Finite element analysis of the tetragonal to monoclinic phase transformation during oxidation of zirconium alloys

Science.gov (United States)

Platt, P.; Frankel, P.; Gass, M.; Howells, R.; Preuss, M.

2014-11-01

Corrosion is a key limiting factor in the degradation of zirconium alloys in light water reactors. Developing a mechanistic understanding of the corrosion process offers a route towards improving safety and efficiency as demand increases for higher burn-up of fuel. Oxides formed on zirconium alloys are composed of both monoclinic and meta-stable tetragonal phases, and are subject to a number of potential mechanical degradation mechanisms. The work presented investigates the link between the tetragonal to monoclinic oxide phase transformation and degradation of the protective character of the oxide layer. To achieve this, Abaqus finite element analysis of the oxide phase transformation has been carried out. Study of the change in transformation strain energy shows how relaxation of oxidation induced stress and fast fracture at the metal-oxide interface could destabilise the tetragonal phase. Central to this is the identification of the transformation variant most likely to form, and understanding why twinning of the transformed grain is likely to occur. Development of transformation strain tensors and analysis of the strain components allows some separation of dilatation and shear effects. Maximum principal stress is used as an indication of fracture in the surrounding oxide layer. Study of the stress distributions shows the way oxide fracture is likely to occur and the differing effects of dilatation and shape change. Comparison with literature provides qualitative validation of the finite element simulations.

Finite element analysis of the tetragonal to monoclinic phase transformation during oxidation of zirconium alloys

International Nuclear Information System (INIS)

Platt, P.; Frankel, P.; Gass, M.; Howells, R.; Preuss, M.

2014-01-01

Corrosion is a key limiting factor in the degradation of zirconium alloys in light water reactors. Developing a mechanistic understanding of the corrosion process offers a route towards improving safety and efficiency as demand increases for higher burn-up of fuel. Oxides formed on zirconium alloys are composed of both monoclinic and meta-stable tetragonal phases, and are subject to a number of potential mechanical degradation mechanisms. The work presented investigates the link between the tetragonal to monoclinic oxide phase transformation and degradation of the protective character of the oxide layer. To achieve this, Abaqus finite element analysis of the oxide phase transformation has been carried out. Study of the change in transformation strain energy shows how relaxation of oxidation induced stress and fast fracture at the metal–oxide interface could destabilise the tetragonal phase. Central to this is the identification of the transformation variant most likely to form, and understanding why twinning of the transformed grain is likely to occur. Development of transformation strain tensors and analysis of the strain components allows some separation of dilatation and shear effects. Maximum principal stress is used as an indication of fracture in the surrounding oxide layer. Study of the stress distributions shows the way oxide fracture is likely to occur and the differing effects of dilatation and shape change. Comparison with literature provides qualitative validation of the finite element simulations

The giant piezoelectric effect: electric field induced monoclinic phase or piezoelectric distortion of the rhombohedral parent?

International Nuclear Information System (INIS)

Kisi, E H; Piltz, R O; Forrester, J S; Howard, C J

2003-01-01

Lead zinc niobate-lead titanate (PZN-PT) single crystals show very large piezoelectric strains for electric fields applied along the unit cell edges e.g. [001] R . It has been widely reported that this effect is caused by an electric field induced phase transition from rhombohedral (R3m) to monoclinic (Cm or Pm) symmetry in an essentially continuous manner. Group theoretical analysis using the computer program ISOTROPY indicates phase transitions between R3m and Cm (or Pm) must be discontinuous under Landau theory. An analysis of the symmetry of a strained unit cell in R3m and a simple expansion of the piezoelectric strain equation indicate that the piezoelectric distortion due to an electric field along a cell edge in rhombohedral perovskite-based ferroelectrics is intrinsically monoclinic (Cm), even for infinitesimal electric fields. PZN-PT crystals have up to nine times the elastic compliance of other piezoelectric perovskites and it might be expected that the piezoelectric strains are also very large. A field induced phase transition is therefore indistinguishable from the piezoelectric distortion and is neither sufficient nor necessary to understand the large piezoelectric response of PZN-PT

Novel monoclinic zirconolite in Bi2O3–CuO–Ta2O5 ternary system: Phase equilibria, structural and electrical properties

International Nuclear Information System (INIS)

Tan, K.B.; Chon, M.P.; Khaw, C.C.; Zainal, Z.; Taufiq Yap, Y.H.; Tan, P.Y.

2014-01-01

Highlights: • Novel BCT monoclinic zirconolite phase was prepared through solid state reaction. • Comprehensive study of reaction mechanism was performed by careful firing control. • Qualitative structural and phase analyses were conducted. • Electrical response in broad range of temperature and frequency was investigated. - Abstract: Synthesis of novel monoclinic zirconolite, Bi 1.92 Cu 0.08 (Cu 0.3 Ta 0.7 ) 2 O 7.06 (β-BCT) using solid state reaction had been finalised at the firing temperature of 900 °C over 24 h. The X–ray diffraction pattern of β-BCT was fully indexed on a monoclinic symmetry, space group, C2/c with lattice constants, a = 13.1052 (8), b = 7.6749 (5), c = 12.162 (6), α = γ = 90° and β = 101.32° (1), respectively. The reaction mechanism study indicated phase formation was greatly influenced by the reaction between intermediate bismuth tantalate binary phases and CuO at elevated temperatures. β-BCT was thermally stable up to a temperature of 900 °C and contained spherulite grains with sizes ranging from 1 to 14 μm. Electrical properties of this material were characterised over a broad temperature range covering temperatures from 10 K to 874 K. At the temperature of 304 K, two semicircles were discernible in complex Cole–Cole plot showing an insulating grain boundary with C gb = 6.63 × 10 −9 F cm −1 and a bulk response capacitance, C b = 6.74 × 10 −12 F cm −1 . The Power law frequency-dependent ac conductivity of β-BCT was apparent in three frequency regimes; a low–frequency plateau regime, a high-frequency plateau regime and a dispersive regime taking place in the temperature range of 220–576 K. The frequency-dependent ac conductivity of β-BCT with increasing temperature was attributed to the thermal activated electrical conduction mechanism within the structure

Monoclinic MB phase and phase instability in [110] field cooled Pb(Zn1/3Nb2/3)O3-4.5%PbTiO3 single crystals

Science.gov (United States)

Yao, Jianjun; Cao, Hu; Ge, Wenwei; Li, Jiefang; Viehland, D.

2009-08-01

We report the finding of a monoclinic MB phase in Pb(Zn1/3Nb2/3)O3-4.5%PbTiO3 single crystals. High precision x-ray diffraction investigations of [110] field cooled crystals have shown a transformation sequence of cubic(C)→tetragonal(T)→orthorhombic(O)→monoclinic(MB), which is different from that previously reported [A.-E. Renault et al., J. Appl. Phys. 97, 044105 (2005)]. Beginning in the zero-field-cooled condition at 383 K, a rhombohedral (R)→MB→O sequence was observed with increasing field. Coexisting MB and O phases were then found upon removal of field, which fully transformed to MB on cooling to room temperature.

Neutron powder investigation of the tetragonal to monoclinic phase transformation in undoped zirconia

International Nuclear Information System (INIS)

Boysen, H.; Frey, F.

1991-01-01

The tetragonal (t) to monoclinic (m) transformation in pure ZrO 2 was investigated by neutron powder diffraction at temperatures between 1900 K and room temperature. The results of a Rietveld analysis are compared with a previous investigation of the m → t transformation. The t → m transformation takes place near 1200 K (implaying a hysteresis of 300 K) and in a much smaller interval (about 150 K compared with about 600 K in the m → t case). There are no indications of a two-stage process as found for the m → t transformation. The structural parameters of the m phase depend only on temperature while those of the t phase differ at the same temperatures for the forward and reverse transformation. The temperature dependence of the lattice constants suggests an orientational relationship a t parallela m * and c t parallelb m . There are no macrostrains whereas the overall microstrain behaviour is similar in both cases, viz. the large microstrains present in both phases are released within the transformation regime. An analysis of temperature factors and diffuse background suggest dynamical disorder in the t phase and static disorder in the m phase. (orig.)

A monoclinic polymorph of theophylline

Directory of Open Access Journals (Sweden)

Shuo Zhang

2011-12-01

Full Text Available A monoclinic polymorph of theophylline, C7H8N4O2, has been obtained from a chloroform/methanol mixture by evaporation under ambient conditions. The new polymorph crystallizes with two molecules in the asymmetric unit. The structure features intermolecular N—H...O hydrogen bonds, resulting in the formation of dimers between two crystallographically different molecules; each molecule acts as both donor and acceptor.

Study of the cubic - to - monoclinic transformation in magnesia partially stabilized zirconia

International Nuclear Information System (INIS)

Muccillo, R.

1988-01-01

The transformation of the cubic phase to the stable monoclinic phase in ZrO 2 : 3%MgO quenched from 1450 0 C to RT has been studied by X-ray diffractometry in order to explain the thermal hysteresis in the electrical conductivity. The monoclinic-to-cubic ratio has been measured for samples annealed in the 500 0 C-1000 0 C temperature range. The results show that the decrease in the cubic phase content is the main responsible for the thermal hysteresis in the electrical conductivity of the magnesia partially stabilized zirconia solid electrolytes. (author) [pt

Novel monoclinic zirconolite in Bi{sub 2}O{sub 3}–CuO–Ta{sub 2}O{sub 5} ternary system: Phase equilibria, structural and electrical properties

Energy Technology Data Exchange (ETDEWEB)

Tan, K.B., E-mail: tankb@science.upm.my [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor (Malaysia); Chon, M.P. [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor (Malaysia); Khaw, C.C. [Department of Mechanical and Material Engineering, Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, 53300 Setapak, Kuala Lumpur (Malaysia); Zainal, Z.; Taufiq Yap, Y.H.; Tan, P.Y. [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor (Malaysia)

2014-04-01

Highlights: • Novel BCT monoclinic zirconolite phase was prepared through solid state reaction. • Comprehensive study of reaction mechanism was performed by careful firing control. • Qualitative structural and phase analyses were conducted. • Electrical response in broad range of temperature and frequency was investigated. - Abstract: Synthesis of novel monoclinic zirconolite, Bi{sub 1.92}Cu{sub 0.08}(Cu{sub 0.3}Ta{sub 0.7}){sub 2}O{sub 7.06} (β-BCT) using solid state reaction had been finalised at the firing temperature of 900 °C over 24 h. The X–ray diffraction pattern of β-BCT was fully indexed on a monoclinic symmetry, space group, C2/c with lattice constants, a = 13.1052 (8), b = 7.6749 (5), c = 12.162 (6), α = γ = 90° and β = 101.32° (1), respectively. The reaction mechanism study indicated phase formation was greatly influenced by the reaction between intermediate bismuth tantalate binary phases and CuO at elevated temperatures. β-BCT was thermally stable up to a temperature of 900 °C and contained spherulite grains with sizes ranging from 1 to 14 μm. Electrical properties of this material were characterised over a broad temperature range covering temperatures from 10 K to 874 K. At the temperature of 304 K, two semicircles were discernible in complex Cole–Cole plot showing an insulating grain boundary with C{sub gb} = 6.63 × 10{sup −9} F cm{sup −1} and a bulk response capacitance, C{sub b} = 6.74 × 10{sup −12} F cm{sup −1}. The Power law frequency-dependent ac conductivity of β-BCT was apparent in three frequency regimes; a low–frequency plateau regime, a high-frequency plateau regime and a dispersive regime taking place in the temperature range of 220–576 K. The frequency-dependent ac conductivity of β-BCT with increasing temperature was attributed to the thermal activated electrical conduction mechanism within the structure.

Evidence for photo-induced monoclinic metallic VO2 under high pressure

International Nuclear Information System (INIS)

Hsieh, Wen-Pin; Mao, Wendy L.; Trigo, Mariano; Reis, David A.; Andrea Artioli, Gianluca; Malavasi, Lorenzo

2014-01-01

We combine ultrafast pump-probe spectroscopy with a diamond-anvil cell to decouple the insulator-metal electronic transition from the lattice symmetry changing structural transition in the archetypal strongly correlated material vanadium dioxide. Coherent phonon spectroscopy enables tracking of the photo-excited phonon vibrational frequencies of the low temperature, monoclinic (M 1 )-insulating phase that transforms into the metallic, tetragonal rutile structured phase at high temperature or via non-thermal photo-excitations. We find that in contrast with ambient pressure experiments where strong photo-excitation promptly induces the electronic transition along with changes in the lattice symmetry, at high pressure, the coherent phonons of the monoclinic (M 1 ) phase are still clearly observed upon the photo-driven phase transition to a metallic state. These results demonstrate the possibility of synthesizing and studying transient phases under extreme conditions

Nucleation in stress-induced tetragonal-monoclinic transformation of constrained zirconia

International Nuclear Information System (INIS)

Chan, S.K.

1992-08-01

A theory for stress-induced tetragonal→monoclinic transformation of constrained zirconia is presented based on the assumption that when forcibly strained to a regime of absolute instability where the free energy density of the tetragonal phase has a negative curvature, the constrained tetragonal zirconia becomes unstable with respect to the development of a modulated strain pattern that will evolve into a band of twin monoclinic domains. The temperature range for such an instability, the critical size of the inclusion, the corresponding critical strain, and the periodicity of the modulation are derived in terms of parameters that can be related to the elastic stiffness coefficients of various orders of the inclusion and the shear modulus of the host matrix. An entirely different mechanism is suggested for the reverse monoclinic→tetragonal transformation because the monoclinic phase is metastable when the extrinsic stress is removed. Estimates for the parameters are inferred from a variety of experimental data for pure zirconia and the numerical values for the predicted physical quantities are obtained

Characteristics of the stress-induced formation of R-phase in ultrafine-grained NiTi shape memory wire

International Nuclear Information System (INIS)

Olbricht, J.; Yawny, A.; Pelegrina, J.L.; Eggeler, G.; Yardley, V.A.

2013-01-01

Highlights: •We investigated the stress-induced formation of R-phase in NiTi shape memory wires. •The R-phase related strains were isolated from the overall stress-strain-behavior. •The stress–strain characteristics of R-phase suggest a homogeneous transformation. •Thermography confirms the homogeneous R-phase formation in ultrafine-grained NiTi. -- Abstract: The transformation between the cubic B2 and monoclinic B19′ phases in ultrafine-grained pseudoelastic NiTi can occur as a two-step process involving the intermediate rhombohedral R-phase. Experimental work using differential scanning calorimetry, electrical resistance measurements and transmission electron microscopy has demonstrated the formation of this intermediate phase during thermal cycling and during mechanical loading. In the present paper, complementary mechanical and thermographic results are presented which allow to further assess the character of the stress-induced R-phase formation. The transformation from B2 to R-phase is demonstrated to occur homogeneously within the gauge length rather than via advancing Lüders-type transition regions as it is the case in the localized transformation from B2 or R-phase to B19′

Effects of monoclinic symmetry on the properties of biaxial liquid crystals

Science.gov (United States)

Solodkov, Nikita V.; Nagaraj, Mamatha; Jones, J. Cliff

2018-04-01

Tilted smectic liquid crystal phases such as the smectic-C phase seen in calamitic liquid crystals are usually treated using the assumption of biaxial orthorhombic symmetry. However, the smectic-C phase has monoclinic symmetry, thereby allowing disassociation of the principal optic and dielectric axes based on symmetry and invariance principles. This is demonstrated here by comparing optical and dielectric measurements for two materials with highly first-order direct transitions from nematic to smectic-C phases. The results show a high difference between the orientations of the principal axes sets, which is interpreted as the existence of two distinct cone angles for optical and dielectric frequencies. Both materials exhibit an increasing degree of monoclinic behavior with decreasing temperature. Due to fast switching speeds, ferroelectric smectic-C* materials are important for fast modulators and LCoS devices, where the dielectric biaxiality influences device operation.

Evidence for existence of functional monoclinic phase in sodium niobate based solid solution by powder neutron diffraction

Science.gov (United States)

Mishra, S. K.; Jauhari, Mrinal; Mittal, R.; Krishna, P. S. R.; Reddy, V. R.; Chaplot, S. L.

2018-04-01

We have carried out systematic temperature-dependent neutron diffraction measurements in conjunction with dielectric spectroscopy from 6 to 300 K for sodium niobate based compounds (1-x) NaNbO3-xBaTiO3 (NNBTx). The dielectric constant is measured as a function of both temperature and frequency. It shows an anomaly at different temperatures in cooling and heating cycles and exhibits a large thermal hysteresis of ˜150 K for the composition x = 0.03. The dielectric constant is found to be dispersive in nature and suggests a relaxor ferroelectric behavior. In order to explore structural changes as a function of temperature, we analyzed the powder neutron diffraction data for the compositions x = 0.03 and 0.05. Drastic changes are observed in the powder profiles near 2θ ˜ 30.6°, 32.1°, and 34.6° in the diffraction pattern below 200 K during cooling and above 190 K in heating cycles, respectively. The disappearance of superlattice reflection and splitting in main perovskite peaks provide a signature for structural phase transition. We observed stabilization of a monoclinic phase (Cc) at low temperature. This monoclinic phase is believed to provide a flexible polarization rotation and considered to be directly linked to the high performance piezoelectricity in materials. The thermal hysteresis for composition x = 0.03 is larger than that for x = 0.05. This suggests that the addition of BaTiO3 to NaNbO3 suppresses the thermal hysteresis. It is also observed that the structural phase transition temperature decreases upon increasing the dopant concentration.

Growth of potassium niobate micro-hexagonal tablets with monoclinic phase and its excellent piezoelectric property

Science.gov (United States)

Chen, Zhong; Huang, Jingyun; Wang, Ye; Yang, Yefeng; Wu, Yongjun; Ye, Zhizhen

2012-09-01

Potassium niobate micro-hexagonal tablets were synthesized through hydrothermal reaction with KOH, H2O and Nb2O5 as source materials by using a polycrystalline Al2O3 as substrate. X-ray diffraction, Raman spectra and selected area electron diffraction analysis results indicated that the tablets exhibit monoclinic phase structure and are highly crystallized. Meanwhile, piezoelectric property of the micro-hexagonal tablets was investigated. The as-synthesized tablets exhibit excellent piezoactivities in the experiments, and an effective piezoelectric coefficient of around 80 pm/V was obtained. The tablets have huge potential applications in micro/nano-integrated piezoelectric and optical devices.

Evidence for photo-induced monoclinic metallic VO{sub 2} under high pressure

Energy Technology Data Exchange (ETDEWEB)

Hsieh, Wen-Pin, E-mail: wphsieh@stanford.edu; Mao, Wendy L. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305 (United States); Trigo, Mariano [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Reis, David A. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Department of Photon Science and Applied Physics, Stanford University, Stanford, California 94305 (United States); Andrea Artioli, Gianluca; Malavasi, Lorenzo [Dipartimento di Chimica, Sezione di Chimica Fisica, INSTM (UdR Pavia), Università di Pavia, Viale Taramelli 16, 27100 Pavia (Italy)

2014-01-13

We combine ultrafast pump-probe spectroscopy with a diamond-anvil cell to decouple the insulator-metal electronic transition from the lattice symmetry changing structural transition in the archetypal strongly correlated material vanadium dioxide. Coherent phonon spectroscopy enables tracking of the photo-excited phonon vibrational frequencies of the low temperature, monoclinic (M{sub 1})-insulating phase that transforms into the metallic, tetragonal rutile structured phase at high temperature or via non-thermal photo-excitations. We find that in contrast with ambient pressure experiments where strong photo-excitation promptly induces the electronic transition along with changes in the lattice symmetry, at high pressure, the coherent phonons of the monoclinic (M{sub 1}) phase are still clearly observed upon the photo-driven phase transition to a metallic state. These results demonstrate the possibility of synthesizing and studying transient phases under extreme conditions.

First principles study of LiAlO2: new dense monoclinic phase under high pressure

Science.gov (United States)

Liu, Guangtao; Liu, Hanyu

2018-03-01

In this work, we have systematically explored the crystal structures of LiAlO2 at high pressures using crystal structure prediction method in combination with the density functional theory calculations. Besides the reported α, β, γ, δ and ɛ-phases, here we propose a new monoclinic ζ-LiAlO2 (C2/m) structure, which becomes thermodynamically and dynamically stable above 27 GPa. It is found that the cation coordination number increases from 4 to 6 under compression. Consisting of the compact {LiO6} and {AlO6} octahedrons, the newly-discovered ζ-phase possesses a very high density. Further electronic calculations show that LiAlO2 is still an insulator up to 60 GPa, and its bandgap increases upon compression. The present study advances our understanding on the crystal structures and high-pressure phase transitions of LiAlO2 that may trigger applications in multiple areas of industry and provoke more related basic science research.

Grain size dependent phase stabilities and presence of a monoclinic (Pm) phase in the MPB region of (1-x)Bi(Mg_1_/_2Ti_1_/_2)O_3_-_xPbTiO_3

International Nuclear Information System (INIS)

Upadhyay, A.; Singh, A.K.

2016-01-01

The results of the room temperature structural studies on (1-x)Bi(Mg_1_/_2Ti_1_/_2)O_3_-_xPbTiO_3 ceramics using Rietveld analysis of the powder X-ray diffraction data in the composition range 0.28≤x≤0.45 are presented. The morphotropic phase boundary region exhibits coexistence of monoclinic (space group Pm) and tetragonal (space group P4mm) phases in the composition range 0.33≤x≤0.40. The structure is nearly single phase monoclinic (space group Pm) in the composition range 0.28≤x≤0.32. The structure for the compositions with x≥0.45 is found to be predominantly tetragonal with space group P4mm. Rietveld refinement of the structure rules out the coexistence of rhombohedral and tetragonal phases in the morphotropic phase boundary region reported by earlier authors. The Rietveld structure analysis for the sample x=0.35 calcined at various temperatures reveals that phase fraction of the coexisting phases in the morphotropic phase boundary region varies with grain size. The structural parameters of the two coexisting phases also change slightly with changing grain size. (author)

Optical and magneto-optical properties of the monoclinic phase of the C{sub 70} crystal

Energy Technology Data Exchange (ETDEWEB)

Yaghobi, Mojtaba [Islamic Azad University, Ayatollah Amoli Branch, Amol (Iran, Islamic Republic of); Koohi, Ardavan, E-mail: m.yaghoubi@iauamol.ac.i [Plasma Physics and Nuclear Fusion Research School, Nuclear Science and Technology Research Institute, AEOI, Tehran (Iran, Islamic Republic of)

2010-12-15

Using the Hartree-Fock (HF) single-excitation configuration interaction (CI) model in conjunction with the local field method, the dielectric tensor, birefringence coefficient, circular dichroism, refractive index and effects of spatial dispersion on the dispersion relation for transverse normal polariton waves of the monoclinic phase of the C{sub 70} crystal are calculated. Our results indicate that the anisotropy of the C{sub 70} molecule remains in C{sub 70} solids. Also, our results on the effect of spatial dispersion, compared with the non-dispersive case, indicate that the coupling of the transverse electromagnetic field with the first and second excitonic states is very weak.

Characterization of a Diamond Ground Y-TZP and Reversion of the Tetragonal to Monoclinic Transformation.

Science.gov (United States)

Candido, L M; Fais, Lmg; Ferreira, E B; Antonio, S G; Pinelli, Lap

To characterize the surface of an yttria-stabilized zirconia (Y-TZP) ceramic after diamond grinding in terms of its crystalline phase, morphology, mean roughness (Ra), and wettability as well as to determine a thermal treatment to reverse the resulting tetragonal to monoclinic (t-m) transformation. Y-TZP specimens were distributed into different groups according to the actions (or no action) of grinding and irrigation. Grinding was accomplished using a diamond stone at a low speed. The samples were characterized by x-ray diffraction (XRD), scanning electron microscopy, goniometry, and profilometry. In situ high-temperature XRD was used to determine an annealing temperature to reverse the t-m transformation. Ra was submitted to the Kruskal-Wallis test, followed by the Dunn test (α=0.05). The volume fraction of the monoclinic phase and contact angle were submitted to one-way analysis of variance, followed by the Tukey test (α=0.05). Monoclinic zirconia was observed on the surface of samples after dry and wet grinding with a diamond stone. The volume fraction of the monoclinic phase was smaller on the dry ground samples (3.6%±0.3%) than on the wet ground samples (5.6%±0.3%). High-temperature XRD showed reversion of the t-m phase transformation, which started at 700°C and completed at 800°C in a conventional oven. Grinding with a diamond stone partially transformed the crystalline phase on the surface of a Y-TZP ceramic from tetragonal to monoclinic zirconia while simultaneously increasing the surface roughness and wettability. The t-m transformation could be reversed by heat treatment at 800°C or 900°C for 60 minutes or 1000°C for 30 minutes.

Fluency over the monoclinic zirconia indentation

International Nuclear Information System (INIS)

Pereira, A.S.; Jornada, J.A.H. da

1992-01-01

It was investigated the environment and the time dependence of the Vickers microhardness of monoclinic zirconia single-crystals. The samples were kept at room temperature and the identifications were performed for different environments (air, toluene and water). An indentation creep process was observed for the samples indented is moist media, indicating for a water activated plastic relaxation mechanism. The possible influence of such effect in the fatigue and phase transformations mechanisms of zirconia based ceramics is discussed. (author)

A study of the formation processes of the 2212 phase in the Bi-based superconductor systems. [BiSrCaCuO

Energy Technology Data Exchange (ETDEWEB)

Wai, Lo; Glowacki, B A [Interdisciplinary Research Centre in Superconductivity, Univ. of Cambridge (United Kingdom)

1992-04-15

A study towards the identification of the reactions contributing to and accompanying the formation of the 2212 phase from oxides and carbonates by solid state reaction processes was conducted. The formation processes were investigated by thermal analysis, powder X-ray diffractometry and AC magnetic susceptometry. The 2212 phase was found to form from reactions between the 2201 phases (the non-superconducting pseudo-tetragonal and the superconducting monoclinic phases), Bi{sub 6}Ca{sub 7}O{sub 16}, CuO and SrCO{sub 3}. The 2201 phases were produced by the reactions of Bi-Sr-Cu-O or Bi-Sr-O compounds with SrCO{sub 3} or CuO. The 2201 phases could also be formed through the direct reaction between Bi{sub 2}CuO{sub 4} and SrCO{sub 3}. (orig.).

Grain size dependent phase stabilities and presence of a monoclinic (Pm) phase in the morphotropic phase boundary region of (1−x)Bi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3}-xPbTiO{sub 3} piezoceramics

Energy Technology Data Exchange (ETDEWEB)

Upadhyay, Ashutosh; Singh, Akhilesh Kumar, E-mail: akhilesh-bhu@yahoo.com, E-mail: aksingh.mst@itbhu.ac.in [School of Materials Science and Technology, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005 (India)

2015-04-14

Results of the room temperature structural studies on (1−x)Bi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3}-xPbTiO{sub 3} ceramics using Rietveld analysis of the powder x-ray diffraction data in the composition range 0.28 ≤ x ≤ 0.45 are presented. The morphotropic phase boundary region exhibits coexistence of monoclinic (space group Pm) and tetragonal (space group P4 mm) phases in the composition range 0.33 ≤ x ≤ 0.40. The structure is nearly single phase monoclinic (space group Pm) in the composition range 0.28 ≤ x ≤ 0.32. The structure for the compositions with x ≥ 0.45 is found to be predominantly tetragonal with space group P4 mm. Rietveld refinement of the structure rules out the coexistence of rhombohedral and tetragonal phases in the morphotropic phase boundary region reported by earlier authors. The Rietveld structure analysis for the sample x = .35 calcined at various temperatures reveals that phase fraction of the coexisting phases in the morphotropic phase boundary region varies with grain size. The structural parameters of the two coexisting phases also change slightly with changing grain size.

In situ TEM observation of the growth and decomposition of monoclinic W18O49 nanowires

International Nuclear Information System (INIS)

Chen, C L; Mori, H

2009-01-01

The growth of monoclinic W 18 O 49 nanowires by heat treatment of a tungsten filament at ∼873 K and the decomposition of these nanowires under 200 keV electron irradiation at ∼1023 K have been investigated using in situ transmission electron microscopy (TEM). In situ TEM observation of the growth confirmed the vapor-solid growth mechanism of the monoclinic W 18 O 49 nanowires. In situ irradiation experiments revealed the formation of metallic bcc tungsten from monoclinic W 18 O 49 nanowires under 200 keV electron irradiation.

Monoclinic phase transformation and mechanical durability of zirconia ceramic after fatigue and autoclave aging.

Science.gov (United States)

Mota, Yasmine A; Cotes, Caroline; Carvalho, Rodrigo F; Machado, João P B; Leite, Fabíola P P; Souza, Rodrigo O A; Özcan, Mutlu

2017-10-01

This study evaluated the influence of two aging procedures on the biaxial flexural strength of yttria-stabilized tetragonal zirconia ceramics. Disc-shaped zirconia specimens and (ZE: E.max ZirCAD, Ivoclar; ZT: Zirkon Translucent, Zirkonzahn) (N = 80) (∅:12 mm; thickness:1.2 mm, ISO 6872) were prepared and randomly divided into four groups (n = 10 per group) according to the aging procedures: C: Control, no aging; M: mechanical cycling (2 × 10 6 cycles/3.8 Hz/200 N); AUT: Aging in autoclave at 134°C, 2 bar for 24 h; AUT + M: Autoclave aging followed by mechanical cycling. After aging, the transformed monoclinic zirconia (%) were evaluated using X-ray diffraction and surface roughness was measured using atomic force microscopy. The average grain size was measured by scanning electron microscopy and the specimens were submitted to biaxial flexural strength testing (1 mm/min, 1000 kgf in water). Data (MPa) were statistically analyzed using 2-way analysis of variance and Tukey's test (α = 0.05). Aging procedures significantly affected (p = 0.000) the flexural strength data but the effect of zirconia type was not significant (p = 0.657). AUT ZT (936.4 ± 120.9 b ) and AUT + M ZE (867.2 ± 49.3 b ) groups presented significantly higher values (p autoclave aging alone or with mechanical aging increased the flexure strength but also induced higher transformation from tetragonal to monoclinic phase in both zirconia materials tested. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1972-1977, 2017. © 2016 Wiley Periodicals, Inc.

Synthesis, characterization and formation mechanism of metastable phase VO2(A) nanorods

International Nuclear Information System (INIS)

Cheng, X.H.; Xu, H.F.; Wang, Z.Z.; Zhu, K.R.; Li, G.; Jin, Shaowei

2013-01-01

Graphical abstract: - Highlights: • Pure phases of VO 2 (B) and VO 2 (A) were prepared by a facile hydrothermal method. • Belt-like particles prepared at 180 °C was indexed as monoclinic VO 2 (B) phase. • Rod-like particles prepared at 230 °C was indexed as tetragonal VO 2 (A) phase. • VO 2 (A) nanorods resulted from VO 2 (B) nanobelts by assembly and crystal adjustment. - Abstract: Pure phase VO 2 (A) nanorods were synthesized via the reduction of V 2 O 5 by oxalic acid during the hydrothermal treatment. Two sets of samples were prepared by varying both system temperature and reaction time under a filling ratio of 0.40 for observing the formation and evolution of VO 2 (A) nanorods. Structures were characterized by X-ray diffraction, scanning and transmission electron microscopies, respectively. It was found that VO 2 (B) was firstly formed and then transformed into VO 2 (A) as the increasing system temperature or extending reaction time. An assembling and following crystal adjustment was proposed for explanation the formation process of VO 2 (A) from VO 2 (B). For VO 2 (A) nanorods, the phase transition temperature of 169.7 °C was higher than that of the VO 2 (A) bulk, it might be ascribed to the lower crystallinity or nonstoichiometry in VO 2 (A) nanorods. VO 2 nanostructures with controllable phases and properties should find their promising applications in a single VO 2 nanodevice

Oxygen vacancies dependent phase transition of Y{sub 2}O{sub 3} films

Energy Technology Data Exchange (ETDEWEB)

Yu, Pengfei; Zhang, Kan [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China); Huang, Hao [Titanium Alloys Lab. Beijing Institute of Aeronautical Materials, Beijing 81-15 100095 (China); Wen, Mao, E-mail: Wenmao225@jlu.edu.cn [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China); Li, Quan; Zhang, Wei; Hu, Chaoquan [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China); Zheng, Weitao, E-mail: WTZheng@jlu.edu.cn [Department of Materials Science, State Key Laboratory of Automotive Simulation and Control and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China)

2017-07-15

Highlights: • Oxygen vacancies for Y{sub 2}O{sub 3} films increase monotonously with increasing T{sub s}. • Oxygen vacancies can promote the nucleation of monoclinic phase. • That monoclinic phase with oxygen deficiency is not thermodynamic stable at high temperature. • Phase transition from monoclinic to oxygen defective occurs at high concentrations of oxygen vacancies. • High hardness just appears in Y{sub 2}O{sub 3} films with mixed phase configurations. - Abstract: Y{sub 2}O{sub 3} films have great application potential in high-temperature metal matrix composite and nuclear engineering, used as interface diffusion and reaction barrier coating owing to their excellent thermal and chemical stability, high melting point and extremely negative Gibbs formation energy, and thus their structural and mechanical properties at elevated temperature are especially important. Oxygen vacancies exist commonly in yttrium oxide (Y{sub 2}O{sub 3}) thin films and act strongly on the phase structure and properties, but oxygen vacancies dependent phase transition at elevated temperature has not been well explored yet. Y{sub 2}O{sub 3} thin films with different oxygen vacancy concentrations have been achieved by reactive sputtering through varying substrate temperature (T{sub s}), in which oxygen vacancies increase monotonously with increasing T{sub s}. For as-deposited Y{sub 2}O{sub 3} films, oxygen vacancies present at high T{sub s} can promote the nucleation of monoclinic phase, meanwhile, high T{sub s} can induce the instability of monoclinic phase. Thus their competition results in forming mixed phases of cubic and monoclinic at high T{sub s}. During vacuum annealing at 1000 °C, a critical oxygen vacancy concentration is observed, below which phase transition from monoclinic to cubic takes place, and above which phase transfer from monoclinic to the oxygen defective phase (ICDD file no. 39-1063), accompanying by stress reversal from compressive to tensile and

SIMS study of oxygen diffusion in monoclinic HfO2

Science.gov (United States)

Mueller, Michael P.; De Souza, Roger A.

2018-01-01

The diffusion of oxygen in dense ceramics of monoclinic HfO2 was studied by means of (18O/16O) isotope exchange annealing and subsequent determination of isotope depth profiles by Secondary Ion Mass Spectrometry. Anneals were performed in the temperature range of 573 ≤T /K ≤ 973 at an oxygen partial pressure of p O2=200 mbar . All measured isotope profiles exhibited two features: the first feature, closer to the surface, was attributed mainly to slow oxygen diffusion in an impurity silicate phase; the second feature, deeper in the sample, was attributed to oxygen diffusion in bulk monoclinic HfO2 . The activation enthalpy of oxygen tracer diffusion in bulk HfO2 was found to be ΔHD∗≈0.5 eV .

Monoclinic mixed crystals of halogenomethanes CBr4-nCln (n = 0, ..., 4)

International Nuclear Information System (INIS)

Negrier, Philippe; Tamarit, Josep Ll.; Barrio, Maria; Pardo, Luis C.; Mondieig, Denise

2007-01-01

On the basis of the isostructural relationship between the low-temperature monoclinic (C2/c, Z = 32) phases of the halogenomethane CBr 4-n Cl n (n = 0, ..., 4), a set of mixed crystals has been analysed by means of high-resolution X-ray powder diffraction. It is shown that the monoclinic structure of pure and mixed crystals does not depend of the particularities of the dipolar (or dipole induced) interactions of the pure compound, neither on the composition of the mixed crystal, but on the relative content of the halogen atoms which controls the size of the molecule or the average molecule for the case of mixed crystals

The tetragonal-monoclinic transformations of zirconia studied by small angle neutron scattering and differential thermal analysis

International Nuclear Information System (INIS)

Li, Z.; Epperson, J.E.; Fang, Y.; Chan, S.K.

1992-08-01

The tetragonal-monoclinic transformations of zirconia have been studied on pristine single crystals and on their cycled crystallites. Two complementary techniques have been used. Small angle neutron scattering experiments were carried out to monitor the degree of completion of a transformation under equilibrium conditions for collections of 20--30 large crystals using the total internal and external surface area as an indicator. Differential thermal analysis experiments were carried out on smaller single-domain crystals of different sizes individually during heating and cooling to measure the rates of latent heat absorption and emission. The investigation establishes the upper limit of stability of the monoclinic phase, the lower limit of stability of the tetragonal phase, and the coexistence temperature between the two phases. The characteristics of the transformations are also inferred from these experiments

Co-existence of tetragonal and monoclinic phases and multiferroic properties for x ⩽ 0.30 in the (1 − x)Pb(Zr{sub 0.52}Ti{sub 0.48})O{sub 3}–(x)BiFeO{sub 3} system

Energy Technology Data Exchange (ETDEWEB)

Sharma, Subhash; Singh, Vikash [Department of Physics and Materials Science and Engineering, Jaypee Institute of Information Technology, A-10, Sector-62, Noida 201307, Uttar Pradesh (India); Kotnala, R.K. [National Physical Laboratory (CSIR), Dr. K.S. Krishnan Marg, New Delhi 110012 (India); Ranjan, Rajeev [Department of Materials Engineering, Indian Institute of Science, Bangalore 560012 (India); Dwivedi, R.K., E-mail: rk.dwivedi@jiit.ac.in [Department of Physics and Materials Science and Engineering, Jaypee Institute of Information Technology, A-10, Sector-62, Noida 201307, Uttar Pradesh (India)

2014-11-25

Highlights: • Synthesis of (1 − x)PbZr{sub 0.52}Ti{sub 0.48}O{sub 3}–(x)BiFeO{sub 3} with x ⩽ 0.30 by sol–gel method. • Structural phase transformation with x has been revealed by Rietveld analysis. • Raman analysis supports structural phase transition. • Occurrence of MC is a strong evidence of magneto-electric coupling. • Enhance magnetization is obtained in the dominant monoclinic phase for x ⩾0.15. - Abstract: Compositions with x ⩽ 0.30 in the system (1 − x)Pb(Zr{sub 0.52}Ti{sub 0.48})O{sub 3}–(x)BiFeO{sub 3} were synthesized by sol–gel method. Rietveld analysis of X-ray diffraction data reveals tetragonal structure (P4mm) for x ⩽ 0.05 and monoclinic (Cm) phase along with the existence of tetragonal phase for 0.10 ⩽ x ⩽ 0.25 and monoclinic phase for x = 0.30. Transformation of E(2TO) and E + B1 vibrational modes in the range 210–250 cm{sup −1} (present for x ⩽ 0.25) into A′ + A″ modes at ∼236 cm{sup −1} for x = 0.30, and occurrence of new vibrational modes A′ and A″ in Raman spectra for x ⩾ 0.10 unambiguously support the presence of monoclinic phase. Occurrence of remnant polarisation and enhanced magnetization with concentration of BiFeO{sub 3} indicates superior multiferroic properties. Variation of magneto-capacitance with applied magnetic field is a strong evidence of magneto-electric multiferroic coupling in these materials.

Investigation of the phase formation and dielectric properties of Bi7Ta3O18

International Nuclear Information System (INIS)

Chon, M.P.; Tan, K.B.; Khaw, C.C.; Zainal, Z.; Taufiq Yap, Y.H.; Chen, S.K.; Tan, P.Y.

2014-01-01

Highlights: • Synthesis condition of Bi 7 TaO 3 O 18 had been determined. • Recombination of intermediate BiTaO 4 and Bi 3 TaO 7 phases are required for the Bi 7 TaO 3 O 18 phase formation. • Stable material as confirmed by thermal and structural analyses. • Typical ferroelectric showing high dielectric constants and low losses. • Resonance and thermal activated polarisation processes are responsible for the excellent dielectric characteristic. -- Abstract: Polycrystalline Bi 7 Ta 3 O 18 was synthesised at the firing temperature of 950 °C over 18 h via conventional solid state method. It crystallised in a monoclinic system with space group C2/m, Z = 4 similar to that reported diffraction pattern in the Inorganic Crystal Structure Database (ICSD), 1-89-6647. The refined lattice parameters were a = 34.060 (3) Å, b = 7.618 (9) Å, c = 6.647 (6) Å with α = γ = 90° and β = 109.210 (7), respectively. The intermediate phase was predominantly in high-symmetry cubic structure below 800 °C and finally evolved into a low-symmetry monoclinic structured, Bi 7 Ta 3 O 18 at 950 °C. The sample contained grains of various shapes with different orientations in the size ranging from 0.33–22.70 μm. The elemental analysis showed the sample had correct stoichiometry with negligible Bi 2 O 3 loss. Bi 7 Ta 3 O 18 was thermally stable and it exhibited a relatively high relative permittivity, 241 and low dielectric loss, 0.004 at room temperature, ∼30 °C and frequency of 1 MHz

Order parameters for symmetry-breaking structural transitions: The tetragonal-monoclinic transition in ZrO2

Science.gov (United States)

Thomas, John C.; Van der Ven, Anton

2017-10-01

Group/subgroup structural phase transitions are exploited in a wide variety of technologies, including those that rely on shape-memory behavior and on transformation toughening. Here, we introduce an approach to identify symmetry-adapted strain and shuffle order parameters for any group/subgroup structural transition between a high-symmetry parent phase and its symmetrically equivalent low-symmetry product phases. We show that symmetry-adapted atomic shuffle order parameters can be determined by the diagonalization of an orbital covariance matrix, formed by taking the covariance among the atomic displacement vectors of all symmetrically equivalent product phase variants. We use this approach to analyze the technologically important tetragonal to monoclinic structural phase transformation of ZrO2. We explore the energy landscapes, as calculated with density functional theory, along distinct paths that connect m ZrO2 to t ZrO2 and to other m ZrO2 variants. The calculations indicate favorable pairs of variants and reveal intermediate structures likely to exist at coherent twin boundaries and having relatively low deformation energy. We identify crystallographic features of the monoclinic ZrO2 variant that make it very sensitive to shape changing strains.

Reflection of P and SV waves at the free surface of a monoclinic ...

Indian Academy of Sciences (India)

The propagation of plane waves in an anisotropic elastic medium possessing monoclinic symmetry is discussed. The expressions for the phase velocity of qP and qSV waves propagating in the plane of elastic symmetry are obtained in terms of the direction cosines of the propagation vector. It is shown that, in general, ...

Crystallite size effect on the monoclinic deformation of the bcc crystal structure of chromium

Science.gov (United States)

Przeniosło, R.; Fabrykiewicz, P.; Sosnowska, I.; Wardecki, D.; Sławiński, W. A.; Playford, H. Y.; Hempelmann, R.; Bukowski, M.

2018-02-01

The modulated spin density wave magnetic orderings observed in chromium suggests that the crystal structure of chromium cannot be described by the cubic space group Im 3 bar m. Our experimental studies of polycrystalline and nanocrystalline chromium by synchrotron radiation (SR) and neutron powder diffraction show a hkl-dependent Bragg peak broadening which can be interpreted by the low-symmetry monoclinic space group P21 / n instead of the high symmetry cubic space group Im 3 bar m. The monoclinic angle is βm = 90.05(1)° and 90.29(1)° for polycrystalline Cr and nanocrystalline Cr, respectively. The relative monoclinic distortion observed in chromium is 5 times larger than those reported for several oxides: BiFeO3, α-Fe2O3, Cr2O3 and calcite. The symmetry of the magnetic transverse spin density wave (TSDW) and the longitudinal spin density wave (LSDW) observed in Cr are described by using the superspace groups P21 / n(0 β 0) 00 and P 21‧ /n‧(0 β 0) 00, respectively. These superspace groups describe both the magnetic modulations and the atomic position modulations reported in the literature. The monoclinic symmetry of chromium is a robust effect which is observed in the paramagnetic as well as in the TSDW and LSDW phases.

Monoclinic BiVO4 micro-/nanostructures: Microwave and ultrasonic wave combined synthesis and their visible-light photocatalytic activities

International Nuclear Information System (INIS)

Zhang, Yafang; Li, Guangfang; Yang, Xiaohui; Yang, Hao; Lu, Zhong; Chen, Rong

2013-01-01

Graphical abstract: Monoclinic BiVO 4 with different sizes and morphologies were synthesized by a facile microwave and ultrasonic wave combined technique for the first time and exhibited different optical properties and visible-light-driven photocatalytic efficiency. Highlights: ► BiVO 4 nanostructures were prepared by microwave and ultrasonic wave combined method. ► BiVO 4 nanostructures could be modulated by varying the solvent and pH value. ► Different BiVO 4 nanostructures exhibited different photocatalytic activities. ► The photocatalytic performance was influenced by the band gap, phase and size. - Abstract: Monoclinic bismuth vanadate (m-BiVO 4 ) micro-/nanostructures with different sizes and morphologies were successfully prepared via a facile and rapid microwave and ultrasonic wave combined technique. The obtained BiVO 4 products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and UV–vis diffuse reflection spectroscopy (DRS). It was found that the solvent and pH value had a significant influence on morphology, size and crystalline structure of the product. Nut-like, potato-like and broccoli-like monoclinic BiVO 4 were fabricated in different solvents. The crystal phase could be modulated by varying the pH value of reaction system. The photocatalytic activities of the products were also evaluated by the degradation of Rhodamine B (RhB) under visible light irradiation. The result revealed that the photocatalytic activities of BiVO 4 nanostructures were closely related to the crystalline phase, band gap and particle size. Monoclinic BiVO 4 nanoparticles with small crystal size and large band gap exhibited remarkable photocatalytic performance.

Electric-field-induced monoclinic phase in (Ba,Sr)TiO3 thin film

International Nuclear Information System (INIS)

Anokhin, A. S.; Yuzyuk, Yu. I.; Golovko, Yu. I.; Mukhortov, V. M.; El Marssi, M.

2011-01-01

We have studied electric-field-induced symmetry lowering in the tetragonal (001)-oriented heteroepitaxial (Ba 0.8 Sr 0.2 )TiO 3 thin film deposited on (001)MgO substrate. Polarized micro-Raman spectra were recorded from the film area in between two planar electrodes deposited on the film surface. Presence of c domains with polarization normal to the substrate was confirmed from polarized Raman study under zero field, while splitting and hardening of the E(TO) soft mode and polarization changes in the Raman spectra suggest monoclinic symmetry under external electric field.

Upper and lower bounds on the set of recoverable strains and on effective energies in cubic-to-monoclinic martensitic phase transformations

Directory of Open Access Journals (Sweden)

Schlömerkemper Anja

2015-01-01

Full Text Available A major open problem in the mathematical analysis of martensitic phase transformations is the derivation of explicit formulae for the set of recoverable strains and for the relaxed energy of the system. These are governed by the mathematical notion of quasiconvexity. Here we focus on bounds on these quasiconvex hulls and envelopes in the setting of geometrically-linear elasticity. Firstly, we will present mathematical results on triples of transformation strains. This yields further insight into the quasiconvex hull of the twelve transformation strains in cubic-to-monoclinic phase transformations. Secondly, we consider bounds on the energy of such materials based on the so-called energy of mixing thus obtaining a lamination upper bound on the quasiconvex envelope of the energy. Here we present a new algorithm that yields improved upper bounds and allows us to relate numerical results for the lamination upper bound on the energy with theoretical inner bounds on the quasiconvex hull of triples of transformation strains.

