidyalaya Gunjoti, Osmanabad, Maharashtra (India); Alone, Suresh T. [Department of Physics, RS Art' s, Science and Commerce College, Pathri, Aurangabad, Maharashtra (India); Mane, Maheshkumar L. [Department of Physics, Rajarshi Shahu Mahavidyalaya, Latur, Maharashtra (India); Biradar, A.R. [Materials Science Research Lab, Shrikrishna Mahavidyalaya Gunjoti, Osmanabad, Maharashtra (India); Shirsath, Sagar E., E-mail: shirsathsagar@hotmail.com [Spin Device Technology Center, Department of Information Engineering, Shinshu University, Nagano 380-8553 (Japan)

2014-04-15

Li{sup +} substituted CoFe{sub 2}O{sub 4} with the chemical formula Li{sub 3x}CoFe{sub 2−x}O{sub 4} were synthesized by sol–gel auto combustion method. The synthesized samples were annealed at 600 °C for 4 h. X-ray diffraction data were used to evaluate the structure of the prepared samples. Spinel ferrite phase of CoFe{sub 2}O{sub 4} changes to ordered like lithium ferrite phase with increase in L{sup i+} substitution. Lattice constant increases whereas particle size found to decrease with Li{sup +} substitution. Infrared spectroscopy also confirmed the phase transition of CoFe{sub 2}O{sub 4} after the incorporation of lithium ions. Substitution of Li{sup +} ions for Fe{sup 3+} caused a decrease in the saturation magnetization from 69.59 emu/g to 47.71 emu/g and the coercivity increased from 647 Oe to 802 Oe. Resistivity and dielectric properties shows inverse relation to each other. - Highlights: • Li{sup +} ion substituted CoFe{sub 2}O{sub 4}. • Single phase cubic spinel structure changes with Li{sup +} substitution. • Magnetization decreases whereas coercivity increases with increasing Li{sup +}. • Resistivity decreases with Li{sup +} substitution.

Enhancement of Electrochemical Performance of LiMn2O4 Spinel Cathode Material by Synergetic Substitution with Ni and S

Directory of Open Access Journals (Sweden)

Monika Bakierska

2016-05-01

Full Text Available Nickel and sulfur doped lithium manganese spinels with a nominal composition of LiMn2−xNixO4–ySy (0.1 ≤ x ≤ 0.5 and y = 0.01 were synthesized by a xerogel-type sol-gel method followed by subsequent calcinations at 300 and 650 °C in air. The samples were investigated in terms of physicochemical properties using X-ray powder diffraction (XRD, transmission electron microscopy (EDS-TEM, N2 adsorption-desorption measurements (N2-BET, differential scanning calorimetry (DSC, and electrical conductivity studies (EC. Electrochemical characteristics of Li/Li+/LiMn2−xNixO4–ySy cells were examined by galvanostatic charge/discharge tests (CELL TEST, electrochemical impedance spectroscopy (EIS, and cyclic voltammetry (CV. The XRD showed that for samples calcined at 650 °C containing 0.1 and 0.2 mole of Ni single phase materials of Fd-3m group symmetry and nanoparticles size of around 50 nm were obtained. The energy dispersive X-ray spectroscopy (EDS mapping confirmed homogenous distribution of nickel and sulfur in the obtained spinel materials. Moreover, it was revealed that the adverse phase transition at around room temperature typical for the stoichiometric spinel was successfully suppressed by Ni and S substitution. Electrochemical results indicated that slight substitution of nickel (x = 0.1 and sulfur (y = 0.01 in the LiMn2O4 enhances the electrochemical performance along with the rate capability and capacity retention.

Petrogenetic importance of Cr - spinel metaperidotite

International Nuclear Information System (INIS)

Snarska, B.

2010-01-01

The research is ultramafic body Komarovce the site, which represents the spinel metaperidotit. In recent works dealing with the problems of genesis and tectonic ultramafic rocks placement consideration, Cr - spinel, which is considered an important petrogenetic indicator. Based on its chemical composition can further characterize the origin of peridotite.

Femtosecond-pulse inscription of fiber Bragg gratings with single or multiple phase-shifts in the structure

Science.gov (United States)

Wolf, Alexey; Dostovalov, Alexandr; Skvortsov, Mikhail; Raspopin, Kirill; Parygin, Alexandr; Babin, Sergey

2018-05-01

In this work, long high-quality fiber Bragg gratings with phase shifts in the structure are inscribed directly in the optical fiber by point-by-point technique using femtosecond laser pulses. Phase shifts are introduced during the inscription process with a piezoelectric actuator, which rapidly shifts the fiber along the direction of its movement in a chosen point of the grating with a chosen shift value. As examples, single and double π phase shifts are introduced in fiber Bragg gratings with a length up to 34 mm in passive fibers, which provide corresponding transmission peaks with bandwidth less than 1 pm. It is shown that 37 mm π -phase-shifted grating inscribed in an active Er-doped fiber forms high-quality DFB laser cavity generating single-frequency radiation at 1550 nm with bandwidth of 20 kHz and signal-to-noise ratio of >70 dB. The inscription technique has a high degree of performance and flexibility and can be easily implemented in fibers of various types.

Tunable phase transition in single-layer TiSe2 via electric field

Science.gov (United States)

Liu, Lei; Zhuang, Houlong L.

2018-06-01

Phase transition represents an intriguing physical phenomenon that exists in a number of single-layer transition-metal dichalcogenides. This phenomenon often occurs below a critical temperature and breaks the long-range crystalline order leading to a reconstructed superstructure called the charge-density wave (CDW) structure, which can therefore be recovered by external stimuli such as temperature. Alternatively, we show here that another external stimulation, electric field can also result in the phase transition between the regular and CDW structures of a single-layer transition-metal dichalcogenide. We used single-layer TiSe2 as an example to elucidate the mechanism of the CDW followed by calculations of the electronic structure using a hybrid density functional. We found that applying electric field can tune the phase transition between the 1T and CDW phases of single-layer TiSe2. Our work opens up a route of tuning the phase transition of single-layer materials via electric field.

Black and green pigments based on chromium-cobalt spinels

Energy Technology Data Exchange (ETDEWEB)

Eliziario, Sayonara A., E-mail: sayonaraea@iq.unesp.br [Departamento de Fisico-Quimica, Instituto de Quimica, UNESP - Univ Estadual Paulista, Araraquara, SP (Brazil); Departamento de Quimica, CCEN, Universidade Federal da Paraiba, Campus I, Joao Pessoa, PB (Brazil); Andrade, Jeferson M. de [Departamento de Quimica, CCEN, Universidade Federal da Paraiba, Campus I, Joao Pessoa, PB (Brazil); Lima, Severino J.G. [Departamento de Engenharia Mecanica, CT, Universidade Federal da Paraiba, Campus I, Joao Pessoa, PB (Brazil); Paskocimas, Carlos A. [Universidade Federal do Rio Grande do Norte, CT, Natal, RN (Brazil); Soledade, Luiz E.B. [Departamento de Quimica, CCEN, Universidade Federal da Paraiba, Campus I, Joao Pessoa, PB (Brazil); Hammer, P.; Longo, E. [Departamento de Fisico-Quimica, Instituto de Quimica, UNESP - Univ Estadual Paulista, Araraquara, SP (Brazil); Souza, Antonio G.; Santos, Ieda M.G. [Departamento de Quimica, CCEN, Universidade Federal da Paraiba, Campus I, Joao Pessoa, PB (Brazil)

2011-09-15

Highlights: {yields} Co(Co{sub 2-x}Cr{sub x})O{sub 4} powders with different chromium concentrations (x = 0, 0.25 and 1) were prepared by the polymeric precursor method. {yields} Co(CoCr)O{sub 4} and Co(Co{sub 1.75}Cr{sub 0.25})O{sub 4} displayed a dark color and CoCr{sub 2}O{sub 4} was green. {yields} The colors were related to the different oxidation states of Cr and Co. {yields} Cobalt enrichment result in an increasing presence of Co(III) and a decrease amount of Cr(VI). - Abstract: Chromium and cobalt oxides are widely used in the manufacture of industrial pigments. In this work, the Co(Co{sub 2-x}Cr{sub x})O{sub 4} powders with different chromium concentrations (x = 0, 0.25 and 1) were synthesized by the polymeric precursor method, heat treatment between 600 and 1000 deg. C. These powders were characterized by X-ray diffraction, infrared spectroscopy, colorimetry, UV-vis absorption and X-ray photoelectron spectroscopies. Even with the addition of chromium, the XRD patterns revealed that all powders crystallize in a single spinel cubic structure. The spinels with higher cobalt amount, Co(CoCr)O{sub 4} and Co(Co{sub 1.75}Cr{sub 0.25})O{sub 4}, displayed a dark color, without the Co{sup 3+} reduction observed in Co{sub 3}O{sub 4} between 900 and 950 deg. C. The spinel with higher chromium amount, CoCr{sub 2}O{sub 4}, was green. The colors were directly related to the occupation of tetrahedral and octahedral sites by the chromophores, as well as to the different oxidation states of chromium and cobalt. The different optical band gap values estimated from UV-vis spectra suggested the existence of intermediary energy levels within the band gap. X-ray photoelectron spectroscopy confirmed an increasing presence of Co(III) and a decreasing amount of Cr(VI) with cobalt enrichment.

Spinel-rich lithologies in the lunar highland crust: Linking lunar samples, crystallization experiments and remote sensing

Science.gov (United States)

Gross, J.; Treiman, A. H.

2012-12-01

melt crystallization and assimilation processes, respectively. We explored different starting compositions, based on natural samples, to place constraints on possible precursor materials and the maximum amount of spinel that could crystallize in an impact event. This will distinguish whether spinel-rich rocks crystallize directly from a melt or whether a concentration mechanism (such as accumulation) is needed. Our preliminary results of the reflectance analysis of the liquidus/crystallization experiments indicate that compositions and modal abundances of coexisting phases influence the spectral reflectance properties; these properties will have implications for quantitative analysis of the spinel-rich areas detected by M3. References: [1] Pieters C.M. 2011. Journal of Geophysical Research 116, E00G08. [2] Demidova et al. 2007. Petrology 15, 386-407. [3] Isaacson et al. 2011. Journal of Geophysical Research 116, E00G11. [4] Gross J. and Treiman A.H. 2011. Journal of Geophysical Research 116, E10009. [5] Gross et al., 2011. 42nd Lunar and Planetary Science Conference (2011), Abstract #2620

Lithium-deficient Li YMn2O4 spinels (0.9 ≤ Y < 1): Lithium content, synthesis temperature, thermal behaviour and electrochemical properties

International Nuclear Information System (INIS)

Pascual, Laura; Perez-Revenga, M. Luz; Rojas, Rosa M.; Rojo, Jose M.; Amarilla, J. Manuel

2006-01-01

Lithium-deficient Li Y Mn 2 O 4 spinels (LD-Li Y Mn 2 O 4 ) with nominal composition (0.9 ≤ Y 2 O 3 and LiNO 3 at temperatures ranging from 700 deg. C to 850 deg. C. X-ray diffraction data show that LD-Li Y Mn 2 O 4 spinels are obtained as single phases in the range Y = 0.975-1 at 700 deg. C and 750 deg. C. Morphological characterization by transmission electron microscopy shows that the particle size of LD-Li Y Mn 2 O 4 spinels increases on decreasing the Li-content. The influence of the Li-content and the synthesis temperature on the thermal and electrochemical behaviours has been systematically studied. Thermal analysis studies indicate that the temperature of the first thermal effect in the differential thermal analysis (DTA)/thermogravimetric (TG) curves, T C1 , linearly increases on decreasing the Li-content. The electrochemical properties of LD-Li Y Mn 2 O 4 spinels, determined by galvanostatic cycling, notably change with the synthesis conditions. So, the first discharge capacity, Q disch. , at C rate increases on rising the Li-content and the synthesis temperature. The sample Li 0.975 Mn 2 O 4 synthesized at 700 deg. C has a Q disch. = 123 mAh g -1 and a capacity retention of 99.77% per cycle. This LD-Li Y Mn 2 O 4 sample had the best electrochemical characteristics of the series

DT fusion neutron irradiation of BNL--LASL superconductor wires, LASL YAG, Al2O3 and Spinel, LASL-IIT MgO, YAG, Al2O3 and Spinel, and NRL GeO2 crystals, December 28, 1977

International Nuclear Information System (INIS)

MacLean, S.C.

1978-01-01

The DT fusion neutron irradiation of eleven BNL-LAST superconductor wires, six NRL GeO 2 crystals, two YAG, two Spinel and two Al 2 O 3 crystals for LASL and four LASL high purity single crystals of MgO, YAG, Spinel and Al 2 O 3 is described. The sample position, beam-on time, and neutron dose record are given. The maximum fluence on any sample was 1.51 x 10 16 neutrons/cm 2

Dielectric and impedance study of praseodymium substituted Mg-based spinel ferrites

Energy Technology Data Exchange (ETDEWEB)

Farid, Hafiz Muhammad Tahir, E-mail: tahirfaridbzu@gmail.com [Department of Physics, Bahauddin Zakariya, University Multan, 60800 (Pakistan); Ahmad, Ishtiaq; Ali, Irshad [Department of Physics, Bahauddin Zakariya, University Multan, 60800 (Pakistan); Ramay, Shahid M. [College of Science, Physics and Astronomy Department, King Saud University, P.O. Box 2455, 11451 Riyadh (Saudi Arabia); Mahmood, Asif [Chemical Engineering Department, College of Engineering, King Saud University, Riyadh (Saudi Arabia); Murtaza, G. [Centre for Advanced Studies in Physics, GC University, Lahore 5400 (Pakistan)

2017-07-15

Highlights: • Magnesium based spinel ferrites were successfully synthesized by sol-gel method. • Dielectric constant shows the normal spinel ferrites behavior. • The dc conductivity are found to decrease with increasing temperature. • The samples with low conductivity have high values of activation energy. • The Impedance decreases with increasing frequency of applied field. - Abstract: Spinel ferrites with nominal composition MgPr{sub y}Fe{sub 2−y}O{sub 4} (y = 0.00, 0.025, 0.05, 0.075, 0.10) were prepared by sol-gel method. Temperature dependent DC electrical conductivity and drift mobility were found in good agreement with each other, reflecting semiconducting behavior. The dielectric properties of all the samples as a function of frequency (1 MHz–3 GHz) were measured at room temperature. The dielectric constant and complex dielectric constant of these samples decreased with the increase of praseodymium concentration. In the present spinel ferrite, Cole–Cole plots were used to separate the grain and grain boundary’s effects. The substitution of praseodymium ions in Mg-based spinel ferrites leads to a remarkable rise of grain boundary’s resistance as compared to the grain’s resistance. As both AC conductivity and Cole–Cole plots are the functions of concentration, they reveal the dominant contribution of grain boundaries in the conduction mechanism. AC activation energy was lower than dc activation energy. Temperature dependence normalized AC susceptibility of spinel ferrites reveals that MgFe{sub 2}O{sub 4} exhibits multi domain (MD) structure with high Curie temperature while on substitution of praseodymium, MD to SD transitions occurs. The low values of conductivity and low dielectric loss make these materials best candidate for high frequency application.

Structural characterisation and physical properties of Li MMnO 4 ( M=Cr, Ti) spinels

Science.gov (United States)

Arillo, M. A.; Cuello, G.; López, M. L.; Martín, P.; Pico, C.; Veiga, M. L.

2005-01-01

New spinel-type phases of general formula Li MMnO 4 ( M=Cr, Ti), derived from LiMn 2O 4 by substitution of Mn 3+ by Cr 3+ or Mn 4+ by Ti 4+, have been obtained and characterised. Neutron diffraction refinements confirm that both phases crystallise in the Fd3m space group, giving the cation distributions [Li] 8 a[CrMn] 16 dO 4 and [Li 0.66Ti 0.34] 8 a[Li 0.34MnTi 0.66] 16 dO 4. Electrical conductivity has been examined by various techniques showing that these materials behave as semiconductors. The electrochemical behaviour indicates different oxidation-reduction steps in both cases concomitant with the insertion/deinsertion of lithium in non-reversible processes. X-ray diffraction patterns show that the above process is topotactic in LiCrMnO 4. Magnetic data and neutron diffraction measurements show that no long-range magnetic ordering is present, suggesting a spin-glass transition for M=Cr at low temperature, while for M=Ti the presence of non-magnetic ions in the octahedral sublattice provokes an inherent magnetic frustration.

Plasma sprayed manganeseecobalt spinel coatings: Process sensitivity on phase, electrical and protective performance

Czech Academy of Sciences Publication Activity Database

Han Jung, S.; Pala, Zdeněk; Sampath, S.

2016-01-01

Roč. 304, February (2016), s. 234-243 ISSN 0378-7753 R&D Projects: GA ČR GB14-36566G Institutional support: RVO:61389021 Keywords : Interconnect protection * Cr-poisoning * Manganese cobalt spinel * Electrical conductivity * Plasma spray Subject RIV: JE - Non-nuclear Energetics, Energy Consumption ; Use Impact factor: 6.395, year: 2016 http://www.sciencedirect.com/science/article/pii/S0378775315305383

Origin of spinel lamella and/or inclusions in olivine of harzburgite form the Pauza ultramafic rocks from the Kurdistan region, northeastern Iraq

Science.gov (United States)

Mohammad, Y.; Maekawa, H.; Karim, K.

2009-04-01

Exsolution lamellae and octahedral inclusions of chromian spinel occur in olivine of harzburgite of the Pauza ultramafic rocks, Kurdistan region, northeastern Iraq. The lamella is up to 80μm long and up to 50 μm wide. The lamellae and octahedral inclusions of chromian spinel are distributed heterogeneously in the host olivine crystal. They are depleted in Al2O3 relative to the subhedral spinel grains in the matrix and spinel lamella in orthopyroxene. Olivine (Fo92 - 93) with spinel lamellae occurs as fine-grained crystals around orthopyroxene, whereas olivine (Fo90-91) free from spinel is found in matrix. Based on back-scattered images analyses, enrichments of both Cr # and Fe+3 in the chromian spinel lamella in olivine (replacive olivine) relative to that in adjacent orthopyroxene. As well as the compositions of chromian spinel lamellae host olivine are more Mg-rich than the matrix olivine. Furthermore the restriction of olivine with spinel lamellae and octahedral inclusions on around orthopyroxene, and the similarity of spinel lamella orientations in both olivine and adjacent orthopyroxene. This study concludes that the spinel inclusions in olivine are remnant (inherited from former orthopyroxene) spinel exsolution lamella in orthopyroxene, that has been formed in upper mantle conditions ( T = 1200 °C, P = 2.5 GPa ). Replacive olivine are formed by reaction of ascending silica poor melt and orthopyroxene in harzburgite as pressure decrease the solubility of silica-rich phase (orthopyroxene) in the system increase, therefore ascending melt dissolve pyroxene with spinel exsolution lamella and precipitate replacive olivine with spinel inclusions. We can conclude that the olivines with spinel lamella are not necessary to be original and presenting ultrahigh-pressure and/or ultra deep-mantle conditions as previously concluded. It has been formed by melting of orthopyroxene (orthopyroxene with spinel exsolution lamella = olivine with spinel lamellae and octahedral

Hybrid Three-Phase/Single-Phase Microgrid Architecture with Power Management Capabilities

DEFF Research Database (Denmark)

Sun, Qiuye; Zhou, Jianguo; Guerrero, Josep M.

2015-01-01

With the fast proliferation of single-phase distributed generation (DG) units and loads integrated into residential microgrids, independent power sharing per phase and full use of the energy generated by DGs have become crucial. To address these issues, this paper proposes a hybrid microgrid...... architecture and its power management strategy. In this microgrid structure, a power sharing unit (PSU), composed of three single-phase back-to-back (SPBTB) converters, is proposed to be installed at the point of common coupling (PCC). The aim of the PSU is mainly to realize the power exchange and coordinated...... control of load power sharing among phases, as well as to allow fully utilization of the energy generated by DGs. Meanwhile, the method combining the modified adaptive backstepping-sliding mode control approach and droop control is also proposed to design the SPBTB system controllers. With the application...

Structural study of intermediate phase in layered perovskite SrBi sub 2 Ta sub 2 O sub 9 single crystal

CERN Document Server

Onodera, A; Yamashita, H

2003-01-01

The crystal structure of an intermediate phase of Bi-layered ferroelectric SrBi sub 2 Ta sub 2 O sub 9 single crystals was studied by means of X-ray diffraction. An analysis of the extinction rules and X-ray intensities demonstrated that the crystal structure is orthorhombic with space group A2 sub 1 am in the ferroelectric phase and Amam in the intermediate phase; this conclusion is in good agreement with the findings of previous powder neutron diffraction studies.

Structural Rietveld refinement and vibrational study of MgCr{sub x}Fe{sub 2−x}O{sub 4} spinel ferrites

Energy Technology Data Exchange (ETDEWEB)

Sabri, K. [Laboratoire des Sciences et technique de l’Environnement et de la Valorisation, département de Génie des Procédés, Université de Mostaganem, Mostaganem (Algeria); Rais, A., E-mail: amrais@yahoo.com [Laboratoire des Sciences et technique de l’Environnement et de la Valorisation, département de Génie des Procédés, Université de Mostaganem, Mostaganem (Algeria); Taibi, K. [Laboratoire de Science et Génie des Matériaux, USTHB, Alger, Algéria (Algeria); Moreau, M.; Ouddane, B. [Laboratory of LASIR Spectrochemistry, University of Science and Technology, 59650 Villeneuve d’Ascq (France); Addou, A. [Laboratoire des Sciences et technique de l’Environnement et de la Valorisation, département de Génie des Procédés, Université de Mostaganem, Mostaganem (Algeria)

2016-11-15

Spinel ferrites with the general formula MgCr{sub x}Fe{sub 2−x}O{sub 4} (0≤x≤1) were synthesized by the standard ceramic technique and characterized by X-ray diffraction. The XRD patterns confirmed that the mixed ferrite samples are in the cubic spinel structure which is further validated by Rietveld refinement in the space group Fd3m. The crystal structure and cell parameters were refined by Rietveld analysis. The vibrational study was achieved using Fourier Transform-InfraRed (FT-IR) and Raman spectroscopy. From FT-IR band frequencies, the force constants K{sub t} and K{sub o} , for tetrahedral (A) and octahedral (B) sites respectively, have been calculated and discussed with the trend of bond lengths obtained from Rietveld refinement. For all compositions, Raman spectra revealed the five active modes showing the vibration of O{sup 2−} ions at both the A-site and B-site ions. The frequencies trend with chromium content of both FT-IR and Raman spectra showed a shift toward higher values for all modes.

Comparison of single distance phase retrieval algorithms by considering different object composition and the effect of statistical and structural noise.

Science.gov (United States)

Chen, R C; Rigon, L; Longo, R

2013-03-25

Phase retrieval is a technique for extracting quantitative phase information from X-ray propagation-based phase-contrast tomography (PPCT). In this paper, the performance of different single distance phase retrieval algorithms will be investigated. The algorithms are herein called phase-attenuation duality Born Algorithm (PAD-BA), phase-attenuation duality Rytov Algorithm (PAD-RA), phase-attenuation duality Modified Bronnikov Algorithm (PAD-MBA), phase-attenuation duality Paganin algorithm (PAD-PA) and phase-attenuation duality Wu Algorithm (PAD-WA), respectively. They are all based on phase-attenuation duality property and on weak absorption of the sample and they employ only a single distance PPCT data. In this paper, they are investigated via simulated noise-free PPCT data considering the fulfillment of PAD property and weakly absorbing conditions, and with experimental PPCT data of a mixture sample containing absorbing and weakly absorbing materials, and of a polymer sample considering different degrees of statistical and structural noise. The simulation shows all algorithms can quantitatively reconstruct the 3D refractive index of a quasi-homogeneous weakly absorbing object from noise-free PPCT data. When the weakly absorbing condition is violated, the PAD-RA and PAD-PA/WA obtain better result than PAD-BA and PAD-MBA that are shown in both simulation and mixture sample results. When considering the statistical noise, the contrast-to-noise ratio values decreases as the photon number is reduced. The structural noise study shows that the result is progressively corrupted by ring-like artifacts with the increase of structural noise (i.e. phantom thickness). The PAD-RA and PAD-PA/WA gain better density resolution than the PAD-BA and PAD-MBA in both statistical and structural noise study.

The characterization of Co xZn7-xSb2O12 spinel obtained by the pechini method

Directory of Open Access Journals (Sweden)

Deiby Santos Gouveia

2005-06-01

Full Text Available Oxides with spinel structures have been studied for many decades as they have been used in a variety of applications like pigments and refractories. They have also been used as a model structure to evaluate the relative stability of ions in octahedral and tetrahedral sites. Zinc- antimony spinels (Zn7Sb2O12 were synthesized by the Pechini method and the cation Zn2+ was substituted by Co2+, taking into consideration the stoichiometry of Co xZn7-xSb2O12 (x = 0 - 7. Characterization of the thermal properties of pyrolyzed powders was carried out with a TG/DTA analyzer, and mass losses were determined as a function of the cobalt content in the resin. The powders were calcined at temperatures in the range 600 to 1000 °C and characterized by XRD, BET and IR spectroscopy. Maximum cristalinity was obtained in powders calcined at 1000 °C. Materials with x = 5 - 7 revealed the presence of a secondary phase (Co, ZnSb2O6. Infrared analysis facilitated in the determination of the possible sites of Zn2+, Co2+ and Sb2+ ions in the lattice.

Thermally-induced electronic relaxation in structurally-modified Cu0.1Ni0.8Co0.2Mn1.9O4 spinel ceramics

International Nuclear Information System (INIS)

Shpotyuk, O.; Balitska, V.; Brunner, M.; Hadzaman, I.; Klym, H.

2015-01-01

Thermally-induced electronic relaxation in structurally-modified Cu 0.1 Ni 0.8 Co 0.2 Mn 1.9 O 4 spinel ceramics is shown to be adequately described by stretched exponential function on time. This kinetics is defined by microsctructure perfectness of the relaxing media, showing obvious onset to stretched exponential behaviour with non-exponentionality index attaining close to 0.43 values for high-monolith ceramics and smaller ones in fine-grained ceramics. Percolation threshold in relaxation-degradation kinetics is detected for ceramics with 10% of NiO extractions, showing the smallest but most prolonged single-path degradation effect. This finding is treated in terms of Phillips’ axiomatic diffusion-to-trap model, where only one of two relaxation channels (caused by operative short-range forces) occurs to be effective, while additional non-operative channels contribute to electronic relaxation in fine-grained ceramics

Neutron Powder Diffraction Measurements of the Spinel MgGa 2 O 4 :Cr 3+ - A Comparative Study between the High Flux Diffractometer D2B at the ILL and the High Resolution Powder Diffractometer Aurora at IPEN

DEFF Research Database (Denmark)

Silva, M A F M da; Sosman, L P; Yokaichiya, F

2012-01-01

Optical materials that emit from the visible to the near-infrared spectral region are of great interest due to their possible application as tunable radiation sources, as signal transmission, display, optoelectronics signal storage, cellulose industry as well as in dosimetry. One important family...... of such systems are the spinel compounds doped with Cr 3+ , in which the physical the properties are related to the insertion of punctual defects in the crystalline structure. The purpose of our work is two fold. First, we compare the luminescence of the MgGa 2 O 4 -Ga 2 O 3 system with the single phase Ga 2 O 3...

Spinel formation for stabilizing simulated nickel-laden sludge with aluminum-rich ceramic precursors.

Science.gov (United States)

Shih, Kaimin; White, Tim; Leckie, James O

2006-08-15

The feasibility of stabilizing nickel-laden sludge from commonly available Al-rich ceramic precursors was investigated and accomplished with high nickel incorporation efficiency. To simulate the process, nickel oxide was mixed alternatively with gamma-alumina, corundum, kaolinite, and mullite and was sintered from 800 to 1480 degrees C. The nickel aluminate spinel (NiAl2O4) was confirmed as the stabilization phase for nickel and crystallized with efficiencies greater than 90% for all precursors above 1250 degrees C and 3-h sintering. The nickel-incorporation reaction pathways with these precursors were identified, and the microstructure and spinel yield were investigated as a function of sintering temperature with fixed sintering time. This study has demonstrated a promising process for forming nickel spinel to stabilize nickel-laden sludge from a wide range of inexpensive ceramic precursors, which may provide an avenue for economically blending waste metal sludges via the building industry processes to reduce the environmental hazards of toxic metals. The correlation of product textures and nickel incorporation efficiencies through selection of different precursors also provides the option of tailoring property-specific products.

In-situ synchrotron PXRD study of spinel LiMn2O4 formation

DEFF Research Database (Denmark)

Birgisson, Steinar; Jensen, Kirsten Marie Ørnsbjerg; Christiansen, Troels Lindahl

structural properties for the reaction being studied. Normally the reactions are started by heating and a constant temperature is kept throughout the experiment. In this study the hydrothermal reaction previously shown to produce spinel LiMn2O4 nanoparticles is studied in-situ to learn more about the phase......O4, depending on the initial concentration if Li-ions. An impurity phase, identified as Mn3O4, is also detected in different concentrations depending on reaction time and temperature. We have developed an experimental technique for in-situ measurements of solvothermal reactions under sub...... in the in-situ measurements it gives a unique opportunity to study reaction kinetics and thermodynamic quantities of the reactions. A temperature study of the reaction has been conducted to see how the formation rate and particle growth is affected by temperature while the precursor concentration is kept...

Direct phase selection of initial phases from single-wavelength anomalous dispersion (SAD) for the improvement of electron density and ab initio structure determination

International Nuclear Information System (INIS)

Chen, Chung-De; Huang, Yen-Chieh; Chiang, Hsin-Lin; Hsieh, Yin-Cheng; Guan, Hong-Hsiang; Chuankhayan, Phimonphan; Chen, Chun-Jung

2014-01-01

A novel direct phase-selection method to select optimized phases from the ambiguous phases of a subset of reflections to replace the corresponding initial SAD phases has been developed. With the improved phases, the completeness of built residues of protein molecules is enhanced for efficient structure determination. Optimization of the initial phasing has been a decisive factor in the success of the subsequent electron-density modification, model building and structure determination of biological macromolecules using the single-wavelength anomalous dispersion (SAD) method. Two possible phase solutions (ϕ 1 and ϕ 2 ) generated from two symmetric phase triangles in the Harker construction for the SAD method cause the well known phase ambiguity. A novel direct phase-selection method utilizing the θ DS list as a criterion to select optimized phases ϕ am from ϕ 1 or ϕ 2 of a subset of reflections with a high percentage of correct phases to replace the corresponding initial SAD phases ϕ SAD has been developed. Based on this work, reflections with an angle θ DS in the range 35–145° are selected for an optimized improvement, where θ DS is the angle between the initial phase ϕ SAD and a preliminary density-modification (DM) phase ϕ DM NHL . The results show that utilizing the additional direct phase-selection step prior to simple solvent flattening without phase combination using existing DM programs, such as RESOLVE or DM from CCP4, significantly improves the final phases in terms of increased correlation coefficients of electron-density maps and diminished mean phase errors. With the improved phases and density maps from the direct phase-selection method, the completeness of residues of protein molecules built with main chains and side chains is enhanced for efficient structure determination

The effects of stress concentrations on reaction progress: an example from experimental growth of magnesio-aluminate spinel at corundum - periclase interfaces under uniaxial load

Science.gov (United States)

Jerabek, Petr; Abart, Rainer; Rybacki, Erik; Habler, Gerlinde

2014-05-01

The study aims to understand the reaction progress and chemical, microstructural and textural evolution of magnesio-aluminate spinel reaction rims formed at varying experimental settings (load, temperature and experiment duration). The spinel rims were grown at the contacts between periclase and corundum at temperatures of 1250°C to 1350°C and dry atmosphere, maintained by a constant argon gas flow, under uniaxial load of 0.026 and 0.26 kN per 9 mm2 of initial contact area. Single crystals of periclase with [100] and of corundum with [0001] perpendicular to the polished reaction interface as well as polycrystalline corundum were used as starting materials. Two loading procedures, immediate application of the load before heating and loading after the desired temperature had been reached, were used. An important byproduct of our experiments stemmed from the immediate application of the load, which led to deformation twinning and fracturing of corundum. This internal deformation of corundum disturbed the reaction interface and introduced loci of concentrated stress due to opening of void spaces in between the reactant crystals. Whenever cracks formed in the initial stages of an experiment, the void space opened immediately and no spinel formed along these interface segments. In the case of deformation twinning, the decreased rim thickness indicates later opening of void spaces. This is because next to twins, the reaction interface is characterized by tight physical contact on the one side and less tight contact on the other side of the twin individual. The tight contacts are characterized by enhanced reaction progress which together with the overall positive volume change of the reaction and limits on plasticity of the studied phases led to the opening of void spaces at places characterized by less tight contacts. The thickness variations are less pronounced in our high load (0.26 kN) experiments where periclase behaves plastically and to some extent reduces the

Ferroelectric InMnO{sub 3}: Growth of single crystals, structure and high-temperature phase transitions

Energy Technology Data Exchange (ETDEWEB)

Bekheet, Maged F., E-mail: maged.bekheet@ceramics.tu-berlin.de [Fachbereich Material‐ und Geowissenschaften, Technische Universität Darmstadt, Alarich-Weiss-Straße 2, 64287 Darmstadt (Germany); Fachgebiet Keramische Werkstoffe / Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften und -technologien, Technische Universität Berlin, Hardenbergstraße 40, 10623 Berlin (Germany); Svoboda, Ingrid; Liu, Na [Fachbereich Material‐ und Geowissenschaften, Technische Universität Darmstadt, Alarich-Weiss-Straße 2, 64287 Darmstadt (Germany); Bayarjargal, Lkhamsuren [Institut für Geowissenschaften, Goethe-Universität, Altenhöferallee 1, d-60438 Frankfurt a.M. (Germany); Irran, Elisabeth [Institut für Chemie, Technische Universität Berlin, Straße des 17, Juni 135, 10623 Berlin (Germany); Dietz, Christian; Stark, Robert W.; Riedel, Ralf [Fachbereich Material‐ und Geowissenschaften, Technische Universität Darmstadt, Alarich-Weiss-Straße 2, 64287 Darmstadt (Germany); Gurlo, Aleksander [Fachgebiet Keramische Werkstoffe / Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften und -technologien, Technische Universität Berlin, Hardenbergstraße 40, 10623 Berlin (Germany)

2016-09-15

To understand the origin of the ferroelectricity in InMnO{sub 3}, single crystals with average size of 1 mm were grown in PbF{sub 2} flux at 950 °C. The results of single crystal X-ray diffraction, second harmonic generation and piezoresponse force microscopy studies of high-quality InMnO{sub 3} single crystals reveal that the room-temperature state in this material is ferroelectric with P6{sub 3}cm symmetry. The polar InMnO{sub 3} specimen undergoes a reversible phase transition from non-centrosymmetric P6{sub 3}cm structure to a centrosymmetric P6{sub 3}/mmc structure at 700 °C as confirmed by the in situ high-temperature Raman spectroscopic and synchrotron X-ray diffraction experiments. - Graphical abstract: Piezoresponse fore microscopy (PFM) studies of high quality InMnO{sub 3} single crystal revealed that the room-temperature state of this material is ferroelectric with a clear cloverleaf pattern corresponding to six antiphase ferroelectric domains with alternating polarization ±P{sub z}. Display Omitted - Highlights: • InMnO{sub 3} single crystals with average size of 1 mm were grown in PbF{sub 2} flux at 950 °C. • The room-temperature state of InMnO{sub 3} is ferroelectric with polar P6{sub 3}cm structure. • PolarInMnO{sub 3} reversibly transforms to a centrosymmetric P6{sub 3}/mmc structure above 700 °C.

The variation of cationic microstructure in Mn-doped spinel ferrite during calcination and its effect on formaldehyde catalytic oxidation

Energy Technology Data Exchange (ETDEWEB)

Liang, Xiaoliang [CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China); Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou 510640 (China); Liu, Peng [CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou 510640 (China); He, Hongping, E-mail: hehp@gig.ac.cn [CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China); Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou 510640 (China); Wei, Gaoling [Guangdong Institute of Eco-Environmental and Soil Sciences, Guangzhou 510650 (China); Chen, Tianhu [School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009 (China); Tan, Wei; Tan, Fuding [CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou 510640 (China); Zhu, Jianxi; Zhu, Runliang [CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China); Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou 510640 (China)

2016-04-05

Highlights: • Calcination causes the activity variation of Mn-doped ferrites for HCHO oxidation. • The variation of catalytic activity of ferrites by calcination is non-linear. • Mn enriches on the calcinated ferrite surface in the valence of +3 and +4. • The reduction temperature of surface Mn{sup 4+} species is well correlated to T50. - Abstract: In this study, a series of Mn substituted spinel ferrites calcinated at different temperatures were used as catalysts for the oxidation of formaldehyde (HCHO). X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and H{sub 2} temperature-programmed reduction were conducted to characterize the structure and physico-chemical properties of catalysts, which were affected by calcination in the range of 200–600 °C. Results show that all the ferrites were with spinel structure, and those calcinated in the range of 300–600 °C were in the phase of maghemite. The calcination changed the valence and distribution of Mn and Fe on the ferrite surface, and accordingly the reducibility of ferrites. The HCHO catalytic oxidation test showed that with the increase of calcination temperature, the activity was initially improved until 400 °C, but then decreased. The variation of HCHO conversion performance was well positively correlated to the variation of reduction temperature of surface Mn{sup 4+} species. The remarkable effect of calcination on the catalytic activity of Mn-doped spinel ferrites for HCHO oxidation was discussed in view of reaction mechanism and variations in cationic microstructure of Mn-doped ferrites.

The variation of cationic microstructure in Mn-doped spinel ferrite during calcination and its effect on formaldehyde catalytic oxidation

International Nuclear Information System (INIS)

Liang, Xiaoliang; Liu, Peng; He, Hongping; Wei, Gaoling; Chen, Tianhu; Tan, Wei; Tan, Fuding; Zhu, Jianxi; Zhu, Runliang

2016-01-01

Highlights: • Calcination causes the activity variation of Mn-doped ferrites for HCHO oxidation. • The variation of catalytic activity of ferrites by calcination is non-linear. • Mn enriches on the calcinated ferrite surface in the valence of +3 and +4. • The reduction temperature of surface Mn"4"+ species is well correlated to T50. - Abstract: In this study, a series of Mn substituted spinel ferrites calcinated at different temperatures were used as catalysts for the oxidation of formaldehyde (HCHO). X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and H_2 temperature-programmed reduction were conducted to characterize the structure and physico-chemical properties of catalysts, which were affected by calcination in the range of 200–600 °C. Results show that all the ferrites were with spinel structure, and those calcinated in the range of 300–600 °C were in the phase of maghemite. The calcination changed the valence and distribution of Mn and Fe on the ferrite surface, and accordingly the reducibility of ferrites. The HCHO catalytic oxidation test showed that with the increase of calcination temperature, the activity was initially improved until 400 °C, but then decreased. The variation of HCHO conversion performance was well positively correlated to the variation of reduction temperature of surface Mn"4"+ species. The remarkable effect of calcination on the catalytic activity of Mn-doped spinel ferrites for HCHO oxidation was discussed in view of reaction mechanism and variations in cationic microstructure of Mn-doped ferrites.

Expansion during the formation of the magnesium aluminate spinel (MgAl(2)O(4)) from its basic oxide (MgO and Al(2)O(3)) powders

Science.gov (United States)

Duncan, Flavia Cunha

The extraordinary expansion during the reaction sintering of the magnesium aluminate spinel (MgAl2O4) from its basic oxide (MgO and Al2O3) powders was studied. Experimental series of different size fractions of the reacting materials were formulated to produce the Mg-Al spinel. After batches were prepared, specimens were compacted and fired in air from 1200° to 1700°C for a fixed firing time. A separate set of specimens was fired as a function of time to determine the reaction kinetic parameters. Dimensional changes confirmed that extraordinary expansions of three to four times greater than the prediction from the reaction of solids occur. The solid-state reactions were monitored by X-ray diffraction. The activation energy of the spinel reaction formation was determined to be 280 +/- 20 kJ/mol. It is believed to be associated with the diffusivity of Mg 2+ in either magnesia or spinel during the development of the final spinel structure. New porosity developed in the compacts during the reaction formation of spinel. Scanning electron microscopy confirmed that the magnesia evaporated leaving behind porous magnesia grains, condensed on the alumina particles and reacted to form a shell of spinel. Hollow spinel particles resulted from the original particles of alumina. These porosities generated within the reacting materials influenced the expansions. Final volumetric expansion could potentially reach 56% as a result of the reaction of solids and the porosity generation within MgO and Al2O3. Models of a single alumina particle with and without development of internal porosity were developed. 3-D arrangements of particles showed additional porosity, influencing on the expansions. The decrease in porosity of some specimens fired at higher temperatures indicated that sintering and densification occur simultaneously with the reaction formation of spinel. The decrease in the interparticle porosity limits the full expansion of the particulates to levels lower than the

Direct phase selection of initial phases from single-wavelength anomalous dispersion (SAD) for the improvement of electron density and ab initio structure determination.

Science.gov (United States)

Chen, Chung-De; Huang, Yen-Chieh; Chiang, Hsin-Lin; Hsieh, Yin-Cheng; Guan, Hong-Hsiang; Chuankhayan, Phimonphan; Chen, Chun-Jung

2014-09-01

Optimization of the initial phasing has been a decisive factor in the success of the subsequent electron-density modification, model building and structure determination of biological macromolecules using the single-wavelength anomalous dispersion (SAD) method. Two possible phase solutions (φ1 and φ2) generated from two symmetric phase triangles in the Harker construction for the SAD method cause the well known phase ambiguity. A novel direct phase-selection method utilizing the θ(DS) list as a criterion to select optimized phases φ(am) from φ1 or φ2 of a subset of reflections with a high percentage of correct phases to replace the corresponding initial SAD phases φ(SAD) has been developed. Based on this work, reflections with an angle θ(DS) in the range 35-145° are selected for an optimized improvement, where θ(DS) is the angle between the initial phase φ(SAD) and a preliminary density-modification (DM) phase φ(DM)(NHL). The results show that utilizing the additional direct phase-selection step prior to simple solvent flattening without phase combination using existing DM programs, such as RESOLVE or DM from CCP4, significantly improves the final phases in terms of increased correlation coefficients of electron-density maps and diminished mean phase errors. With the improved phases and density maps from the direct phase-selection method, the completeness of residues of protein molecules built with main chains and side chains is enhanced for efficient structure determination.

Synthesis of magnesium aluminate spinel by periclase and alumina chlorination

International Nuclear Information System (INIS)

Orosco, Pablo; Barbosa, Lucía; Ruiz, María del Carmen

2014-01-01

Highlights: • Use of chlorination for the synthesis of magnesium aluminate spinel. • The reagents used were alumina, periclase and chlorine. • Isothermal and non-isothermal assays were performed in air and Cl 2 –N 2 flows. • The chlorination produced magnesium aluminate spinel at 700 °C. • Selectivity of the chlorination reaction to obtain spinel is very high. - Abstract: A pyrometallurgical route for the synthesis of magnesium aluminate spinel by thermal treatment of a mechanical mixture containing 29 wt% MgO (periclase) and 71 wt% Al 2 O 3 (alumina) in chlorine atmosphere was developed and the results were compared with those obtained by calcining the same mixture of oxides in air atmosphere. Isothermal and non-isothermal assays were performed in an experimental piece of equipment adapted to work in corrosive atmospheres. Both reagents and products were analyzed by differential thermal analysis (DTA), X-ray diffraction (XRD) and X-ray fluorescence (XRF). Thermal treatment in Cl 2 atmosphere of the MgO–Al 2 O 3 mixture produces magnesium aluminate spinel at 700 °C, while in air, magnesium spinel is generated at 930 °C. The synthesis reaction of magnesium aluminate spinel was complete at 800 °C

Modification of Alumina and Spinel Inclusions by Calcium in Liquid Steel

Science.gov (United States)

Verma, Neerav

2011-12-01

samples were characterized for inclusion shape, size and chemistry through scanning electron microscopy (SEM). Automated inclusion analysis tools (like ASCAT [59, 91, 92], INCA-GSR [126]; Please refer section 6.4., page number 68) were employed to generate statistical information of the inclusions. Thermodynamic database software FACTSAGE [62] was used to determine thermochemistry of reactions, ternary phase diagrams (Ca-Al-S and Ca-Al-Mg systems). The compositions of the inclusions were tracked before and after calcium treatment to determine the effectiveness of calcium treatment. Extraction of inclusions through dissolution of iron in bromine-methanol solution was employed to reveal 3-D geometry of inclusions and analyze inclusions through EDS (Energy-dispersive X-ray spectroscopy) without any matrix effects. Various industrial samples were also analyzed to confirm the feasibility of various reaction mechanisms deduced through experiments. Successful modification of alumina and spinel inclusions by calcium was demonstrated [85, 86]. It was observed that these modification mechanisms proceed through transient phase (CaO, CaS) formation. In the case of spinels, preferential reduction of MgO part was also observed during calcium modification of spinels. The magnesium after MgO reduction by calcium can enter back into the melt or leave the melt in vapor form. The inclusion area fraction decreased after calcium treatment, but the inclusion concentration (number of inclusions per cm2) increased because inclusions shifted to a smaller size distribution after calcium treatment. Severe matrix effects during EDS analysis of inclusions were observed, due to which inclusion composition analyses can be significantly affected. *Please refer to dissertation for footnotes.