Monoclinic BiVO{sub 4} micro-/nanostructures: Microwave and ultrasonic wave combined synthesis and their visible-light photocatalytic activities

Energy Technology Data Exchange (ETDEWEB)

Zhang, Yafang; Li, Guangfang; Yang, Xiaohui; Yang, Hao; Lu, Zhong [Key Laboratory for Green Chemical Process of Ministry of Education and Hubei Novel Reactor and Green Chemical Technology Key Laboratory, Wuhan Institute of Technology, Xiongchu Avenue, Wuhan 430073 (China); Chen, Rong, E-mail: rchenhku@hotmail.com [Key Laboratory for Green Chemical Process of Ministry of Education and Hubei Novel Reactor and Green Chemical Technology Key Laboratory, Wuhan Institute of Technology, Xiongchu Avenue, Wuhan 430073 (China); Engineering Research Center of Nano-Geomaterials of Ministry of Education, China University of Geosciences, Lumo Road, Wuhan 430074 (China)

2013-02-25

Graphical abstract: Monoclinic BiVO{sub 4} with different sizes and morphologies were synthesized by a facile microwave and ultrasonic wave combined technique for the first time and exhibited different optical properties and visible-light-driven photocatalytic efficiency. Highlights: Black-Right-Pointing-Pointer BiVO{sub 4} nanostructures were prepared by microwave and ultrasonic wave combined method. Black-Right-Pointing-Pointer BiVO{sub 4} nanostructures could be modulated by varying the solvent and pH value. Black-Right-Pointing-Pointer Different BiVO{sub 4} nanostructures exhibited different photocatalytic activities. Black-Right-Pointing-Pointer The photocatalytic performance was influenced by the band gap, phase and size. - Abstract: Monoclinic bismuth vanadate (m-BiVO{sub 4}) micro-/nanostructures with different sizes and morphologies were successfully prepared via a facile and rapid microwave and ultrasonic wave combined technique. The obtained BiVO{sub 4} products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and UV-vis diffuse reflection spectroscopy (DRS). It was found that the solvent and pH value had a significant influence on morphology, size and crystalline structure of the product. Nut-like, potato-like and broccoli-like monoclinic BiVO{sub 4} were fabricated in different solvents. The crystal phase could be modulated by varying the pH value of reaction system. The photocatalytic activities of the products were also evaluated by the degradation of Rhodamine B (RhB) under visible light irradiation. The result revealed that the photocatalytic activities of BiVO{sub 4} nanostructures were closely related to the crystalline phase, band gap and particle size. Monoclinic BiVO{sub 4} nanoparticles with small crystal size and large band gap exhibited remarkable photocatalytic performance.

Monoclinic Cc-phase stabilization in magnetically diluted lead free Na1/2Bi1/2TiO3—Evolution of spin glass like behavior with enhanced ferroelectric and dielectric properties

Science.gov (United States)

Thangavelu, Karthik; Asthana, Saket

2015-09-01

The effect of magnetic cation substitution on the phase stabilization, ferroelectric, dielectric and magnetic properties of a lead free Na0.5Bi0.5TiO3 (NBT) system prepared by O2 atmosphere solid state sintering were studied extensively. Cobalt (Co) was chosen as the magnetic cation to substitute at the Ti-site of NBT with optimized 2.5 mol%. Rietveld analysis of x-ray diffraction data favours the monoclinic Cc phase stabilization strongly rather than the parent R3c phase. FE-SEM micrograph supports the single phase characteristics without phase segregation at the grain boundaries. The stabilized Cc space group was explained based on the collective local distortion effects due to spin-orbit stabilization at Co3+ and Co2+ functional centres. The phonon mode changes as observed in the TiO6 octahedral modes also support the Cc phase stabilization. The major Co3+-ion presence was revealed from corresponding crystal field transitions observed through solid state diffuse reflectance spectroscopy. The enhanced spontaneous polarization (Ps) from ≅38 μC cm-2 to 45 μC cm-2 could be due to the easy rotation of polarization vector along the {(1\\bar{1}0)}{{pc}} in Cc phase. An increase in static dielectric response (ɛ) from ɛ ≅ 42 to 60 along with enhanced diffusivity from γ ≅ 1.53 to 1.75 was observed. Magneto-thermal irreversibility and their magnetic field dependent ZFC/FC curves suggest the possibility of a spin glass like behaviour below 50 K. The monoclinic Cc phase stabilization as confirmed from structural studies was well correlated with the observed ferroic properties in magnetically diluted NBT.

Nanoscale monoclinic domains in epitaxial SrRuO3 thin films deposited by pulsed laser deposition

Science.gov (United States)

Ghica, C.; Negrea, R. F.; Nistor, L. C.; Chirila, C. F.; Pintilie, L.

2014-07-01

In this paper, we analyze the structural distortions observed by transmission electron microscopy in thin epitaxial SrRuO3 layers used as bottom electrodes in multiferroic coatings onto SrTiO3 substrates for future multiferroic devices. Regardless of the nature and architecture of the multilayer oxides deposited on the top of the SrRuO3 thin films, selected area electron diffraction patterns systematically revealed the presence of faint diffraction spots appearing in forbidden positions for the SrRuO3 orthorhombic structure. High-resolution transmission electron microscopy (HRTEM) combined with Geometric Phase Analysis (GPA) evidenced the origin of these forbidden diffraction spots in the presence of structurally disordered nanometric domains in the SrRuO3 bottom layers, resulting from a strain-driven phase transformation. The local high compressive strain (-4% ÷ -5%) measured by GPA in the HRTEM images induces a local orthorhombic to monoclinic phase transition by a cooperative rotation of the RuO6 octahedra. A further confirmation of the origin of the forbidden diffraction spots comes from the simulated diffraction patterns obtained from a monoclinic disordered SrRuO3 structure.

On the phase formation of sputtered hafnium oxide and oxynitride films

International Nuclear Information System (INIS)

Sarakinos, K.; Music, D.; Mraz, S.; Baben, M. to; Jiang, K.; Nahif, F.; Braun, A.; Zilkens, C.; Schneider, J. M.; Konstantinidis, S.; Renaux, F.; Cossement, D.; Munnik, F.

2010-01-01

Hafnium oxynitride films are deposited from a Hf target employing direct current magnetron sputtering in an Ar-O 2 -N 2 atmosphere. It is shown that the presence of N 2 allows for the stabilization of the transition zone between the metallic and the compound sputtering mode enabling deposition of films at well defined conditions of target coverage by varying the O 2 partial pressure. Plasma analysis reveals that this experimental strategy facilitates control over the flux of the O - ions which are generated on the oxidized target surface and accelerated by the negative target potential toward the growing film. An arrangement that enables film growth without O - ion bombardment is also implemented. Moreover, stabilization of the transition sputtering zone and control of the O - ion flux without N 2 addition is achieved employing high power pulsed magnetron sputtering. Structural characterization of the deposited films unambiguously proves that the phase formation of hafnium oxide and hafnium oxynitride films with the crystal structure of HfO 2 is independent from the O - bombardment conditions. Experimental and theoretical data indicate that the presence of vacancies and/or the substitution of O by N atoms in the nonmetal sublattice favor the formation of the cubic and/or the tetragonal HfO 2 crystal structure at the expense of the monoclinic HfO 2 one.

Investigation of the phase formation and dielectric properties of Bi{sub 7}Ta{sub 3}O{sub 18}

Energy Technology Data Exchange (ETDEWEB)

Chon, M.P. [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor (Malaysia); Tan, K.B., E-mail: tankb@science.upm.my [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor (Malaysia); Khaw, C.C. [Department of Mechanical and Material Engineering, Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, 53300 Setapak, Kuala Lumpur (Malaysia); Zainal, Z.; Taufiq Yap, Y.H. [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor (Malaysia); Chen, S.K. [Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor (Malaysia); Tan, P.Y. [Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor (Malaysia)

2014-03-25

Highlights: • Synthesis condition of Bi{sub 7}TaO{sub 3}O{sub 18} had been determined. • Recombination of intermediate BiTaO{sub 4} and Bi{sub 3}TaO{sub 7} phases are required for the Bi{sub 7}TaO{sub 3}O{sub 18} phase formation. • Stable material as confirmed by thermal and structural analyses. • Typical ferroelectric showing high dielectric constants and low losses. • Resonance and thermal activated polarisation processes are responsible for the excellent dielectric characteristic. -- Abstract: Polycrystalline Bi{sub 7}Ta{sub 3}O{sub 18} was synthesised at the firing temperature of 950 °C over 18 h via conventional solid state method. It crystallised in a monoclinic system with space group C2/m, Z = 4 similar to that reported diffraction pattern in the Inorganic Crystal Structure Database (ICSD), 1-89-6647. The refined lattice parameters were a = 34.060 (3) Å, b = 7.618 (9) Å, c = 6.647 (6) Å with α = γ = 90° and β = 109.210 (7), respectively. The intermediate phase was predominantly in high-symmetry cubic structure below 800 °C and finally evolved into a low-symmetry monoclinic structured, Bi{sub 7}Ta{sub 3}O{sub 18} at 950 °C. The sample contained grains of various shapes with different orientations in the size ranging from 0.33–22.70 μm. The elemental analysis showed the sample had correct stoichiometry with negligible Bi{sub 2}O{sub 3} loss. Bi{sub 7}Ta{sub 3}O{sub 18} was thermally stable and it exhibited a relatively high relative permittivity, 241 and low dielectric loss, 0.004 at room temperature, ∼30 °C and frequency of 1 MHz.

Synthesis of monoclinic Celsian from Coal Fly Ash by using a one-step solid-state reaction process

Energy Technology Data Exchange (ETDEWEB)

Long-Gonzalez, D.; Lopez-Cuevas, J.; Gutierrez-Chavarria, C.A.; Pena, P.; Baudin, C.; Turrillas, X. [CINVESTAV, Coahuila (Mexico)

2010-03-15

Monoclinic (Celsian) and hexagonal (Hexacelsian) Ba1-xSrxAl{sub 2}Si2O8 solid solutions, where x=0, 0.25, 0.375, 0.5, 0.75 or 1, were synthesized by using Coal Fly Ash (CFA) as main raw material, employing a simple one-step solid-state reaction process involving thermal treatment for 5 h at 850-1300{sup o}C. Fully monoclinic Celsian was obtained at 1200{sup o} C/5 h, for SrO contents of 0.25 {<=} x {<=} 0.75. However, an optimum SrO level of 0.25 {<=} x {<=} 0.375 was recommended for the stabilization of Celsian. These synthesis conditions represent a significant improvement over the higher temperatures, longer times and/or multi-step processes needed to obtain fully monoclinic Celsian, when other raw materials are used for this purpose, according to previous literature. These results were attributed to the role of the chemical and phase constitution of CFA as well as to a likely mineralizing effect of CaO and TiO{sub 2} present in it, which enhanced the Hexacelsian to Celsian conversion.

Gd5(SixGe1−x)4 system – updated phase diagram

International Nuclear Information System (INIS)

Melikhov, Yevgen; Hadimani, R.L.; Raghunathan, Arun

2015-01-01

Gd 5 (Si x Ge 1−x ) 4 for 0.41monoclinic and paramagnetic at higher temperature, and shows a first order magnetic-structural phase transition between the two. In this range, the magnetic moment vs. magnetic field (MH) isotherms measured just above the first order transition temperature carry information about all magnetic and structural transitions. Here, the Curie–Weiss law was applied to the paramagnetic portions of the MH isotherms which allowed identification of the second order magnetic phase transition temperature of the monoclinic phase, a region where the second order transition does not occur due to the existence of the first order transition. The calculated second order phase transition temperatures of the monoclinic phase were added to the existing phase diagram. The completed magnetic-structural phase diagram carries now all the information including the magnetic transition temperatures of both monoclinic and orthorhombic phases. It was also found that the magnetic transition temperature of the monoclinic phase and the first order transition temperature are interrelated. - Highlights: • Magnetocaloric Gd 5 (Si x Ge 1−x ) 4 for 0.41phase transition suppresses second order transition of monoclinic phase. • Curie–Weiss law and Arrott Plot technique were used to analyse M vs. H isotherms. • Second order phase transition temperatures of the monoclinic phase were estimated. • Magnetic-structural phase diagram Gd 5 (Si x Ge 1−x ) 4 for 0.41

Structural, thermal, dielectric and phonon properties of perovskite-like imidazolium magnesium formate.

Science.gov (United States)

Mączka, Mirosław; Marinho Costa, Nathalia Leal; Gągor, Anna; Paraguassu, Waldeci; Sieradzki, Adam; Hanuza, Jerzy

2016-05-18

We report the synthesis and characterisation of a magnesium formate framework templated by protonated imidazole. Single-crystal X-ray diffraction data showed that this compound crystallizes in the monoclinic structure in the P21/n space group with lattice parameters a = 12.1246(4) Å, b = 12.2087(5) Å, c = 12.4991(4) Å and β = 91.39(1)°. The antiparallel arrangement of the dipole moments associated with imidazolium cations suggests the antiferroelectric character of the room-temperature phase. The studied compound undergoes a structural phase transition at 451 K associated with a halving of the c lattice parameter and the disappearance of the antiferroelectric order. The monoclinic symmetry is preserved and the new metrics are a = 12.261(7) Å, b = 12.290(4) Å, c = 6.280(4) Å, and β = 90.62(5)°. Raman and IR data are consistent with the X-ray diffraction data. They also indicate that the disorder of imidazolium cations plays a significant role in the mechanism of the phase transition. Dielectric data show that the phase transition is associated with a relaxor nature of electric ordering. We also report high-pressure Raman scattering studies of this compound that revealed the presence of two pressure-induced phase transitions near 3 and 7 GPa. The first transition is most likely associated with a rearrangement of the imidazolium cations without any significant distortion of these cations and the magnesium formate framework, whereas the second transition leads to strong distortion of both the framework and imidazolium cations. High-pressure data also show that imidazolium magnesium formate does not show any signs of amorphization up to 11.4 GPa.

Structural phase transitions in niobium oxide nanocrystals

Science.gov (United States)

Yuvakkumar, R.; Hong, Sun Ig

2015-09-01

Niobium oxide nanocrystals were successfully synthesized employing the green synthesis method. Phase formation, microstructure and compositional properties of 1, 4 and 7 days incubation treated samples after calcinations at 450 °C were examined using X-ray diffraction, Raman, photoluminescence (PL), infrared, X-ray photoelectron spectra and transmission electron microscopic characterizations. It was observed that phase formation of Nb2O5 nanocrystals was dependent upon the incubation period required to form stable metal oxides. The characteristic results clearly revealed that with increasing incubation and aging, the transformation of cubic, orthorhombic and monoclinic phases were observed. The uniform heating at room temperature (32 °C) and the ligation of niobium atoms due to higher phenolic constituents of utilized rambutan during aging processing plays a vital role in structural phase transitions in niobium oxide nanocrystals. The defects over a period of incubation and the intensities of the PL spectra changing over a period of aging were related to the amount of the defects induced by the phase transition.

Phase formation in the Li2MoO4-Rb2MoO4-Ln2(MoO4)3 systems and the properties of LiRbLn2(MoO4)4

International Nuclear Information System (INIS)

Basovich, O.M.; Khajkina, E.G.; Vasil'ev, E.V.; Frolov, A.M.

1995-01-01

Phase equilibria within subsolidus range of ternary salt systems Li 2 MoO 4 -Rb 2 MoO 4 -Ln 2 (MoO 4 ) 4 (Ln - Nd, Er) are analyzed. Formation of ternary molybdate LiRbNd 2 (MoO 4 ) 4 is proved along LiNd(MoO 4 ) 2 -RbNd(MoO 4 )-2 cross-section. Phase diagram of this cross-section is plotted. Similar compounds are synthesized for Ln = La-Eu. The parameters of their monoclinic elementary cells are determined. Luminescent properties of LiRbLa 2 (MoO 4 ) 4 -Nd 3+ are studied. 17 refs., 4 figs., 2 tabs

Observation of reduced phase transition temperature in N-doped thermochromic film of monoclinic VO_2

International Nuclear Information System (INIS)

Wan, Meinan; Xiong, Mo; Li, Neng; Liu, Baoshun; Wang, Shuo; Ching, Wai-Yim; Zhao, Xiujian

2017-01-01

Highlights: • N-doped VO_2(M1) thin films have been synthesized by annealing in NH_3 atmosphere. • The phase purity, microstructure and optical property of VO_2 thin film can be regulated by NH_3 concentration. • First-principles calculations have been carried out to study the mechanism of N-doping on energy band structures of VO_2(M1). • The energy band gaps of VO_2(M1) are tuned by substitution N-doping or interstitial N-doping. - Abstract: Research on monoclinic (M1) phase of VO_2 has attracted a great of interest for smart coating applications due to its exceptional thermochromic property. Herein, we report the results using a novel approach to synthesize N-doped VO_2(M1) thin films with high purity by heat treatment in NH_3 atmosphere. The N dopant in the film can be regulated by varying NH_3 concentration during the annealing process. We find that the N atoms are located at the interstitial sites or substitute oxygen atoms, and the V-N bonds in the VO_2 thin films increase with NH_3 concentration. The metal to insulator transition (MIT) temperature (τ_c_,_h) of the VO_2 thin film is effectively reduced from 80.0 to 62.9 °C, while the solar modulation efficiency (ΔT_s_o_l) and the modulation efficiency at 2000 nm (ΔT_2_0_0_0_n_m) are 7.36% and 55.6% respectively. The band gap of N-doped VO_2 thin films related to MIT (E_g_1) is estimated to be as low as 0.18–0.25 eV whereas the band gap associated with the visible transparency (E_g_2) is about 1.50–1.58 eV. Based on the highly accurate first-principles calculations, the E_g_1 of VO_2 (M1) is reduced after substituted or interstitial N-doping, while the E_g_2 alters with the mode of N-doping, which is excellent agreement with experimental measurement.

Phase Composition of Samarium Niobate and Tantalate Thin Films Prepared by Sol-Gel Method

Science.gov (United States)

Bruncková, H.; Medvecký, Ľ.; Múdra, E.; Kovalčiková, A.; Ďurišin, J.; Šebek, M.; Girman, V.

2017-12-01

Samarium niobate SmNbO4 (SNO) and tantalate SmTaO4 (STO) thin films ( 100 nm) were prepared by sol-gel/spin-coating process on alumina substrates with PZT interlayer and annealing at 1000°C. The precursors of films were synthesized using Nb or Ta tartrate complexes. The improvement of the crystallinity of monoclinic M'-SmTaO4 phase via heating was observed through the coexistence of small amounts of tetragonal T-SmTa7O19 phase in STO precursor at 1000°C. The XRD results of SNO and STO films confirmed monoclinic M-SmNbO4 and M'-SmTaO4 phases, respectively, with traces of orthorhombic O-SmNbO4 (in SNO). In STO film, the single monoclinic M'-SmTaO4 phase was revealed. The surface morphology and topography of thin films were investigated by SEM and AFM analysis. STO film was smoother with roughness 3.2 nm in comparison with SNO (6.3 nm). In the microstructure of SNO film, small spherical ( 50 nm) and larger cuboidal particles ( 100 nm) of the SmNbO4 phase were observed. In STO, compact clusters composed of fine spherical SmTaO4 particles ( 20-50 nm) were found. Effect of samarium can contribute to the formation different polymorphs of these films for the application to environmental electrolytic thin film devices.

Martensitic phase transformations in Ni–Ti-based shape memory alloys: The Landau theory

International Nuclear Information System (INIS)

Shchyglo, Oleg; Salman, Umut; Finel, Alphonse

2012-01-01

We present a simple Landau free energy functional for cubic-to-orthorhombic and cubic-to-monoclinic martensitic phase transformations. The functional is derived following group–subgroup relations between different martensitic phases – tetragonal, trigonal, orthorhombic and monoclinic – in order to fully capture the symmetry properties of the free energy of the austenite and martensite phases. The derived free energy functional is fitted to the elastic and thermodynamic properties of NiTi and NiTiCu shape memory alloys which exhibit cubic-to-monoclinic and cubic-to-orthorhombic martensitic phase transformations, respectively.

Reflection of P and SV waves at the free surface of a monoclinic ...

Indian Academy of Sciences (India)

R.Narasimhan(krishtel emaging)1461 1996 Oct 15 13:05:22

The propagation of plane waves in an anisotropic elastic medium possessing monoclinic symmetry is discussed. The expressions for ... Keywords. Anisotropic medium; elastic waves; monoclinic half-space; reflection coefficients. Proc. Indian Acad. Sci. ...... In contrast, for C < 0, the angle of reflec- tion is less than the angle of ...

Temperature-dependent index of refraction of monoclinic Ga2O3 single crystal.

Science.gov (United States)

Bhaumik, Indranil; Bhatt, R; Ganesamoorthy, S; Saxena, A; Karnal, A K; Gupta, P K; Sinha, A K; Deb, S K

2011-11-01

We present temperature-dependent refractive index along crystallographic b[010] and a direction perpendicular to (100)-plane for monoclinic phase (β) Ga(2)O(3) single crystal grown by the optical floating zone technique. The experimental results are consistent with the theoretical result of Litimein et al.1. Also, the Sellmeier equation for wavelengths in the range of 0.4-1.55 μm is formulated at different temperatures in the range of 30-175 °C. The thermal coefficient of refractive index in the above specified range is ~10(-5)/°C. © 2011 Optical Society of America

Possible bicollinear nematic state with monoclinic lattice distortions in iron telluride compounds

Energy Technology Data Exchange (ETDEWEB)

Bishop, Christopher B. [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Herbrych, Jacek W. [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Dagotto, Elbio R. [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Moreo, Adriana [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2017-07-15

Here, iron telluride (FeTe) is known to display bicollinear magnetic order at low temperatures together with a monoclinic lattice distortion. Because the bicollinear order can involve two different wave vectors (π/2,π/2) and (π/2,–π/2), symmetry considerations allow for the possible stabilization of a nematic state with short-range bicollinear order coupled to monoclinic lattice distortions at a T_S higher than the temperature T_N where long-range bicollinear order fully develops. As a concrete example, the three-orbital spin-fermion model for iron telluride is studied with an additional coupling ˜λ₁₂ between the monoclinic lattice strain and an orbital-nematic order parameter with B_2g symmetry. Monte Carlo simulations show that with increasing ˜λ₁₂ the first-order transition characteristic of FeTe splits and bicollinear nematicity is stabilized in a (narrow) temperature range. In this new regime, the lattice is monoclinically distorted and short-range spin and orbital order breaks rotational invariance. A discussion of possible realizations of this exotic state is provided.

Study of spinodal decomposition and formation of nc-Al2O3/ZrO2 nanocomposites by combined ab initio density functional theory and thermodynamic modeling

International Nuclear Information System (INIS)

Sheng, S.H.; Zhang, R.F.; Veprek, S.

2011-01-01

Using ab initio density functional theory, the equilibrium properties, such as the total energy, the molar volume, the bulk modulus and its first derivative, as well as the formation enthalpy of monoclinic ZrO 2 and hexagonal α-Al 2 O 3 phases, were calculated and compared with the published theoretical and experimental data. Based on the good agreement of these data, we calculated the lattice instabilities of hypothetical binary hexagonal Zr 2 O 3 and monoclinic AlO 2 , and the interaction parameters of ternary Zr 1-x Al x O y solid solutions. The binodal and spinodal diagrams were then constructed to predict the possibility of the formation of oxide-based nanocomposites which may display hardness enhancement above that of the solid solutions. It is shown that exponential dependence of the interaction parameter on temperature yields the most reliable results. The system should undergo spinodal phase segregation within the composition range that is relevant for the formation of hard or superhard nanocomposites with high thermal and oxidation stability, which are important for their applications.

Molecular dynamics simulations of nucleation and phase transitions in molecular clusters of hexafluorides

International Nuclear Information System (INIS)

Xu, S.

1993-01-01

Molecular dynamics simulations of nucleation and phase transitions in TeF 6 and SeF 6 clusters containing 100-350 molecules were carried out. Simulations successfully reproduced the crystalline structures observed in electron diffraction studies of large clusters (containing about 10 4 molecules) of the same materials. When the clusters were cooled, they spontaneously underwent the same bcc the monoclinic phase transition in simulations as in experiment, despite the million-fold difference in the time scales involved. Other transitions observed included melting and freezing. Several new techniques based on molecular translation and orientation were introduced to identify different condensed phases, to study nucleation and phase transitions, and to define characteristic temperatures of transitions. The solid-state transition temperatures decreased with cluster size in the same way as did the melting temperature, in that the depression of transition temperature was inversely proportional to the cluster radius. Rotational melting temperatures, as inferred from the rotational diffusion of molecules, coincided with those of the solid-state transition. Nucleation in liquid-solid and bcc-monoclinic transitions started in the interior of clusters on cooling, and at the surface on heating. Transition temperatures on cooling were always lower than those on heating due to the barriers to nucleation. Linear growth rates of nuclei in freezing were an order of magnitude lower than those in the bcc-monoclinic transition. Revealing evidence about the molecular behavior associated with phase changes was found. Simulations showed the formation of the actual transition complexes along the transition pathway, i.e., the critical nuclei of the new phase. These nuclei, consisting of a few dozen molecules, were distinguishable in the midst of the surrounding matter

Rapid formation of nanocrystalline HfO2 powders from amorphous hafnium hydroxide under ultrasonically assisted hydrothermal treatment

International Nuclear Information System (INIS)

Meskin, Pavel E.; Sharikov, Felix Yu.; Ivanov, Vladimir K.; Churagulov, Bulat R.; Tretyakov, Yury D.

2007-01-01

Peculiarities of hafnium hydroxide hydrothermal decomposition were studied by in situ heat flux calorimetry for the first time. It was shown that this process occurs in one exothermal stage (ΔH = -17.95 kJ mol -1 ) at 180-250 deg. C resulting in complete crystallization of amorphous phase with formation of pure monoclinic HfO 2 . It was found that the rate of m-HfO 2 formation can be significantly increased by combining hydrothermal treatment with simultaneous ultrasonic activation

Thermodynamics of the tetragonal to monoclinic phase transformation in constrained zirconia microcrystals

International Nuclear Information System (INIS)

Garvie, R.C.; Swain, M.V.

1985-01-01

End-point thermodynamic analyses were made of the tetragonal to monoclinic transformation (t -> m) occurring in ZrO 2 precipitates in a Ca-PSZ alloy and particles in Al 2 O 3 -ZrO 2 composites. Calculated plots of the reciprocal critical size for transformation temperature were in excellent agreement with experiment data for both systems. Contributions to the total free energy change included bulk chemical, dilatational and residual shear strain energies and also interfacial energies. The latter term consisted of contributions from the change in the chemical surface free energy, the presence of twin boundaries in the precipitate (particle) - matrix interfacial energy. The major impediment to the transformation was the shear strain energy which could not be reduced sufficiently by twinning alone. The t -> m reaction proceeded spontaneously when the energy barrier was reduced by the response of the particle - matrix interface. The response comprised loss of coherency and grain boundary microcracking for the Ca/PSZ and Al 2 O 3 -ZrO 2 alloys, respectively. These results are in accord with recent suggestions that either a stress-free strain or a free surface is a necessary condition for the initiation of a martensitic transformation. (author)

The Gas-Phase Formation of Methyl Formate in Hot Molecular Cores

Science.gov (United States)

Horn, Anne; Møllendal, Harald; Sekiguchi, Osamu; Uggerud, Einar; Roberts, Helen; Herbst, Eric; Viggiano, A. A.; Fridgen, Travis D.

2004-08-01

Methyl formate, HCOOCH3, is a well-known interstellar molecule prominent in the spectra of hot molecular cores. The current view of its formation is that it occurs in the gas phase from precursor methanol, which is synthesized on the surfaces of grain mantles during a previous colder era and evaporates while temperatures increase during the process of high-mass star formation. The specific reaction sequence thought to form methyl formate, the ion-molecule reaction between protonated methanol and formaldehyde followed by dissociative recombination of the protonated ion [HCO(H)OCH3]+, has not been studied in detail in the laboratory. We present here the results of both a quantum chemical study of the ion-molecule reaction between [CH3OH2]+ and H2CO as well as new experimental work on the system. In addition, we report theoretical and experimental studies for a variety of other possible gas-phase reactions leading to ion precursors of methyl formate. The studied chemical processes leading to methyl formate are included in a chemical model of hot cores. Our results show that none of these gas-phase processes produces enough methyl formate to explain its observed abundance.

Magnetic ordering in the monoclinic structure of Nd5Si1.45Ge2.55 and Pr5Si1.5Ge2.5 studied by means of neutron powder diffraction

International Nuclear Information System (INIS)

Magen, C; Ritter, C; Morellon, L; Algarabel, P A; Ibarra, M R

2004-01-01

The compounds Nd 5 Si 1.45 Ge 2.55 and Pr 5 Si 1.5 Ge 2.5 have been investigated by means of magnetization measurements and neutron powder diffraction techniques. These alloys present a room-temperature monoclinic Gd 5 Si 2 Ge 2 -type crystallographic structure and, on cooling, both systems order ferromagnetically, at T C = 56 and 32 K, respectively, from a high-temperature paramagnetic to a low-temperature complex canted ferromagnetic state. The monoclinic crystallographic structure remains unchanged upon cooling down to 4 K, demonstrating the existence of a monoclinic ferromagnetic phase, and the possibility of a full decoupling of magnetic and crystallographic degrees of freedom in the 5:4 lanthanide intermetallic compounds

Phase formation in contact of dissimilar metals

Energy Technology Data Exchange (ETDEWEB)

Savvin, V S; Kazachkova, Yu A; Povzner, A A [Ural State Technical University-UPI, Mira st., 19, A-203, Yekaterinburg 620002 (Russian Federation)], E-mail: savvin-vs@yandex.ru

2008-02-15

Formation and growth of intermediate phases in contact of the crystalline samples forming a two-component eutectic system is considered. It is shown that during the competition to a growing liquid phase the intermediate solid phases cannot grow by diffusion. The alternative is formation of metastable areas of a liquid phase. Measurements of liquid layers extent in Pb-Bi and In-Bi systems have allowed to define the composition of liquid on interface where formation of metastable liquid is possible. The results show that the concentration interval of a liquid layer corresponds to a stable constitution diagram. In order to explain the experimental results the hypothesis according to which the intermediate solid phases are formed as a result of precipitation from metastable melt is considered. The experimental confirmation of formation and crystallization of a metastable liquid is the fact that intergrowth of the samples forming system with an intermetallic phase at temperatures below the temperature of fusion of the most low-melting eutectic is observed. The possibility of the processes concerned with the occurrence of metastable areas of a liquid is showed by means of computer imitation.

Phase transformation and spectroscopic adjustment of Gd{sub 2}O{sub 3}:Eu{sup 3+} synthesized by hydrothermal method

Energy Technology Data Exchange (ETDEWEB)

Wang, Zijun; Wang, Pei; Zhong, Jiuping, E-mail: zhongjp@mail.sysu.edu.cn; Liang, Hongbin; Wang, Jing

2014-08-01

The microcrystalline Gd{sub 2}O{sub 3}:Eu{sup 3+} phosphors were synthesized by the hydrothermal method with post annealing treatment. The powder X-ray diffraction (XRD) indicated the phase transformation from cubic to monoclinic occurred at about 1673 K. The morphologies and sizes were characterized by scanning electron microscopy (SEM). It was found that the morphology of Gd{sub 2}O{sub 3}:Eu{sup 3+} was altered from nanorod to microparticle as the phase changed from cubic to monoclinic. In order to evaluate the effects of sites and phases on luminescence behaviors, the photoluminescence (PL) properties of both phases were investigated. Dominant red emission was observed due to an efficient energy transfer among the sites as well as the strong excitation of O{sup 2−}–Eu{sup 3+} charge transfer band. It was calculated that the monoclinic structure has a higher degree of distortion. More importantly, the phase transformation resulted in the red shift of the strongest emission peak of Eu{sup 3+} from 610.5 to 622.5 nm, closer to the optical transmission window for bioimaging. - Highlights: • Raising annealing temperature induces phase transformation from cubic to monoclinic. • Different phases and sites lead to distinct photoluminescence properties. • Monoclinic structure has higher degree of distortion and it is calculated. • Monoclinic phase emitting at longer wavelength is proposed for bioimaging.

Crystal structure and phase transitions of sodium potassium niobate perovskites

Science.gov (United States)

Tellier, J.; Malic, B.; Dkhil, B.; Jenko, D.; Cilensek, J.; Kosec, M.

2009-02-01

This paper presents the crystal structure and the phase transitions of K xNa 1- xNbO 3 (0.4 ≤ x ≤ 0.6). X-ray diffraction measurements were used to follow the change of the unit-cell parameters and the symmetry in the temperature range 100-800 K. At room temperature all the compositions exhibited a monoclinic metric of the unit cell with a small monoclinic distortion (90.32° ≤ β ≤ 90.34°). No major change of symmetry was evidenced in the investigated compositional range, which should be characteristic of the morphotropic phase-boundary region. With increasing temperature, the samples underwent first-order monoclinic-tetragonal and tetragonal-cubic transitions. Only the potassium-rich phases were rhombohedral at 100 K.

Physicochemical investigation of Bi2MoO6 solid-phase interaction with Sm2MoO6

International Nuclear Information System (INIS)

Khajkina, E.G.; Kovba, L.M.; Bazarova, Zh.G.; Khal'baeva, K.M.; Khakhinov, V.V.; Mokhosoev, M.V.

1986-01-01

Bi 2 MoO 6 -Sm 2 MoO 6 interaction in the temperature range of 700-1000 deg C is studied using X-ray phase analysis and vibrational spectroscopy. Formation of monoclinic solid solutions based on γ'-Bi 2 MoO 6 and B 2-x Sm x MoO 6 varied composition phase with α-Ln 2 MoO 6 structure which homogeneity region extent at 1000 deg C constitutes ∼ 50 mol % (0.7≤x≤1.7) is stated. Crystallographic characteristics of the synthesized phases are determined

Phase formation of physically associating polymer blends

International Nuclear Information System (INIS)

Tanaka, Fumihiko

1993-01-01

Polymers exhibit a variety of condensed phases when some of their segments are capable of forming weak bonds which can be created and destroyed by thermal motion. Transition from one phase to another caused by such 'segment association' is reversible by the change of the temperature and the concentration, so that it is called 'reversible phase transition'. What types of reversible phase formation are possible for a given associative interaction? What is the most fundamental laws which govern the competition between molecular association and phase separation? This paper surveys, as typical examples of reversible phases, macroscopic phase separation, microphase formation, solvation, gelation, etc. from the unified point of view, and explores the possibility of new condensed phases caused by their mutual interference. (author)

Raman spectroscopy study of the tetragonal-to-monoclinic transition in zirconium oxide scales and determination of overall oxygen diffusion by nuclear microanalysis of O18

International Nuclear Information System (INIS)

Godlewski, J.; Lambertin, M.; Gros, J.P.; Wadier, J.F.; Weidinger, H.

1991-01-01

This paper reports on two allotropic forms of zirconium oxide, monoclinic and tetragonal that have been identified in the scales formed on zirconium alloys. The transition from tetragonal to monoclinic has been followed by Z-ray measurements and Raman laser spectroscopy. Information on the average content of the tetragonal phase was obtained by X-ray diffraction, whereas Raman laser analyses on tapered sections revealed its distribution through the scale thickness. Oxidation exposures were made in an autoclave, using H 2 O 18 and D 2 O 18 to determine the overall diffusion coefficients. In particular, oxide scales have been studied on Zircaloy-4 with three different precipitate sizes, and on a Zr-1Nb alloy, after exposure in an autoclave for between 3 and 100 days. The specimens were analyzed in detail in the vicinity of the kinetics transition point, where the acceleration of corrosion occurs. Raman spectroscopy analyses enabled the crystallographic nature of the ZrO 2 to be determined. Close to the interface, the tetragonal phase content is about 40%, when after the transition the tetragonal phase is transformed into monoclinic. The O 18 diffusion treatment was carried out in an autoclave at 400 degrees C under pressure on specimens previously oxidized for between 3 and 100 days in natural water vapor pressure. The diffusion profiles were determined by nuclear microanalysis using the O 18 (p, α) → N 15 reaction. Based on these profiles, the volume and grain boundary diffusion coefficients were calculated for each material and for each oxidation time

The three phases of galaxy formation

Science.gov (United States)

Clauwens, Bart; Schaye, Joop; Franx, Marijn; Bower, Richard G.

2018-05-01

We investigate the origin of the Hubble sequence by analysing the evolution of the kinematic morphologies of central galaxies in the EAGLE cosmological simulation. By separating each galaxy into disc and spheroidal stellar components and tracing their evolution along the merger tree, we find that the morphology of galaxies follows a common evolutionary trend. We distinguish three phases of galaxy formation. These phases are determined primarily by mass, rather than redshift. For M* ≲ 109.5M⊙ galaxies grow in a disorganised way, resulting in a morphology that is dominated by random stellar motions. This phase is dominated by in-situ star formation, partly triggered by mergers. In the mass range 109.5M⊙ ≲ M* ≲ 1010.5M⊙ galaxies evolve towards a disc-dominated morphology, driven by in-situ star formation. The central spheroid (i.e. the bulge) at z = 0 consists mostly of stars that formed in-situ, yet the formation of the bulge is to a large degree associated with mergers. Finally, at M* ≳ 1010.5M⊙ growth through in-situ star formation slows down considerably and galaxies transform towards a more spheroidal morphology. This transformation is driven more by the buildup of spheroids than by the destruction of discs. Spheroid formation in these galaxies happens mostly by accretion at large radii of stars formed ex-situ (i.e. the halo rather than the bulge).

2-(4-Fluorobenzylidenepropanedinitrile: monoclinic polymorph

Directory of Open Access Journals (Sweden)

Ahmed M. El-Agrody

2013-04-01

Full Text Available The title compound, C10H5FN2, is a monoclinic (P21/c polymorph of the previously reported triclinic (P-1 form [Antipin et al. (2003. J. Mol. Struct. 650, 1–20]. The 13 non-H atoms in the title polymorph are almost coplanar (r.m.s. deviation = 0.020 Å; a small twist between the fluorobenzene and dinitrile groups [C—C—C—C torsion angle = 175.49 (16°] is evident in the triclinic polymorph. In the crystal, C—H...N interactions lead to supramolecular layers parallel to (-101; these are connected by C—F...π interactions.

Observation of reduced phase transition temperature in N-doped thermochromic film of monoclinic VO{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Wan, Meinan; Xiong, Mo [State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070 (China); Li, Neng, E-mail: lineng@whut.edu.cn [State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070 (China); Liu, Baoshun; Wang, Shuo [State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070 (China); Ching, Wai-Yim [Department of Physics and Astronomy, University of Missouri-Kansas City, Kansas City, MO 64110 (United States); Zhao, Xiujian, E-mail: opluse@whut.edu.cn [State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070 (China)

2017-07-15

Highlights: • N-doped VO{sub 2}(M1) thin films have been synthesized by annealing in NH{sub 3} atmosphere. • The phase purity, microstructure and optical property of VO{sub 2} thin film can be regulated by NH{sub 3} concentration. • First-principles calculations have been carried out to study the mechanism of N-doping on energy band structures of VO{sub 2}(M1). • The energy band gaps of VO{sub 2}(M1) are tuned by substitution N-doping or interstitial N-doping. - Abstract: Research on monoclinic (M1) phase of VO{sub 2} has attracted a great of interest for smart coating applications due to its exceptional thermochromic property. Herein, we report the results using a novel approach to synthesize N-doped VO{sub 2}(M1) thin films with high purity by heat treatment in NH{sub 3} atmosphere. The N dopant in the film can be regulated by varying NH{sub 3} concentration during the annealing process. We find that the N atoms are located at the interstitial sites or substitute oxygen atoms, and the V-N bonds in the VO{sub 2} thin films increase with NH{sub 3} concentration. The metal to insulator transition (MIT) temperature (τ{sub c,h}) of the VO{sub 2} thin film is effectively reduced from 80.0 to 62.9 °C, while the solar modulation efficiency (ΔT{sub sol}) and the modulation efficiency at 2000 nm (ΔT{sub 2000nm}) are 7.36% and 55.6% respectively. The band gap of N-doped VO{sub 2} thin films related to MIT (E{sub g1}) is estimated to be as low as 0.18–0.25 eV whereas the band gap associated with the visible transparency (E{sub g2}) is about 1.50–1.58 eV. Based on the highly accurate first-principles calculations, the E{sub g1} of VO{sub 2} (M1) is reduced after substituted or interstitial N-doping, while the E{sub g2} alters with the mode of N-doping, which is excellent agreement with experimental measurement.

Formation of ω-phase in Zr-4 at.% Cr alloy

International Nuclear Information System (INIS)

Dobromyslov, A.V.; Kazantseva, N.V.

1996-01-01

The ω-phase has been discovered in zirconium-base alloys with the transition metals of Period 4 of the Periodic Table only in Zr-V, Zr-Cr, and Zr-Cu alloys. The first mention about the ω-phase formation in Zr-Cr alloys was given for Zr-4.5 at.%. However, there were no experimental data that confirmed this fact. W.M. Rumball and F.G. Elder presented the X-ray results on the ω-phase formation in Zr-3.9 at.%Cr, but at the present time there are no electron microscope studies of the structure of the ω-phase in this system. Investigations of the features of the ω-phase formation, morphology of the ω-phase and the mechanism of its formation in the different zirconium-base alloys are necessary to establish the common features of the formation of structures with the metastable phases. The task of the present work is to study the conditions and features of the ω-phase formation in the Zr-Cr alloys and the effect of the eutectoid decomposition on the formation of ω-phase. This article is part of the detailed investigations of the feature and condition of the ω-phase formation in zirconium-base alloys with the transition metals of the groups I and V to VIII of the Periodic Table

Phase transformation in nanocrystalline α-quartz GeO2 up to 51.5 GPa

International Nuclear Information System (INIS)

Wang, H; Liu, J F; Wu, H P; He, Y; Chen, W; Wang, Y; Zeng, Y W; Wang, Y W; Luo, C J; Liu, J; Hu, T D; Stahl, K; Jiang, J Z

2006-01-01

The high-pressure behaviour of nanocrystalline α-quartz GeO 2 (q-GeO 2 ) with average crystallite sizes of 40 and 260 nm has been studied by in situ high-pressure synchrotron radiation x-ray diffraction measurements up to about 51.5 GPa at ambient temperature. Two phase transformations, q-GeO 2 to amorphous GeO 2 and amorphous GeO 2 to monoclinic GeO 2 , are detected. The onset and end of the transition pressures for the q-GeO 2 -to-amorphous GeO 2 phase transition are found to be approximately 10.8 and 14.9 GPa for the 40 nm q-GeO 2 sample, and 9.5 and 12.4 GPa for the 260 nm q-GeO 2 sample, respectively. The mixture of amorphous and monoclinic GeO 2 phases remains up to 51.5 GPa during compression and even after pressure release. This result strongly suggests that the difference of free energy between the amorphous phase and the monoclinic phase might be small. Consequently, defects in the starting material, which alter the free energies of the amorphous phase and the monoclinic phase, may play a key role for the phase transformation of q-GeO 2

Spectroscopic studies of dynamically compacted monoclinic ZrO2

NARCIS (Netherlands)

Maczka, M.; Lutz, E.T.G.; Verbeek, H.J.; Oskam, K.; Meijerink, A.; Hanuza, J.; Stuivinga, M.E.C.

1999-01-01

The properties of dynamically compacted monoclinic zirconia have been studied by X-ray powder diffraction, IR, Raman, EPR and luminescence spectroscopy. Compaction introduces a large number of defects into the sample, which leads to a broadening of the X-ray lines, and IR and Raman bands. Besides,

Dielectric function and double absorption onset of monoclinic Cu₂SnS₃

DEFF Research Database (Denmark)

Crovetto, Andrea; Chen, Rongzhen; Ettlinger, Rebecca Bolt

2016-01-01

In this work, we determine experimentally the dielectric function of monoclinic Cu2SnS3 (CTS) by spectroscopic ellipsometry from 0.7 to 5.9 eV. An experimental approach is proposed to overcome the challenges of extracting the dielectric function of Cu2SnS3 when grown on a glass/Mo substrate...... secondary phases, is not needed to explain such an absorption spectrum. Finally, we show that the absorption coefficient of CTS is particularly large in the near-band gap spectral region when compared to similar photovoltaic materials....

Critical Role of Monoclinic Polarization Rotation in High-Performance Perovskite Piezoelectric Materials.

Science.gov (United States)

Liu, Hui; Chen, Jun; Fan, Longlong; Ren, Yang; Pan, Zhao; Lalitha, K V; Rödel, Jürgen; Xing, Xianran

2017-07-07

High-performance piezoelectric materials constantly attract interest for both technological applications and fundamental research. The understanding of the origin of the high-performance piezoelectric property remains a challenge mainly due to the lack of direct experimental evidence. We perform in situ high-energy x-ray diffraction combined with 2D geometry scattering technology to reveal the underlying mechanism for the perovskite-type lead-based high-performance piezoelectric materials. The direct structural evidence reveals that the electric-field-driven continuous polarization rotation within the monoclinic plane plays a critical role to achieve the giant piezoelectric response. An intrinsic relationship between the crystal structure and piezoelectric performance in perovskite ferroelectrics has been established: A strong tendency of electric-field-driven polarization rotation generates peak piezoelectric performance and vice versa. Furthermore, the monoclinic M_{A} structure is the key feature to superior piezoelectric properties as compared to other structures such as monoclinic M_{B}, rhombohedral, and tetragonal. A high piezoelectric response originates from intrinsic lattice strain, but little from extrinsic domain switching. The present results will facilitate designing high-performance perovskite piezoelectric materials by enhancing the intrinsic lattice contribution with easy and continuous polarization rotation.

Pressure-induced phase transitions of multiferroic BiFeO3

International Nuclear Information System (INIS)

Zhang Xiaoli; Dong Juncai; Liu Jing; Chen Dongliang; Wu Ye; Zhang Qian; Wu Xiang; Wu Ziyu

2013-01-01

Pressure-induced phase transitions of multiferroic BiFeO 3 have been investigated using synchrotron radiation X-ray diffraction with diamond anvil cell technique at room temperature. Present experimental data clearly show that rhombohedral (R3c) phase of BiFeO 3 first transforms to monoclinic (C2/m) phase at 7 GPa, then to orthorhombic (Pnma) phase at 11 GPa, which is consistent with recent theoretical ab initio calculation. However, we observe another peak at 2θ=7° in the pressure range of 5-7 GPa that has not been reported previously. Further analysis reveals that this reflection peak is attributed to the orthorhombic (Pbam) phase, indicating the coexistence of monoclinic phase with orthorhombic phase in low pressure range. (authors)

Phase modification and surface plasmon resonance of Au/WO{sub 3} system

Energy Technology Data Exchange (ETDEWEB)

Bose, R. Jolly; Kavitha, V.S. [Department of Optoelectronics, University of Kerala, Kariyavattom, Thiruvananthapuram 691574, Kerala (India); Sudarsanakumar, C. [School of Pure and Applied Physics, Mahatma Gandhi University, Priyadarshini Hills, Kottayam 686560, Kerala (India); Pillai, V.P. Mahadevan, E-mail: vpmpillai9@gmail.com [Department of Optoelectronics, University of Kerala, Kariyavattom, Thiruvananthapuram 691574, Kerala (India)

2016-08-30

Highlights: • We have investigated the role of gold as catalyst and nucleation centers, for the crystallization and phase modification of tungsten oxide, in Au/WO{sub 3} matrix. • The phase change from triclinic WO{sub 3} to monoclinic W{sub 18}O{sub 49} is found to enhance with gold incorporation. • The surface plasmon resonance is observed in gold/tungsten oxide system with the appearance of an absorption band near the wavelength 604 nm. - Abstract: We report the action of gold as catalyst for the modification of phase from triclinic WO{sub 3} to monoclinic W{sub 18}O{sub 49} and nucleation centre for the formation of W{sub 18}O{sub 49} phase, in gold incorporated tungsten oxide films prepared by RF magnetron sputtering technique. A new band is observed near 925 cm{sup −1} in the Raman spectra of gold incorporated tungsten oxide films which is not observed in the pure tungsten oxide film. The intensity of this band enhances with gold content. A localized surface plasmon resonance (LSPR) band is observed near the wavelength 604 nm in gold incorporated tungsten oxide films. The integrated intensities of LSPR band and Raman band (∼925 cm{sup −1}) can be used for sensing the quantity of gold in the Au/WO{sub 3} matrix.