Nd: YAG laser irradiation effects on structural and magnetic properties of Ni1+xZrxFe2-2xO4 nanoparticles

Science.gov (United States)

Saraf, Tukaram S.; Kounsalye, Jitendra S.; Birajdar, Shankar D.; Shamkuwar, N. R.

2018-05-01

The effect of 112 mJ Nd: YAG laser irradiation on structural, morphological, infrared and magnetic properties of Ni1+xZrxFe2-2xO4 spinel ferrite nanoparticles has been systematically investigated in the present work. The sol-gel auto combustion synthesis method was successfully executed for the synthesis of the present system. All the samples were characterized by X-ray diffraction technique (XRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR) technique. The magnetic properties of the present samples were measured by pulse field hysteresis loop technique. All the properties were measured for laser irradiated samples as well, to understand the effect of irradiation on the properties. The single-phase cubic spinel structure was confirmed by X-ray diffraction patterns of all samples and the disordered structure was observed for irradiated samples. The two principle absorption bands in IR spectra also confirm the formation of the spinel structure. Spherical and agglomerated morphology was observed for Zr4+ substituted nickel ferrite, whereas scratched morphology was observed for the irradiated samples. The grain size confirms the nanocrystalline nature, the crystallite size also evident the same. The magnetic parameters decreased after Zr4+ ion doping and strongly influenced by the irradiation.

The first find of spinel peridotite in the Southern Kazakhstan: Structure, composition, and parameters of high-pressure metamorphism

Science.gov (United States)

Pilitsyna, A. V.; Tretyakov, A. A.; Alifirova, T. A.; Degtyarev, K. E.; Kovalchuk, E. V.

2017-09-01

Spinel peridotite, metamorphosed in high-pressure conditions, was first described within the Western part of the Central Asian Orogenic Belt. The spinel peridotite has the characteristics of Mg-Cr ultramafites indicating the mantle origin of its protolith. The preliminary estimation of the metamorphism peak for the model system MgO-Al2O3—SiO2-Cr2O3 (MASCr) is 10-19 kbar at 680-800°C.

Correlação entre dados estruturais e bandas de vibração no infravermelho para a fase espinélio Zn7-xNi xSb2O12 Correlation between structural data and infraved vibrational bands of the Zn7-xNi xSb2O12 spinel phase

Directory of Open Access Journals (Sweden)

L. Gama

2000-12-01

Full Text Available A fase espinélio Zn7-xNi xSb2O12 tem apresentado propriedades magnéticas importantes, comportando-se como spin-glass. Desde que estas propriedades são fortemente dependentes da configuração precisa dos átomos nesta estrutura, foram utilizados neste trabalho, com o intuito de clarificar essa configuração, a espectroscopia de infravermelho, aliada ao refinamento de estruturas pelo método de Rietveld. O espectro de infravermelho mostra nas condições de contorno estudadas a presença de três das quatro bandas ativas comuns aos espinélios. Conforme resultados do refinamento pelo método de Rietveld, o níquel substitui o zinco primeiramente no sítio octaédrico e, em altas concentrações (x > ou = 3, migra para o sítio tetraédrico. Essa migração é indicada pelo "splitting", em torno de 520 cm-1, para (x > ou = 3, apresentado no espectro de infravermelho quando a banda n2 é afetada pela mudança do cátion bivalente.The Zn7-xNi xSb2O12 spinel phase shows important magnetic properties with a spin-glass behavior. As these properties are strongly dependent on the atomic configuration in the spinel structure, infrared spectroscopy and the structure refining by the Rietveld analysis have been studied. The infrared spectrum presents three to four of the common spinel active modes. The Rietveld analysis shows that Ni firstly substitutes for Zn in the octahedral site and, for large (x > or = 3 concentrations, migrates to the tetrahedral site. The indication of that migration is the splitting at approximately 520 cm-1, shown in the infrared spectrum when the nu 2 band is modified by the substitution of the divalent cation.

A Fault-Tolerant Parallel Structure of Single-Phase Full-Bridge Rectifiers for a Wound-Field Doubly Salient Generator

DEFF Research Database (Denmark)

Chen, Zhihui; Chen, Ran; Chen, Zhe

2013-01-01

The fault-tolerance design is widely adopted for high-reliability applications. In this paper, a parallel structure of single-phase full-bridge rectifiers (FBRs) (PS-SPFBR) is proposed for a wound-field doubly salient generator. The analysis shows the potential fault-tolerance capability of the PS...

Compositional Variation of Chrome Spinels in the Ore-bearing Zones of the Kraka Ophiolite and the Chromitite Origin

Directory of Open Access Journals (Sweden)

D. E. Saveliev

2017-07-01

Full Text Available The article considers a chemical variation of accessory and ore-forming chrome spinels from the Kraka ultramafic massif at the different scales, from the deposit to the thin section. A correlation analysis of compositional and structural features of ultramafic rocks and ores was performed. The ultramafic rocks and chromitites in the studied massif show the distinct deformation structures and tectonite olivine fabric. A typical chemical gap (i.e. Cr#=Cr/(Cr+Al was observed between peridotite, on the one hand, and dunite and chromitite, on the other hand, on the scale of deposits and ore-bearing zones. The location and size of this gap depend on the type of deposit. The gap becomes wider from the disseminated tabular bodies to the typical podiform ones. It has been found that in the thin initial dunite veinlets in peridotite the chrome spinels chemistry changes gradually and there is no Cr# gap between peridotite and dunite. The dunite venlets show a strong olivine fabric, which is an evidence of their high-temperature plastic flow origin. It has been revealed that new chrome spinel grains previously formed as rods or needles and then coarsened. We explained this observation as the result of impurity segregation, coalescence and spheroidization induced by the plastic deformation of olivine. It is inferred that a solid crystal flow is the main requirement for the dunite and chromitite body formation in the Kraka ophiolite massif. In the solid stream, the mineral phase separation takes place. For example, olivine and orthopyroxene grains of parental peridotite separate from one another, and weaker (more mobile olivine grains form dunite bodies in which chromitite appears as a result of impurity segregation.

Empirical constraints on partitioning of platinum group elements between Cr-spinel and primitive terrestrial magmas

Science.gov (United States)

Park, Jung-Woo; Kamenetsky, Vadim; Campbell, Ian; Park, Gyuseung; Hanski, Eero; Pushkarev, Evgeny

2017-11-01

Recent experimental studies and in situ LA-ICP-MS analysis on natural Cr-spinel have shown that Rh and IPGEs (Ir-group platinum group elements: Ru, Ir, Os) are enriched in the lattice of Cr-spinel. However, the factors controlling the partitioning behaviour of these elements are not well constrained. In this study, we report the Rh, IPGE, and trace element contents in primitive Cr-spinel, measured by LA-ICP-MS, from nine volcanic suites covering various tectonic settings including island arc picrites, boninites, large igneous province picrites and mid-ocean ridge basalts. The aim is to understand the factors controlling the enrichment of Rh and IPGEs in Cr-spinels, to estimate empirical partition coefficients between Cr-spinel and silicate melts, and to investigate the role of Cr-spinel fractional crystallization on the PGE geochemistry of primitive magmas during the early stages of fractional crystallization. There are systematic differences in trace elements, Rh and IPGEs in Cr-spinels from arc-related magmas (Arc Group Cr-spinel), intraplate magmas (Intraplate Group Cr-spinel), and mid-ocean ridge magmas (MORB Group Cr-spinel). Arc Group Cr-spinels are systematically enriched in Sc, Co and Mn and depleted in Ni compared to the MORB Group Cr-spinels. Intraplate Group Cr-spinels are distinguished from the Arc Group Cr-spinels by their high Ni contents. Both the Arc and Intraplate Group Cr-spinels have total Rh and IPGE contents of 22-689 ppb whereas the MORB Group Cr-spinels are depleted in Rh and IPGE (total time-resolved spectra of LA-ICP-MS data for Cr-spinels mostly show constant count rates for trace element and Rh and IPGEs, suggesting homogeneous distribution of these elements in Cr-spinels. The PGE spikes observed in several Cr-spinels were interpreted to be PGE-bearing mineral inclusions and excluded from calculating the PGE contents of the Cr-spinels. On primitive mantle normalized diagrams the Arc Group Cr-spinels are characterized by a fractionated

Compositional and structural variabilities of Mg-rich iron oxide spinels from tuffite

Directory of Open Access Journals (Sweden)

W. N. Mussel

1999-12-01

Full Text Available Maghemite (γFe2O3 from tuffite is exceptionally rich in Mg, relatively to most of those reportedly found in other mafic lithosystems. To investigate in detail the compositional and structural variabilities of this natural magnetic iron oxide, sets of crystals were isolated from samples collected at different positions in a tuffite weathering mantle. These sets of crystal were individually powdered and studied by X-ray diffractometry, Mössbauer spectroscopy, magnetization measurements and chemical analysis. Lattice parameter of the cubic cell (a0 was found to vary from 0.834(1 to 0.8412(1 nm. Lower a0-values are characteristic of maghemite whereas higher ones are related to a magnetite precursor. FeO content ranges up to 17 mass % and spontaneous magnetization ranges from 8 to 32 J T-1 kg-1. Zero-field room temperature Mössbauer spectra are rather complex, indicating that the hyperfine field distributions due to Fe3+ and mixed valence Fe3+/2+ overlap. The structural variabilities of the (Mg, Ti-rich iron oxide spinels is essentially related to the range of chemical composition of its precursor (Mg, Ti-rich magnetite, and probably to the extent to which it has been oxidized during transformation in soil.

Structural, dielectric and gas sensing behavior of Mn substituted spinel MFe2O4 (M=Zn, Cu, Ni, and Co) ferrite nanoparticles

Science.gov (United States)

Ranjith Kumar, E.; Siva Prasada Reddy, P.; Sarala Devi, G.; Sathiyaraj, S.

2016-01-01

Spinel ferrite (MnZnFe2O4, MnCuFe2O4, MnNiFe2O4 and MnCoFe2O4) nanoparticles have been prepared by evaporation method. The annealing temperature plays an important role on changing particle size of the spinel ferrite nanoparticles was found out by X-ray diffraction and transmission electron microscopy. The role of manganese substitution in the spinel ferrite nanoparticles were also analyzed for different annealing temperature. The substitution of Mn also creates a vital change in dielectric properties have been measured in the frequency range of 100 kHz to 5 MHz. These spinel ferrites are decomposed to α-Fe2O3 after annealing above 550 °C in air. Through the characterization of the prepared powder, the effect of annealing temperature, chemical composition and preparation technique on the microstructure, particle size and dielectric properties of the Mn substituted spinel ferrite nanoparticles are discussed. Furthermore, Conductance response of Mn substituted MFe2O4 ferrite nanoparticles were measured by exposing the materials to reducing gas like liquefied petroleum gas (LPG).

Raman scattering study of the structural phase transition in single crystal KDy(MoO4)2

Science.gov (United States)

Peschanskii, A. V.

2017-11-01

Raman scattering of light in single-crystal KDy(MoO4)2 is studied at frequencies of 3-1000 cm-1 for temperatures ranging from 2 to 300 K, including that of a structural phase transition of the cooperative Jahn-Teller type (TC ˜ 14.5 K). During the transition to the low-temperature phase, a series of additional phonon lines corresponding to the Ag, B1g, B2g, and B3g modes is observed which indicates a doubling of the unit cell during the phase transition. An analysis of the symmetry of the phonon modes shows that the low-temperature phase has a predominantly monoclinic symmetry with conservation of a second order axis along the crystallographic b direction, i.e., perpendicular to the layers. Excitations are discovered which correspond to low-energy electronic transitions between levels of the ground-state 6H15/2 multiplet of the Dy3+ ion, which is split in the crystal field with a C2 symmetry. In the vicinity of the first excited Kramers doublet of the Dy3+ ion in crystalline KDy(MoO4)2, the scattered spectrum contains four lines [16.5, 21.0, 24.9, and 29.1 cm-1 (2 K)] at low temperatures, instead of a single line [18.3 cm-1 (25 K)] above the phase transition temperature (14.5 K). This indicates the existence of four nonequivalent dysprosium ions in the low-temperature phase.

Chemical vs. electrochemical extraction of lithium from the Li-excess Li(1.10)Mn(1.90)O4 spinel followed by NMR and DRX techniques.

Science.gov (United States)

Martinez, S; Sobrados, I; Tonti, D; Amarilla, J M; Sanz, J

2014-02-21

Lithium extraction from the Li-excess Li1.10Mn1.90O4 spinel has been performed by chemical and electrochemical methods in aqueous and in organic media, respectively. De-lithiated samples have been investigated by XRD, SEM, TG, (7)Li and (1)H MAS-NMR techniques. The comparative study has allowed demonstrating that the intermediate de-intercalated samples prepared during the chemical extraction by acid titration are similar to those prepared by the electrochemical way in a non-aqueous electrolyte. LiMn2O4 based spinel with a tailored de-lithiation degree can be prepared as a single phase by controlling the pH used in chemical extraction. (7)Li MAS-NMR spectroscopy has been used to follow the influence of the manganese oxidation state on tetra and octahedral Li-signals detected in Li-extracted samples. The oxidation of Mn(III) ions goes parallel to the partial dissolution of the spinel, following Hunter's mechanism. Based on this mechanism, a generalized chemical reaction has been proposed to explain the formation of intermediate Li(+) de-intercalated samples during acid treatment in aqueous media. By the (1)H MAS NMR study, no evidence of Li-H topotactic exchange in the bulk of the acid treated material was found.

Thermoluminescence of Stoichiometric Magnesium-Aluminium Spinel Defects

International Nuclear Information System (INIS)

Kobyakov, V.A.; Gritsina, V.T.; Kazarinov, Yu.G.; Volokitin, V.N.

2005-01-01

The investigations of thermoluminescence of spinel single crystals MgAl 2 O 4 after UV- and X-ray irradiation was provided by using method of self consisting heating. It was shown, that observed maxima at temperatures of ∼360 and ∼530 K in UV- and green ranges of spectra, respectively, are complex and consist of several strongly overlapping partial maxima. By using method of self consisting heating we have revealed the approximate position of partial maxima, which are included in maxima of ∼360 and ∼530 K, and for some partial maxima there was obtained the order of kinetics, activation energies, and frequency factors

Nanosized spinel oxide catalysts for CO-oxidation prepared via CoMnMgAl quaternary hydrotalcite route

Energy Technology Data Exchange (ETDEWEB)

Mokhtar, M., E-mail: mmoustafa@kau.edu.s [Chemistry Department, Faculty of Science, King Abdulaziz University, 21589 Jeddah, P.O. Box 80203 (Saudi Arabia); Basahel, S.N.; Al-Angary, Y.O. [Chemistry Department, Faculty of Science, King Abdulaziz University, 21589 Jeddah, P.O. Box 80203 (Saudi Arabia)

2010-03-18

Catalytic activity of the Co-Mn-Mg-Al mixed oxide spinel catalysts was examined in CO oxidation by O{sub 2}. The prepared catalysts were characterized by chemical analysis (ICP), infrared spectroscopy (FTIR), thermal analysis (TG, DTG), powder X-ray diffraction (XRD), surface area measurements, and scanning electron microscopy (SEM).The calcined hydrotalcite-like precursor was composed of spinel-like Co-Mn-Mg-Al mixed oxide as the only XRD crystalline phases. The nanosized spinel oxide catalysts produced by calcination of hydrotalcites showed higher S{sub BET} than CoMn-hydrotalcite samples as calcination led to dehydroxylation and carbonate decomposition of anions in interlayer spaces. All the catalysts showed 100% CO conversion at high temperature even those calcined at 800 {sup o}C. A catalyst with Co/Mn = 4 and calcined at 500 {sup o}C showed 100% CO conversion at 160 {sup o}C. Moreover, this catalyst exhibited quite good durability without deactivation in 60 h stability test.

Synthesis and structural characteristics of the spinel-type solid solutions in the Mn-V-Fe-O system

International Nuclear Information System (INIS)

Ponomaryov, V.I.; Dubrovina, I.N.; Zakharov, R.G.

1976-01-01

The part of the spinel region bounded by the compounds Mn 3 O 4 , Mn 2 VO 4 , Fe 2 VO 4 , and Fe 3 O 4 in the four-component system Mn-V-Fe-O was studied. The compounds were synthesized by ceramic technology. Samples were heated in a CO 2 atmosphere free of oxygen at 1100 0 C for 25-50 hr. It was found that the average composition of the spinel compound in the system had the formula Mnsub(1.00)Fesub(1.33)Vsub(0.67)O 4 . X-ray and neutron radiogrphic analyses were made. Crystallo-chemical formulas of the solid solutions considered are tabulated. The magnetic moments of saturation, calculated by the Neel model, are shown, and their experimental values are presented. The crystallo-chemical formulas of the spinel solid solutions in the Mn-V-Fe-O system are of interest in interpreting the concentration dependence of the physico-chemical properties of solid solutions of oxides based on metals with varying valence

Effects of Nd:YAG laser irradiation on structural and magnetic properties of Li{sub 0.5}Fe{sub 2.5}O{sub 4}

Energy Technology Data Exchange (ETDEWEB)

Mane, Maheshkumar L. [Department of Physics, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad (M.S.) 431004 (India); Sundar, R.; Ranganathan, K.; Oak, S.M. [Solid State Laser Division, Raja Raman Research Center for Advanced Technology, Indore (M.P.) (India); Jadhav, K.M., E-mail: drkmjadhav@yahoo.co [Department of Physics, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad (M.S.) 431004 (India)

2011-02-15

In the present paper we report our results on the effect of Nd:YAG laser irradiation on the structural and magnetic properties of Li{sub 0.5}Fe{sub 2.5}O{sub 4} spinel ferrite prepared by solid-state reaction technique. X-ray diffraction analysis was carried out to confirm the formation of the single phase cubic spinel structure. The lattice constant calculated from X-ray diffraction data (XRD) goes on increasing with non irradiated phase to exceeding higher doses of irradiation. The distribution of the substituted ions over the different lattice sites is determined from XRD and infrared spectra. The damage structure and morphological investigations were carried out by using scanning electron microscopy and transmission electron microscopy techniques. It has been observed from our data on magnetic properties that laser irradiation severely affects the magnetization. From the magnetization measurements it has been observed that the saturation magnetization decreases with increase in the laser dose rate. The observed reduction in the saturation magnetization after irradiation is understood on the basis of the partial formation of paramagnetic centers and rearrangement of cations in the lattice.

Ferrimagnetism and spin excitation in a Ni–Mn partially inverted spinel prepared using a modified polymeric precursor method

Energy Technology Data Exchange (ETDEWEB)

Ferreira, Rafael A. [Programa de Pos-Graduação em Ciência e Tecnologia de Materiais (POSMAT), Universidade Estadual Paulista, Faculdade de Ciências, Caixa Postal 473, 17033-360 Bauru, São Paulo (Brazil); Institut des Sciences Chimiques de Rennes – UMR 6226, Université de Rennes 1, F-35042 Rennes (France); Tedesco, Julio C.G.; Birk, Jonas O. [The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen (Denmark); Kalceff, Walter, E-mail: wkalceff@uts.edu.au [School of Physics and Advanced Materials, University of Technology Sydney (UTS), P.O. Box 123, Broadway, NSW 2007 (Australia); Yokaichiya, Fabiano [Laboratório Nacional de Luz Síncrotron (LNLS), Caixa Postal 6192, CEP 13083-970 Campinas, São Paulo (Brazil); Comissao Nacional de Energia Nuclear (CNEN), Instituto de Pesquisas Energeticas e Nucleares (IPEN), Reactor Multiproposito Brasileiro - RMB, Avenida Lineo Prestes 2242, Bloco A, Cidade Universitaria Armando Salles de Oliveira, Sao Paulo (Brazil); Rasmussen, Nina [The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen (Denmark); Peña, Octavio [Institut des Sciences Chimiques de Rennes – UMR 6226, Université de Rennes 1, F-35042 Rennes (France); Henry, Paul F. [European Spallation Source ESS AB, Box 176, 22100 Lund (Sweden); Simeoni, Giovanna G. [Heinz Maier-Leibnitz Zentrum (MLZ) and Physics Department, Technische Universität München, Lichtenbergstr. 1, 85748 Garching (Germany); Bordallo, Heloisa N. [The Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen (Denmark); European Spallation Source ESS AB, Box 176, 22100 Lund (Sweden); and others

2014-07-01

We demonstrate that a Ni–Mn oxide partially inverted spinel (Ni{sub 1−ν}Mn{sub ν})[Ni{sub ν}Mn{sub 2−ν}]O{sub 4} having inversion degree ν ≈ 0.8 and produced by a modified polymeric precursor method exhibits behaviour previously reported only in monophased samples. The structure of the specimen was determined using Rietveld analysis of X-ray and neutron powder diffraction data, showing that at room temperature the material crystallizes in the Fd3{sup ¯}m space group with a lattice constant a = 8.392 Å. Combining magnetization measurements with neutron powder diffraction, we show that the magnetic structure of this spinel is associated with the interplay between the ferromagnetic and antiferromagnetic lattices which coexist due to the cations' presence on both tetrahedral and octahedral sites. Our analysis of the neutron diffraction data confirms the postulated magnetic structure involving a star-like moment arrangement, arising from competition for the B (octahedral) spinel sites by the Ni and Mn cations. Finally, we show that strong magnetic fluctuations are observed in the inelastic neutron scattering data. - Highlights: • Ni–Mn oxide partially-inverted spinel made by modified polymeric precursor method. • Magnetic measurements showed a ferrimagnetic and a parasitic magnetic transition. • NPD revealed a magnetic structure consistent with a star-like moment arrangement. • INS measurements indicated four distinct temperature-dependent magnetic regimes.

Incorporation of zinc for fabrication of low-cost spinel-based composite ceramic membrane support to achieve its stabilization.

Science.gov (United States)

Li, Lingling; Dong, Xinfa; Dong, Yingchao; Zhu, Li; You, Sheng-Jie; Wang, Ya-Fen

2015-04-28

In order to reduce environment risk of zinc, a spinel-based porous membrane support was prepared by the high-temperature reaction of zinc and bauxite mineral. The phase evolution process, shrinkage, porosity, mechanical property, pore size distribution, gas permeation flux and microstructure were systematically studied. The XRD results, based on a Zn/Al stoichiometric composition of 1/2, show a formation of ZnAl2O4 structure starting from 1000°C and then accomplished at 1300°C. For spinel-based composite membrane, shrinkage and porosity are mainly influenced by a combination of an expansion induced by ZnAl2O4 formation and a general densification due to amorphous liquid SiO2. The highest porosity, as high as 44%, is observed in ZnAl4 membrane support among all the investigated compositions. Compared with pure bauxite (Al), ZnAl4 composite membrane support is reinforced by ZnAl2O4 phase and inter-locked mullite crystals, which is proved by the empirical strength-porosity relationships. Also, an increase in average pore diameter and gas flux can be observed in ZnAl4. A prolonged leaching experiment reveals the zinc can be successfully incorporated into ceramic membrane support via formation of ZnAl2O4, which has substantially better resistance toward acidic attack. Copyright © 2015 Elsevier B.V. All rights reserved.

Experimental Determination of Spinel/Melt, Olivine/Melt, and Pyroxene/Melt Partition Coefficients for Re, Ru, Pd, Au, and Pt

Science.gov (United States)

Righter, K.; Campbell, A. J.; Humayun, M.

2003-01-01

Experimental studies have identified spinels as important hosts phases for many of the highly siderophile elements (HSE). Yet experimental studies involving chromite or Cr-rich spinel have been lacking. Experimental studies of partitioning of HSEs between silicate, oxides and silicate melt are plagued by low solubilities and the presence of small metallic nuggets at oxygen fugacities relevant to magmas, which interfere with analysis of the phases of interest. We have circumvented these problems in two ways: 1) performing experiments at oxidized conditions, which are still relevant to natural systems but in which nuggets are not observed, and 2) analysis of run products with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), allowing a combination of high sensitivity and good spatial resolution.

Specific heat and magnetic properties of single-crystalline ZnxDyyCrzSe4 spinels

International Nuclear Information System (INIS)

Jendrzejewska, Izabela; Groń, Tadeusz; Maciążek, Ewa; Duda, Henryk; Kubisztal, Marian; Ślebarski, Andrzej; Pietrasik, Ewa; Fijałkowski, Marcin

2016-01-01

The crystal structure, magnetic isotherm, magnetic susceptibility, electrical conductivity and specific heat measurements for single-crystalline Zn x Dy y Cr z Se 4 (where x+y+z≈3) spinels are presented. A semiconducting behavior with the activation energy of 0.53 eV, an antiferromagnetic order with a Néel temperature T N =22 K and a strong ferromagnetic exchange evidenced by a positive Curie–Weiss temperature θ=79, 71 and 70 K with increasing Dy-content in the sequence 0.05, 0.13 and 0.19 were established. Below T N the magnetic field dependence of magnetization, M(H), shows two peaks at critical fields H c1 and H c2 . The values of H c1 decrease slightly with temperature, especially for the larger Dy-content, while the values of H c2 drop rapidly with temperature. The magnetic contribution to the specific heat displays a sharp peak at T N , which is strongly shifted to much lower temperatures in the applied magnetic fields. Similar behavior was found for the temperature dependence of the specific heat C(T) plotted as C(T)/T vs. T. The value of the magnetic and phonon contribution to the entropy at T N and at H=0 is only ∼4.8, ∼4.4 and ∼4.2 J mol −1 K −1 /Cr 3+ for y=0.05, 0.13 and 0.19, respectively, much lower than the average magnetic contribution S m =(z/2)Rln(2S+1)=12.33 J mol −1 K −1 /Cr 3+ calculated for Cr 3+ ion with S=3/2, as the dysprosium one is paramagnetic. - Highlights: • Dy-substitution does not affect the Cr 3+ 3d 3 electronic configuration and AFM order. • The larger Dy-content, the smaller FM short-range interactions. • The magnetic and phonon contribution to the entropy decreases as Dy-content increases.

Naturally occurring crystalline phases: analogues for radioactive waste forms

International Nuclear Information System (INIS)

Haaker, R.F.; Ewing, R.C.

1981-01-01

Naturally occurring mineral analogues to crystalline phases that are constituents of crystalline radioactive waste forms provide a basis for comparison by which the long-term stability of these phases may be estimated. The crystal structures and the crystal chemistry of the following natural analogues are presented: baddeleyite, hematite, nepheline; pollucite, scheelite;sodalite, spinel, apatite, monazite, uraninite, hollandite-priderite, perovskite, and zirconolite. For each phase in geochemistry, occurrence, alteration and radiation effects are described. A selected bibliography for each phase is included

Naturally occurring crystalline phases: analogues for radioactive waste forms

Energy Technology Data Exchange (ETDEWEB)

Haaker, R.F.; Ewing, R.C.

1981-01-01

Naturally occurring mineral analogues to crystalline phases that are constituents of crystalline radioactive waste forms provide a basis for comparison by which the long-term stability of these phases may be estimated. The crystal structures and the crystal chemistry of the following natural analogues are presented: baddeleyite, hematite, nepheline; pollucite, scheelite;sodalite, spinel, apatite, monazite, uraninite, hollandite-priderite, perovskite, and zirconolite. For each phase in geochemistry, occurrence, alteration and radiation effects are described. A selected bibliography for each phase is included.

Delithiation/relithiation process of LiCoMnO4 spinel as 5 V electrode material

Science.gov (United States)

Dräger, Christoph; Sigel, Florian; Indris, Sylvio; Mikhailova, Daria; Pfaffmann, Lukas; Knapp, Michael; Ehrenberg, Helmut

2017-12-01

In this work, the LiCoMnO4 spinel has been synthesized by a two-step sol-gel based method, followed by sintering at temperatures up to 750 °C in oxygen. After structural characterization of the pristine material via synchrotron and neutron diffraction, the material was characterized via SEM and 6Li-MAS-NMR spectroscopy. 6Li-MAS-NMR spectroscopy in different states of charge revealed, that manganese and cobalt are distributed homogenously throughout the material and the delithiation primary occurs from the manganese environments. It was also shown, that it is not possible to fully delithiate the material in a practical voltage range of an electrolyte. Electrochemical cycling results reveal that about 70% of the lithium can be extracted and reinserted electrochemically in the voltage window from 4.5 to 5.4 V against lithium from/into LiCoMnO4. In situ synchrotron powder diffraction results show that lithium extraction/insertion occurs via a single-phase mechanism over the whole range of lithium contents and that the discharge capacity is mainly restricted by the voltage-window of the electrolyte. Furthermore it was shown, that the delithiation occurs up to a potential of 5.6 V.

Ultrafast photoinduced structure phase transition in antimony single crystals

NARCIS (Netherlands)

Fausti, Daniele; Misochko, Oleg V.; van Loosdrecht, Paul H. M.

2009-01-01

Picosecond Raman scattering is used to study the photoinduced ultrafast dynamics in Peierls distorted antimony. We find evidence for an ultrafast nonthermal reversible structural phase transition. Most surprisingly, we find evidence that this transition evolves toward a lower symmetry in contrast to

Unconventional phase transitions in a constrained single polymer chain

International Nuclear Information System (INIS)

Klushin, L I; Skvortsov, A M

2011-01-01

Phase transitions were recognized among the most fascinating phenomena in physics. Exactly solved models are especially important in the theory of phase transitions. A number of exactly solved models of phase transitions in a single polymer chain are discussed in this review. These are three models demonstrating the second order phase transitions with some unusual features: two-dimensional model of β-structure formation, the model of coil–globule transition and adsorption of a polymer chain grafted on the solid surface. We also discuss models with first order phase transitions in a single macromolecule which admit not only exact analytical solutions for the partition function with explicit finite-size effects but also the non-equilibrium free energy as a function of the order parameter (Landau function) in closed analytical form. One of them is a model of mechanical desorption of a macromolecule, which demonstrates an unusual first order phase transition with phase coexistence within a single chain. Features of first and second order transitions become mixed here due to phase coexistence which is not accompanied by additional interfacial free energy. Apart from that, there exist several single-chain models belonging to the same class (adsorption of a polymer chain tethered near the solid surface or liquid–liquid interface, and escape transition upon compressing a polymer between small pistons) that represent examples of a highly unconventional first order phase transition with several inter-related unusual features: no simultaneous phase coexistence, and hence no phase boundary, non-concave thermodynamic potential and non-equivalence of conjugate ensembles. An analysis of complex zeros of partition functions upon approaching the thermodynamic limit is presented for models with and without phase coexistence. (topical review)

Berry's Phase and Fine Structure

CERN Document Server

Binder, B

2002-01-01

Irrational numbers can be assigned to physical entities based on iterative processes of geometric objects. It is likely that iterative round trips of vector signals include a geometric phase component. If so, this component will couple back to the round trip frequency or path length generating an non-linear feedback loop (i.e. induced by precession). In this paper such a quantum feedback mechanism is defined including generalized fine structure constants in accordance with the fundamental gravitomagnetic relation of spin-orbit coupling. Supported by measurements, the general relativistic and topological background allows to propose, that the deviation of the fine structure constant from 1/137 could be assigned to Berry's phase. The interpretation is straightforward: spacetime curvature effects can be greatly amplified by non-linear phase-locked feedback-loops adjusted to single-valued phase relationships in the quantum regime.

Phase relations and gibbs energies in the system Mn-Rh-O

Science.gov (United States)

Jacob, K. T.; Sriram, M. V.

1994-07-01

Phase relations in the system Mn-Rh-O are established at 1273 K by equilibrating different compositions either in evacuated quartz ampules or in pure oxygen at a pressure of 1.01 × 105 Pa. The quenched samples are examined by optical microscopy, X-ray diffraction, and energy-dispersive X-ray analysis (EDAX). The alloys and intermetallics in the binary Mn-Rh system are found to be in equilibrium with MnO. There is only one ternary compound, MnRh2O4, with normal spinel structure in the system. The compound Mn3O4 has a tetragonal structure at 1273 K. A solid solution is formed between MnRh2O4 and Mn3O4. The solid solution has the cubic structure over a large range of composition and coexists with metallic rhodium. The partial pressure of oxygen corresponding to this two-phase equilibrium is measured as a function of the composition of the spinel solid solution and temperature. A new solid-state cell, with three separate electrode compartments, is designed to measure accurately the chemical potential of oxygen in the two-phase mixture, Rh + Mn3-2xRh2xO4, which has 1 degree of freedom at constant temperature. From the electromotive force (emf), thermodynamic mixing properties of the Mn3O4-MnRh2O4 solid solution and Gibbs energy of formation of MnRh2O4 are deduced. The activities exhibit negative deviations from Raoult’s law for most of the composition range, except near Mn3O4, where a two-phase region exists. In the cubic phase, the entropy of mixing of the two Rh3+ and Mn3+ ions on the octahedral site of the spinel is ideal, and the enthalpy of mixing is positive and symmetric with respect to composition. For the formation of the spinel (sp) from component oxides with rock salt (rs) and orthorhombic (orth) structures according to the reaction, MnO (rs) + Rh2O3 (orth) → MnRh2O4 (sp), ΔG° = -49,680 + 1.56T (±500) J mol-1 The oxygen potentials corresponding to MnO + Mn3O4 and Rh + Rh2O3 equilibria are also obtained from potentiometric measurements on galvanic

Electrochemically synthesized nanocrystalline spinel thin film for high performance supercapacitor

Energy Technology Data Exchange (ETDEWEB)

Gupta, Vinay [Carbon Technology Unit, Engineering Materials Division, National Physical Laboratory, New-Delhi, 110012 (India); Art, Science and Technology Center for Cooperative Research, Kyushu University, Kasuga-shi, Fukuoka, 816-8580 (Japan); Japan Science and Technology Agency, Kawaguchi-shi, Saitama, 332-0012 (Japan); Gupta, Shubhra; Miura, Norio [Art, Science and Technology Center for Cooperative Research, Kyushu University, Kasuga-shi, Fukuoka, 816-8580 (Japan)

2010-06-01

Spinels are not known for their supercapacitive nature. Here, we have explored electrochemically synthesized nanostructured NiCo{sub 2}O{sub 4} spinel thin-film electrode for electrochemical supercapacitors. The nanostructured NiCo{sub 2}O{sub 4} spinel thin film exhibited a high specific capacitance value of 580 F g{sup -1} and an energy density of 32 Wh kg{sup -1} at the power density of 4 kW kg{sup -1}, accompanying with good cyclic stability. (author)

Lattice parameters and stability of the spinel compounds in relation to the ionic radii and electronegativities of constituting chemical elements.

Science.gov (United States)

Brik, Mikhail G; Suchocki, Andrzej; Kamińska, Agata

2014-05-19

A thorough consideration of the relation between the lattice parameters of 185 binary and ternary spinel compounds, on one side, and ionic radii and electronegativities of the constituting ions, on the other side, allowed for establishing a simple empirical model and finding its linear equation, which links together the above-mentioned quantities. The derived equation gives good agreement between the experimental and modeled values of the lattice parameters in the considered group of spinels, with an average relative error of about 1% only. The proposed model was improved further by separate consideration of several groups of spinels, depending on the nature of the anion (oxygen, sulfur, selenium/tellurium, nitrogen). The developed approach can be efficiently used for prediction of lattice constants for new isostructural materials. In particular, the lattice constants of new hypothetic spinels ZnRE2O4, CdRE2S4, CdRE2Se4 (RE = rare earth elements) are predicted in the present Article. In addition, the upper and lower limits for the variation of the ionic radii, electronegativities, and their certain combinations were established, which can be considered as stability criteria for the spinel compounds. The findings of the present Article offer a systematic overview of the structural properties of spinels and can serve as helpful guides for synthesis of new spinel compounds.

Detailed Investigation of the Structural, Thermal, and Electronic Properties of Gold Isocyanide Complexes with Mechano-Triggered Single-Crystal-to-Single-Crystal Phase Transitions.

Science.gov (United States)

Seki, Tomohiro; Sakurada, Kenta; Muromoto, Mai; Seki, Shu; Ito, Hajime

2016-02-01

Mechano-induced phase transitions in organic crystalline materials, which can alter their properties, have received much attention. However, most mechano-responsive molecular crystals exhibit crystal-to-amorphous phase transitions, and the intermolecular interaction patterns in the daughter phase are difficult to characterize. We have investigated phenyl(phenylisocyanide)gold(I) (1) and phenyl(3,5-dimethylphenylisocyanide)gold(I) (2) complexes, which exhibit a mechano-triggered single-crystal-to-single-crystal phase transition. Previous reports of complexes 1 and 2 have focused on the relationships between the crystalline structures and photoluminescence properties; in this work we have focused on other aspects. The face index measurements of complexes 1 and 2 before and after the mechano-induced phase transitions have indicated that they undergo non-epitaxial phase transitions without a rigorous orientational relationship between the mother and daughter phases. Differential scanning calorimetry analyses revealed the phase transition of complex 1 to be enthalpically driven by the formation of new aurophilic interactions. In contrast, the phase transition of complex 2 was found to be entropically driven, with the closure of an empty void in the mother phase. Scanning electron microscopy observation showed that the degree of the charging effect of both complexes 1 and 2 was changed by the phase transitions, which suggests that the formation of the aurophilic interactions affords more effective conductive pathways. Moreover, flash-photolysis time-resolved microwave conductivity measurements revealed that complex 1 increased in conductivity after the phase change, whereas the conductivity of complex 2 decreased. These contrasting results were explained by the different patterns in the aurophilic interactions. Finally, an intriguing disappearing polymorphism of complex 2 has been reported, in which a polymorph form could not be obtained again after some period of time

Magnetic and catalytic properties of inverse spinel CuFe{sub 2}O{sub 4} nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Anandan, S., E-mail: sanand@nitt.edu [Nanomaterials and Solar Energy Conversion Lab, Department of Chemistry, National Institute of Technology, Trichy 620 015 (India); Department of Environmental Engineering and Science, Feng Chia University, Taichung 407, Taiwan (China); Selvamani, T.; Prasad, G. Guru [Nanomaterials and Solar Energy Conversion Lab, Department of Chemistry, National Institute of Technology, Trichy 620 015 (India); Asiri, A.M. [The Center of Excellence for Advanced Materials Research, King Abdulaziz University, P.O. Box 80203, Jeddah 21413 (Saudi Arabia); Wu, J.J., E-mail: jjwu@fcu.edu.tw [Department of Environmental Engineering and Science, Feng Chia University, Taichung 407, Taiwan (China)

2017-06-15

Highlights: • Copper ferrite (CuFe{sub 2}O{sub 4}) nanoparticles were synthesized via citrate-nitrate combustion method. • Spectroscopic information’s have found that CuFe{sub 2}O{sub 4} nanoparticles as an inverse spinel structure. • Magnetic study exhibits CuFe{sub 2}O{sub 4} nanoparticles have ferromagnetic behavior. • CuFe{sub 2}O{sub 4} nanoparticles employed for photocatalytic decolourisation of methylene blue under visible light irradiation. - Abstract: In this research, inverse spinel copper ferrite nanoparticles (CuFe{sub 2}O{sub 4} NPs) were synthesized via citrate-nitrate combustion method. The crystal structure, particle size, morphology and magnetic studies were investigated using various instrumental tools to illustrate the formation of the inverse spinel structure. Mossbauer spectrometry identified Fe is located both in the tetrahedral and octahedral site in the ratio (40:60) and the observed magnetic parameters values such as saturation magnetization (M{sub s} = 20.62 emu g{sup −1}), remnant magnetization (M{sub r} = 11.66 emu g{sup −1}) and coercivity (H{sub c} = 63.1 mTesla) revealed that the synthesized CuFe{sub 2}O{sub 4} NPs have a typical ferromagnetic behaviour. Also tested CuFe{sub 2}O{sub 4} nanoparticles as a photocatalyst for the decolourisation of methylene blue (MB) in the presence of peroxydisulphate as the oxidant.

Structural, morphological and electrical properties of Sn-substituted Ni-Zn ferrites synthesized by double sintering technique

Energy Technology Data Exchange (ETDEWEB)

Ali, M.A. [Department of Physics, Chittagong University of Engineering and Technology (CUET), Chittagong 4349 (Bangladesh); Uddin, M.M., E-mail: mohi@cuet.ac.bd [Department of Physics, Chittagong University of Engineering and Technology (CUET), Chittagong 4349 (Bangladesh); Khan, M.N.I. [Materials Science Division, Atomic Energy Center, Dhaka 1000 (Bangladesh); Chowdhury, F.U.-Z. [Department of Physics, Chittagong University of Engineering and Technology (CUET), Chittagong 4349 (Bangladesh); Haque, S.M. [Materials Science Division, Atomic Energy Center, Dhaka 1000 (Bangladesh)

2017-02-15

The Sn-substituted Ni-Zn ferrites, (0.0≤x≤0.30), have been synthesized by the standard double sintering technique from the oxide nanopowders of Ni, Zn, Fe and Sn. The structural and electrical properties have been investigated by the X-ray diffraction (XRD), scanning electron microscopy (SEM), DC resistivity and dielectric measurements. From XRD data, the single cubic spinel phase has been confirmed for x≤0.1, whereas for x>0.1 an extra intermediate phase has been detected along with the cubic spinel phase of Ni-Zn ferrite. The grain size is increased due to Sn substitution in Ni-Zn ferrites. DC resistivity as a function of temperature has been measured by two probe method. The semiconducting nature has been found operative in the samples. The DC resistivity was found to decrease whilst the dielectric constant increased with increasing Sn content in Ni-Zn ferrites. The unusual behavior of the dielectric loss factor of the ferrites was explained by the Rezlescu model. The electrical relaxation of the ferrites has been studied in terms of electric modulus formalism and the time for dielectric relaxation was calculated. The contribution of grain resistance has been studied from the Cole-Cole plot. The suitability to use the as prepared samples in the miniaturized memory devices based capacitive components or energy storage principles are confirmed from the values of dielectric constant. - Highlights: • Sn-substituted Ni-Zn ferrites with cubic spinel structure have been synthesized. • a{sub th} is calculated and well compared with a{sub expt}. • Dielectric unusual behavior has been successfully explained by the Rezlescu model. • Long τ (ns) is determined, can be utilized for memory and spintronics devices.

Synthesis, structural, dielectric and magnetic properties of polyol assisted copper ferrite nano particles

Energy Technology Data Exchange (ETDEWEB)

Pavithradevi, S. [Assistant Professor, Department of Physics, Park College of Engineering and Technology, Coimbatore (India); Suriyanarayanan, N., E-mail: madurasuri2210@yahoo.com [Prof & Head, Department of Physics, Government College of Technology, Coimbatore (India); Boobalan, T. [Lecturer, Department of Physics, PSG Polytechnic College, Coimbatore (India)

2017-03-15

Nanocrystalline copper ferrite CuFe{sub 2}O{sub 4} is synthesized by co-precipitation method in ethylene glycol as chelating agent, using sodium Hydroxide as precipitator at pH 8. The as synthesized CuFe{sub 2}O{sub 4} is annealed at temperatures of 350 °C, 700 °C, and 1050 °C for 2 h respectively. The thermal analysis of the synthesized sample is done by TG technique. It is shown that at 260 °C ethylene glycol has evaporated completely and after 715 °C, spinel ferrite is formed with a cubic structure. The calculated lattice parameters are in agreement with the reported values. FTIR spectra of CuFe{sub 2}O{sub 4} nano particles are as synthesized and annealed at 1050 °C and recorded between 400 cm{sup −1} and 4000 cm{sup −1}. It shows that when the temperature increases ethylene glycol gradually evaporates. Finally, nano crystalline single phase spinel ferrite is obtained. X-ray diffraction (XRD) and electron diffraction (EDS) studies show that the sample is indexed as the face centered cubic spinel structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the particles are flaky and spherical with the crystallite size in the range of 25–34 nm. From the dielectric studies, the dielectric constant decreases as the frequency increases. Low value of dielectric loss at higher frequencies suggests that the material is suitable for high frequency applications. AC conductivity increases with frequency. The magnetic properties of the samples are measured using a vibrating sample magnetometer (VSM) at room temperature, which shows that the sample exhibited a typical super paramagnetic behavior at low temperature. The saturation magnetization, remanant magnetism, and coercivity increases with applied field. - Highlights: • Complete removal of hematite phase along with ethylene glycol at 1050 °C. • Large decrease in particle sizes noticed along with ethylene glycol. • Ethylene glycol improves purity of the

Petrology of spinel lherzolite xenoliths in alkali basalts from Liri ...