Structural, mechanical, and electronic properties of monoclinic N{sub 2}H{sub 5}N{sub 3} under pressure

Energy Technology Data Exchange (ETDEWEB)

Qi-Jun, Liu; Fu-Sheng, Liu, E-mail: qijunliu@home.swjtu.edu.cn [School of Physical Science and Technology, Southwest Jiaotong University, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Chengdu (China); Bond and Band Engineering Group, Sichuan Provincial Key Laboratory (for Universities) of High Pressure Science and Technology, Southwest Jiaotong University, Chengdu (China); Zheng-Tang, Liu [State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi' an, (China)

2015-08-15

Structural, elastic, mechanical, and electronic properties of monoclinic N{sub 2}H{sub 5}N{sub 3} at zero and high pressure have been investigated using the plane-wave ultrasoft pseudopotential method within the density-functional theory (DFT). The pressure dependences of structural parameters, elastic constants, mechanical properties, band gaps, and density of states of monoclinic N{sub 2}H{sub 5}N{sub 3} have been calculated and discussed. The obtained results show that monoclinic N{sub 2}H{sub 5}N{sub 3} is unstable at pressures exceeding the value 126.1 GPa. The ratio of B/G and the Cauchy’s pressure indicate that monoclinic N{sub 2}H{sub 5}N{sub 3} behaves in ductile nature with pressure ranging from 0 to 200 GPa. (author)

The Monoclinic Phase in PZT : New Light on Morphotropic Phase Boundaries

NARCIS (Netherlands)

Noheda, B.; Gonzalo, J.A.; Guo, R.; Park, S.-E.; Cross, L.E.; Cox, D.E.; Shirane, G.

2000-01-01

A summary of the work recently carried out on the morphotropic phase boundary (MPB) of PZT is presented. By means of x-ray powder diffraction on ceramic samples of excellent quality, the MPB has been successfully characterized by changing temperature in a series of closely spaced compositions. As a

Modeling of metastable phase formation diagrams for sputtered thin films.

Science.gov (United States)

Chang, Keke; Music, Denis; To Baben, Moritz; Lange, Dennis; Bolvardi, Hamid; Schneider, Jochen M

2016-01-01

A method to model the metastable phase formation in the Cu-W system based on the critical surface diffusion distance has been developed. The driver for the formation of a second phase is the critical diffusion distance which is dependent on the solubility of W in Cu and on the solubility of Cu in W. Based on comparative theoretical and experimental data, we can describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation. Metastable phase formation diagrams for Cu-W and Cu-V thin films are predicted and validated by combinatorial magnetron sputtering experiments. The correlative experimental and theoretical research strategy adopted here enables us to efficiently describe the relationship between the solubilities and the critical diffusion distances in order to model the metastable phase formation during magnetron sputtering.

Tuning Eu"3"+ emission in europium sesquioxide films by changing the crystalline phase

International Nuclear Information System (INIS)

Mariscal, A.; Quesada, A.; Camps, I.; Palomares, F.J.; Fernández, J.F.; Serna, R.

2016-01-01

Highlights: • PLD production of high quality europium sesquioxide (Eu_2O_3) films. • The deposition of Al_2O_3 capping and/or buffer layers modifies the crystallization for Eu_2O_3 films upon annealing. • The formation of cubic or monoclinic phases can be favored. • Eu"3"+ emission tuning is achieved as a consequence of crystal field effects. - Abstract: We report the growth of europium sesquioxide (Eu_2O_3) thin films by pulsed laser deposition (PLD) in vacuum at room temperature from a pure Eu_2O_3 ceramic bulk target. The films were deposited in different configurations formed by adding capping and/or buffer layers of amorphous aluminum oxide (a-Al_2O_3). The optical properties, refractive index and extinction coefficient of the as deposited Eu_2O_3 layers were obtained. X-ray photoelectron spectroscopy (XPS) measurements were done to assess its chemical composition. Post-deposition annealing was performed at 500 °C and 850 °C in air in order to achieve the formation of crystalline films and to accomplish photoluminescence emission. According to the analysis of X-ray diffraction (XRD) spectra, cubic and monoclinic phases were formed. It is found that the relative amount of the phases is related to the different film configurations, showing that the control over the crystallization phase can be realized by adequately designing the structures. All the films showed photoluminescence emission peaks (under excitation at 355 nm) that are attributed to the intra 4f-transitions of Eu"3"+ ions. The emission spectral shape depends on the crystalline phase of the Eu_2O_3 layer. Specifically, changes in the hypersensitive "5D_0 → "7F_2 emission confirm the strong influence of the crystal field effect on the Eu"3"+ energy levels.

The monoclinic polymorph of dimethylarsinic acid

Directory of Open Access Journals (Sweden)

Richard Betz

2011-08-01

Full Text Available The title compound, C2H7AsO2 or [As(CH32O(OH], is an organic derivative of arsinic acid, and is also known by its trivial name cacodylic acid. In contrast to the first polymorph (triclinic, space group Poverline{1}, Z = 2, the current study revealed monoclinic symmetry (space group C2/c, Z = 8 for the second polymorph. The configuration of the tetrahedral molecule shows approximate Cs symmetry. Strong O—H...O hydrogen bonds connect the molecules to infinite zigzag chains along [010], which are further connected by weak intermolecular C—H...O contacts into a three-dimensional network.

Quantitative determination of phases in ZrO2 (MgO) (Y2O3) using the Rietveld method

International Nuclear Information System (INIS)

Castro, Antonio Carlos de

2007-01-01

The key objective of this work is the crystallographic characterization of the zircon co-doped with Yttria and magnesium with the application of the Rietveld method for quantitative phase analysis of zircon polymorph (zircon monoclinic, tetragonal, and cubic). Samples of zircon polymorph were obtained from zircon doped with Yttria and magnesium at defined molar concentrations. The zircon polymorph stability during subeutetoid aging at 1350 deg C were investigated to determine ZrO 2 - MgO - Y 2 0 3 phases degradation and to define the solid solutions stability environment. ZrO 2 powders doped with 8 mol por cent of MgO and 1 mol por cent of Y 2 O 3 , and 9 mol por cent of MgO and 0 mol por cent of Y 2 O 3 have been prepared by chemical route using the co-precipitation method. These samples have been calcinate at 550 deg C, sintered at 1500 deg C and characterized by the Rietveld method using the X-ray diffraction data. The variation of the lattice parameter, changes in the phase composition and their microstructures are discussed. The application of the Rietveld method for quantitative phase analysis of zircon polymorph (zircon tetragonal and cubic) reveals no formation of tetragonal phase and indicating that the matrix is the cubic phase with low concentration of monoclinic phase.(author)

Effect of cooling rate on tetragonal to monoclinic transformation in hot pressed ZrO2(Y2O3) ceramics

International Nuclear Information System (INIS)

Zhu, W.Z.; Ding, Z.S.; Lei, T.C.; Zhou, Y.

1995-01-01

It is well documented that the tetragonal (T) to monoclinic (M) transition in either pure zirconia or partially stabilized zirconia is the origin of toughening in that resistance to the propagation of cracks can be greatly enhanced by the concurrent appearance of the stress field of the transformation. In the present paper, the effect of cooling rate on the T → M phase transformation in yttria-containing zirconia and its resultant mechanical properties have been studied by means of thermal expansion analysis. Both the T → M and M → T transformations are affected by the cooling and heating rates, respectively. The amount of M-phase decreases with increasing cooling rate. T → M transition occurring within the interior part of specimen can be completely inhibited by the cooling rate of 100 C/min for ZrO 2 (2mol% Y 2 O 3 ) ceramic sintered at 1,600 C. The start point and end point of the T → M transformation decreases and increases, respectively, with increasing cooling rate. Both the start point and end point of the M → T transformation increase with increasing cooling rate. The divergence between the results of X-ray diffraction and the thermal expansion analysis has been rationalized in terms of the both internal and external factors, namely, preferential sites of surface for the formation of the M-phase and limited sensitivity of measurement of the thermal expansion apparatus. Both the water-cooled and air-cooled specimens show much improved mechanical properties regardless of the sintering temperatures or yttria content because of the relatively higher T-phase fraction retained to room temperature

Growth kinetics of tetragonal and monoclinic ZrO2 crystallites in 3 mol% yttria partially stabilized ZrO2 (3Y-PSZ) precursor powder

International Nuclear Information System (INIS)

Kuo, Chih-Wei; Lee, Kuen-Chan; Yen, Feng-Lin; Shen, Yun-Hwei; Lee, Huey-Er; Wen, Shaw-Bing; Wang, Moo-Chin; Stack, Margaret Mary

2014-01-01

Highlights: • The crystalline structures were composed of tetragonal and monoclinic ZrO 2 . • Growth kinetics of t-ZrO 2 in the 3Y-PSZ precursor powder is described as: D te 2 =(4.57±0.55)t 0.12±0.02 exp(-((24.79±0.38)×10 3 )/(RT) ). • Growth kinetics of m-ZrO 2 in the 3Y-PSZ precursor powder is described as: D m 2 =(4.40±1.63)t 0.17±0.08 exp(-((66.47±3.97)×10 3 )/(RT) ). - Abstract: The growth kinetics of tetragonal and monoclinic ZrO 2 crystallites in 3 mol% yttria partially stabilized ZrO 2 (3Y-PSZ) precursor powder has been investigated using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) specific surface area analysis, transmission electron microscopy (TEM) and high resolution TEM (HRTEM). After calcination of the 3Y-PSZ precursor powder between 773 and 1073 K for 2 h, the crystalline structures were composed of tetragonal and monoclinic ZrO 2 as the primary and secondary phases, respectively. When the 3Y-PSZ precursor powder was calcined at 773 K for 2 h, the BET specific surface area was 97.13 m 2 /g, which is equivalent to a particle size of 10.30 nm. The crystallite sizes determined via XRD and BET agreed well, indicating that the powder was virtually non-agglomerated. The growth kinetics of tetragonal and monoclinic ZrO 2 crystallite isothermal growth in the 3Y-PSZ precursor powder are described by: D te 2 =(4.57±0.55)t 0.12±0.02 exp(-((24.79±0.38)×10 3 )/(RT) ) and D m 2 =(4.40±1.63)t 0.17±0.08 exp(-((66.47±3.97)×10 3 )/(RT) ), respectively, for 773K≤T≤1073K. D te and D m denote the crystallite size of tetragonal and monoclinic ZrO 2 at time t and temperature T, respectively

Effect of alteration phase formation on the glass dissolution rate

International Nuclear Information System (INIS)

Ebert, W.L.

1997-01-01

The dissolution rates of many glasses have been observed to increase upon the formation of certain alteration phases. While simulations have predicted the accelerating effect of formation of certain phases, the phases predicted to form in computer simulations are usually different than those observed to form in experiments. This is because kinetically favored phases form first in experiments, while simulations predict the thermodynamically favored phases. Static dissolution tests with crushed glass have been used to measure the glass dissolution rate after alteration phases form. Because glass dissolution rates are calculated on a per area basis, an important effect in tests conducted with crushed glass is the decrease in the surface area of glass that is available for reaction as the glass dissolves. This loss of surface area must be taken into account when calculating the dissolution rate. The phases that form and their effect on the dissolution rate are probably related to the glass composition. The impact of phase formation on the glass dissolution rate also varies according to the solubility products of the alteration phases and how the orthocilicic acid activity is affected. Insight into the relationship between the glass dissolution rate, solution chemistry and alteration phase formation is provided by the results of accelerated dissolution tests

Effect of alteration phase formation on the glass dissolution rate

Energy Technology Data Exchange (ETDEWEB)

Ebert, W L [Argonne National Laboratory, Chemical Technology Div. (United States)

1997-07-01

The dissolution rates of many glasses have been observed to increase upon the formation of certain alteration phases. While simulations have predicted the accelerating effect of formation of certain phases, the phases predicted to form in computer simulations are usually different than those observed to form in experiments. This is because kinetically favored phases form first in experiments, while simulations predict the thermodynamically favored phases. Static dissolution tests with crushed glass have been used to measure the glass dissolution rate after alteration phases form. Because glass dissolution rates are calculated on a per area basis, an important effect in tests conducted with crushed glass is the decrease in the surface area of glass that is available for reaction as the glass dissolves. This loss of surface area must be taken into account when calculating the dissolution rate. The phases that form and their effect on the dissolution rate are probably related to the glass composition. The impact of phase formation on the glass dissolution rate also varies according to the solubility products of the alteration phases and how the orthocilicic acid activity is affected. Insight into the relationship between the glass dissolution rate, solution chemistry and alteration phase formation is provided by the results of accelerated dissolution tests.

Kinetics of sigma phase formation in a Duplex Stainless Steel

Directory of Open Access Journals (Sweden)

Rodrigo Magnabosco

2009-09-01

Full Text Available This work determines the kinetics of sigma phase formation in UNS S31803 Duplex Stainless Steel (DSS, describing the phase transformations that occur in isothermal aging between 700 and 900 ºC for time periods up to 1032 hours, allowing the determination of the Time-Temperature-Precipitation (TTP diagram for sigma phase and proposing a model to predict the kinetics of sigma phase formation using a Johnson-Mehl-Avrami (JMA type expression. The higher kinetics of sigma phase formation occurs at 850 ºC. However, isothermal aging between 700 and 900 ºC for time periods up to 1032 hours are not sufficient to the establishment of thermodynamic equilibrium. Activation energy for both nucleation and growth of sigma phase is determined (185 kJ.mol-1 and its value is equivalent to the activation energy for Cr diffusion in ferrite, indicating that diffusion of Cr is probably the major thermally activated process involved in sigma phase formation. The determined JMA type expression presents good fit with experimental data between 700 and 850 ºC.

Pressure-induced phase transformation of HfO2

International Nuclear Information System (INIS)

Arashi, H.

1992-01-01

This paper reports on the pressure dependence of the Raman spectra of HfO 2 that was measured by a micro-Raman technique using a single-crystal specimen in the pressure range from 0 to 10 GPa at room temperature. The symmetry assignment of Raman bands of the monoclinic phase was experimentally accomplished from the polarization measurements for the single crystal. With increased pressure, a phase transformation for the monoclinic phase took place at 4.3 ± 0.3 GPa. Nineteen Raman bands were observed for the high-pressure phase. The spectral structure of the Raman bands for the high-pressure phase was similar with those reported previously for ZrO 2 . The space group for the high pressure phase of HfO 2 was determined as Pbcm, which was the same as that of the high-pressure phase for ZrO 2 on the basis of the number and the spectral structure of the Raman bands

Presence of a monoclinic (Pm) phase in the morphotropic phase boundary region of multiferroic (1 − x)Bi(Ni{sub 1/2}Ti{sub 1/2})O{sub 3}-xPbTiO{sub 3} solid solution: A Rietveld study

Energy Technology Data Exchange (ETDEWEB)

Pandey, Rishikesh, E-mail: akhilesh-bhu@yahoo.com, E-mail: aksingh.mst@itbhu.ac.in; Singh, Akhilesh Kumar, E-mail: akhilesh-bhu@yahoo.com, E-mail: aksingh.mst@itbhu.ac.in [School of Materials Science and Technology, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005 (India)

2014-07-28

We present here the results of structural studies on multiferroic (1 − x)Bi(Ni{sub 1/2}Ti{sub 1/2})O{sub 3}-xPbTiO{sub 3} solid solution using Rietveld analysis on powder x-ray diffraction data in the composition range 0.35 ≤ x ≤ 0.55. The stability region of various crystallographic phases at room temperature for (1 − x)Bi(Ni{sub 1/2}Ti{sub 1/2})O{sub 3}-xPbTiO{sub 3} is determined precisely. Structural transformation from pseudo-cubic (x ≤ 0.40) to tetragonal (x ≥ 0.50) phase is observed via phase coexistence region demarcating the morphotropic phase boundary. The morphotropic phase boundary region consists of coexisting tetragonal and monoclinic structures with space group P4mm and Pm, respectively, stable in composition range 0.41 ≤ x ≤ 0.49 as confirmed by Rietveld analysis. The results of Rietveld analysis completely rule out the coexistence of rhombohedral and tetragonal phases in the morphotropic phase boundary region reported by earlier workers. A comparison between the bond lengths for “B-site cations-oxygen anions” obtained after Rietveld refinement, with the bond length calculated using Shannon-Prewitt ionic radii, reveals the ionic nature of B-O (Ni/Ti-O) bonds for the cubic phase and partial covalent character for the other crystallographic phases.

High temperature-induced phase transitions in Sr2GdRuO6 complex perovskite

International Nuclear Information System (INIS)

Triana, C.A.; Corredor, L.T.; Landínez Téllez, D.A.; Roa-Rojas, J.

2011-01-01

Highlights: ► Crystal structure, thermal expansion and phase transitions at high-temperature of Sr 2 GdRuO 6 perovskite has been investigated. ► X-ray diffraction pattern at 298 K of Sr 2 GdRuO 6 corresponds to monoclinic perovskite-type structure with P2 1 /n space group. ► Evolution of X-ray diffraction patterns at high-temperature shows that the Sr 2 GdRuO 6 perovskite suffers two-phase transitions. ► At 573 K the X-ray diffraction pattern of Sr 2 GdRuO 6 corresponds to monoclinic perovskite-type structure with I2/m space group. ► At 1273 K the Sr 2 GdRuO 6 perovskite suffers a complete phase-transition from monoclinic I2/m (no. 12) to tetragonal I4/m (no. 87). -- Abstract: The crystal structure behavior of the Sr 2 GdRuO 6 complex perovskite at high-temperature has been investigated over a wide temperature range between 298 K ≤ T ≤ 1273 K. Measurements of X-ray diffraction at room-temperature and Rietveld analysis of the experimental patterns show that this compound crystallizes in a monoclinic perovskite-like structure, which belongs to the P2 1 /n (no. 14) space group and 1:1 ordered arrangement of Ru 5+ and Gd 3+ cations over the six-coordinate M sites. Experimental lattice parameters were obtained to be a =5.8103(5) Å, b =5.8234(1) Å, c =8.2193(9) Å, V = 278.11(2) Å 3 and angle β = 90.310(5)°. The high-temperature analysis shows the occurrence of two-phase transitions on this material. First, at 573 K it adopts a monoclinic perovskite-type structure with I2/m (no. 12) space group with lattice parameters a = 5.8275(6) Å, b = 5.8326(3) Å, c = 8.2449(2) Å, V = 280.31(3) Å 3 and angle β = 90.251(3)°. Close to 1273 K it undergoes a complete phase-transition from monoclinic I2/m (no. 12) to tetragonal I4/m (no. 87), with lattice parameters a = 5.8726(1) Å, c = 8.3051(4) Å, V = 286.39(8) Å 3 and angle β = 90.0°. The high-temperature phase transition from monoclinic I2/m (no. 12) to tetragonal I4/m (no. 87) is characterized

Gel phase formation in dilute triblock copolyelectrolyte complexes

Science.gov (United States)

Srivastava, Samanvaya; Andreev, Marat; Levi, Adam E.; Goldfeld, David J.; Mao, Jun; Heller, William T.; Prabhu, Vivek M.; de Pablo, Juan J.; Tirrell, Matthew V.

2017-02-01

Assembly of oppositely charged triblock copolyelectrolytes into phase-separated gels at low polymer concentrations (simulations. Here we show that in contrast to uncharged, amphiphilic block copolymers that form discrete micelles at low concentrations and enter a phase of strongly interacting micelles in a gradual manner with increasing concentration, the formation of a dilute phase of individual micelles is prevented in polyelectrolyte complexation-driven assembly of triblock copolyelectrolytes. Gel phases form and phase separate almost instantaneously on solvation of the copolymers. Furthermore, molecular models of self-assembly demonstrate the presence of oligo-chain aggregates in early stages of copolyelectrolyte assembly, at experimentally unobservable polymer concentrations. Our discoveries contribute to the fundamental understanding of the structure and pathways of complexation-driven assemblies, and raise intriguing prospects for gel formation at extraordinarily low concentrations, with applications in tissue engineering, agriculture, water purification and theranostics.

Static deformation of two welded monoclinic elastic half-spaces due ...

Indian Academy of Sciences (India)

M. Senthilkumar (Newgen Imaging) 1461 1996 Oct 15 13:05:22

Static deformation of two monoclinic elastic half-spaces in welded contact due to a long inclined strike-slip fault situated in one of the half-spaces is studied analytically and numerically. Closed- form algebraic expressions for the displacement at any point of the medium are obtained. The variation of the displacement at the ...

Calculation of magnetization curves and probability distribution for monoclinic and uniaxial systems

International Nuclear Information System (INIS)

Sobh, Hala A.; Aly, Samy H.; Yehia, Sherif

2013-01-01

We present the application of a simple classical statistical mechanics-based model to selected monoclinic and hexagonal model systems. In this model, we treat the magnetization as a classical vector whose angular orientation is dictated by the laws of equilibrium classical statistical mechanics. We calculate for these anisotropic systems, the magnetization curves, energy landscapes and probability distribution for different sets of relevant parameters and magnetic fields of different strengths and directions. Our results demonstrate a correlation between the most probable orientation of the magnetization vector, the system's parameters, and the external magnetic field. -- Highlights: ► We calculate magnetization curves and probability angular distribution of the magnetization. ► The magnetization curves are consistent with probability results for the studied systems. ► Monoclinic and hexagonal systems behave differently due to their different anisotropies

Correlation of Structure, Tunable Colors, and Lifetimes of (Sr, Ca, Ba)Al₂O₄:Eu2+, Dy3+ Phosphors.

Science.gov (United States)

Xie, Qidi; Li, Bowen; He, Xin; Zhang, Mei; Chen, Yan; Zeng, Qingguang

2017-10-18

(Sr, Ca, Ba)Al₂O₄:Eu 2+ , Dy 3+ phosphors were prepared via a high temperature solid-state reaction method. The correlation of phase structure, optical properties and lifetimes of the phosphors are investigated in this work. For the (Sr, Ca)Al₂O₄:Eu 2+ ,Dy 3+ phosphors, the different phase formation from monoclinic SrAl₂O₄ phase to hexagonal SrAl₂O₄ phase to monoclinic CaAl₂O₄ phase was observed when the Ca content increased. The emission color of SrAl₂O₄:Eu 2+ , Dy 3+ phosphors varied from green to blue. For the (Sr, Ba)Al₂O₄:Eu 2+ , Dy 3+ phosphors, different phase formation from the monoclinic SrAl₂O₄ phase to the hexagonal BaAl₂O₄ phase was observed, along with a shift of emission wavelength from 520 nm to 500 nm. More interestingly, the decay time of SrAl₂O₄:Eu 2+ , Dy 3+ changed due to the different phase formations. Lifetime can be dramatically shortened by the substitution of Sr 2+ with Ba 2+ cations, resulting in improving the performance of the alternating current light emitting diode (AC-LED). Finally, intense LEDs are successfully obtained by combining these phosphors with Ga(In)N near UV chips.

Lifting the geometric frustration through a monoclinic distortion in “114” YBaFe4O7.0: Magnetism and transport

International Nuclear Information System (INIS)

Duffort, V.; Sarkar, T.; Caignaert, V.; Pralong, V.; Raveau, B.; Avdeev, M.; Cervellino, A.; Waerenborgh, J.C.; Tsipis, E.V.

2013-01-01

The possibility to lift the geometric frustration in the “114” stoichiomeric tetragonal oxide YBaFe 4 O 7.0 by decreasing the temperature has been investigated using neutron and synchrotron powder diffraction techniques. Besides the structural transition from tetragonal to monoclinic symmetry that appears at T S =180 K, a magnetic transition is observed below T N =95 K. The latter corresponds to a lifting of the 3D geometric frustration toward an antiferromagnetic long range ordering, never observed to date in a cubic based “114’” oxide. The magnetic structure, characterized by the propagation vector k 1 =(0,0,½), shows that one iron Fe2 exhibits a larger magnetic moment than the three others, suggesting a possible charge ordering according to the formula YBaFe 3+ Fe 3 2+ O 7.0 . The magnetic M(T) and χ′(T) curves, in agreement with neutron data, confirm the structural and magnetic transitions and evidence the coexistence of residual magnetic frustration. Moreover, the transport measurements show a resistive transition from a thermally activated conduction mechanism to a variable range hopping mechanism at T S =180 K, with a significant increase of the dependence of the resistivity vs. temperature. Mössbauer spectroscopy clearly evidences a change in the electronic configuration of the iron framework at the structural transition as well as coexistence of several oxidation states. The role of barium underbonding in these transitions is discussed. - Graphical abstract: Atomic displacements at the tetragonal-monoclinic transition in YBaFe 4 O 7 . Display Omitted - Highlights: • The structural and magnetic phase transitions of YBaFe 4 O 7 were studied below room temperature. • The tetragonal to monoclinic transition, characterized by NPD and SXRD, was studied using mode crystallography approach. • Monoclinic distortion allows the lifting of the geometrical frustration on the iron sublattice, leading to AF order at T=95 K

Temperature dependence of the dielectric tensor of monoclinic Ga2O3 single crystals in the spectral range 1.0-8.5 eV

Science.gov (United States)

Sturm, C.; Schmidt-Grund, R.; Zviagin, V.; Grundmann, M.

2017-08-01

The full dielectric tensor of monoclinic Ga2O3 (β-phase) was determined by generalized spectroscopic ellipsometry in the spectral range from 1.0 eV up to 8.5 eV and temperatures in the range from 10 K up to 300 K. By using the oriented dipole approach, the energies and broadenings of the excitonic transitions are determined as a function of the temperature, and the exciton-phonon coupling properties are deduced.

Conversion of Phase II Unsteady Aerodynamics Experiment Data to Common Format; TOPICAL

International Nuclear Information System (INIS)

Hand, M. M.

1999-01-01

A vast amount of aerodynamic, structural, and turbine performance data were collected during three phases of the National Renewable Energy Laboratory's Unsteady Aerodynamics Experiment (UAE). To compare data from the three phases, a similar format of engineering unit data is required. The process of converting Phase II data from a previous engineering unit format to raw integer counts is discussed. The integer count files can then be input to the new post-processing software, MUNCH. The resulting Phase II engineering unit files are in a common format with current and future UAE engineering unit files. An additional objective for changing the file format was to convert the Phase II data from English units to SI units of measurement

Experimental formation enthalpies for intermetallic phases and other inorganic compounds

Science.gov (United States)

Kim, George; Meschel, S. V.; Nash, Philip; Chen, Wei

2017-01-01

The standard enthalpy of formation of a compound is the energy associated with the reaction to form the compound from its component elements. The standard enthalpy of formation is a fundamental thermodynamic property that determines its phase stability, which can be coupled with other thermodynamic data to calculate phase diagrams. Calorimetry provides the only direct method by which the standard enthalpy of formation is experimentally measured. However, the measurement is often a time and energy intensive process. We present a dataset of enthalpies of formation measured by high-temperature calorimetry. The phases measured in this dataset include intermetallic compounds with transition metal and rare-earth elements, metal borides, metal carbides, and metallic silicides. These measurements were collected from over 50 years of calorimetric experiments. The dataset contains 1,276 entries on experimental enthalpy of formation values and structural information. Most of the entries are for binary compounds but ternary and quaternary compounds are being added as they become available. The dataset also contains predictions of enthalpy of formation from first-principles calculations for comparison. PMID:29064466

Thermodynamic study of CVD-ZrO2 phase diagrams

International Nuclear Information System (INIS)

Torres-Huerta, A.M.; Vargas-Garcia, J.R.; Dominguez-Crespo, M.A.; Romero-Serrano, J.A.

2009-01-01

Chemical vapor deposition (CVD) of zirconium oxide (ZrO 2 ) from zirconium acetylacetonate Zr(acac) 4 has been thermodynamically investigated using the Gibbs' free energy minimization method and the FACTSAGE program. Thermodynamic data Cp o , ΔH o and S o for Zr(acac) 4 have been estimated using the Meghreblian-Crawford-Parr and Benson methods because they are not available in the literature. The effect of deposition parameters, such as temperature and pressure, on the extension of the region where pure ZrO 2 can be deposited was analyzed. The results are presented as calculated CVD stability diagrams. The phase diagrams showed two zones, one of them corresponds to pure monoclinic phase of ZrO 2 and the other one corresponds to a mix of monoclinic phase of ZrO 2 and graphite carbon.

Phase transformation in sol-gel prepared zirconia using in-situ high temperature X-ray diffraction

International Nuclear Information System (INIS)

Srinivasan, R.; Davis, B.H.; Hubbard, C.R.; Cavin, O.B.; Porter, W.D.

1991-01-01

Zirconia was precipitated at a pH of 10.5 by admixing a solution of ZrCl 4 and NH 4 OH both rapidly (∼ 1 min) and slowly (∼ 8 hr). The precipitate was calcined at 500C for 5 hours and then furnace cooled. The former exhibited monoclinic phase while the latter yielded tetragonal phase. The pathway from amorphous to crystalline form was followed by in-situ high temperature X-ray diffraction in flowing air and in He. The data showed the evolution of the tetragonal crystalline phase on heating. On rapid cooling the tetragonal phase is retained at R.T., and on slow cooling the transformation to monoclinic phase occurs in air

Correlation of Structure, Tunable Colors, and Lifetimes of (Sr, Ca, Ba)Al2O4:Eu2+, Dy3+ Phosphors

Science.gov (United States)

Xie, Qidi; Li, Bowen; He, Xin; Zhang, Mei; Chen, Yan; Zeng, Qingguang

2017-01-01

(Sr, Ca, Ba)Al2O4:Eu2+, Dy3+ phosphors were prepared via a high temperature solid-state reaction method. The correlation of phase structure, optical properties and lifetimes of the phosphors are investigated in this work. For the (Sr, Ca)Al2O4:Eu2+, Dy3+ phosphors, the different phase formation from monoclinic SrAl2O4 phase to hexagonal SrAl2O4 phase to monoclinic CaAl2O4 phase was observed when the Ca content increased. The emission color of SrAl2O4:Eu2+, Dy3+ phosphors varied from green to blue. For the (Sr, Ba)Al2O4:Eu2+, Dy3+ phosphors, different phase formation from the monoclinic SrAl2O4 phase to the hexagonal BaAl2O4 phase was observed, along with a shift of emission wavelength from 520 nm to 500 nm. More interestingly, the decay time of SrAl2O4:Eu2+, Dy3+ changed due to the different phase formations. Lifetime can be dramatically shortened by the substitution of Sr2+ with Ba2+ cations, resulting in improving the performance of the alternating current light emitting diode (AC-LED). Finally, intense LEDs are successfully obtained by combining these phosphors with Ga(In)N near UV chips. PMID:29057839

Correlation of Structure, Tunable Colors, and Lifetimes of (Sr, Ca, BaAl2O4:Eu2+, Dy3+ Phosphors

Directory of Open Access Journals (Sweden)

Qidi Xie

2017-10-01

Full Text Available (Sr, Ca, BaAl2O4:Eu2+, Dy3+ phosphors were prepared via a high temperature solid-state reaction method. The correlation of phase structure, optical properties and lifetimes of the phosphors are investigated in this work. For the (Sr, CaAl2O4:Eu2+,Dy3+ phosphors, the different phase formation from monoclinic SrAl2O4 phase to hexagonal SrAl2O4 phase to monoclinic CaAl2O4 phase was observed when the Ca content increased. The emission color of SrAl2O4:Eu2+, Dy3+ phosphors varied from green to blue. For the (Sr, BaAl2O4:Eu2+, Dy3+ phosphors, different phase formation from the monoclinic SrAl2O4 phase to the hexagonal BaAl2O4 phase was observed, along with a shift of emission wavelength from 520 nm to 500 nm. More interestingly, the decay time of SrAl2O4:Eu2+, Dy3+changed due to the different phase formations. Lifetime can be dramatically shortened by the substitution of Sr2+ with Ba2+ cations, resulting in improving the performance of the alternating current light emitting diode (AC-LED. Finally, intense LEDs are successfully obtained by combining these phosphors with Ga(InN near UV chips.

Paleomagnetic and structural evidence for oblique slip in a fault-related fold, Grayback monocline, Colorado

Science.gov (United States)

Tetreault, J.; Jones, C.H.; Erslev, E.; Larson, S.; Hudson, M.; Holdaway, S.

2008-01-01

Significant fold-axis-parallel slip is accommodated in the folded strata of the Grayback monocline, northeastern Front Range, Colorado, without visible large strike-slip displacement on the fold surface. In many cases, oblique-slip deformation is partitioned; fold-axis-normal slip is accommodated within folds, and fold-axis-parallel slip is resolved onto adjacent strike-slip faults. Unlike partitioning strike-parallel slip onto adjacent strike-slip faults, fold-axis-parallel slip has deformed the forelimb of the Grayback monocline. Mean compressive paleostress orientations in the forelimb are deflected 15??-37?? clockwise from the regional paleostress orientation of the northeastern Front Range. Paleomagnetic directions from the Permian Ingleside Formation in the forelimb are rotated 16??-42?? clockwise about a bedding-normal axis relative to the North American Permian reference direction. The paleostress and paleomagnetic rotations increase with the bedding dip angle and decrease along strike toward the fold tip. These measurements allow for 50-120 m of fold-axis-parallel slip within the forelimb, depending on the kinematics of strike-slip shear. This resolved horizontal slip is nearly equal in magnitude to the ???180 m vertical throw across the fold. For 200 m of oblique-slip displacement (120 m of strike slip and 180 m of reverse slip), the true shortening direction across the fold is N90??E, indistinguishable from the regionally inferred direction of N90??E and quite different from the S53??E fold-normal direction. Recognition of this deformational style means that significant amounts of strike slip can be accommodated within folds without axis-parallel surficial faulting. ?? 2008 Geological Society of America.

Formation of Ion Phase-Space Vortexes

DEFF Research Database (Denmark)

Pécseli, Hans; Trulsen, J.; Armstrong, R. J.

1984-01-01

The formation of ion phase space vortexes in the ion two stream region behind electrostatic ion acoustic shocks are observed in a laboratory experiment. A detailed analysis demonstrates that the evolution of such vortexes is associated with ion-ion beam instabilities and a nonlinear equation for ...

Initial stages of ion beam-induced phase transformations in Gd2O3 and Lu2O3

Science.gov (United States)

Chen, Chien-Hung; Tracy, Cameron L.; Wang, Chenxu; Lang, Maik; Ewing, Rodney C.

2018-02-01

The atomic-scale evolution of lanthanide sesquioxides Gd2O3 and Lu2O3 irradiated with 1 MeV Kr ions at room temperature and 120 K, up to fluences of 1 × 1016 ions/cm2 (˜20 dpa), has been characterized by in situ transmission electron microscopy. At room temperature, both oxides exhibited high radiation tolerance. Irradiation did not cause any observable structural change in either material, likely due to the mobility of irradiation-induced point defects, causing efficient defect annihilation. For Gd2O3, having the larger cation ionic radius of the two materials, an irradiation-induced stacking fault structure appeared at low fluences in the low temperature irradiation. As compared with the cubic-to-monoclinic phase transformations known to result from higher energy (˜GeV) ion irradiation, Kr ions of lower energies (˜MeV) yield much lower rates of damage accumulation and thus less extensive structural modification. At a fluence of 2.5 × 1015 ions/cm2, only the initial stages of the cubic-to-monoclinic (C to B) phase transformation process, consisting of the formation and aggregation of defects, have been observed.

Tuning Eu{sup 3+} emission in europium sesquioxide films by changing the crystalline phase

Energy Technology Data Exchange (ETDEWEB)

Mariscal, A., E-mail: antonio.mariscal@csic.es [Laser Processing Group, Instituto de Óptica, CSIC, C/ Serrano 121, 28006 Madrid (Spain); Quesada, A. [Ceramics for Smart Systems Group, Instituto de Cerámica y Vidrio, C/ Kelsen 5, 28049 Madrid (Spain); Camps, I. [Laser Processing Group, Instituto de Óptica, CSIC, C/ Serrano 121, 28006 Madrid (Spain); Palomares, F.J. [Instituto de Ciencia de Materiales de Madrid, C/ Sor Juana Inés de la Cruz 3, 28049 Madrid (Spain); Fernández, J.F. [Ceramics for Smart Systems Group, Instituto de Cerámica y Vidrio, C/ Kelsen 5, 28049 Madrid (Spain); Serna, R. [Laser Processing Group, Instituto de Óptica, CSIC, C/ Serrano 121, 28006 Madrid (Spain)

2016-06-30

Highlights: • PLD production of high quality europium sesquioxide (Eu{sub 2}O{sub 3}) films. • The deposition of Al{sub 2}O{sub 3} capping and/or buffer layers modifies the crystallization for Eu{sub 2}O{sub 3} films upon annealing. • The formation of cubic or monoclinic phases can be favored. • Eu{sup 3+} emission tuning is achieved as a consequence of crystal field effects. - Abstract: We report the growth of europium sesquioxide (Eu{sub 2}O{sub 3}) thin films by pulsed laser deposition (PLD) in vacuum at room temperature from a pure Eu{sub 2}O{sub 3} ceramic bulk target. The films were deposited in different configurations formed by adding capping and/or buffer layers of amorphous aluminum oxide (a-Al{sub 2}O{sub 3}). The optical properties, refractive index and extinction coefficient of the as deposited Eu{sub 2}O{sub 3} layers were obtained. X-ray photoelectron spectroscopy (XPS) measurements were done to assess its chemical composition. Post-deposition annealing was performed at 500 °C and 850 °C in air in order to achieve the formation of crystalline films and to accomplish photoluminescence emission. According to the analysis of X-ray diffraction (XRD) spectra, cubic and monoclinic phases were formed. It is found that the relative amount of the phases is related to the different film configurations, showing that the control over the crystallization phase can be realized by adequately designing the structures. All the films showed photoluminescence emission peaks (under excitation at 355 nm) that are attributed to the intra 4f-transitions of Eu{sup 3+} ions. The emission spectral shape depends on the crystalline phase of the Eu{sub 2}O{sub 3} layer. Specifically, changes in the hypersensitive {sup 5}D{sub 0} → {sup 7}F{sub 2} emission confirm the strong influence of the crystal field effect on the Eu{sup 3+} energy levels.

Nanosize stabilization of cubic and tetragonal phases in reactive plasma synthesized zirconia powders

Energy Technology Data Exchange (ETDEWEB)

Jayakumar, S., E-mail: sjayakumar.physics@gmail.com [Research and Development Centre, Bharathiar University, Coimbatore 641 014 (India); Department of Physics, Pollachi Institute of Engineering and Technology, Pollachi 642 205 (India); Ananthapadmanabhan, P.V.; Thiyagarajan, T.K. [Laser and Plasma Technology Division, BARC, Trombay, Mumbai 400 085 (India); Perumal, K. [Vision for Wisdom, Temple of Consciousness, Aliyar 642 101 (India); Mishra, S.C. [Department of Metallurgical and Materials Engg, National Institute of Technology, Rourkela 769 008 (India); Suresh, G. [Department of Physics, Park College of Engineering and Technology, Coimbatore 641 659 (India); Su, L.T.; Tok, A.I.Y. [School of Materials Science and Engg, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639 798 (Singapore)

2013-06-15

Pure zirconium oxide powders with particle size 2–33 nm are synthesized by reactive plasma processing. Transmission electron microscopy investigation of these particles revealed size dependent behavior for their phase stabilization. The monoclinic phase is found to be stable when particle size is ≥20 nm; Tetragonal is found to be stabilized in the range of 7–20 nm and as the particle size decreases to 6 nm and less, the cubic phase is stabilized. - Highlights: ► Direct conversion of micron-sized zirconium hydride powder to single crystal ZrO{sub 2} nanopowder. ► Size dependent stabilization of cubic, tetragonal and monoclinic phases in the reactive plasma synthesized ZrO{sub 2} nanopowder. ► Transmission electron microscopic investigation to identify particles of different sizes and their corresponding phase structure.

Temperature dependent emission characteristics of monoclinic YBO{sub 3}: Eu{sup 3+}/Tb{sup 3+} phosphor

Energy Technology Data Exchange (ETDEWEB)

Sharma, Suchinder K., E-mail: suchindersharma@gmail.com [AMO-Physics Division, Physical Research Laboratory, Navrangpura, Ahmedabad 380009 (India); Malik, M. Manzar [Department of Physics, Maulana Azad National Institute of Technology (MANIT), Bhopal (India)

2016-05-15

YBO{sub 3}:Eu{sup 3+}/Tb{sup 3+} phosphor samples synthesized by modified combustion method are studied in the present work using powder X-ray diffraction, UV–visible absorption spectroscopy, X-ray excited luminescence spectroscopy and optical parametric oscillator (OPO) based laser excited emission spectroscopy. The temperature dependence of luminescence emission is also studied. The structural analysis suggests that the samples possess monoclinic structure with C2/c space group. The emission maximum was excitation wavelength dependent and prominent emission was observed at 593 nm (241 nm excitation) and 613 nm (300 nm excitation) for YBO{sub 3}:Eu{sup 3+} samples. The prominent magnetic/ electric (593/613 nm) dipole-moment allowed transitions are attributed to the presence of Eu{sup 3+} at different sites. For YBO{sub 3}:Tb{sup 3+} phosphor, 543 nm emission was prominent and had no impact of the cite symmetry. The increase in PL intensity in Eu{sup 3+} doped samples above 225 K is associated with the carrier mobility. An energy level scheme showing the positions of the 4f and 5d energy levels of all divalent and trivalent lanthanide ions relative to the valence and conduction band of the YBO{sub 3} has been constructed opening the possibility of using YBO{sub 3} for other interesting applications. - Highlights: • Synthesis of YBO{sub 3} by modified combustion method using glycine as fuel. • Crystallization in monoclinic phase (rarely investigated). • Eu and Tb doping and investigation of temperature dependent PL. • VRBE diagram generated in YBO{sub 3} to develop new optical materials.

Effect of grinding and polishing on near-surface phase transformations in zirconia

International Nuclear Information System (INIS)

Reed, J.S.; Lejus, A.M.

1977-01-01

The transformation of near-surface material on grinding and polishing has been investigated in sintered zirconia of 1 μm grain size and 99 percent density containing 4.5 and 7.0 mole percent Y 2 O 3 . Rough wet and dry grinding transformed about 20 percent cubic phase into 18 percent tetragonal and 2 percent monoclinic in material initially 47 percent cubic and 53 percent tetragonal (4.5 mole percent Y 2 O 3 ) but no change of phase in material that was fully cubic (7.0 mole percent Y 2 O 3 ). Annealing and polishing reduced lattice strain but only polishing reduced the concentration of monoclinic and tetragonal phases. Microhardness studies indicated that lattice strain and the phase transformations increased the penetration hardness to a depth of about 4 μm

Phase formation in the (1-y)BiFeO{sub 3}-yBiScO{sub 3} system under ambient and high pressure

Energy Technology Data Exchange (ETDEWEB)

Salak, A.N., E-mail: salak@ua.pt [Department of Materials and Ceramic Engineering and CICECO – Aveiro Institute of Materials, University of Aveiro, 3810-193 Aveiro (Portugal); Khalyavin, D.D., E-mail: dmitry.khalyavin@stfc.ac.uk [ISIS Facility, Rutherford Appleton Laboratory, Chilton, OX11 0QX Didcot (United Kingdom); Pushkarev, A.V.; Radyush, Yu.V.; Olekhnovich, N.M. [Scientific-Practical Materials Research Centre of NAS of Belarus, P. Brovka Street, 19, 220072 Minsk (Belarus); Shilin, A.D.; Rubanik, V.V. [Institute of Technical Acoustics of NAS of Belarus, Lyudnikov Avenue, 13, 210023 Vitebsk (Belarus)

2017-03-15

Formation and thermal stability of perovskite phases in the BiFe{sub 1-y}Sc{sub y}O{sub 3} system (0≤y≤0.70) were studied. When the iron-to-scandium substitution rate does not exceed about 15 at%, the single-phase perovskite ceramics with the rhombohedral R3c symmetry (as that of the parent compound, BiFeO{sub 3}) can be prepared from the stoichiometric mixture of the respective oxides at ambient pressure. Thermal treatment of the oxide mixtures with a higher content of scandium results in formation of two main phases, namely a BiFeO{sub 3}-like R3c phase and a cubic (I23) sillenite-type phase based on γ-Bi{sub 2}O{sub 3}. Single-phase perovskite ceramics of the BiFe{sub 1-y}Sc{sub y}O{sub 3} composition were synthesized under high pressure from the thermally treated oxide mixtures. When y is between 0 and 0.25 the high-pressure prepared phase is the rhombohedral R3c with the √2a{sub p}×√2a{sub p}×2√3a{sub p} superstructure (a{sub p} ~ 4 Å is the pseudocubic perovskite unit-cell parameter). The orthorhombic Pnma phase (√2a{sub p}×4a{sub p}×2√2a{sub p}) was obtained in the range of 0.30≤y≤0.60, while the monoclinic C2/c phase (√6a{sub p}×√2a{sub p}×√6a{sub p}) is formed when y=0.70. The normalized unit-cell volume drops at the crossover from the rhombohedral to the orthorhombic composition range. The perovskite BiFe{sub 1-y}Sc{sub y}O{sub 3} phases prepared under high pressure are metastable regardless of their symmetry. At ambient pressure, the phases with the compositions in the ranges of 0.20≤y≤0.25, 0.30≤y<0.50 and 0.50≤y≤0.70 start to decompose above 970, 920 and 870 K, respectively. - Graphical abstract: Formation of perovskite phases in the BiFe{sub 1-y}Sc{sub y}O{sub 3} system when y≥0.15 requires application of pressure of several GPa. The phases formed under high pressure: R3c (0.20≤y≤0.25), Pnma (0.30≤y≤0.60) and C2/c (y≥0.70) are metastable. - Highlights: • Maximal Fe-to-Sc substitution rate in Bi

Formation of nano quasicrystalline and crystalline phases by mechanical alloying

International Nuclear Information System (INIS)

Shamah, A.M.; Ibrahim, S.; Hanna, F.F.

2011-01-01

Research highlights: → Mechanical alloying (MA) is an important method to investigate the formation of nano sized quasicrystalline phases in Al 86 Cr 14 , Al 84 Fe 16 and Al 62.5 Cu 25 Fe 12.5 compounds. The second part of the present work is an attempt to examine the possibility of formation of the i-phase of the Al 62.5 Cu 25 Fe 12.5 , which lies in the region of the perfect i-phase in the ternary phase diagram, by rapid solidification method. To perform the obtained quasi phase mechanical alloying and heat treatment at the rapid solidified sample were done. - Abstract: In the present work, the formation of nano quasicrystalline icosahedral phase in Al 86 Cr 14 , Al 84 Fe 16 and Al 62.5 Cu 25 Fe 12.5 alloys has been investigated by mechanical alloying. Mixtures of quasicrystalline and related crystalline phases have been observed under various milling conditions. The X-ray diffraction, differential thermal analysis and electrical resistivity techniques have been used for characterization and physical property measurements. The particle size was calculated by X-ray profile using Williamson-Hall plot method and it was found to be 25-50 nm size.

Excited State Dynamics and Semiconductor-to-Metallic Phase Transition of VO2 Thin Film

National Research Council Canada - National Science Library

Liu, Huimin

2004-01-01

.... Vanadium dioxide shows an ultrafast, passive phase transition (PT) from a monoclinic semiconductor phase to a metallic tetragonal rutile structure when the sample temperature is above 68 degrees C...

Phase formation in multicomponent monotectic aluminium alloys

Energy Technology Data Exchange (ETDEWEB)

Mirkovic, Djordje; Groebner, Joachim; Schmid-Fetzer, Rainer [Institute of Metallurgy, Clausthal University of Technology (Germany)

2008-07-01

Alloys with a miscibility gap in the liquid state are potential materials for advanced bearings in automotive and other applications. While binary alloys, such as Al-Pb or Al-Bi, are well known, the information available for ternary monotectic Al-alloys is scarce. However, the phase formation in multicomponent alloys is not only more challenging from a scientific aspect, it is also a prerequisite for a focused development of advanced alloys. This motivated our detailed study of monotectic Al-Bi-Cu-Sn alloys including both experimental and computational thermodynamic methods. Based on the initially established systematic classification of monotectic ternary Al-alloys, the first promising monotectic reaction was observed in the ternary Al-Bi-Zn system. Further ternary systems Al-Cu-Sn, Al-Bi-Sn, Al-Bi-Cu and Bi-Cu-Sn were investigated as basis for quaternary Al-Bi-Cu-Sn alloys. Experimental investigations of phase equilibria, enthalpies and solidification microstructures were combined with thermodynamic modeling. The results demonstrate that the developed precise thermodynamic description is vital to reveal the distinct multicomponent monotectic features of pertinent phase diagrams. The solidification paths of ternary monotectic alloy systems, Al-Bi-Zn, Al-Sn-Cu and Al-Bi-Cu, were also studied using thermodynamic calculations, revealing specific details of phase formation during solidification of selected alloys.