African Journals Online (AJOL)

Al2O3), and Al-rich spinel occur in alkali basalts from Liri, South of the ... these spinel lherzolite xenoliths are reported, along with the analyses of ...... erupted in the Liri region. .... and temperatures with controlled activities of water, carbon.

Domain switching in single-phase multiferroics

Science.gov (United States)

Jia, Tingting; Cheng, Zhenxiang; Zhao, Hongyang; Kimura, Hideo

2018-06-01

Multiferroics are a time-honoured research subject by reason for their tremendous application potential in the information industry, such as in multi-state information storage devices and new types of sensors. An outburst of studies on multiferroicity has been witnessed in the 21st century, although this field has a long research history since the 19th century. Multiferroicity has now become one of the hottest research topics in condensed matter physics and materials science. Numerous efforts have been made to investigate the cross-coupling phenomena among ferroic orders such as ferroelectricity, (anti-)ferromagnetism, and ferroelasticity, especially the coupling between electric and magnetic orderings that would account for the magnetoelectric (ME) effect in multiferroic materials. The magnetoelectric properties and coupling behavior of single phase multiferroics are dominated by their domain structures. It was also noted that, however, the multiferroic materials exhibit very complicated domain structures. Studies on domain structure characterization and domain switching are a crucial step in the exploration of approaches to the control and manipulation of magnetic (electric) properties using an electric (magnetic) field or other means. In this review, following a concise outline of our current basic knowledge on the magnetoelectric (ME) effect, we summarize some important research activities on domain switching in single-phase multiferroic materials in the form of single crystals and thin films, especially domain switching behavior involving strain and the related physics in the last decade. We also introduce recent developments in characterization techniques for domain structures of ferroelectric or multiferroic materials, which have significantly advanced our understanding of domain switching dynamics and interactions. The effects of a series of issues such as electric field, magnetic field, and stress effects on domain switching are been discussed as well. It

Preparation of the electrochemically formed spinel-lithium manganese oxides

Energy Technology Data Exchange (ETDEWEB)

Katakura, Katsumi; Wada, Kohei; Kajiki, Yoshiyuki; Yamamoto, Akiko [Department of Chemical Engineering, Nara National College of Technology, 22 Yata-cho Yamotokoriyama, Nara 639-1080 (Japan); Ogumi, Zempachi [Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510 (Japan)

2009-04-01

Electrochemically formed spinel-lithium manganese oxides were synthesized from manganese hydroxides prepared by a cathodic electrochemical precipitation from various concentrations of manganese nitrate solutions. Two types of manganese hydroxides were formed from diluted and concentrated Mn(NO{sub 3}){sub 2} aqueous solutions. Uniform and equi-sized disk shaped Mn(OH){sub 2} crystals of 0.2-5 {mu}m in diameter were obtained on a Pt substrate after the electrochemical precipitation from lower concentration of ranging from 2 mmol dm{sup -3} to 2 mol dm{sup -3} Mn(NO{sub 3}){sub 2} aq., while the grass blade-like precipitate which is ascribed to manganese hydroxide with 20-80 {mu}m long and 1-5 {mu}m wide were formed from concentrated Mn(NO{sub 3}){sub 2} aq. Both manganese hydroxides gave the electrochemically formed spinel-LiMn{sub 2}O{sub 4} onto a Pt sheet, which is ready for electrochemical measurement, after calcination of the Li incorporated precipitate at 750 C without any additives. While the shape and size of the secondary particle frameworks (aggregates) of the electrochemically formed spinel-LiMn{sub 2}O{sub 4} can be controlled by the electrolysis conditions, the nanostructured primary crystals of 200 nm in diameter were obtained in all cases except that the fiber-like nanostructured spinel-LiMn{sub 2}O{sub 4} crystals with 200 nm in diameter were obtained from concentrated Mn(NO{sub 3}){sub 2} aq. Though these two types of electrochemically formed spinel-LiMn{sub 2}O{sub 4} showed well-shaped CVs even in higher scan rates, it would be suitable for high power density battery applications. These behaviors are assumed to be ascribed to the crystal size and shape of the processed spinel-LiMn{sub 2}O{sub 4}. (author)

Sepentinized Peridotite Spinel Composition: Northern Central Indian Ridge at 6°39

Science.gov (United States)

Ray, D.; Banerjee, R.; Iyer, S. D.; Balaram, V.; Speakman, J.

2005-12-01

Exposures of serpentinized peridotites on the seafloor at slow-spreading ridges have been interpreted either as accretion of ridge segments in a magma-starved condition along the non-transform setting or as preferential outcrops at ridge offsets in transform fault setting. Here we present the mineral chemistry and geochemistry of serpentinites and serpentinized spinel peridotites recovered from an off axis region (corner high) at south of Vityaz transform fault (6°39'S), Northern Central Indian Ridge. Our purpose is to use mineral chemical data of serpentine and spinel to investigate the effect of low temperature alteration processes and degree of partial melting. Serpentine composition shows presence of high Mg-rich lizardite and chrysotile pseudomorphs and these rocks mostly preserve `mesh rim', `window' and `hourglass' textures, representing extensive hydration during low temperature hydrothermal alteration. In thin section, serpentine veins (mainly lensoidal, pinch and swell or anastomosing) are common, sometime crosscutting the `mesh rim' textures to attest to the intensity of serpentinization process. In one sample, a 1.9 cm-thick feldspathic vein crosscut the serpentinite as a porphyroblast and this indicates discontinuity in magmatic crust caused due to less magma input at off-axis region facilitate the intrusion of short-living feeder dykes of highly fractionated late magmatic liquids within the peridotite. In addition, in hand specimen, presence of smaller-scale striations analogous to slickenlines on serpentinite surfaces suggests low-angle faulting, which could have enhanced pervasive serpentinization during their subsequent emplacement. Individual serpentine grain displays very low Ca content (0.01 wt%) suggesting possible absence of any secondary Ca-rich phases also verified by very low Sr content (connotation. Limited data on composition of individual spinel porphyroclast exhibits substantial variation in their Mg# (mole [Mg/ Mg+Fe2]) and Cr# (mole

Structural investigation of chemically synthesized ferrite magnetic nanomaterials

Science.gov (United States)

Uyanga, E.; Sangaa, D.; Hirazawa, H.; Tsogbadrakh, N.; Jargalan, N.; Bobrikov, I. A.; Balagurov, A. M.

2018-05-01

In recent times, interest in ferrite magnetic nanomaterials has considerably grown, mainly due to their highly promising medical and biological applications. Spinel ferrite powder samples, with high heat generation abilities in AC magnetic fields, were studied for their application to the hyperthermia treatment of cancer tumors. These properties of ferrites strongly depend on their chemical composition, ion distribution between crystallographic positions, magnetic structure and method of preparation. In this study, crystal and magnetic structures of several magnetic spinels were investigated by neutron diffraction. The explanation of the mechanism triggering the heat generation ability in the magnetic materials, and the electronic and magnetic states of ferrite-spinel type structures, were theoretically defined by a first-principles method. Ferrites with the composition of CuxMg1-xFe2O4 have been investigated as a heat generating magnetic nanomaterial. Atomic fraction of copper in ferrite was varied between 0 and 100% (that is, x between 0 and 1.0 with 0.2 steps), with the copper dope limit corresponding to appear a tetragonal phase.

An Integrated, Layered-Spinel Composite Cathode for Energy Storage Applications

Science.gov (United States)

Hagh, Nader; Skandan, Ganesh

2012-01-01

At low operating temperatures, commercially available electrode materials for lithium-ion batteries do not fully meet the energy and power requirements for NASA fs exploration activities. The composite cathode under development is projected to provide the required energy and power densities at low temperatures and its usage will considerably reduce the overall volume and weight of the battery pack. The newly developed composite electrode material can provide superior electrochemical performance relative to a commercially available lithium cobalt system. One advantage of using a composite cathode is its higher energy density, which can lead to smaller and lighter battery packs. In the current program, different series of layered-spinel composite materials with at least two different systems in an integrated structure were synthesized, and the volumetric and gravimetric energy densities were evaluated. In an integrated network of a composite electrode, the effect of the combined structures is to enhance the capacity and power capabilities of the material to levels greater than what is possible in current state-of-the-art cathode systems. The main objective of the current program is to implement a novel cathode material that meets NASA fs low temperature energy density requirements. An important feature of the composite cathode is that it has at least two components (e.g., layered and spinel) that are structurally integrated. The layered material by itself is electrochemically inactive; however, upon structural integration with a spinel material, the layered material can be electrochemically activated, thereby delivering a large amount of energy with stable cycling. A key aspect of the innovation has been the development of a scalable process to produce submicronand micron-scale particles of these composite materials. An additional advantage of using such a composite electrode material is its low irreversible loss (.5%), which is primarily due to the unique activation

Crystal field and site deformation in spinels and pentavalent uranium compounds

International Nuclear Information System (INIS)

Drifford, M.; Soulie, E.

1976-01-01

Magnesium aluminates with different alumina contents have the spinel structure. The optical absorption spectra of doped spinel compounds (Cr 3+ , Ni 2+ , Co 2+ ) or E.S.R. spectra (Cr 3+ , Mn 2+ ) are used for the investigation of the position of the doping materials and the deformation of the crystal sites, and give information on the structural disorders. The local structural information given by the doping materials are compared with the mean structure parameters obtained from X-ray diffraction. The optical absorption spectrum and the principal components of the g tensor for UF 6 Cs and the thermal variation in the magnetic susceptibility for UF 8 Cs 3 and UF 8 (NH 4 ) are used for determining the parameters of the electron Hamiltonian for the f 1 configuration. A rather significant covalent aspect is evidenced for UF 6 Cs, in the framework of the model of Eisenstein and Pryce, this property being weaker for the other two complex compounds. The three parameters giving the crystal field at a deformed cubic site with Dsub(3d) symmetry in the Newman superposition model are noticeably weaker for the 8-coordination than for the 6-coordination. As for UF 8 Cs 3 and UF 8 (NH 4 ) 3 a calculation predicts an electronic levels with a very low excitation, at about 110 and 70cm -1 respectively [fr

Influence of strong single-ion anisotropy on phase states of 3D and 2D frustrated magnets

International Nuclear Information System (INIS)

Fridman, Yu.A.; Kosmachev, O.A.; Matunin, D.A.; Gorelikov, G.A.; Klevets, Ph.N.

2010-01-01

We investigated the influence of strong single-ion anisotropy, exceeding exchange interaction, and frustrated exchange interaction on spin-wave excitation spectra and phase states using the Hubbard operators' technique, allowing the exact account of single-ion anisotropy. The results show that both the homogeneous phases (ferromagnetic and quadrupolar) and the spatially inhomogeneous phase (spiral structure) are possible in the 3D magnetic crystal. The region of existence of the spiral structure is considerably smaller than that in the analogues system, but with weak single-ion anisotropy. The situation is more complex in the 2D system; another spatially inhomogeneous state (the domain structure) can be realized in addition to the spiral magnetic structure. The phase diagrams for both the 3D and 2D systems were plotted.

Structural, magnetic, and dielectric properties of multiferroic Co1−xMgxCr2O4 nanoparticles

International Nuclear Information System (INIS)

Kamran, M.; Ullah, A.; Rahman, S.; Tahir, A.; Nadeem, K.; Anis ur Rehman, M.; Hussain, S.

2017-01-01

Highlights: • Properties of multiferroic Co 1−x Mg x Cr 2 O 4 nanoparticles have been studied. • XRD showed that CoCr 2 O 4 and MgCr 2 O 4 are cubic normal spinel structure. • Rietveld refinement of XRD showed no impurity phases. • T c and T s showed decreasing trend with increasing Mg concentration. • Dielectric properties were improved for x = 0.6 Mg concentration. - Abstract: We examined the structural, magnetic, and dielectric properties of Co 1−x Mg x Cr 2 O 4 nanoparticles with composition x = 0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1 in detail. X-ray diffraction (XRD) revealed normal spinel structure for all the samples. Rietveld refinement fitting results of the XRD showed no impurity phases which signifies the formation of single phase Co 1−x Mg x Cr 2 O 4 nanoparticles. The average crystallite size showed a peak behaviour with maxima at x = 0.6. Raman and Fourier transform infrared (FTIR) spectroscopy also confirmed the formation of single phase normal spinel for all the samples and exhibited dominant vibrational changes for x ≥ 0.6. For x = 0 (CoCr 2 O 4 ), zero field cooled/field cooled (ZFC/FC) magnetization curves showed paramagnetic (PM) to ferrimagnetic (FiM) transition at T c = 97 K and a conical spiral magnetic order at T s = 30 K. The end members CoCr 2 O 4 (x = 0) and MgCr 2 O 4 (x = 1) are FiM and antiferromagnetic (AFM), respectively. T c and T s showed decreasing trend with increasing x, followed by an additional AFM transition at T N = 15 K for x = 0.6. The system finally stabilized and changed to highly frustrated AFM structure at x = 1 due to formation of pure MgCr 2 O 4 . High field FC curves (5T) depicted nearly no effect on spiral magnetic state, which is attributed to strong exchange B-B magnetic interactions at low temperatures. Dielectric parameters showed a non-monotonous behaviour with Mg concentration and were explained with the help of Maxwell-Wagner model and Koop’s theory. Dielectric properties were improved for

Unprecedented Al supersaturation in single-phase rock salt structure VAlN films by Al+ subplantation

Science.gov (United States)

Greczynski, G.; Mráz, S.; Hans, M.; Primetzhofer, D.; Lu, J.; Hultman, L.; Schneider, J. M.

2017-05-01

Modern applications of refractory ceramic thin films, predominantly as wear-protective coatings on cutting tools and on components utilized in automotive engines, require a combination of excellent mechanical properties, thermal stability, and oxidation resistance. Conventional design approaches for transition metal nitride coatings with improved thermal and chemical stability are based on alloying with Al. It is well known that the solubility of Al in NaCl-structure transition metal nitrides is limited. Hence, the great challenge is to increase the Al concentration substantially while avoiding precipitation of the thermodynamically favored wurtzite-AlN phase, which is detrimental to mechanical properties. Here, we use VAlN as a model system to illustrate a new concept for the synthesis of metastable single-phase NaCl-structure thin films with the Al content far beyond solubility limits obtained with conventional plasma processes. This supersaturation is achieved by separating the film-forming species in time and energy domains through synchronization of the 70-μs-long pulsed substrate bias with intense periodic fluxes of energetic Al+ metal ions during reactive hybrid high power impulse magnetron sputtering of the Al target and direct current magnetron sputtering of the V target in the Ar/N2 gas mixture. Hereby, Al is subplanted into the cubic VN grains formed by the continuous flux of low-energy V neutrals. We show that Al subplantation enables an unprecedented 42% increase in metastable Al solubility limit in V1-xAlxN, from x = 0.52 obtained with the conventional method to 0.75. The elastic modulus is 325 ± 5 GPa, in excellent agreement with density functional theory calculations, and approximately 50% higher than for corresponding films grown by dc magnetron sputtering. The extension of the presented strategy to other Al-ion-assisted vapor deposition methods or materials systems is straightforward, which opens up the way for producing supersaturated single-phase

Nanocrystalline spinel ferrite (MFe2O4, M = Ni, Co, Mn, Mg, Zn) powders prepared by a simple aloe vera plant-extracted solution hydrothermal route

International Nuclear Information System (INIS)

Phumying, Santi; Labuayai, Sarawuth; Swatsitang, Ekaphan; Amornkitbamrung, Vittaya; Maensiri, Santi

2013-01-01

Graphical abstract: This figure shows the specific magnetization curves of the as-prepared MFe 2 O 4 (M = Ni, Co, Mn, Mg, Zn) powders obtained from room temperature VSM measurement. These curves are typical for a soft magnetic material and indicate hysteresis ferromagnetism in the field ranges of ±500 Oe, ±1000 Oe, and ±2000 Oe for the CoFe 2 O 4 , MgFe 2 O 4 and MnFe 2 O 4 respectively, whereas the samples of NiFe 2 O 4 and ZnFe 2 O 4 show a superparamagnetic behavior. Highlights: ► Nanocrystalline MFe 2 O 4 powders were synthesized by a novel hydrothermal method. ► Metal acetylacetonates and aloe vera plant-extracted solution are used. ► This biosynthetic route is very simple and provides high-yield oxide nanomaterials. ► XRD and TEM results indicate that the prepared samples have only spinel structure. ► The maximum M s of 68.9 emu/g at 10 kOe were observed for the samples of MnFe 2 O 4 . - Abstract: Nanocrystalline spinel ferrite MFe 2 O 4 (M = Ni, Co, Mn, Mg, Zn) powders were synthesized by a novel hydrothermal method using Fe(acac) 3 , M(acac) 3 (M = Ni, Co, Mn, Mg, Zn) and aloe vera plant extracted solution. The X-ray diffraction and selected-area electron diffraction results indicate that the synthesized nanocrystalline have only spinel structure without the presence of other phase impurities. The crystal structure and morphology of the spinel ferrite powders, as revealed by TEM, show that the NiFe 2 O 4 and CoFe 2 O 4 samples contain nanoparticles, whereas the MnFe 2 O 4 and MgFe 2 O 4 samples consist of many nanoplatelets and nanoparticles. Interestingly, the ZnFe 2 O 4 sample contains plate-like structure of networked nanocrystalline particles. Room temperature magnetization results show a ferromagnetic behavior of the CoFe 2 O 4 , MnFe 2 O 4 and MgFe 2 O 4 samples, whereas the samples of NiFe 2 O 4 and ZnFe 2 O 4 exhibit a superparamagnetic behavior

Magnetic properties of Co{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} spinel ferrite nanoparticles synthesized by starch-assisted sol–gel autocombustion method and its ball milling

Energy Technology Data Exchange (ETDEWEB)

Yadav, Raghvendra Singh, E-mail: yadav@fch.vutbr.cz [Materials Research Centre, Brno University of Technology, Purkyňova 464/118, 61200 Brno (Czech Republic); Havlica, Jaromir [Materials Research Centre, Brno University of Technology, Purkyňova 464/118, 61200 Brno (Czech Republic); Hnatko, Miroslav; Šajgalík, Pavol [Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 36 Bratislava (Slovakia); Alexander, Cigáň [Institute of Measurement Science, Slovak Academy of Sciences, Dúbravská cesta 9, SK-841 04 Bratislava (Slovakia); Palou, Martin; Bartoníčková, Eva; Boháč, Martin; Frajkorová, Františka; Masilko, Jiri; Zmrzlý, Martin; Kalina, Lukas; Hajdúchová, Miroslava; Enev, Vojtěch [Materials Research Centre, Brno University of Technology, Purkyňova 464/118, 61200 Brno (Czech Republic)

2015-03-15

In this article, Co{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} (x=0.0 and 0.5) spinel ferrite nanoparticles were achieved at 800 °C by starch-assisted sol–gel autocombustion method. To further reduce the particle size, these synthesized ferrite nanoparticles were ball-milled for 2 h. X-ray diffraction patterns demonstrated single phase formation of Co{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} (x=0.0 and 0.5) spinel ferrite nanoparticles. FE-SEM analysis indicated the nanosized spherical particles formation with spherical morphology. The change in Raman modes and relative intensity were observed due to ball milling and consequently decrease of particle size and cationic redistribution. An X-ray Photoelectron Spectroscopy (XPS) result indicated that Co{sup 2+}, Zn{sup 2+} and Fe{sup 3+} exist in octahedral and tetrahedral sites. The cationic redistribution of Zn{sup 2+} and consequently Fe{sup 3+} occurred between octahedral and tetrahedral sites after ball-milling. The change in saturation magnetization (M{sub s}) and coercivity (H{sub c}) with decrease of nanocrystalline size and distribution of cations in spinel ferrite were observed. - Highlights: • Co{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} spinel ferrite nanoparticles. • Starch-assisted sol–gel auto-combustion method. • Effect of ball-milling on particle size and cation distribution. • Magnetic property dependent on cations and particle size.

Structure analysis of turbulent liquid phase by POD and LSE techniques

International Nuclear Information System (INIS)

Munir, S.; Muthuvalu, M. S.; Siddiqui, M. I.; Heikal, M. R.; Aziz, A. Rashid A.

2014-01-01

In this paper, vortical structures and turbulence characteristics of liquid phase in both single liquid phase and two-phase slug flow in pipes were studied. Two dimensional velocity vector fields of liquid phase were obtained by Particle image velocimetry (PIV). Two cases were considered one single phase liquid flow at 80 l/m and second slug flow by introducing gas at 60 l/m while keeping liquid flow rate same. Proper orthogonal decomposition (POD) and Linear stochastic estimation techniques were used for the extraction of coherent structures and analysis of turbulence in liquid phase for both cases. POD has successfully revealed large energy containing structures. The time dependent POD spatial mode coefficients oscillate with high frequency for high mode numbers. The energy distribution of spatial modes was also achieved. LSE has pointed out the coherent structured for both cases and the reconstructed velocity fields are in well agreement with the instantaneous velocity fields

Structure analysis of turbulent liquid phase by POD and LSE techniques

Energy Technology Data Exchange (ETDEWEB)

Munir, S., E-mail: shahzad-munir@comsats.edu.pk; Muthuvalu, M. S.; Siddiqui, M. I. [Department of Fundamental and Applied Science, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak Darul Ridzuan (Malaysia); Heikal, M. R., E-mail: morgan.heikal@petronas.com.my; Aziz, A. Rashid A., E-mail: morgan.heikal@petronas.com.my [Department of Mechanical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak Darul Ridzuan (Malaysia)

2014-10-24

In this paper, vortical structures and turbulence characteristics of liquid phase in both single liquid phase and two-phase slug flow in pipes were studied. Two dimensional velocity vector fields of liquid phase were obtained by Particle image velocimetry (PIV). Two cases were considered one single phase liquid flow at 80 l/m and second slug flow by introducing gas at 60 l/m while keeping liquid flow rate same. Proper orthogonal decomposition (POD) and Linear stochastic estimation techniques were used for the extraction of coherent structures and analysis of turbulence in liquid phase for both cases. POD has successfully revealed large energy containing structures. The time dependent POD spatial mode coefficients oscillate with high frequency for high mode numbers. The energy distribution of spatial modes was also achieved. LSE has pointed out the coherent structured for both cases and the reconstructed velocity fields are in well agreement with the instantaneous velocity fields.

Nature of the Electrochemical Properties of Sulphur Substituted LiMn2O4 Spinel Cathode Material Studied by Electrochemical Impedance Spectroscopy

Directory of Open Access Journals (Sweden)

Monika Bakierska

2016-08-01

Full Text Available In this work, nanostructured LiMn2O4 (LMO and LiMn2O3.99S0.01 (LMOS1 spinel cathode materials were comprehensively investigated in terms of electrochemical properties. For this purpose, electrochemical impedance spectroscopy (EIS measurements as a function of state of charge (SOC were conducted on a representative charge and discharge cycle. The changes in the electrochemical performance of the stoichiometric and sulphur-substituted lithium manganese oxide spinels were examined, and suggested explanations for the observed dependencies were given. A strong influence of sulphur introduction into the spinel structure on the chemical stability and electrochemical characteristic was observed. It was demonstrated that the significant improvement in coulombic efficiency and capacity retention of lithium cell with LMOS1 active material arises from a more stable solid electrolyte interphase (SEI layer. Based on EIS studies, the Li ion diffusion coefficients in the cathodes were estimated, and the influence of sulphur on Li+ diffusivity in the spinel structure was established. The obtained results support the assumption that sulphur substitution is an effective way to promote chemical stability and the electrochemical performance of LiMn2O4 cathode material.

Determination of ferrous and total iron in refractory spinels

Energy Technology Data Exchange (ETDEWEB)

Amonette, J.E. [Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352 (United States); Matyáš, J. [Material Science Department, Pacific Northwest National Laboratory, Richland, WA 99352 (United States)

2016-03-03

Accurate and precise determination of the redox state of iron (Fe) in spinels presents a significant challenge due to their refractory nature. The resultant extreme conditions needed to obtain complete dissolution generally oxidize some of the Fe(II) initially present and thus prevent the use of colorimetric methods for Fe(II) measurements. To overcome this challenge we developed a hybrid oxidimetric/colorimetric approach, using Ag(I) as the oxidimetric reagent for determination of Fe(II) and 1,10-phenanthroline as the colorimetric reagent for determination of total Fe. This approach, which allows determination of Fe(II) and total Fe on the same sample, was tested on a series of four geochemical reference materials and then applied to the analysis of Fe(Ni) spinel crystals isolated from simulated high-level-waste (HLW) glass and of several reagent magnetites. Results for the reference materials were in excellent agreement with recommended values, with the exception of USGS BIR-1, for which higher Fe(II) values and lower total Fe values were obtained. The Fe(Ni) spinels showed Fe(II) values at the detection limit (ca. 0.03 wt% Fe) and total Fe values higher than obtained by ICP-AES analysis after decomposition by lithium metaborate/tetraborate fusion. For the magnetite samples, total Fe values were in agreement with reference results, but a wide range in Fe(II) values was obtained indicating various degrees of conversion to maghemite. Formal comparisons of accuracy and precision were made with 13 existing methods. Accuracy for Fe(II) and total Fe was at or near the top of the group. Precision varied with the parameter used to measure it but was generally in the middle to upper part of the group for Fe(II) while that for total Fe ranged from the bottom of the group to near the top. - Highlights: • Refractory samples, such as spinels, are the most difficult for Fe redox analysis. • Oxidimetric(Ag{sup +})/colorimetric (phen) method allows analysis of a single

Structural relaxation and colour in the spinel-magnesiochromite (MgAl2O4-MgCr2O4) and gahnite-zincochromite (ZnAl2O4-ZnCr2O4) solid solution series

Science.gov (United States)

Hålenius, U.; Andreozzi, G. B.; Skogby, H.

2009-04-01

Recent studies on binary mineral solid solution series utilising synchrotron based x-ray absorption spectroscopies have indicated strong structural relaxation. For instance, it has been suggested that the real Cr-O bond distances remain nearly constant (relaxation parameter (ɛ) of 0.85, where ɛ=1 equals full relaxation) over the entire compositional range of the MgAl2O4-MgCr2O4 series (Juhin et al. 2007). In the present study we have measured room temperature optical absorption spectra of synthetic single crystals of the ZnAl2-2xCr2xO4 (0.03?x?1) and MgAl2-2xCr2xO4(0.02?x?1) series with the aim to explore the real architecture of the structure and in particular the Cr-O distance as function of composition. Our crystals were synthesized by means of flux-growth methods under atmospheric pressure and temperature profiles resulting in an estimated cation ordering temperature of ca 850 °C. Crystals close to the spinel (sensu stricto) and gahnite end-member compositions were faintly red in colour. With increasing Cr-content the crystals become more intensely red-coloured and at the higher Cr-contents there is a distinct shift towards a dark greenish colouration. These colour changes are reflected in the measured optical spectra by the position and intensity of the two spin-allowed electronic d-d transitions in octahedrally coordinated Cr3+ at ca 18000 (4A2g -4T2g (4F) transition) and 25000 cm-1(4A2g -4T1g (4F) transition). The energy of the first transition (?1-band) is ca 1200 cm-1 lower in magnesiochromite than in weakly Cr-doped spinel (x=0.02) and ca 1400 cm-1 lower in zincochromite than in gahnite with the lowest Cr-content (x=0.03). Concomitantly the energy of the second transition (?2-band) decreases with increasing Cr-content in both series by ca. 1800 cm-1. From the position of the ?1-band, a decrease in crystal field splitting, 10Dq, for six-coordinated Cr3+ with increasing Cr-content in the MgAl2-2xCr2xO4 and ZnAl2-2xCr2xO4 series of 6.5 and 7

Moessbauer study of iron-cobalt-rhodium spinels

Energy Technology Data Exchange (ETDEWEB)

Spencer, C D; Smith, P A; Karnes, C M; Shepard, W A [Ithaca Coll., NY (USA). Dept. of Physics

1980-01-01

Moessbauer source and absorber studies have been carried out on the spinel system CoFesub(x)Rhsub(2-x)O/sub 4/ for x 0.005, 0.3, 0.5, 1.0, 1.2 and 1.5. For 0.005 =< x =< 1.2, the cation distribution is normal with Co/sup 2 +/ on A sites. At x = 1.5, the distribution is nearly inverse. In the cases x = 0.005 and 0.3, iron on the B sites does not produce a quadrupole doublet indicating that the B sites are cubic which is contrary to the usual case in spinels.

The role of particle size on the electrochemical properties at 25 and at 55 deg. C of the LiCr0.2Ni0.4Mn1.4O4 spinel as 5 V-cathode materials for lithium-ion batteries

International Nuclear Information System (INIS)

Aklalouch, Mohamed; Rojas, Rosa M.; Rojo, Jose Maria; Saadoune, Ismael; Amarilla, Jose Manuel

2009-01-01

The role of the particle size on the electrochemical properties at 25 and at 55 deg. C of the LiCr 0.2 Ni 0.4 Mn 1.4 O 4 spinel synthesized by combustion method has been determined. Samples with different particle size were obtained by heating the raw spinel from 700 to 1100 deg. C, for 1 h in air. X-ray diffraction patterns revealed that all the prepared materials are single-phase spinels. The main effect of the thermal treatment is the remarkable increase of the particles size from ∼60 to ∼3000 nm as determined by transmission electron microscopy. The electrochemical properties were determined at high discharge currents (1C rate) in two-electrode Li-cells. At 25 and at 55 deg. C, in spite of the great differences in particle size, the discharge capacity drained by all samples is similar (Q dch ∼ 135 mAh g -1 ). Instead, the cycling performances strongly change with the particle size. The spinels with Φ > 500 nm show better cycling stability at 25 and at 55 deg. C than those with Φ -1 ), and remarkable cycling performances (capacity retention after 250 cycles >96%) are very attractive materials as 5V-cathodes for high-energy Li-ion batteries.

Cotectic proportions of olivine and spinel in olivine-tholeiitic basalt and evaluation of pre-eruptive processes

Science.gov (United States)

Roeder, Peter; Gofton, Emma; Thornber, Carl

2006-01-01

The volume %, distribution, texture and composition of coexisting olivine, Cr-spinel and glass has been determined in quenched lava samples from Hawaii, Iceland and mid-oceanic ridges. The volume ratio of olivine to spinel varies from 60 to 2800 and samples with >0·02% spinel have a volume ratio of olivine to spinel of approximately 100. A plot of wt % MgO vs ppm Cr for natural and experimental basaltic glasses suggests that the general trend of the glasses can be explained by the crystallization of a cotectic ratio of olivine to spinel of about 100. One group of samples has an olivine to spinel ratio of approximately 100, with skeletal olivine phenocrysts and small (within olivine phenocrysts is thought to be due to skeletal olivine phenocrysts coming into physical contact with spinel by synneusis during the chaotic conditions of ascent and extrusion. A second group of samples tend to have large olivine phenocrysts relatively free of included spinel, a few large (>100 μm) spinel crystals that show evidence of two stages of growth, and a volume ratio of olivine to spinel of 100 to well over 1000. The olivine and spinel in this group have crystallized more slowly with little physical interaction, and show evidence that they have accumulated in a magma chamber.

Epitaxial Fe{sub 3-x}Ti{sub x}O{sub 4} films from magnetite to ulvöspinel by pulsed laser deposition

Energy Technology Data Exchange (ETDEWEB)

Droubay, T.C.; Pearce, C.I.; Ilton, E.S.; Engelhard, M.H.; Engelhard, M.H.; Heald, S.M.; Arenholz, E.; Rosso, K.M.

2011-07-21

Epitaxial films along the Fe{sub 3-x}Ti{sub x}O{sub 4} (titanomagnetite) compositional series from pure end-members magnetite (Fe{sub 3}O{sub 4}) to ulvöspinel (Fe{sub 2}TiO{sub 4}) were successfully grown by pulsed laser deposition on MgO(100) substrates. Spectroscopic characterization including high resolution x-ray diffraction, x-ray photoelectron spectroscopy, and synchrotron-based x-ray absorption and magnetic circular dichroism consistently shows that Ti(IV) substitutes for Fe(III) in the inverse spinel lattice with a proportional increase in lattice Fe(II) concentration. No evidence of Ti interstitials, spinodal decomposition, or secondary phases was found in the bulk of the grown films. At the uppermost few nanometers of the Ti-bearing film surfaces, evidence suggests that Fe(II) is susceptible to facile oxidation, and that an associated lower Fe/Ti ratio in this region is consistent with surface compositional incompleteness or alteration to a titanomaghemite-like composition and structure. The surface of these films nonetheless appear to remain highly ordered and commensurate with the underlying structure despite facile oxidation, a surface condition that is found to be reversible to some extent by heating in low oxygen environments.

Detection of Mg spinel lithologies on central peak of crater ...

Indian Academy of Sciences (India)

identified Fe bearing Mg-spinel-rich rock types are defined by their strong 2-μm ... The Modified Gaussian Modeling (MGM) analysis ... study the deep crustal and/or upper mantle composition and may lead to a fresh ... Lunar surface; Mg-spinel; central peak; Theophilus; remote sensing. .... The explanation of these spec-.

Photoelectrochemical and theoretical investigations of spinel type ferrites (MxFe3-xO4) for water splitting: a mini-review

Science.gov (United States)

Taffa, Dereje H.; Dillert, Ralf; Ulpe, Anna C.; Bauerfeind, Katharina C. L.; Bredow, Thomas; Bahnemann, Detlef W.; Wark, Michael

2017-01-01

Solar-assisted water splitting using photoelectrochemical cells (PECs) is one of the promising pathways for the production of hydrogen for renewable energy storage. The nature of the semiconductor material is the primary factor that controls the overall energy conversion efficiency. Finding semiconductor materials with appropriate semiconducting properties (stability, efficient charge separation and transport, abundant, visible light absorption) is still a challenge for developing materials for solar water splitting. Owing to the suitable bandgap for visible light harvesting and the abundance of iron-based oxide semiconductors, they are promising candidates for PECs and have received much research attention. Spinel ferrites are subclasses of iron oxides derived from the classical magnetite (FeIIFe2IIIO4) in which the FeII is replaced by one (some cases two) additional divalent metals. They are generally denoted as MxFe3-xO4 (M=Ca, Mg, Zn, Co, Ni, Mn, and so on) and mostly crystallize in spinel or inverse spinel structures. In this mini review, we present the current state of research in spinel ferrites as photoelectrode materials for PECs application. Strategies to improve energy conversion efficiency (nanostructuring, surface modification, and heterostructuring) will be presented. Furthermore, theoretical findings related to the electronic structure, bandgap, and magnetic properties will be presented and compared with experimental results.

Structural Changes and Material Transport in Al2O3-Supported Cu/Fe Spinel Particles in a Simulated Chemical Looping Combustion Environment

Science.gov (United States)

Nealley, W. H. Harrison; Nakano, Anna; Nakano, Jinichiro; Bennett, James P.

2018-05-01

Alumina-supported Cu/Fe spinel particles were exposed to oxidation/reduction atmospheres at 800°C. Structural changes of the particles subjected to gas cycles between air and 10 vol.% CO-90 vol.% Ar were studied from physical data and real-time images collected using a confocal scanning laser microscope equipped with a heating chamber. Overall particle volume slowly expanded with cycles while surface roughness decreased. Cross-sections of the exposed particles showed segregation of Cu and Fe to the edges of inner grains, which may have acted as oxygen carriers during the exposures. The particles remained whole during the cyclic exposures without any noticeable structural breakdown.

The Effect of Composition on Spinel Crystals Equilibrium in Low-Silica High-Level Waste Glasses

International Nuclear Information System (INIS)

Jiricka, Milos; Hrma, Pavel R.; Vienna, John D.

2003-01-01

The liquidus temperature (TL) and the equilibrium mass fraction of spinel were measured in the regions of low-silica (less than 42 mass% SiO2) high-level waste borosilicate glasses within the spinel primary phase field as functions of glass composition. The components that varied, one at a time, were Al2O3, B2O3, Cr2O3, Fe2O3, Li2O, MnO, Na2O, NiO, SiO2, and ZrO2. The effects of Al2O3, B2O3, Fe2O3, NiO, SiO2, and ZrO2 on the TL in this region and in glasses with 42 to 56 mass% SiO2 were similar. However, in the low-silica region, Cr2O3 increased the TL substantially less, and Li2O and Na2O decreased the TL significantly less than in the region with 42 to 56 mass% SiO2. The effect of MnO on the TL of the higher SiO2 glasses is not yet understood with sufficient accuracy. The temperature at which the equilibrium mass fraction of spinel was 1 mass% was 25C to 64C below the TL

Optical study of phase transitions in single-crystalline RuP

Science.gov (United States)

Chen, R. Y.; Shi, Y. G.; Zheng, P.; Wang, L.; Dong, T.; Wang, N. L.

2015-03-01

RuP single crystals of MnP-type orthorhombic structure were synthesized by the Sn flux method. Temperature-dependent x-ray diffraction measurements reveal that the compound experiences two structural phase transitions, which are further confirmed by enormous anomalies shown in temperature-dependent resistivity and magnetic susceptibility. Particularly, the resistivity drops monotonically upon temperature cooling below the second transition, indicating that the material shows metallic behavior, in sharp contrast with the insulating ground state of polycrystalline samples. Optical conductivity measurements were also performed in order to unravel the mechanism of these two transitions. The measurement revealed a sudden reconstruction of band structure over a broad energy scale and a significant removal of conducting carriers below the first phase transition, while a charge-density-wave-like energy gap opens below the second phase transition.

Single phase inverter for a three phase power generation and distribution system

Science.gov (United States)

Lindena, S. J.

1976-01-01

A breadboard design of a single-phase inverter with sinusoidal output voltage for a three-phase power generation and distribution system was developed. The three-phase system consists of three single-phase inverters, whose output voltages are connected in a delta configuration. Upon failure of one inverter the two remaining inverters will continue to deliver three-phase power. Parallel redundancy as offered by two three-phase inverters is substituted by one three-phase inverter assembly with high savings in volume, weight, components count and complexity, and a considerable increase in reliability. The following requirements must be met: (1) Each single-phase, current-fed inverter must be capable of being synchronized to a three-phase reference system such that its output voltage remains phaselocked to its respective reference voltage. (2) Each single-phase, current-fed inverter must be capable of accepting leading and lagging power factors over a range from -0.7 through 1 to +0.7.

Solution-combustion synthesized aluminium-doped spinel (LiAl(subx)Mn(sub2-x)O(sub4) as a high-performance lithium-ion battery cathode material

CSIR Research Space (South Africa)

Kebede, MA

2015-06-01

Full Text Available High-performing (LiAl(subx)Mn(sub2-x)O(sub4) (x = 0, 0.125, 0.25, 0.375, and 0.5) spinel cathode materials for lithium-ion battery were developed using a solution combustion method. The as-synthesized cathode materials have spinel cubic structure...

Preparation of single phase molybdenum boride

International Nuclear Information System (INIS)

Camurlu, Hasan Erdem

2011-01-01

Highlights: → Formation of Mo and a mixture of molybdenum boride phases take place in preparation of molybdenum borides. → It is intricate to prepare single phase molybdenum borides. → Formation of single phase MoB from MoO 3 + B 2 O 3 + Mg mixtures has not been reported previously. → Single phase MoB was successfully prepared through a combination of mechanochemical synthesis and annealing process. - Abstract: The formation of MoB through volume combustion synthesis (VCS), and through mechanochemical synthesis (MCS) followed by annealing has been investigated. MoO 3 , B 2 O 3 and Mg were used as reactants while MgO and NaCl were introduced as diluents. Products were leached in dilute HCl solution and were subjected to X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) examinations. Mo was the major phase component in the VCS products under all the experimental conditions. Mo 2 B, MoB, MoB 2 and Mo 2 B 5 were found as minor phases. Products of MCS contained a mixture of Mo 2 B, MoB, MoB 2 and Mo. After annealing the MCS product at 1400 deg. C for 3 h, single phase α-MoB was obtained.

Nodal structure and phase shifts of zero-incident-energy wave functions: Multiparticle single-channel scattering

International Nuclear Information System (INIS)

Iwinski, Z.R.; Rosenberg, L.; Spruch, L.

1986-01-01

For potential scattering, with delta/sub L/(k) the phase shift modulo π for an incident wave number k, Levinson's theorem gives delta/sub L/(0)-delta/sub L/(infinity) in terms of N/sub L/, the number of bound states of angular momentum L, for delta/sub L/(k) assumed to be a continuous function of k. N/sub L/ also determines the number of nodes of the zero-energy wave function u/sub L/(r). A knowledge of the nodal structure and of the absolute value of delta/sub L/(0) is very useful in theoretical studies of low-energy potential scattering. Two preliminary attempts, one formal and one ''physical,'' are made to extend the above results to single-channel scattering by a compound system initially in its ground state. The nodal structure will be of greater interest to us here than an extension of Levinson's theorem

Thermally-induced electronic relaxation in structurally-modified Cu{sub 0.1}Ni{sub 0.8}Co{sub 0.2}Mn{sub 1.9}O{sub 4} spinel ceramics

Energy Technology Data Exchange (ETDEWEB)

Shpotyuk, O., E-mail: shpotyuk@novas.lviv.ua [Institute of Materials, Scientific Research Company “Carat”, 202, Stryjska Street, Lviv 79031 (Ukraine); Institute of Physics, Jan Dlugosz University, 13/15, al. Armii Krajowej, Czestochowa 42200 Poland (Poland); Balitska, V. [Institute of Materials, Scientific Research Company “Carat”, 202, Stryjska Street, Lviv 79031 (Ukraine); Lviv State University of Vital Activity Safety, 35, Kleparivska Street, Lviv 79007 (Ukraine); Brunner, M. [Fachhochschule Köln/University of Applied Sciences, 2, Betzdorfer Strasse, Köln 50679 (Germany); Hadzaman, I. [Institute of Materials, Scientific Research Company “Carat”, 202, Stryjska Street, Lviv 79031 (Ukraine); Drohobych Ivan Franko State Pedagogical University, 24, I. Franko Street, Drohobych 82100 (Ukraine); Klym, H. [Institute of Materials, Scientific Research Company “Carat”, 202, Stryjska Street, Lviv 79031 (Ukraine); Lviv Polytechnic National University, 12, Bandera Street, Lviv 79013 (Ukraine)

2015-02-15

Thermally-induced electronic relaxation in structurally-modified Cu{sub 0.1}Ni{sub 0.8}Co{sub 0.2}Mn{sub 1.9}O{sub 4} spinel ceramics is shown to be adequately described by stretched exponential function on time. This kinetics is defined by microsctructure perfectness of the relaxing media, showing obvious onset to stretched exponential behaviour with non-exponentionality index attaining close to 0.43 values for high-monolith ceramics and smaller ones in fine-grained ceramics. Percolation threshold in relaxation-degradation kinetics is detected for ceramics with 10% of NiO extractions, showing the smallest but most prolonged single-path degradation effect. This finding is treated in terms of Phillips’ axiomatic diffusion-to-trap model, where only one of two relaxation channels (caused by operative short-range forces) occurs to be effective, while additional non-operative channels contribute to electronic relaxation in fine-grained ceramics.

Structural, magnetic, and dielectric properties of multiferroic Co1-xMgxCr2O4 nanoparticles

Science.gov (United States)

Kamran, M.; Ullah, A.; Rahman, S.; Tahir, A.; Nadeem, K.; Anis ur Rehman, M.; Hussain, S.