Effect of aluminium on formation of metastable phases in titanium-niobium alloys

International Nuclear Information System (INIS)

Trenogina, T.L.; Derevyanko, V.N.; Vozilkin, V.A.

2001-01-01

Specific features of phase transformations in the alloy of Ti-20Nb-29Al (at.%) are investigated in comparison with those in the aluminium-free Ti-21Nb alloy. It is states that in the alloy Ti-20Nb-29Al on quenching the ordering of β-solid solution takes place with B2-structure formation. The B2-matrix experiences decomposition with the formation of ordered Ω 0 -phase which field ranges up to 700 deg C. The investigation results show that the sequence of phase formation in Ti-Nb-Al and aluminium-free alloys is much the same. The only difference between them is the formation of ordered phases in the alloy Ti-20Nb-29Al [ru

Appearance of large crystalline domains in VO{sub 2} films grown on sapphire (001) and their phase transition characteristics

Energy Technology Data Exchange (ETDEWEB)

Azhan, Nurul Hanis; Su, Kui; Okimura, Kunio, E-mail: okifn@keyaki.cc.u-tokai.ac.jp [Graduate School of Science and Technology, Tokai University, Hiratsuka 259-1292 (Japan); Zaghrioui, Mustapha; Sakai, Joe [GREMAN, UMR 7347 CNRS, Université François Rabelais de Tours, Parc de Grandmont 37200 Tours (France)

2015-06-28

We report the first observation of large crystalline domains of several μm-size in VO{sub 2} films deposited on Al{sub 2}O{sub 3} (001) substrates by rf-biased reactive sputtering technique. The large crystalline domains, dominated with random in-plane oriented growth of (011){sub M1}-orientation, appear only under adequate substrate biasing, such as 10 W, while most biasing conditions result in conventional nanosized grains of highly oriented (010){sub M1}-orientation. Two temperature-controlled analyses, x-ray diffraction and micro-Raman spectroscopy, have revealed that some parts of large crystalline domains undergo intermediate monoclinic (M2) phase during the thermally-induced structural phase transition from monoclinic (M1) to rutile-tetragonal (R) phase. As an effect of the appearance of large crystalline domains, the film showed in-plane tensile stress, resulting in high T{sub IMT} of 69 °C due to the elongation of the V-V distance in its low-temperature monoclinic phase.

Assessment of phase constitution on the Al-rich region of rapidly solidified Al-Co-Fe-Cr alloys

International Nuclear Information System (INIS)

Wolf, W.; Bolfarini, C.; Kiminami, C.S.; Botta, W.J.

2016-01-01

The formation of quasicrystalline approximants in rapidly solidified Al-Co-Fe-Cr alloys was investigated. Alloys of atomic composition Al 71 Co 13 Fe 8 Cr 8 , Al 77 Co 11 Fe 6 Cr 6 and Al 76 Co 19 Fe 4 Cr 1 were produced using melt spinning and arc melting methods and their microstructural characterization was carried out by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Up to the present there is no consensus in the literature regarding the formation of quasicrystalline phase or quasicrystalline approximants in the Al 71 Co 13 Fe 8 Cr 8 alloy. This work presents, for the first time, a detailed structural characterization of selected alloys in the Al-Co-Fe-Cr system close to the atomic composition Al 71 Co 13 Fe 8 Cr 8 . The results indicated the samples to be composed, mostly, by two intermetallic phases, which are quaternary extensions of Al 5 Co 2 and Al 13 Co 4 and are quasicrystalline approximants. Although the Al 5 Co 2 phase has already been reported in the Al 71 Co 13 Fe 8 Cr 8 alloy, the presence of the monoclinic Al 13 Co 4 is now identified for the first time in the as cast state. In the binary Al-Co system a quasicrystalline phase is known to form in a rapidly solidified alloy with composition close to the monoclinic and orthorhombic Al 13 Co 4 phases. This binary quasicrystalline phase presents an average valence electron per atom (e/a) between 1.7 and 1.9; thus, in addition to the Al 71 Co 13 Fe 8 Cr 8 alloy, the compositions Al 77 Co 11 Fe 6 Cr 6 and Al 76 Co 19 Fe 4 Cr 1 were chosen to be within the region of formation of the quaternary extension of the Al 13 Co 4 phase and also within the (e/a) of 1.7 to 1.9. However, no quasicrystalline phase is present in any of the studied alloys. The Al-Co-Fe-Cr system, around the compositions studied, is composed of quaternary extensions of Al-Co intermetallic phases, which present solubility of Fe and Cr at Co atomic sites. - Highlights: •The Al rich region of the Al

Modeling of formation of binary-phase hollow nanospheres from metallic solid nanospheres

International Nuclear Information System (INIS)

Svoboda, J.; Fischer, F.D.; Vollath, D.

2009-01-01

Spontaneous formation of binary-phase hollow nanospheres by reaction of a metallic nanosphere with a non-metallic component in the surrounding atmosphere is observed for many systems. The kinetic model describing this phenomenon is derived by application of the thermodynamic extremal principle. The necessary condition of formation of the binary-phase hollow nanospheres is that the diffusion coefficient of the metallic component in the binary phase is higher than that of the non-metallic component (Kirkendall effect occurs in the correct direction). The model predictions of the time to formation of the binary-phase hollow nanospheres agree with the experimental observations

Growth kinetics of tetragonal and monoclinic ZrO{sub 2} crystallites in 3 mol% yttria partially stabilized ZrO{sub 2} (3Y-PSZ) precursor powder

Energy Technology Data Exchange (ETDEWEB)

Kuo, Chih-Wei [Department of Resources Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan (China); Lee, Kuen-Chan [Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan (China); Yen, Feng-Lin, E-mail: flyen@kmu.edu.tw [Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan (China); Shen, Yun-Hwei [Department of Resources Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan (China); Lee, Huey-Er [Department of Dentistry, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan (China); Department of Dentistry, Kaohsiung Medical University, Chung Ho Memorial Hospital, 100 Tzyou 1st Road, Kaohsiung 807, Taiwan (China); Wen, Shaw-Bing [General Education Center, Meiho Institute of Technology, 23 Pingguang Road, Neipu, Pingtung 91202, Taiwan (China); Wang, Moo-Chin, E-mail: mcwang@kmu.edu.tw [Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan (China); Stack, Margaret Mary [Department of Mechanical and Aerospace Engineering, University of Strathclyde, 75 Montrose Street, Glasgow (United Kingdom)

2014-04-01

Highlights: • The crystalline structures were composed of tetragonal and monoclinic ZrO{sub 2}. • Growth kinetics of t-ZrO{sub 2} in the 3Y-PSZ precursor powder is described as: D{sub te}{sup 2}=(4.57±0.55)t{sup 0.12±0.02}exp(-((24.79±0.38)×10{sup 3})/(RT) ). • Growth kinetics of m-ZrO{sub 2} in the 3Y-PSZ precursor powder is described as: D{sub m}{sup 2}=(4.40±1.63)t{sup 0.17±0.08}exp(-((66.47±3.97)×10{sup 3})/(RT) ). - Abstract: The growth kinetics of tetragonal and monoclinic ZrO{sub 2} crystallites in 3 mol% yttria partially stabilized ZrO{sub 2} (3Y-PSZ) precursor powder has been investigated using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) specific surface area analysis, transmission electron microscopy (TEM) and high resolution TEM (HRTEM). After calcination of the 3Y-PSZ precursor powder between 773 and 1073 K for 2 h, the crystalline structures were composed of tetragonal and monoclinic ZrO{sub 2} as the primary and secondary phases, respectively. When the 3Y-PSZ precursor powder was calcined at 773 K for 2 h, the BET specific surface area was 97.13 m{sup 2}/g, which is equivalent to a particle size of 10.30 nm. The crystallite sizes determined via XRD and BET agreed well, indicating that the powder was virtually non-agglomerated. The growth kinetics of tetragonal and monoclinic ZrO{sub 2} crystallite isothermal growth in the 3Y-PSZ precursor powder are described by: D{sub te}{sup 2}=(4.57±0.55)t{sup 0.12±0.02}exp(-((24.79±0.38)×10{sup 3})/(RT) ) and D{sub m}{sup 2}=(4.40±1.63)t{sup 0.17±0.08}exp(-((66.47±3.97)×10{sup 3})/(RT) ), respectively, for 773K≤T≤1073K. D{sub te} and D{sub m} denote the crystallite size of tetragonal and monoclinic ZrO{sub 2} at time t and temperature T, respectively.

Structural formation of aluminide phases on titanium alloy during annealing

International Nuclear Information System (INIS)

Mamaeva, A.A.; Romankov, S.E.; Sagdoldina, Zh.

2006-01-01

Full text: The aluminum layer on the surface of titanium alloy has been formed by thermal deposition. The structural formation of aluminide phases on the surface has been studied. The sequence of structural transformations at the Ti/Al interface is limited by the reaction temperature and time. The sequence of aluminide phase formation is occurred in compliance with Ti-Al equilibrium phase diagram. At the initial stages at the Ti/Al interface the Al3Ti alloy starts forming as a result of interdiffusion, and gradually the whole aluminum films is spent on the formation of this layer. The Al3Ti layer decomposes with the increase of temperature (>600C). At 800C the two-phase (Ti3Al+TiAl) layer is formed on the titanium surface. The TiAl compound is unstable and later on with the increase of the exposure time at 800C gradually transforms into the Ti3Al. The chain of these successive transformations leads to the formation of the continuous homogeneous layer consisting of the Ti3Al compound on the surface. At temperatures exceeding the allotropic transformation temperature (>900C) the Ti3Al compound starts decomposing. All structural changes taking place at the Ti/Al interface are accompanied by considerable changes in micro hardness. The structure of initial substrate influences on kinetics of phase transformation and microstructure development. (author)

Crystal structure, hydrogen bonding, and sup 8 sup 1 Br NQR of low-temperature phase of 4-aminopyridinium tetrabromoantimonate (3)

CERN Document Server

Hashimoto, M; Fuess, H; Svoboda, I; Ehrenberg, H

2003-01-01

The crystal structure of the low-temperature phase (LTP) of the title compound was determined at 220 K (monoclinic, P2 sub 1 sub / sub c). The 4-aminopyridinium cations (4-NH sub 2 C sub 5 H sub 4 NH sup +) were found to be ordered in LTP, while being severely disordered in the room-temperature phase (monoclinic, C2/c). The tetrabromoantimonate anions (SbBr sub 4 sup -) were incorporated into the infinite polyanion chains of irregular SbBr sub 6 octahedra with two-edges sharing. The trans-Br-Sb-Br moiety in the SbBr sub 4 sup - anion was approximately symmetric differing from the asymmetric Br-Sb centre dot centre dot centre dot Br moiety found in LTP of pyridinium tetrabromoantimonate (3). The N-H moieties in both of the pyridine ring and the amino (-NH sub 2) group participate in the formation of N-H centre dot centre dot centre dot Br hydrogen bonds. It was shown that the sup 8 sup 1 Br NQR spectrum of LTP is closely related to the anion structure and the hydrogen bonds. The distinctive anion structures, a...

Evidence for monoclinic distortion in the ground state phase of underdoped La_1_._9_5Sr_0_._0_5CuO_4: A single crystal neutron diffraction study

International Nuclear Information System (INIS)

Singh, Anar; Schefer, Jürg; Frontzek, Matthias; Sura, Ravi; Conder, Kazimierz; Sibille, Romain F.; Ceretti, Monica; Paulus, Werner

2016-01-01

The existing controversy about the symmetry of the crystal structure of the ground state of the critical doped La_1_._9_5Sr_0_._0_5CuO_4 has been resolved by analyzing the single crystal neutron diffraction data collected between 5 and 730 K. We observed small but significant intensities for “forbidden” reflections given by extinction rules of the orthorhombic Bmab space group at low temperatures. A careful investigation of neutron diffraction data reveals that the crystal structure of La_1_._9_5Sr_0_._0_5CuO_4 at 5 K is monoclinic with B2/m (2/m 1 1) space group. The monoclinic structure emerges from the orthorhombic structure in a continuous way; however, the structure is stable below ∼120 K which agrees with other observed phenomena. Our results on symmetry changes are crucial for the interpretation of physical properties also in other high temperature superconductors with similar structures.

Formation of nano quasicrystalline and crystalline phases by mechanical alloying

Energy Technology Data Exchange (ETDEWEB)

Shamah, A.M.; Ibrahim, S. [Faculty of Petroleum and Mining Engineering, Suez Canal University, Suez (Egypt); Hanna, F.F., E-mail: fariedhanna@yahoo.com [Faculty of Petroleum and Mining Engineering, Suez Canal University, Suez (Egypt)

2011-02-03

Research highlights: > Mechanical alloying (MA) is an important method to investigate the formation of nano sized quasicrystalline phases in Al{sub 86}Cr{sub 14}, Al{sub 84}Fe{sub 16} and Al{sub 62.5}Cu{sub 25}Fe{sub 12.5} compounds. The second part of the present work is an attempt to examine the possibility of formation of the i-phase of the Al{sub 62.5}Cu{sub 25}Fe{sub 12.5}, which lies in the region of the perfect i-phase in the ternary phase diagram, by rapid solidification method. To perform the obtained quasi phase mechanical alloying and heat treatment at the rapid solidified sample were done. - Abstract: In the present work, the formation of nano quasicrystalline icosahedral phase in Al{sub 86}Cr{sub 14}, Al{sub 84}Fe{sub 16} and Al{sub 62.5}Cu{sub 25}Fe{sub 12.5} alloys has been investigated by mechanical alloying. Mixtures of quasicrystalline and related crystalline phases have been observed under various milling conditions. The X-ray diffraction, differential thermal analysis and electrical resistivity techniques have been used for characterization and physical property measurements. The particle size was calculated by X-ray profile using Williamson-Hall plot method and it was found to be 25-50 nm size.

Thermal stability and phase transformation in fully indium oxide (InO{sub 1.5}) stabilized zirconia

Energy Technology Data Exchange (ETDEWEB)

Piva, R.H., E-mail: honorato.piva@ua.pt; Piva, D.H.; Morelli, M.R.

2017-01-15

Indium oxide (InO{sub 1.5}) stabilized zirconia (InSZ) is an attractive material as electrolyte, or electrode, in solid oxide fuel cells (SOFCs), and as corrosion resistant top coat in thermal barrier coatings. However, little is known about the phase stability of cubic InSZ at temperatures that simulate the conditions in an operating SOFC or turbine. This article provides an investigation of the phase stability and phase transformations in cubic InSZ after heat treatments at 800, 1000, and 1200 °C for periods up to 2000 h. The results revealed that cubic InSZ is not stable during annealing at 1000 and 1200 °C, owing to a fast destabilization of the initial cubic phase to tetragonal, and eventually to monoclinic (c → t → m). The c → t → m transition in InSZ is intimately associated with the indium volatilization. On the other hand, cubic InSZ remained stable for 2000 h at 800 °C, although the partial formation of the tetragonal phase was observed along with a 0.25% contraction in the unit cell volume of the cubic phase, caused by short-range ordering. These results demonstrate that technological applications of cubic InSZ are restricted to temperatures at which the volatilization of the InO{sub 1.5} stabilizer does not occur. - Highlights: •Phase stability of fully InO{sub 1.5} stabilized zirconia (cubic InSZ) was evaluated. •Cubic InSZ is instable at temperatures ≥ 1000 °C, owing to the cubic-to-tetragonal-to-monoclinic destabilization. •Cubic InSZ undergoes the cubic-to-tetragonal transformation at ~ 800 °C. •Owing to the low phase stability, applications of cubic InSZ in TBCs or SOFCs are restricted.

Identification of monoclinic calcium pyrophosphate dihydrate and hydroxyapatite in human sclera using Raman microspectroscopy.

Science.gov (United States)

Chen, Ko-Hua; Li, Mei-Jane; Cheng, Wen-Ting; Balic-Zunic, Tonci; Lin, Shan-Yang

2009-02-01

Raman microspectroscopy was first used to determine the composition of a calcified plaque located at the pterygium-excision site of a 51-year-old female patient's left nasal sclera after surgery. It was unexpectedly found that the Raman spectrum of the calcified sample at 1149, 1108, 1049, 756, 517, 376 and 352/cm was similar to the Raman spectrum of monoclinic form of calcium pyrophosphate dihydrate (CPPD) crystal, but differed from the Raman spectrum of triclinic form of CPPD. An additional peak at 958/cm was also observed in the Raman spectrum of the calcified plaque, which was identical to the characteristic peak at 958/cm of hydroxyapatite (HA). This is the first study to report the spectral biodiagnosis of both monoclinic CPPD and HA co-deposited in the calcified plaque of a patient with sclera dystrophic calcification using Raman microspectroscopy.

A new molybdenum trioxide hydrate MoO3.1/3H2O and a new monoclinic form of MoO3

International Nuclear Information System (INIS)

Harb, F.; Gerand, B.; Nowogrocki, G.; Figlarz, M.

1986-01-01

A new hydrate of molybdenum trioxide MoO 3 .1/3H 2 O has been obtained by hydrothermal treatment at 110 0 C of either aqueous suspensions of MoO 3 .2H 2 O or aqueous molybdic acid solutions. The hydrate crystallizes in the orthorhombic system, lattice parameters are given; a structural model is proposed by comparison with the isostructural WO 3 .1/3H 2 O phase. The dehydration of MoO 3 .1/3H 2 O leads to a new anhydrous molybdenum trioxide, monoclinic, the structure of which is of ReO 3 type [fr

Laws of phase formation in ion-implanted metals

International Nuclear Information System (INIS)

Kazdaev, H.R.; Abylkhalykova, R.B.; Skakov, M.K.

2004-01-01

Full text: Main laws of ordered structures formation at molybdenum implantation by elements forming phases of introduction (B, C, N, 0, Si, P, S) are discovered in this work. According to them the character of structural and phase transformations in molybdenum at ion implantation is determined not by kinetic parameters of bombarding particles and their chemical activity but by size factor η x/Me (ratio of nuclear radii of introduced elements and atoms of a matrix). At change of its meaning in the certain limits the following can be observed: superstructures formation (η x/Mo x/Mo x/Mo >0.69). In the latter case at the further implantation doze increasing recrystallization of molybdenum monocrystalline layers amorphized during previous bombarding with chemical connection formation takes place, characterized by us as ion-inducted synthesis. The phenomenon discovered on the samples implanted by phosphorus ions. As the result, the high-temperature phase of molybdenum monophosphide MoP having densely situated lattice was synthesized. The complete confirmation of the main laws of structural and phased transformations at ion implantation established by results on molybdenum monocrystals with OCC lattice was achieved at realization of similar researches on the other transitive metal - zirconium which differs from molybdenum according to a number of attributes: a type of an initial lattice structural condition (large scaled polycrystal), presence of interparticle borders and high solubility of atmospheric impurities (nitrogen, carbon, oxygen). The discovered laws have proved to be true also according to ion implanted samples of monocrystal tungsten and polycrystal tantalum

Phase separation and nanocrystal formation in Al-based metallic glasses

International Nuclear Information System (INIS)

Antonowicz, Jerzy

2007-01-01

Nanocrystallization in a group of Al-RE and Al-RE-TM (RE = rare earth, TM = transition metal) melt-spun amorphous alloys was studied using in situ small- and wide-angle X-ray scattering techniques (SAXS/WAXS) and transmission electron microscopy (TEM). The SAXS/WAXS measurements were carried out during isothermal annealing at temperatures close to crystallization point. A continuously growing interference maximum shifting progressively toward lower angles was found to develop in SAXS regime. Simultaneously taken WAXS spectra reveal formation of the primary fcc-Al nanocrystalline phase. The presence of the SAXS signal maximum indicates the spatial correlation between the compositional fluctuations. The peak position decay is an evidence of an increase of the fluctuation spacing characteristic for the coarsening stage of phase separation. The SAXS/WAXS data analysis indicates that amorphous phase decomposition triggers and controls the fcc-Al nanocrystalline phase formation. The glassy phase initially decomposes into Al-rich and RE-rich regions with typical lengths scale of about 10 nm. The nanocrystals nucleate preferentially inside the Al-rich amorphous regions and their growth is constrained by the region size because of the sluggish atomic diffusion in the RE-rich zones. A different crystallization mechanism is demonstrated in Al-Y-Ni-Co glass where WAXS spectra show formation of the fcc-Al primary phase but no interference peak in SAXS regime was found

Thermoelectric power and phase transitions in lanthanides under pressure up to 20 GPa

International Nuclear Information System (INIS)

Ovsyannikov, Sergey V.; Shchennikov, Vladimir V.; Goshchitskii, Boris N.

2007-01-01

Pressure dependencies of thermopower S of rare-earth metals (Ce and Pr) in a pressure P range of 0-20 GPa and at room temperature are reported. A non-monotonic behaviour of S(P) has been established both at pressure-induced phase transitions: fcc → modified fcc → monoclinic → tetragonal lattice for Ce, and double hexagonal close packed (dhcp) → fcc → modified fcc → monoclinic for Pr. S kept a positive sign for the all high-pressure phases mentioned. Simultaneous measurements of sample contraction have revealed anomalies in the vicinity of the transitions in qualitative agreement with diffraction volumetric data published before. The S(P) dependencies were analysed on the basis of the known results of electronic structure calculation for the Ce and Pr phases. An advantage was demonstrated of the thermopower method in the study of phase transitions and electronic structure of high-pressure phases

High temperature-induced phase transitions in Sr{sub 2}GdRuO{sub 6} complex perovskite

Energy Technology Data Exchange (ETDEWEB)

Triana, C.A.; Corredor, L.T.; Landinez Tellez, D.A. [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, Bogota D.C. A.A. 14490 (Colombia); Roa-Rojas, J., E-mail: jroar@unal.edu.co [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, Bogota D.C. A.A. 14490 (Colombia)

2011-12-15

Highlights: Black-Right-Pointing-Pointer Crystal structure, thermal expansion and phase transitions at high-temperature of Sr{sub 2}GdRuO{sub 6} perovskite has been investigated. Black-Right-Pointing-Pointer X-ray diffraction pattern at 298 K of Sr{sub 2}GdRuO{sub 6} corresponds to monoclinic perovskite-type structure with P2{sub 1}/n space group. Black-Right-Pointing-Pointer Evolution of X-ray diffraction patterns at high-temperature shows that the Sr{sub 2}GdRuO{sub 6} perovskite suffers two-phase transitions. Black-Right-Pointing-Pointer At 573 K the X-ray diffraction pattern of Sr{sub 2}GdRuO{sub 6} corresponds to monoclinic perovskite-type structure with I2/m space group. Black-Right-Pointing-Pointer At 1273 K the Sr{sub 2}GdRuO{sub 6} perovskite suffers a complete phase-transition from monoclinic I2/m (no. 12) to tetragonal I4/m (no. 87). -- Abstract: The crystal structure behavior of the Sr{sub 2}GdRuO{sub 6} complex perovskite at high-temperature has been investigated over a wide temperature range between 298 K {<=} T {<=} 1273 K. Measurements of X-ray diffraction at room-temperature and Rietveld analysis of the experimental patterns show that this compound crystallizes in a monoclinic perovskite-like structure, which belongs to the P2{sub 1}/n (no. 14) space group and 1:1 ordered arrangement of Ru{sup 5+} and Gd{sup 3+} cations over the six-coordinate M sites. Experimental lattice parameters were obtained to be a =5.8103(5) Angstrom-Sign , b =5.8234(1) Angstrom-Sign , c =8.2193(9) Angstrom-Sign , V = 278.11(2) Angstrom-Sign {sup 3} and angle {beta} = 90.310(5) Degree-Sign . The high-temperature analysis shows the occurrence of two-phase transitions on this material. First, at 573 K it adopts a monoclinic perovskite-type structure with I2/m (no. 12) space group with lattice parameters a = 5.8275(6) Angstrom-Sign , b = 5.8326(3) Angstrom-Sign , c = 8.2449(2) Angstrom-Sign , V = 280.31(3) Angstrom-Sign {sup 3} and angle {beta} = 90.251(3) Degree-Sign . Close

Monoclinic β-Li{sub 2}TiO{sub 3} nanocrystalline particles employing novel urea assisted solid state route: Synthesis, characterization and sintering behavior

Energy Technology Data Exchange (ETDEWEB)

Tripathi, Biranchi M., E-mail: biranchi.barc@gmail.com [Powder Metallurgy Division, Bhabha Atomic Research Centre, Vashi Complex, Navi Mumbai 400705 (India); Mohanty, Trupti; Prakash, Deep [Powder Metallurgy Division, Bhabha Atomic Research Centre, Vashi Complex, Navi Mumbai 400705 (India); Tyagi, A.K. [Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Sinha, P.K. [Powder Metallurgy Division, Bhabha Atomic Research Centre, Vashi Complex, Navi Mumbai 400705 (India)

2017-07-15

Pure phase monoclinic nano-crystalline Li{sub 2}TiO{sub 3} powder was synthesized by a novel urea assisted solid state synthesis method using readily available and economical precursors. A single phase and well crystalline Li{sub 2}TiO{sub 3} powder has been obtained at slightly lower temperature (600–700 °C) and shorter duration (2 h) as compared to the conventional solid state method. The proposed method has significant advantages in comparison to other viable methods mainly in terms of phase purity, powder properties and sinterability. Analysis of chemical composition using inductively coupled plasma atomic emission spectroscopy (ICP-AES) shows no loss of lithium from Li{sub 2}TiO{sub 3} in the proposed method. The emergence of monoclinic Li{sub 2}TiO{sub 3} phase was confirmed by X-ray diffraction (XRD) pattern of as-synthesized powder. The crystallite size of Li{sub 2}TiO{sub 3} powder was calculated to be in the range of 15–80 nm, which varied as a function of urea composition and temperature. The morphology of as-prepared Li{sub 2}TiO{sub 3} powders was examined by scanning electron microscope (SEM). The effect of urea composition on phase and morphology was investigated so as to delineate the role of urea. Upon sintering at < 1000 °C temperature, the Li{sub 2}TiO{sub 3} powder compact attained about 98% of the theoretical density with fine grained (grain size: 2–3 μm) microstructure. It indicates excellent sinter-ability of Li{sub 2}TiO{sub 3} powder synthesized by the proposed method. The fine grained structure is desirable for better tritium breeding performance of Li{sub 2}TiO{sub 3}. Electrochemical impedance spectroscopy at variable temperature showed good electrical properties of Li{sub 2}TiO{sub 3}. The proposed method is simple, anticipated to be cost effective and convenient to realise for large scale production of phase pure nanocrystalline and having significantly enhanced sinter-ability Li{sub 2}TiO{sub 3} powder.

Pressure-induced phase transitions in nanocrystalline ReO3

International Nuclear Information System (INIS)

Biswas, Kanishka; Muthu, D V S; Sood, A K; Kruger, M B; Chen, B; Rao, C N R

2007-01-01

Pressure-induced phase transitions in the nanocrystals of ReO 3 with an average diameter of ∼12 nm have been investigated in detail by using synchrotron x-ray diffraction and the results compared with the literature data of bulk samples of ReO 3 . The study shows that the ambient-pressure cubic I phase (space group Pm3-barm) transforms to a monoclinic phase (space group C 2/c), then to a rhombohedral I phase (space group R3-barc), and finally to another rhombohedral phase (rhombohedral II, space group R3-barc) with increasing pressure over the 0.0-20.3 GPa range. The cubic I to monoclinic transition is associated with the largest volume change (∼5%), indicative of a reconstructive transition. The transition pressures are generally lower than those known for bulk ReO 3 . The cubic II (Im3-bar) or tetragonal (P4/mbm) phases do not occur at lower pressures. The nanocrystals are found to be more compressible than bulk ReO 3 . On decompression to ambient pressure, the structure does not revert back to the cubic I structure

Structural phase transition in monolayer MoTe2 driven by electrostatic doping

Science.gov (United States)

Wang, Ying; Xiao, Jun; Zhu, Hanyu; Li, Yao; Alsaid, Yousif; Fong, King Yan; Zhou, Yao; Wang, Siqi; Shi, Wu; Wang, Yuan; Zettl, Alex; Reed, Evan J.; Zhang, Xiang

2017-10-01

Monolayers of transition-metal dichalcogenides (TMDs) exhibit numerous crystal phases with distinct structures, symmetries and physical properties. Exploring the physics of transitions between these different structural phases in two dimensions may provide a means of switching material properties, with implications for potential applications. Structural phase transitions in TMDs have so far been induced by thermal or chemical means; purely electrostatic control over crystal phases through electrostatic doping was recently proposed as a theoretical possibility, but has not yet been realized. Here we report the experimental demonstration of an electrostatic-doping-driven phase transition between the hexagonal and monoclinic phases of monolayer molybdenum ditelluride (MoTe2). We find that the phase transition shows a hysteretic loop in Raman spectra, and can be reversed by increasing or decreasing the gate voltage. We also combine second-harmonic generation spectroscopy with polarization-resolved Raman spectroscopy to show that the induced monoclinic phase preserves the crystal orientation of the original hexagonal phase. Moreover, this structural phase transition occurs simultaneously across the whole sample. This electrostatic-doping control of structural phase transition opens up new possibilities for developing phase-change devices based on atomically thin membranes.

Phase separation and formation of omega phase in the beta matrix of a Ti-V-Cu alloy

Energy Technology Data Exchange (ETDEWEB)

Ng, H.P. [ARC Centre of Excellence for Design in Light Metals, Department of Materials Engineering, Monash University, Victoria 3800 (Australia); Devaraj, A.; Nag, S. [Center for Advanced Research and Technology, Department of Materials Science and Engineering, University of North Texas, Denton, TX (United States); Bettles, C.J. [ARC Centre of Excellence for Design in Light Metals, Department of Materials Engineering, Monash University, Victoria 3800 (Australia); Gibson, M. [CSIRO Process Science and Engineering, Locked Bag 10, Clayton South, Victoria 3169 (Australia); Fraser, H.L. [Center for the Accelerated Maturation of Materials, Department of Materials Science and Engineering, The Ohio State University, Columbus, OH (United States); Muddle, B.C. [ARC Centre of Excellence for Design in Light Metals, Department of Materials Engineering, Monash University, Victoria 3800 (Australia); Banerjee, R., E-mail: rajarshi.banerjee@unt.edu [Center for Advanced Research and Technology, Department of Materials Science and Engineering, University of North Texas, Denton, TX (United States)

2011-05-15

The formation of the {omega} phase in the presence of simultaneous development of compositional modulations (or phase separation) within the body-centered cubic {beta} matrix phase of a Ti-10V-6Cu (wt.%) alloy during continuous cooling has been investigated using a combination of transmission electron microscopy and atom probe tomography. While a water quench from the high-temperature {beta} phase field allows apparently athermal formation of {omega} domains without any significant partitioning of solute or modulation in matrix composition, subsequent annealing at 500 {sup o}C for just 60 s leads to unusually rapid growth of the {omega} domains concurrent with, but apparently independent of, a slower development of finer-scale modulations in solute composition occurring apparently uniformly across both {omega} and {beta} phases. In contrast, on slower air cooling from the solution treatment temperature, there are pronounced compositional fluctuations within the {beta} phase, presumably as a product of spinodal decomposition, that are detectable prior to the formation of {omega} phase. The {omega} phase subsequently forms preferentially in solute-depleted regions of the matrix {beta}, with a composition reflecting the local matrix composition and a solute content significantly lower than the average matrix composition. As a result, it has a cuboidal morphology, distinguishably different from the elliposoidal form that is observed in samples water-quenched and annealed at 500 deg. C.

Formation of aqueous-phase α-hydroxyhydroperoxides (α-HHP: potential atmospheric impacts

Directory of Open Access Journals (Sweden)

R. Zhao

2013-06-01

Full Text Available The focus of this work is on quantifying the degree of the aqueous-phase formation of α-hydroxyhydroperoxides (α-HHPs via reversible nucleophilic addition of H2O2 to aldehydes. Formation of this class of highly oxygenated organic hydroperoxides represents a poorly characterized aqueous-phase processing pathway that may lead to enhanced SOA formation and aerosol toxicity. Specifically, the equilibrium constants of α-HHP formation have been determined using proton nuclear-magnetic-resonance (1H NMR spectroscopy and proton-transfer-reaction mass spectrometry (PTR-MS. Significant α-HHP formation was observed from formaldehyde, acetaldehyde, propionaldehyde, glycolaldehyde, glyoxylic acid, and methylglyoxal, but not from methacrolein and ketones. Low temperatures enhanced the formation of α-HHPs but slowed their formation rates. High inorganic salt concentrations shifted the equilibria toward the hydrated form of the aldehydes and slightly suppressed α-HHP formation. Using the experimental equilibrium constants, we predict the equilibrium concentration of α-HHPs to be in the μM level in cloud water, but it may also be present in the mM level in aerosol liquid water (ALW, where the concentrations of H2O2 and aldehydes can be high. Formation of α-HHPs in ALW may significantly affect the effective Henry's law constants of H2O2 and aldehydes but may not affect their gas-phase levels. The photochemistry and reactivity of this class of atmospheric species have not been studied.

Formation of InN phase by sequential ion implantation

International Nuclear Information System (INIS)

Santhana Raman, P.; Ravichandran, V.; Nair, K.G.M.; Kesavamoorthy, R.; Kalavathi, S.; Panigrahi, B.K.; Dhara, S.

2006-01-01

Formation of InN phase by sequentially implanting nitrogen on indium implanted silica was demonstrated. The growth of embedded InN phase on as-implanted and post-implantation annealed sample was studied using Glancing Incidence X-Ray Diffraction (GIXRD) and Raman spectroscopy. Existence of both cubic and hexagonal phases of InN was observed. Results of irradiation induced ripening of In nanoclusters due to N + ion implantation was also studied. (author)

Maps of Fe-Al phases formation kinetics parameters during isothermal sintering

Energy Technology Data Exchange (ETDEWEB)

Pochec, Ewelina, E-mail: epochec@wat.edu.pl [Department of Advanced Materials and Technology, Military University of Technology (Poland); Jozwiak, Stanislaw; Karczewski, Krzysztof; Bojar, Zbigniew [Department of Advanced Materials and Technology, Military University of Technology (Poland)

2012-10-10

Highlights: Black-Right-Pointing-Pointer The sintering temperature and compaction pressure have a strong influence on the sinters structure. Black-Right-Pointing-Pointer The measurements confirmed the presence of the high-aluminium phases from Fe-Al equilibrium system in tested sinters. Black-Right-Pointing-Pointer The kinetics of Fe-Al phase formation can be described by Johnson-Mehl-Avrami modelling. - Abstract: The influence of technological parameters (compaction pressure and sintering temperature) on Fe-Al phase formation was investigated. The kinetics of phase transformation preceding and during an SHS reaction was studied in isothermal conditions by DSC using the JMA (Johnson-Mehl-Avrami) model. This model allowed us to determine basic kinetic parameters, including the Avrami exponent, which characterises the rate and manner of particular phase nucleation. The activation energy (E{sub a}) of particular phase formation was determined by the Kissinger method. XRD analysis and SEM observations of sintered material showed that not only Fe{sub 2}Al{sub 5} phase and low-aluminium solid solution in iron but also aluminium-rich FeAl{sub 2} and FeAl{sub 3} phases are formed during the sintering of an FeAl50 elementary powder mixture in isothermal conditions with an SHS reaction. The above conclusions were confirmed by iron-based solid solution lattice parameter studies and microhardness measurements.

Thermodynamic study of CVD-ZrO{sub 2} phase diagrams

Energy Technology Data Exchange (ETDEWEB)

Torres-Huerta, A.M., E-mail: atorresh@ipn.m [Research Center for Applied Science and Advanced Technology, Altamira-IPN, Altamira C.P.89600 Tamaulipas (Mexico); Vargas-Garcia, J.R. [Dept of Metallurgical Eng., ESIQIE-IPN, Mexico 07300 D.F. (Mexico); Dominguez-Crespo, M.A. [Research Center for Applied Science and Advanced Technology, Altamira-IPN, Altamira C.P.89600 Tamaulipas (Mexico); Romero-Serrano, J.A. [Dept of Metallurgical Eng., ESIQIE-IPN, Mexico 07300 D.F. (Mexico)

2009-08-26

Chemical vapor deposition (CVD) of zirconium oxide (ZrO{sub 2}) from zirconium acetylacetonate Zr(acac){sub 4} has been thermodynamically investigated using the Gibbs' free energy minimization method and the FACTSAGE program. Thermodynamic data Cp{sup o}, DELTAH{sup o} and S{sup o} for Zr(acac){sub 4} have been estimated using the Meghreblian-Crawford-Parr and Benson methods because they are not available in the literature. The effect of deposition parameters, such as temperature and pressure, on the extension of the region where pure ZrO{sub 2} can be deposited was analyzed. The results are presented as calculated CVD stability diagrams. The phase diagrams showed two zones, one of them corresponds to pure monoclinic phase of ZrO{sub 2} and the other one corresponds to a mix of monoclinic phase of ZrO{sub 2} and graphite carbon.

Evidence of hexatic phase formation in two-dimensional Lennard-Jones binary arrays

International Nuclear Information System (INIS)

Li, M.; Johnson, W.L.; Goddard, W.A. III

1996-01-01

We report evidence of the hexatic phase formation in Lennard-Jones binary substitutional random arrays from isothermal-isobaric molecular-dynamics simulations. The hexatic phase is analogous to those predicted in Kosterlitz-Thouless theory of melting that is characterized by short-range translational order and quasi-long-range orientational order. At the crystal to hexatic phase transition, dislocation pairs are observed to unbind into isolated dislocations. Further disordering of the hexatic phase, however, does not lead to dissociation of dislocations into disclinations. Instead, the dislocations become clustered and form dislocation networks which results in formation of amorphous phases. copyright 1996 The American Physical Society

BCT phase formation in synthesis via microwave assisted hydrothermal method

International Nuclear Information System (INIS)

Barra, B.C.; Souza, A.E.; Teixeira, S.R.; Santos, G.T.A.; Lanzi, C.A.C.

2012-01-01

In previous work, samples of barium and calcium titanate (Ba1-xCaxTiO3 (BCT x = 0- 1) were prepared using the microwave assisted hydrothermal method in conditions of relatively short time and temperature. To the sample with 75wt% of Ca no BCT phase was formed but the photoluminescent emission was improved. In the present study, these titanates were synthesized by the same method with other concentrations of Ca, Ba1-xCaxTiO3 (x = 0, 0.20, 0.40, 0. 60, 0.80 and 1) to evaluate the limit of BCT phase formation. Results of X-ray diffraction showed that the phase BCT is formed between zero and 50wt%-Ca, in Ba substitution. Above this concentration, was observed only the formation of carbonates, and to x = 1 there was carbonate formation together with CaTiO3. These results were confirmed by micro Raman spectroscopy. (author)

Correlation of Structure, Tunable Colors, and Lifetimes of (Sr, Ca, Ba)Al2O4:Eu2+, Dy3+ Phosphors

OpenAIRE

Qidi Xie; Bowen Li; Xin He; Mei Zhang; Yan Chen; Qingguang Zeng

2017-01-01

(Sr, Ca, Ba)Al2O4:Eu2+, Dy3+ phosphors were prepared via a high temperature solid-state reaction method. The correlation of phase structure, optical properties and lifetimes of the phosphors are investigated in this work. For the (Sr, Ca)Al2O4:Eu2+, Dy3+ phosphors, the different phase formation from monoclinic SrAl2O4 phase to hexagonal SrAl2O4 phase to monoclinic CaAl2O4 phase was observed when the Ca content increased. The emission color of SrAl2O4:Eu2+, Dy3+ phosphors varied from green to ...

Ab initio velocity-field curves in monoclinic β-Ga2O3

Science.gov (United States)

Ghosh, Krishnendu; Singisetti, Uttam

2017-07-01

We investigate the high-field transport in monoclinic β-Ga2O3 using a combination of ab initio calculations and full band Monte Carlo (FBMC) simulation. Scattering rate calculation and the final state selection in the FBMC simulation use complete wave-vector (both electron and phonon) and crystal direction dependent electron phonon interaction (EPI) elements. We propose and implement a semi-coarse version of the Wannier-Fourier interpolation method [Giustino et al., Phys. Rev. B 76, 165108 (2007)] for short-range non-polar optical phonon (EPI) elements in order to ease the computational requirement in FBMC simulation. During the interpolation of the EPI, the inverse Fourier sum over the real-space electronic grids is done on a coarse mesh while the unitary rotations are done on a fine mesh. This paper reports the high field transport in monoclinic β-Ga2O3 with deep insight into the contribution of electron-phonon interactions and velocity-field characteristics for electric fields ranging up to 450 kV/cm in different crystal directions. A peak velocity of 2 × 107 cm/s is estimated at an electric field of 200 kV/cm.

An eigenstrain approach to predict phase transformation and self-accommodation in partially stabilized zirconia

International Nuclear Information System (INIS)

Hensl, Th.; Mühlich, U.; Budnitzki, M.; Kuna, M.

2015-01-01

Highlights: • Analytical model to predict phase transformation in PSZ is developed. • Analytical model to predict number of twins in monoclinic inclusions in PSZ. • Models consider inclusions size, shape, temperature, remote loading and surface energy. - Abstract: This work focuses on micromechanical modeling of the tetragonal to monoclinic phase transformation (t–m transformation) in partially stabilized zirconia (PSZ). Tetragonal particles dispersed in a cubic matrix may transform into the monoclinic phase under sufficiently high mechanical loading or if the material is cooled down below a critical temperature. This phase transformation is supposed to be responsible for the so called transformation toughening effect of PSZ. The transformation is usually accompanied by a self-accommodation process, which reduces the occurring eigenstresses in the surrounding matrix. The influences of particle size and geometry, chemical driving force, temperature, surface energy and remote loading on the t–m transformation are estimated by a thermostatic approach. We assume, that transformations occur, once the Gibbs free energy of the transformed equilibrium state is lower than that of the untransformed reference state. To obtain an analytical solution, the microstructure is modeled as an inclusion of rectangular cross section, restrained by an infinite elastic matrix, under plane strain conditions. The developed model for phase transformation captures the well-known size and temperature dependencies. Furthermore, it indicates a significant influence of the particle geometry, that large aspect ratios of the inclusion’s cross section lower the trigger stress for phase transformation

Assessment of phase constitution on the Al-rich region of rapidly solidified Al-Co-Fe-Cr alloys

Energy Technology Data Exchange (ETDEWEB)

Wolf, W., E-mail: witorw@gmail.com [Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Universidade Federal de São Carlos, Rod. Washington Luiz, Km 235, 13565-905 São Carlos, SP (Brazil); Bolfarini, C., E-mail: cbolfa@ufscar.br [Departamento de Engenharia de Materiais, Universidade Federal de São Carlos, Rod. Washington Luiz, Km 235, 13565-905 São Carlos, SP (Brazil); Kiminami, C.S., E-mail: kiminami@ufscar.br [Departamento de Engenharia de Materiais, Universidade Federal de São Carlos, Rod. Washington Luiz, Km 235, 13565-905 São Carlos, SP (Brazil); Botta, W.J., E-mail: wjbotta@ufscar.br [Departamento de Engenharia de Materiais, Universidade Federal de São Carlos, Rod. Washington Luiz, Km 235, 13565-905 São Carlos, SP (Brazil)

2016-12-15

The formation of quasicrystalline approximants in rapidly solidified Al-Co-Fe-Cr alloys was investigated. Alloys of atomic composition Al{sub 71}Co{sub 13}Fe{sub 8}Cr{sub 8}, Al{sub 77}Co{sub 11}Fe{sub 6}Cr{sub 6} and Al{sub 76}Co{sub 19}Fe{sub 4}Cr{sub 1} were produced using melt spinning and arc melting methods and their microstructural characterization was carried out by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Up to the present there is no consensus in the literature regarding the formation of quasicrystalline phase or quasicrystalline approximants in the Al{sub 71}Co{sub 13}Fe{sub 8}Cr{sub 8} alloy. This work presents, for the first time, a detailed structural characterization of selected alloys in the Al-Co-Fe-Cr system close to the atomic composition Al{sub 71}Co{sub 13}Fe{sub 8}Cr{sub 8}. The results indicated the samples to be composed, mostly, by two intermetallic phases, which are quaternary extensions of Al{sub 5}Co{sub 2} and Al{sub 13}Co{sub 4} and are quasicrystalline approximants. Although the Al{sub 5}Co{sub 2} phase has already been reported in the Al{sub 71}Co{sub 13}Fe{sub 8}Cr{sub 8} alloy, the presence of the monoclinic Al{sub 13}Co{sub 4} is now identified for the first time in the as cast state. In the binary Al-Co system a quasicrystalline phase is known to form in a rapidly solidified alloy with composition close to the monoclinic and orthorhombic Al{sub 13}Co{sub 4} phases. This binary quasicrystalline phase presents an average valence electron per atom (e/a) between 1.7 and 1.9; thus, in addition to the Al{sub 71}Co{sub 13}Fe{sub 8}Cr{sub 8} alloy, the compositions Al{sub 77}Co{sub 11}Fe{sub 6}Cr{sub 6} and Al{sub 76}Co{sub 19}Fe{sub 4}Cr{sub 1} were chosen to be within the region of formation of the quaternary extension of the Al{sub 13}Co{sub 4} phase and also within the (e/a) of 1.7 to 1.9. However, no quasicrystalline phase is present in any of the studied alloys. The Al-Co-Fe-Cr system

High pressure monoclinic phases of Sb{sub 2}Te{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Souza, S.M.; Poffo, C.M.; Triches, D.M. [Departamento de Engenharia Mecanica, Universidade Federal de Santa Catarina, Campus Universitario Trindade, S/N, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Lima, J.C. de, E-mail: fsc1jcd@fisica.ufsc.br [Departamento de Fisica, Universidade Federal de Santa Catarina, Campus Universitario Trindade, S/N, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Grandi, T.A. [Departamento de Fisica, Universidade Federal de Santa Catarina, Campus Universitario Trindade, S/N, C.P. 476, 88040-900 Florianopolis, Santa Catarina (Brazil); Polian, A.; Gauthier, M. [Physique des Milieux Denses, IMPMC, CNRS-UMR 7590, Universite Pierre et Marie Curie-Paris 6, 4 Place Jussieu, 75252 Paris Cedex 05 (France)

2012-09-15

The effect of pressure on nanostructured rhombohedral {alpha}-Sb{sub 2}Te{sub 3} (phase I) was investigated using X-ray diffraction (XRD) and Raman spectroscopy (RS) up to 19.2 and 25.5 GPa, respectively. XRD patterns showed two new high pressure phases (named phases II and III). From a Rietveld refinement of XRD patterns of {alpha}-Sb{sub 2}Te{sub 3}, the unit cell volume as a function of pressure was obtained and the values were fitted to a Birch-Murnaghan equation of state (BM-EOS). The best fit was obtained for bulk modulus B{sub 0}=36.1{+-}0.9 GPa and its derivative B{sub 0}{sup Prime }=6.2{+-}0.4 (not fixed). Using the refined structural data for {alpha}-Sb{sub 2}Te{sub 3}, for pressures up to 9.8 GPa, changes in the angle of succession [Te-Sb-Te-Sb-Te], in the interaromic distances of Sb and Te atoms belonging to this angle of succession and in the interatomic distances of atoms located on the c axis were examined. This analysis revealed an electronic topological transition (ETT) along the a and c axes at close to 3.7 GPa. From the RS spectra, the full widths at half maximum (FWHM) of the Raman active modes of {alpha}-Sb{sub 2}Te{sub 3} were plotted as functions of pressure and showed an ETT along the a and c axes at close to 3.2 GPa. The XRD patterns of phases II and III were well reproduced assuming {beta}-Bi{sub 2}Te{sub 3} and {gamma}-Bi{sub 2}Te{sub 3} structures similar to those reported in the literature for {alpha}-Bi{sub 2}Te{sub 3}.

Phase formation and strain relaxation of Ga2O3 on c-plane and a-plane sapphire substrates as studied by synchrotron-based x-ray diffraction

Science.gov (United States)

Cheng, Zongzhe; Hanke, Michael; Vogt, Patrick; Bierwagen, Oliver; Trampert, Achim

2017-10-01

Heteroepitaxial Ga2O3 was deposited on c-plane and a-plane oriented sapphire by plasma-assisted molecular beam epitaxy and probed by ex-situ and in-situ synchrotron-based x-ray diffraction. The investigation on c-plane sapphire determined a critical thickness of around 33 Å, at which the monoclinic β-phase forms on top of the hexagonal α-phase. A 143 Å thick single phase α-Ga2O3 was observed on a-plane sapphire, much thicker than the α-Ga2O3 on c-plane sapphire. The α-Ga2O3 relaxed very fast in the first 30 Å in both out-of-plane and in-plane directions as measured by the in-situ study.

In pursuit of the rhabdophane crystal structure: from the hydrated monoclinic LnPO{sub 4}.0.667H{sub 2}O to the hexagonal LnPO{sub 4} (Ln = Nd, Sm, Gd, Eu and Dy)

Energy Technology Data Exchange (ETDEWEB)

Mesbah, Adel, E-mail: adel.mesbah@cea.fr [ICSM, UMR 5257 CNRS – CEA – ENSCM – Université de Montpellier, Site de Marcoule - Bât 426, BP 17171, 30207 Bagnols/Cèze (France); Clavier, Nicolas [ICSM, UMR 5257 CNRS – CEA – ENSCM – Université de Montpellier, Site de Marcoule - Bât 426, BP 17171, 30207 Bagnols/Cèze (France); Elkaim, Erik [Synchrotron SOLEIL, L' Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex (France); Szenknect, Stéphanie; Dacheux, Nicolas [ICSM, UMR 5257 CNRS – CEA – ENSCM – Université de Montpellier, Site de Marcoule - Bât 426, BP 17171, 30207 Bagnols/Cèze (France)

2017-05-15

The dehydration process of the hydrated rhabdophane LnPO{sub 4}.0.667H{sub 2}O (Ln = La to Dy) was thoroughly studied over the combination of in situ high resolution synchrotron powder diffraction and TGA experiments. In the case of SmPO{sub 4}.0.667H{sub 2}O (monoclinic, C2), a first dehydration step was identified around 80 °C leading to the formation of SmPO{sub 4}.0.5H{sub 2}O (Monoclinic, C2) with Z =12 and a =17.6264(1) Å, b =6.9704(1) Å, c =12.1141(1) Å, β=133.74(1) °, V =1075.33(1) Å{sup 3}. In agreement with the TGA and dilatometry experiments, all the water molecules were evacuated above 220 °C yielding to the anhydrous form, which crystallizes in the hexagonal P3{sub 1}21 space group with a =7.0389(1) Å, c =6.3702(1) Å and V =273.34(1) Å{sup 3}. This study was extended to selected LnPO{sub 4}.0.667H{sub 2}O samples (Ln= Nd, Gd, Eu, Dy) and the obtained results confirmed the existence of two dehydration steps before the stabilization of the anhydrous form, with the transitory formation of LnPO{sub 4}.0.5H{sub 2}O. - Graphical abstract: The dehydration process of the rhabdophane SmPO{sub 4}.0.667H{sub 2}O was studied over combination of in situ high resolution synchrotron powder diffraction and TGA techniques, a first dehydration was identified around 80 °C leading to the formation of SmPO{sub 4}.0.5H{sub 2}O (Monoclinic, C2). Then above 220 °C, the anhydrous form of the rhabdophane SmPO{sub 4} was stabilized and crystallizes in the hexagonal P3{sub 1}21 space group. - Highlights: • In situ synchrotron powder diffraction was carried out during the dehydration of the rhabdopahe LnPO{sub 4}.0.667H{sub 2}O. • The heat of the rhabdophane LnPO{sub 4}.0.667H{sub 2}O leads to LnPO{sub 4}.0.5H{sub 2}O then to anhydrous rhabdophane LnPO{sub 4}. • LnPO{sub 4}.0.5H{sub 2}O (monoclinic, C2) and LnPO{sub 4} (Hexagonal, P3{sub 1}21) were solved over the use of direct methods.

The measurement of stress and phase fraction distributions in pre and post-transition Zircaloy oxides using nano-beam synchrotron X-ray diffraction

Energy Technology Data Exchange (ETDEWEB)

Swan, H., E-mail: helen.swan@nnl.co.uk [National Nuclear Laboratory, Building D5, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB (United Kingdom); Blackmur, M.S., E-mail: matthew.s.blackmur@nnl.co.uk [National Nuclear Laboratory, Building D5, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB (United Kingdom); Hyde, J.M., E-mail: jonathan.m.hyde@nnl.co.uk [National Nuclear Laboratory, Building D5, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB (United Kingdom); Laferrere, A., E-mail: alice.laferrere@atkinsglobal.com [W.S.Atkins, The Hub, Aztec West, 500 Park Ave, Almondsbury, Bristol BS32 4RZ (United Kingdom); Ortner, S.R., E-mail: susan.r.ortner@nnl.co.uk [National Nuclear Laboratory, Building D5, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB (United Kingdom); Styman, P.D., E-mail: paul.d.styman@nnl.co.uk [National Nuclear Laboratory, Building D5, Culham Science Centre, Abingdon, Oxfordshire, OX14 3DB (United Kingdom); Staines, C., E-mail: cassie.staines@nnl.co.uk [National Nuclear Laboratory, 102B, Stonehouse Park, Stonehouse, Gloucestershire, GL10 3UT (United Kingdom); Gass, M., E-mail: mhairi.gass@amecfw.com [Amec Foster Wheeler Clean Energy Europe, Walton House, Birchwood, WA3 6GA (United Kingdom); Hulme, H., E-mail: helen.hulme@amecfw.com [Amec Foster Wheeler Clean Energy Europe, Walton House, Birchwood, WA3 6GA (United Kingdom); Cole-Baker, A., E-mail: aidan.cole-baker@rolls-royce.com [Rolls-Royce plc, PO Box 2000, Derby, DE21 7XX (United Kingdom); Frankel, P., E-mail: philipp.frankel@manchester.ac.uk [Materials Performance Centre, School of Materials, The University of Manchester, Manchester, M13 9PL (United Kingdom)

2016-10-15

Zircaloy-4 oxide stress profiles and tetragonal:monoclinic oxide phase fraction distributions were studied using nano-beam transmission X-ray diffraction. Continuous stress relief and phase transformation during the first cycle of oxide growth was observed. The in-plane monoclinic stress was shown to relax strongly up to each transition, whereas in-plane tetragonal stress-relief (near the metal-oxide interface) was only observed post transition. The research demonstrates that plasticity in the metal and the development of a band of in-plane cracking both relax the monoclinic in-plane stress. The observations are consistent with a model of transition in which in-plane cracking becomes interlinked prior to transition. These cracks, combined with the development of cracks with a through-thickness component (driven primarily by plasticity in the metal) and/or a porous network of fine cracks (associated with phase transformation), form a percolation path through the oxide layer. The oxidising species can then percolate from the oxide surface to the metal/oxide interface, at which stage transition then ensues. - Highlights: • Measurement of stress in Zr-4 oxides using nano-beam transmission X-ray diffraction. • In-plane monoclinic stress relaxes strongly up to each transition. • In-plane tetragonal stress relaxation is only observed post transition. • Development of band of cracking is related to monoclinic in-plane stress relaxation. • Linking of in-plane cracking with through-plane crack/porosity leads to transition.

Phase formation in Zr/Fe multilayers during Kr ion irradiation

International Nuclear Information System (INIS)

Motta, A. T.

1998-01-01

A detailed study has been conducted of the effect of Kr ion irradiation on phase formation in Zr-Fe metallic multilayers, using the Intermediate Voltage Electron Microscopy (IVEM) at Argonne National Laboratory. Metallic multilayers were prepared with different overall compositions (near 50-50 and Fe-rich), and with different wavelengths (repetition thicknesses). These samples were irradiated with 300 keV Kr ions at various temperatures to investigate the final products, as well as the kinetics of phase formation. For the shorter wavelength samples, the final product was in all cases an amorphous Zr-Fe phase, in combination with Fe, while specially for the larger wavelength samples, in the Fe-rich samples the intermetallic compounds ZrFe 2 and Zr 3 Fe were formed in addition to the amorphous phase. The dose to full reaction decreases with temperature, and with wavelength in a manner consistent with a diffusion-controlled reaction

Effect of alloying elements on σ phase formation in Fe-Cr-Mn alloys

International Nuclear Information System (INIS)

Okazaki, Yoshimitsu; Miyahara, Kazuya; Hosoi, Yuzo; Tanino, Mitsuru; Komatsu, Hazime.

1989-01-01

Alloys of Fe-(8∼12%) Cr-(5∼30%) Mn were solution-treated at 1373 K for 3.6 ks, followed by cold-working of 50% reduction. Both solution-treated and 50% cold-worked materials were aged in the temperature range from 773 to 973 K for 3.6 x 10 3 ks. The identification of σ phase formation was made by using X-ray diffraction from the electrolytically extracted residues of the aged specimens. The region of σ phase formation determined by the present work is wider than that on the phase diagram already reported. It is to be noted that Mn promotes markedly the σ phase formation, and that three different types of σ phase formation are observed depending on Mn content: α→γ + α→γ + α + σ in 10% Mn, α→γ + σ in 15 to 20% Mn alloys, α→χ(Chi) →χ + σ + γ in 25 to 30% Mn alloys. An average electron concentration (e/a) in the σ phase was estimated by quantitative analysis of alloying elements using EPMA. The e/a value in the σ phase formed in Fe-(12∼16%) Cr-Mn alloys aged at 873 K for 3.6 x 10 3 ks is about 7.3, which is independent of Mn content. In order to prevent σ phase formation in Fe-12% Cr-15% Mn alloy, the value of Ni * eq of 11 (Ni * eq = Ni + 30(C) + 25(N)) is required. (author)

The coercive force of fine particles of monoclinic pyrrhotite (Fe7S8 ...

African Journals Online (AJOL)

The temperature dependence of coercive force (Hc) between 77 K and 600 K has been investigated for fine particles of monoclinic pyrrhotite (Fe7S8) of < 1 mm and 1- 30 mm particle sizes. The study has shown that Hc is strongly dependent on temperature, as temperature rises above room temperature (293 K) to near the ...

Chinese Script vs Plate-Like Precipitation of Beta-Al9Fe2Si2 Phase in an Al-6.5Si-1Fe Alloy

Science.gov (United States)

Ferdian, Deni; Josse, Claudie; Nguyen, Patrick; Gey, Nathalie; Ratel-Ramond, Nicolas; de Parseval, Philippe; Thebault, Yannick; Malard, Benoit; Lacaze, Jacques; Salvo, Luc

2015-07-01

The microstructure of a high-purity Al-6.5Si-1Fe (wt pct) alloy after solidification at various cooling rates was investigated. In most of the cases, the monoclinic beta-Al9Fe2Si2 phase was observed as long and thin lamellae. However, at a very slow cooling rate, Fe-bearing precipitates with Chinese script morphology appeared together with lamellae. Further analysis showed all these Chinese script precipitates correspond also to the monoclinic beta phase. This finding stresses that differentiating second phases according to their shape may be misleading.

Characterization of monoclinic crystals in tablets by pattern-fitting procedure using X-ray powder diffraction data.

Science.gov (United States)

Yamamura, Shigeo; Momose, Yasunori

2003-06-18

The purpose of this study is to characterize the monoclinic crystals in tablets by using X-ray powder diffraction data and to evaluate the deformation feature of crystals during compression. The monoclinic crystals of acetaminophen and benzoic acid were used as the samples. The observed X-ray diffraction intensities were fitted to the analytic expression, and the fitting parameters, such as the lattice parameters, the peak-width parameters, the preferred orientation parameter and peak asymmetric parameter were optimized by a non-linear least-squares procedure. The Gauss and March distribution functions were used to correct the preferred orientation of crystallites in the tablet. The March function performed better in correcting the modification of diffraction intensity by preferred orientation of crystallites, suggesting that the crystallites in the tablets had fiber texture with axial orientation. Although a broadening of diffraction peaks was observed in acetaminophen tablets with an increase of compression pressure, little broadening was observed in the benzoic tablets. These results suggest that "acetaminophen is a material consolidating by fragmentation of crystalline particles and benzoic acid is a material consolidating by plastic deformation then occurred rearrangement of molecules during compression". A pattern-fitting procedure is the superior method for characterizing the crystalline drugs of monoclinic crystals in the tablets, as well as orthorhombic isoniazid and mannitol crystals reported in the previous paper.

Size distribution dynamics reveal particle-phase chemistry in organic aerosol formation

Science.gov (United States)

Shiraiwa, Manabu; Yee, Lindsay D.; Schilling, Katherine A.; Loza, Christine L.; Craven, Jill S.; Zuend, Andreas; Ziemann, Paul J.; Seinfeld, John H.

2013-01-01

Organic aerosols are ubiquitous in the atmosphere and play a central role in climate, air quality, and public health. The aerosol size distribution is key in determining its optical properties and cloud condensation nucleus activity. The dominant portion of organic aerosol is formed through gas-phase oxidation of volatile organic compounds, so-called secondary organic aerosols (SOAs). Typical experimental measurements of SOA formation include total SOA mass and atomic oxygen-to-carbon ratio. These measurements, alone, are generally insufficient to reveal the extent to which condensed-phase reactions occur in conjunction with the multigeneration gas-phase photooxidation. Combining laboratory chamber experiments and kinetic gas-particle modeling for the dodecane SOA system, here we show that the presence of particle-phase chemistry is reflected in the evolution of the SOA size distribution as well as its mass concentration. Particle-phase reactions are predicted to occur mainly at the particle surface, and the reaction products contribute more than half of the SOA mass. Chamber photooxidation with a midexperiment aldehyde injection confirms that heterogeneous reaction of aldehydes with organic hydroperoxides forming peroxyhemiacetals can lead to a large increase in SOA mass. Although experiments need to be conducted with other SOA precursor hydrocarbons, current results demonstrate coupling between particle-phase chemistry and size distribution dynamics in the formation of SOAs, thereby opening up an avenue for analysis of the SOA formation process. PMID:23818634

Size distribution dynamics reveal particle-phase chemistry in organic aerosol formation.

Science.gov (United States)

Shiraiwa, Manabu; Yee, Lindsay D; Schilling, Katherine A; Loza, Christine L; Craven, Jill S; Zuend, Andreas; Ziemann, Paul J; Seinfeld, John H

2013-07-16

Organic aerosols are ubiquitous in the atmosphere and play a central role in climate, air quality, and public health. The aerosol size distribution is key in determining its optical properties and cloud condensation nucleus activity. The dominant portion of organic aerosol is formed through gas-phase oxidation of volatile organic compounds, so-called secondary organic aerosols (SOAs). Typical experimental measurements of SOA formation include total SOA mass and atomic oxygen-to-carbon ratio. These measurements, alone, are generally insufficient to reveal the extent to which condensed-phase reactions occur in conjunction with the multigeneration gas-phase photooxidation. Combining laboratory chamber experiments and kinetic gas-particle modeling for the dodecane SOA system, here we show that the presence of particle-phase chemistry is reflected in the evolution of the SOA size distribution as well as its mass concentration. Particle-phase reactions are predicted to occur mainly at the particle surface, and the reaction products contribute more than half of the SOA mass. Chamber photooxidation with a midexperiment aldehyde injection confirms that heterogeneous reaction of aldehydes with organic hydroperoxides forming peroxyhemiacetals can lead to a large increase in SOA mass. Although experiments need to be conducted with other SOA precursor hydrocarbons, current results demonstrate coupling between particle-phase chemistry and size distribution dynamics in the formation of SOAs, thereby opening up an avenue for analysis of the SOA formation process.

Numerical modeling of experimental observations on gas formation and multi-phase flow of carbon dioxide in subsurface formations

Science.gov (United States)

Pawar, R.; Dash, Z.; Sakaki, T.; Plampin, M. R.; Lassen, R. N.; Illangasekare, T. H.; Zyvoloski, G.

2011-12-01

One of the concerns related to geologic CO2 sequestration is potential leakage of CO2 and its subsequent migration to shallow groundwater resources leading to geochemical impacts. Developing approaches to monitor CO2 migration in shallow aquifer and mitigate leakage impacts will require improving our understanding of gas phase formation and multi-phase flow subsequent to CO2 leakage in shallow aquifers. We are utilizing an integrated approach combining laboratory experiments and numerical simulations to characterize the multi-phase flow of CO2 in shallow aquifers. The laboratory experiments involve a series of highly controlled experiments in which CO2 dissolved water is injected in homogeneous and heterogeneous soil columns and tanks. The experimental results are used to study the effects of soil properties, temperature, pressure gradients and heterogeneities on gas formation and migration. We utilize the Finite Element Heat and Mass (FEHM) simulator (Zyvoloski et al, 2010) to numerically model the experimental results. The numerical models capture the physics of CO2 exsolution, multi-phase fluid flow as well as sand heterogeneity. Experimental observations of pressure, temperature and gas saturations are used to develop and constrain conceptual models for CO2 gas-phase formation and multi-phase CO2 flow in porous media. This talk will provide details of development of conceptual models based on experimental observation, development of numerical models for laboratory experiments and modelling results.

Phase evolution and photoluminescence enhancement of CePO4 nanowires from a low phosphate concentration system

International Nuclear Information System (INIS)

Xu Pengfei; Yu Ranbo; Zong Lingbo; Wang Jiali; Wang Dan; Deng Jinxia; Chen Jun; Xing Xianran

2013-01-01

Uniform CePO 4 nanowires have been successfully synthesized in a low phosphate concentration system through a single-step hydrothermal process. The low phosphate concentration might decrease the surface PO 4 3− adsorption of the as-synthesized CePO 4 nanowires efficiently and benefit their photoluminescence. The CePO 4 nanowires were identified to go through phase evolution from pure monoclinic to mixed hexagonal and monoclinic phase by only increasing the initial molar ratio of cerium and phosphate source (denoted as Ce/P). Interestingly, the strongest photoluminescence was observed in the CePO 4 nanowires synthesized with the initial Ce/P of 4:1, which proved to be the critical phase evolution point between the hexagonal and monoclinic CePO 4 . Therefore, the strong photoluminescence could be explained by the existence of the structure-sensitive energy level in the CePO 4 . This kind of photoluminescence enhancement would be a meaningful reference for design of other photoluminescent materials, in which the photoluminescent emission might be related to the structure-sensitive energy level. Additionally, the growth processes of CePO 4 nanowires based on related well-designed experiments were proposed.

Phase formation and crystallization behavior of melt spun Sm-Fe-based alloys

International Nuclear Information System (INIS)

Shield, J.E.

1999-01-01

The phase formation and microstructures of Sm-Fe alloys have been investigated at Sm levels of 11 and 17 atomic percent and with alloying additions of Ti and C. At lower Sm content, virtually phase pure SmFe 7 formed, while higher Sm content resulted in the formation of SmFe 7 , SmFe 2 and amorphous phases. The addition of Ti and C resulted in greater stability and a larger volume fraction of the amorphous phase. The binary Sm-Fe alloys at both Sm levels had tremendously variable microstructures, with large discrepancies in grain size and phase distribution from region to region. The addition of Ti and C tended to result in a more homogeneous microstructure, as well as a refinement in the microstructural scale. (orig.)

Domain wall and interphase boundary motion in (1−x)Bi(Mg{sub 0.5}Ti{sub 0.5})O{sub 3}–xPbTiO{sub 3} near the morphotropic phase boundary

Energy Technology Data Exchange (ETDEWEB)

Tutuncu, Goknur [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States); Chen, Jun; Fan, Longlong [Department of Physical Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Fancher, Chris M.; Zhao, Jianwei [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Forrester, Jennifer S.; Jones, Jacob L., E-mail: JacobJones@ncsu.edu [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States); Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States)

2016-07-28

Electric field-induced changes in the domain wall motion of (1−x)Bi(Mg{sub 0.5}Ti{sub 0.5})O{sub 3}–xPbTiO{sub 3} (BMT-xPT) near the morphotropic phase boundary (MPB) where x = 0.37 (BMT-37PT) and x = 0.38 (BMT-38PT), are studied by means of synchrotron x-ray diffraction. Through Rietveld analysis and profile fitting, a mixture of coexisting monoclinic (Cm) and tetragonal (P4mm) phases is identified at room temperature. Extrinsic contributions to the property coefficients are evident from electric-field-induced domain wall motion in both the tetragonal and monoclinic phases, as well as through the interphase boundary motion between the two phases. Domain wall motion in the tetragonal and monoclinic phases for BMT-37PT is larger than that of BMT-38PT, possibly due to this composition's closer proximity to the MPB. Increased interphase boundary motion was also observed in BMT-37PT. Lattice strain, which is a function of both intrinsic piezoelectric strain and elastic interactions of the grains (the latter originating from domain wall and interphase boundary motion), is similar for the respective tetragonal and monoclinic phases.

Tuning the pure monoclinic phase of WO3 and WO3-Ag nanostructures for non-enzymatic glucose sensing application with theoretical insight from electronic structure simulations

Science.gov (United States)

Ponnusamy, Rajeswari; Gangan, Abhijeet; Chakraborty, Brahmananda; Sekhar Rout, Chandra

2018-01-01

Here, we report the controlled hydrothermal synthesis and tuning of the pure monoclinic phase of WO3 and WO3-Ag nanostructures. Comparative electrochemical nonenzymatic glucose sensing properties of WO3 and WO3-Ag were investigated by cyclic voltammetry and chronoamperometric tests. We observed enhanced glucose sensing performance of WO3-Ag porous spheres as compared to bare WO3 nanoslabs. The sensitivity of the pure WO3 nanoslabs is 11.1 μA μM-1 cm-2 whereas WO3-Ag porous spheres exhibit sensitivity of 23.3 μA μM-1 cm-2. The WO3-Ag porous spheres exhibited a good linear range (5-375 μM) with excellent anti-interference property. Our experimental observations are qualitatively supported by density functional theory simulations through investigation of bonding and charge transfer mechanism of glucose on WO3 and Ag doped WO3. As the binding energy of glucose is more on the Ag doped WO3 (100) surface compared to the bare WO3 (100) surface and the Ag doped WO3 (100) surface becomes more conducting due to enhancement of density of states near the Fermi level, we can infer that Ag doped WO3 exhibits a better charge transfer media compared to bare WO3 resulting in enhanced glucose sensitivity in consistency with our experimental data.

Formation and Disruption of W-Phase in High-Entropy Alloys

Directory of Open Access Journals (Sweden)

Sephira Riva

2016-05-01

Full Text Available High-entropy alloys (HEAs are single-phase systems prepared from equimolar or near-equimolar concentrations of at least five principal elements. The combination of high mixing entropy, severe lattice distortion, sluggish diffusion and cocktail effect favours the formation of simple phases—usually a bcc or fcc matrix with minor inclusions of ordered binary intermetallics. HEAs have been proposed for applications in which high temperature stability (including mechanical and chemical stability under high temperature and high mechanical impact is required. On the other hand, the major challenge to overcome for HEAs to become commercially attractive is the achievement of lightweight alloys of extreme hardness and low brittleness. The multicomponent AlCrCuScTi alloy was prepared and characterized using powder X-ray diffraction (PXRD, scanning-electron microscope (SEM and atomic-force microscope equipped with scanning Kelvin probe (AFM/SKP techniques. Results show that the formation of complex multicomponent ternary intermetallic compounds upon heating plays a key role in phase evolution. The formation and degradation of W-phase, Al2Cu3Sc, in the AlCrCuScTi alloy plays a crucial role in its properties and stability. Analysis of as-melted and annealed alloy suggests that the W-phase is favoured kinetically, but thermodynamically unstable. The disruption of the W-phase in the alloy matrix has a positive effect on hardness (890 HV, density (4.83 g·cm−3 and crack propagation. The hardness/density ratio obtained for this alloy shows a record value in comparison with ordinary heavy refractory HEAs.

Quantitative determination of phases in ZrO{sub 2} (MgO) (Y{sub 2}O{sub 3}) using the Rietveld method; Determinacao quantitativa de fases em ZrO{sub 2} - MgO - Y{sub 2}O{sub 3} utilizando o metodo de Rietveld

Energy Technology Data Exchange (ETDEWEB)

Castro, Antonio Carlos de

2007-07-01

The key objective of this work is the crystallographic characterization of the zircon co-doped with Yttria and magnesium with the application of the Rietveld method for quantitative phase analysis of zircon polymorph (zircon monoclinic, tetragonal, and cubic). Samples of zircon polymorph were obtained from zircon doped with Yttria and magnesium at defined molar concentrations. The zircon polymorph stability during subeutetoid aging at 1350 deg C were investigated to determine ZrO{sub 2} - MgO - Y{sub 2}0{sub 3} phases degradation and to define the solid solutions stability environment. ZrO{sub 2} powders doped with 8 mol por cent of MgO and 1 mol por cent of Y{sub 2}O{sub 3}, and 9 mol por cent of MgO and 0 mol por cent of Y{sub 2}O{sub 3} have been prepared by chemical route using the co-precipitation method. These samples have been calcinate at 550 deg C, sintered at 1500 deg C and characterized by the Rietveld method using the X-ray diffraction data. The variation of the lattice parameter, changes in the phase composition and their microstructures are discussed. The application of the Rietveld method for quantitative phase analysis of zircon polymorph (zircon tetragonal and cubic) reveals no formation of tetragonal phase and indicating that the matrix is the cubic phase with low concentration of monoclinic phase.(author)

In-situ investigation of the icosahedral Al-Cu-Fe phase formation in thin films

Energy Technology Data Exchange (ETDEWEB)

Haidara, F., E-mail: fanta.haidara@im2np.fr [IM2NP, UMR 6242 CNRS - Universite Aix-Marseille, Av. Escadrille Normandie-Niemen, Case 142, 13397 Marseille Cedex 20 (France); Duployer, B. [Universite Paul Sabatier CIRIMAT-LCMIE 2R1, 118, Route de Narbonne, 31062 Toulouse Cedex 09 (France); Mangelinck, D.; Record, M.-C. [IM2NP, UMR 6242 CNRS - Universite Aix-Marseille, Av. Escadrille Normandie-Niemen, Case 142, 13397 Marseille Cedex 20 (France)

2012-09-05

Highlights: Black-Right-Pointing-Pointer We investigated the phase formation of i-Al{sub 62.5}Cu{sub 25}Fe{sub 12.5} in thin films. Black-Right-Pointing-Pointer We characterized the samples by DSC and in-situ XRD and resistance measurements. Black-Right-Pointing-Pointer The resistivity value for i-Al{sub 62.5}Cu{sub 25}Fe{sub 12.5} was determined. - Abstract: This work is an investigation of the formation by reactive diffusion at high temperatures of the icosahedral phase, i-Al{sub 62.5}Cu{sub 25}Fe{sub 12.5}, in thin films. The samples were prepared by sputtering at room temperature. The elements Al, Cu and Fe were sequentially deposited onto oxidized silicon substrates. The two following stacking sequences, Al/Cu/Fe and Al/Fe/Cu, were investigated. The phase formation was studied using in situ resistivity, in situ X-ray Diffraction and Differential Scanning Calorimetry measurements. Whatever the stacking sequence, the sequences of phase formation evidenced during the heating treatment are similar. However the temperatures of formation for the first phases that are formed are different; they are higher in the case of the Al/Fe/Cu stacking sequence.

Adaptive ferroelectric state at morphotropic phase boundary: Coexisting tetragonal and rhombohedral phases

International Nuclear Information System (INIS)

Zhang, Yang; Xue, Dezhen; Wu, Haijun; Ding, Xiangdong; Lookman, Turab; Ren, Xiaobing

2014-01-01

With a focus on local symmetry, the microstructural basis for high piezoelectric performance in PbMg 1/3 Nb 2/3 O 3 –xPbTiO 3 (PMN–PT) ceramics at the morphotropic phase boundary (MPB) composition was investigated by means of convergent-beam electron diffraction analysis and twin diffraction pattern analysis. The local structure was found to consist of coexisting (1 0 1)-type tetragonal nanotwins and (0 0 1)-type rhombohedral nanotwins. A phenomenological theory based on crystallography is proposed to show that such nanoscale coexistence can give rise to an average monoclinic structure through strain accommodation. The average monoclinic structures (Ma and Mc) vary with temperature and composition due to the dependence on temperature and composition of the lattice parameters. Based on in situ X-ray diffraction data, we demonstrate how the polarization rotates across the MPB region in PMN–PT ceramics with varying temperatures and compositions

Insights on the High-Temperature Operational Limits of ZrO2-Y2O3 TBCs Manufactured via Air Plasma Spray

Science.gov (United States)

Lima, Rogerio S.; Marple, Basil R.

2017-03-01

The effective high-temperature operation limit of a ZrO2-7-8 wt.%Y2O3 (YSZ) thermal barrier coating (TBC) manufactured via air plasma spray (APS) is considered to be 1300 °C. This is related to the metastable tetragonal t'-phase formed during the rapid quenching of the YSZ particles during spraying. The t'-phase transforms into the equilibrium tetragonal and cubic phases at temperatures ≥ 1300 °C, which can lead to the formation of the monoclinic phase of YSZ upon cooling to room temperature. This formation of the monoclinic phase is accompanied by a volume expansion that leads to TBC failure due to extensive micro-cracking. To further investigate this limitation, an APS YSZ TBC was sprayed on a CMSX-4 substrate. By using a thermal (laser) gradient cyclic testing, a temperature gradient was generated across the TBC/substrate system. The YSZ T- front and substrate backside T- back temperature levels were 1500 and 1000 °C, respectively. In cycle conditions (5-min or 1-h hot and 2-min cool), no TBC failure has been observed. This behavior was partially attributed to the unexpected absence of the monoclinic phase of the YSZ in the cycled coatings. Although preliminary, these results are promising regarding increasing the effective high-temperature operational limits of APS YSZ TBCs.

Elimination of impurity phase formation in FePt magnetic thin films prepared by pulsed laser deposition

International Nuclear Information System (INIS)

Wang, Ying; Medwal, Rohit; Sehdev, Neeru; Yadian, Boluo; Tan, T.L.; Lee, P.; Talebitaher, A.; Ilyas, Usman; Ramanujan, R.V.; Huang, Yizhong; Rawat, R.S.

2014-01-01

The formation of impurity phases in FePt thin films severely degrades its magnetic properties. The X-ray diffraction patterns of FePt thin films, synthesized using pulsed laser deposition (PLD), showed peaks corresponding to impurity phases, resulting in softer magnetic properties. A systematic investigation was carried to determine the factors that might have led to impurity phase formation. The factors include (i) PLD target composition, (ii) substrate material, (iii) annealing parameters such as temperature, duration and ambience and (iv) PLD deposition parameters such as chamber ambience, laser energy fluence and target–substrate distance. Depositions on the different substrates revealed impurity phase formation only on Si substrates. It was found that the target composition, PLD chamber ambience, and annealing ambience were not the factors that caused the impurity phase formation. The annealing temperature and duration influenced the impurity phases, but are not the cause of their formation. A decrease in the laser energy fluence and increase of the target–substrate distance resulted in elimination of the impurity phases and enhancement in the magnetic and structural properties of FePt thin films. The energy of the ablated plasma species, controlled by the laser energy fluence and the target–substrate distance, is found to be the main factor responsible for the formation of the impurity phases.

Electric field-induced phase transitions in Li-modified Na{sub 0.5}K{sub 0.5}NbO{sub 3} at the polymorphic phase boundary

Energy Technology Data Exchange (ETDEWEB)

Iamsasri, Thanakorn; Jones, Jacob L., E-mail: jacobjones@ncsu.edu [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States); Tutuncu, Goknur [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States); Uthaisar, Chunmanus; Pojprapai, Soodkhet [School of Ceramic Engineering, Institute of Engineering, Suranaree University of Technology, Nakorn Ratchasima 30000 (Thailand); Wongsaenmai, Supattra [Program in Materials Science, Faculty of Science, Maejo University, Chiang Mai 50290 (Thailand)

2015-01-14

The electric field-induced phase transitions in Li-modified Na{sub 0.5}K{sub 0.5}NbO{sub 3} at the polymorphic phase boundary (PPB) were observed using in situ X-ray diffraction. The ratio of monoclinic to tetragonal phase fraction was used as an indicator of the extent and reversibility of the phase transitions. The reversibility of the phase transition was greater in compositions further from the PPB. These results demonstrate that the field-induced phase transition is one of the origins of high piezoelectric properties in lead-free ferroelectric materials.

A new method in prediction of TCP phases formation in superalloys

International Nuclear Information System (INIS)

Mousavi Anijdan, S.H.; Bahrami, A.

2005-01-01

The purpose of this investigation is to develop a model for prediction of topologically closed-packed (TCP) phases formation in superalloys. In this study, artificial neural networks (ANN), using several different network architectures, were used to investigate the complex relationships between TCP phases and chemical composition of superalloys. In order to develop an optimum ANN structure, more than 200 experimental data were used to train and test the neural network. The results of this investigation shows that a multilayer perceptron (MLP) form of the neural networks with one hidden layer and 10 nodes in the hidden layer has the lowest mean absolute error (MAE) and can be accurately used to predict the electron-hole number (N v ) and TCP phases formation in superalloys

Oxygen vacancy formation and migration in Sr- and Mg-doped LaGaO3: a density functional theory study

International Nuclear Information System (INIS)

Zhang Jie; Liang Er-Jun; Sun Qiang; Jia Yu

2012-01-01

Oxygen vacancy formation and migration in La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3−δ (LSGM) with various crystal symmetries (cubic, rhombohedral, orthorhombic, and monoclinic) are studied by employing first-principles calculations based on density functional theory (DFT). It is shown that the cubic LSGM has the smallest band gap, oxygen vacancy formation energy, and migration barrier, while the other three structures give rise to much larger values for these quantities, implying the best oxygen ion conductivity of the cubic LSGM among the four crystal structures. In our calculations, one oxygen vacancy migration pathway is considered in the cubic and rhombohedral structures due to all the oxygen sites being equivalent in them, while two vacancy migration pathways with different migration barriers are found in the orthorhombic and monoclinic symmetries owing to the existence of nonequivalent O 1 and O 2 oxygen sites. The migration energies along the migration pathway linking the two O 2 sites are obviously lower than those along the pathway linking the O 1 and O 2 sites. Considering the phase transitions at high temperatures, the results obtained in this paper can not only explain the experimentally observed different behaviours of the oxygen ionic conductivity of LSGM with different symmetries, but also predict the rational crystal structures of LSGM for solid oxide fuel cell applications. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Synthesis and luminescent properties of two different Y{sub 2}WO{sub 6}:Eu{sup 3+} phosphor phases

Energy Technology Data Exchange (ETDEWEB)

Llanos, Jaime, E-mail: jllanos@ucn.cl [Departamento de Química, Universidad Católica del Norte, Avda. Angamos 0610, Antofagasta (Chile); Olivares, Douglas [Departamento de Química, Universidad Católica del Norte, Avda. Angamos 0610, Antofagasta (Chile); Manríquez, Víctor; Espinoza, Darío [Departamento de Química, Universidad de Chile, Las Palmeras 3425, Santiago (Chile); Brito, Ivan [Departamento de Química, Universidad de Antofagasta, Campus Coloso, Antofagasta (Chile)

2015-04-15

Highlights: • Synthesis of two phases Y{sub 2−x}Eu{sub x}WO{sub 6}. One of them crystallizes as Aurivillius phase. • Optical properties of the phosphors Y{sub 2}WO{sub 6}:Eu{sup 3+} (monoclinic and orthorhombic phases). • The orthorhombic phase was prepared via low-temperature combustion synthesis method. - Abstract: In this paper, two different Y{sub 2−x}Eu{sub x}WO{sub 6} phases were synthesized. The monoclinic phase was prepared via a conventional solid-state reaction, whereas the orthorhombic phase was obtained via a facile, low-temperature combustion synthesis method. X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and photoluminescence (PL) spectroscopy were used to characterize the resulting phosphors. The XRD results indicate the orthorhombic phase crystallized isostructurally with the Aurivillius Bi{sub 2}WO{sub 6} phase, whereas the other polymorph crystallized isostructurally with Yb{sub 2}WO{sub 6} in the monoclinic system. The SEM studies revealed both phases had a strong tendency to form agglomerates averaging nanometers in size. The photoluminescence emission spectra confirmed all of the samples were efficiently excited by near UV light and were dominated by the electric dipole transition {sup 5}D{sub 0} → {sup 7}F{sub 2}. The orthorhombic Y{sub 2−x}Eu{sub x}WO{sub 6} excitation spectrum possessed a broad band across the entire UV region (220–400 nm); therefore, Y{sub 1.86}Eu{sub 0.14}WO{sub 6} could be considered an efficient spectral converter material for use in dye-sensitized solar cells.

Structural phase transitions at high-temperature in double perovskite Sr{sub 2}GdRuO{sub 6}

Energy Technology Data Exchange (ETDEWEB)

Triana, C.A.; Corredor, L.T.; Landinez Tellez, D.A. [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, A.A. 14490, Bogota D.C (Colombia); Roa-Rojas, J., E-mail: jroar@unal.edu.co [Grupo de Fisica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, A.A. 14490, Bogota D.C (Colombia)

2012-08-15

The crystal structure evolution of the Sr{sub 2}GdRuO{sub 6} complex perovskite at high-temperature has been investigated over a wide temperature range between 298 K{<=}T{<=}1273 K. Powder X-ray diffraction measurements at room temperature and Rietveld analysis show that this compounds crystallizes in a monoclinic perovskite-type structure with P2{sub 1}/n (no. 14) space group and the 1:1 ordered arrangement of Ru{sup 5+} and Gd{sup 3+} cations over the six-coordinate M sites, with lattice parameters a=5.81032(8) A, b=5.82341(4) A, c=8.21939(7) A, V=278.11(6) A{sup 3} and angle {beta}=90.311(2){sup o}. The high-temperature analysis shows that this material suffers two-phase transitions. At 373 K it adopts a monoclinic perovskite structure with I2/m space group, and lattice parameters a=5.81383(2) A, b=5.82526(4) A, c=8.22486(1) A, V=278.56(2) A{sup 3} and angle {beta}=90.28(2){sup o}. Above of 773 K, it suffers a phase transition from monoclinic I2/m to tetragonal I4/m, with lattice parameters a=5.84779(1) A, c=8.27261(1) A, V=282.89(5) A{sup 3} and angle {beta}=90.02(9){sup o}. The high-temperature phase transition from monoclinic I2/m to tetragonal I4/m is characterized by strongly anisotropic displacements of the anions.

Anisotropy and phonon modes from analysis of the dielectric function tensor and the inverse dielectric function tensor of monoclinic yttrium orthosilicate

Science.gov (United States)

Mock, A.; Korlacki, R.; Knight, S.; Schubert, M.

2018-04-01

We determine the frequency dependence of the four independent Cartesian tensor elements of the dielectric function for monoclinic symmetry Y2SiO5 using generalized spectroscopic ellipsometry from 40-1200 cm-1. Three different crystal cuts, each perpendicular to a principle axis, are investigated. We apply our recently described augmentation of lattice anharmonicity onto the eigendielectric displacement vector summation approach [A. Mock et al., Phys. Rev. B 95, 165202 (2017), 10.1103/PhysRevB.95.165202], and we present and demonstrate the application of an eigendielectric displacement loss vector summation approach with anharmonic broadening. We obtain an excellent match between all measured and model-calculated dielectric function tensor elements and all dielectric loss function tensor elements. We obtain 23 Au and 22 Bu symmetry long-wavelength active transverse and longitudinal optical mode parameters including their eigenvector orientation within the monoclinic lattice. We perform density functional theory calculations and obtain 23 Au symmetry and 22 Bu transverse and longitudinal optical mode parameters and their orientation within the monoclinic lattice. We compare our results from ellipsometry and density functional theory and find excellent agreement. We also determine the static and above reststrahlen spectral range dielectric tensor values and find a recently derived generalization of the Lyddane-Sachs-Teller relation for polar phonons in monoclinic symmetry materials satisfied [M. Schubert, Phys Rev. Lett. 117, 215502 (2016), 10.1103/PhysRevLett.117.215502].

In situ disordering of monoclinic titanium monoxide Ti5O5 studied by transmission electron microscope TEM.

Science.gov (United States)

Rempel, А А; Van Renterghem, W; Valeeva, А А; Verwerft, M; Van den Berghe, S

2017-09-07

The superlattice and domain structures exhibited by ordered titanium monoxide Ti 5 O 5 are disrupted by low energy electron beam irradiation. The effect is attributed to the disordering of the oxygen and titanium sublattices. This disordering is caused by the displacement of both oxygen and titanium atoms by the incident electrons and results in a phase transformation of the monoclinic phase Ti 5 O 5 into cubic B1 titanium monoxide. In order to determine the energies required for the displacement of titanium or oxygen atoms, i.e. threshold displacement energies, a systematic study of the disappearance of superstructure reflections with increasing electron energy and electron bombardment dose has been performed in situ in a transmission electron microscope (TEM). An incident electron energy threshold between 120 and 140 keV has been observed. This threshold can be ascribed to the displacements of titanium atoms with 4 as well as with 5 oxygen atoms as nearest neighbors. The displacement threshold energy of titanium atoms in Ti 5 O 5 corresponding with the observed incident electron threshold energy lies between 6.0 and 7.5 eV. This surprisingly low value can be explained by the presence of either one or two vacant oxygen lattice sites in the nearest neighbors of all titanium atoms.

Third phase formation revisited: the U(VI), HNO3 - TBP, n-dodecane system

International Nuclear Information System (INIS)

Chiarizia, R.; Jensen, M.P.; Borkowski, M.; Ferraro, J.R.; Thiyagarajan, P.; Littrell, K.C.

2003-01-01

In this work, the system U(VI), HNO 3 -tri-n-butylphosphate (TBP), n-dodecane has been revisited with the objective of gaining information on the coordination chemistry and structural evolution of the species formed in the organic phase before and after third phase formation. Chemical analyses, spectroscopic and EXAFS data indicate that U(VI) is extracted as the UO 2 (NO 3 ) 2 ·2TBP adduct, while the third phase species have the average composition UO 2 (NO 3 ) 2 ·2TBP·HNO 3 . Small-angle neutron scattering (SANS) measurements on TBP solutions loaded with only HNO 3 or with increasing amounts of U(VI) have revealed the presence, before phase splitting, of ellipsoidal aggregates with the major and minor axes up to about 64 and 15 A, respectively. The formation of these aggregates, very likely of the reverse micelle-type, is observed in all cases, that is, when only HNO 3 , only UO 2 (NO 3 ) 2 , or both HNO 3 and UO 2 (NO 3 ) 2 are extracted by the TBP solution. Upon third phase formation, the SANS data reveal the presence of smaller aggregates in the light organic phase, while the heavy organic phase contains pockets of diluent, each with an average of about two molecules of n-dodecane.

Growth Law For Peritectic Phases Formation In The Zinc Coating

Directory of Open Access Journals (Sweden)

Guzik E.

2015-09-01

Full Text Available Some experiments dealing with the isothermal hot dip galvanizing were carried out. The (Zn – coating settled on the Armco-iron substrate were examined after arresting the solidification for different periods of time. The measurement of the thickness of each sub-layer in the coating were performed due to the SEM – analysis. The zinc segregation on the cross-section of the studied sub-layers were also determined by the EDS technique. The growth laws are formulated mathematically for each of the observed sub-layer. The mechanism of the sub-layer formation is also analysed due to the observation of the birth/nucleation of the phases in the sub-layers and the effect of flux onto the sub-layers morphology formation. The appearance of each phase is referred to the Fe-Zn diagram for stable equilibrium according to which these phases are the products of the adequate peritectic transformation.

Lattice dynamical study of omega phase formation in Zr-Al system

International Nuclear Information System (INIS)

Ghosh, P.S.; Arya, A.; Kulkarni, U.D.; Dey, G.K.

2011-01-01

The hexagonal ω phase occurs in the alloys in which the high temperature β phase (bcc) is stabilized with respect to the martensitic β -> ω transformation. The compositional ranges over which the ω phase can be stabilized is the characteristic of the alloy system under consideration. The formation of ordered ω (B8 2 -Zr 2 Al) phase, having space group P6 3 /mmc has been viewed in terms of a superimposition of displacive and replacive components of phase transformation. While the lattice collapse mechanism of β -> ω transformation is displacive in nature; a replacive transformation involving diffusion is required for decorating different sublattice sites by different atomic species. Although, the extent of overlap of these transformations in the formation of ordered ω phase has not been established so far; attempts have been made to explore this aspect by examining the sequential formation of several intermediate stable/metastable phases. The partial collapse of 2nd - 3rd and 5th - 6th planes along (111) direction leads to intermediate trigonal ω ' phase upto which the transformation is purely displacive in nature. A chemical ordering sets in after this step leading to B82 structure via ω'' structure. Density functional plane wave based calculations using the projector augmented wave (PAW) potentials are employed under the generalized gradient approximation to exchange and correlation to study (a) relative ground state stabilities of these phases, (b) variation of total energy as a function of displacement (z, z = 0 to 1/12) and (c) Frozen-phonon calculations for 2/3 longitudinal phonon along (111) direction. The energy-displacement curve for the B2 structure shows nearly harmonic behavior for small displacements but shows strong anharmonic behavior for large displacements making trigonal ω ' structure metastable with respect to this kind of transformations. The phonon dispersion of B2 structure exhibits imaginary frequencies along (111) making it a

Pressure-induced phase transitions of multiferroic BiFeO3

OpenAIRE

XiaoLi, Zhang; Ye, Wu; Qian, Zhang; JunCai, Dong; Xiang, Wu; Jing, Liu; ZiYu, Wu; DongLiang, Chen

2013-01-01

Pressure-induced phase transitions of multiferroic BiFeO3 have been investigated using synchrotron radiation X-ray diffraction with diamond anvil cell technique at room temperature. Present experimental data clearly show that rhombohedral (R3c) phase of BiFeO3 first transforms to monoclinic (C2/m) phase at 7 GPa, then to orthorhombic (Pnma) phase at 11 GPa, which is consistent with recent theoretical ab initio calculation. However, we observe another peak at 2{\\theta}=7{\\deg} in the pressure ...

Effect of hardness of martensite and ferrite on void formation in dual phase steel

DEFF Research Database (Denmark)

Azuma, M.; Goutianos, Stergios; Hansen, Niels

2012-01-01

The influence of the hardness of martensite and ferrite phases in dual phase steel on void formation has been investigated by in situ tensile loading in a scanning electron microscope. Microstructural observations have shown that most voids form in martensite by evolving four steps: plastic...... deformation of martensite, crack initiation at the martensite/ferrite interface, crack propagation leading to fracture of martensite particles and void formation by separation of particle fragments. It has been identified that the hardness effect is associated with the following aspects: strain partitioning...... between martensite and ferrite, strain localisation and critical strain required for void formation. Reducing the hardness difference between martensite and ferrite phases by tempering has been shown to be an effective approach to retard the void formation in martensite and thereby is expected to improve...

Enhancement of polar crystalline phase formation in transparent PVDF-CaF{sub 2} composite films

Energy Technology Data Exchange (ETDEWEB)

Lee, Sang Goo; Ha, Jong-Wook, E-mail: jongwook@krict.re.kr; Sohn, Eun-Ho; Park, In Jun; Lee, Soo-Bok

2016-12-30

Highlights: • The crystalline phase in transparent PVDF-CaF{sub 2} composite films was investigated. • CaF{sub 2} promoted the formation of polar crystalline phases in PVDF matrix. • Ordered γ-phase was obtained by thermal treatment of as-cast films at the vicinity of its melting temperature. - Abstract: We consider the influence of calcium fluoride (CaF{sub 2}) nanoparticles on the crystalline phase formation of poly(vinylidene fluoride) (PVDF) for the first time. The transparent PVDF-CaF{sub 2} composite films were prepared by casting on PET substrates using N,N-dimethylacetamide (DMAc) as a solvent. It was found that CaF{sub 2} promoted the formation of polar crystalline phase of PVDF in composites, whereas nonpolar α-phase was dominant in the neat PVDF film prepared at the same condition. The portion of polar crystalline phase increased in proportional to the weight fraction of CaF{sub 2} in the composite films up to 10 wt%. Further addition of CaF{sub 2} suppressed completely the α-phase formation. Polar crystalline phase observed in as-cast composite films was a mixture of β- and γ-polymorph structures. It was also shown that much ordered γ-phase could be obtained through thermal treatment of as-cast PVDF-CaF{sub 2} composite film at the temperatures above the melting temperature of the composite films, but below that of γ-phase.