2017-07-01

We examined the structural, magnetic, and dielectric properties of Co1-xMgxCr2O4 nanoparticles with composition x = 0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1 in detail. X-ray diffraction (XRD) revealed normal spinel structure for all the samples. Rietveld refinement fitting results of the XRD showed no impurity phases which signifies the formation of single phase Co1-xMgxCr2O4 nanoparticles. The average crystallite size showed a peak behaviour with maxima at x = 0.6. Raman and Fourier transform infrared (FTIR) spectroscopy also confirmed the formation of single phase normal spinel for all the samples and exhibited dominant vibrational changes for x ≥ 0.6. For x = 0 (CoCr2O4), zero field cooled/field cooled (ZFC/FC) magnetization curves showed paramagnetic (PM) to ferrimagnetic (FiM) transition at Tc = 97 K and a conical spiral magnetic order at Ts = 30 K. The end members CoCr2O4 (x = 0) and MgCr2O4 (x = 1) are FiM and antiferromagnetic (AFM), respectively. Tc and Ts showed decreasing trend with increasing x, followed by an additional AFM transition at TN = 15 K for x = 0.6. The system finally stabilized and changed to highly frustrated AFM structure at x = 1 due to formation of pure MgCr2O4. High field FC curves (5T) depicted nearly no effect on spiral magnetic state, which is attributed to strong exchange B-B magnetic interactions at low temperatures. Dielectric parameters showed a non-monotonous behaviour with Mg concentration and were explained with the help of Maxwell-Wagner model and Koop's theory. Dielectric properties were improved for nanoparticles with x = 0.6 and is attributed to their larger average crystallite size. In summary, Mg doping has significantly affects the structural, magnetic, and dielectric properties of CoCr2O4 nanoparticles, which can be attributed to variations in local magnetic exchange interactions and variation in average crystallite size of these chromite nanoparticles.

Structural, dielectric and gas sensing behavior of Mn substituted spinel MFe{sub 2}O{sub 4} (M=Zn, Cu, Ni, and Co) ferrite nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Ranjith Kumar, E., E-mail: ranjueaswar@gmail.com [Department of Physics, Dr. NGP Institute of Technology, Coimbatore 641048, Tamil Nadu (India); Siva Prasada Reddy, P.; Sarala Devi, G. [Inorganic and Physical Chemistry Division, Indian Institute Chemical Technology, Hyderabad 500607 (India); Sathiyaraj, S. [Department of Chemistry, Dr. NGP Institute of Technology, Coimbatore 641048, Tamil Nadu (India)

2016-01-15

Spinel ferrite (MnZnFe{sub 2}O{sub 4}, MnCuFe{sub 2}O{sub 4}, MnNiFe{sub 2}O{sub 4} and MnCoFe{sub 2}O{sub 4}) nanoparticles have been prepared by evaporation method. The annealing temperature plays an important role on changing particle size of the spinel ferrite nanoparticles was found out by X-ray diffraction and transmission electron microscopy. The role of manganese substitution in the spinel ferrite nanoparticles were also analyzed for different annealing temperature. The substitution of Mn also creates a vital change in dielectric properties have been measured in the frequency range of 100 kHz to 5 MHz. These spinel ferrites are decomposed to α-Fe{sub 2}O{sub 3} after annealing above 550 °C in air. Through the characterization of the prepared powder, the effect of annealing temperature, chemical composition and preparation technique on the microstructure, particle size and dielectric properties of the Mn substituted spinel ferrite nanoparticles are discussed. Furthermore, Conductance response of Mn substituted MFe{sub 2}O{sub 4} ferrite nanoparticles were measured by exposing the materials to reducing gas like liquefied petroleum gas (LPG). - Highlights: • The egg white support to achieve sample with shorter reaction time. • Manganese plays a significant role in sensor response. • Nature of the ferrites was affected with increasing annealing temperature.

A Spinel-integrated P2-type Layered Composite: High-rate Cathode for Sodium-ion Batteries

Energy Technology Data Exchange (ETDEWEB)

Zheng, Jianming; Yan, Pengfei; Kan, Wang Hay; Wang, Chong M.; Manthiram, Arumugam

2016-01-14

Sodium-ion batteries (SIB) are being intensively investigated, owing to the natural abundance and low cost of Na resources. However, the SIBs still suffer from poor rate capability due to the large ionic radius of Na+ ion and the significant kinetic barrier to Na+-ion transport. Here, we present an Fd-3m spinel-integrated P2-type layered composite (P2 + Fd-3m) material as a high-rate cathode for SIBs. The P2 + Fd-3m composite material Na0.50Ni1/6Co1/6Mn2/3O2 shows significantly enhanced discharge capacity, energy density, and rate capability as compared to the pure P2-type counterpart. The composite delivers a high capacity of 85 mA h g-1 when discharging at a very high current density of 1500 mA g-1 (10C rate) between 2.0 and 4.5 V, validating it as a promising cathode candidate for high-power SIBs. The superior performance is ascribed to the improved kinetics in the presence of the integrated-spinel phase, which facilitates fast electron transport to coordinate with the timely Na+-ion insertion/extraction. The findings of this work also shed light on the importance of developing lattice doping, surface coating, and electrolyte additives to further improve the structural and interfacial stability of P2-type cathode materials and fully realize their practical applications in sodium-ion batteries.

Paramagnetism and antiferromagnetic interactions in single-phase Fe-implanted ZnO

CERN Document Server

Pereira, Lino Miguel da Costa; Correia, João Guilherme; Van Bael, M J; Temst, Kristiaan; Vantomme, André; Araújo, João Pedro

2013-01-01

As the intrinsic origin of the high temperature ferromagnetism often observed in wide-gap dilute magnetic semiconductors becomes increasingly debated, there is a growing need for comprehensive studies on the single-phase region of the phase diagram of these materials. Here we report on the magnetic and structural properties of Fe-doped ZnO prepared by ion implantation of ZnO single crystals. A detailed structural characterization shows that the Fe impurities substitute for Zn in ZnO in a wurtzite Zn$_{1−x}$Fe$_{x}$O phase which is coherent with the ZnO host. In addition, the density of beam-induced defects is progressively decreased by thermal annealing up to 900$^{\\circ}$C, from highly disordered after implantation to highly crystalline upon subsequent annealing. Based on a detailed analysis of the magnetometry data, we demonstrate that isolated Fe impurities occupying Zn substitutional sites behave as localized paramagnetic moments down to 2$^{\\circ}$K, irrespective of the Fe concentration and the density...

Versatile electronic behavior of the Li{sub x}Mn{sub 3−x−y}Fe{sub y}O{sub 4} spinels

Energy Technology Data Exchange (ETDEWEB)

Alonso-Domínguez, D. [Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Avda. Complutense s/n, 28040 Madrid (Spain); CEI Moncloa, UCM-UPM, Madrid (Spain); Álvarez-Serrano, I., E-mail: ias@quim.ucm.es [Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Avda. Complutense s/n, 28040 Madrid (Spain); López, M.L.; Veiga, M.L.; Pico, C. [Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Avda. Complutense s/n, 28040 Madrid (Spain); Mompeán, F.; García-Hernández, M. [Instituto de Ciencia de Materiales, CSIC, Cantoblanco, 28049 Madrid (Spain); Cuello, G.J. [Institut Laue-Langevin, 6 rue Jules Horowitz, F-38042 Grenoble (France)

2013-11-15

Highlights: •The Li{sub x}Mn{sub 3−x−y}Fe{sub y}O{sub 4} spinels show a versatile electronic behavior. •Optimal compositional ranges for different application fields are proposed. •Frustrated ferromagnetic response is compositionally driven. •High ε′ values are obtained when B sites are occupied by both Mn and Fe cations. •High lithium contents are linked to the electrochemical behavior. -- Abstract: The detailed structural and electronic characterization of microcrystalline powders of new spinels Li{sub x}Mn{sub 3−x−y}Fe{sub y}O{sub 4} (0.4 ⩽ x ⩽ 1.33; 0 ⩽ y ⩽ 1.30), obtained by the “liquid mix” method, is reported. Compositional characterization was carried out by means of thermogravimetric analysis, energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy, and their structure was refined from neutron and X-ray diffraction showing a cubic symmetry between 5 and 550 K, Space Group Fd3{sup ¯}m. However, at temperatures above ca. 950 K, a reversible transformation, probably implying the formation of an ordered vacant phase, has been detected. The magnetic behavior, analyzed from neutron diffraction data and magnetization measurements, is interpreted considering an “incomplete” ferrimagnetic response, due to magnetic frustration in the B sites. Potential applications have been evaluated from the magnetocaloric, electrochemical and dielectric behavior in selected compositional ranges.

Effect on the structural, DC resistivity and magnetic properties of Zr and Cu co-SubstitutedNi0.5Zn0.5Fe2O4using sol-gel auto-combustion method

Science.gov (United States)

Jalaiah, K.; Vijaya Babu, K.; Chandra mouli, K.; Subba Rao, P. S. V.

2018-04-01

The Zr and Cu co-substituted Ni0.5Zn0.5Fe2O4 ferrite nanoparticles have been synthesized by the sol-gel auto combustion method. The XRD patterns confirmed single phase cubic spinel structure for present ferrite systems. The substitution of co-dopants in the spinel structure initially decreases the lattice parameter from x = 0.00 to 0.08 and thereafter increases and the same tendency reflecting in cell volume. The DC resistivity was initially increased later followed the decreasing trend; however the drift mobility of all ferrite samples appears to be in opposite phenomenon to DC resistivity. The saturation magnetization and net magnetic moments of all ferrite samples are decreasing with increasing dopant concentration. The coercive field and Y-K angles are increased with dopant concentration. The initial permeability of all samples is decreased with increasing dopant concentration. The Q-Factor for all samples shows the narrow frequency band with increasing frequency.

Preparation of Fischer-Tropsch catalysts from cobalt/iron hydrotalcites

Energy Technology Data Exchange (ETDEWEB)

Howard, B.H.; Boff, J.J.; Zarochak, M.F. [Pittsburgh Energy Technology Center, PA (United States)] [and others

1995-12-31

Compounds with the (hydrotalcites) have properties that make them attractive as precursors for Fischer-Tropsch catalysts. A series of single-phase hydrotalcites with cobalt/iron atom ratios ranging from 75/25 to 25/75 has been synthesized. Mixed cobalt/iron oxides have been prepared from these hydrotalcites by controlled thermal decomposition. Thermal decomposition at temperatures below 600 {degrees}C typically produced a single-phase mixed metal oxide with a spinel structure. The BET surface areas of the spinal samples have been found to be as high as about 150 m{sup 2}/g. Appropriate reducing pretreatments have been developed for several of these spinels and their activity, selectivity, and activity and selectivity maintenance have been examined at 13 MPa in a fixed-bed microreactor.

Effect of lapping slurry on critical cutting depth of spinel

International Nuclear Information System (INIS)

Wang, Zhan-kui; Wang, Zhuan-kui; Zhu, Yong-wei; Su, Jian-xiu

2015-01-01

Highlights: • Measured spinel wafers’ hardness and crack length in different slurries. • Evaluated the softened layer thickness in different slurries. • Discussed the effect of slurries on critical cutting depth of spinel. - Abstract: The critical cutting depth for lapping process is very important because it influences the mode of material removal. In this paper, a serial of microscopic indentation experiments were carried out for measuring spinel wafers’ hardness and crack length in different lapping slurries. Their critical cutting depth and fracture toughness were calculated. X-ray photoelectron spectroscopy (XPS) was also employed to study the surface chemical composition and softened layer thickness of wafers in different slurries. Experimental results indicate that the softened layers of spinel wafers are formed due to the corrosion of lapping slurries, which leads to a lower hardness and a larger fracture toughness of samples, and increases the critical cutting depth. Among them, the critical cutting depth in ethylene glycol solution is the largest and up to 21.8 nm. The increase of critical cutting depth is helpful to modify the surface quality of the work-piece being lapped via ductile removal mode instead of brittle fracture mode

Gas-phase structure and fragmentation pathways of singly protonated peptides with N-terminal arginine.

Science.gov (United States)

Bythell, Benjamin J; Csonka, István P; Suhai, Sándor; Barofsky, Douglas F; Paizs, Béla

2010-11-25

The gas-phase structures and fragmentation pathways of the singly protonated peptide arginylglycylaspartic acid (RGD) are investigated by means of collision-induced-dissociation (CID) and detailed molecular mechanics and density functional theory (DFT) calculations. It is demonstrated that despite the ionizing proton being strongly sequestered at the guanidine group, protonated RGD can easily be fragmented on charge directed fragmentation pathways. This is due to facile mobilization of the C-terminal or aspartic acid COOH protons thereby generating salt-bridge (SB) stabilized structures. These SB intermediates can directly fragment to generate b(2) ions or facilely rearrange to form anhydrides from which both b(2) and b(2)+H(2)O fragments can be formed. The salt-bridge stabilized and anhydride transition structures (TSs) necessary to form b(2) and b(2)+H(2)O are much lower in energy than their traditional charge solvated counterparts. These mechanisms provide compelling evidence of the role of SB and anhydride structures in protonated peptide fragmentation which complements and supports our recent findings for tryptic systems (Bythell, B. J.; Suhai, S.; Somogyi, A.; Paizs, B. J. Am. Chem. Soc. 2009, 131, 14057-14065.). In addition to these findings we also report on the mechanisms for the formation of the b(1) ion, neutral loss (H(2)O, NH(3), guanidine) fragment ions, and the d(3) ion.

Re4As6S3, a thio-spinel-related cluster system

DEFF Research Database (Denmark)

Besnard, Celine; Svensson, Christer; Ståhl, Kenny

2003-01-01

. The rhenium atoms form tetrahedral clusters linked via tetrahedral arsenic clusters to produce an NaCl-type arrangement. The oxidation state of rhenium is IV and the number of electrons shared by the rhenium atoms in the cluster is 12. The structure is based on an ordered defect thio-spinel A((1-x))B(2)X(4......) where the B-type atoms form tetrahedral clusters....

100-nm thick single-phase wurtzite BAlN films with boron contents over 10%

KAUST Repository

Li, Xiaohang; Wang, Shuo; Liu, Hanxiao; Ponce, Fernando A.; Detchprohm, Theeradetch; Dupuis, Russell D.

2017-01-01

Growing thicker BAlN films while maintaining single-phase wurtzite structure and boron content over 10% has been challenging. In this study, we report on the growth of 100 nm-thick single-phase wurtzite BAlN films with boron contents up to 14.4% by MOCVD. Flow-modulated epitaxy was employed to increase diffusion length of group-III atoms and reduce parasitic reactions between the metalorganics and NH3. A large growth efficiency of ∼2000 μm mol−1 was achieved as a result. Small B/III ratios up to 17% in conjunction with high temperatures up to 1010 °C were utilized to prevent formation of the cubic phase and maintain wurtzite structure.

100-nm thick single-phase wurtzite BAlN films with boron contents over 10%

KAUST Repository

Li, Xiaohang

2017-01-11

Growing thicker BAlN films while maintaining single-phase wurtzite structure and boron content over 10% has been challenging. In this study, we report on the growth of 100 nm-thick single-phase wurtzite BAlN films with boron contents up to 14.4% by MOCVD. Flow-modulated epitaxy was employed to increase diffusion length of group-III atoms and reduce parasitic reactions between the metalorganics and NH3. A large growth efficiency of ∼2000 μm mol−1 was achieved as a result. Small B/III ratios up to 17% in conjunction with high temperatures up to 1010 °C were utilized to prevent formation of the cubic phase and maintain wurtzite structure.

A Finite-Volume approach for compressible single- and two-phase flows in flexible pipelines with fluid-structure interaction

Science.gov (United States)

Daude, F.; Galon, P.

2018-06-01

A Finite-Volume scheme for the numerical computations of compressible single- and two-phase flows in flexible pipelines is proposed based on an approximate Godunov-type approach. The spatial discretization is here obtained using the HLLC scheme. In addition, the numerical treatment of abrupt changes in area and network including several pipelines connected at junctions is also considered. The proposed approach is based on the integral form of the governing equations making it possible to tackle general equations of state. A coupled approach for the resolution of fluid-structure interaction of compressible fluid flowing in flexible pipes is considered. The structural problem is solved using Euler-Bernoulli beam finite elements. The present Finite-Volume method is applied to ideal gas and two-phase steam-water based on the Homogeneous Equilibrium Model (HEM) in conjunction with a tabulated equation of state in order to demonstrate its ability to tackle general equations of state. The extensive application of the scheme for both shock tube and other transient flow problems demonstrates its capability to resolve such problems accurately and robustly. Finally, the proposed 1-D fluid-structure interaction model appears to be computationally efficient.

Synthesis and magnetic properties of tin spinel ferrites doped manganese

Science.gov (United States)

El Moussaoui, H.; Mahfoud, T.; Habouti, S.; El Maalam, K.; Ben Ali, M.; Hamedoun, M.; Mounkachi, O.; Masrour, R.; Hlil, E. K.; Benyoussef, A.

2016-05-01

In this work we report the synthesis, the microstructural characterization and the magnetic properties of tin spinel ferrites doped manganese (Sn1-xMnxFe2O4 with x=0.25, 0.5, 0.75, and 1) nanoparticles prepared by co-precipitation method. The effect of annealing temperature on the structure, morphology and magnetic properties of Sn0.5Mn0.5Fe2O4 has been investigated. The synthesized nanoparticle sizes have been controlled between 4 and 9 nm, with uniform spherical morphology as confirmed by transmission electron microscopy (TEM). All the samples prepared possess single domain magnetic. The nanoparticles of Sn0.5Mn0.5Fe2O4 with 4 nm in diameter have a blocking temperature close to 100 K. In addition, the cation distribution obtained from the X-ray diffraction of this sample was confirmed by magnetic measurement. For the Sn1-xMnxFe2O4; (0≤x≤1) samples, the magnetization and coercive fields increase when the augmentation of Mn content increases. For x=0.5, such parameters decrease when the calcination temperature increases.

Crystal structure, Raman scattering and magnetic properties of CuCr2-xZrxSe4 and CuCr2-xSnxSe4 selenospinels

Science.gov (United States)

Pinto, C.; Galdámez, A.; Barahona, P.; Moris, S.; Peña, O.

2018-06-01

Selenospinels, CuCr2-xMxSe4 (M = Zr and Sn), were synthesized via conventional solid-state reactions. The crystal structure of CuCr1.5Sn0.5Se4, CuCr1.7Sn0.3Se4, CuCr1.5Zr0.5Se4, and CuCr1.8Zr0.2Se4 were determined using single-crystal X-ray diffraction. All the phases crystallized in a cubic spinel-type structure. The chemical compositions of the single-crystals were examined using energy-dispersive X-ray analysis (EDS). Powder X-ray diffraction patterns of CuCr1.3Sn0.7Se4 and CuCr1.7Sn0.3Se4 were consistent with phases belonging to the Fd 3 bar m Space group. An analysis of the vibrational properties on the single-crystals was performed using Raman scattering measurements. The magnetic properties showed a spin glass behavior with increasing Sn content and ferromagnetic order for CuCr1.7Sn0.3Se4.

Enhancement photocatalytic activity of spinel oxide (Co, Ni3O4 by combination with carbon nanotubes

Directory of Open Access Journals (Sweden)

Kahdum Bashaer J.

2017-09-01

Full Text Available In this study, some types of composites consisting of multi-walled carbon nanotubes (MWCNTs and spinel oxide (Co, Ni3O4 were synthesized by simple evaporation method. These composites were characterized by UV–Vis diffuse reflectance spectroscopy, X-rays diffraction(XRD, Scanning electron microscopy (SEM and specific surface area(SBET. The photocatalytic activity of the prepared composites was investigated by the following removal of Bismarck brown G (BBG dye from its aqueous solutions. The obtained results showed that using MWCNTs in combination with spinel oxide to produced composites (spinel/MWCNTs which succeeded in increasing the activity of spinel oxide and exhibited higher photocatalytic activity than spinel oxide alone. Also it was found that, multiwalled carbon nanotubes were successful in increasing the adsorption and improving the activity of photocatalytic degradation of Bismarck brown G dye(BBG. The obtained results showed that spinel/MWCNTs was more active in dye removal in comparison with each of spinel oxide and MWCNTs alone under the same reaction conditions. Also band gap energies for the prepared composites showed lower values in comparison with neat spinel. This point represents a promising observation as these composites can be excited using a lower energy radiation sources.

Influence of pH and fuels on the combustion synthesis, structural, morphological, electrical and magnetic properties of CoFe{sub 2}O{sub 4} nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Shanmugavani, A. [Solid State Ionics and Energy Devices Laboratory, Department of Physics, Bharathiar University, Coimbatore 641 046 (India); Selvan, R.Kalai, E-mail: selvankram@buc.edu.in [Solid State Ionics and Energy Devices Laboratory, Department of Physics, Bharathiar University, Coimbatore 641 046 (India); Layek, Samar [Department of Physics, Indian Institute of Technology, Kanpur 208016 (India); Vasylechko, Leonid [Semiconductor Electronics Department, Lviv Polytechnic National University, 12 Bandera Street, Lviv 79013 (Ukraine); Sanjeeviraja, C. [Department of Physics, Alagappa Chettiar College of Engineering and Technology, Karaikudi 630 004 (India)

2015-11-15

Nanocrystalline spinel cobalt ferrite particles are synthesized by simple combustion method using aspartic acid and glycine as fuels. The single phase cubic structure of CoFe{sub 2}O{sub 4} is revealed through X-ray diffraction analysis (XRD). Further the Rietveld refinement confirms the formation of inverse spinel structure of CoFe{sub 2}O{sub 4}. The characteristic functional groups of Co–O and Fe–O are identified from Fourier Transform Infrared (FT-IR) analysis. Uniform distribution of of nearly spherical particles with the size range of 40–80 nm is identified through field emission scanning electron microscope (FESEM) images. The calculated DC conductivity is 1.469 × 10{sup −7} and 2.214 × 10{sup −8} S cm{sup −1}, for CoFe{sub 2}O{sub 4} synthesized using aspartic acid and glycine, respectively. The dielectric behavior obeys the Maxwell–Wagner interfacial polarization. The ferromagnetic behavior of CoFe{sub 2}O{sub 4} is identified using VSM analysis and the calculated coercivity is 27 Oe and saturation magnetization is 68 emu/g.

Phase transformation mechanism in lithium manganese nickel oxide revealed by single-crystal hard X-ray microscopy

Science.gov (United States)

Kuppan, Saravanan; Xu, Yahong; Liu, Yijin; Chen, Guoying

2017-02-01

Understanding the reaction pathway and kinetics of solid-state phase transformation is critical in designing advanced electrode materials with better performance and stability. Despite the first-order phase transition with a large lattice mismatch between the involved phases, spinel LiMn1.5Ni0.5O4 is capable of fast rate even at large particle size, presenting an enigma yet to be understood. The present study uses advanced two-dimensional and three-dimensional nano-tomography on a series of well-formed LixMn1.5Ni0.5O4 (0growth process instead of a shrinking-core or a particle-by-particle process. Superior kinetics of (100) facets at the vertices of truncated octahedral particles promote preferential delithiation, whereas the observation of strain-induced cracking suggests mechanical degradation in the material.

Comparative study of nano copper aluminate spinel prepared by sol–gel and modified sol–gel techniques: Structural, electrical, optical and catalytic studies

International Nuclear Information System (INIS)

Kumar, R. Thinesh; Suresh, P.; Selvam, N. Clament Sagaya; Kennedy, L. John; Vijaya, J. Judith

2012-01-01

Highlights: ► A modified sol–gel method for the preparation of nano CuAl 2 O 4 spinel using ethylenediamine was studied. ► Role of ethylenediamine in enhancing the structural, electrical, optical and catalytic properties of copper aluminate is highlighted. ► Effect of preparation method on the activity and selectivity of the samples on the oxidation of benzyl alcohol by CuAl 2 O 4 is studied. - Abstract: The effect of ethylenediamine addition in the sol–gel method for the preparation of nano CuAl 2 O 4 spinel for the enhancement in their structural, electrical, optical and catalytic properties was investigated. The samples were prepared by two different methods: sol–gel and modified sol–gel technique using ethylenediamine. X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), scanning electron microscopy (SEM), high resolution-transmission electron microscopy (HR-TEM), energy dispersive X-ray analysis (EDX), nitrogen adsorption/desorption isotherms, temperature dependent conductance measurements, thermoelectric power (TEP) measurements and UV–visible diffuse reflectance (UV–vis-DRS) spectra were used to characterize the samples prepared. CuAl 2 O 4 prepared by modified sol–gel technique was found to possess a higher surface area, lower crystallite size, lower activation energy and high porosity than the one prepared by sol–gel method which in turn lead to the improved performance of it towards the selective oxidation of benzyl alcohol to benzaldehyde. Effect of solvent on the catalytic oxidation of benzyl alcohol by the nano CuAl 2 O 4 prepared by modified sol–gel technique was also investigated.

Current Harmonics from Single-Phase Grid-Connected Inverters

DEFF Research Database (Denmark)

Yang, Yongheng; Zhou, Keliang; Blaabjerg, Frede

2016-01-01

Environmental conditions and operational modes may significantly impact the distortion level of the injected current from single-phase grid-connected inverter systems, such as photovoltaic (PV) inverters, which may operate in cloudy days with a maximum power point tracking, in a non-unity power...... factor, or in the low voltage ride through mode with reactive current injection. In this paper, the mechanism of the harmonic current injection from grid-connected single-phase inverter systems is thus explored, and the analysis is conducted on single-phase PV systems. In particular, the analysis...... is focused on the impacts of the power factor and the feed-in grid current level on the quality of the feed-in grid current from single-phase inverters. As a consequence, an internal model principle based high performance current control solution is tailor-made and developed for single-phase grid-connected...

High Quality Model Predictive Control for Single Phase Grid Connected Photovoltaic Inverters

DEFF Research Database (Denmark)

Zangeneh Bighash, Esmaeil; Sadeghzadeh, Seyed Mohammad; Ebrahimzadeh, Esmaeil

2018-01-01

Single phase grid-connected inverters with LCL filter are widely used to connect the photovoltaic systems to the utility grid. Among the presented control schemes, predictive control methods are faster and more accurate but are more complex to implement. Recently, the model-predictive control...... algorithm for single-phase inverter has been presented, where the algorithm implementation is straightforward. In the proposed approach, all switching states are tested in each switching period to achieve the control objectives. However, since the number of the switching states in single-phase inverter...... is low, the inverter output current has a high total harmonic distortions. In order to reduce the total harmonic distortions of the injected current, this paper presents a high-quality model-predictive control for one of the newest structure of the grid connected photovoltaic inverter, i.e., HERIC...

A single-phase axially-magnetized permanent-magnet oscillating machine for miniature aerospace power sources

Directory of Open Access Journals (Sweden)

Yi Sui

2017-05-01

Full Text Available A single-phase axially-magnetized permanent-magnet (PM oscillating machine which can be integrated with a free-piston Stirling engine to generate electric power, is investigated for miniature aerospace power sources. Machine structure, operating principle and detent force characteristic are elaborately studied. With the sinusoidal speed characteristic of the mover considered, the proposed machine is designed by 2D finite-element analysis (FEA, and some main structural parameters such as air gap diameter, dimensions of PMs, pole pitches of both stator and mover, and the pole-pitch combinations, etc., are optimized to improve both the power density and force capability. Compared with the three-phase PM linear machines, the proposed single-phase machine features less PM use, simple control and low controller cost. The power density of the proposed machine is higher than that of the three-phase radially-magnetized PM linear machine, but lower than the three-phase axially-magnetized PM linear machine.

A single-phase axially-magnetized permanent-magnet oscillating machine for miniature aerospace power sources

Science.gov (United States)

Sui, Yi; Zheng, Ping; Cheng, Luming; Wang, Weinan; Liu, Jiaqi

2017-05-01

A single-phase axially-magnetized permanent-magnet (PM) oscillating machine which can be integrated with a free-piston Stirling engine to generate electric power, is investigated for miniature aerospace power sources. Machine structure, operating principle and detent force characteristic are elaborately studied. With the sinusoidal speed characteristic of the mover considered, the proposed machine is designed by 2D finite-element analysis (FEA), and some main structural parameters such as air gap diameter, dimensions of PMs, pole pitches of both stator and mover, and the pole-pitch combinations, etc., are optimized to improve both the power density and force capability. Compared with the three-phase PM linear machines, the proposed single-phase machine features less PM use, simple control and low controller cost. The power density of the proposed machine is higher than that of the three-phase radially-magnetized PM linear machine, but lower than the three-phase axially-magnetized PM linear machine.

The crystal structure and the phase transitions of pyridinium trifluoromethanesulfonate

International Nuclear Information System (INIS)

Jesariew, Dominik; Ilczyszyn, Maria M; Pietraszko, Adam

2014-01-01

The calorimetric and optical studies and the structural properties of pyridinium trifluoromethanesulfonate (abbreviated as PyHOTf) are reported. A sequence of four fully reversible solid–solid phase transitions, at 223.0, 309.0, 359.9 and 394.3 K, has been discovered. The phase transition sequence was confirmed by x-ray diffraction data. The crystal structures of three phases (V, IV and III) have been determined from the single crystal x-ray diffraction data. Structural properties of the high temperature phases are characterized using powder x-ray diffraction data measured in the 290–425 K temperature range. The structural changes triggered by the temperature change are discussed in relation to the phase transitions. Two low temperature phases (V and IV) belong to the P4 3 2 1 2 space group of the tetragonal system. The intermediate phases (III and II) are monoclinic and the prototype high temperature phase (I) is a pseudo-cubic (tetragonal) one. The low temperature phases (V and IV) are well ordered. The crystal structure of intermediate (III and II) and prototype (I) phases are characterized by high disorder of the pyridinium cations and triflate anions. (papers)

Structural, morphological and magnetic properties of Eu-doped CoFe2O4 nano-ferrites

Directory of Open Access Journals (Sweden)

Aiman Zubair

Full Text Available Europium (Eu doped spinel cobalt ferrites having composition CoEuxFe2−xO4 where x = 0.00, 0.03, 0.06, 0.09, 0.12 were fabricated by co-precipitation route. In order to observe the phase development of the ferrite samples, thermo-gravimetric analysis was carried out. The synthesized samples were subjected to X-ray diffraction analysis for structural investigation. All the samples were found to constitute face centered cubic (FCC spinel structure belonging to Fd3m space group. Scanning electron microscopy revealed the formation of nanocrystalline grains with spherical shape. Energy dispersive X-ray spectra confirmed the presence of Co, Eu, Fe and O elements with no existence of any impurity. The magnetic hysteresis curves measured at room temperature exhibited ferrimagnetic behavior with maximum saturation magnetization (Ms of 65 emu/g and coercivity (Hc of 966 Oe. The origin of ferrimagnetism in Eu doped cobalt ferrites was discussed in detail with reverence to the allocation of Co2+ and Fe3+ ions within the spinel lattice. The overall coercivity was increased (944–966 Oe and magnetization was decreased (65–46 emu/g with the substitution of Eu3+. The enhancement of former is ascribed to the transition from multi domain to single domain state and reduction in lateral is attributed to the incorporation of nonmagnetic Eu ions for Fe, resulting in weak superexchange interactions. Keywords: Europium doped cobalt ferrites, Co-precipitation, X-ray diffraction, Scanning electron microscopy, Magnetic properties

P-type zinc oxide spinels: application to transparent conductors and spintronics

International Nuclear Information System (INIS)

Stoica, Maria; S Lo, Cynthia

2014-01-01

We report on the electronic and optical properties of two theoretically predicted stable spinel compounds of the form ZnB 2 O 4 , where B = Ni or Cu; neither compound has been previously synthesized, so we compare them to the previously studied p-type ZnCo 2 O 4 spinel. These new materials exhibit spin polarization, which is useful for spintronics applications, and broad conductivity maxima near the valence band edge that indicate good p-type dopability. We show that 3d electrons on the octahedrally coordinated Zn atom fall deep within the valence band and do not contribute significantly to the electronic structure near the band edge of the material, while the O 2p and tetrahedrally coordinated B 3d electrons hybridize broadly in the shallow valence states, resulting in increasing curvature (i.e., decreased electron effective mass) of valence bands near the band edge. In particular, ZnCu 2 O 4 exhibits high electrical conductivities in the p-doping region near the valence band edge that, at σ=2×10 4  S cm −1 , are twice the maximum found for ZnCo 2 O 4 , a previously synthesized compound in this class of materials. This material also exhibits ferromagnetism in all of its most stable structures, which makes it a good candidate for further study as a dilute magnetic semiconductor. (paper)

Nanoparticles of spinel and perovskite ferromagnets and prospects for their application in medicine

Energy Technology Data Exchange (ETDEWEB)

Belous, A. G., E-mail: belous@ionc.kar.net, E-mail: solopan@ukr.net, E-mail: yelenicho@ukr.net; Solopan, S. O., E-mail: belous@ionc.kar.net, E-mail: solopan@ukr.net, E-mail: yelenicho@ukr.net; Yelenich, O. V., E-mail: belous@ionc.kar.net, E-mail: solopan@ukr.net, E-mail: yelenicho@ukr.net [Institute of General and Inorganic Chemistry, prospekt Palladina 32-34, 03142 Kyiv (Ukraine); Tovstolytkin, A. I., E-mail: atov@imag.kiev.ua [Institute of Magnetism, bulvar Vernadskoho 36-b, 03142 Kyiv (Ukraine); Kolodiazhnyi, T. V., E-mail: kolodiazhnyi.taras@nims.go.jp [National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Osinsky, S. P., E-mail: osion@onconet.kiev.ua, E-mail: bybnovskayal@ukr.net; Bubnovskaya, L. N., E-mail: osion@onconet.kiev.ua, E-mail: bybnovskayal@ukr.net [R.E. Kavetsky Institute of Experimental Pathology, Oncology and Radiobiology, vul. Vasylkivska 45, 03022 Kyiv (Ukraine)

2014-11-05

In this work, nanoparticles of La{sub 0.75}Sr{sub 0.25}MnO{sub 3} compounds with perovskite structure and AFe{sub 2}O{sub 4} (A = Mn, Fe, Co, Ni, Zn) with spinel structure have been synthesized by precipitation from diethylene glycol and microemulsion using Triton X-100 surfactant. Comparative X-ray diffraction and magnetic studies of the synthesized nanoparticles have been carried out. Magnetic fluids prepared from synthesized nanopowders have been characterized by calorimetric measurements of specific loss power (SLP)

Textures in spinel peridotite mantle xenoliths using micro-CT scanning: Examples from Canary Islands and France

Science.gov (United States)

Bhanot, K. K.; Downes, H.; Petrone, C. M.; Humphreys-Williams, E.

2017-04-01

Spinel pyroxene-clusters, which are intergrowths of spinel, orthopyroxene and clinopyroxene in mantle xenoliths, have been investigated through the use of micro-CT (μ-CT) in this study. Samples have been studied from two different tectonic settings: (1) the northern Massif Central, France, an uplifted and rifted plateau on continental lithosphere and (2) Lanzarote in the Canary Islands, an intraplate volcanic island on old oceanic lithosphere. μ-CT analysis of samples from both locations has revealed a range of spinel textures from small Lanzarote are regions that have experienced significant lithospheric thinning. This process provides a mechanism where the sub-solidus reaction of olivine + garnet = orthopyroxene + clinopyroxene + spinel is satisfied by providing a pathway from garnet peridotite to spinel peridotite. We predict that such textures would only occur in the mantle beneath regions that show evidence of thinning of the lithospheric mantle. Metasomatic reactions are seen around spinel-pyroxene clusters in some Lanzarote xenoliths, so metasomatism post-dated cluster formation.

30 CFR 77.905 - Connection of single-phase loads.

Science.gov (United States)

2010-07-01

... COAL MINES Low- and Medium-Voltage Alternating Current Circuits § 77.905 Connection of single-phase loads. Single-phase loads shall be connected phase-to-phase in resistance grounded systems. ...

30 CFR 77.806 - Connection of single-phase loads.

Science.gov (United States)

2010-07-01

... COAL MINES Surface High-Voltage Distribution § 77.806 Connection of single-phase loads. Single-phase loads, such as transformer primaries, shall be connected phase to phase in resistance grounded systems. ...

Comparative Study of Phase Transformation in Single-Crystal Germanium during Single and Cyclic Nanoindentation

Directory of Open Access Journals (Sweden)

Koji Kosai

2017-11-01

Full Text Available Single-crystal germanium is a semiconductor material which shows complicated phase transformation under high pressure. In this study, new insight into the phase transformation of diamond-cubic germanium (dc-Ge was attempted by controlled cyclic nanoindentation combined with Raman spectroscopic analysis. Phase transformation from dc-Ge to rhombohedral phase (r8-Ge was experimentally confirmed for both single and cyclic nanoindentation under high loading/unloading rates. However, compared to single indentation, double cyclic indentation with a low holding load between the cycles caused more frequent phase transformation events. Double cyclic indentation caused more stress in Ge than single indentation and increased the possibility of phase transformation. With increase in the holding load, the number of phase transformation events decreased and finally became less than that under single indentation. This phenomenon was possibly caused by defect nucleation and shear accumulation during the holding process, which were promoted by a high holding load. The defect nucleation suppressed the phase transformation from dc-Ge to r8-Ge, and shear accumulation led to another phase transformation pathway, respectively. A high holding load promoted these two phenomena, and thus decreased the possibility of phase transformation from dc-Ge to r8-Ge.

protoDUNE-Single Phase and protDUNE-DualPhase

CERN Multimedia

Brice, Maximilien

2016-01-01

At the EHN1 two big 8m x 8m x8m detector prototypes (protoDUNE-Single Phase and protDUNE-DualPhase) are being constructed. The aim is to test technologies and detector performances for DUNE, a new generation of LBN neutr

Nanocrystalline spinel ferrite (MFe{sub 2}O{sub 4}, M = Ni, Co, Mn, Mg, Zn) powders prepared by a simple aloe vera plant-extracted solution hydrothermal route

Energy Technology Data Exchange (ETDEWEB)

Phumying, Santi; Labuayai, Sarawuth; Swatsitang, Ekaphan; Amornkitbamrung, Vittaya [Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002 (Thailand); Integrated Nanotechnology Research Center (INRC), Khon Kaen University, Khon Kaen 40002 (Thailand); Maensiri, Santi, E-mail: santimaensiri@gmail.com [School of Physics, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima 30000 (Thailand)

2013-06-01

Graphical abstract: This figure shows the specific magnetization curves of the as-prepared MFe{sub 2}O{sub 4} (M = Ni, Co, Mn, Mg, Zn) powders obtained from room temperature VSM measurement. These curves are typical for a soft magnetic material and indicate hysteresis ferromagnetism in the field ranges of ±500 Oe, ±1000 Oe, and ±2000 Oe for the CoFe{sub 2}O{sub 4}, MgFe{sub 2}O{sub 4} and MnFe{sub 2}O{sub 4} respectively, whereas the samples of NiFe{sub 2}O{sub 4} and ZnFe{sub 2}O{sub 4} show a superparamagnetic behavior. Highlights: ► Nanocrystalline MFe{sub 2}O{sub 4} powders were synthesized by a novel hydrothermal method. ► Metal acetylacetonates and aloe vera plant-extracted solution are used. ► This biosynthetic route is very simple and provides high-yield oxide nanomaterials. ► XRD and TEM results indicate that the prepared samples have only spinel structure. ► The maximum M{sub s} of 68.9 emu/g at 10 kOe were observed for the samples of MnFe{sub 2}O{sub 4}. - Abstract: Nanocrystalline spinel ferrite MFe{sub 2}O{sub 4} (M = Ni, Co, Mn, Mg, Zn) powders were synthesized by a novel hydrothermal method using Fe(acac){sub 3}, M(acac){sub 3} (M = Ni, Co, Mn, Mg, Zn) and aloe vera plant extracted solution. The X-ray diffraction and selected-area electron diffraction results indicate that the synthesized nanocrystalline have only spinel structure without the presence of other phase impurities. The crystal structure and morphology of the spinel ferrite powders, as revealed by TEM, show that the NiFe{sub 2}O{sub 4} and CoFe{sub 2}O{sub 4} samples contain nanoparticles, whereas the MnFe{sub 2}O{sub 4} and MgFe{sub 2}O{sub 4} samples consist of many nanoplatelets and nanoparticles. Interestingly, the ZnFe{sub 2}O{sub 4} sample contains plate-like structure of networked nanocrystalline particles. Room temperature magnetization results show a ferromagnetic behavior of the CoFe{sub 2}O{sub 4}, MnFe{sub 2}O{sub 4} and MgFe{sub 2}O{sub 4} samples, whereas the

Improved state observers for sensorless single phase BLDC-PM motor drives

DEFF Research Database (Denmark)

Lepure, Liviu L.; Boldea, Ion; Andreescu, Gheorghe Daniel

2010-01-01

Two methods of extracting the rotor position and speed for a sensorless single phase BLDC-PM motor drive by measuring only the phase current are presented here. Both methods are based on a generated orthogonal flux system. The first method extracts the position information by using the tan−1...... function and then an improved observer is created by adding a 4th order harmonic term in the estimated position, while the second method uses a phase locked loop structure. The proposed state observers are detailed using simulation results and then validated by experimental results....

A Critical Review of Spinel Structured Iron Cobalt Oxides Based Materials for Electrochemical Energy Storage and Conversion

Directory of Open Access Journals (Sweden)

Hongyan Gao

2017-11-01

Full Text Available Iron cobalt oxides, such as typical FeCo2O4 and CoFe2O4, are two spinel structured transitional metal oxide materials with excellent electrochemical performance. As the electrodes, they have been widely applied in the current energy storage and conversion processes such as supercapacitors, Lithium-ion batteries and fuel cells. Based on synthesis approaches and controlled conditions, these two materials exhibited broad morphologies and nanostructures and thus distinct electrochemical performance. Some of them have shown promising applications as electrodes in energy storage and conversion. The incorporation with other materials to form composites further improved their performance. This review briefly summarized the recent applications of FeCo2O4 and CoFe2O4 in energy storage and conversion, current understandings on mechanisms and especially the relevance of morphologies and structures and composites to electrochemical performance. Some recommendations were finally put forward addressing current issues and future prospects on electrodes of FeCo2O4 and CoFe2O4 based materials in energy storage and conversion, implying there was still space to further optimize their performance.

Synthesis and properties of Pr-substituted MgZn ferrites for core materials and high frequency applications

International Nuclear Information System (INIS)

Mukhtar, Muhammad Waqas; Irfan, Muhammad; Ahmad, Ishtiaq; Ali, Ihsan; Akhtar, Majid Niaz; Khan, Muhammad Azhar; Abbas, Ghazanfar; Rana, M.U.; Ali, Akbar; Ahmad, Mukhtar

2015-01-01

A series of single phase spinel ferrites having chemical formula Mg 0.5 Zn 0.5 Pr x Fe 2−x O 4 (x=0.00, 0.05, 0.10, 0.15, 0.20, 0.25) were prepared using the sol–gel technique after sintering at 700 °C. The thermal decomposition behavior of an as prepared powder was investigated by means of DTA/TGA analyses. The sintered powders were then characterized by Fourier transform infrared spectroscope, X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscope and vibrating sample magnetometer. X-ray diffraction patterns confirm the single phase spinel structure of prepared ferrites without the presence of any impurity phase. The value of lattice parameter (a) increases with the increase of Pr contents (x) into the spinel lattice. The grain size estimated from electron microscope images is in the range of 2.75–5.4 µm which confirms the spinel crystalline nature of the investigated samples. The saturation magnetization (M s ) decreases whereas coercivity (H c ) increases with the increase of Pr contents (x). The measured parameters suggest that these materials are favorable for high frequency applications and as core materials. - Highlights: • Pr-substituted spinel ferrites synthesized by autocombustion route have been investigated. • The average grain size was in the range of 2.75–5.4 µm estimated by SEM technique. • The (M s ) decreases whereas (H c ) increases with the increase of Pr contents (x). • These parameters are favorable for high frequency applications and as core materials

Pressure-induced structural and semiconductor-semiconductor transitions in C o0.5M g0.5C r2O4

Science.gov (United States)

Rahman, S.; Saqib, Hajra; Zhang, Jinbo; Errandonea, D.; Menéndez, C.; Cazorla, C.; Samanta, Sudeshna; Li, Xiaodong; Lu, Junling; Wang, Lin

2018-05-01

The effect of pressure on the structural, vibrational, and electronic properties of Mg-doped Cr bearing spinel C o0.5M g0.5C r2O4 was studied up to 55 GPa at room-temperature using x-ray diffraction, Raman spectroscopy, electrical transport measurements, and ab initio calculations. We found that the ambient-pressure phase is cubic (spinel-type, F d 3 ¯m ) and underwent a pressure-induced structural transition to a tetragonal phase (space group I 4 ¯m 2 ) above 28 GPa. The ab initio calculation confirmed this first-order phase transition. The resistivity of the sample decreased at low pressures with the existence of a low-pressure (LP) phase and started to increase with the emergence of a high-pressure (HP) phase. The temperature dependent resistivity experiments at different pressures illustrated the wide band gap semiconducting nature of both the LP and HP phases with different activation energies, suggesting a semiconductor-semiconductor transition at HP. No evidence of chemical decomposition or a semiconductor-metal transition was observed in our studies.