Antiferrodistortive phase transitions and ground state of PZT ceramics

International Nuclear Information System (INIS)

Pandey, Dhananjai

2013-01-01

The ground state of the technologically important Pb(Zr x Ti (1-x) )O 3 , commonly known as PZT, ceramics is currently under intense debate. The phase diagram of this material shows a morphotropic phase boundary (MPB) for x∼0.52 at 300K, across which a composition induced structural phase transition occurs leading to maximization of the piezoelectric properties. In search for the true ground state of the PZT in the MPB region, Beatrix Noheda and coworkers first discovered a phase transition from tetragonal (space group P4mm) to an M A type monoclinic phase (space group Cm) at low temperatures for x=0.52. Soon afterwards, we discovered yet another low temperature phase transition for the same composition in which the M A type (Cm) monoclinic phase transforms to another monoclinic phase with Cc space group. We have shown that the Cm to Cc phase transition is an antiferrodistortive (AFD) transition involving tilting of oxygen octahedra leading to unit cell doubling and causing appearance of superlattice reflections which are observable in the electron and neutron diffraction patterns only and not in the XRD patterns, as a result of which Noheda and coworkers missed the Cc phase in their synchrotron XRD studies at low temperatures. Our findings were confirmed by leading groups using neutron, TEM, Raman and high pressure diffraction studies. The first principles calculations also confirmed that the true ground state of PZT in the MPB region has Cc space group. However, in the last couple of years, the Cc space group of the ground state has become controversial with an alternative proposal of R3c as the space group of the ground state phase which is proposed to coexist with the metastable Cm phase. In order to resolve this controversy, we recently revisited the issue using pure PZT and 6% Sr 2+ substituted PZT, the latter samples show larger tilt angle on account of the reduction in the average cationic radius at the Pb 2+ site. Using high wavelength neutrons and high

Coexistence of different charge states in Ta-doped monoclinic HfO2: Theoretical and experimental approaches

DEFF Research Database (Denmark)

Taylor, M.A.; Alonso, R.E.; Errico, L.A.

2010-01-01

A combination of experiments and ab initio quantum-mechanical calculations has been applied to examine hyperfine interactions in Ta-doped hafnium dioxide. Although the properties of monoclinic HfO2 have been the subject of several earlier studies, some aspects remain open. In particular, time dif...

Experimental redetermination of the gas-phase enthalpy of formation of ethyl 2-thiophenecarboxylate

International Nuclear Information System (INIS)

Santos, Ana Filipa L.O.M.; Ribeiro da Silva, Manuel A.V.

2013-01-01

The condensed phase standard (p° = 0.1 MPa) molar enthalpy of formation of ethyl-2-thiophenecarboxylate was derived from the remeasured standard molar energy of combustion, in oxygen, at T = 298.15 K, by rotating bomb combustion calorimetry and the standard molar enthalpy of vaporization, at T = 298.15 K, remeasured by Calvet microcalorimetry. Combining these two values, the following enthalpy of formation in the gas phase, at T = 298.15 K, was then derived for ethyl-2-thiophenecarboxylate: −(277.7 ± 2.9) kJ · mol −1 . The calculated gas-phase enthalpy of formation of the title compound, through the G3(MP2)//B3LYP approach was found to be 278.9 kJ · mol −1 , in excellent agreement with the experimental measured value

Crystal structure of a new monoclinic polymorph of N-(4-methylphenyl-3-nitropyridin-2-amine

Directory of Open Access Journals (Sweden)

Aina Mardia Akhmad Aznan

2014-08-01

Full Text Available The title compound, C12H11N3O2, is a second monoclinic polymorph (P21, with Z′ = 4 of the previously reported monoclinic (P21/c, with Z′ = 2 form [Akhmad Aznan et al. (2010. Acta Cryst. E66, o2400]. Four independent molecules comprise the asymmetric unit, which have the common features of a syn disposition of the pyridine N atom and the toluene ring, and an intramolecular amine–nitro N—H...O hydrogen bond. The differences between molecules relate to the dihedral angles between the rings which range from 2.92 (19 to 26.24 (19°. The geometry-optimized structure [B3LYP level of theory and 6–311 g+(d,p basis set] has the same features except that the entire molecule is planar. In the crystal, the three-dimensional architecture is consolidated by a combination of C—H...O, C—H...π, nitro-N—O...π and π–π interactions [inter-centroid distances = 3.649 (2–3.916 (2 Å].

Structural control of void formation in dual phase steels

DEFF Research Database (Denmark)

Azuma, Masafumi

The objective of this study is to explore the void formation mechanisms and to clarify the influence of the hardness and structural parameters (volume fraction, size and morphology) of martensite particles on the void formation and mechanical properties in dual phase steels composed of ferrite...... and (iii) strain localization. The critical strain for void formation depends on hardness of the martensite, but is independent of the volume fraction, shape, size and distribution of the martensite. The strain partitioning between the martensite and ferrite depends on the volume fraction and hardness...... of the martensite accelerates the void formation in the martensite by enlarging the size of voids both in the martensite and ferrite. It is suggested that controlling the hardness and structural parameters associated with the martensite particles such as morphology, size and volume fraction are the essential...

Statistics of errors in fibre communication lines with a phase-modulation format and optical phase conjugation

International Nuclear Information System (INIS)

Shapiro, Elena G; Fedoruk, Mikhail P

2011-01-01

Analytical formulas are derived to approximate the probability density functions of 'zero' and 'one' bits in a linear communication channel with a binary format of optical signal phase modulation. Direct numerical simulation of the propagation of optical pulses in a communication line with optical phase conjugation is performed. The results of the numerical simulation are in good agreement with the analytical approximation. (fibreoptic communication lines)

Paramagnetic centers in two phases of manganese-doped lanthanum gallate

Science.gov (United States)

Vazhenin, V. A.; Potapov, A. P.; Guseva, V. B.; Artyomov, M. Yu.

2009-05-01

An EPR study of two phases of manganese-doped lanthanum gallate (with a first-order structural transition occurring at 430 K) has revealed Gd3+, Fe3+, and Mn4+ centers at room temperature and 438 K. The parameters of spin Hamiltonians are determined for the Gd3+, Fe3+, and Mn4+ rhombohedral centers in the high-temperature phase (with no other centers found here) and for the monoclinic center Gd3+ in the low-temperature phase. Both in the orthorhombic and in the rhombohedral phase, crystallographic twins (or ferroelastic domains) are observed.

Droplets formation and merging in two-phase flow microfluidics.

Science.gov (United States)

Gu, Hao; Duits, Michel H G; Mugele, Frieder

2011-01-01

Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i) the emulsification step should lead to a very well controlled drop size (distribution); and (ii) the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed.

Equation of state, phase stability, and phase transformations of uranium-6 wt. % niobium under high pressure and temperature

Science.gov (United States)

Zhang, Jianzhong; Vogel, Sven; Brown, Donald; Clausen, Bjorn; Hackenberg, Robert

2018-05-01

In-situ time-of-flight neutron diffraction experiments were conducted on the uranium-niobium alloy with 6 wt. % Nb (U-6Nb) at pressures up to 4.7 GPa and temperatures up to 1073 K. Upon static compression at room temperature, the monoclinic structure of U-6Nb (α″ U-6Nb) remains stable up to the highest experimental pressure. Based on the pressure-volume measurements at room temperature, the least-squares fit using the finite-strain equation of state (EOS) yields an isothermal bulk modulus of B0 = 127 ± 2 GPa for the α″-phase of U-6Nb. The calculated zero-pressure bulk sound speed from this EOS is 2.706 ± 0.022 km/s, which is in good agreement with the linear extrapolation of the previous Hugoniot data above 12 GPa for α″ U-6Nb, indicating that the dynamic response under those shock-loading conditions is consistent with the stabilization of the initial monoclinic phase of U-6Nb. Upon heating at ambient and high pressures, the metastable α″ U-6Nb exhibits complex transformation paths leading to the diffusional phase decomposition, which are sensitive to applied pressure, stress state, and temperature-time path. These findings provide new insight into the behavior of atypical systems such as U-Nb and suggest that the different U-Nb phases are separated by rather small energies and hence highly sensitive to compositional, thermal, and mechanical perturbations.

Influence of second phase dispersion on void formation during irradiation

International Nuclear Information System (INIS)

Sundararaman, M.; Banerjee, S.; Krishnan, R.

Irradiation-induced void formation in alloys has been found to be strongly influenced by the microstructure, the important microstructural parameters being the dislocation density and the nature, density and distribution of second-phase precipitates. The effects of various types of precipitates on void swelling have been examined using the generally-accepted model of void formation : void embryos are assumed to grow in a situation where equal numbers of vacancies and interstitials are continuously generated by the incident irradiation, the interstitials being somewhat perferentially absorbed in some sinks present in the material. The mechanism of the trapping of defects by a distribution of precipitates has been discussed and the available experimental results on the suppression of void formation in materials containing coherent precipitates have been reviewed. Experimental results on the microstructure developed in a nickel-base alloys, Inconel-718 (considered to be a candidate material for structural applications in fast reactors), have been presented. The method of determination of the coherency strain associated with the precipitates has been illustrated with the help of certain observations made on this alloy. The major difficulty in using a two-phase alloy in an irradiation environment is associated with the irradiation-induced instability of the precipitates. Several processes such as precipitate dislocation (in which the incident radiation removes the outer layer of precipitates by recoil), enhanced diffusion disordering, fragmentation of precipitates, etc. are responsible for bringinq about a significant change in the structure of a two-phase material during irradiation. The effect of these processes on the continued performance of a two-phase alloy subjected to irradiation at an elevated temperature has been discussed. (auth.)

Investigation of the phase formation from nickel coated nanostructured silicon

Science.gov (United States)

Shilyaeva, Yulia I.; Pyatilova, Olga V.; Berezkina, Alexandra Yu.; Sysa, Artem V.; Dudin, Alexander A.; Smirnov, Dmitry I.; Gavrilov, Sergey A.

2016-12-01

In this paper, the influence of the conditions of chemical and electrochemical nickel plating of nanostructured silicon and subsequent heat treatment on the phase composition of Si/Ni structures with advanced interface is studied. Nanostructured silicon formed by chemical and electrochemical etching was used for the formation of a developed interphase surface. The resulting Si/Ni samples were analyzed using scanning electron microscopy, energy dispersive X-ray analysis, and X-ray phase analysis. The experiments have revealed the differences in phase composition of the Si/Ni structures obtained by different methods, both before and after heat treatment.

Light modulation in phase change disordered metamaterial - A smart cermet concept

OpenAIRE

Kumar , Sunil; Maury , Francis; Bahlawane , Naoufal

2017-01-01

International audience; Cermet coatings are popular solar selective absorbers as they allow capturing most of the solar energywhile minimising radiative losses. Embedded metallic nanoparticles in dielectric matrices promotemultiple internal reflection of light and provide an overall low emissivity. VO2 in the metamaterial stateis regarded in this study as a responsive mixed phase comprising metallic rutile VO2 inclusions insemiconducting monoclinic VO2 phase mimicking cermet. The smart cermet...

On mechanism of substructure formation in SmS during isomorphic phase transformations

International Nuclear Information System (INIS)

Aptekar', I.L.; Ivanov, V.I.; Tonkov, E.Yu.; Shmyt'ko, I.M.

1986-01-01

X-ray diffraction study of substructure characteristics of SmS samples subjected to treatment at different temrerature and pressure in media with different viscosity ( graphite, silicon oil) for realization of P-M-P transformations ( p-semiconductor phase, M - high pressure phase) is performed. It is assumed that with M - phase formation P - matrix volume relaxation delays, therefore the new phase particles occupy smaller volume than the initial matrix which causes the M - phase disorientation. The difference between the phase transformation rate and deformation rate under the pressure in media with various viscosity results in arising different substructural characteristics

Dielectric tensor of monoclinic Ga2O3 single crystals in the spectral range 0.5–8.5 eV

Directory of Open Access Journals (Sweden)

C. Sturm

2015-10-01

Full Text Available The dielectric tensor of Ga2O3 in the monoclinic (β phase was determined by generalized spectroscopic ellipsometry in a wide spectral range from 0.5 eV to 8.5 eV as well as by density functional theory calculations combined with many-body perturbation theory including quasiparticle and excitonic effects. The dielectric tensors obtained by both methods are in excellent agreement with each other and the observed transitions in the dielectric function are assigned to the corresponding valence bands. It is shown that the off-diagonal element of the dielectric tensor reaches values up to |εxz| ≈ 0.30 and cannot be neglected. Even in the transparent spectral range where it is quite small (|εxz| < 0.02 it causes a rotation of the dielectric axes around the symmetry axis of up to 20°.

Phase formation and texture of thin nickel germanides on Ge(001) and Ge(111)

Energy Technology Data Exchange (ETDEWEB)

De Schutter, B., E-mail: deschutter.bob@ugent.be; Detavernier, C. [Department of Solid-State Sciences, Ghent University, Krijgslaan 281/S1, 9000 Ghent (Belgium); Van Stiphout, K.; Santos, N. M.; Vantomme, A. [Instituut voor Kern- en Stralingsfysica, KU Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium); Bladt, E.; Bals, S. [Electron Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp (Belgium); Jordan-Sweet, J.; Lavoie, C. [IBM T.J. Watson Research Center, Yorktown Heights, New York 10598 (United States); Comrie, C. M. [Department of Physics, University of Cape Town, Rondebosch 7700 (South Africa)

2016-04-07

We studied the solid-phase reaction between a thin Ni film and a single crystal Ge(001) or Ge(111) substrate during a ramp anneal. The phase formation sequence was determined using in situ X-ray diffraction and in situ Rutherford backscattering spectrometry (RBS), while the nature and the texture of the phases were studied using X-ray pole figures and transmission electron microscopy. The phase sequence is characterized by the formation of a single transient phase before NiGe forms as the final and stable phase. X-ray pole figures were used to unambiguously identify the transient phase as the ϵ-phase, a non-stoichiometric Ni-rich germanide with a hexagonal crystal structure that can exist for Ge concentrations between 34% and 48% and which forms with a different epitaxial texture on both substrate orientations. The complementary information gained from both RBS and X-ray pole figure measurements revealed a simultaneous growth of both the ϵ-phase and NiGe over a small temperature window on both substrate orientations.

Droplets Formation and Merging in Two-Phase Flow Microfluidics

Directory of Open Access Journals (Sweden)

Hao Gu

2011-04-01

Full Text Available Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i the emulsification step should lead to a very well controlled drop size (distribution; and (ii the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed.

Low temperature phase transition and crystal structure of CsMgPO{sub 4}

Energy Technology Data Exchange (ETDEWEB)

Orlova, Maria, E-mail: maria.p.orlova@gmail.com [Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, Innsbruck 6020 (Austria); Khainakov, Sergey [Departamento de Química Física y Analítica, Universidad de Oviedo—CINN, 33006 Oviedo (Spain); Servicios Científico Técnicos, Universidad de Oviedo, 33006 Oviedo (Spain); Michailov, Dmitriy [Department of Chemistry, University of Nizhny Novgorod, 23 Gagarin av., Nizhny Novgorod 603950 (Russian Federation); Perfler, Lukas [Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, Innsbruck 6020 (Austria); Langes, Christoph [Institute of Pharmacy, University of Innsbruck, Innrain 52, Innsbruck 6020 (Austria); Kahlenberg, Volker [Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52, Innsbruck 6020 (Austria); Orlova, Albina [Department of Chemistry, University of Nizhny Novgorod, 23 Gagarin av., Nizhny Novgorod 603950 (Russian Federation)

2015-01-15

CsMgPO{sub 4} doped with radioisotopes is a promising compound for usage as a radioactive medical source. However, a low temperature phase transition at temperatures close to ambient conditions (∼−40 °C) was observed. Information about such kind of structural changes is important in order to understand whether it can cause any problem for medical use of this compound. The phase transition has been investigated in detail using synchrotron powder diffraction, Raman spectroscopy and DFT calculations. The structure undergoes a transformation from an orthorhombic modification, space group Pnma (RT phase) to a monoclinic polymorph, space group P2{sub 1}/n (LT phase). New LT modification adopts similar to RT but slightly distorted unit cell: a=9.58199(2) Å, b=8.95501(1) Å, c=5.50344(2) Å, β=90.68583(1)°, V=472.198(3) Å{sup 3}. CsMgPO{sub 4} belongs to the group of framework compounds and is made up of strictly alternating MgO{sub 4}- and PO{sub 4}-tetrahedra sharing vertices. The cesium counter cations are located in the resulting channel-like cavities. Upon the transformation a combined tilting of the tetrahedra is observed. A comparison with other phase transitions in ABW-type framework compounds is given. - Graphical abstract: Structural behavior of β-tridymite-type phosphate CsMgPO{sub 4}, considered as potential chemical form for radioactive Cs-source has been studied at near ambient temperatures. A phase transition at (∼−40 °C) has been found and investigated. It has been established that the known orthorhombic RT modification, space group Pnma, adopts a monoclinic cell with space group P2{sub 1}/n at low temperatures. In this paper, we present results of structural analysis of changes accompanying this phase transition and discuss its possible impact on the application properties. - Highlights: • β-Tridymite type phosphate CsMgPO{sub 4} undergoes so called translationengleiche phase transition of index 2 at −40 °C. • The structure

Formation of the minor phase shell on the surface of hypermonotectic alloy powders

International Nuclear Information System (INIS)

Zhao, J.Z.

2006-01-01

The microstructure evolution in an atomized hypermonotectic alloy drop is calculated. The results indicate that the formation of the minor phase shell on the surface of the powder is due to the heterogeneous nucleation of the minor phase droplets on the atomized drop surface and the resultant diffusional transfer of solute during the liquid-liquid phase transformation

Monoclinic α-Bi2O3 photocatalyst for efficient removal of gaseous NO and HCHO under visible light irradiation

International Nuclear Information System (INIS)

Ai Zhihui; Huang Yu; Lee Shuncheng; Zhang Lizhi

2011-01-01

Research highlights: → We got the monoclinic α-Bi 2 O 3 powders after the calcinations of the plate-like (BiO) 2 CO 3 precursors at 500 deg. C for 4 h. → The synthetic α-Bi 2 O 3 showed high visible light photocatalytic activity for removal of NO and HCHO. - Abstract: The investigation was focused on the visible-light-driven photocatalytic removal of gaseous NO and HCHO at typical indoor air concentration over synthetic α-Bi 2 O 3 . Monoclinic α-Bi 2 O 3 was synthesized via calcination of hydrothermally prepared (BiO) 2 CO 3 precursor at 500 deg. C for 4 h. The synthetic α-Bi 2 O 3 samples were systematically characterized by XRD, SEM, FT-IR, and UV-vis diffuse reflectance spectra (DRS). The optical band gap energy of the resulting α-Bi 2 O 3 was estimated to be 2.72 eV from the UV-vis absorption spectra. Comparing with the commercial Bi 2 O 3 counterpart, the fabricated α-Bi 2 O 3 showed superior visible-light-induced photocatalytic activity on degradation of nitrogen monoxide (NO) and formaldehyde (HCHO) at typical indoor air concentration. No obvious deactivation of synthetic α-Bi 2 O 3 was observed during the prolonged photocatalytic reaction. This work suggests that the synthesized monoclinic α-Bi 2 O 3 with suitable band gap and high activity is promising photocatalyst for indoor air purification.

Salts and Co-crystals of Theobromine and their phase ...

Indian Academy of Sciences (India)

These results suggest that even though traditional salts are .... Water filtered through a double deionized purification system (AquaDM,. Bhanu, Hyderabad, India) was used in all experiments. ... vent(s) was mounted on the goniometer of Oxford .... Monoclin ic. Monoclin ic. Monoclin ic. Monoclin ic. T riclin ic. S p ace group.

Molecular dynamics simulation and x-ray structural studies of mode-coupling in monoclinic K2ZnBr4

International Nuclear Information System (INIS)

Machida, Mitsuo; Itoh, Hideaki; Koyano, Nobumitsu

2003-01-01

The mode-coupling between the rotational and translational motions in the monoclinic K 2 ZnBr 4 was studied by the molecular dynamics simulation and X-ray structure analysis. In the structure analysis, the Fourier analysis indicates that, in the paraelectric phase, electron densities of the bromines Br1 and Br2 on the mirror plane are fairly elongated in the b direction, while the density of the bromine Br3 at the general position spreads more or less in the a direction. In the ferroelectric phase, the elongation is suppressed in particular for Br1 and Br2, and the densities of Br3 and Br4, which are equivalent each other in the paraelectric phase, are nearly isotropic. In addition, Br1 and Br2 displace in the b direction through the rotation of the ZnBr 4 2- ion about the a axis. In the simulation, the ZnBr 4 2- ions are treated as rigid-bodies. The trajectories of the bromines reproduce satisfactorily the characteristic feature of the Fourier maps. This means that the ZnBr 4 2- ions are approximately regarded as rigid-bodies even in the real K 2 ZnBr 4 . The mode-coupling analysis shows that, in the ZnBr 4 2- rigid-bodies, the rotational motion about the a axis and the translational motion in the b direction couple strongly. Moreover, the displacements of rotational and translational motions in the b direction are almost synchronous for Br1 and Br2, and almost asynchronous for Br3 and Br4. (author)

High-pressure phase transition in Ho2O3

International Nuclear Information System (INIS)

Lonappan, Dayana; Shekar, N.V. Chandra; Ravindran, T.R.; Sahu, P. Ch.

2010-01-01

High-pressure X-ray diffraction and Raman studies on holmium sesquioxide (Ho 2 O 3 ) have been carried out up to a pressure of ∼17 GPa in a diamond-anvil cell at room temperature. Holmium oxide, which has a cubic or bixbyite structure under ambient conditions, undergoes an irreversible structural phase transition at around 9.5 GPa. The high-pressure phase has been identified to be low symmetry monoclinic type. The two phases coexist to up to about 16 GPa, above which the parent phase disappears. The high-pressure laser-Raman studies have revealed that the prominent Raman band ∼370 cm -1 disappears around the similar transition pressure. The bulk modulus of the parent phase is reported.

Pressure-induced phase transformations in L-alanine crystals

DEFF Research Database (Denmark)

Olsen, J. Staun; Gerward, Leif; Freire, P.T.C.

2008-01-01

Raman scattering and synchrotron X-ray diffraction have been used to investigate the high-pressure behavior of L-alanine. This study has confirmed a structural phase transition observed by Raman scattering at 2.3 GPa and identified it as a change from orthorhombic to tetragonal structure. Another...... phase transformation from tetragonal to monoclinic structure has been observed at about 9 GPa. From the equation of state, the zero-pressure bulk modulus and its pressure derivative have been determined as (31.5 +/- 1.4) GPa and 4.4 +/- 0.4, respectively....

Pressure induced structural phase transition in SnS—An ab initio study

Indian Academy of Sciences (India)

Unknown

Abstract. The structural behaviour of SnS under pressure has been investigated by first principle density functional ... tural phase transition from orthorhombic type to monoclinic type structure around 17 GPa which is in good agreement with the ... is achieved by performing the electronic structure and total energy calculation ...

Nonequilibrium phase formation in oxides prepared at low temperature: Fergusonite-related phases

International Nuclear Information System (INIS)

Mather, S.A.; Davies, P.K.

1995-01-01

Sol-gel methods have been developed to prepare YNbO 4 , YTaO 4 , and other rare-earth niobates and tantalates with fergusonite-related crystal structures. At low temperatures, all of the fergusonites, with the exception of SmTaO 4 , crystallize in a metastable tetragonal (T') structure similar to that of tetragonal zirconia. Although all of the equilibrium forms of these oxides adopt a crystal structure containing an ordered distribution of the trivalent and pentavalent cations, a random cation distribution is obtained in the metastable T' phase. Metastable phase formation is often ascribed solely to kinetically limited topotactic crystallization. However, the changes in the grain size and unit-cell volumes that accompany the metastable-to-equilibrium fergusonite conversions imply that other physical phenomena induced by small-particle synthesis, namely the Gibbs-Thompson pressure effect and the increased contribution of surface energy, cannot be ignored

Formation, stability and crystal structure of the {sigma} phase in Mo-Re-Si alloys

Energy Technology Data Exchange (ETDEWEB)

Bei, H., E-mail: beih@ornl.gov [Oak Ridge National Laboratory, Materials Science and Technology Division, Oak Ridge, TN 37831 (United States); Yang, Y., E-mail: ying.yang@computherm.com [CompuTherm LLC, Madison, WI 53719 (United States); Viswanathan, G.B. [Air Force Research Laboratory, Wright-Patterson AFB, OH 45433 (United States); Rawn, C.J.; George, E.P. [Oak Ridge National Laboratory, Materials Science and Technology Division, Oak Ridge, TN 37831 (United States)] [University of Tennessee, Department of Materials Science and Engineering, Knoxville, TN 37996 (United States); Tiley, J. [Air Force Research Laboratory, Wright-Patterson AFB, OH 45433 (United States); Chang, Y.A. [CompuTherm LLC, Madison, WI 53719 (United States)] [University of Wisconsin-Madison, Madison, WI 53705 (United States)

2010-10-15

The formation, stability and crystal structure of the {sigma} phase in Mo-Re-Si alloys were investigated. Guided by thermodynamic calculations, six critically selected alloys were arc melted and annealed at 1600 deg. C for 150 h. Their as-cast and annealed microstructures, including phase fractions and distributions, the compositions of the constituent phases and the crystal structure of the {sigma} phase were analyzed by thermodynamic modeling coupled with experimental characterization by scanning electron microscopy, electron probe microanalysis, X-ray diffraction and transmission electron microscopy. Two key findings resulted from this work. One is the large homogeneity range of the {sigma} phase region, extending from binary Mo-Re to ternary Mo-Re-Si. The other is the formation of a {sigma} phase in Mo-rich alloys either through the peritectic reaction of liquid + Mo{sub ss} {yields} {sigma} or primary solidification. These findings are important in understanding the effects of Re on the microstructure and providing guidance on the design of Mo-Re-Si alloys.

A comparative structural and electrochemical study of monoclinic Li3V2(PO4)3/C and rhombohedral Li2.5Na0.5V(2−2x/3)Nix(PO4)3/C

International Nuclear Information System (INIS)

Wang, Wenhui; Chen, Zhenyu; Zhang, Jiaolong; Dai, Changsong; Li, Jiajie; Ji, Dalong

2013-01-01

In order to synthesize pure derivative of rhombohedral Li 3 V 2 (PO 4 ) 3 (LVP), lithium-ion batteries materials Li 2.5 Na 0.5 V (2−2x/3) Ni x (PO 4 ) 3 /C (x = 0.03, 0.06, 0.09) and its control, monoclinic Li 3 V 2 (PO 4 ) 3 /C (LVP/C), were prepared by sol–gel method. The samples were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), Raman spectroscopy, and electrochemical methods. The XRD patterns of Li 2.5 Na 0.5 V (2−2x/3) Ni x (PO 4 ) 3 /C are in good agreement with that of rhombohedral LVP, which indicates that the Na + –Ni 2+ composite doping can change the structure of monoclinic LVP. All the composite doping samples displayed a single flat plateau at 3.7 V in the charge/discharge voltage profile, which is caused by transformation of multi-phase mechanism to single-phase mechanism. For Li 2.5 Na 0.5 V 1.98 Ni 0.03 (PO 4 ) 3 /C, a specific discharge capacity of 108 mAh g −1 was achieved at a 0.5 C charge rate and a 1 C discharge rate, and a 99.0% retention rate of the initial capacity was obtained after 50 cycles

A new method for determining gas phase heat of formation of aromatic energetic compounds

Energy Technology Data Exchange (ETDEWEB)

Keshavarz, Mohammad H. [Department of Chemistry, Malek-ashtar University of Technology, Shahin-shahr P. O. Box 83145/115 (Iran); Tehrani, Masoud K. [Department of Physics, Malek-ashtar University of Technology, Shahin-shahr P. O. Box 83145/115 (Iran)

2007-04-15

A new correlation is introduced for desk calculation of gas phase heat of formation of aromatic energetic compounds that contain the elements of carbon, hydrogen, nitrogen and oxygen. Predicted gas phase heats of formation for 26 energetic compounds have a root mean square of deviation from experiment of 20.67 kJ/mol, which is in good agreement with respect to measured values of oxygen-lean and oxygen-rich aromatic energetic compounds. (Abstract Copyright [2007], Wiley Periodicals, Inc.)

New insights in third phase formation in the U(VI)-HNO3, TBP-alkane system

International Nuclear Information System (INIS)

Jensen, M. P.; Chiarizia, R.; Ferraro, J. R.; Borkowski, M.; Nash, K. L.; Thiyagarajan, P.; Littrell, K. C.

2001-01-01

In this work, the system U(VI)-HNO 3 -tributylphosphate (TBP)-n-dodecane has been revisited with the objective of gaining coordination chemistry and structural information on the species that are formed in the organic phase before and after third phase formation. Chemical analyses, spectroscopic and EXAFS data indicate that U(VI) is extracted as the UO 2 (NO 3 ) 2 · 2TBP adduct, while the third phase species has the composition UO 2 (NO 3 ) 2 · 2TBP · HNO 3 . Small-angle neutron scattering (SANS) data reveal the presence in the organic phase, both before and after phase splitting, of ellipsoidal aggregates whose formation seems to depend more on the extraction of HNO 3 than that of U(VI)

Kinetics and mechanism of solid-phase reactions of formation of yttrium ferrite with garnet structure

Energy Technology Data Exchange (ETDEWEB)

Pashchenko, V P; Yakushevskaya, F T; Chalyi, V P

1977-04-01

The perovskite phase is formed in the process of ferrogarnet formation both from the mixture of Y and Fe oxides and from mutually precipitated carbonates. The amount of the perovskite phase decreases with increasing duration of annealing. The process of the ferritoformation in the investigated systems can be presented as isovalent cationic substitution on the basis of the crystalline structure of Y/sub 2/O/sub 3/ with the formation of the perovskite structure. When the Fe concentration in orthoferrite increases, the phase with a garnet structure is formed.

Vibrational spectroscopic and dielectric properties investigations of phase transitions in KMgPO4 compound

Science.gov (United States)

Miladi, L.; Oueslati, A.; Guidara, K.

2017-11-01

The potassium orthophosphate KMgPO4 with a β-tridymite structure was synthesized via solid-state reaction. X-ray diffraction study confirms the formation of a single phase material which crystallizes at room temperature in monoclinic system. This compound has been investigated by vibrational spectroscopy in the temperature range573-723 K. Thermal analysis shows that this composition undergoes two phase transitions at T1=633Kand T2=693 K.The evolution of Raman line ν and half -width Δν versus temperature introduces huge changes which are associated with the phase transitions originating from the reorientation of the PO4 tetrahedron. Besides, an analysis of the dielectric constants ε‧ and ε″versus temperature at several frequencies shows a distribution of relaxation times. This relaxation is probably due to the change in dynamical state of the K+ cation. The ac conductivity behavior can be understood in terms of the motions of K+ cations along the tunnels which are formed by six-membered rings of MgO4 and PO4 tetrahedron linked by common vertices. The activation energies values obtained from the thermal evolution of the conductivity are: Ea1=0.52 eV (T693 K).

Phase transformations during machining and properties of surface layers in zirconium dioxide ceramics

International Nuclear Information System (INIS)

Grigor'ev, O.N.; Krivoshej, G.S.; Stel'mashenko, N.A.; Trefilov, V.I.; Shevchenko, A.V.

1991-01-01

The methods of X-ray allow studying phase composition and inner stresses in the surface layers of partially stabilized zirconium dioxide after mashining. It is shown that under conditions of abrasive treatment transitions from tetragonal into rhomboedric and monoclinic phases initiate. As a result of phase transitions fields of compressible stresses achieving 900 MPa under grinding with ACM abrasive are created on the surface. An essential increase of hardness due to growth of the brittle fauilure resistance and deformation hardening is revealed

Simulating the formation and evolution of galaxies: multi-phase description of the interstellar medium, star formation, and energy feedback

Science.gov (United States)

Merlin, E.; Chiosi, C.

2007-10-01

Context: Modelling the gaseous component of the interstellar medium (ISM) by Smoothed Particles Hydrodynamics in N-Body simulations (NB-TSPH) is still very crude when compared to the complex real situation. In the real ISM, many different and almost physically decoupled components (phases) coexist for long periods of time, and since they spread over wide ranges of density and temperature, they cannot be correctly represented by a unique continuous fluid. This would influence star formation which is thought to take place in clumps of cold, dense, molecular clouds, embedded in a warmer, neutral medium, that are almost freely moving throughout the tenuous hot ISM. Therefore, assuming that star formation is simply related to the gas content without specifying the component in which this is both observed and expected to occur may not be physically sound. Aims: We consider a multi-phase representation of the ISM in NB-TSPH simulations of galaxy formation and evolution with particular attention to the case of early-type galaxies. Methods: Cold gas clouds are described by the so-called sticky particles algorithm. They can freely move throughout the hot ISM medium; stars form within these clouds and the mass exchange among the three baryonic phases (hot gas, cold clouds, stars) is governed by radiative and Compton cooling and energy feedback by supernova (SN) explosions, stellar winds, and UV radiation. We also consider thermal conduction, cloud-cloud collisions, and chemical enrichment. Results: Our model agrees with and improves upon previous studies on the same subject. The results for the star formation rate agree with recent observational data on early-type galaxies. Conclusions: These models lend further support to the revised monolithic scheme of galaxy formation, which has recently been strengthened by high redshift data leading to the so-called downsizing and top-down scenarios.

Magnesium nitride phase formation by means of ion beam implantation technique

International Nuclear Information System (INIS)

Hoeche, Daniel; Blawert, Carsten; Cavellier, Matthieu; Busardo, Denis; Gloriant, Thierry

2011-01-01

Nitrogen implantation technique (Hardion + ) has been applied in order to modify the surface properties of magnesium and Mg-based alloys (AM50, AZ31). Nitrogen ions with an energy of approximately 100 keV were used to form the Mg 3 N 2 phase leading to improved surface properties. The samples were investigated using various characterization methods. Mechanical properties have been tested by means of nanoindention, the electrochemical behavior was measured by potentiodynamic polarization and impedance spectroscopy, phase formation by using grazing incidence Xray diffraction, the chemical state was determined by means of Xray induced photoelectron spectroscopy (XPS) and depth profiling by using secondary ions mass spectroscopy (SIMS). Additionally, the results were compared to calculated depth profiles using SRIM2008. The correlation of the results shows the nitride formation behavior to a depth of about 600 nm.

640 Gbit/s RZ-to-NRZ format conversion based on optical phase filtering

DEFF Research Database (Denmark)

Maram, Reza; Kong, Deming; Galili, Michael

2014-01-01

We propose a novel approach for all optical RZ-to-NRZ conversion based on optical phase filtering. The proposed concept is experimentally validated through format conversion of a 640 Gbit/s coherent RZ signal to NRZ signal using a simple phase filter implemented by a commercial optical waveshaper....

Phase control studies in Gd5Si2Ge2 giant magnetocaloric compound

International Nuclear Information System (INIS)

Belo, J.H.; Pereira, A.M.; Ventura, J.; Oliveira, G.N.P.; Araújo, J.P.; Tavares, P.B.; Fernandes, L.; Algarabel, P.A.; Magen, C.; Morellon, L.

2012-01-01

Highlights: ► Study of time dependence of O(I) to M phase. ► Determination of the optimal annealing time. ► New method for phase amount estimation (O(I) and M). ► Effect of annealing on the MCE. ► Analysis of the nature of the magnetic transition through the Arrot plot representation. - Abstract: A systematic set of annealings on arc-melted synthesized Gd 5 Si 2 Ge 2 sample was performed. Through powder X-ray diffraction (XRD) and magnetometry measurements we monitored the effect of varying the annealing time with constant temperature (T = 1473 K) on the formation of the monoclinic (M) crystallographic phase fraction, which is the one responsible for the giant magnetocaloric effect (GMCE) in this compound. The conversion of the orthorhombic O(I) crystallographic phase into M was achieved, resulting in a significant increase of the M mass fraction. Such conversion led to a change in the magnetic transition nature, evolving from a second to a first order transition for the as-cast and annealed samples, respectively. An optimal annealing time range for the M phase conversion was identified to be within 80–120 min at T = 1473 K followed by a rapid quenching to liquid N 2 . Furthermore, an increase up to ∼50% of the magnetocaloric effect was obtained for the sample annealed during 120 min.

Fundamental thermochemical properties of amino acids: gas-phase and aqueous acidities and gas-phase heats of formation.

Science.gov (United States)

Stover, Michele L; Jackson, Virgil E; Matus, Myrna H; Adams, Margaret A; Cassady, Carolyn J; Dixon, David A

2012-03-08

The gas-phase acidities of the 20 L-amino acids have been predicted at the composite G3(MP2) level. A broad range of structures of the neutral and anion were studied to determine the lowest energy conformer. Excellent agreement is found with the available experimental gas-phase deprotonation enthalpies, and the calculated values are within experimental error. We predict that tyrosine is deprotonated at the CO(2)H site. Cysteine is predicted to be deprotonated at the SH but the proton on the CO(2)H is shared with the S(-) site. Self-consistent reaction field (SCRF) calculations with the COSMO parametrization were used to predict the pK(a)'s of the non-zwitterion form in aqueous solution. The differences in the non-zwitterion pK(a) values were used to estimate the free energy difference between the zwitterion and nonzwitterion forms in solution. The heats of formation of the neutral compounds were calculated from atomization energies and isodesmic reactions to provide the first reliable set of these values in the gas phase. Further calculations were performed on five rare amino acids to predict their heats of formation, acidities, and pK(a) values.

Coarsening and pattern formation during true morphological phase separation in unstable thin films under gravity

Science.gov (United States)

Kumar, Avanish; Narayanam, Chaitanya; Khanna, Rajesh; Puri, Sanjay

2017-12-01

We address in detail the problem of true morphological phase separation (MPS) in three-dimensional or (2 +1 )-dimensional unstable thin liquid films (>100 nm) under the influence of gravity. The free-energy functionals of these films are asymmetric and show two points of common tangency, which facilitates the formation of two equilibrium phases. Three distinct patterns formed by relative preponderance of these phases are clearly identified in "true MPS". Asymmetricity induces two different pathways of pattern formation, viz., defect and direct pathway for true MPS. The pattern formation and phase-ordering dynamics have been studied using statistical measures such as structure factor, correlation function, and growth laws. In the late stage of coarsening, the system reaches into a scaling regime for both pathways, and the characteristic domain size follows the Lifshitz-Slyozov growth law [L (t ) ˜t1 /3] . However, for the defect pathway, there is a crossover of domain growth behavior from L (t ) ˜t1 /4→t1 /3 in the dynamical scaling regime. We also underline the analogies and differences behind the mechanisms of MPS and true MPS in thin liquid films and generic spinodal phase separation in binary mixtures.

Keeping a Step Ahead: formative phase of a workplace intervention trial to prevent obesity.

Science.gov (United States)

Zapka, Jane; Lemon, Stephenie C; Estabrook, Barbara B; Jolicoeur, Denise G

2007-11-01

Ecological interventions hold promise for promoting overweight and obesity prevention in worksites. Given the paucity of evaluative research in the hospital worksite setting, considerable formative work is required for successful implementation and evaluation. This paper describes the formative phases of Step Ahead, a site-randomized controlled trial of a multilevel intervention that promotes physical activity and healthy eating in six hospitals in central Massachusetts. The purpose of the formative research phase was to increase the feasibility, effectiveness, and likelihood of sustainability of the intervention. The Step Ahead ecological intervention approach targets change at the organization, interpersonal work environment, and individual levels. The intervention was developed using fundamental steps of intervention mapping and important tenets of participatory research. Formative research methods were used to engage leadership support and assistance and to develop an intervention plan that is both theoretically and practically grounded. This report uses observational data, program minutes and reports, and process tracking data. Leadership involvement (key informant interviews and advisory boards), employee focus groups and advisory boards, and quantitative environmental assessments cultivated participation and support. Determining multiple foci of change and designing measurable objectives and generic assessment tools to document progress are complex challenges encountered in planning phases. Multilevel trials in diverse organizations require flexibility and balance of theory application and practice-based perspectives to affect impact and outcome objectives. Formative research is an essential component.

Effect of lead addition on the formation of superconducting phases in Bi-Sr-Ca-Cu-O ceramics

International Nuclear Information System (INIS)

Martinelli, A.E.

1991-01-01

Superconducting ceramics with starting composition Bi 2 - x Pb x Sr 2 Ca 2 Cu 3 O y (0,0 ≤ X ≤ 0,6) were prepared in order to investigate the effects of partial substitution of Pb for Bi and sintering time and atmosphere in the formation of superconducting phases. For all samples X-ray diffraction analyses were performed to estimate the amount of superconducting phases; superconductivity was analysed by dc electrical resistance and ac magnetic susceptibility measurements. The main results show that: a) the longer the sintering time (up to 168 h), the larger the volume fraction of superconducting phases with critical temperature (T c ) greater than the temperature of nitrogen liquefaction; b) by partially substituting Pb for Bi it is possible to restrain the formation of 2212 phase (T c = 80 K) and to enhance the amount of 2223 phase (T c = 105 K); C) a heat treatment under oxygen atmosphere before sintering enhances the formation of 2223 phase. (author)

The sensitivities of in cloud and cloud top phase distributions to primary ice formation in ICON-LEM

Science.gov (United States)

Beydoun, H.; Karrer, M.; Tonttila, J.; Hoose, C.

2017-12-01

Mixed phase clouds remain a leading source of uncertainty in our attempt to quantify cloud-climate and aerosol-cloud climate interactions. Nevertheless, recent advances in parametrizing the primary ice formation process, high resolution cloud modelling, and retrievals of cloud phase distributions from satellite data offer an excellent opportunity to conduct closure studies on the sensitivity of the cloud phase to microphysical and dynamical processes. Particularly, the reliability of satellite data to resolve the phase at the top of the cloud provides a promising benchmark to compare model output to. We run large eddy simulations with the new ICOsahedral Non-hydrostatic atmosphere model (ICON) to place bounds on the sensitivity of in cloud and cloud top phase to the primary ice formation process. State of the art primary ice formation parametrizations in the form of the cumulative ice active site density ns are implemented in idealized deep convective cloud simulations. We exploit the ability of ICON-LEM to switch between a two moment microphysics scheme and the newly developed Predicted Particle Properties (P3) scheme by running our simulations in both configurations for comparison. To quantify the sensitivity of cloud phase to primary ice formation, cloud ice content is evaluated against order of magnitude changes in ns at variable convective strengths. Furthermore, we assess differences between in cloud and cloud top phase distributions as well as the potential impact of updraft velocity on the suppression of the Wegener-Bergeron-Findeisen process. The study aims to evaluate our practical understanding of primary ice formation in the context of predicting the structure and evolution of mixed phase clouds.

Effect of Fe and Zr additions on ω phase formation in β-type Ti-Mo alloys

International Nuclear Information System (INIS)

Min, X.H.; Emura, S.; Zhang, L.; Tsuzaki, K.

2008-01-01

The effect of 1% Fe and/or 5% Zr (mass%) additions on ω phase formation was investigated for the Ti-15Mo alloy by means of X-ray diffraction analysis and hardness testing. Upon water quenching following solution treatment in the β phase region, the athermal ω phase formation could not be observed in all the alloys, regardless of Fe and Zr additions. The lattice parameter of the β phase decreases with Fe addition, while it increases with Zr addition. Solid solution strengthening by Fe and Zr is not recognized for the β phase. The isothermal ω phase formed after aging at 723 K and 773 K for 3.6 ks, which results in a decrease in the lattice parameter of the β phase and an increase in the hardness. The isothermal ω phase formation is suppressed with Fe and/or Zr additions. This is interpreted as the consequence of the increase in the average value of the bond order (Bo) for the Ti-15Mo-5Zr and Ti-15Mo-5Zr-1Fe alloys, and of the decrease in the average value of the metal d-orbital energy level (Md) for the Ti-15Mo-1Fe alloy. In addition, the degree of the suppression of isothermal ω phase can be predicted by the average values of Bo and Md

Formation of tungsten blue oxide and its phase constitution

International Nuclear Information System (INIS)

Zou, Z.; Wu, E.; Tan, A.; Qian, C.

1984-01-01

By means of X-ray diffraction structure analysis, SEM observation, chemical analysis and particle specific surface analysis etc., an investigation was made in order to determine the regularity of tungsten blue oxide formation during reductional calcine process of APT. It was found that the oxygen index (OI) decreased continuously with increasing calcine temperature. The decrease rate of OI variated as the calcine atmosphere being changed, the stronger the reductivity of the atmosphere is, the more OI decreases. The deammonia-dewater process and the phase constitution variation during calcine was studied, some idea for description of phase transformation path was suggested. It was found that the most important parameter affecting phase constitution and transformation is calcine temperature. At the temperature lower than 450 0 C, the main formed phase was ATB, while at higher temperature, the different phase like W/sub 20/O/sub 58/, WO/sub 3/ etc., could be formed by different ways depending on the atmosphere reductivity. The composition and the OI of ATB are changeable. An experiment for some blue oxides reduction at low temperature was carried out. It was found that OI and the constitution of blue oxide strongly affected the particle size of the formed W-powder

Phase separation like dynamics during Myxococcus xanthus fruiting body formation

Science.gov (United States)

Liu, Guannan; Thutupalli, Shashi; Wigbers, Manon; Shaevitz, Joshua

2015-03-01

Collective motion exists in many living organisms as an advantageous strategy to help the entire group with predation, forage, and survival. However, the principles of self-organization underlying such collective motions remain unclear. During various developmental stages of the soil-dwelling bacterium, Myxococcus xanthus, different types of collective motions are observed. In particular, when starved, M. xanthus cells eventually aggregate together to form 3-dimensional structures (fruiting bodies), inside which cells sporulate in response to the stress. We study the fruiting body formation process as an out of equilibrium phase separation process. As local cell density increases, the dynamics of the aggregation M. xanthus cells switch from a spatio-temporally random process, resembling nucleation and growth, to an emergent pattern formation process similar to a spinodal decomposition. By employing high-resolution microscopy and a video analysis system, we are able to track the motion of single cells within motile collective groups, while separately tuning local cell density, cell velocity and reversal frequency, probing the multi-dimensional phase space of M. xanthus development.

σ and η Phase formation in advanced polycrystalline Ni-base superalloys

Energy Technology Data Exchange (ETDEWEB)

Antonov, Stoichko, E-mail: santonov@hawk.iit.edu [Illinois Institute of Technology, 10 W. 32nd Street, Chicago, IL 60616 (United States); Huo, Jiajie; Feng, Qiang [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); Isheim, Dieter; Seidman, David N. [Department of Materials Science and Engineering, Northwestern University, 2220 Campus Drive, Evanston, IL 60208 (United States); Northwestern University Center for Atom Probe Tomography (NUCAPT), 2220 Campus Drive, Evanston, IL 60208 (United States); Helmink, Randolph C.; Sun, Eugene [Rolls-Royce Corporation, 450 S. Meridian Street, Indianapolis, IN 46225 (United States); Tin, Sammy [Illinois Institute of Technology, 10 W. 32nd Street, Chicago, IL 60616 (United States)

2017-02-27

In polycrystalline Ni-base superalloys, grain boundary precipitation of secondary phases can be significant due to the effects they pose on the mechanical properties. As new alloying concepts for polycrystalline Ni-base superalloys are being developed to extend their temperature capability, the effect of increasing levels of Nb alloying additions on long term phase stability and the formation of topologically close packed (TCP) phases needs to be studied. Elevated levels of Nb can result in increased matrix supersaturation and promote the precipitation of secondary phases. Long term thermal exposures on two experimental powder processed Ni-base superalloys containing various levels of Nb were completed to assess the stability and precipitation of TCP phases. It was found that additions of Nb promoted the precipitation of η-Ni{sub 6}AlNb along the grain boundaries in powder processed, polycrystalline Ni-base superalloys, while reduced Nb levels favored the precipitation of blocky Cr and Mo – rich σ phase precipitates along the grain boundary. Evaluation of the thermodynamic stability of these two phases in both alloys using Thermo-calc showed that while σ phase predictions are fairly accurate, predictions of the η phase are limited.