Morphology and composition tailoring of Co x Fe3 - x O4 nanoparticles

Science.gov (United States)

Fernandes de Medeiros, I. A.; Madigou, V.; Lopes-Moriyama, A. L.; Pereira de Souza, C.; Leroux, Ch.

2018-01-01

Nano-octahedra of cobalt ferrite Co x Fe3 - x O4 (1 ≤ x hydrothermal method using nitrates as precursors. For the first time, single-phased nano-octahedra of cobalt-rich ferrite Co x Fe3 - x O4 ( x = 1.5) were synthesized. The nano-octahedra are crystallized in a normal spinel structure, with tetrahedral sites occupied by Co2+. This specific octahedral shape was obtained with anionic, cationic, and nonionic surfactants. The nature of the surfactant influenced the chemical composition of the powder and the size of the nano-octahedra. The {100} truncation of the octahedra is more pronounced for the small particles. For the first time, single-phased nanoparticles with as much as x = 1.8 cobalt were synthesized with ethylene glycol as solvent. These nanoparticles, around 8 nm in size, have no specific shape and possess a lacunar spinel structure similar to maghemite. The samples were characterized by X-ray diffraction, transmission electron microscopy, and energy-dispersive spectroscopy.

Single-crystal FCC and DHCP phases in Ce/Pr superlattices

International Nuclear Information System (INIS)

Lee, S.; Goff, J.P.; Ward, R.C.C.; Wells, M.R.; McIntyre, G.J.

2002-01-01

Cerium usually comprises a mixture of polycrystalline FCC and DHCP allotropes. Single-crystal Ce has been stabilised in Ce/Pr superlattices grown using molecular beam epitaxy. It is found that FCC or DHCP phases can be obtained depending on superlattice composition and growth conditions. Low-temperature neutron scattering was performed on Ce/Pr samples using the triple-axis spectrometer D10 at the ILL. Such measurements revealed one sample, [Ce 20 Pr 20 ] 60 , to be a single crystal with a DHCP unit cell; while another, [Ce 30 Pr 10 ] 56 , was a mixture of FCC and DHCP phases. Antiferromagnetic ordering of magnetic moments was observed in the DHCP sample (T N =11.1 K) with a magnetic structure similar to that found in bulk β-Ce. Surprisingly, the magnetic ordering was found to be confined to single Ce blocks. Furthermore, it was found that, at low temperatures, the lattice contraction observed for bulk FCC Ce was suppressed in Ce/Pr superlattices. (orig.)

Optical and magneto-optical effects in Hg{sub 1-x}Cd{sub x}Cr{sub 2}Se{sub 4} (0 ⩽ x ⩽ 1) single crystals

Energy Technology Data Exchange (ETDEWEB)

Sukhorukov, Yu. P., E-mail: suhorukov@imp.uran.ru; Telegin, A. V.; Bebenin, N. G.; Zainullina, R. I.; Mostovshchikova, E. V.; Viglin, N. A. [Ural Branch, Russian Academy of Sciences, Mikheev Institute of Metal Physics (Russian Federation); Gan’shina, E. A.; Zykov, G. S. [Moscow State University (Russian Federation); Fedorov, V. A. [Russian Academy of Sciences, Kurnakov Institute of Inorganic Chemistry (Russian Federation); Menshchikova, T. K.; Buchkevich, A. A. [Ural Branch, Russian Academy of Sciences, Mikheev Institute of Metal Physics (Russian Federation)

2015-09-15

The concentration, temperature, and magnetic-field dependences of the magnetoreflection and magnetotransmission of natural light in the infrared spectral range and the Kerr effect in single crystals of ferromagnetic Hg{sub 1-x}Cd{sub x}Cr{sub 2}Se{sub 4} (0 ⩽ x ⩽ 1) spinels have been studied. A relationship of the magneto-optical properties to the electronic band structure of spinels has been established. The most significant changes in the spectra of magnetoreflection, magnetotransmission, and the Kerr effect are shown to be observed for 0.1 < x < 0.25 and are attributable to a rearrangement of the band structure as the composition changes.

Structural study of the controlled hydrothermal synthesis of LiMn2O4 and LixMnyO2

DEFF Research Database (Denmark)

Christiansen, Troels Lindahl; Jensen, Kirsten Marie Ørnsbjerg; Shen, Yanbin

, a layered structure, which can also be described as a defective spinel structure. Here, we show that both LiMn2O4 and LixMnyO2 nanoparticles can be synthesized from a simple, low-temperature hydrothermal synthesis. By tuning a single synthesis parameter (Li-concentration) each of the 2 structures...

Unexpectedly normal phase behavior of single homopolymer chains

International Nuclear Information System (INIS)

Paul, W.; Strauch, T.; Rampf, F.; Binder, K.

2007-01-01

Employing Monte Carlo simulations, we show that the topology of the phase diagram of a single flexible homopolymer chain changes in dependence on the range of an attractive square well interaction between the monomers. For a range of attraction larger than a critical value, the equilibrium phase diagram of the single polymer chain and the corresponding polymer solution phase diagram exhibit vapor (swollen coil, dilute solution), liquid (collapsed globule, dense solution), and solid phases. Otherwise, the liquid-vapor transition vanishes from the equilibrium phase diagram for both the single chain and the polymer solution. This change in topology of the phase diagram resembles the behavior known for colloidal dispersions. The interplay of enthalpy and conformational entropy in the polymer case thus can lead to the same topology of phase diagrams as the interplay of enthalpy and translational entropy in simple liquids

Spectral decomposition of single-tone-driven quantum phase modulation

International Nuclear Information System (INIS)

Capmany, Jose; Fernandez-Pousa, Carlos R

2011-01-01

Electro-optic phase modulators driven by a single radio-frequency tone Ω can be described at the quantum level as scattering devices where input single-mode radiation undergoes energy changes in multiples of ℎΩ. In this paper, we study the spectral representation of the unitary, multimode scattering operator describing these devices. The eigenvalue equation, phase modulation being a process preserving the photon number, is solved at each subspace with definite number of photons. In the one-photon subspace F 1 , the problem is equivalent to the computation of the continuous spectrum of the Susskind-Glogower cosine operator of the harmonic oscillator. Using this analogy, the spectral decomposition in F 1 is constructed and shown to be equivalent to the usual Fock-space representation. The result is then generalized to arbitrary N-photon subspaces, where eigenvectors are symmetrized combinations of N one-photon eigenvectors and the continuous spectrum spans the entire unit circle. Approximate normalizable one-photon eigenstates are constructed in terms of London phase states truncated to optical bands. Finally, we show that synchronous ultrashort pulse trains represent classical field configurations with the same structure as these approximate eigenstates, and that they can be considered as approximate eigenvectors of the classical formulation of phase modulation.

Spectral decomposition of single-tone-driven quantum phase modulation

Energy Technology Data Exchange (ETDEWEB)

Capmany, Jose [ITEAM Research Institute, Univ. Politecnica de Valencia, 46022 Valencia (Spain); Fernandez-Pousa, Carlos R, E-mail: c.pousa@umh.es [Signal Theory and Communications, Department of Physics and Computer Science, Univ. Miguel Hernandez, 03202 Elche (Spain)

2011-02-14

Electro-optic phase modulators driven by a single radio-frequency tone {Omega} can be described at the quantum level as scattering devices where input single-mode radiation undergoes energy changes in multiples of {h_bar}{Omega}. In this paper, we study the spectral representation of the unitary, multimode scattering operator describing these devices. The eigenvalue equation, phase modulation being a process preserving the photon number, is solved at each subspace with definite number of photons. In the one-photon subspace F{sub 1}, the problem is equivalent to the computation of the continuous spectrum of the Susskind-Glogower cosine operator of the harmonic oscillator. Using this analogy, the spectral decomposition in F{sub 1} is constructed and shown to be equivalent to the usual Fock-space representation. The result is then generalized to arbitrary N-photon subspaces, where eigenvectors are symmetrized combinations of N one-photon eigenvectors and the continuous spectrum spans the entire unit circle. Approximate normalizable one-photon eigenstates are constructed in terms of London phase states truncated to optical bands. Finally, we show that synchronous ultrashort pulse trains represent classical field configurations with the same structure as these approximate eigenstates, and that they can be considered as approximate eigenvectors of the classical formulation of phase modulation.

Equivalence of two models in single-phase multicomponent flow simulations

KAUST Repository

Wu, Yuanqing

2016-02-28

In this work, two models to simulate the single-phase multicomponent flow in reservoirs are introduced: single-phase multicomponent flow model and two-phase compositional flow model. Because the single-phase multicomponent flow is a special case of the two-phase compositional flow, the two-phase compositional flow model can also simulate the case. We compare and analyze the two models when simulating the single-phase multicomponent flow, and then demonstrate the equivalence of the two models mathematically. An experiment is also carried out to verify the equivalence of the two models.

Equivalence of two models in single-phase multicomponent flow simulations

KAUST Repository

Wu, Yuanqing; Sun, Shuyu

2016-01-01

In this work, two models to simulate the single-phase multicomponent flow in reservoirs are introduced: single-phase multicomponent flow model and two-phase compositional flow model. Because the single-phase multicomponent flow is a special case of the two-phase compositional flow, the two-phase compositional flow model can also simulate the case. We compare and analyze the two models when simulating the single-phase multicomponent flow, and then demonstrate the equivalence of the two models mathematically. An experiment is also carried out to verify the equivalence of the two models.

Water in orthopyroxene from abyssal spinel peridotites of the East Pacific Rise (ODP Leg 147: Hess Deep)

Science.gov (United States)

Hesse, Kirsten T.; Gose, Jürgen; Stalder, Roland; Schmädicke, Esther

2015-09-01

Abyssal spinel peridotites from Hess Deep, East Pacific Rise (ODP Leg 147) were investigated concerning their major, minor, and trace element mineral chemistry and the incorporation of structural water in orthopyroxene. The rocks are partially serpentinized harzburgites containing primary minerals of olivine, orthopyroxene, clinopyroxene, and spinel. Orthopyroxene is enstatitic with Mg# (Mg/(Mg + Fe)) between 0.90 and 0.92 and Al2O3 from 0.5 to 2.9 wt.%. The residual harzburgite experienced high degrees of melt removal in the spinel peridotite stability field. The average degree of partial melting was calculated to be 17.5% (range: 16.4-17.8%). Trace element data of ortho- and clinopyroxenes reflect this strong depletion, characteristic for the restitic nature of abyssal peridotites. Mantle re-equilibration temperatures around 1000 °C indicate that, after melt extraction and before exhumation to the ocean floor, the rocks experienced significant cooling in the spinel peridotite facies. Water contents of orthopyroxene range from 86 to 233 wt. ppm H2O with an average concentration of 142 wt. ppm H2O. These results represent the first data on water contents in the sub-pacific mantle obtained by direct measurements of sub-oceanic peridotite. The water contents are not related to mineral chemistry, stratigraphy, melting degree, mantle equilibrium conditions or oxidation state. Calculated post-melt peridotite water contents vary between 40 and 100 wt. ppm H2O. Compared to Mid-Atlantic Ridge peridotites, the East Pacific Rise samples of Leg 147 contain somewhat lower water concentrations than samples from Leg 153 and considerably higher contents than those of Leg 209 (Gose et al., 2009; Schmädicke et al., 2011). In Leg 147, the strongest OH absorbtion band occurs at 3420 cm- 1, wheras orthopyroxene from MAR peridotite (Legs 153 and 209) has its strongest absorbtion band at 3566 and 3522 cm- 1. The mantle equilibrium temperature of Leg 147 peridotites is lower than that

Symmetries of nonrelativistic phase space and the structure of quark-lepton generation

International Nuclear Information System (INIS)

Zenczykowski, Piotr

2009-01-01

According to the Hamiltonian formalism, nonrelativistic phase space may be considered as an arena of physics, with momentum and position treated as independent variables. Invariance of x 2 + p 2 constitutes then a natural generalization of ordinary rotational invariance. We consider Dirac-like linearization of this form, with position and momentum satisfying standard commutation relations. This leads to the identification of a quantum-level structure from which some phase space properties might emerge. Genuine rotations and reflections in phase space are tied to the existence of new quantum numbers, unrelated to ordinary 3D space. Their properties allow their identification with the internal quantum numbers characterising the structure of a single quark-lepton generation in the Standard Model. In particular, the algebraic structure of the Harari-Shupe preon model of fundamental particles is reproduced exactly and without invoking any subparticles. Analysis of the Clifford algebra of nonrelativistic phase space singles out an element which might be associated with the concept of lepton mass. This element is transformed into a corresponding element for a single coloured quark, leading to a generalization of the concept of mass and a different starting point for the discussion of quark unobservability.

Structural and magnetic properties of Zn.sub.x./sub.Mn.sub.3-x./sub.O.sub.4./sub. spinels

Czech Academy of Sciences Publication Activity Database

Nádherný, L.; Maryško, Miroslav; Sedmidubský, D.; Martin, C.

2016-01-01

Roč. 413, Sep (2016), s. 89-96 ISSN 0304-8853 Institutional support: RVO:68378271 Keywords : Zn-Mn-O spinels * solid-state reaction * ferrimagnetic clusters * ZnO Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.630, year: 2016

Structural, magnetic, and dielectric properties of multiferroic Co{sub 1−x}Mg{sub x}Cr{sub 2}O{sub 4} nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Kamran, M.; Ullah, A. [Nanomagnetism and Nanotechnology Laboratory, International Islamic University, Islamabad 44000 (Pakistan); Rahman, S. [Department of Material Science and Engineering, University of Science and Technology of China Hefei, Anhui 230026 (China); Tahir, A. [Department of Physics, Quaid-e-Azam University, Islamabad 44000 (Pakistan); Nadeem, K., E-mail: kashif.nadeem@iiu.edu.pk [Nanomagnetism and Nanotechnology Laboratory, International Islamic University, Islamabad 44000 (Pakistan); Beijing National Laboratory for Condensed Matter Physics, National Laboratory for Superconductivity, Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190 (China); Anis ur Rehman, M. [Applied Thermal Physics Laboratory, Department of Physics, COMSATS Institute of Information Technology, Islamabad 44000 (Pakistan); Hussain, S. [Magnetism Laboratory, Department of Physics, COMSATS Institute of Information Technology, Islamabad 44000 (Pakistan)

2017-07-01

Highlights: • Properties of multiferroic Co{sub 1−x}Mg{sub x}Cr{sub 2}O{sub 4} nanoparticles have been studied. • XRD showed that CoCr{sub 2}O{sub 4} and MgCr{sub 2}O{sub 4} are cubic normal spinel structure. • Rietveld refinement of XRD showed no impurity phases. • T{sub c} and T{sub s} showed decreasing trend with increasing Mg concentration. • Dielectric properties were improved for x = 0.6 Mg concentration. - Abstract: We examined the structural, magnetic, and dielectric properties of Co{sub 1−x}Mg{sub x}Cr{sub 2}O{sub 4} nanoparticles with composition x = 0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1 in detail. X-ray diffraction (XRD) revealed normal spinel structure for all the samples. Rietveld refinement fitting results of the XRD showed no impurity phases which signifies the formation of single phase Co{sub 1−x}Mg{sub x}Cr{sub 2}O{sub 4} nanoparticles. The average crystallite size showed a peak behaviour with maxima at x = 0.6. Raman and Fourier transform infrared (FTIR) spectroscopy also confirmed the formation of single phase normal spinel for all the samples and exhibited dominant vibrational changes for x ≥ 0.6. For x = 0 (CoCr{sub 2}O{sub 4}), zero field cooled/field cooled (ZFC/FC) magnetization curves showed paramagnetic (PM) to ferrimagnetic (FiM) transition at T{sub c} = 97 K and a conical spiral magnetic order at T{sub s} = 30 K. The end members CoCr{sub 2}O{sub 4} (x = 0) and MgCr{sub 2}O{sub 4} (x = 1) are FiM and antiferromagnetic (AFM), respectively. T{sub c} and T{sub s} showed decreasing trend with increasing x, followed by an additional AFM transition at T{sub N} = 15 K for x = 0.6. The system finally stabilized and changed to highly frustrated AFM structure at x = 1 due to formation of pure MgCr{sub 2}O{sub 4}. High field FC curves (5T) depicted nearly no effect on spiral magnetic state, which is attributed to strong exchange B-B magnetic interactions at low temperatures. Dielectric parameters showed a non-monotonous behaviour with

Neutron Powder Diffraction Measurements of the Spinel MgGa2O4:Cr3+ - A Comparative Study between the High Flux Diffractometer D2B at the ILL and the High Resolution Powder Diffractometer Aurora at IPEN

International Nuclear Information System (INIS)

Da Silva, M A F M; Sosman, L P; Yokaichiya, F; Henry, P F; Bordallo, H N; Mazzocchi, V L; Parente, C B R; Mestnik-Filho, J

2012-01-01

Optical materials that emit from the visible to the near-infrared spectral region are of great interest due to their possible application as tunable radiation sources, as signal transmission, display, optoelectronics signal storage, cellulose industry as well as in dosimetry. One important family of such systems are the spinel compounds doped with Cr 3+ , in which the physical the properties are related to the insertion of punctual defects in the crystalline structure. The purpose of our work is two fold. First, we compare the luminescence of the MgGa 2 O 4 -Ga 2 O 3 system with the single phase Ga 2 O 3 and MgGa 2 O 4 and relate structural changes observed in MgGa 2 O 4 -Ga 2 O 3 system to the optical properties, and secondly, to compare the neutron powder diffraction results obtained using two diffractometers: D2B located at the ILL (Grenoble, France) and Aurora located at IPEN (São Paulo, Brazil). In the configuration chosen, Aurora shows an improved resolution, which is related to the design of its silicon focusing monochromator.

Single-phase high-entropy alloys. An overview

Energy Technology Data Exchange (ETDEWEB)

Kozak, Roksolana; Steurer, Walter [ETH Zurich (Switzerland). Lab. of Crystallography; Sologubenko, Alla [ETH Zurich (Switzerland). Lab. of Nanotechnology

2015-02-01

The term 'high-entropy alloys (HEAs)' first appeared about 10 years ago defining alloys composed of n=5-13 principal elements with concentrations of approximately 100/n at.% each. Since then many equiatomic (or near equiatomic) single- and multi-phase multicomponent alloys were developed, which are reported for a combination of tunable properties: high hardness, strength and ductility, oxidation and wear resistance, magnetism, etc. In our paper, we focus on probably single-phase HEAs (solid solutions) out of all HEAs studied so far, discuss ways of their prediction, mechanical properties. In contrast to classical multielement/multiphase alloys, only single-phase multielement alloys (solid solutions) represent the basic concept underlying HEAs as mixing-entropy stabilized homogenous materials. The literature overview is complemented by own studies demonstrating that the alloys CrFeCoNi, CrFeCoNiAl{sub 0.3} and PdFeCoNi homogenized at 1300 and 1100 C, respectively, for 1 week are not single-phase HEAs, but a coherent mixture of two solid solutions.

Magnetic phase transitions in Er7Rh3 studied on single crystals

International Nuclear Information System (INIS)

Tsutaoka, Takanori; Obata, Keisuke; Cheyvuth, Seng; Koyama, Keiichi

2014-01-01

Highlights: • Magnetic and electrical properties of Er 7 Rh 3 were studied on single crystals. • The magnetic phase diagram along the c-axis was constructed. • The field-induced magnetic transitions in Er 7 Rh 3 can be explained by the magnetic structure with two magnetic propagation vectors. • The anomalies of electrical resistivity can also be described by the magnetic structure in Er 7 Rh 3 . - Abstract: Magnetic phase transitions in Er 7 Rh 3 with the Th 7 Fe 3 type hexagonal structure have been studied on single crystals by measuring magnetization, magnetic susceptibility and electrical resistivity. Er 7 Rh 3 possesses antiferromagnetic state below T N = 13 K. In the ordered state, the two successive magnetic transitions at T t1 = 6.2 K and T t2 = 4.5 K were observed. Several field-induced magnetic transitions were also observed along the a- and c-axes below T N ; magnetic field H – temperature T phase diagram along the c-axis was constructed. The field-induced magnetic transitions in Er 7 Rh 3 can be explained by the magnetic structure with two magnetic propagation vectors which were derived by the previous neutron diffraction studies. Electrical resistivity shows humps just below the magnetic transition temperatures, T N and T t1 due to the super-zone gap formation at the Fermi level; these anomalies can also be described by the magnetic structure changes in Er 7 Rh 3

Irradiation effects and behaviour of fission products in zirconia and spinel; Effets d'irradiation et comportement des produits de fission dans la zircone et le spinelle

Energy Technology Data Exchange (ETDEWEB)

Gentils, A

2003-10-01

Crystalline oxides, such as zirconia (ZrO{sub 2}) and spinel (MgAl{sub 2}O{sub 4}), are promising inert matrices for the transmutation of plutonium and minor actinides. This work deals with the study of the physico-chemical properties of these matrices, more specifically their behaviour under irradiation and their capacity to retain fission products. Irradiations at low energy and incorporation of stable analogs of fission products (Cs, I, Xe) into yttria-stabilized zirconia and magnesium-aluminate spinel single crystals were performed by using the ion implanter IRMA (CSNSM-Orsay). Irradiations at high energy were made on several heavy ion accelerators (GANIL-Caen, ISL-Berlin, HIL-Warsaw). The damage induced by irradiation and the release of fission products were monitored by in situ Rutherford Backscattering Spectrometry experiments. Transmission electron microscopy was also used in order to determine the nature of the damage induced by irradiation. The results show that irradiation of ZrO{sub 2} and MgAl{sub 2}O{sub 4} with heavy ions (about hundred keV and about hundred MeV) induces a huge structural damage in crystalline matrices. Total disorder (amorphization) is however never reached in zirconia, contrary to what is observed in the case of spinel. The results also emphasize the essential role played by the concentration of implanted species on their retention capacity. A dramatic release of fission products was observed when the concentration exceeds a threshold of a few atomic percent. Irradiation of implanted samples with medium-energy noble-gas ions leads to an enhancement of the fission product release. The exfoliation of spinel crystals implanted at high concentration of Cs ions is observed after a thermal treatment at high temperature. (author)

Pressure Drop Correlations of Single-Phase and Two-Phase Flow in Rolling Tubes

International Nuclear Information System (INIS)

Xia-xin Cao; Chang-qi Yan; Pu-zhen Gao; Zhong-ning Sun

2006-01-01

A series of experimental studies of frictional pressure drop for single phase and two-phase bubble flow in smooth rolling tubes were carried out. The tube inside diameters were 15 mm, 25 mm and 34.5 mm respectively, the rolling angles of tubes could be set as 10 deg. and 20 deg., and the rolling periods could be set as 5 s, 10 s and 15 s. Combining with the analysis of single-phase water motion, it was found that the traditional correlations for calculating single-phase frictional coefficient were not suitable for the rolling condition. Based on the experimental data, a new correlation for calculating single-phase frictional coefficient under rolling condition was presented, and the calculations not only agreed well with the experimental data, but also could display the periodically dynamic characteristics of frictional coefficients. Applying the new correlation to homogeneous flow model, two-phase frictional pressure drop of bubble flow in rolling tubes could be calculated, the results showed that the relative error between calculation and experimental data was less than ± 25%. (authors)

Synthesis of {gamma}-aluminium oxynitride spinel using thermal plasma technique

Energy Technology Data Exchange (ETDEWEB)

Panda, Pravuram; Singh, S. K.; Sinha, S. P. [School of Applied Science (Physics), KIIT University, Bhubaneswar 751024 (India); Advanced Materials Technology Department, IMMT (CSIR), Bhubaneswar 751013 (India); School of Applied Science (Physics), KIIT University, Bhubaneswar 751024 (India)

2012-07-23

The synthesis technique of {gamma}-AlON in NH{sub 3} plasma using extended arc thermal plasma reactor have been reported. Dense cubic AlON spinel was synthesized in liquid state by fusion of mixture of Al{sub 2}O{sub 3} and AlN powder under thermal plasma. The density of the fused AlON was found to be 3.64 g/cc which is 98.11% of theoretical value. The formation of AlON was confirmed from XRD and Raman studies. Well faceted structure of plasma fused AlON was observed in FE-SEM micrograph.

Chemical synthesis of nanocrystalline magnesium aluminate spinel via nitrate-citrate combustion route

International Nuclear Information System (INIS)

Saberi, Ali; Golestani-Fard, Farhad; Sarpoolaky, Hosein; Willert-Porada, Monika; Gerdes, Thorsten; Simon, Reinhard

2008-01-01

Nanocrystalline magnesium aluminate spinel (MgAl 2 O 4 ) was synthesized using metal nitrates, citric acid and ammonium solutions. The precursor and the calcined powders at different temperatures were characterized by X-ray diffraction (XRD), simultaneous thermal analysis (STA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The combustion mechanism was also studied by a quadrupole mass spectrometer (QMS) which coupled to STA. The generated heat through the combustion of the mixture of ammonium nitrate and citrate based complexes decreased the synthesis temperature of MgAl 2 O 4 spinel. The synthesized MgAl 2 O 4 spinel at 900 deg. C has faced shape with crystallite size in the range of 18-24 nm

Effect of Zn- and Ca-oxides on the structure and chemical durability of simulant alkali borosilicate glasses for immobilisation of UK high level wastes

International Nuclear Information System (INIS)

Zhang, Hua; Corkhill, Claire L.; Heath, Paul G.; Hand, Russell J.; Stennett, Martin C.; Hyatt, Neil C.

2015-01-01

Highlights: • Spinel crystallization incorporates ZnO from base glass, displacing Mg and Ni. • Raman spectroscopy demonstrates significant impact on glass structure by addition of ZnO to base glass. • Addition of ZnO reduces glass dissolution rate at early time periods (up to 28 days). - Abstract: Compositional modification of United Kingdom high level nuclear waste (HLW) glasses was investigated with the aim of understanding the impact of adopting a ZnO/CaO modified base glass on the vitrified product phase assemblage, glass structure, processing characteristics and dissolution kinetics. Crystalline spinel phases were identified in the vitrified products derived from the Na 2 O/Li 2 O and the ZnO/CaO modified base glass compositions; the volume fraction of the spinel crystallites increased with increasing waste loading from 15 to 20 wt%. The spinel composition was influenced by the base glass components; in the vitrified product obtained with the ZnO/CaO modified base glass, the spinel phase contained a greater proportion of Zn, with a nominal composition of (Zn 0.60 Ni 0.20 Mg 0.20 )(Cr 1.37 Fe 0.63 )O 4 . The addition of ZnO and CaO to the base glass was also found to significantly alter the glass structure, with changes identified in both borate and silicate glass networks using Raman spectroscopy. In particular, these glasses were characterised by a significantly higher Q 3 species, which we attribute to Si–O–Zn linkages; addition of ZnO and CaO to the glass composition therefore enhanced glass network polymerisation. The increase in network polymerisation, and the presence of spinel crystallites, were found to increase the glass viscosity of the ZnO/CaO modified base glass; however, the viscosities were within the accepted range for nuclear waste glass processing. The ZnO/CaO modified glass compositions were observed to be significantly more durable than the Na 2 O/Li 2 O base glass up to 28 days, due to a combination of the enhanced network

On the Utility of Spinel Oxide Hosts for Magnesium-Ion Batteries.

Science.gov (United States)

Knight, James C; Therese, Soosairaj; Manthiram, Arumugam

2015-10-21

There is immense interest to develop Mg-ion batteries, but finding suitable cathode materials has been a challenge. The spinel structure has many advantages for ion insertion and has been successfully used in Li-ion batteries. We present here findings on the attempts to extract Mg from MgMn2O4-based spinels with acid (H2SO4) and with NO2BF4. The acid treatment was able to fully remove all Mg from MgMn2O4 by following a mechanism involving the disproportionation of Mn(3+), and the extraction rate decreased with increasing cation disorder. Samples with additional Mg(2+) ions in the octahedral sites (e.g., Mg1.1Mn1.9O4 and Mg1.5Mn1.5O4) also exhibit complete or near complete demagnesiation due to an additional mechanism involving ion exchange of Mg(2+) by H(+), but no Mg could be extracted from MgMnAlO4 due to the disruption of Mn-Mn interaction/contact across shared octahedral edges. In contrast, no Mg could be extracted with the oxidizing agent NO2BF4 from MgMn2O4 or Mg1.5Mn1.5O4 as the electrostatic repulsion between the divalent Mg(2+) ions prevents Mg(2+) diffusion through the 16c octahedral sites, unlike Li(+) diffusion, suggesting that spinels may not serve as potential hosts for Mg-ion batteries. The ability to extract Mg with acid in contrast to that with NO2BF4 is attributed to Mn dissolution from the lattice and the consequent reduction in electrostatic repulsion. The findings could provide insights toward the design of Mg hosts for Mg-ion batteries.

Origin of peraluminous minerals (corundum, spinel, and sapphirine) in a highly calcic anorthosite from the Sittampundi Layered Complex, Tamil Nadu, India

Science.gov (United States)

Karmakar, Shreya; Mukherjee, Subham; Sanyal, Sanjoy; Sengupta, Pulak

2017-08-01

The highly calcic anorthosite (An>95) from the Sittampundi Layered Complex (SLC) develops corundum, spinel and sapphirine that are hitherto not reported from any anorthositic rocks in the world. Petrological observations indicate the following sequence of mineral growth: plagioclasematrix → corundum; clinopyroxene → amphibole; corundum + amphibole → plagioclasecorona + spinel; and spinel + corundum → coronitic sapphirine. Phase relations in the CaO-Na2O-Al2O3-SiO2-H2O (CNASH) system suggest that corundum was presumably developed through vapour present incongruent melting of the highly calcic plagioclase during ultra-high temperature (UHT) metamorphism ( T ≥ 1000 °C, P ≥ 9 kbar). Topological constraints in parts of the Na2O-CaO-MgO-Al2O3-SiO2-H2O (NCMASH) system suggest that subsequent to the UHT metamorphism, aqueous fluid(s) permeated the rock and the assemblage corundum + amphibole + anorthite + clinozoisite was stabilized during high-pressure (HP) metamorphism (11 ± 2 kbar, 750 ± 50 °C). Constraints of the NCMASH topology and thermodynamic and textural modeling study suggest that coronitic plagioclase and spinel formed at the expense of corundum + amphibole during a steeply decompressive retrograde P- T path (7-8 kbar and 700-800 °C) in an open system. Textural modeling studies combined with chemical potential diagrams (μSiO2-μMgO) in the MASH system support the view that sapphirine also formed from due to silica and Mg metasomatism of the precursor spinel ± corundum, on the steeply decompressive retrograde P- T path, prior to onset of significant cooling of the SLC. Extremely channelized fluid flow and large positive solid volume change of the stoichiometrically balanced sapphirine forming reaction explains the localized growth of sapphirine.

Phase purity of NiCo2O4, a catalyst candidate for electrolysis of water

Science.gov (United States)

Singer, J.; Fielder, W. L.; Garlick, R. G.; Negas, T.

1987-01-01

NiCo2O4 is shown to be difficult to obtain as a pure phase, and may never have been so obtained. High resolution x-ray diffractometry is required for its precise characterization. Film XRD is not likely to show the asymmetry in the spinel diffraction lines, caused by poorly crystallized NiO, as seen in diffractometer traces. The Co3O4 which is expected to accompany NiO as an impurity in NiCo2O4 syntheses has the same diffraction pattern as the binary oxide. Firings of the co-precipitated hydroxides at 300, 350, and 400 C, including one in pure O2, failed to produce single phase cobaltate. Scanning electron microscopy showed all the sintered products to range over several orders of magnitude in agglomerate/particle size. Surface areas by BET were all in the range 40 to 110 m sq/g, equivalent to particles of 200 to 100 Angstrom diameter. The spinel diffraction line breadths were compatible with those approximate dimensions.

Single-phase DECT with VNCT compared with three-phase CTU in patients with haematuria

Energy Technology Data Exchange (ETDEWEB)

Park, Jung Jae; Park, Byung Kwan; Kim, Chan Kyo [Sungkyunkwan University School of Medicine, Department of Radiology, Samsung Medical Center, Seoul (Korea, Republic of)

2016-10-15

To retrospectively evaluate the diagnostic performance of single-phase dual-energy CT (DECT) with virtual non-contrast CT (VNCT) compared with three-phase CT urography (CTU) in patients with haematuria. A total of 296 patients underwent three-phase CTU (NCT at 120 kVp; nephrographic phase and excretory phase DECTs at 140 kVp and 80 kVp) owing to haematuria. Diagnostic performances of CT scans were compared for detecting urothelial tumours and urinary stones. Dose-length product (DLP) was compared in relation to single-phase DECT and three-phase CTU Dose-length product (DLP) was compared in relation to single-phase DECT and three-phase CTU. Sensitivity and specificity for tumour were 95 % (19/20) and 98.9 % (273/276) on CTU, 95 % (19/20) and 98.2 % (271/276) on nephrographic phase DECT, and 90 % (18/20) and 98.2 % (271/276) on excretory phase DECT (P > 0.1). Of the 148 stones detected on NCT, 108 (73 %) and 100 (67.6 %) were detected on nephrographic phase and excretory phase VNCTs, respectively. The mean size of stones undetected on nephrographic and excretory VNCTs was measured as 1.5 ± 0.5 mm and 1.6 ± 0.6 mm, respectively. The mean DLPs of three-phase CTU, nephrographic phase DECT and excretory phase DECT were 1076 ± 248 mGy . cm, 410 ± 98 mGy . cm, and 360 ± 87 mGy . cm, respectively (P < 0.001). Single-phase DECT has a potential to replace three-phase CTU for detecting tumours with a lower radiation dose. (orig.)

On the use of spinel-based nuclear fuels for the transmutation of actinides

International Nuclear Information System (INIS)

Konings, R.J.M.; Bakker, K.; Boshoven, J.G.; Hein, H.; Huntelaar, M.E.; Zhang, H.; Meeldijk, J.D.; Woensdregt, C.F.

1997-01-01

The properties of spinel-based nuclear fuels for the transmutation of actinides are investigated. The results of laboratory experiments, thermodynamic calculations and irradiations in the High Flux Reactor (HFR) at Petten are presented, and allow us to evaluate the potential of spinel as an inert matrix for fuels and targets for transmutation. (author)

Impact of Nd{sup 3+} in CoFe{sub 2}O{sub 4} spinel ferrite nanoparticles on cation distribution, structural and magnetic properties

Energy Technology Data Exchange (ETDEWEB)

Yadav, Raghvendra Singh, E-mail: yadav@fch.vutbr.cz [Materials Research Centre, Brno University of Technology, Purkyňova 464/118, 61200 Brno (Czech Republic); Havlica, Jaromir; Masilko, Jiri; Kalina, Lukas; Wasserbauer, Jaromir; Hajdúchová, Miroslava; Enev, Vojtěch [Materials Research Centre, Brno University of Technology, Purkyňova 464/118, 61200 Brno (Czech Republic); Kuřitka, Ivo; Kožáková, Zuzana [Centre of Polymer Systems, University Institute, Tomas Bata University in Zlín, Nad Ovčírnou 3685, 760 01 Zlín (Czech Republic)

2016-02-01

Nd{sup 3+} doped cobalt ferrite nanoparticles have been synthesized by starch-assisted sol–gel auto-combustion method. The significant role played by Nd{sup 3+} added to cobalt ferrite in changing cation distribution and further in influencing structural and magnetic properties, was explored and reported. The crystal structure formation and crystallite size were studied from X-ray diffraction studies. The microstructural features were investigated by field emission scanning electron microscopy and transmission electron microscopy that demonstrates the nanocrystalline grain formation with spherical morphology. An infrared spectroscopy study shows the presence of two absorption bands related to tetrahedral and octahedral group complexes within the spinel ferrite lattice system. The change in Raman modes in synthesized ferrite system were observed with Nd{sup 3+} substitution, particle size and cation redistribution. The impact of Nd{sup 3+} on cation distribution of Co{sup 2+} and Fe{sup 3+} at octahedral and tetrahedral sites in spinel ferrite cobalt ferrite nanoparticles was investigated by X-ray photoelectron spectroscopy. Room temperature magnetization measurements showed that the saturation magnetization and coercivity increase with addition of Nd{sup 3+} substitution in cobalt ferrite. - Highlights: • Nd{sup 3+} doped CoFe{sub 2}O{sub 4} nanoparticles by starch-assisted sol–gel auto-combustion method. • The change in Raman modes with Nd{sup 3+} substitution. • Presence of absorption infrared bands related to octahedral and tetrahedral site. • The impact of Nd{sup 3+} on cation distribution at octahedral and tetrahedral sites. • Influence of Nd{sup 3+} substitution in cobalt ferrite on magnetic properties.

Magnetic ordering in the spinel compound Li[Mn2?xLix]O4(x = 0,0.04)

NARCIS (Netherlands)

Gaddy, J.; Lamsal, J.; Petrovic, M.; Montfrooij, W.; Schmets, A.; Vojta, T.

2009-01-01

The two B-site ions Mn3+ and Mn4+ in the stoichiometric spinel structure LiMn2O4 form a complex, columnar ordered pattern below the charge-ordering transition at room temperature. On further cooling to below 66 K, the system develops long-range antiferromagnetic order. In contrast, whereas

Modification of electronic structure, magnetic structure, and topological phase of bismuthene by point defects

Science.gov (United States)

Kadioglu, Yelda; Kilic, Sevket Berkay; Demirci, Salih; Aktürk, O. Üzengi; Aktürk, Ethem; Ciraci, Salim

2017-12-01

This paper reveals how the electronic structure, magnetic structure, and topological phase of two-dimensional (2D), single-layer structures of bismuth are modified by point defects. We first showed that a free-standing, single-layer, hexagonal structure of bismuth, named h-bismuthene, exhibits nontrivial band topology. We then investigated interactions between single foreign adatoms and bismuthene structures, which comprise stability, bonding, electronic structure, and magnetic structures. Localized states in diverse locations of the band gap and resonant states in band continua of bismuthene are induced upon the adsorption of different adatoms, which modify electronic and magnetic properties. Specific adatoms result in reconstruction around the adsorption site. Single vacancies and divacancies can form readily in bismuthene structures and remain stable at high temperatures. Through rebondings, Stone-Whales-type defects are constructed by divacancies, which transform into a large hole at high temperature. Like adsorbed adatoms, vacancies induce also localized gap states, which can be eliminated through rebondings in divacancies. We also showed that not only the optical and magnetic properties, but also the topological features of pristine h-bismuthene can be modified by point defects. The modification of the topological features depends on the energies of localized states and also on the strength of coupling between point defects.

Experimental Investigation of Gas/Slag/Matte/Spinel Equilibria in the Cu-Fe-O-S-Si System at 1473 K (1200 °C) and P(SO2) = 0.25 atm

Science.gov (United States)

Hidayat, Taufiq; Fallah-Mehrjardi, Ata; Hayes, Peter C.; Jak, Evgueni

2018-04-01

New experimental data were obtained on the gas/slag/matte/spinel equilibria in the Cu-Fe-O-S-Si system at 1473 K (1200 °C) and P(SO2) = 0.25 atm covering Cu concentrations in matte between 42 and 78 wt pct Cu. Accurate measurements were obtained using high-temperature equilibration and the rapid quenching technique, followed by electron-probe X-ray microanalysis of equilibrium phase compositions. The use of spinel substrates made to support the samples ensures equilibrium with this primary phase solid, eliminates crucible contamination, and facilitates direct gas-condensed phase equilibrium and high quenching rates. Particular attention was given to the confirmation of the achievement of equilibrium. The results quantify the relationship between Cu in matte and oxygen partial pressure, sulfur in matte, oxygen in matte, Fe/SiO2 at slag liquidus, sulfur in slag, and dissolved copper in slag.

Temperature dependent viscosity of cobalt ferrite / ethylene glycol ferrofluids

Science.gov (United States)

Kharat, Prashant B.; Somvanshi, Sandeep B.; Kounsalye, Jitendra S.; Deshmukh, Suraj S.; Khirade, Pankaj P.; Jadhav, K. M.

2018-04-01

In the present work, cobalt ferrite / ethylene glycol ferrofluid is prepared in 0 to 1 (in the step of 0.2) volume fraction of cobalt ferrite nanoparticles synthesized by co-precipitation method. The XRD results confirmed the formation of single phase spinel structure. The Raman spectra have been deconvoluted into individual Lorentzian peaks. Cobalt ferrite has cubic spinel structure with Fd3m space group. FT-IR spectra consist of two major absorption bands, first at about 586 cm-1 (υ1) and second at about 392 cm-1 (υ2). These absorption bands confirm the formation of spinel-structured cobalt ferrite. Brookfield DV-III viscometer and programmable temperature-controlled bath was used to study the relationship between viscosity and temperature. Viscosity behavior with respect to temperature has been studied and it is revealed that the viscosity of cobalt ferrite / ethylene glycol ferrofluids increases with an increase in volume fraction of cobalt ferrite. The viscosity of the present ferrofluid was found to decrease with increase in temperature.

Characterization of LT-LiXO1-YNIYO2 electrodes for rechargeable lithium cells

CSIR Research Space (South Africa)

Gummow, RJ

1993-12-01

Full Text Available -spinel in character and that LT- Li0.4Co0.sNi0.102 is a defect spinel with spinel notation {Li0.s\\[:\\]0.2}sa \\[Co, 6Nio.2D0.2104. Electrochemical data.--The charge and discharge pro- files for the first four cycles of Li/LT-LiCoO2, Li... on the B sites of an A\\[B2104 spinel structure. The spinel phase is significantly more stable to lithium insertion/extraction reactions than the quasi-spinel phase. It is believed that by optimizing the processing conditions...

Synthesis and properties of Pr-substituted MgZn ferrites for core materials and high frequency applications

Energy Technology Data Exchange (ETDEWEB)

Mukhtar, Muhammad Waqas; Irfan, Muhammad [Department of Physics, Federal Urdu University of Arts, Science and Technology, Islamabad 44000 (Pakistan); Ahmad, Ishtiaq; Ali, Ihsan [Department of Physics, Bahauddin Zakariya University, Multan 60800 (Pakistan); Akhtar, Majid Niaz [Department of Physics, COMSATS Institute of Information Technology, Lahore (Pakistan); Khan, Muhammad Azhar [Department of Physics, Islamia University, Bahawalpur (Pakistan); Abbas, Ghazanfar [Department of Physics, COMSATS Institute of Information Technology, Islamabad 44000 (Pakistan); Rana, M.U. [Center of Excellence in Solid State Physics, University of the Punjab, Lahore (Pakistan); Ali, Akbar [Department of Basic Sciences, Riphah International University, Islamabad-44000 (Pakistan); Ahmad, Mukhtar, E-mail: ahmadmr25@yahoo.com [Department of Physics, COMSATS Institute of Information Technology, Islamabad 44000 (Pakistan)

2015-05-01

A series of single phase spinel ferrites having chemical formula Mg{sub 0.5}Zn{sub 0.5}Pr{sub x}Fe{sub 2−x}O{sub 4} (x=0.00, 0.05, 0.10, 0.15, 0.20, 0.25) were prepared using the sol–gel technique after sintering at 700 °C. The thermal decomposition behavior of an as prepared powder was investigated by means of DTA/TGA analyses. The sintered powders were then characterized by Fourier transform infrared spectroscope, X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscope and vibrating sample magnetometer. X-ray diffraction patterns confirm the single phase spinel structure of prepared ferrites without the presence of any impurity phase. The value of lattice parameter (a) increases with the increase of Pr contents (x) into the spinel lattice. The grain size estimated from electron microscope images is in the range of 2.75–5.4 µm which confirms the spinel crystalline nature of the investigated samples. The saturation magnetization (M{sub s}) decreases whereas coercivity (H{sub c}) increases with the increase of Pr contents (x). The measured parameters suggest that these materials are favorable for high frequency applications and as core materials. - Highlights: • Pr-substituted spinel ferrites synthesized by autocombustion route have been investigated. • The average grain size was in the range of 2.75–5.4 µm estimated by SEM technique. • The (M{sub s}) decreases whereas (H{sub c}) increases with the increase of Pr contents (x). • These parameters are favorable for high frequency applications and as core materials.

Atomistic simulation of fcc—bcc phase transition in single crystal Al under uniform compression

International Nuclear Information System (INIS)

Li Li; Liang Jiu-Qing; Shao Jian-Li; Duan Su-Qing; Li Yan-Fang

2012-01-01

By molecular dynamics simulations employing an embedded atom model potential, we investigate the fcc-to-bcc phase transition in single crystal Al, caused by uniform compression. Results show that the fcc structure is unstable when the pressure is over 250 GPa, in reasonable agreement with the calculated value through the density functional theory. The morphology evolution of the structural transition and the corresponding transition mechanism are analysed in detail. The bcc (011) planes are transited from the fcc (111-bar) plane and the (11-bar1) plane. We suggest that the transition mechanism consists mainly of compression, shear, slid and rotation of the lattice. In addition, our radial distribution function analysis explicitly indicates the phase transition of Al from fcc phase to bcc structure. (condensed matter: structural, mechanical, and thermal properties)

Effect of Zn addition on structural, magnetic properties, antistructural modeling of Co1-xZnxFe2O4 nano ferrite

Science.gov (United States)

Raghuvanshi, S.; Kane, S. N.; Tatarchuk, T. R.; Mazaleyrat, F.

2018-05-01

Effect of Zn addition on cationic distribution, structural properties, magnetic properties, antistructural modeling of nanocrystalline Co1-xZnxFe2O4 (0.08 ≤ x ≤ 0.56) ferrite is reported. XRD confirms the formation of single phase cubic spinel nano ferrites with average grain diameter ranging between 41.2 - 54.9 nm. Coercivity (Hc), anisotropy constant (K1) decreases with Zn addition, but experimental, theoretical saturation magnetization (Ms, Ms(t)) increases upto x = 0.32, then decreases, attributed to the breaking of collinear ferrimagnetic phase. Variation of magnetic properties is correlated with cationic distribution. A new antistructural modeling for describing active surface centers is discussed to explain change in concentration of donor's active centers Zn'B, Co'B, acceptor's active centers Fe*A are explained.

Magnetic behavior of the oxide spinels

Indian Academy of Sciences (India)

... Refresher Courses · Symposia · Live Streaming. Home; Journals; Pramana – Journal of Physics; Volume 58; Issue 5-6. Magnetic behavior of the oxide spinels: Li0.5Fe2.5-2AlCrO4. U N Trivedi K B Modi H H Joshi. Colossal Magnetoresistance & Other Materials Volume 58 Issue 5-6 May-June 2002 pp 1031-1034 ...

Three-dimensional numerical modeling of turbulent single-phase and two-phase flow in curved pipes

International Nuclear Information System (INIS)

Xin, R.C.; Dong, Z.F.; Ebadian, M.A.

1996-01-01

In this study, three-dimensional single-phase and two-phase flows in curved pipes have been investigated numerically. Two different pipe configurations were computed. When the results of the single-phase flow simulation were compared with the experimental data, a fairly good agreement was achieved. A flow-developing process has been suggested in single-phase flow, in which the turbulence is stronger near the outer tube wall than near the inner tube wall. For two-phase flow, the Eulerian multiphase model was used to simulate the phase distribution of a three-dimensional gas-liquid bubble flow in curved pipe. The RNG/κ-ε turbulence model was used to determine the turbulence field. An inlet gas void fraction of 5 percent was simulated. The gas phase effects on the liquid phase flow velocity have been examined by comparing the results of single-phase flow and two-phase flow. The findings show that for the downward flow in the U bend, the gas concentrates at the inner portion of the cross section at φ = π/18 - π/6 in most cases. The results of the phase distribution simulation are compared to experimental observations qualitatively and topologically

Dislocation loops in spinel crystals irradiated successively with deep and shallow ion implants

International Nuclear Information System (INIS)

Ai, R.X.; Cooper, E.A.; Sickafus, K.E.; Nastasi, M.; Bordes, N.; Ewing, R.C.

1993-01-01

This study examines the influence of microstructural defects on irradiation damage accumulation in the oxide spinel. Single crystals of the compound MgAl 2 O 4 with surface normal [111] were irradiated under cryogenic temperature (100K) either with 50 keV Ne ions (fluence 5.0 x 10 12 /cm 2 ), 400 keV Ne ions (fluence 6.7 x 10 13 /cm 2 ) or successively with 400 keV Ne ions followed by 50 keV Ne ions. The projected range of 50 keV Ne ions in spinel is ∼50 mn (''shallow'') while the projected range of 400 keV Ne ions is ∼500 mn (''deep''). Transmission electron microscopy (TEM) was used to examine dislocation loops/defect clusters formed by the implantation process. Measurements of the dislocation loop size were made using weak-beam imaging technique on cross-sectional TEM ion-implanted specimens. Defect clusters were observed in both deep and shallow implanted specimens, while dislocation loops were observed in the shallow implanted sample that was previously irradiated by 400 keV Ne ions. Cluster size was seen to increase for shallow implants in crystals irradiated with a deep implant (size ∼8.5 nm) as compared to crystals treated only to a shallow implant (size ∼3.1 nm)

Swelling of spinel after low-dose neutron irradiation

International Nuclear Information System (INIS)

Coghlan, W.A.; Clinard, F.W. Jr.; Itoh, N.; Greenwood, L.R.

1986-01-01

Swelling was determined in samples of single-crystal MgAl 2 O 4 spinel, irradiated to doses as high as 8 x 10 22 n/m 2 (E > 0.1 MeV) at approx. =50 0 C in the Omega West Reactor. Swelling effectively saturated at approx. =2 x 10 22 n/m 2 which corresponds to a damage level of only approx. =2 x 10 -3 dpa. In addition subsequent measurements after irradiation have revealed that the samples continued swelling for several weeks. These results imply that irradiation defects begin to interact by recombination and aggregation at low damage levels in this material at 50 0 C and perhaps continue to cluster at room temperature after irradiation. Rate equations have been employed to determine defect concentrations at saturation. Results to date show that the observed swelling is consistent with the number of surviving defects if swelling per Frenkel defect pair is taken to be one atomic volume

Guidelines for the formulation of Lagrangian stochastic models for particle simulations of single-phase and dispersed two-phase turbulent flows

Science.gov (United States)

Minier, Jean-Pierre; Chibbaro, Sergio; Pope, Stephen B.

2014-11-01

In this paper, we establish a set of criteria which are applied to discuss various formulations under which Lagrangian stochastic models can be found. These models are used for the simulation of fluid particles in single-phase turbulence as well as for the fluid seen by discrete particles in dispersed turbulent two-phase flows. The purpose of the present work is to provide guidelines, useful for experts and non-experts alike, which are shown to be helpful to clarify issues related to the form of Lagrangian stochastic models. A central issue is to put forward reliable requirements which must be met by Lagrangian stochastic models and a new element brought by the present analysis is to address the single- and two-phase flow situations from a unified point of view. For that purpose, we consider first the single-phase flow case and check whether models are fully consistent with the structure of the Reynolds-stress models. In the two-phase flow situation, coming up with clear-cut criteria is more difficult and the present choice is to require that the single-phase situation be well-retrieved in the fluid-limit case, elementary predictive abilities be respected and that some simple statistical features of homogeneous fluid turbulence be correctly reproduced. This analysis does not address the question of the relative predictive capacities of different models but concentrates on their formulation since advantages and disadvantages of different formulations are not always clear. Indeed, hidden in the changes from one structure to another are some possible pitfalls which can lead to flaws in the construction of practical models and to physically unsound numerical calculations. A first interest of the present approach is illustrated by considering some models proposed in the literature and by showing that these criteria help to assess whether these Lagrangian stochastic models can be regarded as acceptable descriptions. A second interest is to indicate how future

Guidelines for the formulation of Lagrangian stochastic models for particle simulations of single-phase and dispersed two-phase turbulent flows

International Nuclear Information System (INIS)

Minier, Jean-Pierre; Chibbaro, Sergio; Pope, Stephen B.

2014-01-01

In this paper, we establish a set of criteria which are applied to discuss various formulations under which Lagrangian stochastic models can be found. These models are used for the simulation of fluid particles in single-phase turbulence as well as for the fluid seen by discrete particles in dispersed turbulent two-phase flows. The purpose of the present work is to provide guidelines, useful for experts and non-experts alike, which are shown to be helpful to clarify issues related to the form of Lagrangian stochastic models. A central issue is to put forward reliable requirements which must be met by Lagrangian stochastic models and a new element brought by the present analysis is to address the single- and two-phase flow situations from a unified point of view. For that purpose, we consider first the single-phase flow case and check whether models are fully consistent with the structure of the Reynolds-stress models. In the two-phase flow situation, coming up with clear-cut criteria is more difficult and the present choice is to require that the single-phase situation be well-retrieved in the fluid-limit case, elementary predictive abilities be respected and that some simple statistical features of homogeneous fluid turbulence be correctly reproduced. This analysis does not address the question of the relative predictive capacities of different models but concentrates on their formulation since advantages and disadvantages of different formulations are not always clear. Indeed, hidden in the changes from one structure to another are some possible pitfalls which can lead to flaws in the construction of practical models and to physically unsound numerical calculations. A first interest of the present approach is illustrated by considering some models proposed in the literature and by showing that these criteria help to assess whether these Lagrangian stochastic models can be regarded as acceptable descriptions. A second interest is to indicate how future

Searching for Next Single-Phase High-Entropy Alloy Compositions

Directory of Open Access Journals (Sweden)

David E. Alman

2013-10-01

Full Text Available There has been considerable technological interest in high-entropy alloys (HEAs since the initial publications on the topic appeared in 2004. However, only several of the alloys investigated are truly single-phase solid solution compositions. These include the FCC alloys CoCrFeNi and CoCrFeMnNi based on 3d transition metals elements and BCC alloys NbMoTaW, NbMoTaVW, and HfNbTaTiZr based on refractory metals. The search for new single-phase HEAs compositions has been hindered by a lack of an effective scientific strategy for alloy design. This report shows that the chemical interactions and atomic diffusivities predicted from ab initio molecular dynamics simulations which are closely related to primary crystallization during solidification can be used to assist in identifying single phase high-entropy solid solution compositions. Further, combining these simulations with phase diagram calculations via the CALPHAD method and inspection of existing phase diagrams is an effective strategy to accelerate the discovery of new single-phase HEAs. This methodology was used to predict new single-phase HEA compositions. These are FCC alloys comprised of CoFeMnNi, CuNiPdPt and CuNiPdPtRh, and HCP alloys of CoOsReRu.

Mossbauer, Raman and X-ray diffraction studies of superparamagnetic NiFe2O4 nanoparticles prepared by sol-gel auto-combustion method

International Nuclear Information System (INIS)

Ahlawat, Anju; Sathe, V.G.; Reddy, V.R.; Gupta, Ajay

2011-01-01

Superparamagnetic nickel ferrite single phase nanoparticles with the average crystallite size of ∼9 nm have been synthesized at a low temperature (220 o C) by the sol-gel auto-combustion method. In the present study the as prepared powder was further calcined at different temperatures for 4 h, resulting in nanoparticles of larger size. The nanoparticles exhibited superparamagnetic behavior and changes in cation distribution as revealed by the Mossbauer, Raman and X-ray diffraction studies. The Mossbauer spectra collected at 5 K and under 5 T applied magnetic field showed mixed spinel structure and canted spin order for the nanoparticles, whereas there is collinear spin order with inverse spinel structure for larger particles. The vibrational spectra of the nanoparticles showed a redshift and broadening in the Raman line shape due to confinement effects. - Highlights: → Mossbauer spectra show a canting angle of 48 o for the nanoparticle samples measured at 5 K and 5 T applied magnetic field, the highest canting angle obtained so far in NiFe 2 O 4 nanoparticles. Site inversion in nanoparticles, thus converting it from inverse spinel to mixed spinel structure. → X-ray diffraction results showed a change in sign for the strain of the nanoparticle sample that showed mixed spinel structure. → Our Raman measurements showed a redshift and broadening for nanoparticle samples that is generally interpreted as a signature of quantum confinement.

Evaluation of thermobarometry for spinel lherzolite fragments in alkali basalts

Science.gov (United States)

Ozawa, Kazuhito; Youbi, Nasrrddine; Boumehdi, Moulay Ahmed; McKenzie, Dan; Nagahara, Hiroko

2017-04-01

Geothermobarometry of solid fragments in kimberlite and alkali basalts, generally called "xenoliths", provides information on thermal and chemical structure of lithospheric and asthenospheric mantle, based on which various chemical, thermal, and rheological models of lithosphere have been constructed (e.g., Griffin et al., 2003; McKenzie et al., 2005; Ave Lallemant et al., 1980). Geothermobarometry for spinel-bearing peridotite fragments, which are frequently sampled from Phanerozoic provinces in various tectonic environments (Nixon and Davies, 1987), has essential difficulties, and it is usually believed that appropriated barometers do not exist for them (O'Reilly et al., 1997; Medaris et al., 1999). Ozawa et al. (2016; EGU) proposed a method of geothermobarometry for spinel lherzolite fragments. They applied the method to mantle fragments in alkali basalts from Bou Ibalhatene maars in the Middle Atlas in Morocco (Raffone et al. 2009; El Azzouzi et al., 2010; Witting et al., 2010; El Messbahi et al., 2015). Ozawa et al. (2016) obtained 0.5GPa pressure difference (1.5-2.0GPa) for 100°C variation in temperatures (950-1050°C). However, it is imperative to verify the results on the basis of completely independent data. There are three types of independent information: (1) time scale of solid fragment extraction, which may be provided by kinetics of reactions induced by heating and/or decompression during their entrapment in the host magma and transportation to the Earth's surface (Smith, 1999), (2) depth of the host basalt formation, which may be provided by the petrological and geochemical studies of the host basalts, and (3) lithosphere-asthenosphere boundary depths, which may be estimated by geophysical observations. Among which, (3) is shown to be consistent with the result in Ozawa et al. (2016). We here present that the estimated thermal structure just before the fragment extraction is fully supported by the information of (1) and (2). Spera (1984) reviewed

Chromian spinels in highly altered ultramafic rocks from the Sartohay ophiolitic mélange, Xinjiang, NW China

Science.gov (United States)

Qiu, Tian; Zhu, Yongfeng

2018-06-01

The Sartohay ophiolitic mélange is located in western Junggar (Xinjiang province, NW China), which is a major component of the core part of the Central Asian Orogenic Belt (CAOB). Chromian spinels in serpentinite, talc schist, carbonate-talc schist and listwaenite in Sartohay ophiolitic mélange retain primary compositions with Cr# of 0.39-0.65, Mg# = 0.48-0.67, and Fe3+# evolution of chromian spinels in highly altered ultramafic rocks from the Sartohay ophiolitic mélange. Chromian spinels in serpentinite and talc schist were rimmed by Cr-magnetite, which was dissolved completely during transformation from serpentinite/talc schist to listwaenite. Chromian spinels were then transformed into Fe2+-rich chromite in shear zones, which characterized by high fluid/rock ratios. This Fe2+-rich chromite and/or chromian spinels could then be transformed into Fe3+-rich chromite in oxidizing conditions at shallow levels.

MgAl2O4 spinel refractory as containment liner for high-temperature alkali salt containing environments

Science.gov (United States)

Peascoe-Meisner, Roberta A [Knoxville, TN; Keiser, James R [Oak Ridge, TN; Hemric, James G [Knoxville, TN; Hubbard, Camden R [Oak Ridge, TN; Gorog, J Peter [Kent, WA; Gupta, Amul [Jamestown, NY

2008-10-21

A method includes containing a high-temperature alkali salt containing environment using a refractory containment liner containing MgAl.sub.2O.sub.4 spinel. A method, includes forming a refractory brick containing MgAl.sub.2O.sub.4 spinel having an exterior chill zone defined by substantially columnar crystallization and an interior zone defined by substantially equiaxed crystallization; and removing at least a portion of the exterior chill zone from the refractory brick containing MgAl.sub.2O.sub.4 spinel by scalping the refractory brick containing MgAl.sub.2O.sub.4 spinel to define at least one outer surface having an area of substantially equiaxed crystallization. A product of manufacture includes a refractory brick containing MgAl.sub.2O.sub.4 spinel including an interior zone defined by substantially equiaxed crystallization; and at least one outer surface having an area of substantially equiaxed crystallization.

Film boiling from spheres in single- and two-phase flow

International Nuclear Information System (INIS)

Liu, C.; Theofanous, T.G.; Yuen, W.W.

1992-01-01

Experimental data on film boiling heat transfer from single, inductively heated, spheres in single- and two-phase flow (saturated water and steam, respectively) are presented. In the single-phase-flow experiments water velocities ranged from 0.1 to 2.0 m/s; in the two-phase-flow experiments superficial water and steam velocities covered 0.1 to 0.6 m/s and 4 to 10 m/s, respectively. All experiments were run at atmospheric pressure and with sphere temperatures from 900C down to quenching. Limited interpretations of the single-phase- flow data are possible, but the two-phase-flow data are new and unique

Hydrogen-induced structural transition in single layer ReS2

Science.gov (United States)

Yagmurcukardes, M.; Bacaksiz, C.; Senger, R. T.; Sahin, H.

2017-09-01

By performing density functional theory-based calculations, we investigate how structural, electronic and mechanical properties of single layer ReS2 can be tuned upon hydrogenation of its surfaces. It is found that a stable, fully hydrogenated structure can be obtained by formation of strong S-H bonds. The optimized atomic structure of ReS2H2 is considerably different than that of the monolayer ReS2 which has a distorted-1T phase. By performing phonon dispersion calculations, we also predict that the Re2-dimerized 1T structure (called 1T {{}\\text{R{{\\text{e}}2}}} ) of the ReS2H2 is dynamically stable. Unlike the bare ReS2 the 1T {{}\\text{R{{\\text{e}}2}}} -ReS2H2 structure which is formed by breaking the Re4 clusters into separated Re2 dimers, is an indirect-gap semiconductor. Furthermore, mechanical properties of the 1T {{}\\text{R{{\\text{e}}2}}} phase in terms of elastic constants, in-plane stiffness (C) and Poisson ratio (ν) are investigated. It is found that full hydrogenation not only enhances the flexibility of the single layer ReS2 crystal but also increases anisotropy of the elastic constants.

Single-shot quantitative phase microscopy with color-multiplexed differential phase contrast (cDPC.

Directory of Open Access Journals (Sweden)

Zachary F Phillips

Full Text Available We present a new technique for quantitative phase and amplitude microscopy from a single color image with coded illumination. Our system consists of a commercial brightfield microscope with one hardware modification-an inexpensive 3D printed condenser insert. The method, color-multiplexed Differential Phase Contrast (cDPC, is a single-shot variant of Differential Phase Contrast (DPC, which recovers the phase of a sample from images with asymmetric illumination. We employ partially coherent illumination to achieve resolution corresponding to 2× the objective NA. Quantitative phase can then be used to synthesize DIC and phase contrast images or extract shape and density. We demonstrate amplitude and phase recovery at camera-limited frame rates (50 fps for various in vitro cell samples and c. elegans in a micro-fluidic channel.

X-ray and neutron single crystal diffraction on (NH4)3H(SO4)2. II. Refinement of crystal structure of phase II at room temperature

International Nuclear Information System (INIS)

Reehuis, M.; Wozniak, K.; Dominiak, P.; Smirnov, L.S.; Natkaniec, I.; Baranov, A.I.; Dolbinina, V.V.

2006-01-01

The (NH 4 ) 3 H(SO 4 ) 2 is of special interest due to the possible influence of ammonium ions on a series of phase transitions: I => II => III => IV => V => VII. Earlier, the X-ray single crystal diffraction study of phase II of (NH 4 ) 3 H(SO 4 ) 2 showed that the crystal structure of this compound has two crystallographically independent groups of ammonium ions NH 4 (1) and NH 4 (2), but orientational positions of these ammonium ions were not determined exactly. The refinement of NH 4 (1) and NH 4 (2) orientational positions in phase II is carried out with the help of the X-ray and neutron single crystal diffraction study. The analyses of differential Fourier maps of electron charge density and nuclear density point out the possibility of disordering of NH 4 (2) ammonium ions

Synthesis route and structural properties of nanoferrites

International Nuclear Information System (INIS)

Zaharieva, Katerina; Cherkezova-Zheleva, Zara; Kunev, Boris; Shopska, Maya; Mitov, Ivan

2013-01-01

The nano dimensional magnesium ferrite materials Mg 0.25 Fe 2.75 O 4 , Mg 0.5 Fe 2.5 O 4 and MgFe 2 O 4 with different stoichiometry were prepared by co-precipitation procedure using MgCl 2 •6H 2 O, FeCl 2 •4H 2 O and FeCl 3 •6H 2 O and NaOH as precipitant. The physicochemical methods - X-ray diffraction analysis, Moessbauer spectroscopy and FTIR spectroscopy were performed to investigate the structural properties of obtained nano size magnesium ferrite type samples. The registered experimental data were determined the presence of spinel ferrites and additional precursor phases as iron oxihydroxides and double layered hydroxides in ferrite materials MgxFe 3-x O 4 (x=0.5;1). In the case of magnesium ferrite sample Mg x Fe 3-x O 4 (x=0.25) the existence of non-stoichiometric spinel ferrite and intermediate phase - iron oxihydroxides were observed only. Key words: magnesium ferrites, co-precipitation, physicochemical methods

Annealing temperature dependent structural and magnetic properties of MnFe{sub 2}O{sub 4} nanoparticles grown by sol-gel auto-combustion method

Energy Technology Data Exchange (ETDEWEB)

Bhandare, S.V. [Department of Physics, Gulbarga University, Gulbarga 585106 (India); Kumar, R.; Anupama, A.V.; Choudhary, H.K. [Materials Research Centre, Indian Institute of Science, Bangalore 560012 (India); Jali, V.M., E-mail: vmjali@gmail.com [Department of Physics, Gulbarga University, Gulbarga 585106 (India); Sahoo, B., E-mail: bsahoo@mrc.iisc.ernet.in [Materials Research Centre, Indian Institute of Science, Bangalore 560012 (India)

2017-07-01

Highlights: • Phase pure MnFe{sub 2}O{sub 4} samples were prepared by sol-gel auto-combustion method. • Annealing MnFe{sub 2}O{sub 4} below ∼500 °C, two spinel phases were observed indicating partial oxidation of Mn{sup 2+} to Mn{sup 3+}. • Oxidation of Mn{sup 2+} to Mn{sup 3+} results in decrease in lattice parameter of the spinel lattice. • Annealing at ≥ 600 °C, MnFe{sub 2}O{sub 4} decomposes into crystalline α-Mn{sub 2}O{sub 3} and α-Fe{sub 2}O{sub 3} along with amorphous-FeO phase. - Abstract: Manganese ferrite (MnFe{sub 2}O{sub 4}) nanoparticles were synthesized by sol-gel auto-combustion method using manganese nitrate and ferric nitrate as precursors and citric acid as a fuel. Scanning electron micrographs show irregularly shaped morphology of the particles. The as-prepared samples were annealed at 400, 500, 600 and 800 °C for 2 h in air. The phase identification and structural characterizations were performed using powder X-ray diffraction technique along with Mössbauer spectroscopy. Magnetization loops and {sup 57}Fe Mössbauer spectra were measured at RT. After annealing the sample at or below ∼ 500 °C, we observed two different spinel phases corresponding to two different lattice parameters. This is originating due to the partial oxidation of Mn{sup 2+} to Mn{sup 3+}. At high annealing temperatures (∼ 600 °C or above) the spinel MnFe{sub 2}O{sub 4} phase decomposes into crystalline α-Mn{sub 2}O{sub 3} and α-Fe{sub 2}O{sub 3} phases, and amorphous FeO phase.

Single-shot femtosecond-pulsed phase-shifting digital holography.

Science.gov (United States)

Kakue, Takashi; Itoh, Seiya; Xia, Peng; Tahara, Tatsuki; Awatsuji, Yasuhiro; Nishio, Kenzo; Ura, Shogo; Kubota, Toshihiro; Matoba, Osamu

2012-08-27

Parallel phase-shifting digital holography is capable of three-dimensional measurement of a dynamically moving object with a single-shot recording. In this letter, we demonstrated a parallel phase-shifting digital holography using a single femtosecond light pulse whose central wavelength and temporal duration were 800 nm and 96 fs, respectively. As an object, we set spark discharge in atmospheric pressure air induced by applying a high voltage to between two electrodes. The instantaneous change in phase caused by the spark discharge was clearly reconstructed. The reconstructed phase image shows the change of refractive index of air was -3.7 × 10(-4).

Spinels as cathodes for the electrochemical reduction of O2 and NO

DEFF Research Database (Denmark)

Simonsen, Vibe Louise Ernlund; Find, D.; Lilliedal, M.

2007-01-01

the largest difference in activity between reduction of oxygen and the reduction of nitric oxide, the activity being highest for the reduction of nitric oxide. The material is probably not stable when polarised cathodically. However it seems that the electrode material can be regenerated upon oxidation. NiFe2......Spinels were synthesised and investigated as electro-catalyst for the electrochemical reduction of oxygen and nitric oxide using cyclic voltammetry and cone shaped electrodes. The following four spinels were investigated; CoFe2O4, NiFe2O4, CuFe2O4 and Co3O4. The composition CuFe2O4 revealed......O4 is also more active for the reduction of nitric oxide than for the reduction of oxygen, whereas the cobalt containing spinels have a higher activity for the reduction of oxygen than for the reduction of nitric oxide....

Synthesis and optical property of zinc aluminate spinel cryogels

Directory of Open Access Journals (Sweden)

Lifen Su

2016-06-01

Full Text Available Zinc aluminate spinel cryogels with various molar ratio of Al/Zn are synthesized by sol–gel technology followed by vacuum freeze drying. The structures and optical properties are both found to be affected by the molar ratios of Al/Zn and annealed temperatures. The peaks of zinc oxide (ZnO and zinc dialuminum oxide (ZnAl2O4 are both obtained for the samples with more Zn content annealed at 750 °C or upward. The composites have a large surface area (137 m2/g with mesoporous structure after annealing at 750 °C. The SEM images reveal that the ZnAl2O4 crystals formed a multilayer structure with redundant ZnO particles which deposited on it. Furthermore, the maximum infrared reflectance is about 80% with an improvement of 35% in the infrared region after annealing at 950 °C compared with that of 450 °C, which indicates that these porous cryogels have a potential application as thermal insulating materials at a high temperature.

Sliding three-phase contact line of printed droplets for single-crystal arrays

International Nuclear Information System (INIS)

Kuang, Minxuan; Wu, Lei; Li, Yifan; Gao, Meng; Zhang, Xingye; Jiang, Lei; Song, Yanlin

2016-01-01

Controlling the behaviours of printed droplets is an essential requirement for inkjet printing of delicate three-dimensional (3D) structures or high-resolution patterns. In this work, molecular deposition and crystallization are regulated by manipulating the three-phase contact line (TCL) behaviour of the printed droplets. The results show that oriented single-crystal arrays are fabricated based on the continuously sliding TCL. Owing to the sliding of the TCL on the substrate, the outward capillary flow within the evaporating droplet is suppressed and the molecules are brought to the centre of the droplet, resulting in the formation of a single crystal. This work provides a facile strategy for controlling the structures of printed units by manipulating the TCL of printed droplets, which is significant for realizing high-resolution patterns and delicate 3D structures. (paper)

High-voltage LiNi0.5Mn1.5O4-d spinel material synthesized by microwave-assisted thermo-polymerization: some insights into the microwave-enhancing physico-chemistry

CSIR Research Space (South Africa)

Kebede, Mesfin A

2017-10-01

Full Text Available candidates as cathode materials29 for rechargeable lithium-ion batteries due to its ability to provide a30 high operating voltage (∼4.7 V) and 3-D channels for diffusion of31 lithium ions in its spinel structure.1–11 The advantageous properties32 of the LMNO... capability and long-term58 cycling) of nanostructured LMNO by virtue of tuning its Mn3+ con-59 centration.60 Aside from controlling the concentration of the Mn3+ in the61 spinel structure,11 it is known that the electrochemical performance62 of lithium-ion...

Thorough XPS analyses on overlithiated manganese spinel cycled around the 3V plateau

Energy Technology Data Exchange (ETDEWEB)

Grissa, R. [IPREM ECP − UMR CNRS 5254, Université de Pau et des Pays de l’Adour, Hélioparc Pau-Pyrénées, 2 Avenue du Président Angot, 64053 Pau Cedex 9 (France); Martinez, H., E-mail: herve.martinez@univ-pau.fr [IPREM ECP − UMR CNRS 5254, Université de Pau et des Pays de l’Adour, Hélioparc Pau-Pyrénées, 2 Avenue du Président Angot, 64053 Pau Cedex 9 (France); Cotte, S.; Galipaud, J.; Pecquenard, B. [CNRS, Université de Bordeaux, ICMCB–UPR 9048 and Bordeaux INP, 87 Avenue du Dr. Schweitzer, F-33600 Pessac (France); Cras, F.Le [CEA LETI, 17 rue des Martyrs, F-38054 Grenoble (France); Université Grenoble Alpes, F-38000 Grenoble (France)

2017-07-31

Highlights: • Mn2p XPS spectra of Li{sub 1+x}Mn{sub 2-x}O{sub 4} (0 < x < 0.25) fitted with reference samples. • XPS Mn mean oxidation states agrees with XRD structural study. • Li{sub 1.2}Mn{sub 1.8}O{sub 4} thin films cycled versus lithium arounds 3 V in liquid electrolyte. • Electrochemical results (over 20 cycles) related to Mn oxidation states evolution. • Irreversible capacity explained on the basis of XPS by active material delamination. - Abstract: Lithium-rich spinel Li{sub 1.2}Mn{sub 1.8}O{sub 4} thin film electrodes operated at 3 V/Li{sup +}/Li are studied by means of X-ray photoelectron spectroscopy (XPS), mainly on the basis of the evolution of the Mn2p XPS peak during the electrode cycling. The analysis of this core peak has long been debated in literature given its complex character. Based on manganese oxide references, MnO (Mn{sup 2+}), Mn{sub 2}O{sub 3}(Mn{sup 3+}) and Li{sub 2}MnO{sub 3}(Mn{sup 4+}), we propose a deconvolution method to identify each Mn oxidation state. This method is then used for the deconvolution of Mn2p XPS peaks of bulk lithium-rich spinels Li{sub 1+x}Mn{sub 2-x}O{sub 4} (0 ≤ x ≤ 0.25) for validation before proceeding to the study of cycled Li{sub 1.2}Mn{sub 1.8}O{sub 4} thin film electrodes. Electrochemical measurements exhibit significant capacity loss during the first cycle. Based on XPS analyses, this phenomenon could be explained by mechanical breakup of parts of the electrode. A stable behavior during subsequent cycles is then observed. The presence of Mn{sup 2+} species (XPS) at the most top surface of the electrode and the significant polarization observed during the discharge illustrate the kinetical limitation of the two-phase reaction, despite the reduced thickness of the electrode material.

Reduction of waveform distortion in grid-injection current from single-phase utility interactive PV-inverter

International Nuclear Information System (INIS)

Hamid, Muhammad Imran; Jusoh, Awang

2014-01-01

Highlights: • A reduction scheme for harmonics from utility interactive PV-inverter is proposed. • Single-phase conditioner with 3-phase expandability structure is used. • The single-phase conditioner in 3-phase structure work independently. • The scheme works effectively within overall operation range of the PV-inverter. • Conditioner in the scheme also improves the PV-inverter and plant’s utility factor. - Abstract: As the natural behavior of energy source and design characteristic, the current generated by a grid-interactive PV-inverter may contain harmonics. This distortion component will be carried on from the PV-inverter during injection power into the grid. Excessive harmonics in a grid will lead to a variety of power quality problems. This paper presents a distortion reduction scheme, utilizing a fed forward single-phase, generation-side power conditioner with a structure that can be expanded for use in a three-phase system and can work independently under imbalanced condition. Conditioner is placed in parallel with the photovoltaic plant and it functions to compensate the plant’s output current distortion, so that the total current flow to the grid is sinusoidal. This method also includes the implementation of a simpler control system for the conditioner, which consists of a combination of distortion current extraction, synchronization and a current control system, and realized through a TMS320F28335: a 150 MHz floating point DSP controller. Testing of the conditioner prototype, which was conducted on a real operation of a PV plant, showed that the scheme worked effectively within the overall operation range of the PV plant. This paper also discusses the potential of utility factor improvement of the PV-inverter and plant due to implementation of conditioner in the scheme

High-pressure phase transition and properties of spinel ZnMn2O4

DEFF Research Database (Denmark)

Åbrink, S.; Waskowska, A.; Gerward, Leif

1999-01-01

to normal pressure. The c/a ratio reduces from 1.62 to 1.10 above P-c and remains nearly pressure independent in the high-pressure phase. The transition is attributed to the changes in electron configuration of the Mn3+ ions. According to the crystal field theory, the e(g) electron of octahedrally......-pressure behavior of ZnMn2O4 was investigated up to 52 GPa using the energy-dispersive x-ray diffraction technique and synchrotron radiation. The structural first-order phase transition from the body-centered to primitive-tetragonal cell takes place at P-c = 23 GPa. The high-pressure phase is metastable down...... coordinated Mn3+ is either in the d(z)(2) orbital or in the d(x2-y2). In the first configuration the MnO6 octahedron will be elongated and this is the case at normal pressure, while the second configuration gives the flattened octahedron. In the high-pressure phase some proportion of the e(g) electrons...

Characterization and evaluation of employment of nanostructured spinel MA on oxidation resistance of graffiti; Caracterizacao e avaliacao do emprego de espinelio MA nanoestruturado na resistencia a oxidacao de grafites

Energy Technology Data Exchange (ETDEWEB)

Vitor, P.A.M.; Guaglianoni, W.C.; Braganca, S.R.; Bergmann, C.P., E-mail: pedroaugusto89@hotmail.com [Universidade Federal do Rio Grande do Sul (LACER/UFRS), Porto Alegre, RS (Brazil). Laboratorio de Materiais Ceramicos

2016-07-01

This study aimed to investigate the obtaining of nanostructured powders of spinel MA (MgAl2O4) via synthesis of combustion in solution (SCS), and the influence of its incorporation in oxidation resistance in natural graphites. The crystalline phase only was obtained after a heat treatment at 900 ° C of the powder as-synthesized. The powders were characterized by differential thermal analysis (DTA) and thermogravimetric (ATG) and crystallographic analysis by X-ray diffraction (XRD) and Raman spectroscopy. The results, using thermogravimetric dynamic and isothermal analysis showed a relationship between embedded content of spinel (as-synthesized and calcined) and the raising of the temperature to start the oxidation process (onset temperature) of the samples. The rate of oxidation is reduced at temperatures from 700 ° C, retarding the oxidation of graphite with increasing level of spinel, but this effect ceases at temperatures above 1000 ° C. (author)

Electrochemical evaluation of the a carbon-paste electrode modified with spinel manganese(IV) oxide under flow conditions for amperometric determination of lithium

International Nuclear Information System (INIS)

Raymundo-Pereira, Paulo A.; Martin, Cibely S.; Bergamini, Marcio F.; Bocchi, Nerilso; Teixeira, Marcos F.S.

2011-01-01

The participation of cations in redox reactions of manganese oxides provides an opportunity for development of chemical sensors for non-electroactive ions. This paper describes the amperometric determination of lithium ions using carbon-paste electrode modified with spinel manganese(IV) oxide under flow conditions. Systematic investigations were made to optimize the experimental parameters for lithium sensor by flow injection analysis. The detection was based on the measurement of anodic current generated by oxidation of Mn(III) to Mn(IV) at the surface of the electrode and consequently the lithium ions extraction into the spinel structure. An operating potential of 0.50 V (vs. Ag/AgCl/3 KCl mol/L) was exploited for amperometric monitoring. The amperometric signal was linearly dependent on the lithium ions concentration over the range 4.0 x 10 -5 to 1.0 x 10 -3 mol L -1 . The equilibrium constant of insertion/extraction of the lithium ion in the spinel structure, apparent Gibbs energy of insertion, and surface coverage of the electrode with manganese oxide, were calculated by peak charge (Q) in different concentration under flow conditions. Considering selectivity, the peak charge of the sensor was found to be linearly dependent on the ionic radius of the alkaline and earth-alkaline cations.

Load compensation for single phase system using series active filter

African Journals Online (AJOL)

user

Keywords: Active power filter (APF), current source type of harmonic load ... Single phase active filters could attract less attention than three phase due to its low ..... Generalised single-phase p-q theory for active power filtering: simulation and.

Structural phase transitions in BaMo6S8: Evidence for an incommensurate phase

International Nuclear Information System (INIS)

Jorgensen, J.D.; Hinks, D.G.; Hatch, D.M.; Putnam, R.M.

1986-01-01

The structure of BaMo 6 S 8 has been studied over the temperature range 19 K to 573 K by time-of-flight neutron powder diffraction. Below 175 K the data can be suitably refined in a triclinic, P1, cell with volume equal to the rhombohedral, R3, cell common to most Chevrel-phase structures. At temperatures immediately above 175 K, the rhombohedral, R3, Bragg peaks are broadened by satellite reflections which appear to be identical to those recently observed at low temperature in PbMo 6 S 8 and SnMo 6 S 8 . An abrupt change in the sign of the temperature dependence of the hexagonal c axis (∂c/∂T) signals the transition to an undistorted rhombohedral, R3, structure at temperatures above about 350 K. An extended Landau theory determines both continuous and discontinuous transitions from R3 induced by a single order parameter. Analysis of the order parameters inducing commensurate transitions imposes symmetry restrictions on the atomic displacements in the lower symmetry phases. The assumption of an R3 commensurate phase is not consistent with the bond lengths obtained for the distortions to the P1 (or P1) phase for any of the possible cells preserving order parameters. Thus the phase immediately above 175 K cannot be a commensurate R3 structure. This is consistent with experimental evidence. 25 refs., 11 figs., 8 tabs

Flotation Behaviors of Perovskite, Titanaugite, and Magnesium Aluminate Spinel Using Octyl Hydroxamic Acid as the Collector

Directory of Open Access Journals (Sweden)

Weiqing Wang

2017-08-01

Full Text Available The flotation behaviors of perovskite, titanaugite, and magnesium aluminate spinel (MA-spinel, using octyl hydroxamic acid (OHA as the collector, were investigated using microflotation experiments, zeta-potential measurements, Fourier transform infrared (FT-IR analyses, X-ray photoelectron spectroscopy (XPS analyses, and flotation experiments on artificially mixed minerals. The microflotation experiments show that the floatability of perovskite is clearly better than titanaugite and MA-spinel at around pH 5.5, while titanaugite possesses certain floatability at pH 6.0–6.5, and MA-spinel displays good floatability at pH > 8.0. The results of the FT-IR and XPS analyses show that OHA mainly interacts with Ti, resulting in perovskite flotation, and that the Al on titanaugite, as well as the Mg and Al on the MA-spinel surface, chemically react with OHA under acidic conditions. However, OHA mainly reacts with the Ti and Ca on the perovskite surface, Ca and Mg on the titanaugite surface, and Mg and Al on the MA-spinel surface under alkaline conditions. The results of the artificially mixed mineral flotation experiment show that the concentrate of TiO2 grade increased from 19.73% to 30.18% at pH 5.4, which indicates that a weakly acidic solution is the appropriate condition for the flotation separation of perovskite from titanaugite and MA-spinel. The results of the modified slag flotation experiments show that the TiO2 grade of concentrate increased from 18.13% to 23.88% at pH 5.4, through the open circuit test of “one roughing and one cleaning”. OHA displays selectivity toward perovskite in the modified slag flotation, but the consumption of H2SO4 is very high. The CaSO4 precipitate covered on the mineral surfaces results in poor TiO2 grade and recovery.

Topotactic conversion route to mesoporous quasi-single-crystalline Co{sub 3}O{sub 4} nanobelts with optimizable electrochemical performance

Energy Technology Data Exchange (ETDEWEB)

Tian, Li [MOE Key Laboratory of Bioinorganic and Synthetic Chemistry State Key Laboratory of Optoelectronic Materials and Technology School of Chemistry and Chemical Engineering School of Physics and Engineering Sun Yat-Sen University Guangzhou, 510275 (China); School of Chemistry and Chemical Engineering, Hunan University of Science and Technology Xiangtan, 411201 (China); Zou, Hongli; Fu, Junxiang; Yang, Xianfeng; Wang, Yi; Fu, Xionghui; Liang, Chaolun; Wu, Mingmei; Shen, Pei Kang [MOE Key Laboratory of Bioinorganic and Synthetic Chemistry State Key Laboratory of Optoelectronic Materials and Technology School of Chemistry and Chemical Engineering School of Physics and Engineering Sun Yat-Sen University Guangzhou, 510275 (China); Guo, Hongliang; Gao, Qiuming [State Key Laboratory of High Performance Ceramics and Superfine Microstructures Shanghai Institute of Ceramics, Graduate School, Chinese Academy of Sciences 1295 Dingxi Rd., Shanghai 200050 (China)

2010-02-22

The growth of mesoporous quasi-single-crystalline Co{sub 3}O{sub 4} nanobelts by topotactic chemical transformation from {alpha}-Co(OH){sub 2} nanobelts is realized. During the topotactic transformation process, the primary {alpha}-Co(OH){sub 2} nanobelt frameworks can be preserved. The phases, crystal structures, morphologies, and growth behavior of both the precursory and resultant products are characterized by powder X-ray diffraction (XRD), electron microscopy - scanning electron (SEM) and transmission electron (TEM) microscopy, and selected area electron diffraction (SAED). Detailed investigation of the formation mechanism of the porous Co{sub 3}O{sub 4} nanobelts indicates topotactic nucleation and oriented growth of textured spinel Co{sub 3}O{sub 4} nanowalls (nanoparticles) inside the nanobelts. Co{sub 3}O{sub 4} nanocrystals prefer [0001] epitaxial growth direction of hexagonal {alpha}-Co(OH){sub 2} nanobelts due to the structural matching of [0001] {alpha}-Co(OH){sub 2}//[111] Co{sub 3}O{sub 4}. The surface-areas and pore sizes of the spinel Co{sub 3}O{sub 4} products can be tuned through heat treatment of {alpha}-Co(OH){sub 2} precursors at different temperatures. The galvanostatic cycling measurement of the Co{sub 3}O{sub 4} products indicates that their charge-discharge performance can be optimized. In the voltage range of 0.0-3.0 V versus Li{sup +}/Li at 40 mA g{sup -1}, reversible capacities of a sample consisting of mesoporous quasi-single-crystalline Co{sub 3}O{sub 4} nanobelts can reach up to 1400 mA h g{sup -1}, much larger than the theoretical capacity of bulk Co{sub 3}O{sub 4} (892 mA h g{sup -1}). (Abstract Copyright [2010], Wiley Periodicals, Inc.)

Synthesis and characterization of nanosized MgxMn1−xFe2O4 ferrites by both sol-gel and thermal decomposition methods

International Nuclear Information System (INIS)

De-León-Prado, Laura Elena; Cortés-Hernández, Dora Alicia; Almanza-Robles, José Manuel; Escobedo-Bocardo, José Concepción; Sánchez, Javier; Reyes-Rdz, Pamela Yajaira; Jasso-Terán, Rosario Argentina; Hurtado-López, Gilberto Francisco

2017-01-01

This work reports the synthesis of Mg x Mn 1−x Fe 2 O 4 (x=0–1) nanoparticles by both sol-gel and thermal decomposition methods. In order to determine the effect of synthesis conditions on the crystal structure and magnetic properties of the ferrites, the synthesis was carried out varying some parameters, including composition. By both methods it was possible to obtain ferrites having a single crystalline phase with cubic inverse spinel structure and a behavior near to that of superparamagnetic materials. Saturation magnetization values were higher for materials synthesized by sol-gel. Furthermore, in both cases particles have a spherical-like morphology and nanometric sizes (11–15 nm). Therefore, these materials can be used as thermoseeds for the treatment of cancer by magnetic hyperthermia. - Highlights: • Mg–Mn ferrites were synthesized by sol-gel and thermal decomposition methods. • Materials showed a single cubic inverse spinel crystalline structure. • Ferrites have a soft ferrimagnetic behavior close to superparamagnetic materials.