Liquid phase stabilization versus bubble formation at a nanoscale curved interface

Science.gov (United States)

Schiffbauer, Jarrod; Luo, Tengfei

2018-03-01

We investigate the nature of vapor bubble formation near a nanoscale-curved convex liquid-solid interface using two models: an equilibrium Gibbs model for homogenous nucleation, and a nonequilibrium dynamic van der Waals-diffuse-interface model for phase change in an initially cool liquid. Vapor bubble formation is shown to occur for sufficiently large radius of curvature and is suppressed for smaller radii. Solid-fluid interactions are accounted for and it is shown that liquid-vapor interfacial energy, and hence Laplace pressure, has limited influence over bubble formation. The dominant factor is the energetic cost of creating the solid-vapor interface from the existing solid-liquid interface, as demonstrated via both equilibrium and nonequilibrium arguments.

Novel criterion for formation of metastable phase from undercooled melt

International Nuclear Information System (INIS)

Kuribayashi, Kazuhiko; Nagashio, Kosuke; Niwata, Kenji; Kumar, M.S. Vijaya; Hibiya, Taketoshi

2007-01-01

Undercooling a melt facilitates the preferential nucleation of a metastable phase. In the present study, the formation of metastable phases from undercooled melts was considered from the viewpoint of the competitive nucleation criterion. The classical nucleation theory shows us that the most critical factor for forming a critical nucleus is the interface free energy σ. Furthermore, Spaepen's negentropic model on σ generated the role of the scaling factor α that depends on the polyhedral order in the liquid and solid phases prominent in simple liquids such as the melt of monoatomic metals. In ionic materials such as oxides, however, in which oxygen polyhedrons including a cation at their center are the structural units both in the solid and liquid phases, the entropy of fusion, rather than α, can be expected to become dominant in the determination of σ. In accordance with this idea, using REFeO 3 as the model material (where RE denotes rare-earth elements) the entropy-undercooling regime criterion was proposed and verified

Identification of monoclinic calcium pyrophosphate dihydrate and hydroxyapatite in human sclera using Raman microspectroscopy

DEFF Research Database (Denmark)

Chen, Ko-Hua; Li, Mei-Jane; Cheng, Wen-Ting

2009-01-01

Raman microspectroscopy was first used to determine the composition of a calcified plaque located at the pterygium-excision site of a 51-year-old female patient's left nasal sclera after surgery. It was unexpectedly found that the Raman spectrum of the calcified sample at 1149, 1108, 1049, 756, 5...... to the characteristic peak at 958/cm of hydroxyapatite (HA). This is the first study to report the spectral biodiagnosis of both monoclinic CPPD and HA co-deposited in the calcified plaque of a patient with sclera dystrophic calcification using Raman microspectroscopy....

Phase transitions during formation of Ag nanoparticles on In{sub 2}S{sub 3} precursor layers

Energy Technology Data Exchange (ETDEWEB)

Liu, Yang, E-mail: yang.liu@helmholtz-berlin.de; Fu, Yanpeng; Dittrich, Thomas; Sáez-Araoz, Rodrigo; Schmid, Martina; Hinrichs, Volker; Lux-Steiner, Martha Ch.; Fischer, Christian-Herbert

2015-09-01

Phase transitions have been investigated for silver deposition onto In{sub 2}S{sub 3} precursor layers by spray chemical vapor deposition from a trimethylphosphine (hexafluoroacetylacetonato) silver (Ag(hfacac)(PMe{sub 3})) solution. The formation of Ag nanoparticles (Ag NPs) on top of the semiconductor layer set on concomitant with the formation of AgIn{sub 5}S{sub 8}. The increase of the diameter of Ag NPs was accompanied by the evolution of orthorhombic AgInS{sub 2}. The formation of Ag{sub 2}S at the interface between Ag NPs and the semiconductor layer was observed. Surface photovoltage spectroscopy indicated charge separation and electronic transitions in the ranges of corresponding band gaps. The phase transition approach is aimed to be applied for the formation of plasmonic nanostructures on top of extremely thin semiconducting layers. - Highlights: • Silver nanoparticles were deposited onto In{sub 2}S{sub 3} precursor layer by spray pyrolysis. • The silver nanoparticle size and density could be controlled by deposition time. • Phase transitions during deposition and material properties were investigated. • The layers still show semiconducting properties after phase transitions. • Plasmonic absorption enhancement has been demonstrated.

Acid-base equilibrium. A thermodynamic study of formation and stability of the Bi-2223 phase

International Nuclear Information System (INIS)

Xi, Z.; Zhou, L.

1993-01-01

A general acid-base equilibrium theory was proposed to explain the formation and stability of the Bi-2223 phase based on the Lewis acid base theory and principle of metallurgical physical chemistry. The acid-base nature of oxide was defined according to the electrostatic force between cation and oxygen anion. A series of experimental facts were systematically explained based on the theory: substitution of Bi for Ca in the Pb-free 2223 phase, and the effect of substitution of the high-valent cation for Bi 3+ ; oxygen-pressure atmosphere, and the heat-schocking technique on the formation and stability of the 2223 phase. 14 refs., 2 tabs

Investigation of phase stability in the scandia-zirconia

International Nuclear Information System (INIS)

Grosso, Robson Lopes

2016-01-01

In this work, the phase stability of scandia-zirconia (ScSZ) system was investigated by the thermodynamic study of nanoparticles, within the range of 0 to 20 mol% Sc 2 O 3 , and by codoping of ZrO 2 -10 mol% Sc 2 O 3 (10ScSZ) with Dy 2 O 3 and Nb 2 O 5 . The phase stability of ScSZ was evaluated based on thermodynamic data collected by water adsorption microcalorimetry and high temperature oxide melt solution. Nanostructured zirconia-scandia solid solutions were synthesized by coprecipitation method. Thermodynamic data were determined for ScSZ polymorph (monoclinic, tetragonal, cubic, rhombohedral β and γ) found by X-ray diffraction. This systemic work resulted in an unprecedented phase diagram at the nanoscale of particle size-composition. The effects of additives on 10ScSZ were investigated aiming to stabilize the cubic (c) structure at room temperature and to suppress the characteristic cubic-rhombohedral β phase transformation. Compositions were prepared by coprecipitation and solid state reaction. Materials were sintered by conventional and spark plasma sintering. Full stabilization of the cubic phase was attained by 1 mol% Dy 2 O 3 and 0.5 mol% Nb 2 O 5 additions. The smallest Nb 2 O 5 content required for cubic phase stabilization was attributed to liquid phase formation during sintering and to small ionic radius of Nb 5+ . Results of high temperature X-ray diffraction and thermal analysis show suppression of the c-β transformation. Samples containing 0.5 mol% Nb 2 O 5 show total ionic conductivity similar to 10ScSZ without additives within a broad temperature range with high stability during 170 h at 600 °C. (author)

Complex 3D Vortex Lattice Formation by Phase-Engineered Multiple Beam Interference

Directory of Open Access Journals (Sweden)

Jolly Xavier

2012-01-01

Full Text Available We present the computational results on the formation of diverse complex 3D vortex lattices by a designed superposition of multiple plane waves. Special combinations of multiples of three noncoplanar plane waves with a designed relative phase shift between one another are perturbed by a nonsingular beam to generate various complex 3D vortex lattice structures. The formation of complex gyrating lattice structures carrying designed vortices by means of relatively phase-engineered plane waves is also computationally investigated. The generated structures are configured with both periodic as well as transversely quasicrystallographic basis, while these whirling complex lattices possess a long-range order of designed symmetry in a given plane. Various computational analytical tools are used to verify the presence of engineered geometry of vortices in these complex 3D vortex lattices.

Determination of Stress Coefficient Terms in Cracked Solids for Monoclinic Materials with Plane Symmetry at x3 = 0

Science.gov (United States)

Yuan, F. G.

1998-01-01

Determination of all the coefficients in the crack tip field expansion for monoclinic materials under two-dimensional deformation is presented in this report. For monoclinic materials with a plane of material symmetry at x(sub 3) = 0, the in-plane deformation is decoupled from the anti-plane deformation. In the case of in-plane deformation, utilizing conservation laws of elasticity and Betti's reciprocal theorem, together with selected auxiliary fields, T-stress and third-order stress coefficients near the crack tip are evaluated first from path-independent line integrals. To determine the T-stress terms using the J-integral and Betti's reciprocal work theorem, auxiliary fields under a concentrated force and moment acting at the crack tip are used respectively. Through the use of Stroh formalism in anisotropic elasticity, analytical expressions for all the coefficients including the stress intensity factors are derived in a compact form that has surprisingly simple structure in terms of the Barnett-Lothe tensors, L. The solution forms for degenerated materials, orthotropic, and isotropic materials are presented.

Crystal structure of a new monoclinic polymorph of N-(4-methyl-phen-yl)-3-nitro-pyridin-2-amine.

Science.gov (United States)

Aznan, Aina Mardia Akhmad; Abdullah, Zanariah; Lee, Vannajan Sanghiran; Tiekink, Edward R T

2014-08-01

The title compound, C12H11N3O2, is a second monoclinic polymorph (P21, with Z' = 4) of the previously reported monoclinic (P21/c, with Z' = 2) form [Akhmad Aznan et al. (2010 ▶). Acta Cryst. E66, o2400]. Four independent mol-ecules comprise the asymmetric unit, which have the common features of a syn disposition of the pyridine N atom and the toluene ring, and an intra-molecular amine-nitro N-H⋯O hydrogen bond. The differences between mol-ecules relate to the dihedral angles between the rings which range from 2.92 (19) to 26.24 (19)°. The geometry-optimized structure [B3LYP level of theory and 6-311 g+(d,p) basis set] has the same features except that the entire mol-ecule is planar. In the crystal, the three-dimensional architecture is consolidated by a combination of C-H⋯O, C-H⋯π, nitro-N-O⋯π and π-π inter-actions [inter-centroid distances = 3.649 (2)-3.916 (2) Å].

Gas phase enthalpies of formation of nitrobenzamides using combustion calorimetry and thermal analysis

International Nuclear Information System (INIS)

Ximello, Arturo; Flores, Henoc; Rojas, Aarón; Adriana Camarillo, E.; Patricia Amador, M.

2014-01-01

Graphical abstract: - Highlights: • Formation enthalpies of the nitrobenzamides were derived from combustion calorimetry. • Enthalpies of vaporisation and sublimation were calculated by thermogravimetry. • From gas phase enthalpies of formation the stability of the isomers is studied. • Stability of isomers is not driven by a steric hindrance between functional groups. - Abstract: The standard molar energies of combustion of 2-nitrobenzamide, 3-nitrobenzamide and 4-nitrobenzamide were determined with an isoperibolic, static-bomb, combustion calorimeter. From the combustion results, the standard molar enthalpies of combustion and formation for these compounds in the condensed phase at T = 298.15 K were derived. Subsequently, to determine the enthalpies of sublimation, the vapour pressure data as a function of the temperature for the compounds under investigation were estimated using thermogravimetry by applying Langmuir’s equation, and the enthalpies of vaporisation were derived. Standard enthalpies of fusion were measured by differential scanning calorimetry then added to those of vaporisation to obtain reliable results for the enthalpy of sublimation. From the combustion and sublimation data, the gas phase enthalpies of formation were determined to be (−138.9 ± 3.5) kJ · mol −1 , (−122.9 ± 2.9) kJ · mol −1 and (−108.5 ± 3.7) kJ · mol −1 for the ortho, meta and para isomers of nitrobenzamide, respectively. The meaning of these results with regard to the enthalpic stability of these molecular structures is discussed herein

Ferroelastic Phase Transition in Pb_3(PO_4)_2 Studied by Computer Simulation

Science.gov (United States)

Parlinski, K.; Kawazoe, Y.

1997-01-01

A model of lead phosphate which describes its rhombohedral-monoclinic improper ferroelastic phase transition is proposed. It contains a reduced number of degrees of freedom but it is constructed consistently with symmetry changes at the phase transition. Potential parameters of the model are derived from available experimental data. The crystallites of 25× 25× 25 and 121× 121 × 25 unit cells have been simulated by the molecular-dynamics technique. The results determine the phase transition at the L point of reciprocal space, the order parameter, and the temperature behavior of monoclinic lattice parameters. In the rhombohedral phase the calculated dynamical structure factor shows inelastic peaks from which a soft branch of underdamped phonons has been established. The model has been used to calculate a diffuse scattering function which shows above T_c a maximum at an incommensurate wave vector located along the L F line of the Brillouin zone. The mentioned line is parallel to the ternary symmetry axis. On the basis of the above results we were able to vizualize the nature of the dynamical monoclinic microdomains persisting in the high-temperature rhombohedral phase. It has been shown that above T_c the fluctuations can be treated as temporary orientational monoclinic microdomains. Each type of microdomains always contains an irregular sequence of antiphase domains. Un modèle permettant de décrire la transition de phase ferroélastique impropre, rhomboédrique-monoclinique, du phosphate de plomb est proposé ci-dessous. Il est construit à partir d'un nombre réduit de degrés de liberté, tout en tenant compte des changements de symétrie caractéristique de la transition de phase. Les paramètres du modèle sont déduits quantitativement des résultats expérimentaux disponibles. La technique de dynamique moléculaire a permis de simuler le comportement des cristallites comportant 25× 25× 25 et 121× 121 × 25 mailles. Les résultats permettent de d

Electron diffraction and resistivity measurements on the one-dimensional orthorhombic and monoclinic structures of TaS3

International Nuclear Information System (INIS)

Roucau, C.; Ayroles, R.; Monceau, P.

1980-01-01

Electron diffraction patterns are obtained of the orthorhombic and monoclinic structures of TaS 3 . For the orthorhombic structure one set of superlattice spots is observed at (l+-0.5)a*, (m+-0.125)b*, (n+-0.25)c* below 210 K. For the monoclinic structure two sets of superlattice spots are observed, the first one at la*, (m+-0.253)b*, nc* below 240 K, the second one at (l+-0.5)a*, (m+-0.245)b*, (n+-0.5)c* below 160 K. Diffuse scattering lines are present for the two structures. Resistivity measurements are performed on crystals with the two structures which show strong increase of the resistivity indicating metal-semiconducting transitions at the same temperatures where the superlattice spots appear. These transitions are interpreted as successive Peierls transitions on the different types of chains of TaS 3 . Also electron diffraction patterns are shown of NbSe 3 at very low temperatures where the two charge density waves that occur at 145 and 59 K are formed. A comparison is given between TaS 3 and NbSe 3 . (author)

Phase equilibria and crystal chemistry in the ternary system BaO-TiO 2-Nb 2O 5. II. New barium polytitanates with <5 mole% Nb 2O 5

Science.gov (United States)

Roth, R. S.; Ettlinger, L. D.; Parker, H. S.

1987-06-01

Four new compounds were found in the BaO-TiO 2-Nb 2O 5 system, each containing orth ≈ 9.9A˚, b mon ≈ a orth ≈ 17A˚). Ba 14Ti 40Nb 2O 99 is a 20-layer orthorhombic phase, Cmc*, withc ≈ 46.86A˚. Ba 10Ti 28Nb 2O 72 is a 7-layer monoclinic phase, C2m, c ≈ 16.72A˚, β ≈ 101.2°. Ba 18Ti 54Nb 2O 132 is a 13-layer monoclinic phase, C2m, c ≈ 30.65A˚, β ≈ 96°. The compositions were derived by analogy to the layers in Ba 4Ti 13 O 30 and Ba 6Ti 17O 40 and are consistent with limited phase equilibria data.

Synthesis of Zr-Si-O-N phases by carbonitriding reaction. Characterization of crystalline phases using the Rietveld method

Directory of Open Access Journals (Sweden)

Mazzoni A.D.

2001-01-01

Full Text Available Zirconium compounds are of great interest for ceramic application due to their excellent thermal and mechanical properties. Zirconium phases of the system Zr-O-C-N were obtained using carbonitriding reactions of zircon mineral (ZrO2.SiO2, under different reaction conditions. The reaction products were studied by X-ray diffraction (XRD using the Rietveld method. Silicon was employed as internal standard. Zirconium compounds formed were m-ZrO2 (monoclinic, beta"-zirconium oxynitride and a cubic Zr(C,N,O phase whose lattice parameter a o depends on the composition. The crystallite sizes of the three zirconium phases were determined also by XRD. The minority phases present are the ones of the Si-O-N-C system. The reaction conditions employed allows to obtain reaction products with low or without silicon content.

Metastable phases in yttrium oxide plasma spray deposits and their effect on coating properties

International Nuclear Information System (INIS)

Gourlaouen, V.; Schnedecker, G.; Boncoeur, M.; Lejus, A.M.; Collongues, R.

1993-01-01

Yttrium oxide coatings were obtained by plasma spray. Structural investigations on these deposits show that, due to the drastic conditions of this technique, a minor monoclinic B phase is formed in the neighborhood of the major cubic C form. The authors discuss here the influence of different plasma spray parameters on the amount of the B phase formed. They describe also the main properties of Y 2 O 3 B and C phases in these deposits such as structural characteristics, thermal stability and mechanical behavior

The kinetics of the β→α transformation in unalloyed plutonium after partial formation of the β phase

International Nuclear Information System (INIS)

Robinson, A.C.; Stacey, R.J.

1976-01-01

The kinetics of the isothermal β→α transformation after complete and only partial formation of the β phase in unalloyed plutonium containing about 900 ppm of impurity are reported and compared with previously published and conventionally accepted β→α transformation kinetics after complete formation of the β phase in this material. In these experiments the heating was provided by constant temperature oil baths and the transformations were monitored by electrical resistance measurements on 0.63 mm diameter wire samples at temperatures ranging from -65 0 C to +75 0 C. After complete formation of the β phase in the plutonium used in these experiments the kinetics of the β→α transformation were in general agreement with previously published data, although the present transformations were slower than reported by previous workers. After only partial formation of the β phase the subsequent β→α transformations were found to be very fast and to be characterised by zero or very short incubation periods, rapid rates of transformation and a final equilibrium consisting of more than 90% β phase. (Auth.)

Pressure tuning of the morphotropic phase boundary in piezoelectric lead zirconate titanate

International Nuclear Information System (INIS)

Rouquette, J.; Haines, J.; Bornand, V.; Pintard, M.; Papet, Ph.; Bousquet, C.; Konczewicz, L.; Gorelli, F. A.; Hull, S.

2004-01-01

Titanium-rich PZT solid solutions were studied under high pressure by neutron and x-ray diffraction, Raman spectroscopy and dielectric measurements. The results show that high pressure stabilizes the ferroelectric monoclinic phases, which are proposed to be responsible for the high piezoelectric properties characteristic of the morphotropic composition PbZr 0.52 Ti 0.48 O 3 . Pressure may thus be used to tune the morphotropic phase boundary in the composition-pressure plane to include a wide range of titanium-rich PZT compositions

Systematic Search for Chemical Reactions in Gas Phase Contributing to Methanol Formation in Interstellar Space.

Science.gov (United States)

Gamez-Garcia, Victoria G; Galano, Annia

2017-10-05

A massive search for chemical routes leading to methanol formation in gas phase has been conducted using computational chemistry, at the CBS-QB3 level of theory. The calculations were performed at five different temperatures (100, 80, 50, 20, and 10 K) and at three pressures (0.1, 0.01, and 0.001 atm) for each temperature. The search was focused on identifying reactions with the necessary features to be viable in the interstellar medium (ISM). A searching strategy was applied to that purpose, which allowed to reduce an initial set of 678 possible reactions to a subset of 11 chemical routes that are recommended, for the first time, as potential candidates for contributing to methanol formation in the gas phase of the ISM. They are all barrier-less, and thus they are expected to take place at collision rates. Hopefully, including these reactions in the currently available models, for the gas-phase methanol formation in the ISM, would help improving the predicted fractional abundance of this molecule in dark clouds. Further investigations, especially those dealing with grain chemistry and electronic excited states, would be crucial to get a complete picture of the methanol formation in the ISM.

Regularities of texture formation in alloys undergoing phase transformations during heat treatment and plastic working

International Nuclear Information System (INIS)

Ageev, N.V.; Babarehko, A.A.

1983-01-01

Peculiarities of texture formation in metals undergoing phase transformations in the temperature range of heat treatment and hot working are investigated theoretically and experimentally. A low-temperature phase after hot working is shown to inherite a high-temperature phase texture due to definite orientation conformity during phase transformation. Strengthened heat and thermomechanical treatments, as a rule, do not destroy material texture but change it

Deposition and characterization of ZrMoN thin films by reactive magnetron sputtering

International Nuclear Information System (INIS)

Fontes Junir, A.S.; Felix, L.C.; Oliveira, G.B. de; Fernandez, D.R.; Carvalho, R.G.; Tentardini, E.K.; Silva Junior, A.H. da

2016-01-01

Thin films of ZrMoN were deposited by magnetron reactive sputtering technique in order to study the molybdenum influence on the mechanical properties and oxidation resistance of these coatings. Three thin films with molybdenum concentrations from 25 to 40 at.% were selected. The displacement of characteristic peaks of ZrN where identified by GIXRD results of films with larger Mo content. This result is indicative of the Mo accommodation in the lattice structure. Hardness tests revealed favorable results with values up to 33 GPa. Oxidation tests showed that ZrN oxidized at 500 °C with a monoclinic ZrO 2 and tetragonal formation; whereas the thin films with Mo addition impeded the formation of the monoclinic ZrO 2 phase at partial oxidation. (author)

Formation of omega phase under shock pressure, hydrostatic pressure and irradiation

International Nuclear Information System (INIS)

Dey, G.K.

2016-01-01

The omega transformation is one of the most intriguing phase transformations. The aspects which make it unique and interesting are the facts that this phase can form from two different parent phases viz. the alpha phase and the beta phase. The alpha to omega transformation has been observed under shock and static pressure and the mechanism involved has been studied in detail. Starting from the nucleation stage to the completion of the transformation, various interesting aspects of the mechanism of transformation has emerged in these studies. Although the parent and product phases are same under these conditions of transformation, a variation in the morphology and the kinetics of the product phase indicate different pathways for alpha to omega transformations. Similarly, the beta to omega transformation is also replete with several interesting features. This transformation can occur under application of pressure, thermal activation and also under irradiation. Here again the morphology of the product phase, the nucleation mechanisms and the kinetics of the phase transformation depend on the path of transformation, though the parent and product phases are same in each path. This presentation highlights the formation of the omega phase under different activations including the ones in extreme conditions in pure Zr and Zr based alloys. Theoretical aspects of the feasibility, pathways and kinetics of the transformations are also emphasized. (author)

Bit-rate-transparent optical RZ-to-NRZ format conversion based on linear spectral phase filtering

DEFF Research Database (Denmark)

Maram, Reza; Da Ros, Francesco; Guan, Pengyu

2017-01-01

We propose a novel and strikingly simple design for all-optical bit-rate-transparent RZ-to-NRZ conversion based on optical phase filtering. The proposed concept is experimentally validated through format conversion of a 640 Gbit/s coherent RZ signal to NRZ signal.......We propose a novel and strikingly simple design for all-optical bit-rate-transparent RZ-to-NRZ conversion based on optical phase filtering. The proposed concept is experimentally validated through format conversion of a 640 Gbit/s coherent RZ signal to NRZ signal....

Synthesis and characterization of monoclinic KGd(WO4)2 particles for non-cubic transparent ceramics

Science.gov (United States)

Thangaraju, D.; Durairajan, A.; Balaji, D.; Moorthy Babu, S.

2013-02-01

Monoclinic KGd(WO4)2 (KGW) particles were synthesized using polymeric metal complex sol-gel synthesis method. The derived particles were made as colloidal suspension form for better rotation of particles to have optimum response for applied magnetic field. The KGW fine particle suspension was prepared using electrostatic repulsion by electrolyte polymer. Prepared suspension was kept at 2 T and particles were settled using electrophoretic sedimentation using pH adjustment. The derived sediment was dried at 100 °C and the properties were characterized using XRD.

Formation of U(IV) Nanoparticles and Their Growth Mechanism in Mildly Acidic Aqueous Phases

Energy Technology Data Exchange (ETDEWEB)

Cha, Wan Sik; Kim, Sun Tae; Cho, Hye Ryun; Jung, Euo Chang [KAERI, Daejeon (Korea, Republic of)

2016-05-15

Previous studies suggest that U(IV) nanoparticle (NP) formation is one of key steps in mineralization or immobilization of uranium which can be mediated either by microbes or by abiotic geochemical reactions. Colloidal NPs in a groundwater system are potential carrier phases influencing RN migration in subsurface environment. However, the mechanism of U(IV) NP formation and the potential reaction intermediates during this solid phase formation process have not been elucidated in detail so far. In this study we attempted to examine the U(IV) nanoparticle formation reactions preceded by the hydrolysis of U{sup 4+} at different pHs, concentrations and temperatures. The kinetics of U(IV) NP formation from dissolved U(IV) species was monitored under mildly acidic conditions (pH 2 ∼ 3) mainly by using UV-Vis absorption spectrophotometry. Dynamic light scattering (DLS) analysis, nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM) were used to characterize the NPs produced during the reactions. The results demonstrate that the U(IV) NP formation process is very sensitive toward temperature variation. The main outcome of this study is the discovery of the autocatalytic nature of U(IV) NP formation from the supersaturated U(OH){sup 3+} solution in a mildly acidic aqueous solution. The structure of reaction intermediates is proposed to contain oxide linkage. In the presentation the proposed mechanism of the U(IV) NP formation reaction and the properties of primary NPs and their clusters will be discussed in detail.

Liquid phase diffusion bonding of A1070 by using metal formate coated Zn sheet

Science.gov (United States)

Ozawa, K.; Koyama, S.; shohji, I.

2017-05-01

Aluminium alloy have high strength and easily recycle due to its low melting point. Therefore, aluminium is widely used in the manufacturing of cars and electronic devices. In recent years, the most common way for bonding aluminium alloy is brazing and friction stir welding. However, brazing requires positional accuracy and results in the formation of voids by the flax residue. Moreover, aluminium is an excellent heat radiating and electricity conducting material; therefore, it is difficult to bond together using other bonding methods. Because of these limitations, liquid phase diffusion bonding is considered to the suitable method for bonding aluminium at low temperature and low bonding pressure. In this study, the effect of metal formate coating processing of zinc surface on the bond strength of the liquid phase diffusion bonded interface of A1070 has been investigated by SEM observation of the interfacial microstructures and fractured surfaces after tensile test. Liquid phase diffusion bonding was carried out under a nitrogen gas atmosphere at a bonding temperature of 673 K and 713 K and a bonding load of 6 MPa (bonding time: 15 min). As a result of the metal formate coating processing, a joint having the ultimate tensile strength of the base aluminium was provided. It is hypothesized that this is because metallic zinc is generated as a result of thermal decomposition of formate in the bonded interface at lower bonding temperatures.

Charge disproportionation of mixed-valent Cr triggered by Bi lone-pair effect in the A -site-ordered perovskite BiC u3C r4O12

Science.gov (United States)

Etter, Martin; Isobe, Masahiko; Sakurai, Hiroya; Yaresko, Alexander; Dinnebier, Robert E.; Takagi, Hidenori

2018-05-01

A new A -site-ordered perovskite BiC u3C r4O12 is synthesized under a high pressure of 7.7 GPa. A phase transition from a paramagnetic metal to a ferrimagnetic metal is observed at Tc=190 K accompanied with a structural change from cubic to monoclinic. Structural analysis of the low-temperature monoclinic phase reveals that this transition represents a charge disproportionation of C r3.75 + into C r4 + and C r3.5 + . We argue that the asymmetric displacement of Bi caused by a lone-pair effect triggers the formation of a dimeric Cr4+2O5 unit and leads to an ordering of C r4 + and C r3.5 + below the transition.

X-Ray Diffraction and μ-Raman Investigation of the Monoclinic-Orthorhombic Phase Transition in Th1-xUx(C2O4)2. 2H2O Solid Solutions

International Nuclear Information System (INIS)

Clavier, N.; Dacheux, N.; Clavier, N.; Hingant, N.; Dacheux, N.; Barre, N.; Rivenet, M.; Obbade, S.; Abraham, F.

2010-01-01

A complete Th 1-x U x (C 2 O 4 ) 2 . 2H 2 O solid solution was prepared by mild hydrothermal synthesis from a mixture of hydrochloric solutions containing cations and oxalic acid. The crystal structure has been solved from twinned single crystals for x=0, 0. 5, and 1 with monoclinic symmetry, space group C2/c, leading to unit cell parameters of a ≅ to 10. 5 Angstroms, b ≅ 8. 5 Angstrom, and c ≅ 9. 6 Angstrom. The crystal structure consists of a two-dimensional arrangement of actinide centers connected through bis-bidentate oxalate ions forming squares. The actinide metal is coordinated by eight oxygen atoms from four oxalate entities and two water oxygen atoms forming a bi-capped square anti-prism. The connection between the layers is assumed by hydrogen bonds between the water molecules and the oxygen of oxalate of an adjacent layer. Under these conditions, the unit cell contains two independent oxalate ions. From high-temperature μ-Raman and X-ray diffraction studies, the compounds were found to undergo a transition to an orthorhombic form (space group Ccca). The major differences in the structural arrangement concern the symmetry of uranium, which decreases from C2 to D2, leading to a unique oxalate group. Consequently, the ν s (C-O) double band observed in the Raman spectra recorded at room temperature turned into a singlet. This transformation was then used to make the phase transition temperature more precise as a function of the uranium content of the sample. (authors)

Correlative theoretical and experimental investigation of the formation of AlYB_1_4 and competing phases

International Nuclear Information System (INIS)

Hunold, Oliver; Chen, Yen-Ting; Music, Denis; Baben, Moritz to; Achenbach, Jan-Ole; Keuter, Philipp; Schneider, Jochen M.; Persson, Per O. Å.; Primetzhofer, Daniel

2016-01-01

The phase formation in the boron-rich section of the Al-Y-B system has been explored by a correlative theoretical and experimental research approach. The structure of coatings deposited via high power pulsed magnetron sputtering from a compound target was studied using elastic recoil detection analysis, electron energy loss spectroscopy spectrum imaging, as well as X-ray and electron diffraction data. The formation of AlYB_1_4 together with the (Y,Al)B_6 impurity phase, containing 1.8 at. % less B than AlYB_1_4, was observed at a growth temperature of 800 °C and hence 600 °C below the bulk synthesis temperature. Based on quantum mechanical calculations, we infer that minute compositional variations within the film may be responsible for the formation of both icosahedrally bonded AlYB_1_4 and cubic (Y,Al)B_6 phases. These findings are relevant for synthesis attempts of all boron rich icosahedrally bonded compounds with the space group: Imma that form ternary phases at similar compositions.

Correlative theoretical and experimental investigation of the formation of AlYB{sub 14} and competing phases

Energy Technology Data Exchange (ETDEWEB)

Hunold, Oliver, E-mail: hunold@mch.rwth-aachen.de; Chen, Yen-Ting; Music, Denis; Baben, Moritz to; Achenbach, Jan-Ole; Keuter, Philipp; Schneider, Jochen M. [Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, D-52074 Aachen (Germany); Persson, Per O. Å. [Department of Physics, Chemistry and Biology (IFM), Linköping University, S-58183 Linköping (Sweden); Primetzhofer, Daniel [Department of Physics and Astronomy, Uppsala University, Lägerhyddsvägen 1, S-75120 Uppsala (Sweden)

2016-02-28

The phase formation in the boron-rich section of the Al-Y-B system has been explored by a correlative theoretical and experimental research approach. The structure of coatings deposited via high power pulsed magnetron sputtering from a compound target was studied using elastic recoil detection analysis, electron energy loss spectroscopy spectrum imaging, as well as X-ray and electron diffraction data. The formation of AlYB{sub 14} together with the (Y,Al)B{sub 6} impurity phase, containing 1.8 at. % less B than AlYB{sub 14}, was observed at a growth temperature of 800 °C and hence 600 °C below the bulk synthesis temperature. Based on quantum mechanical calculations, we infer that minute compositional variations within the film may be responsible for the formation of both icosahedrally bonded AlYB{sub 14} and cubic (Y,Al)B{sub 6} phases. These findings are relevant for synthesis attempts of all boron rich icosahedrally bonded compounds with the space group: Imma that form ternary phases at similar compositions.

Magnetic field effect on Gd2(MoO4)3 domain structure formation in the phase transformation range

International Nuclear Information System (INIS)

Flerova, S.A.; Tsinman, I.L.

1987-01-01

The behaviour of ferroelastic-ferroelectric domain structure of gadolinium molybdate crystal (GMO)during its formation in the magnetic field in the vicinity of phase transformation is studied.It is shown that the formation of domain structure in the presence of a temperature gradient occurs in the field of mechanical stresses whose mainly stretching effect is concentrated near phase boundaries.The magnetic field intensifies summary mechanical stresses where a domain structure in a ferroelectric phase is formed due to interaction with the elements of inhomogeneous and differently oriented currents near phase boundaries

NEPHELINE FORMATION STUDY FOR SLUDGE BATCH 4: PHASE 3 EXPERIMENTAL RESULTS

International Nuclear Information System (INIS)

Fox, K

2006-01-01

This Phase 3 study was undertaken to complement the previous phases of the nepheline formation studies1, 2 by continuing the investigation into the ability of the nepheline discriminator to predict the occurrence of nepheline crystallization in Sludge Batch 4 (SB4) glasses and into the impact of such phases on the durability of the SB4 glasses. The Phase 3 study had two primary objectives. The first was to continue to demonstrate the ability of the discriminator value to adequately predict the nepheline formation potential for specific glass systems of interest. The second was to generate additional data that have a high probability of supporting the SB4 variability study. To support these two objectives, sixteen glasses were selected based on the most recent SB4 compositional projection, Case 15C Blend 1.3 Four different frits were included, based on previous assessments of projected operating windows and melt rate,4, 5 with four WLs selected for each frit. Eight of these frit-sludge combinations covered WLs which tightly bound the nepheline discriminator value of 0.62, with the intent of refining this value to a level of confidence where it can be incorporated into offline administrative controls and/or the Process Composition Control System (PCCS) to support Slurry Mix Evaporator (SME) acceptability decisions. The remaining eight frit-sludge combinations targeted lower WLs (35 and 40%) and were prepared and analyzed to contribute needed data to the ComPro database6 to support a potential variability study for SB4

Propagation dynamics and X-pulse formation in phase-mismatched second-harmonic generation

International Nuclear Information System (INIS)

Valiulis, G.; Jukna, V.; Jedrkiewicz, O.; Clerici, M.; Rubino, E.; DiTrapani, P.

2011-01-01

This paper concerns the theoretical, numerical, and experimental study of the second-harmonic-generation (SHG) process under conditions of phase and group-velocity mismatch and aims to demonstrate the dimensionality transition of the SHG process caused by the change of the fundamental wave diameter. We show that SHG from a narrow fundamental beam leads to the spontaneous self-phase-matching process with, in addition, the appearance of angular dispersion for the off-axis frequency components generated. The angular dispersion sustains the formation of the short X pulse in the second harmonic (SH) and is recognized as three-dimensional (3D) dynamics. On the contrary, the large-diameter fundamental beam reduces the number of the degrees of freedom, does not allow the generation of the angular dispersion, and maintains the so-called one-dimensional (1D) SHG dynamics, where the self-phase-matching appears just for axial components and is accompanied by the shrinking of the SH temporal bandwidth, and sustains a long SH pulse formation. The transition from long SH pulse generation typical of the 1D dynamics to the short 3D X pulse is illustrated numerically and experimentally by changing the conditions from the self-defocusing to the self-focusing regime by simply tuning the phase mismatch. The numerical and experimental verification of the analytical results are also presented.

The study of membrane formation via phase inversion method by cloud point and light scattering experiment

Science.gov (United States)

Arahman, Nasrul; Maimun, Teuku; Mukramah, Syawaliah

2017-01-01

The composition of polymer solution and the methods of membrane preparation determine the solidification process of membrane. The formation of membrane structure prepared via non-solvent induced phase separation (NIPS) method is mostly determined by phase separation process between polymer, solvent, and non-solvent. This paper discusses the phase separation process of polymer solution containing Polyethersulfone (PES), N-methylpirrolidone (NMP), and surfactant Tetronic 1307 (Tet). Cloud point experiment is conducted to determine the amount of non-solvent needed on induced phase separation. Amount of water required as a non-solvent decreases by the addition of surfactant Tet. Kinetics of phase separation for such system is studied by the light scattering measurement. With the addition of Tet., the delayed phase separation is observed and the structure growth rate decreases. Moreover, the morphology of fabricated membrane from those polymer systems is analyzed by scanning electron microscopy (SEM). The images of both systems show the formation of finger-like macrovoids through the cross-section.

On the role of Nb in Z-phase formation in a 12% Cr steel

DEFF Research Database (Denmark)

Cipolla, L.; Danielsen, Hilmar Kjartansson; Di Nunzio, P.E.

2010-01-01

Z-phase precipitation in two model alloys, 12CrVNbN and 12CrVN, has been investigated. The alloys were aged up to 104 h and their precipitate evolution was followed by X-ray diffraction and transmission electron microscopy. The formation rate of Z-phase from vanadium-based nitrides, (V,Nb)N, in t...

Thermodynamic evidence for phase transition in MoO2-δ

International Nuclear Information System (INIS)

Jacob, K.T.; Saji, V.S.; Gopalakrishnan, J.; Waseda, Y.

2007-01-01

The standard Gibbs free energy of formation of MoO 2-δ , Δ f G 0 (MoO 2-δ ), has been measured over a wide temperature range (925 to 1925) K using an advanced version of bi-electrolyte solid-state electrochemical cell incorporating a buffer electrode: Pt vertical bar Mo + MoO 2-δ -parallel (Y 2 O 3 )ThO 2 -parallel (CaO)ZrO 2 -parallel O 2 (0.1 MPa) vertical bar Pt The Gibbs free energy of formation of MoO 2-δ , which is directly related to the measured cell e.m.f., can be represented by two linear segments: Δ f G 0 (MoO 2-δ )±570/(J.mol -1 )=-579,821+170.003(T/K), in the temperature range (925 to 1533) K, and Δ f G 0 (MoO 2-δ )±510/(J.mol -1 )=-564,634+160.096(T/K), in the temperature range (1533 to 1925) K. The change in slope at T = 1533 K is probably related to the phase transition of MoO 2 from monoclinic structure with space group P2 1 /c to tetragonal structure characteristic of rutile with space group P4 2 /mnm. The enthalpy and entropy change for the phase transition are: ΔH tr = (15.19 ± 2.1) kJ . mol -1 ; ΔS tr (9.91 ± 1.27) J . mol -1 . K -1 . The standard enthalpy of formation of MoO 2-δ at T = 298.15 K assessed by the third-law method is: Δ f H 0 (MoO 2-δ ) = (-592.28 ± 0.33) kJ . mol -1 . The new measurements refine thermodynamic data for MoO 2

A Phase Transformation with no Change in Space Group Symmetry: Octafluoronaphtalene

DEFF Research Database (Denmark)

Pawley, G. S.; Dietrich, O. W.

1975-01-01

A solid-state phase transformation in octafluoronaphthalene has been discovered at 266.5K on cooling, and at 15K higher on heating. The symmetry of both phases is found to be the same, namely monoclinic with space group P21/c. The unit cell parameters change by up to 10%, but the integrity...... of a single crystal, which shatters on cooling, is good enough for a single-crystal structure determination. This has been done in both phases to a sufficient accuracy that a mechanism for the transformation can be proposed. Molecules which lie parallel to one another shear to a new parallel position...

Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic β -Ga2O3

Science.gov (United States)

Mock, Alyssa; Korlacki, Rafał; Briley, Chad; Darakchieva, Vanya; Monemar, Bo; Kumagai, Yoshinao; Goto, Ken; Higashiwaki, Masataka; Schubert, Mathias

2017-12-01

We employ an eigenpolarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic β -Ga2O3 yielding a comprehensive analysis of generalized ellipsometry data obtained from 0.75-9 eV. The eigenpolarization model permits complete description of the dielectric response. We obtain, for single-electron and excitonic band-to-band transitions, anisotropic critical point model parameters including their polarization vectors within the monoclinic lattice. We compare our experimental analysis with results from density functional theory calculations performed using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional. We present and discuss the order of the fundamental direct band-to-band transitions and their polarization selection rules, the electron and hole effective mass parameters for the three lowest band-to-band transitions, and their excitonic contributions. We find that the effective masses for holes are highly anisotropic and correlate with the selection rules for the fundamental band-to-band transitions. The observed transitions are polarized close to the direction of the lowest hole effective mass for the valence band participating in the transition.

Simulating the Phases of the Moon Shortly after Its Formation

Science.gov (United States)

Noordeh, Emil; Hall, Patrick; Cuk, Matija

2014-01-01

The leading theory for the origin of the Moon is the giant impact hypothesis, in which the Moon was formed out of the debris left over from the collision of a Mars sized body with the Earth. Soon after its formation, the orbit of the Moon may have been very different than it is today. We have simulated the phases of the Moon in a model for its…

Instability of a Lamellar Phase under Shear Flow: Formation of Multilamellar Vesicles

Science.gov (United States)

Courbin, L.; Delville, J. P.; Rouch, J.; Panizza, P.

2002-09-01

The formation of closed-compact multilamellar vesicles (referred to in the literature as the ``onion texture'') obtained upon shearing lamellar phases is studied using small-angle light scattering and cross-polarized microscopy. By varying the shear rate γ ˙, the gap cell D, and the smectic distance d, we show that: (i)the formation of this structure occurs homogeneously in the cell at a well-defined wave vector qi, via a strain-controlled process, and (ii)the value of qi varies as (dγ ˙/D)1/3. These results strongly suggest that formation of multilamellar vesicles may be monitored by an undulation (buckling) instability of the membranes, as expected from theory.

Formation of residual NAPL in three-phase systems: Experiments and numerical simulations

NARCIS (Netherlands)

Hofstee, C.; Oostrom, M.

2002-01-01

The formation of residual, discontinuous nonaqueous phase liquids (NAPLs) in the vadose zone is a process that is not well understood. The simulators have conveniently implemented the Leverett concept (Leverett and Lewis, 1941) which states that in a water-wet porous media, when fluid wettabilities

Misfit strain phase diagrams of epitaxial PMN–PT films

Energy Technology Data Exchange (ETDEWEB)

Khakpash, N.; Khassaf, H.; Rossetti, G. A. [Department of Materials Science and Engineering and Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269 (United States); Alpay, S. P., E-mail: p.alpay@ims.uconn.edu [Department of Materials Science and Engineering and Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269 (United States); Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States)

2015-02-23

Misfit strain–temperature phase diagrams of three compositions of (001) pseudocubic (1 − x)·Pb (Mg{sub l/3}Nb{sub 2/3})O{sub 3} − x·PbTiO{sub 3} (PMN–PT) thin films are computed using a phenomenological model. Two (x = 0.30, 0.42) are located near the morphotropic phase boundary (MPB) of bulk PMN–PT at room temperature (RT) and one (x = 0.70) is located far from the MPB. The results show that it is possible to stabilize an adaptive monoclinic phase over a wide range of misfit strains. At RT, the stability region of this phase is much larger for PMN–PT compared to barium strontium titanate and lead zirconate titanate films.

Pressure-induced magnetic collapse and metallization of molecular oxygen: The ζ-O2 phase

International Nuclear Information System (INIS)

Serra, S.; Chiarotti, G.; Scandolo, S.; Tosatti, E.

1998-01-01

The behavior of solid oxygen in the pressure range between 5-116 GPa is studied by ab-initio simulations, showing a spontaneous phase transformation from the antiferromagnetic insulating δ-O 2 phase to a non-magnetic, metallic molecular phase. The calculated static structure factor of this phase is in excellent agreement with X-ray diffraction data in the metallic ζ-O 2 phase above 96 GPa. We thus propose that ζ-O 2 should be base centered monoclinic with space group C2/m and 4 molecules per cell, suggesting a re-indexing of the experimental diffraction peaks. Physical constraints on the intermediate-pressure ε - O 2 phase are also obtained. (author)

Oxygen self-diffusion mechanisms in monoclinic Zr O2 revealed and quantified by density functional theory, random walk analysis, and kinetic Monte Carlo calculations

Science.gov (United States)

Yang, Jing; Youssef, Mostafa; Yildiz, Bilge

2018-01-01

In this work, we quantify oxygen self-diffusion in monoclinic-phase zirconium oxide as a function of temperature and oxygen partial pressure. A migration barrier of each type of oxygen defect was obtained by first-principles calculations. Random walk theory was used to quantify the diffusivities of oxygen interstitials by using the calculated migration barriers. Kinetic Monte Carlo simulations were used to calculate diffusivities of oxygen vacancies by distinguishing the threefold- and fourfold-coordinated lattice oxygen. By combining the equilibrium defect concentrations obtained in our previous work together with the herein calculated diffusivity of each defect species, we present the resulting oxygen self-diffusion coefficients and the corresponding atomistically resolved transport mechanisms. The predicted effective migration barriers and diffusion prefactors are in reasonable agreement with the experimentally reported values. This work provides insights into oxygen diffusion engineering in Zr O2 -related devices and parametrization for continuum transport modeling.

Effect of phase formation on valence band photoemission and photoresonance study of Ti/Ni multilayers using synchrotron radiation

International Nuclear Information System (INIS)

Bhatt, Pramod; Chaudhari, S.M.

2006-01-01

This paper presents investigation of Ti-Ni alloy phase formation and its effect on valence band (VB) photoemission and photoresonance study of as-deposited as well as annealed Ti/Ni multilayers (MLs) up to 600 deg. C using synchrotron radiation. For this purpose [Ti (50 A)/Ni (50 A)]X 10 ML structures were deposited by using electron-beam evaporation technique under ultra-high vacuum (UHV) conditions. Formation of different phases of Ti-Ni alloy due to annealing treatment has been confirmed by the X-ray diffraction (XRD) technique. The XRD pattern corresponding as-deposited ML sample shows crystalline nature of both Ti and Ni deposited layers, whereas 300 deg. C annealed ML sample show solid-state reaction (SSR) leading to amorphization and subsequent recrystallisation at higher temperatures of annealing (≥400 deg. C) with the formation of TiNi, TiNi 3 and Ti 2 Ni alloy phases. The survey scans corresponding to 400, 500 and 600 deg. C annealed ML sample shows interdiffusion and intermixing of Ni atoms into Ti layers leading to chemical Ti-Ni alloys phase formation at interface. The corresponding recorded VB spectra using synchrotron radiation at 134 eV on as-deposited ML sample with successive sputtering shows alternately photoemission bands due to Ti 3d and Ni 3d, respectively, indicating there is no mixing of the consequent layers and any phase formation at the interface during deposition. However, ML samples annealed at higher temperatures of annealing, particularly at 400, 500 and 600 deg. C show a clear shift in Ni 3d band and its satellite peak position to higher BE side indicates Ti-Ni alloy phase formation. In addition to this, reduction of satellite peak intensity and Ni 3d density of states (DOS) near Fermi level is also observed due to Ti-Ni phase formation with higher annealing temperatures. The variable photon energy VB measurements on as-deposited and ML samples annealed at 400 deg. C confirms existence and BE position of observed Ni 3d satellite

Two-Phase Flow Effect on the Ex-Vessel Corium Debris Bed Formation in Severe Accident

International Nuclear Information System (INIS)

Kim, Eunho; Park, Jin Ho; Kim, Moo Hwan; Park, Hyun Sun; Ma, Weimin; Bechta, Sevostian V.