The effect of bismuth on the structure, magnetic and electric properties of Co2MnO4 spinel multiferroic

Science.gov (United States)

Chouaya, H.; Smari, M.; Walha, I.; Dhahri, E.; Graça, M. P. F.; Valente, M. A.

2018-04-01

Mixed Co2Mn1-xBixO4 (x = 0, x = 0.05 and x = 0.1) samples were prepared by the sol-gel method using the citric acid route and characterized by various techniques. The X-ray diffraction (XRD) and Raman spectroscopic analyses confirmed the formation of inverse spinel cubic structure with Fd 3 ‾ m space group. The introduction of Bismuth (Bi) into Co2MnO4 did not modify the ferrimagnetic character of the parent compound Co2MnO4, whereas the field-cooled magnetizations MFC and the Curie temperature Tc decreased when increasing the Bi content. The electrical properties showed an activation energy (Ea) increase caused by the decrease of the double-exchange interaction following the substitution of Mn3+ by Bi3+. Eventually, the temperature coefficient of resistance (TCR) shows significant values for all samples can be investigated also as good candidates for bolometer applications.

Symmetry transition via tetravalent impurity and investigations on magnetic properties of Li0.5Fe2.5O4

Science.gov (United States)

Kounsalye, Jitendra S.; Kharat, Prashant B.; Chavan, Apparao R.; Humbe, Ashok V.; Borade, R. M.; Jadhav, K. M.

2018-04-01

The present study, deals with the phase symmetry transformation of lithium ferrite after introducing tetravalent (Ti4+) impurity. The sol-gel auto combustion technique was adopted for the synthesis of nanoparticle samples with generic chemical formula Li0.5Fe2.5O4 and Li0.55Ti0.10Fe2.35O4. The synthesized nanoparticles were characterized by X-ray diffraction (XRD) technique for structural analysis. The XRD patterns show the single phase cubic structure without any impurity phase but the P4332 to Fd-3m transformation was observed after introducing Ti4+ impurity. The Nano size of the synthesized particles was confirmed by crystallite size ( 20nm) calculated using Debye-Scherrer's formula. The Fourier transform infrared spectroscopy (FTIR) studies shows shifting of band frequencies which reflect the structural changes after tetravalent substitutional impurities. The magnetic properties were studied through pulse field hysteresis loop (M-H loop) technique at room temperature, the M-H loops showdecrease in magnetic properties afternonmagnetic Ti4+ ion substitution. This is attributed to transition of inverse spinel structure of lithium ferrite to random spinel structure.

Effect of bismuth ion substitution on structural properties of zinc ferrite nanoparticles

Directory of Open Access Journals (Sweden)

Naraavula Suresh Kumar

2016-06-01

Full Text Available Bismuth doped nano zinc ferrite particles having the general formula ZnFe2-xBixO4 (x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.25 were synthesized by sol-gel combustion method. The effect of bismuth doping on structural properties were investigated. The X-ray diffraction (XRD spectra confirm the single phase cubic spinel structure. The average crystallite sizes of all the samples were determined by Debye-Scherrer equation and are in the range 16–20 nm. The lattice parameter increases with the increase of bismuth ion concentration. This is due to the larger ionic radius of Bi3+ ions substituting smaller Fe3+ ions at octahedral sites (B-sites. The surface morphology of all compounds was studied by scanning electron microscope (SEM. The microstructure analysis and the particle size were examined by transmission electron microscope (TEM. The compositional stoichiometry of these samples was verified by energy dispersive spectroscopy (EDS analysis.

Optical properties of Ni-doped MgGa2O4 single crystals grown by floating zone method

International Nuclear Information System (INIS)

Suzuki, Takenobu; Hughes, Mark; Ohishi, Yasutake

2010-01-01

The single crystal growth conditions and spectroscopic characterization of Ni-doped MgGa 2 O 4 with inverse-spinel structure crystal family are described. Single crystals of this material have been grown by floating zone method. Ni-doped MgGa 2 O 4 single crystals have broadband fluorescence in the 1100-1600 nm wavelength range, 1.6 ms room temperature lifetime, 56% quantum efficiency and 1.05x10 -21 cm 2 stimulated emission cross section at the emission peak. This new material is very promising for tunable laser applications covering the important optical communication and eye safe wavelength region.

Orbital physics in sulfur spinels: ordered, liquid and glassy ground states

International Nuclear Information System (INIS)

Buettgen, N; Hemberger, J; Fritsch, V; Krimmel, A; Muecksch, M; Nidda, H-A Krug von; Lunkenheimer, P; Fichtl, R; Tsurkan, V; Loidl, A

2004-01-01

Measurements of magnetization M(T, H), heat capacity C(T), NMR lineshift K(T) and linewidth Δ(T), neutron scattering S(Q, ω, T) and broadband dielectric spectroscopy ε(ω, T) provide experimental evidence of the different orbital ground states in the cubic sulfur spinels under investigation. In all compounds, the tetrahedrally coordinated Jahn-Teller ions Fe 2+ are characterized by a degeneracy of the orbital degrees of freedom. Particularly, we found a long-range orbital ordering in polycrystalline (PC) FeCr 2 S 4 , and a glassy freezing of the orbital degrees of freedom in FeCr 2 S 4 (single crystals) (SCs). In contrast, FeSc 2 S 4 belongs to the rare class of spin-orbital liquids, where quantum fluctuations accompanying the glassy freezing of the orbitals suppress long-range magnetic order

Magnetic and Structural Investigations of Nanocrystalline Cobalt-Ferrite

Directory of Open Access Journals (Sweden)

I. Sharifi

2012-10-01

Full Text Available Cobalt ferrite is an important magnetic material due to their large magneto-crystalline anisotropy, high cohercivity, moderate saturation magnetization and chemical stability.In this study, cobalt ferrites Nanoparticles have been synthesized by the co-precipitation method and a new microemulsion route. We examined the cation occupancy in the spinel structure based on the “Rietveld with energies” method. The Xray measurements revealed the production of a broad single ferrite cubic phase with the average particle sizes of about 12 nm and 7nm, for co-precipitation and micro-emulsion methods, respectively. The FTIR measurements between 400 and 4000 cm-1 confirmed the intrinsic cation vibrations of the spinelstructure for the two methods. Furthermore, the Vibrating Sample Magnetometer (VSM was carried out at room temperature to study the structural and magnetic properties. The results revealed that by changing the method from co-precipitation to the reverse micelle the material exhibits a softer magnetic behavior in such a way that both saturation magnetization and coercivity decrease from 58 to 29 emu/g and from 286 to 25 Oe, respectively.

Study of irradiation damages in MgAl{sub 2}O{sub 4} and ZnAl{sub 2}O{sub 4} spinels in the framework of nuclear waste transmutation; Dommages d'irradiation dans des ceramiques de structure spinelle MgAl{sub 2}O{sub 4} et ZnAl{sub 2}O{sub 4} application a la transmutation des dechets nucleaires

Energy Technology Data Exchange (ETDEWEB)

Thiriet-Dodane, C

2002-07-01

The transmutation of minor actinides in-reactor is one solution currently being studied for the long time management of nuclear waste. In the heterogeneous concept the radionuclides are incorporating in an inert ceramic matrix. The support material must be insensitive to radiation damage. Fission product damage is the main radiation damage source during the transmutation process and therefore it is of the utmost importance to study their effects. We irradiated spinels MgAl{sub 2}O{sub 4} (matrix of reference) and ZnAl{sub 2}O{sub 4} by fast ions (by example: {sup 86}Kr of approximately 400 MeV) simulating the fission products. Under these conditions, the damage is primarily due to the electronic energy losses (S{sub e}). One of the structural features of spinel AB{sub 2}O{sub 4} is that the two cations (A{sup 2+} and B{sup 3+}) can exchange their site. This phenomenon is quantified by the inversion parameter. We highlight by XRD in grazing incidence that the structural changes observed in MgAl{sub 2}O{sub 4} correspond to an order-disorder transition from the cation sub-networks and not to a phase shift as described in the literature. Using other techniques characterizing the space group (Raman spectroscopy) as well as the local order (NMR 27Al, spectroscopy of absorption X with the thresholds K of Al and Zn), we confirm this interpretation. Moreover, for a fluence of 10{sup 14} ions/cm{sup 2}, the loss of the order at long distance is observed thus meaning a beginning of amorphization of material. The ZnAl{sub 2}O{sub 4} spinel presents the same behaviour. For this last spinel, an evolution of the inversion parameter according to the stopping power 2 was highlighted after irradiation by ions {sup 86}Kr from approximately 20 MeV. We illustrate our study by the analysis of the results obtained in XRD of an irradiation out of composite fuel (MgAl{sub 2}O{sub 4} + UO{sub 2}) called THERMHET. (authors)

Observation Of Electron-beam-induced Phase Evolution Mimicking The Effect Of Charge-discharge Cycle In Li-rich Layered Cathode Materials Used For Li-ion Batteries

Energy Technology Data Exchange (ETDEWEB)

Lu, Ping; Yan, Pengfei; Romero, Eric; Spoerke, Erik D.; Zhang, Jiguang; Wang, Chong M.

2015-02-24

Capacity loss, and voltage fade upon electrochemical charge-discharge cycling observed in lithium-rich layered cathode oxides (Li[LixMnyTM1-x-y]O2 , TM = Ni, Co or Fe) have recently been identified to be correlated to the gradual phase transformation, featuring the formation of a surface reconstructed layer (SRL) that evolves from a thin (<2 nm), defect spinel layer upon the first charge, to a relatively thick (~5 nm), spinel or rock-salt layer upon continuous charge-discharge cycling. Here we report observations of a SRL and structural evolution of the SRL on the Li[Li0.2Ni0.2Mn0.6]O2 (LMR) particles, which are identical to those reported due to the charge-discharge cycle but are a result of electron-beam irradiation during scanning transmission electron microscopy (STEM) imaging. Sensitivity of the lithium-rich layered oxides to high-energy electrons leads to the formation of thin, defect spinel layer on surfaces of the particles when exposed to a 200 kV electron beam for as little as 30 seconds under normal high-resolution STEM imaging conditions. Further electron irradiation produces a thicker layer of the spinel phase, ultimately producing a rock-salt layer at a higher electron exposure. Atomic-scale chemical mapping by energy dispersive X-ray spectroscopy in STEM indicates the electron-beam-induced SRL formation on LMR is accomplished by migration of the transition metal ions to the Li sites without breaking down the lattice. This study provides an insight for understanding the mechanism of forming the SRL and also possibly a mean to study structural evolution in the Li-rich layered oxides without involving the electrochemistry.

Simulation of the phenomenon of single-phase and two-phase natural circulation

International Nuclear Information System (INIS)

Castrillo, Lazara Silveira

1998-02-01

Natural convection phenomenon is often used to remove the residual heat from the surfaces of bodies where the heat is generated e.g. during accidents or transients of nuclear power plants. Experimental study of natural circulation can be done in small scale experimental circuits and the results can be extrapolated for larger operational facilities. The numerical analysis of transients can be carried out by using large computational codes that simulate the thermohydraulic behavior in such facilities. The computational code RELAP5/MOD2, (Reactor Excursion and Leak Analysis Program) was developed by U.S. Nuclear Regulatory Commissions's. Division of Reactor Safety Research with the objective of analysis of transients and postulated accidents in the light water reactor (LWR) systems, including small and large ruptures with loss of coolant accidents (LOCA's). The results obtained by the simulation of single-phase and two-phase natural circulation, using the RELAP5/MOD2, are presented in this work. The study was carried out using the experimental circuit built at the 'Departamento de Engenharia Quimica da Escola Politecnica da Universidade de Sao Paulo'. In the circuit, two experiments were carried out with different conditions of power and mass flow, obtaining a single-phase regime with a level of power of 4706 W and flow of 5.10 -5 m 3 /s (3 l/min) and a two-phase regime with a level of power of 6536 W and secondary flow 2,33.10 -5 m 3 /s (1,4 l/min). The study allowed tio evaluate the capacity of the code for representing such phenomena as well as comparing the transients obtained theoretically with the experimental results. The comparative analysis shows that the code represents fairly well the single-phase transient, but the results for two-phase transients, starting from the nodalization and calibration used for the case single-phase transient, did not reproduce faithfully some experimental results. (author)

Morphology, Structure and Nonstoichiometry of ZnCr2O4 Nanophased Powder

Directory of Open Access Journals (Sweden)

O. Milosevic

2003-10-01

Full Text Available It is well established that gas/humidity-sensing properties of spinels are markedly influenced by their stoichiometry and microstructure. In this work nucleation and spinel phase development in the Zn-Cr-O system were investigated from the viewpoint of structural and morphological phenomena occurred during nanophased particle synthesis through aerosol reaction. The aerosol was generated from nitrates precursor solution using ultrasonic atomizer operated at 1.7 MHz. The influence of different decomposition schedules on the particle chemical content and morphology was determined by adjusting the processing parameters (aerosol droplet density 3.9x106 droplets/cm3, droplet velocity 0.035m/s, max. temperature 900oC and residence times 3, 6 and 9s. A composite particle structure comprised of primary crystallites sized from 22 to 44nm is revealed by SEM and TEM analysis. XRD structural analysis (crystallite size, microstrains, unit cell and ionic occupancies is performed in accordance with procedure based on Koalariet-Xfit program. A certain degree of non-stochiometry is characteristic for all powders. Homogenous distribution of the constituting elements and Zn/Cr ratio of about 0.68 are proved by EDAX mapping analysis in 470nm sized as-prepared particles. After additional treatment at 1000oC octahedral crystals form with the (111 surface dominat. Evaluated spinel non-stochiometry (Zn/Cr=0.58 is a result of the ZnO dissolving (1.9%wt in the stoichiometric ZnCr2O4. Determination of the way by which the ZnO is incorporated into the spinel lattice is performed according to the procedure based on calculation of both formation and attachment energies.

Influence of La3+ Substitution on Structure, Morphology and Magnetic Properties of Nanocrystalline Ni-Zn Ferrite.

Directory of Open Access Journals (Sweden)

Y K Dasan

Full Text Available Lanthanum substituted Ni-Zn ferrite nanoparticles (Ni0.5Zn0.5LaxFe1-xO4; 0.00 ≤x≤ 1.00 synthesized by sol-gel method were presented. X-ray diffraction patterns reveal the typical single phase spinel cubic ferrite structure, with the traces of secondary phase for lanthanum substituted nanocrystals. In addition, the structural analysis also demonstrates that the average crystallite size varied in the range of 21-25 nm. FTIR spectra present the two prominent absorption bands in the range of 400 to 600 cm-1 which are the fingerprint region of all ferrites. Surface morphology of both substituted and unsubstituted Ni-Zn ferrite nanoparticle samples was studied using FESEM technique and it indicates a significant increase in the size of spherical shaped particles with La3+ substitution. Magnetic properties of all samples were analyzed using vibrating sample magnetometer (VSM. The results revealed that saturation magnetization (Ms and coercivity (Hc of La3+ substituted samples has decreased as compared to the Ni-Zn ferrite samples. Hence, the observed results affirm that the lanthanum ion substitution has greatly influenced the structural, morphology and magnetic properties of Ni-Zn ferrite nanoparticles.

Tensile strain effect in ferroelectric perovskite oxide thin films on spinel magnesium aluminum oxide substrate

Science.gov (United States)

Zhou, Xiaolan

Ferroelectrics are used in FeRAM (Ferroelectric random-access memory). Currently (Pb,Zr)TiO3 is the most common ferroelectric material. To get lead-free and high performance ferroelectric material, we investigated perovskite ferroelectric oxides (Ba,Sr)TiO3 and BiFeO3 films with strain. Compressive strain has been investigated intensively, but the effects of tensile strain on the perovskite films have yet to be explored. We have deposited (Ba,Sr)TiO3, BiFeO3 and related films by pulsed laser deposition (PLD) and analyzed the films by X-ray diffractometry (XRD), atomic force microscopy (AFM), etc. To obtain inherently fully strained films, the selection of the appropriate substrates is crucial. MgAl2O4 matches best with good quality and size, yet the spinel structure has an intrinsic incompatibility to that of perovskite. We introduced a rock-salt structure material (Ni 1-xAlxO1+delta) as a buffer layer to mediate the structural mismatch for (Ba,Sr)TiO3 films. With buffer layer Ni1-xAlxO1+delta, we show that the BST films have high quality crystallization and are coherently epitaxial. AFM images show that the films have smoother surfaces when including the buffer layer, indicating an inherent compatibility between BST-NAO and NAO-MAO. In-plane Ferroelectricity measurement shows double hysteresis loops, indicating an antiferroelectric-like behavior: pinned ferroelectric domains with antiparallel alignments of polarization. The Curie temperatures of the coherent fully strained BST films are also measured. It is higher than 900°C, at least 800°C higher than that of bulk. The improved Curie temperature makes the use of BST as FeRAM feasible. We found that the special behaviors of ferroelectricity including hysteresis loop and Curie temperature are due to inherent fully tensile strain. This might be a clue of physics inside ferroelectric stain engineering. An out-of-plane ferroelectricity measurement would provide a full whole story of the tensile strain. However, a

Novel low temperature synthesis of spinel nano-magnesium chromites from secondary resources

Energy Technology Data Exchange (ETDEWEB)

El-Sheikh, S.M., E-mail: selsheikh2001@gmail.com [Nanostructured Materials Laboratory, Advanced Material Department, Central Metallurgical R and D Institute (CMRDI), P.O. Box 78, Helwan, 11421 Cairo (Egypt); Rabbah, M., E-mail: mahmoud.rabah@ymail.com [Electrochemical and Chemical Treatment Laboratory, Minerals Department, Central Metallurgical R and D Institute (CMRDI), P.O. Box 78, Helwan, 11421 Cairo (Egypt)

2013-09-20

Graphical abstract: FE-SEM micrograph and TEM image of magnesium chromite sample heated at 500 °C. - Highlights: • No study has been reported to prepare spinel magnesium chromite form waste resources. • Novel low synthesis temperature of magnesium chromite. • Selective removal of Ca ions from industrial waste tannery solution is rarely reported. • The method applied is simple and safe. - Abstract: A novel low temperature method for synthesis of nano-crystalline magnesium chromites from the tannery waste solution was investigated. Magnesium and chromium hydroxides gel was co-precipitated at pH 8.5 using ammonia solution. MgCr{sub 2}O{sub 4} was obtained by heating the gel formed at different temperatures 300–500 °C for to 8 h. FT-IR, TG-DTG-DTA, FE-SEM and TEM were used to investigate the produced materials. XRD patterns of the primary oxides revealed the formation of amorphous oxide phase by heating at 300 °C. Heating at 400 °C produces nano-crystallite magnesium chromites partly having the structure MgCrO{sub 4} and mainly MgCr{sub 2}O{sub 4} and traces of Cr{sub 2}O{sub 3}{sup +} 500 °C MgCrO{sub 4} mostly decomposed into MgCr{sub 2}O{sub 4} structure{sub .} After 8 h of heating at 500 °C, Cr{sub 2}O{sub 3} completely disappeared. A high surface area about 42.6 m{sup 2}/g and mesoporous structure was obtained for the produced sample at 500 °C for 8 h. A thermodynamic model has been suggested to explain the findings.

Structural and Chemical Evolution of Li- and Mn-rich Layered Cathode Material

Energy Technology Data Exchange (ETDEWEB)

Zheng, Jianming; Xu, Pinghong; Gu, Meng; Xiao, Jie; Browning, Nigel D.; Yan, Pengfei; Wang, Chong M.; Zhang, Jiguang

2015-02-24

Lithium (Li)- and manganese-rich (LMR) layered-structure materials are very promising cathodes for high energy density lithium-ion batteries. However, their voltage fading mechanism and its relationships with fundamental structural changes are far from being sufficiently understood. Here we report the detailed phase transformation pathway in the LMR cathode (Li[Li0.2Ni0.2Mn0.6]O2) during cycling for the samples prepared by hydro-thermal assistant method. It is found the transformation pathway of LMR cathode is closely correlated to its initial structure and preparation conditions. The results reveal that LMR cathode prepared by HA approach experiences a phase transformation from the layered structure to a LT-LiCoO2 type defect spinel-like structure (Fd-3m space group) and then to a disordered rock-salt structure (Fm-3m space group). The voltage fade can be well correlated with the Li ion insertion into octahedral sites, rather than tetrahedral sites, in both defect spinel-like structure and disordered rock-salt structure. The reversible Li insertion/removal into/from the disordered rock-salt structure is ascribed to the Li excess environment that can satisfy the Li percolating in the disordered rock-salt structure despite the increased kinetic barrier. Meanwhile, because of the presence of a great amount of oxygen vacancies, a significant decrease of Mn valence is detected in the cycled particle, which is below that anticipated for a potentially damaging Jahn-Teller distortion (+3.5). Clarification of the phase transformation pathway, cation redistribution, oxygen vacancy and Mn valence change undoubtedly provides insights into a profound understanding on the voltage fade, and capacity degradation of LMR cathode. The results also inspire us to further enhance the reversibility of LMR cathode via improving its surface structural stability.

Structural, magnetic, and electrical properties of (1-x)Bi0.85La0.15FeO3-(x)CoFe2O4 multiferroic composites

Science.gov (United States)

Pandey, Rabichandra; Pradhan, Lagen Kumar; Kar, Manoranjan

2018-04-01

In this study, the tartaric acid modified sol-gel method was used to synthesize (1-x)Bi0.85La0.15FeO3-(x)CoFe2O4 (BLFO-CFO) composites where x = 0.00, 0.10, 0.20, 0.30, 0.40, and 0.50. The X-ray diffraction (XRD) patterns indicated the formation of composites with both BLFO and CFO crystal symmetry, i.e., perovskite and spinel structures, respectively. Rietveld refinement of the XRD patterns was performed for all of the samples in order to analyze the crystal phases and obtain the structural parameters. There were decreases in the lattice parameters of the perovskite phase as the CFO spinel phase increased in the composites, which may be explained by the strain at the interface of the BLFO and CFO phases. Electrical polarization and dielectric constant enhancements were observed in the BLFO-CFO composites compared with BLFO. The saturation magnetization increased as the CFO phase increased in the composites. The theoretical saturation magnetization (calculated using Vegard's law) was less than the experimentally observed value, possibly due to the spin interaction at the interface of BLFO and CFO.

Microstructure and strengthening mechanisms in an FCC structured single-phase nanocrystalline Co25Ni25Fe25Al7.5Cu17.5 high-entropy alloy

International Nuclear Information System (INIS)

Fu, Zhiqiang; Chen, Weiping; Wen, Haiming; Zhang, Dalong; Chen, Zhen; Zheng, Baolong; Zhou, Yizhang; Lavernia, Enrique J.

2016-01-01

We report on a study of the design, phase formation, microstructure, mechanical behavior and strengthening mechanisms of a novel single-phase Co 25 Ni 25 Fe 25 Al 7.5 Cu 17.5 (at.%) high-entropy alloy (HEA). In this investigation, a bulk nanocrystalline (nc) Co 25 Ni 25 Fe 25 Al 7.5 Cu 17.5 HEA with the face-centered cubic (FCC) crystal structure was fabricated by mechanical alloying (MA) followed by consolidation via spark plasma sintering (SPS). The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results revealed that a single FCC solid-solution phase with an average grain diameter of 24 nm was produced following MA. Following SPS, bulk samples exhibiting a bimodal microstructure with both nanoscale grains and ultra-fine grains (UFGs) and with an average grain diameter of 95 nm were obtained, possessing a single FCC solid-solution phase identical to that in the milled powders. The single-phase feature of the Co 25 Ni 25 Fe 25 Al 7.5 Cu 17.5 HEA principally resulted from remarkably high mutual solubility in most binary atom-pairs of the constituent elements, which appears to correspond to a high entropy of mixing. Approximately 5 vol.% of nanoscale twins were observed in the bulk nc samples. The bulk nc Co 25 Ni 25 Fe 25 Al 7.5 Cu 17.5 HEA exhibits a compressive yield strength of 1795 MPa with a hardness of 454 Hv, which is dramatically higher than the yield strength of most previously reported FCC structured HEAs (∼130–700 MPa). Compared to those of the bulk coarse-grained (CG) Co 25 Ni 25 Fe 25 Al 7.5 Cu 17.5 HEA fabricated by arc-melting, the yield strength and Vickers hardness values of the bulk nc samples increased by 834.9% and 251.9%, respectively. Quantitative calculations of the respective contributions from each strengthening mechanism demonstrate that grain boundary strengthening and dislocation strengthening are principally responsible for the measured ultra-high strength of the bulk nc Co 25 Ni 25 Fe 25 Al 7.5 Cu 17.5 HEA.

The Formation of Lithiated Ti-Doped α-Fe2O3 Nanocrystalline Particles by Mechanical Milling of Ti-Doped Lithium Spinel Ferrite

International Nuclear Information System (INIS)

Widatallah, H. M.; Gismelseed, A. M.; Bouziane, K.; Berry, F. J.; Al Rawas, A. D.; Al-Omari, I. A.; Yousif, A. A.; Elzain, M. E.

2004-01-01

The milling of spinel-related Ti-doped Li 0.5 Fe 2.5 O 4 for different times is studied with XRD, Moessbauer spectroscopy and magnetic measurements. Milling converts the material to Li-Ti-doped α-Fe 2 O 3 nanocrystalline particles via an intermediate γ-LiFeO 2 -related phase. The role played by the dopant Ti-ion in the process is emphasized.

The comparative study of the structural and the electrical properties of the nano spinel ferrites prepared by the soft mehanochemical synthesis

Directory of Open Access Journals (Sweden)

Sekulić D.L.

2014-01-01

Full Text Available Nano spinel ferrites MFe2O4 (M=Ni, Mn, Zn were obtained by soft mechanochemical synthesis in a planetary ball mill. The appropriate mixture of oxide and hydroxide powders was used as initial compounds. All of this mixture of powders was mechanically activated, uniaxial pressed and sintered at 1100°C/2h. The phase composition of the powders and sintered samples were analyzed by XRD and Raman spectroscopy. Morphologies were examined by SEM. In this study, the AC-conductivity and DC-resistivity of sintered samples of MFe2O4 (M= Ni, Mn, Zn ferrites were measured at different frequencies and at room temperature. The values of the electrical conductivities show an increase with increasing temperature, which indicated the semiconducting behavior of the studied ferrites. The conduction phenomenon of the investigated samples could be explained on the basis of hopping model. The complex impedance spectroscopy analysis was used to study the effect of grain and grain boundary on the electrical properties of all three obtained ferrites [Projekat Ministarstva nauke Republike Srbije, br. III 45003

Single-Phase Phase-Locked Loop Based on Derivative Elements

DEFF Research Database (Denmark)

Guan, Qingxin; Zhang, Yu; Kang, Yong

2017-01-01

High-performance phase-locked loops (PLLs) are critical for power control in grid-connected systems. This paper presents a new method of designing a PLL for single-phase systems based on derivative elements (DEs). The quadrature signal generator (QSG) is constructed by two DEs with the same...... PLL to achieve high performance when the grid frequency changes rapidly. This paper presents the model of the PLL and a theoretical performance analysis with respect to both the frequency-domain and time-domain behavior. The error arising from the discretization process is also compensated, ensuring...

Characterization of Li4Ti5O12 and LiMn2O4 spinel materials treated with aqueous acidic solutions

NARCIS (Netherlands)

Simon, D.R.

2007-01-01

In this thesis an investigation of two spinel materials, Li4Ti5O12 and LiMn2O4 used for Li-ion battery applications is performed interms of formation and reactivity towards acidic solutions. Subsequent characterizations such as structural, magnetic, chemical, and electrochemical characterizations

Regio-Regular Oligo and Poly(3-hexyl thiophene): Precise Structural Markers from the Vibrational Spectra of Oligomer Single Crystals.

KAUST Repository

Brambilla, Luigi

2014-10-14

© 2014 American Chemical Society. In this work, we report a comparative analysis of the infrared and Raman spectra of octa(3-hexylthiophene) (3HT)8, trideca(3-hexylthiophene) (3HT)13, and poly(3-hexylthiophene) P3HT recorded in various phases, namely, amorphous, semicrystalline, polycrystalline and single crystal. We have based our analysis on the spectra of the (3HT)8 single crystal (whose structure has been determined by selected area electron diffraction) taken as reference and on the results of DFT calculations and molecular vibrational dynamics. New and precise spectroscopic markers of the molecular structures show the existence of three phases, namely: hairy (phase 1), ordered (phase 2), and disordered/amorphous (phase 3). Conceptually, the identified markers can be used for the molecular structure analysis of other similar systems.

Phase diagram of the Ge-rich of the Ba–Ge system and characterisation of single-phase BaGe4

International Nuclear Information System (INIS)

Prokofieva, Violetta K.; Pavlova, Lydia M.

2014-01-01

Highlights: • The Ba-Ge phase diagram for the range 50–100 at.% Ge was constructed. • Single-phase BaGe 4 grown by the Czochralski method was characterised. • A phenomenological model for a liquid-liquid phase transition is proposed. - Abstract: The Ba–Ge binary system has been investigated by several authors, but some uncertainties remain regarding phases with Ba/Ge ⩽ 2. The goal of this work was to resolve the uncertainty about the current phase diagram of Ba–Ge by performing DTA, X-ray powder diffraction, metallographic and chemical analyses, and measurements of the electrical conductivity and viscosity. The experimental Ba–Ge phase diagram over the composition range of 50–100 at.% Ge was constructed from the cooling curves and single-phase BaGe 4 grown by the Czochralski crystal pulling method was characterised. Semiconducting BaGe 4 crystallised peritectically from the liquid phase near the eutectic. In the liquid state, the caloric effects were observed in the DTA curves at 1050 °C where there are no definite phase lines in the Ba–Ge phase diagram. These effects are confirmed by significant changes in the viscosity and electrical conductivity of a Ba–Ge alloy with eutectic composition at this temperature. A phenomenological model based on two different approaches, a phase approach and a chemical approach, is proposed to explain the isothermal liquid–liquid phase transition observed in the Ba–Ge system from the Ge side. Our results suggest that this transition is due to the peritectic reactions in the liquid phase. This reversible phase transition results in the formation of precursors of various metastable clathrate phases and is associated with sudden changes in the structure of Ba–Ge liquid alloys. Characteristics of both first- and second-order phase transitions are observed. Charge transfer appears to play an important role in this transition

The centralized control of elemental mercury emission from the flue gas by a magnetic rengenerable Fe-Ti-Mn spinel.

Science.gov (United States)

Liao, Yong; Xiong, Shangchao; Dang, Hao; Xiao, Xin; Yang, Shijian; Wong, Po Keung

2015-12-15

A magnetic Fe-Ti-Mn spinel was developed to adsorb gaseous Hg(0) in our previous study. However, it is currently extremely restricted in the control of Hg(0) emission from the flue gas for at least three reasons: sorbent recovery, sorbent regeneration and the interference of the chemical composition in the flue gas. Therefore, the effect of SO2 and H2O on the adsorption of gaseous Hg(0) on the Fe-Ti-Mn spinel and the regeneration of spent Fe-Ti-Mn spinel were investigated in this study. Meanwhile, the procedure of the centralized control of Hg(0) emission from the flue gas by the magnetic Fe-Ti-Mn spinel has been analyzed for industrial application. The spent Fe-Ti-Mn spinel can be regenerated by water washing followed by the thermal treatment at 450 °C with no obvious decrease of its ability for Hg(0) capture. Meanwhile, gaseous Hg(0) in the flue gas can be remarkably concentrated during the regeneration, facilitating its safe disposal. Initial pilot test demonstrated that gaseous Hg(0) in the real flue gas can be concentrated at least 100 times by the Fe-Ti-Mn spinel. Therefore, Fe-Ti-Mn spinel was a novel magnetic regenerable sorbent, which can be used for the centralized control of Hg(0) emission from the flue gas. Copyright © 2015 Elsevier B.V. All rights reserved.

A Novel Single Phase Hybrid Switched Reluctance Motor Drive System

DEFF Research Database (Denmark)

Liang, Jianing; Xu, Guoqing; Jian, Linni

2011-01-01

In this paper, a novel single phase hybrid switched reluctance motor(SRM) drive system is proposed. It integrated a single phase hybrid SRM and a novel single phase boost converter. This motor can reduce the number of phase switch. And the permanent magnet which is used in the motor can improve...... the performance and efficiency of SR motor. However, the inherent characteristic of this motor is that the negative torque is very sensitive with the excitation current near the turn-on angle. The slow excitation current limits the torque generation region and reduces the average torque. Therefore, a novel single...... phase boost converter is applied to improve the performance of this motor. It is easy to generate a double dclink voltage and dc-link voltage and switch both of them. The voltage of boost capacitor is self balance, so the protective circuit is not need to consider. The fast excitation mode helps hybrid...

Twinning in ZnO ceramics with Sb sub 2 O sub 3 additions

Energy Technology Data Exchange (ETDEWEB)

Senda, T. (Ministry of Transportation, Tokyo (Japan). Ship Research Inst.); Bradt, R.C. (Univ. of Nevada-Reno, Nevada (U.S.A.). Mackay School of Mines)

1991-09-01

A mechanism is proposed for the nucleation of ZnO growth twins which is based on the crystallography of the wurtzite and spinel structures. In this paper, possible twin origins from either phase transformation or a result of deformation are both rejected. It is concluded that the ZnO twins are growth twins which nucleate in the early stages of sintering and grain growth of the ceramic powder compacts. Consideration of the oxygen anion stacking layer sequences in the hexagonal ZnO wurtzite structure and the cubic Zn {sub 7} Sb {sub 2} O {sub 12} spinel structure suggests that the nuclei for the twins may form as embryos consisting of a faulted region of the spinel-oxygen anion layer stacking sequence. And then, the faulted layer sequence is created by the presence of the antimony oxide and its reaction with the ZnO. Further, the fact that the wurtzite structure is polar and the ZnO twins are inversion twins explains why there is only a single twin per grain, as multiple twins would result in the unfavorable structural configuration. 24 refs., 2 figs.

The gas phase structure of α -pinene, a main biogenic volatile organic compound

Science.gov (United States)

Neeman, Elias M.; Avilés Moreno, Juan Ramón; Huet, Thérèse R.

2017-12-01

The gas phase structure of the bicyclic atmospheric aerosol precursor α-pinene was investigated employing a combination of quantum chemical calculation and Fourier transform microwave spectroscopy coupled to a supersonic jet expansion. The very weak rotational spectra of the parent species and all singly substituted 13C in natural abundance have been identified, from 2 to 20 GHz, and fitted to Watson's Hamiltonian model. The rotational constants were used together with geometrical parameters from density functional theory and ab initio calculations to determine the rs, r0, and rm(1 ) structures of the skeleton, without any structural assumption in the fit concerning the heavy atoms. The double C=C bond was found to belong to a quasiplanar skeleton structure containing 6 carbon atoms. Comparison with solid phase structure is reported. The significant differences of α-pinene in gas phase and other gas phase bicyclic monoterpene structures (β-pinene, nopinone, myrtenal, and bicyclo[3.1.1]heptane) are discussed.

Quasicrystalline Approach to Prediting the Spinel-Nepheline Liquidus: Application to Nuclear Waste Glass Processing

Energy Technology Data Exchange (ETDEWEB)

Jantzen, Carol

2005-10-10

The crystal-melt equilibria in complex fifteen component melts are modeled based on quasicrystalline concepts. A pseudobinary phase diagram between acmite (which melts incongruently to a transition metal ferrite spinel) and nepheline is defined. The pseudobinary lies within the Al{sub 2}O{sub 3}-Fe{sub 2}O{sub 3}-Na{sub 2}O-SiO{sub 2} quaternary system that defines the crystallization of basalt glass melts. The pseudobinary provides the partitioning of species between the melt and the primary liquidus phases. The medium range order of the melt and the melt-crystal exchange equilibria are defined based on a constrained mathematical treatment that considers the crystallochemical coordination of the elemental species in acmite and nepheline. The liquidus phases that form are shown to be governed by the melt polymerization and the octahedral site preference energies. This quasicrystalline liquidus model has been used to prevent unwanted crystallization in the world's largest high level waste (HLW) melter for the past three years while allowing >10 wt% higher waste loadings to be processed.

Cellulose-precursor synthesis of nanocrystalline Co0.5Cu0.5Fe2O4 spinel ferrites

International Nuclear Information System (INIS)

Ounnunkad, Kontad; Phanichphant, Sukon

2012-01-01

Highlights: ► Synthesis of spinel copper cobalt nanoferrite particles from a cellulose precursor for the first time. Control of nanosize and properties of nanoferrites can take place by varying the calcining temperature. The simple, low cost, easy cellulose process is a choice of nanoparticle processing technology. -- Abstract: Nanocrystalline Cu 0.5 Co 0.5 Fe 2 O 4 powders were prepared via a metal-cellulose precursor synthetic route. Cellulose was used as a fuel and a dispersing agent. The resulting precursors were calcined in the temperature range of 450–600 °C. The phase development of the samples was determined by using Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (XRD). The field-dependent magnetizations of the nanopowders were measured by vibrating sample magnetometer (VSM). All XRD patterns are of a spinel ferrite with cubic symmetry. Microstructure of the ferrites showed irregular shapes and uniform particles with agglomeration. From XRD data, the crystallite sizes are in range of 16–42 nm. Saturation magnetization and coercivity increased with increasing calcining temperature due to enhancement of crystallinity and reduction of oxygen vacancies.

Photoluminescence Polarization Anisotropy in a Single Heterostructured III-V Nanowire with Mixed Crystal Phases

International Nuclear Information System (INIS)

Moses, A. F.; Hoang, T. B.; Ahtapodov, L.; Dheeraj, D. L.; Fimland, B. O.; Weman, H.; Helvoort, A. T. J. van

2011-01-01

Low temperature (10 K) micro-photoluminescence (μ-PL) of single GaAs/AlGaAs core-shell nanowires with single GaAsSb inserts were measured. The PL emission from the zinc blende GaAsSb insert is strongly polarized along the nanowire axis while the PL emission from the wurtzite GaAs nanowire is perpendiculary polarized to the nanowire axis. The result indicates that the crystal phase, through the optical selection rules, has significant effect on the polarization of the PL from NWs besides the dielectric mismatch. The analysis of the PL results based on the electronic structure of these nanowires supports the correlation between the crystal phase and the PL emission.

Synthesis route and structural properties of nanoferrites

Energy Technology Data Exchange (ETDEWEB)

Zaharieva, Katerina; Cherkezova-Zheleva, Zara; Kunev, Boris; Shopska, Maya; Mitov, Ivan [Institute of Catalysis, Bulgarian Academy of Sciences, Sofia (Bulgaria)

2013-07-01

The nano dimensional magnesium ferrite materials Mg{sub 0.25}Fe{sub 2.75}O{sub 4} , Mg{sub 0.5}Fe{sub 2.5}O{sub 4} and MgFe{sub 2}O{sub 4} with different stoichiometry were prepared by co-precipitation procedure using MgCl{sub 2} •6H{sub 2}O, FeCl{sub 2} •4H{sub 2}O and FeCl{sub 3} •6H{sub 2}O and NaOH as precipitant. The physicochemical methods - X-ray diffraction analysis, Moessbauer spectroscopy and FTIR spectroscopy were performed to investigate the structural properties of obtained nano size magnesium ferrite type samples. The registered experimental data were determined the presence of spinel ferrites and additional precursor phases as iron oxihydroxides and double layered hydroxides in ferrite materials MgxFe{sub 3-x}O{sub 4} (x=0.5;1). In the case of magnesium ferrite sample Mg{sub x}Fe{sub 3-x}O{sub 4} (x=0.25) the existence of non-stoichiometric spinel ferrite and intermediate phase - iron oxihydroxides were observed only. Key words: magnesium ferrites, co-precipitation, physicochemical methods.

Microseismic Monitoring of the Olivine → Spinel Transition in Fayalite Under Non-Hydrostatic Stress

Science.gov (United States)

Officer, T.; Secco, R. A.

2016-12-01

In subduction zones, deep earthquakes are thought to be associated with faulting that arises from phase transformations. In order to test the viability of this mechanism experimentally, it is necessary to make microseismic measurements while the mineral under investigation is subjected to the pressure and temperature (P,T) environment at depth. A system has been developed capable of making in situ acoustic emission (AE) measurements on samples under P,T conditions representative of the upper mantle and transition zone. Experiments are performed in a 3000-ton multi-anvil press using an 18/11 octahedral cell with 6 piezoelectric transducers mounted on the rear side of the anvils. AE signals are collected at a sampling rate of 40 MHz using a triggered system and a data buffer for continuous recording so full waveforms of AE events are captured. The use of multiple transducers distributed in a microseismic array allows for events to be located within the sample through automatic arrival time picking and least squares inversion techniques. The multi-anvil apparatus constitutes an inherently noisy environment both acoustically and electrically, therefore methods of noise reduction were developed and will be discussed. This technique has been used to measure acoustic signals generated from the fracturing of quartz beads during high pressure deformation and to investigate the possibility that the phase transformation from olivine to spinel, known to occur in subduction zones, is associated with deep-focus earthquakes (300 - 690 km depth). The analog material fayalite (Fe2SiO4), the iron end member of olivine, has been examined. Information about its synthesis and sintering will be discussed as well as results of AE experiments on samples experiencing deviatoric stress under high pressure (P = 4-9 GPa) and high temperature (T = 773-1273 K) conditions in the spinel stability field.

Manufacturing process scale-up of optical grade transparent spinel ceramic at ArmorLine Corporation

Science.gov (United States)

Spilman, Joseph; Voyles, John; Nick, Joseph; Shaffer, Lawrence

2013-06-01

While transparent Spinel ceramic's mechanical and optical characteristics are ideal for many Ultraviolet (UV), visible, Short-Wave Infrared (SWIR), Mid-Wave Infrared (MWIR), and multispectral sensor window applications, commercial adoption of the material has been hampered because the material has historically been available in relatively small sizes (one square foot per window or less), low volumes, unreliable supply, and with unreliable quality. Recent efforts, most notably by Technology Assessment and Transfer (TA and T), have scaled-up manufacturing processes and demonstrated the capability to produce larger windows on the order of two square feet, but with limited output not suitable for production type programs. ArmorLine Corporation licensed the hot-pressed Spinel manufacturing know-how of TA and T in 2009 with the goal of building the world's first dedicated full-scale Spinel production facility, enabling the supply of a reliable and sufficient volume of large Transparent Armor and Optical Grade Spinel plates. With over $20 million of private investment by J.F. Lehman and Company, ArmorLine has installed and commissioned the largest vacuum hot press in the world, the largest high-temperature/high-pressure hot isostatic press in the world, and supporting manufacturing processes within 75,000 square feet of manufacturing space. ArmorLine's equipment is capable of producing window blanks as large as 50" x 30" and the facility is capable of producing substantial volumes of material with its Lean configuration and 24/7 operation. Initial production capability was achieved in 2012. ArmorLine will discuss the challenges that were encountered during scale-up of the manufacturing processes, ArmorLine Optical Grade Spinel optical performance, and provide an overview of the facility and its capabilities.

Influence of pH on structural morphology and magnetic properties of ordered phase cobalt doped lithium ferrites nanoparticles synthesized by sol-gel method

International Nuclear Information System (INIS)

Srivastava, Manish; Ojha, Animesh K.; Chaubey, S.; Sharma, Prashant K.; Pandey, Avinash C.

2010-01-01

Cobalt doped lithium ferrite nanoparticles were synthesized at different pH by sol-gel method. The effect of pH on the physical properties of cobalt doped lithium ferrite nanoparticles has been investigated. The nanoparticles synthesized at different pH were characterized through X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Raman spectroscopy (RS), Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and vibrating sample magnetometer (VSM). The XRD patterns were analyzed to determine the crystal phase of cobalt doped lithium ferrites nanoparticles synthesized at different pH. The XRD results show the formation of impurity free cobalt doped lithium ferrites having ordered phase spinel structure. A similar kind of conclusion was also drawn through the analysis of Raman spectra of the nanoparticles synthesized at different pH. SEM micrographs show that the structural morphology of the nanoparticles is highly sensitive to the pH during the synthesis process. The magnetic properties such as; saturation magnetization (Ms), remnant magnetization (Mr) and coercivety (Hc) have been also investigated and found to be different for the nanoparticles synthesized at different pH, which may be attributed to the different size and surface morphology of the nanoparticles.

Investigation on a Novel Discontinuous Pulse-Width Modulation Algorithm for Single-phase Voltage Source Rectifier

DEFF Research Database (Denmark)

Qu, Hao; Yang, Xijun; Guo, Yougui

2014-01-01

Single-phase voltage source converter (VSC) is an important power electronic converter (PEC), including single-phase voltage source inverter (VSI), single-phase voltage source rectifier (VSR), single-phase active power filter (APF) and single-phase grid-connection inverter (GCI). Single-phase VSC...

Spinel dissolution via addition of glass forming chemicals. Results of preliminary experiments

Energy Technology Data Exchange (ETDEWEB)

Fox, K. M. [Savannah River Site (SRS), Aiken, SC (United States); Johnson, F. C. [Savannah River Site (SRS), Aiken, SC (United States)

2015-11-01

Increased loading of high level waste in glass can lead to crystallization within the glass. Some crystalline species, such as spinel, have no practical impact on the chemical durability of the glass, and therefore may be acceptable from both a processing and a product performance standpoint. In order to operate a melter with a controlled amount of crystallization, options must be developed for remediating an unacceptable accumulation of crystals. This report describes preliminary experiments designed to evaluate the ability to dissolve spinel crystals in simulated waste glass melts via the addition of glass forming chemicals (GFCs).

Phase Structure Of Fuzzy Field Theories And Multi trace Matrix Models

International Nuclear Information System (INIS)

Tekel, J.

2015-01-01

We review the interplay of fuzzy field theories and matrix models, with an emphasis on the phase structure of fuzzy scalar field theories. We give a self-contained introduction to these topics and give the details concerning the saddle point approach for the usual single trace and multi trace matrix models. We then review the attempts to explain the phase structure of the fuzzy field theory using a corresponding random matrix ensemble, showing the strength and weaknesses of this approach. We conclude with a list of challenges one needs to overcome and the most interesting open problems one can try to solve. (author)

True atomic-scale imaging of a spinel Li{sub 4}Ti{sub 5}O{sub 12}(111) surface in aqueous solution by frequency-modulation atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Kitta, Mitsunori, E-mail: m-kitta@aist.go.jp; Kohyama, Masanori [Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577 (Japan); Onishi, Hiroshi [Department of Chemistry, Graduate School of Science, Kobe University 1-1 Rokkodai, Nada, Kobe 657-8501 (Japan)

2014-09-15

Spinel-type lithium titanium oxide (LTO; Li{sub 4}Ti{sub 5}O{sub 12}) is a negative electrode material for lithium-ion batteries. Revealing the atomic-scale surface structure of LTO in liquid is highly necessary to investigate its surface properties in practical environments. Here, we reveal an atomic-scale image of the LTO(111) surface in LiCl aqueous solution using frequency-modulation atomic force microscopy. Atomically flat terraces and single steps having heights of multiples of 0.5 nm were observed in the aqueous solution. Hexagonal bright spots separated by 0.6 nm were also observed on the flat terrace part, corresponding to the atomistic contrast observed in the ultrahigh vacuum condition, which suggests that the basic atomic structure of the LTO(111) surface is retained without dramatic reconstruction even in the aqueous solution.

Atomic Structure of a Spinel-like Transition Al₂O₃ (100) Surface

DEFF Research Database (Denmark)

Jensen, Thomas Nørregaard; Meinander, Kristoffer; Helveg, Stig

2014-01-01

We study a crystalline epitaxial alumina thin film with the characteristics of a spinel-type transition Al2O3(100) surface by using atom-resolved noncontact atomic force microscopy and density functional theory. It is shown that the films are terminated by an Al-O layer rich in Al vacancies......, exhibiting a strong preference for surface hydroxyl group formation in two configurations. The transition alumina films are crystalline and perfectly stable in ambient atmospheres, a quality which is expected to open the door to new fundamental studies of the surfaces of transition aluminas....

Experimental and ab initio investigations on textured Li–Mn–O spinel thin film cathodes

Energy Technology Data Exchange (ETDEWEB)

Fischer, J., E-mail: Julian.Fischer@kit.edu [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Music, D. [RWTH Aachen University, Materials Chemistry, Kopernikusstrasse 10, 52074 Aachen (Germany); Bergfeldt, T.; Ziebert, C.; Ulrich, S.; Seifert, H.J. [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)

2014-12-01

This paper describes the tailored preparation of nearly identical lithium–manganese–oxide thin film cathodes with different global grain orientations. The thin films were synthesized by rf magnetron sputtering from a LiMn{sub 2}O{sub 4}-target in a pure argon plasma. Under appropriate processing conditions, thin films with a cubic spinel structure and a nearly similar density and surface topography but different grain orientation, i.e. (111)- and (440)-textured films, were achieved. The chemical composition was determined by inductively coupled plasma optical emission spectroscopy and carrier gas hot extraction. The constitution- and microstructure were evaluated by X-ray diffraction and Raman spectroscopy. The surface morphology and roughness were investigated by scanning electron and atomic force microscopy. The differently textured films represent an ideal model system for studying potential effects of grain orientation on the lithium ion diffusion and electrochemical behavior in LiMn{sub 2}O{sub 4}-based thin films. They are nearly identical in their chemical composition, atomic bonding behavior, surface-roughness, morphology and thickness. Our initial ab initio molecular dynamics data indicate that Li ion transport is faster in (111)-textured structure than in (440)-textured one. - Highlights: • Thin film model system of differently textured cubic Li–Mn–O spinels. • Investigation of the Li–Mn–O thin film mass density by X-ray reflectivity. • Ab initio molecular dynamics simulation on Li ion diffusion in LiMn{sub 2}O{sub 4}.

Experimental and ab initio investigations on textured Li–Mn–O spinel thin film cathodes

International Nuclear Information System (INIS)

Fischer, J.; Music, D.; Bergfeldt, T.; Ziebert, C.; Ulrich, S.; Seifert, H.J.

2014-01-01

This paper describes the tailored preparation of nearly identical lithium–manganese–oxide thin film cathodes with different global grain orientations. The thin films were synthesized by rf magnetron sputtering from a LiMn 2 O 4 -target in a pure argon plasma. Under appropriate processing conditions, thin films with a cubic spinel structure and a nearly similar density and surface topography but different grain orientation, i.e. (111)- and (440)-textured films, were achieved. The chemical composition was determined by inductively coupled plasma optical emission spectroscopy and carrier gas hot extraction. The constitution- and microstructure were evaluated by X-ray diffraction and Raman spectroscopy. The surface morphology and roughness were investigated by scanning electron and atomic force microscopy. The differently textured films represent an ideal model system for studying potential effects of grain orientation on the lithium ion diffusion and electrochemical behavior in LiMn 2 O 4 -based thin films. They are nearly identical in their chemical composition, atomic bonding behavior, surface-roughness, morphology and thickness. Our initial ab initio molecular dynamics data indicate that Li ion transport is faster in (111)-textured structure than in (440)-textured one. - Highlights: • Thin film model system of differently textured cubic Li–Mn–O spinels. • Investigation of the Li–Mn–O thin film mass density by X-ray reflectivity. • Ab initio molecular dynamics simulation on Li ion diffusion in LiMn 2 O 4

Coincident site lattice-matched InGaN on (111) spinel substrates

International Nuclear Information System (INIS)

Norman, A. G.; Dippo, P. C.; Moutinho, H. R.; Simon, J.; Ptak, A. J.

2012-01-01

Coincident site lattice-matched wurtzite (0001) In 0.31 Ga 0.69 N, emitting in the important green wavelength region, is demonstrated by molecular beam epitaxy on a cubic (111) MgAl 2 O 4 spinel substrate. The coincident site lattice matching condition involves a 30 deg. rotation between the lattice of the InGaN epitaxial layer and the lattice of the spinel. This work describes an alternative approach towards realizing more compositionally homogenous InGaN films with low dislocation density emitting in the ''green gap'' of low efficiency currently observed for semiconductor light emitting diodes (LEDs). This approach could lead to higher efficiency green LEDs presently of great interest for solid-state lighting applications.

Al and PEG effect on structural and physicochemical properties of CoFe{sub 2}O{sub 4}

Energy Technology Data Exchange (ETDEWEB)

Mostaghni, Fatemeh; Abed, Yasaman, E-mail: mostaghnif@yahoo.com [Payam Noor University (Iran, Islamic Republic of)

2017-05-15

In this work, pure and Alumina doped cobalt ferrite nanoparticles CoFe{sub 2-x}Al{sub x}O{sub 4} (for x = 0.44) have been synthesized by the sol gel method. The influence of alumina doping on the morphological and mechanical properties of CoFe{sub 2}O{sub 4} nano-particles were investigated by means of X-ray powder diffraction (XRD) and Rietveld analysis. XRD analysis confirmed that the single phase formation of pure nano particles with the expected cubic inverse spinel structure with Fd3m space group and without any impurity phase. Alumina doping were led to a decrease in the crystallite size, lattice parameter, elastic constants and magnitude of moduli. It is explained on the basis of the replacement of Fe ions with half-filled d-shell (3d{sup 5}) and larger radius by Al{sup 3+} ions with a completely filled shell (2p{sup 6}) and smaller radius. (author)

Shear-induced structural transitions in Newtonian non-Newtonian two-phase flow

Science.gov (United States)

Cristobal, G.; Rouch, J.; Colin, A.; Panizza, P.

2000-09-01

We show the existence under shear flow of steady states in a two-phase region of a brine-surfactant system in which lyotropic dilute lamellar (non-Newtonian) and sponge (Newtonian) phases are coexisting. At high shear rates and low sponge phase-volume fractions, we report on the existence of a dynamic transition corresponding to the formation of a colloidal crystal of multilamellar vesicles (or ``onions'') immersed in the sponge matrix. As the sponge phase-volume fraction increases, this transition exhibits a hysteresis loop leading to a structural bistability of the two-phase flow. Contrary to single phase lamellar systems where it is always 100%, the onion volume fraction can be monitored continuously from 0 to 100 %.

Phase locking of a semiconductor double-quantum-dot single-atom maser

Science.gov (United States)

Liu, Y.-Y.; Hartke, T. R.; Stehlik, J.; Petta, J. R.

2017-11-01

We experimentally study the phase stabilization of a semiconductor double-quantum-dot (DQD) single-atom maser by injection locking. A voltage-biased DQD serves as an electrically tunable microwave frequency gain medium. The statistics of the maser output field demonstrate that the maser can be phase locked to an external cavity drive, with a resulting phase noise L =-99 dBc/Hz at a frequency offset of 1.3 MHz. The injection locking range, and the phase of the maser output relative to the injection locking input tone are in good agreement with Adler's theory. Furthermore, the electrically tunable DQD energy level structure allows us to rapidly switch the gain medium on and off, resulting in an emission spectrum that resembles a frequency comb. The free running frequency comb linewidth is ≈8 kHz and can be improved to less than 1 Hz by operating the comb in the injection locked regime.

Analysis of free-surface flows through energy considerations: Single-phase versus two-phase modeling.

Science.gov (United States)

Marrone, Salvatore; Colagrossi, Andrea; Di Mascio, Andrea; Le Touzé, David

2016-05-01

The study of energetic free-surface flows is challenging because of the large range of interface scales involved due to multiple fragmentations and reconnections of the air-water interface with the formation of drops and bubbles. Because of their complexity the investigation of such phenomena through numerical simulation largely increased during recent years. Actually, in the last decades different numerical models have been developed to study these flows, especially in the context of particle methods. In the latter a single-phase approximation is usually adopted to reduce the computational costs and the model complexity. While it is well known that the role of air largely affects the local flow evolution, it is still not clear whether this single-phase approximation is able to predict global flow features like the evolution of the global mechanical energy dissipation. The present work is dedicated to this topic through the study of a selected problem simulated with both single-phase and two-phase models. It is shown that, interestingly, even though flow evolutions are different, energy evolutions can be similar when including or not the presence of air. This is remarkable since, in the problem considered, with the two-phase model about half of the energy is lost in the air phase while in the one-phase model the energy is mainly dissipated by cavity collapses.

Molecular dynamics simulations of spinels: LiMn2O4 and Li4Mn5O12 at high temperatures

International Nuclear Information System (INIS)

Ledwaba, R S; Matshaba, M G; Ngoepe, P E

2015-01-01

Energy storage technologies are critical in addressing the global challenge of clean sustainable energy. Spinel lithium manganates have attracted attention due to their electrochemical properties and also as promising cathode materials for lithium-ion batteries. The current study focused on the effects of high temperatures on the materials, in order to understand the sustainability in cases where the battery heats up to high temperature and analysis of lithium diffusion aids in terms of intercalation host compatibility. It is also essential to understand the high temperature behaviour and lithium ion host capability of these materials in order to perform the armorphization and recrystalization of spinel nano-architectures. Molecular dynamics simulations carried out to predict high temperature behaviour of the spinel systems. The NVE ensemble was employed, in the range 300 - 3000K. The melting temperature, lithium-ion diffusion and structural behaviour were monitored in both supercell systems. LiMn 2 O 4 indicated a diffusion rate that increased rapidly above 1500K, just before melting (∼1700K) and reached its maximum diffusion at 2.756 × 10 -7 cm 2 s -1 before it decreased. Li 4 Mn 5 O 12 indicated an exponential increase above 700K reaching 8.303 × 10 −7 cm 2 s −1 at 2000K and allowing lithium intercalation even above its melting point of around 1300K. This indicated better structural stability of Li 4 Mn 5 O 12 and capability to host lithium ions at very high temperatures (up to 3000 K) compared to LiMn 2 O 4 . (paper)

Nanocrystalline spinel ferrites by solid state reaction route

Indian Academy of Sciences (India)

Wintec

Nanocrystalline spinel ferrites by solid state reaction route. T K KUNDU* and S MISHRA. Department of Physics, Visva-Bharati, Santiniketan 731 235, India. Abstract. Nanostructured NiFe2O4, MnFe2O4 and (NiZn)Fe2O4 were synthesized by aliovalent ion doping using conventional solid-state reaction route. With the ...

Synthesis and magnetic properties of Zn Spinel ceramics

Czech Academy of Sciences Publication Activity Database

Huber, Š.; Sofer, Z.; Nádherný, L.; Jankovský, O.; Šimek, P.; Sedmidubský, D.; Maryško, Miroslav

2013-01-01

Roč. 57, č. 2 (2013), s. 162-166 ISSN 0862-5468 R&D Projects: GA ČR GA13-17538S; GA MŠk(CZ) 7AMB12FR019 Institutional support: RVO:68378271 Keywords : Zn spinel * synthesis * magnetic properties * antiferromagnet * bulk ZnO Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.434, year: 2013

Formation of graphene-like 2D spinel MnCo₂O₄ and its lithium storage properties

DEFF Research Database (Denmark)

Huang, Guoyong; Guo, Xueyi; Cao, Xiao

2017-01-01

Two-dimensional (2D) materials fulfill the requirements for fast lithium storage due to the large exposed surface area and the open shortened path for Li insertion/extraction. Novel graphene-like 2D spinel MnCo2O4 powders have been synthesized, which inherit the morphology and structure of specia...

First-principle investigation on stability of Co-doped spinel λ-Mn4-xCoxO8

Institute of Scientific and Technical Information of China (English)

HUANG Ke-long; CHEN Chun-an; LIU Su-qin; LUO Qiong; LIU Zhi-guo

2007-01-01

The mechanism of stability of Co-doped spinel λ-MnO2 that is referred to as spinel LiχMn2O4 (χ=0) was studied by using the first-principle calculation method. The total energy and formation enthalpy can be decreased remarkably due to the Co substation,resulting in a more stable structure of λ-MnχCr2-χO4. The bond order and DOS analysis were given in detail to explain the nature of stability improvement. The calculated results show that as the content of Co dopant increases, the bond order of Mn-O becomes larger and the peak of density of states around Fermi level shifts toward lower energy. The charge density distribution illustrates that the Mn-O bonding is ionic and partially covalent, and the covalent Mn-O bonding becomes stronger with the increase of Co dopant content. The results confirm that the Co-doping will enhance the stability of λ-MnO2 and hence improve the electrochemistry performance of LiχMn2O4.

Local probing spinel and perovskite complex magnetic systems

CERN Document Server

De Pinho Oliveira, Goncalo; Lima Lopes, Armandina Maria

Materials with multifunctional physical properties are crucial for the modern society, especially those which display a strong coupling between magnetic, lattice and polar degrees of freedom. This by far unexploited capability promises new paradigm-shift technologies for cooling technologies, magnetic data storage, high-frequency magnetic devices, spintronics, and micro-electromechanical systems. Alongside with the understanding of the properties of these materials, the need to improve them and to make them smaller and more efficient is a current goal. Device miniaturization towards very high-density data storage stands also as a trend in modern science and technology. Here, the integration of several functions into one material system has become highly desirable. Research in this area has already highlighted complex magnetic materials with po- tential for multifunctional applications based on spinel type structures like CdMn2O4 or multiferroic CdCr2S4 or even RCrO3 with orthorhombically distorted perovskite ...

Single-shot mega-electronvolt ultrafast electron diffraction for structure dynamic studies of warm dense matter

Energy Technology Data Exchange (ETDEWEB)

Mo, M. Z., E-mail: mmo09@slac.stanford.edu; Shen, X.; Chen, Z.; Li, R. K.; Dunning, M.; Zheng, Q.; Weathersby, S. P.; Reid, A. H.; Coffee, R.; Makasyuk, I.; Edstrom, S.; McCormick, D.; Jobe, K.; Hast, C.; Glenzer, S. H.; Wang, X. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Sokolowski-Tinten, K. [Faculty of Physics and Centre for Nanointegration Duisburg-Essen, University of Duisburg-Essen, Lotharstrasse 1, D-47048 Duisburg (Germany)

2016-11-15

We have developed a single-shot mega-electronvolt ultrafast-electron-diffraction system to measure the structural dynamics of warm dense matter. The electron probe in this system is featured by a kinetic energy of 3.2 MeV and a total charge of 20 fC, with the FWHM pulse duration and spot size at sample of 350 fs and 120 μm respectively. We demonstrate its unique capability by visualizing the atomic structural changes of warm dense gold formed from a laser-excited 35-nm freestanding single-crystal gold foil. The temporal evolution of the Bragg peak intensity and of the liquid signal during solid-liquid phase transition are quantitatively determined. This experimental capability opens up an exciting opportunity to unravel the atomic dynamics of structural phase transitions in warm dense matter regime.

Single-crystal neutron diffraction study of ammonium nitrate phase III

International Nuclear Information System (INIS)

Choi, C.S.; Prask, H.J.

1982-01-01

The crystal structure of ammonium nitrate phase III has been studied at room temperature by neutron diffraction using a single crystal containing 5% KNO 3 in solid-solution form. The space group is Pnma, with a = 7.6772 (4), b = 5.8208 (4), c = 7.1396 (5) A, Z = 4. The final residual after full-matrix least-squares refinement was R = 0.042 for 348 observed reflections. The ammonium ions are thermally disordered into two orientations, displaced by an angle of approximately 42 0 about an axis parallel to the c axis. (Auth.)

Reinvestigation of the structures of lithium-cobalt-oxides with neutron-diffraction data

CSIR Research Space (South Africa)

Gummow, RJ

1993-11-01

Full Text Available an ideal layered and an ideal lithiated spinel structure. On the other hand, refinement of the data of LT-Li0.4CoO2 prepared by reacting LT-LiCoO2 with acid shows, unequivocally, that a spinel-type structure is formed. These structures are discussed...

Phase equilibria and phase structures of polymer blends

International Nuclear Information System (INIS)

Chalykh, Anatolii E; Gerasimov, Vladimir K

2004-01-01

Experimental, methodical and theoretical studies dealing with phase equilibria and phase structures of polymer blends are generalised. The general and specific features of the change in solubility of polymers with changes in the molecular mass and copolymer composition and upon the formation of three-dimensional cross-linked networks are described. The results of the effect of the prehistory on the phase structure and the non-equilibrium state of polymer blends are considered in detail.

A novel single-phase flux-switching permanent magnet linear generator used for free-piston Stirling engine

Science.gov (United States)

Zheng, Ping; Sui, Yi; Tong, Chengde; Bai, Jingang; Yu, Bin; Lin, Fei

2014-05-01

This paper investigates a novel single-phase flux-switching permanent-magnet (PM) linear machine used for free-piston Stirling engines. The machine topology and operating principle are studied. A flux-switching PM linear machine is designed based on the quasi-sinusoidal speed characteristic of the resonant piston. Considering the performance of back electromotive force and thrust capability, some leading structural parameters, including the air gap length, the PM thickness, the ratio of the outer radius of mover to that of stator, the mover tooth width, the stator tooth width, etc., are optimized by finite element analysis. Compared with conventional three-phase moving-magnet linear machine, the proposed single-phase flux-switching topology shows advantages in less PM use, lighter mover, and higher volume power density.

MECHANICAL CHARACTERISTICS OF THREE-PHASE INDUCTION MOTORS WITH SINGLE-PHASE POWER SUPPLY

Directory of Open Access Journals (Sweden)

V.S. Malyar

2016-06-01

Full Text Available Aim. Development of a method for calculating mechanical characteristics of three-phase induction motors with single-phase power supply. Methods. The developed algorithm is based on the high-adequacy mathematical model of motor and projection method for solving the boundary problem for equations of electrical circuits balance presented in the three-phase coordinate system. As a result of asymmetry of power supply to the stator windings, in steady state, flux-linkage and current change according to the periodic law. They are determined by solving the boundary problem. Results. The developed mathematical model allows determining periodic dependence of coordinates as a function of slip and, based on them, mechanical characteristics of motors. Academic novelty. The developed method relies on a completely new mathematical approach to calculation of stationary modes of nonlinear electromagnetic circuits, which allows obtaining periodic solution in a timeless domain. Practical value. Using the developed calculation algorithm, one can select capacitance required to start an induction motor with single-phase power supply and calculate static mechanical characteristics at a given capacitance.

Coincident site lattice-matched InGaN on (111) spinel substrates

Energy Technology Data Exchange (ETDEWEB)

Norman, A. G.; Dippo, P. C.; Moutinho, H. R.; Simon, J.; Ptak, A. J. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)

2012-04-09

Coincident site lattice-matched wurtzite (0001) In{sub 0.31}Ga{sub 0.69}N, emitting in the important green wavelength region, is demonstrated by molecular beam epitaxy on a cubic (111) MgAl{sub 2}O{sub 4} spinel substrate. The coincident site lattice matching condition involves a 30 deg. rotation between the lattice of the InGaN epitaxial layer and the lattice of the spinel. This work describes an alternative approach towards realizing more compositionally homogenous InGaN films with low dislocation density emitting in the ''green gap'' of low efficiency currently observed for semiconductor light emitting diodes (LEDs). This approach could lead to higher efficiency green LEDs presently of great interest for solid-state lighting applications.

Volatile-rich komatiitic and picritic melt inclusions in Cr-spinel beach sand from Gorgona Island, Colombia

Science.gov (United States)

Shimizu, K.; Shimizu, N.; Suzuki, K.; Tatsumi, Y.; Komiya, T.; Maruyama, S.

2007-12-01

Volatile content of komatiite is a key to constrain thermal evolution of the deep Earth. We report volatile contents with major and trace element compositions of melt inclusions (MIs) in chromian spinel (Cr-spinel) from beach sands of Gorgona Island, Colombia. Gorgona Island is ~90 Ma volcanic island, where picrites and the world-youngest komatiites occur. As Cr-spinel is dense and rigid oxide mineral that crystallizes only at early stages of crystallization, it is considered to be a superior container for retaining primitive melt, even including volatiles. Volatile (H2O, CO2, S, F and Cl) and trace element (K2O, Sr, Y, Zr, Nb, Ba, La, Ce, Sm, Dy, Yb) compositions of ~80 MIs were analyzed by SIMS (Cameca-1280 and 3f, respectively) at WHOI. MIs in the Cr-spinel from Gorgona Is. are classified into three types by their host Cr-spinel compositions such as low-Ti (P-type), high-Ti with high-Cr# (BK-type) and high-Ti with low-Cr# (K-type). MIs of P-type, BK-type and K-type are mostly in compositional ranges of picrite, high TiO2 komatiite (some basalt) and low TiO2 komatiite in Gorgona Island, respectively. Water content of P-type MIs is variable, ranging from 0.05 to 0.9 wt%, whereas those of BK and K-type MIs are limited (500 ppm) do not contain (shrinkage) bubbles and many of them are low in K2O. H2O/K2O, CO2/K2O, S/K2O and F/K2O ratios are positively correlated with Y/Sr ratios, indicating degassing trends of melt at crystallization, magma mixing and/or assimilation. Undegassed H2O/K2O, CO2/K2O, S/K2O and F/K2O ratios of komatiitic (picritic) melt are estimated to be ~10 (~40), ~80 (n.d.), ~7(~3) and ~1(~0.5), respectively, which are much higher than those estimated for the depleted source mantle of the MORB [1.6, 0.7, 1.6 and 0.2, respectively; Salters, V. & Stracke, A. (2004), Composition of the depleted mantle. Geochem. Geophys. Geosys. 5 (2003GC000597)]. The results suggest that Gorgona komatiite and picrite magmas were derived from volatile-rich sources. CO2

Adaptive nonlinear control of single-phase to three-phase UPS system

Directory of Open Access Journals (Sweden)

Kissaoui M.

2014-01-01

Full Text Available This work deals with the problems of uninterruptible power supplies (UPS based on the single-phase to three-phase converters built in two stages: an input bridge rectifier and an output three phase inverter. The two blocks are joined by a continuous intermediate bus. The objective of control is threefold: i power factor correction “PFC”, ii generating a symmetrical three-phase system at the output even if the load is unknown, iii regulating the DC bus voltage. The synthesis of controllers has been reached by two nonlinear techniques that are the sliding mode and adaptive backstepping control. The performances of regulators have been validated by numerical simulation in MATLAB / SIMULINK.

Synthesis, structural investigation and magnetic properties of Zn2+ substituted cobalt ferrite nanoparticles prepared by the sol–gel auto-combustion technique

International Nuclear Information System (INIS)

Raut, A.V.; Barkule, R.S.; Shengule, D.R.; Jadhav, K.M.

2014-01-01

Structural morphology and magnetic properties of the Co 1−x Zn x Fe 2 O 4 (0.0≤x≥1.0) spinel ferrite system synthesized by the sol–gel auto-combustion technique using nitrates of respective metal ions have been studied. The ratio of metal nitrates to citric acid was taken at 1:3. The as prepared powder of cobalt zinc ferrite was sintered at 600 °C for 12 h after TG/DTA thermal studies. Compositional stoichiometry was confirmed by energy dispersive analysis of the X-ray (EDAX) technique. Single phase cubic spinel structure of Co–Zn nanoparticles was confirmed by XRD data. The average crystallite size (t), lattice constant (a) and other structural parameters of zinc substituted cobalt ferrite nanoparticles were calculated from XRD followed by SEM and FTIR. It is observed that the sol–gel auto-combustion technique has many advantages for the synthesis of technologically applicable Co–Zn ferrite nanoparticles. The present investigation clearly shows the effect of the synthesis method and possible relation between magnetic properties and microstructure of the prepared samples. Increase in nonmagnetic Zn 2+ content in cobalt ferrite nanoparticles is followed by decrease in n B , M s and other magnetic parameters. Squareness ratio for the Co-ferrite was 1.096 at room temperature. - Highlights: • Co–Zn nanoparticles are prepared by sol–gel auto-combustion method. • Structural properties were characterized by XRD, SEM, and FTIR. • Compositional stoichiometry was confirmed by EDAX analysis. • Magnetic parameters were measured by the pulse field hysteresis loop technique

Cations in Octahedral Sites: A Descriptor for Oxygen Electrocatalysis on Transition-Metal Spinels

Energy Technology Data Exchange (ETDEWEB)

Wei, Chao; Feng, Zhenxing; Scherer, Günther G.; Barber, James; Shao-Horn, Yang; Xu, Zhichuan J. (Nanyang); (ICL); (Oregon State U.); (TUM-CREATE); (MIT)

2017-04-10

Exploring efficient and low-cost electrocatalysts for the oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER) is critical for developing renewable energy technologies such as fuel cells, metal–air batteries, and water electrolyzers. A rational design of a catalyst can be guided by identifying descriptors that determine its activity. Here, a descriptor study on the ORR/OER of spinel oxides is presented. With a series of MnCo2O4, the Mn in octahedral sites is identified as an active site. This finding is then applied to successfully explain the ORR/OER activities of other transition-metal spinels, including MnxCo3-xO4 (x = 2, 2.5, 3), LixMn2O4 (x = 0.7, 1), XCo2O4 (X = Co, Ni, Zn), and XFe2O4 (X = Mn, Co, Ni). A general principle is concluded that the eg occupancy of the active cation in the octahedral site is the activity descriptor for the ORR/OER of spinels, consolidating the role of electron orbital filling in metal oxide catalysis.

RHEED oscillations in spinel ferrite epitaxial films grown by conventional planar magnetron sputtering

Science.gov (United States)

Ojima, T.; Tainosho, T.; Sharmin, S.; Yanagihara, H.

2018-04-01

Real-time in situ reflection high energy electron diffraction (RHEED) observations of Fe3O4, γ-Fe2O3, and (Co,Fe)3O4 films on MgO(001) substrates grown by a conventional planar magnetron sputtering was studied. The change in periodical intensity of the specular reflection spot in the RHEED images of three different spinel ferrite compounds grown by two different sputtering systems was examined. The oscillation period was found to correspond to the 1/4 unit cell of each spinel ferrite, similar to that observed in molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) experiments. This suggests that the layer-by-layer growth of spinel ferrite (001) films is general in most physical vapor deposition (PVD) processes. The surfaces of the films were as flat as the surface of the substrate, consistent with the observed layer-by-layer growth process. The observed RHEED oscillation indicates that even a conventional sputtering method can be used to control film thickness during atomic layer depositions.

RHEED oscillations in spinel ferrite epitaxial films grown by conventional planar magnetron sputtering

Directory of Open Access Journals (Sweden)

T. Ojima

2018-04-01

Full Text Available Real-time in situ reflection high energy electron diffraction (RHEED observations of Fe3O4, γ-Fe2O3, and (Co,Fe3O4 films on MgO(001 substrates grown by a conventional planar magnetron sputtering was studied. The change in periodical intensity of the specular reflection spot in the RHEED images of three different spinel ferrite compounds grown by two different sputtering systems was examined. The oscillation period was found to correspond to the 1/4 unit cell of each spinel ferrite, similar to that observed in molecular beam epitaxy (MBE and pulsed laser deposition (PLD experiments. This suggests that the layer-by-layer growth of spinel ferrite (001 films is general in most physical vapor deposition (PVD processes. The surfaces of the films were as flat as the surface of the substrate, consistent with the observed layer-by-layer growth process. The observed RHEED oscillation indicates that even a conventional sputtering method can be used to control film thickness during atomic layer depositions.

Dynamics of mineral crystallization from precipitated slab-derived fluid phase: first in situ synchrotron X-ray measurements

Science.gov (United States)

Malaspina, Nadia; Alvaro, Matteo; Campione, Marcello; Wilhelm, Heribert; Nestola, Fabrizio

2015-03-01

Remnants of the fluid phase at ultrahigh pressure (UHP) in subduction environments may be preserved as primary multiphase inclusions in UHP minerals. The mode of crystallization of daughter minerals during precipitation within the inclusion and/or the mechanism of interaction between the fluid at supercritical conditions and the host mineral are still poorly understood from a crystallographic point of view. A case study is represented by garnet-orthopyroxenites from the Maowu Ultramafic Complex (China) deriving from harzburgite precursors metasomatized at ~4 GPa, 750 °C by a silica- and incompatible trace element-rich fluid phase. This metasomatism produced poikilitic orthopyroxene and inclusion-rich garnet porphyroblasts. Solid multiphase primary inclusions in garnet display a size within a few tens of micrometres and negative crystal shapes. Infilling minerals (spinel: 10-20 vol%; amphibole, chlorite, talc, mica: 80-90 vol%) occur with constant volume proportions and derive from trapped solute-rich aqueous fluids. To constrain the possible mode of precipitation of daughter minerals, we performed for the first time a single-crystal X-ray diffraction experiment by synchrotron radiation at Diamond Light Source. In combination with electron probe microanalyses, this measurement allowed the unique identification of each mineral phase and reciprocal orientations. We demonstrated the epitaxial relationship between spinel and garnet and between some hydrous minerals. Such information is discussed in relation to the physico-chemical aspects of nucleation and growth, shedding light on the mode of mineral crystallization from a fluid phase trapped at supercritical conditions.

Influence of crystal structure on the CoII diffusion behavior in the Zn1-xCoxO system

International Nuclear Information System (INIS)

Peiteado, M.; Makovec, D.; Villegas, M.; Caballero, A.C.

2008-01-01

The solid state interaction of the Zn 1-x Co x O nominal system is investigated by means of diffusion couples and analysis of co-precipitated samples. The formation of a homogeneous Co:ZnO solid solution is found to be determined by the crystal structure from which Co II ions diffuse into the wurtzite lattice. No diffusion is observed whenever the CoO rock-salt structure is formed from the Co II precursor. On the contrary, the diffusion from the Co 3 O 4 spinel phase is feasible but has a limited temperature range defined by the reduction at a high temperature of Co III -Co II , since this process again leads to the formation of the rock-salt structure. However, when using a highly reactive and homogeneous co-precipitated starting powder, neither the spinel phase nor the rock-salt structure is formed, and a Co II :ZnO solid solution is obtained, which remains stable up to high temperatures. - Graphical abstract: Maximum diffusion distance for the ZnO-CoO x couple as a function of temperature. Dashed gray lines represent the temperature values at which the transformations between CoO and Co 3 O 4 compounds take place

Attestation in self-propagating combustion approach of spinel AFe_2O_4 (A = Co, Mg and Mn) complexes bearing mixed oxidation states: Magnetostructural properties

International Nuclear Information System (INIS)

Bennet, J.; Tholkappiyan, R.; Vishista, K.; Jaya, N. Victor; Hamed, Fathalla

2016-01-01

Highlights: • Spinel type ferrite compounds AFe_2O_4 (A = Co, Mg and Mn) have been successfully prepared by self-propagating combustion method using glycine as fuel. • To investigate and confirms the presence of phases in the synthesized ferrite nanoparticles by XRD and FTIR analysis. • The formation of mixed oxidation state of cobalt (Co"2"+ and Co"3"+), iron (Fe"2"+ and Fe"3"+) and manganese (Mn"2"+ and Mn"3"+) ions were studied and confirmed from XPS analysis. • The magnetic properties of the synthesized ferrites were studied by VSM measurement. - Abstract: Spinel type nano-sized ferrite compounds AFe_2O_4 (A = Co, Mg and Mn) have been successfully prepared by self-propagating combustion method using glycine as fuel at 400 °C under air atmosphere for 4 h. The crystal structure, chemical composition, morphology and magnetic properties of the synthesized samples were characterized by X−ray diffraction, Fourier transform infrared spectroscopy, X−ray photoelectron spectroscopy, Energy dispersive X−ray, Scanning and Transmission electron microscopy and vibrating sample magnetometer. The chemical reaction and role of fuel on the nanoparticles formation were discussed. The XRD pattern of the synthesized samples shows the formation of pure phase with average crystallite size of 97, 57 and 98 nm from Scherrer formula and 86, 54 and 87 nm from Williamson and Hall (W–H) formula respectively. FTIR absorption spectra revealed that the presence of strong absorption peaks near 400–600 cm"−"1 corresponds to tetrahedral and octahedral complex of spinel ferrites. The relative concentrations of electronic states of elements such as cobalt (Co"2"+ and Co"3"+), iron (Fe"2"+ and Fe"3"+) and manganese (Mn"2"+ and Mn"3"+) oxidation states were studied from XPS and it is found that 55% of Fe ions are in Fe"2"+ state and the remaining is in Fe"3"+ state and thus the cationic distribution of Fe ions occurred in both tetrahedral and octahedral sites. SEM analysis

Structural, electrical and magnetic properties of Sc{sup 3+} doped Mn-Zn ferrite nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Angadi, V. Jagdeesha [Department of Physics, Bangalore University, Bangalore 560056 (India); Choudhury, Leema [Department of Physics, K.G. Reddy College of Engineering & Technology, Moinabad, 501504 Ranga Reddy, Telangana (India); Sadhana, K. [Department of Physics, University College of Science, Osmania University, Saifabad, Hyderabad 500004 (India); Liu, Hsiang-Lin [Department of Physics, National Taiwan Normal University, Taipei 11677, Taiwan (China); Sandhya, R. [Department of Physics, University College of Science, Osmania University, Hyderabad 500007 (India); Matteppanavar, Shidaling; Rudraswamy, B.; Pattar, Vinayak; Anavekar, R.V. [Department of Physics, Bangalore University, Bangalore 560056 (India); Praveena, K., E-mail: praveenaou@gmail.com [Department of Physics, National Taiwan Normal University, Taipei 11677, Taiwan (China)

2017-02-15

Sc{sup 3+} doped Mn{sub 0.5}Zn{sub 0.5}Sc{sub y}Fe{sub 2−y}O{sub 4} (y=0.00, 0.01, 0.03 and 0.05) nanoparticles were synthesized by solution combustion method using mixture of fuels were reported for the first time. The mixture of fuels plays an important role in obtaining nano crystalline, single phase present without any heat treatment. X-ray diffraction (XRD) results confirm the formation of the single-phase ferrites which crystallize in cubic spinel structure. The Fourier transform infrared spectra (FTIR) exhibit two prominent bands around 360 cm{sup −1} and 540 cm{sup −1} which are characteristic feature of spinel ferrite. The transmission electron microscope (TEM) micrographs revealed the nanoparticles to be nearly spherical in shape and of fairly uniform size. The room temperature impedance spectra (IS) and vibrating sample magnetometry (VSM) measurements were carried out in order to study the effect of doping (Sc{sup 3+}) on the characteristic properties of Mn-Zn ferrites. Further, the frequency dependent dielectric constant and dielectric loss were found to decrease with increasing multiple Sc{sup 3+} concentration. Nyquist plot in the complex impedance spectra suggest the existence of multiple electrical responses. Magnetic measurements reveals that saturation magnetization (M{sub s}), remnant magnetization (M{sub r}), magnetic moment (η{sub B}) and magnetic particle size (D{sub m}) increase with Sc{sup 3+} ion concentration up to x=0.03 and then decrease. The values of spin canting angle (α{sub Y-K}) and the magnetic particle size (D{sub m}) are found to be in the range of 68–75° and 10–19 nm respectively with Sc{sup 3+} concentration. The room temperature Mössbauer spectra were fitted with two sextets corresponding to ions at tetrahedral (A-) and octahedral (B-) sites confirms the spinel lattice. The ferromagnetic resonance (FMR) spectra's has shown that high concentration of scandium doping leads to an increase in dipolar interaction

Synthesis and structural characterization of bulk Sb2Te3 single crystal

Science.gov (United States)

Sultana, Rabia; Gahtori, Bhasker; Meena, R. S.; Awana, V. P. S.

2018-05-01

We report the growth and characterization of bulk Sb2Te3 single crystal synthesized by the self flux method via solid state reaction route from high temperature melt (850˚C) and slow cooling (2˚C/hour) of constituent elements. The single crystal X-ray diffraction pattern showed the 00l alignment and the high crystalline nature of the resultant sample. The rietveld fitted room temperature powder XRD revealed the phase purity and rhombohedral structure of the synthesized crystal. The formation and analysis of unit cell structure further verified the rhombohedral structure composed of three quintuple layers stacked one over the other. The SEM image showed the layered directional growth of the synthesized crystal carried out using the ZEISS-EVOMA-10 scanning electron microscope The electrical resistivity measurement was carried out using the conventional four-probe method on a quantum design Physical Property Measurement System (PPMS). The temperature dependent electrical resistivity plot for studied Sb2Te3 single crystal depicts metallic behaviour in the absence of any applied magnetic field. The synthesis as well as the structural characterization of as grown Sb2Te3 single crystal is reported and discussed in the present letter.

Orientational Phase Transition Around 274 K in C60 Single Crystal

Institute of Scientific and Technical Information of China (English)

徐亚伯; 何丕模; 杨宏顺; 郑萍; 余朝文; 陈兆甲; 张宣嘉; 李文铸

1994-01-01

The electrical conductivity of a C60 single crystal around 274 K and the specific heat of C60 crystals from 150 to 340 K have been measured.The delta-like specific heat peak at about 251 K related to the first-order phase transition has been reported.The activation energy change around 274 K and the lambda-like specific heat peak beginning at 270 K and ending at 310 K show that there is an orientational phase transition in fcc C60 crystals above 251 K.By taking the symmetry into consideration and further analyzing lambda-like specific heat peak and the activation energy change around 274 K,the conclusion has been reached that this new phase transition is an orientational structure transition from the merohedral twinning fcc to the orientationally disordered fcc.The temperature of free rotation of C60 molecules is about 281 K.

Synthesis and characterization of nanosized Mg{sub x}Mn{sub 1−x}Fe{sub 2}O{sub 4} ferrites by both sol-gel and thermal decomposition methods

Energy Technology Data Exchange (ETDEWEB)

De-León-Prado, Laura Elena, E-mail: laura.elena.prado@gmail.com [Cinvestav-Unidad Saltillo, Av. Industria Metalúrgica #1062, Parque Industrial Saltillo-Ramos Arizpe, CP 25900, Ramos Arizpe, Coahuila, México (Mexico); Cortés-Hernández, Dora Alicia; Almanza-Robles, José Manuel; Escobedo-Bocardo, José Concepción; Sánchez, Javier; Reyes-Rdz, Pamela Yajaira; Jasso-Terán, Rosario Argentina [Cinvestav-Unidad Saltillo, Av. Industria Metalúrgica #1062, Parque Industrial Saltillo-Ramos Arizpe, CP 25900, Ramos Arizpe, Coahuila, México (Mexico); Hurtado-López, Gilberto Francisco [Centro de Investigación en Química Aplicada, Blvd. Enrique Reyna Hermosillo #140, CP 25294, Saltillo, Coahuila, México (Mexico)

2017-04-01

This work reports the synthesis of Mg{sub x}Mn{sub 1−x}Fe{sub 2}O{sub 4} (x=0–1) nanoparticles by both sol-gel and thermal decomposition methods. In order to determine the effect of synthesis conditions on the crystal structure and magnetic properties of the ferrites, the synthesis was carried out varying some parameters, including composition. By both methods it was possible to obtain ferrites having a single crystalline phase with cubic inverse spinel structure and a behavior near to that of superparamagnetic materials. Saturation magnetization values were higher for materials synthesized by sol-gel. Furthermore, in both cases particles have a spherical-like morphology and nanometric sizes (11–15 nm). Therefore, these materials can be used as thermoseeds for the treatment of cancer by magnetic hyperthermia. - Highlights: • Mg–Mn ferrites were synthesized by sol-gel and thermal decomposition methods. • Materials showed a single cubic inverse spinel crystalline structure. • Ferrites have a soft ferrimagnetic behavior close to superparamagnetic materials.

Effect of Large Negative Phase of Blast Loading on Structural Response of RC Elements

Directory of Open Access Journals (Sweden)

Syed Zubair Iman

2016-01-01

Full Text Available Structural response of reinforced concrete (RC elements for analysis and design are often obtained using the positive phase of the blast pressure curve disregarding the negative phase assuming insignificant contribution from the negative phase of the loading. Although, some insight on the effect of negative phase of blast pressure based on elastic single-degree-of-freedom (SDOF analysis was presented before, the influence of negative phase on different types of resistance functions of SDOF models and on realistic finite element analysis has not been explored. In this study, the effects of inclusion of pulse negative phase on structural response of RC elements from SDOF analysis and from more detailed finite element analysis have been investigated. Investigation of SDOF part has been conducted using MATLAB code that utilizes non-linear resistance functions of SDOF model. Detailed numerical investigation using finite element code DIANA was conducted on the significance of the negative phase on structural response. In the FE model, different support stiffness was used to explore the effect of support stiffness on the structural response due to blast negative phase. Results from SDOF and FE analyses present specific situations where the effect of large negative phase was found to be significant on the structural response of RC elements.