2014-01-01

In Korean IVR-ERVC(In-Vessel Retention of molten corium through External Reactor Vessel Cooling) strategy, if the situation degenerates into insufficient external vessel cooling, the molten core mixture can directly erupt into the flooded cavity pool from the weakest point of the vessel. Then, FCI (molten Fuel Coolant Interaction) will fragment the corium jet into small particulates settling down to make porous debris bed on the cavity basemat. To secure the containment integrity against the MCCI (Molten Core - Concrete Interaction), cooling of the heat generating porous corium debris bed is essential and it depends on the characteristics of the bed itself. For the characteristics of corium debris bed, many previous experimental studies with simulant melts reported the heap-like shape mostly. There were also following experiments to develop the correlation for the heap-like shaped debris bed. However, recent studies started to consider the effect of the decay heat and reported some noticeable results with the two-phase flow effect on the debris bed formation. The Kyushu University and JAEA group reported the experimental studies on the 'self-leveling' effect which is the flattening effect of the particulate bed by the inside gas generation. The DECOSIM simulation study of RIT (Royal Institute of Technology, Sweden) with Russian researchers showed the 'large cavity pool convection' effect, which is driven by the up-rising gas bubble flow from the pre-settled debris bed, on the particle settling trajectories and ultimately final bed shape. The objective of this study is verification of the two-phase flow effect on the ex-vessel corium debris bed formation in the severe accident. From the analysis on the test movie and resultant particle beds, the two-phase flow effect on the debris bed formation, which has been reported in the previous studies, was verified and the additional findings were also suggested. For the first, in quiescent pool the

Parasitic phase formation in the La Ba2 Cu3 O7-x superconductor

International Nuclear Information System (INIS)

Baltra, T.; Fuenzalida, V.M.; Grahmann, C.R.

1996-01-01

The parasitic phase formation during the thermal processing of the H Tc La Ba 2 Cu 3 O 7-x superconductor, particularly the Ba Cu O 2 , is studied. The formation of the stable parasitic phase depends on the temperature of the initial treatments and on the heating rate during the sintering process. The superconducting highest purity material is obtained with treatment at 900 deg C and lowest heating rate. The temperature during the final annealing in oxygen of the sample did also affect the transport properties. Samples with the lowest resistivity in the normal state were produced by annealing in oxygen at 300 deg C. The largest orthorhombic distortion was obtained at 325 deg C. (author)

Water-gas shift. An examination of Pt promoted MgO and tetragonal and monoclinic ZrO2 by in situ drifts

International Nuclear Information System (INIS)

Chenu, Emilie; Jacobs, Gary; Crawford, Adam C.; Keogh, Robert A.; Patterson, Patricia M.; Sparks, Dennis E.; Davis, Burtron H.

2005-01-01

In situ DRIFTS measurements on unpromoted and Pt promoted MgO and ZrO 2 (both tetragonal and monoclinic) indicate that at high H 2 O/CO ratios, where the reaction rate has been reported to be zero order in H 2 O and first order in CO, the mechanism involved in the catalysis of water-gas shift is likely a surface formate mechanism, in agreement with Shido and Iwasawa. Pt was found to catalyze the removal of surface carbonates and to facilitate the generation of active OH groups relative to the unpromoted catalyst. Comparison with Pt/ceria revealed that the OH groups involved in the catalysis of magnesia and zirconia may be those of the bridging variety which occur at defect sites. That is, water dissociated over vacancies to produce bridging OH groups, as observed by infrared spectroscopy. The existence of such an adsorbed species is implied in the zero reaction order for water, where kinetics suggests that the surface should be saturated by an adsorbed water species. The lower extent of vacancy formation for magnesia and zirconia-based materials in comparison with ceria could explain a lower surface population of active bridging OH groups. CO was used as a probe molecule of the reduced centers, as it reacts with bridging OH groups to generate surface formates, a proposed WGS intermediate, and the decomposition of which is proposed to be the rate-limiting step. The trends in formate intensity by CO adsorption and CO conversion in WGS catalytic testing both followed the order: Pt/ceria>Pt/m-zirconia>Pt/t-zirconia>Pt/magnesia. In all cases, a normal kinetic isotope effect was observed in switching from H 2 O to D 2 O, consistent with a link between the rate-limiting step and the decomposition of surface formates, as noted previously by Shido and Iwasawa for Rh/ceria, MgO, and ZnO

Effects of Phytoplankton Growth Phase on the Formation and Properties of Marine Snow

Science.gov (United States)

Montgomery, Q. W.; Proctor, K. W.; Prairie, J. C.

2016-02-01

Marine snow aggregates often dominate carbon export from the upper mixed layer to the deep ocean. Thus, understanding the formation and the properties of these aggregates is essential to the study of the biological pump. Aggregate formation is determined by both the encounter rate and the stickiness of the particles that they are composed of. Stickiness of phytoplankton has been linked to production of transparent exopolymer particles (TEP), which has been previously shown to vary in concentration throughout different parts of the phytoplankton growth cycle. The objective of this study is to determine the effects of the growth phase of the diatom Thalassiosira weissflogii to both TEP production and the properties of the resulting aggregates produced. Cultures of T. weissflogii were stopped at separate phases of the phytoplankton growth curve and incubated in rotating cylindrical tanks to form aggregates. Aggregate properties such as size, density, and porosity were measured at the end of each period of roller incubation. Preliminary results describe little variation in the size of the aggregates formed from different parts of the growth phase, but show a significant effect of growth phase on aggregate density. Density is an important factor in the settling of marine aggregates. Therefore, variations in aggregate density during different growth phases may have large implications for the efficiency of the biological pump during different stages of a phytoplankton bloom. Further examination will be performed on the potential effects of TEP abundance on the properties of the aggregates formed at separate growth phases and the resulting implications for carbon flux.

The formation of quasicrystal phase in Al-Cu-Fe system by mechanical alloying

Directory of Open Access Journals (Sweden)

Dilermando Nagle Travessa

2012-10-01

Full Text Available In order to obtain quasicrystalline (QC phase by mechanical alloying (MA in the Al-Cu-Fe system, mixtures of elementary Al, Cu and Fe in the proportion of 65-20-15 (at. % were produced by high energy ball milling (HEBM. A very high energy type mill (spex and short milling times (up to 5 hours were employed. The resulting powders were characterized by X-ray diffraction (XRD, differential scanning calorimetry (DSC and scanning electron microscopy (SEM. QC phase was not directly formed by milling under the conditions employed in this work. However, phase transformations identified by DSC analysis reveals that annealing after HEBM possibly results in the formation of the ψ QC phase.

Condensed-phase biogenic-anthropogenic interactions with implications for cold cloud formation.

Science.gov (United States)

Charnawskas, Joseph C; Alpert, Peter A; Lambe, Andrew T; Berkemeier, Thomas; O'Brien, Rachel E; Massoli, Paola; Onasch, Timothy B; Shiraiwa, Manabu; Moffet, Ryan C; Gilles, Mary K; Davidovits, Paul; Worsnop, Douglas R; Knopf, Daniel A

2017-08-24

Anthropogenic and biogenic gas emissions contribute to the formation of secondary organic aerosol (SOA). When present, soot particles from fossil fuel combustion can acquire a coating of SOA. We investigate SOA-soot biogenic-anthropogenic interactions and their impact on ice nucleation in relation to the particles' organic phase state. SOA particles were generated from the OH oxidation of naphthalene, α-pinene, longifolene, or isoprene, with or without the presence of sulfate or soot particles. Corresponding particle glass transition (T g ) and full deliquescence relative humidity (FDRH) were estimated using a numerical diffusion model. Longifolene SOA particles are solid-like and all biogenic SOA sulfate mixtures exhibit a core-shell configuration (i.e. a sulfate-rich core coated with SOA). Biogenic SOA with or without sulfate formed ice at conditions expected for homogeneous ice nucleation, in agreement with respective T g and FDRH. α-pinene SOA coated soot particles nucleated ice above the homogeneous freezing temperature with soot acting as ice nuclei (IN). At lower temperatures the α-pinene SOA coating can be semisolid, inducing ice nucleation. Naphthalene SOA coated soot particles acted as ice nuclei above and below the homogeneous freezing limit, which can be explained by the presence of a highly viscous SOA phase. Our results suggest that biogenic SOA does not play a significant role in mixed-phase cloud formation and the presence of sulfate renders this even less likely. However, anthropogenic SOA may have an enhancing effect on cloud glaciation under mixed-phase and cirrus cloud conditions compared to biogenic SOA that dominate during pre-industrial times or in pristine areas.

X-Ray diffraction and mu-Raman investigation of the monoclinic-orthorhombic phase transition in Th(1-x)U(x)(C(2)O(4))(2).2H(2)O solid solutions.

Science.gov (United States)

Clavier, Nicolas; Hingant, Nina; Rivenet, Murielle; Obbade, Saïd; Dacheux, Nicolas; Barré, Nicole; Abraham, Francis

2010-02-15

A complete Th(1-x)U(x)(C(2)O(4))(2).2H(2)O solid solution was prepared by mild hydrothermal synthesis from a mixture of hydrochloric solutions containing cations and oxalic acid. The crystal structure has been solved from twinned single crystals for x = 0, 0.5, and 1 with monoclinic symmetry, space group C2/c, leading to unit cell parameters of a approximately 10.5 A, b approximately 8.5 A, and c approximately 9.6 A. The crystal structure consists of a two-dimensional arrangement of actinide centers connected through bis-bidentate oxalate ions forming squares. The actinide metal is coordinated by eight oxygen atoms from four oxalate entities and two water oxygen atoms forming a bicapped square antiprism. The connection between the layers is assumed by hydrogen bonds between the water molecules and the oxygen of oxalate of an adjacent layer. Under these conditions, the unit cell contains two independent oxalate ions. From high-temperature mu-Raman and X-ray diffraction studies, the compounds were found to undergo a transition to an orthorhombic form (space group Ccca). The major differences in the structural arrangement concern the symmetry of uranium, which decreases from C2 to D2, leading to a unique oxalate group. Consequently, the nu(s)(C-O) double band observed in the Raman spectra recorded at room temperature turned into a singlet. This transformation was then used to make the phase transition temperature more precise as a function of the uranium content of the sample.

Preparation and characterization of sulfated zirconia acid catalysts for application in the esterification of cottonseed oil; Preparacao e caracterizacao de catalisadores acidos de zirconia sulfatada para aplicacao na esterificacao do oleo de algodao

Energy Technology Data Exchange (ETDEWEB)

Silva, F. N.; Moura, T. F. B.; Silva, A.S.; Costa, A.C.F.M., E-mail: fnilson.s@hotmail.com [Universidade Federal de Campina Grande (UFCG), PB (Brazil). Pos-graduacao em Engenharia de Materiais; Pallone, E.M.J.A. [Universidade de Sao Paulo (USP), Pirassununga, SP (Brazil). Dept. de Ciencias Basicas

2017-07-15

This work aimed to produce zirconia by combustion synthesis, to analyze the structure and morphology comparatively with a commercial monoclinic ZrO{sub 2} , as well as, to investigate the sulfation, aiming to obtain acid catalysts for its use in the esterification of cotton oil for biodiesel. The samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), specific surface area by BET method, infrared spectroscopy (FTIR), thermal analysis (TG/DrTG/DTA), granulometric distribution, pH and chromatography. The synthesized sample evidenced the formation of the monoclinic phase with traces of the orthorhombic phase, while in the commercial sample only the monoclinic phase was observed. In the sulfation process, traces of the tetragonal phase, typical of sulfated zirconia, were observed with the presence of the monoclinic phase in the two samples. With the impregnation of the sulfate ion on the surface of the samples, an increase in the particle size was observed, as seen in the characterization of BET, granulometric distribution and SEM, which also indicated a homogeneous morphology consisting of fine particles of approximately spherical shape for both samples. The chromatography indicated conversion of 65.5 and 91.8% in methyl esters to the synthesized and commercial SO{sub 4} {sup 2-}/ZrO{sub 2} , respectively. The results indicated that the sulfation increased the acidity, which was evidenced by the decrease in the pH, ranging from 5.12 to 2.65, which contributed significantly to the increase of the conversion, indicating that the SO{sub 4} {sup 2-}/ZrO{sub 2} is a promising catalyst in the esterification. (author)

Chemical-Reaction-Controlled Phase Separated Drops: Formation, Size Selection, and Coarsening

Science.gov (United States)

Wurtz, Jean David; Lee, Chiu Fan

2018-02-01

Phase separation under nonequilibrium conditions is exploited by biological cells to organize their cytoplasm but remains poorly understood as a physical phenomenon. Here, we study a ternary fluid model in which phase-separating molecules can be converted into soluble molecules, and vice versa, via chemical reactions. We elucidate using analytical and simulation methods how drop size, formation, and coarsening can be controlled by the chemical reaction rates, and categorize the qualitative behavior of the system into distinct regimes. Ostwald ripening arrest occurs above critical reaction rates, demonstrating that this transition belongs entirely to the nonequilibrium regime. Our model is a minimal representation of the cell cytoplasm.

Nematic phase formation in suspensions of graphene oxide

Science.gov (United States)

Fresneau, Nathalie; Campidelli, Stéphane

The last decade has seen the rise of graphene. Graphene is a single layer of graphite; it can be obtained by direct liquid phase exfoliation of the latter through harsh sonication. This technique presents the disadvantage to produce small graphene flakes (typically in the 0.05 to 0.4 μm2 range for the monolayers) and multilayer graphene with uncontrolled thickness distributions. In order to improve the exfoliation process, one has to counter the strong van der Waals interactions between the carbon planes of graphite. This implies to increase the distance between two planes and it can be done, for example, by oxidizing graphite to introduce oxygen species in the graphenic planes. The fabrication of graphite oxide is known for almost 150 years, and it became popular again these last ten years. Generally, the oxidation of graphite is performed following a method described by Hummers in the 1950's and the material produced by this technique exfoliates quasi-spontaneously into monolayer species called graphene oxide (GO). The highly anisotropic shape of GO (several μm in length and width for a thickness of ca. 1 nm) combined with the presence of oxygenated functions on the sp2 carbon structure of graphene lead to the formation of a lyotropic liquid crystalline phase in water. Above a certain concentration of graphene flakes the gain in translational entropy for a long-range ordered phase outweighs the loss in rotational entropy, and the liquid crystal phase then forms. The value of the threshold is affected by the aspect ratio of the graphene flakes but other factors such as the interactions also play a strong role.

Starless Clumps and the Earliest Phases of High-mass Star Formation in the Milky Way

Science.gov (United States)

Svoboda, Brian

2018-01-01

High-mass stars are key to regulating the interstellar medium, star formation activity, and overall evolution of galaxies, but their formation remains an open problem in astrophysics. In order to understand the physical conditions during the earliest phases of high-mass star formation, I report on observational studies of dense starless clump candidates (SCCs) that show no signatures of star formation activity. I identify 2223 SCCs from the 1.1 mm Bolocam Galactic Plane Survey, systematically analyze their physical properties, and show that the starless phase is not represented by a single timescale, but evolves more rapidly with increasing clump mass. To investigate the sub-structure in SCCs at high spatial resolution, I study the 12 most high-mass SCCs within 5 kpc using ALMA. I report previously undetected low-luminosity protostars in 11 out of 12 SCCs, fragmentation equal to the thermal Jeans length of the clump, and no starless cores exceeding 30 solar masses. While uncertainties remain concerning the star formation effeciency in this sample, these observational facts are consistent with models where high-mass stars form from intially low- to intermediate-mass protostars that accrete most of their mass from the surrounding clump.

The quasicrystalline phase formation in Al-Cu-Cr alloys produced by mechanical alloying

Energy Technology Data Exchange (ETDEWEB)

Sviridova, T.A.; Shevchukov, A.P.; Shelekhov, E.V. [National University of Science and Technology ' MISIS' , Moscow 119049 (Russian Federation); Diakonov, D.L. [Bardin Central Research Institute for the Iron and Steel Industry, Moscow 105005 (Russian Federation); Tcherdyntsev, V.V.; Kaloshkin, S.D. [National University of Science and Technology ' MISIS' , Moscow 119049 (Russian Federation)

2011-06-15

Research highlights: > Formation of decagonal quasicrystalline phase in Al-Cu-Cr alloys. > Obtained decagonal phase belongs to D{sub 3} family of decagonal quasicrystals. > Decagonal phase has 1.26 nm periodicity along 10-fold axis. > Alloys were produced by combination of mechanical alloying and subsequent annealing. > Phase composition of as-milled powders depending on annealing temperature. - Abstract: Almost single-phase decagonal quasicrystal with periodicity of 1.26 nm along 10-fold axis was produced in Al{sub 69}Cu{sub 21}Cr{sub 10} and Al{sub 72.5}Cu{sub 16.5}Cr{sub 11} alloys using combination of mechanical alloying (MA) and subsequent annealing. Phase transformations of as-milled powders depending on annealing temperature in the range of 200-800 deg. C are examined. Since the transformations can be explained based on kinetic and thermodynamic reasons it seems that applied technique (short preliminary MA followed by the annealing) permits to produce the equilibrium phases rather than metastable ones.

Relation between Kitaev magnetism and structure in α -RuCl3

Science.gov (United States)

Glamazda, A.; Lemmens, P.; Do, S.-H.; Kwon, Y. S.; Choi, K.-Y.

2017-05-01

Raman scattering has been employed to investigate lattice and magnetic excitations of the honeycomb Kitaev material α -RuCl3 and its Heisenberg counterpart CrCl3. Our phonon Raman spectra give evidence for a first-order structural transition from a monoclinic to a rhombohedral structure for both compounds. Significantly, only α -RuCl3 features a large thermal hysteresis, consistent with the formation of a wide phase of coexistence. In the related temperature interval of 70 -170 K, we observe a hysteretic behavior of magnetic excitations as well. The stronger magnetic response in the rhombohedral compared to the monoclinic phase evidences a coupling between the crystallographic structure and low-energy magnetic response. Our results demonstrate that the Kitaev magnetism concomitant with fractionalized excitations is susceptible to small variations of bonding geometry.

Evaluation of commercial and sulfated ZrO_2 aiming application catalysis

International Nuclear Information System (INIS)

Silva, F.N.; Dantas, J.; Costa, A.C.F.M.; Pallone, E.M.J.A.; Dutra, R.C.L.

2014-01-01

This study evaluates the performance of commercial and sulfated ZrO_2 for future application in catalysis. Commercial ZrO_2 was provided by the company Saint-Gobain Zirpro. The sulfation occurred with SO_4"-"2 ion content of 30% compared to the mass of ZrO_2. The samples were characterized by XRD, FTIR, EDX and GD. The results revealed the formation of a monoclinic phase for the commercial sample, and a monoclinic major phase with tetragonal traces for the sulfated sample. The commercial ZrO_2 showed a narrow, bimodal and asymmetric agglomerates distribution, while the sulfated sample showed a narrow, tetramodal and asymmetric agglomerates distribution. The presence of traces of the tetragonal phase in the SO_4"-"2/ZrO_2 XRD, and the presence of SO_3 in the EDX were good indicators for future use in catalysis to provide ester. (author)

Piezo-optic and elasto-optic properties of monoclinic triglycine sulfate crystals.

Science.gov (United States)

Mytsyk, Bogdan; Demyanyshyn, Natalya; Erba, Alessandro; Shut, Viktor; Mozzharov, Sergey; Kost, Yaroslav; Mys, Oksana; Vlokh, Rostyslav

2017-12-01

For the first time, to the best of our knowledge, we have experimentally determined all of the components of the piezo-optic tensor for monoclinic crystals. This has been implemented on a specific example of triglycine sulfate crystals. Based on the results obtained, the complete elasto-optic tensor has been calculated. Acousto-optic figures of merit (AOFMs) have been estimated for the case of acousto-optic interaction occurring in the principal planes of the optical indicatrix ellipsoid and for geometries in which the highest elasto-optic coefficients are involved as effective parameters. It has been found that the highest AOFM value is equal to 6.8×10 -15   s 3 /kg for the case of isotropic acousto-optic interaction with quasi-longitudinal acoustic waves in the principal planes. This AOFM is higher than the corresponding values typical for canonic acousto-optic materials, which are transparent in the deep ultraviolet spectral range.

Superconductivity optimization and phase formation kinetics study of internal-Sn Nb3Sn superconducting wires

International Nuclear Information System (INIS)

Zhang, Chaowu

2007-07-01

Superconductors Nb 3 Sn wires are one of the most applicable cryogenic superconducting materials and the best choice for high-field magnets exceeding 10 T. One of the most significant utilization is the ITER project which is regarded as the hope of future energy source. The high-Cu composite designs with smaller number of sub-element and non-reactive diffusion barrier, and the RRP (Restacked Rod Process) internal-Sn technology are usually applied for the wire manufacturing. Such designed and processed wires were supplied by MSA/Alstom and WST/NIN in this research. The systematic investigation on internal-Sn superconducting wires includes the optimization of heat treatment (HT) conditions, phase formation and its relation with superconductivity, microstructure analysis, and the phase formation kinetics. Because of the anfractuosity of the configuration design and metallurgical processing, the MF wires are not sufficient for studying a sole factor effect on superconductivity. Therefore, four sets of mono-element (ME) wires with different Sn ratios and different third-element addition were designed and fabricated in order to explore the relationship between phase formation and superconducting performances, particularly the A15 layer growth kinetics. Different characterization technic have been used (magnetization measurements, neutron diffraction and SEM/TEM/EDX analysis). The A15 layer thicknesses of various ME samples were measured and carried out linear and non-linear fits by means of two model equations. The results have clearly demonstrated that the phase formation kinetics of Nb 3 Sn solid-state reaction is in accordance with an n power relation and the n value is increased with the increase of HT temperature and the Sn ratio in the wire composite. (author)

Low-temperature structural phase transition in synthetic libethenite Cu2PO4OH

International Nuclear Information System (INIS)

Belik, Alexei A.; Naumov, Pance; Kim, Jungeun; Tsuda, Shunsuke

2011-01-01

Low-temperature structural properties of the synthetic mineral libethenite Cu 2 PO 4 OH were investigated by single-crystal X-ray diffraction, synchrotron X-ray powder diffraction, specific heat measurements, and Raman spectroscopy. A second-order structural phase transition from the Pnnm symmetry (a=8.0553(8) A, b=8.3750(9) A, c=5.8818(6) A at 180 K) to the P2 1 /n symmetry (a=8.0545(8) A, b=8.3622(9) A, c=5.8755(6) A, β=90.0012(15) at 120 K) was found at 160 K during cooling. At 120 K, the monoclinic angle is 90.0012(15) from single crystal X-ray data vs 90.083(1) from powder X-ray diffraction data. The P2 1 /n-to-Pnnm transition may be a general feature of the adamite-type compounds, M 2 XO 4 OH. - Graphical Abstract: Fragments of experimental synchrotron X-ray powder diffraction patterns of Cu 2 PO 4 OH between 100 and 280 K. Arrows show additional reflections that appear below 160 K in the monoclinic P2 1 /n phase. Highlights: → A low-temperature phase transition was found in the mineral libethenite Cu 2 PO 4 OH. → No magnetic anomalies and weak specific heat anomalies are detected. → Phase transition is of the second order. → Libethenite may exemplify a general feature of the adamite-type compounds.

Effect of Al doping on phase formation and thermal stability of iron nitride thin films

Energy Technology Data Exchange (ETDEWEB)

Tayal, Akhil [Amity Center for Spintronic Materials, Amity University, Sector 125, Noida 201 303 (India); Gupta, Mukul, E-mail: mgupta@csr.res.in [Amity Center for Spintronic Materials, Amity University, Sector 125, Noida 201 303 (India); Pandey, Nidhi [Amity Center for Spintronic Materials, Amity University, Sector 125, Noida 201 303 (India); Gupta, Ajay [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452 001 (India); Horisberger, Michael [Laboratory for Developments and Methods, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Stahn, Jochen [Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland)

2015-11-25

In the present work, we systematically studied the effect of Al doping on the phase formation of iron nitride (Fe–N) thin films. Fe–N thin films with different concentration of Al (Al = 0, 2, 3, 6, and 12 at.%) were deposited using dc magnetron sputtering by varying the nitrogen partial pressure between 0 and 100%. The structural and magnetic properties of the films were studied using x-ray diffraction and polarized neutron reflectivity. It was observed that at the lowest doping level (2 at.% of Al), nitrogen rich non-magnetic Fe–N phase gets formed at a lower nitrogen partial pressure as compared to the un-doped sample. Interestingly, we observed that as Al doping is increased beyond 3 at.%, nitrogen rich non-magnetic Fe–N phase appears at higher nitrogen partial pressure as compared to un-doped sample. The thermal stability of films were also investigated. Un-doped Fe–N films deposited at 10% nitrogen partial pressure possess poor thermal stability. Doping of Al at 2 at.% improves it marginally, whereas, for 3, 6 and 12 at.% Al doping, it shows significant improvement. The obtained results have been explained in terms of thermodynamics of Fe–N and Al–N. - Highlights: • Doping effects of Al on Fe–N phase formation is studied. • Phase formation shows a non-monotonic behavior with Al doping. • Low doping levels of Al enhance and high levels retard the nitridation process. • Al doping beyond 3 at.% improve thermal stability of Fe–N films.

The effect of crystallization pressure on macromolecular structure, phase evolution, and fracture resistance of nano-calcium carbonate-reinforced high density polyethylene

International Nuclear Information System (INIS)

Yuan, Q.; Yang, Y.; Chen, J.; Ramuni, V.; Misra, R.D.K.; Bertrand, K.J.

2010-01-01

We describe here phase evolution and structural changes that are induced when high density polyethylene (HDPE) containing dispersion of nano-calcium carbonate is isothermally crystallized in the pressure range of 0.1-100 MPa. To delineate and separate the effects of applied crystallization pressure from nanoparticle effects, a relative comparison is made between neat HDPE and HDPE containing nano-calcium carbonate under similar experimental conditions. X-ray diffraction studies point toward the evolution of monoclinic phase at high crystallization pressure together with the commonly observed orthorhombic phase of HDPE. Furthermore, the nucleation of monoclinic phase is promoted by nanoparticles even at low crystallization pressure. The equilibrium melting point is insignificantly influenced on the addition of nanoparticle, such that the crystallization pressure has no obvious effect. The strong thermodynamic interaction between nano-calcium carbonate and HDPE is supported by the shift in glass transition temperature and changes in the modification of absorption bands of HDPE in Fourier transform infrared (FTIR) spectrum. Furthermore, the reinforcement of HDPE with nano-calcium carbonate increases impact strength and alters the micromechanism from crazing-tearing in polyethylene to fibrillated fracture in polymer nanocomposite, such that the fibrillation increases with crystallization pressure.

SURVIVAL OF INTERSTELLAR MOLECULES TO PRESTELLAR DENSE CORE COLLAPSE AND EARLY PHASES OF DISK FORMATION

International Nuclear Information System (INIS)

Hincelin, U.; Wakelam, V.; Hersant, F.; Guilloteau, S.; Commerçon, B.

2013-01-01

An outstanding question of astrobiology is the link between the chemical composition of planets, comets, and other solar system bodies and the molecules formed in the interstellar medium. Understanding the chemical and physical evolution of the matter leading to the formation of protoplanetary disks is an important step for this. We provide some new clues to this long-standing problem using three-dimensional chemical simulations of the early phases of disk formation: we interfaced the full gas-grain chemical model Nautilus with the radiation-magnetohydrodynamic model RAMSES, for different configurations and intensities of the magnetic field. Our results show that the chemical content (gas and ices) is globally conserved during the collapsing process, from the parent molecular cloud to the young disk surrounding the first Larson core. A qualitative comparison with cometary composition suggests that comets are constituted of different phases, some molecules being direct tracers of interstellar chemistry, while others, including complex molecules, seem to have been formed in disks, where higher densities and temperatures allow for an active grain surface chemistry. The latter phase, and its connection with the formation of the first Larson core, remains to be modeled

Araçatuba Formation: palustrine deposits from the initial sedimentation phase of the Bauru Basin

Directory of Open Access Journals (Sweden)

Fernandes Luiz A.

2003-01-01

Full Text Available The Bauru Basin (Upper Cretaceous accumulated an essentially sandy continental sedimentary sequence. In a first desertic phase the basaltic substratum was covered by a widespread and homogeneous aeolian sand unit with minor loess intercalations. The substratum relief favored the formation of an endorheic drainage system under semi-arid climate, a process that started the development of the Araçatuba Paleoswamp. The palustrine deposits (Araçatuba Formation comprise siltstone and tipically greenish gray narrow tabular strata of sandstone cemented by carbonate. Moulds and gypsite and dolomite pseudomorphs were identified. The moulds seem to be genetically associated with desiccation cracks, root marks and climbing ripple lamination levels, that, on the whole, indicate calm shallow saline waters undergoing phases of subaerial exposition. At the boundaries of the study area, sand units may exhibit sigmoidal features and convolute bedding structure, which is characteristic of marginal deltaic deposits. The Araçatuba Formation is enclosed in and later overlaid by the aeolian deposits of the Vale do Rio do Peixe Formation.

Phase stability of zirconium oxide films during focused ion beam milling

Science.gov (United States)

Baxter, Felicity; Garner, Alistair; Topping, Matthew; Hulme, Helen; Preuss, Michael; Frankel, Philipp

2018-06-01

Focused ion beam (FIB) is a widely used technique for preparation of electron transparent samples and so it is vital to understand the potential for introduction of FIB-induced microstructural artefacts. The bombardment of both Xe+ and Ga+ ions is observed to cause extensive monoclinic to tetragonal phase transformation in ZrO2 corrosion films, however, this effect is diminished with reduced energy and is not observed below 5 KeV. This study emphasises the importance of careful FIB sample preparation with a low energy cleaning step, and also gives insight into the stabilisation mechanism of the tetragonal phase during oxidation.

First-principles investigation of U doping in ZrO2

International Nuclear Information System (INIS)

Huang, H.W.; Pan, Y.; Yu, C.; Yang, J.; Wang, H.; Yi, W.; Peng, J.C.

2014-01-01

Highlights: • U-doped system with cubic structure is more stable than the monoclinic structure. • The elastic modulus of cubic structure is higher than the monoclinic structure. • U-doped weakens the resistance to shear deformation of ZrO 2 . • U-doped enhances the resistance to shape deformation for monoclinic structure. -- Abstract: The formation energies, elastic properties, Debye temperature and electronic structure of U-doped ZrO 2 within cubic and monoclinic structures are investigated by first-principles approach. The calculated formation energies show that the U-doped with cubic structure is more stable than that of monoclinic structure. The U-doped weakens the resistance to shear deformation whether cubic structure or monoclinic structure. However, the U-doped decreases the shape deformation of cubic structure in contrast to enhances the shape deformation for monoclinic structure. The Debye temperature of U-doped system is lower than the corresponding ZrO 2 . We found that the calculated electronic structure of these systems are consistent with the variation of formation energies

Thermal behavior and phase transformation of ZrO2–10%SiO2 precursor powder prepared by a co-precipitation route without adding stability agent

International Nuclear Information System (INIS)

Chu, Hsueh-Liang; Hwang, Weng-Sing; Wang, Cheng-Li; Wang, Moo-Chin; Lee, Kuen-Chan; Huang, Hong-Hsin; Lee, Huey-Er

2014-01-01

Highlights: • The precursor powders contained about 68.3 wt% ZrO 2 , which corresponds to ZrO 2 ·1/8 H 2 O. • The exothermic peak temperature of tetragonal ZrO 2 formation occurred at 1014 K. • The activation energy of ZrO 2 –10%SiO 2 precursors crystallization is 993.7 kJ/mol. • Only the tetragonal ZrO 2 formed when the precursor calcined at 1173–1373 K for 2 h. • As calcined at 1473 K for 2 h, tetragonal ZrO 2 fully converted to monoclinic ZrO 2 . - Abstract: Thermal behavior and phase transformation of ZrO 2 –10%SiO 2 precursor powder prepared by a co-precipitation route without adding stability agent has been studied using different thermal analysis/thermogravimetry (DTA/TG), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano beam electron diffraction (NBED), high-resolution TEM (HRTEM) and energy-dispersive X-ray spectrometer (EDS). The TG results show that four weight loss regions were from 298 to 443 K, 443 to 743 K, 743 to 793 K and 793 to 1400 K. The DTA result shows that the ZrO 2 freeze-dried precursor powders crystallization at 1014 K. The activation energy of 993.7 kJ/mol was obtained for tetragonal ZrO 2 crystallization using a non-isothermal process. The XRD result shows that only a single phase of tetragonal ZrO 2 appears when the freeze-dried precursor powders after calcination between 1173 and 1373 K for 2 h. Moreover, when calcined at 1473 K for 2 h, the phase transformation from tetragonal ZrO 2 fully converted to monoclinic ZrO 2 occurred

Formation of primary pit connection during conchocelis phase of Porphyra yezoensis (Bangiophyceae, Rhodophyta)

Science.gov (United States)

Shual, Li; Jiang, Ming; Duan, Delin

2006-09-01

The formation of pit connection during conchocelis phase of Porphyra yezoensis Ueda was observed and examined with transmission electron microscope (TEM) and epifluorence microscope. It is indicated that the pit connection was formed in late stage of conchocelis phase and the early stages of conchosporangial cell development, and disappeared in bispore stage. The pit connection contained a thin membrane layer at outer pit plug. Stained with 4', 6'-diamidino-2-phenylidole dihydrochloride hydrate (DAPI), transferring of DNA or RNA between adjacent cells were observed in late stage of conchocelis development, it was deduced that pit connection might serve as a channel for signal transduction and genetic substance transportation in conchocelis phase.

Photo-, thermo- and optically stimulated luminescence of monoclinic zirconia

Energy Technology Data Exchange (ETDEWEB)

Kiisk, Valter, E-mail: valter.kiisk@ut.ee [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia); Puust, Laurits; Utt, Kathriin; Maaroos, Aarne; Mändar, Hugo [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia); Viviani, Erica; Piccinelli, Fabio [Department of Biotechnology, University of Verona, Strada Le Grazie 15, 37134 Verona (Italy); Saar, Rando; Joost, Urmas; Sildos, Ilmo [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia)

2016-06-15

We carried out a careful photoluminescence (PL) and thermoluminescence (TL) characterization of nominally pure monoclinic ZrO{sub 2} nanopowders subject to oxidative vs reductive annealing (up to 1450 °C). The two kinds of studied zirconia (sol-gel-prepared vs commercial powder) exhibited virtually identical 490 nm PL emission band and 280 nm PL excitation band with slight, but clearly detectable variations in the spectral shape. The TL glow peaks, recorded over the temperature range −100 to 300 °C, showed an interplay depending on the type and treatment of sample. There is a strong evidence that the −35 and 205 °C glow peaks are due to oxygen vacancies whereas the 5 °C glow peak may relate to oxygen interstitials and the 110 °C glow peak to surface defects. Although a number of distinct glow peaks emerge, the material still seems to contain a quasi-continuous distribution of trap depths. In comparison to TL, we also demonstrate effective optically stimulated luminescence (OSL) from this polymorph of ZrO{sub 2} under red and NIR illumination at ~1 W/cm{sup 2}. All traps responsible for the principal TL peaks were also found to be OSL-active, which widens the applied importance of the material.

Influence of phase transition on pattern formation during catalytic reactions

OpenAIRE

Andrade, Roberto Fernandes Silva; Lima, D.; Cunha, F. B.

2000-01-01

p.434–445 We investigate the influence of the order of surface phase transitions on pattern formation during chemical reaction on mono-crystal catalysts. We use a model consisting of two partial differential equations, one of which describes the dynamics of the surface state with the help of a Ginzburg–Landau potential. Second- or first-order transitions are described by decreasing or increasing the relative value of the third-order coefficient of the potential. We concentrate on the stabi...

Modeling of Eutectic Formation in Al-Si Alloy Using A Phase-Field Method

Directory of Open Access Journals (Sweden)

Ebrahimi Z.

2017-12-01

Full Text Available We have utilized a phase-field model to investigate the evolution of eutectic silicon in Al-Si alloy. The interfacial fluctuations are included into a phase-field model of two-phase solidification, as stochastic noise terms and their dominant role in eutectic silicon formation is discussed. We have observed that silicon spherical particles nucleate on the foundation of primary aluminum phase and their nucleation continues on concentric rings, through the Al matrix. The nucleation of silicon particles is attributed to the inclusion of fluctuations into the phase-field equations. The simulation results have shown needle-like, fish-bone like and flakes of silicon phase by adjusting the noise coefficients to larger values. Moreover, the role of primary Al phase on nucleation of silicon particles in Al-Si alloy is elaborated. We have found that the addition of fluctuations plays the role of modifiers in our simulations and is essential for phase-field modeling of eutectic growth in Al-Si system. The simulated finger-like Al phases and spherical Si particles are very similar to those of experimental eutectic growth in modified Al-Si alloy.

Pressure-induced anomalous phase transitions and colossal enhancement of piezoelectricity in PbTiO3.

Science.gov (United States)

Wu, Zhigang; Cohen, Ronald E

2005-07-15

We find an unexpected tetragonal-to-monoclinic-to-rhombohedral-to-cubic phase transition sequence induced by pressure, and a morphotropic phase boundary in a pure compound using first-principles calculations. Huge dielectric and piezoelectric coupling constants occur in the transition regions, comparable to those observed in the new complex single-crystal solid-solution piezoelectrics such as Pb(Mg(1/3)Nb(2/3))O3-PbTiO3, which are expected to revolutionize electromechanical applications. Our results show that morphotropic phase boundaries and giant piezoelectric effects do not require intrinsic disorder, and open the possibility of studying this effect in simple systems.

The structure of ZrO2 phases and deviltrification processes in a Ca-Zr-Si-O-based glass ceramic: a combined a-XRD and XAS study

International Nuclear Information System (INIS)

Meneghini, C.; Mobilio, S.

2004-01-01

The structure of Zr atomic environment in a CaO-ZrO 2 -Si 2 glass ceramic as a function of thermal treatments has been studied, combining X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD) and anomalous XRD (a-XRD) techniques. The analysis of XRD patterns demonstrates that the devitrification process proceeds through the partial segregation of Zr-depleted phases (wollastonite-like) and Zr-rich phases (Zr oxides). The XAS and a-XRD measurements at the Zr K-edge have been exploited in order to obtain a closer insight into the atomic structure around the Zr atoms. In the as-quenched glass the Zr atom is sixfold coordinated to O atoms in an amorphous environment rich in Ca and Si. Thermal treatment firstly (T=1273-1323 K) causes partial segragation of Zr in the form of an oxide with a tetragonal zirconia (t-ZrO 2 ) crystalline structure. Raising the temperature (T=1373 K) causes the formation of ZrO 2 crystallites in the monoclinic crystallographic phase (baddeleyite, m-ZrO 2 ). Analysis of the XAS data shows that a considerable amount of Zr remains in an amorphous calcium silicate phase. (orig.)

In-situ transmission electron microscopy imaging of formation and evolution of LixWO3 during lithiation of WO3 nanowires

International Nuclear Information System (INIS)

Qi, Kuo; Li, Xiaomin; Sun, Muhua; Huang, Qianming; Wei, Jiake; Xu, Zhi; Wang, Wenlong; Bai, Xuedong; Wang, Enge

2016-01-01

The phase transition from monoclinic WO 3 to cubic Li x WO 3 during lithiation of WO 3 is one of the key features for tungsten oxide as the most used electrochromic material. Conventionally, the lithium intercalation of WO 3 has been studied by building generic layered electrochromic device combining with structural characterization and electrochemistry measurement at macro scale. In-situ transmission electron microscopy (in-situ TEM) has been proposed as a method for revealing the detailed mechanism of structural, physical, and chemical properties. Here, we use in-situ TEM method to investigate the formation and evolution of Li x WO 3 in real-time during the electrochemical lithiation of WO 3 nanowires. The dynamic lithiation process is recorded by TEM imaging, diffraction, and electron energy loss spectroscopy. The WO 3 -Li x WO 3 phase boundary of reaction front has been observed at high resolution. The timeliness of crystallinity of Li x WO 3 and the intercalation channels for Li ions are also identified. Moreover, the co-existence of both polycrystalline Li-poor area and amorphous Li-rich phases of Li x WO 3 was found. Our results provide an insight into the basic lithiation process of WO 3 , which is significantly important for understanding the electrochromic mechanism of tungsten oxide.

Swift heavy ion induced phase transformation and thermoluminescence properties of zirconium oxide

Energy Technology Data Exchange (ETDEWEB)

Lokesha, H.S. [Physics R & D Centre, PES Institute of Technology, BSK 3rd Stage, Bangalore 560085 (India); Nagabhushana, K.R., E-mail: bhushankr@gmail.com [Physics R & D Centre, PES Institute of Technology, BSK 3rd Stage, Bangalore 560085 (India); Department of Physics, PES University, BSK 3rd Stage, Bangalore 560085 (India); Singh, Fouran [Inter University Accelerator Center, Aruna Asaf Ali Marg, New Delhi 110 067 (India)

2016-07-15

Zirconium oxide (ZrO{sub 2}) powder is synthesized by combustion technique. XRD pattern of ZrO{sub 2} shows monoclinic phase with average crystallite size 35 nm. Pellets of ZrO{sub 2} are irradiated with 100 MeV swift Si{sup 7+}, Ni{sup 7+} and 120 MeV swift Ag{sup 9+} ions in the fluence range 3 × 10{sup 10}–3 × 10{sup 13} ions cm{sup −2}. XRD pattern show the main diffraction peak correspond to monoclinic and tetragonal phase of ZrO{sub 2} in 2θ range 27–33°. Structural phase transformation is observed for Ni{sup 7+} and Ag{sup 9+} ion irradiated samples at a fluence 1 × 10{sup 13} ions cm{sup −2} and 3 × 10{sup 12} ions cm{sup −2} respectively, since the deposited electronic energy loss exceeds an effective threshold (>12 keV nm{sup −1}). Phase transition induced by Ag{sup 9+} ion is nearly 2.9 times faster than Ni{sup 7+} ion at 1 × 10{sup 13} ions cm{sup −2}. Ag{sup 9+} ion irradiation leads two ion impact processes. Thermoluminescence (TL) glow curves exhibit two glows, a well resolved peak at ∼424 K and unresolved peak at 550 K for all SHI irradiated samples. TL response is decreased with increase of ion fluence. Beyond 3 × 10{sup 12} ions cm{sup −2}, samples don’t exhibit TL due to annihilation of defects.

Phase Transformation and Lattice Parameter Changes of Non-trivalent Rare Earth-Doped YSZ as a Function of Temperature

Science.gov (United States)

Jiang, Shengli; Huang, Xiao; He, Zhang; Buyers, Andrew

2018-05-01

To examine the effect of doping/co-doping on high-temperature phase compositions of YSZ, stand-alone YSZ and CeO2 and Nb2O5 co-doped YSZ samples were prepared using mechanical alloy and high-temperature sintering. XRD analysis was performed on these samples from room temperature to 1100 °C. The results show that the structure for the co-doped samples tends to be thermally stable when the test temperature is higher than a critical value. Monoclinic phase was dominant in Nb2O5 co-doped YSZ at temperatures lower than 600 °C, while for the YSZ and CeO2 co-doped YSZ, cubic/tetragonal phase was dominant in the whole test temperature range. The lattice parameters for all the samples increase with increasing test temperature generally. The lattice parameters for the two non-trivalent rare earth oxides co-doped YSZ show that the lattice parameter a for the cubic phase of the Ce4+ co-doped YSZ is consistently greater than that of 7YSZ which is related to the presence of larger radius of Ce4+ in the matrix. The lattice parameters a, b, c for the monoclinic phase of Ce4+ co-doped YSZ are much closer to each other than that of the Nb5+ co-doped YSZ, indicating the former has better tendency to form cubic/tetragonal phase, which is desired for vast engineering applications.

Metallurgical features of the formation of a solid-phase metal joint upon electric-circuit heating

Science.gov (United States)

Latypov, R. A.; Bulychev, V. V.; Zybin, I. N.

2017-06-01

The thermodynamic conditions of formation of a joint between metals using the solid-phase methods of powder metallurgy, welding, and deposition of functional coatings upon electric-current heating of the surfaces to be joined are studied. Relations are obtained to quantitatively estimate the critical sizes of the circular and linear active centers that result in the formation of stable bonding zones.

Spontaneous and Flow-Driven Interfacial Phase Change: Dynamics of Microemulsion Formation at the Pore Scale.

Science.gov (United States)

Tagavifar, Mohsen; Xu, Ke; Jang, Sung Hyun; Balhoff, Matthew T; Pope, Gary A

2017-11-14

The dynamic behavior of microemulsion-forming water-oil-amphiphiles mixtures is investigated in a 2.5D micromodel. The equilibrium phase behavior of such mixtures is well-understood in terms of macroscopic phase transitions. However, what is less understood and where experimental data are lacking is the coupling between the phase change and the bulk flow. Herein, we study the flow of an aqueous surfactant solution-oil mixture in porous media and analyze the dependence of phase formation and spatial phase configurations on the bulk flow rate. We find that a microemulsion forms instantaneously as a boundary layer at the initial surface of contact between the surfactant solution and oil. The boundary layer is temporally continuous because of the imposed convection. In addition to the imposed flow, we observe spontaneous pulsed Marangoni flows that drag the microemulsion and surfactant solution into the oil stream, forming large (macro)emulsion droplets. The formation of the microemulsion phase at the interface distinguishes the situation from that of the more common Marangoni flow with only two phases present. Additionally, an emulsion forms via liquid-liquid nucleation or the Ouzo effect (i.e., spontaneous emulsification) at low flow rates and via mechanical mixing at high flow rates. With regard to multiphase flow, contrary to the common belief that the microemulsion is the wetting liquid, we observe that the minor oil phase wets the solid surface. We show that a layered flow pattern is formed because of the out-of-equilibrium phase behavior at high volumetric flow rates (order of 2 m/day) where advection is much faster than the diffusive interfacial mass transfer and transverse mixing, which promote equilibrium behavior. At lower flow rates (order of 30 cm/day), however, the dynamic and equilibrium phase behaviors are well-correlated. These results clearly show that the phase change influences the macroscale flow behavior.

Transformation plasticity and hot pressing

International Nuclear Information System (INIS)

Chaklader, A.C.D.

1975-01-01

The transformation plasticity during the phase transition of quartz to cristobalite, monoclinic reversible tetragonal of zirconia, metakaolin to a spinel phase, and brucite to periclase was investigated by studying their compaction characteristics. Viscous flow was found to be the predominant mechanism of mass transport (after an initial particle rearrangement stage) in the case of quartz to cristobalite phase change where the transformation was associated with the formation of an intermediate amorphous silica phase. The results on the monoclinic reversible tetragonal transformation of zirconia indicated that it is most likely controlled by internal strain induced by the stress associated with the volume change (ΔV/V) and the flow stress of the weaker phase. Particle movement and deformation of the weaker phase (possibly tetragonal) may be the manifestation of this plasticity. The plasticity in the case of metakaolin to a spinel phase appeared to start before the exothermic reaction (generally encountered in a dta plot) and may be diffusion controlled. The plasticity encountered during brucite to periclase transformation may be the combined effect of disintegration of precursor particles, vapor-phase lubrication and some deformability of freshly formed very fine MgO particles

Circular Formation Control of Multiagent Systems with Any Preset Phase Arrangement

Directory of Open Access Journals (Sweden)

Lina Jin

2018-01-01

Full Text Available This paper deals with the circular formation control problem of multiagent systems for achieving any preset phase distribution. The control problem is decomposed into two parts: the first is to drive all the agents to a circle which either needs a target or not and the other is to arrange them in positions distributed on the circle according to the preset relative phases. The first part is solved by designing a circular motion control law to push the agents to approach a rotating transformed trajectory, and the other is settled using a phase-distributed protocol to decide the agents’ positioning on the circle, where the ring topology is adopted such that each agent can only sense the relative positions of its neighboring two agents that are immediately in front of or behind it. The stability of the closed-loop system is analyzed, and the performance of the proposed controller is verified through simulations.

Crystal structure of Cs3H(SeO4)2 (T=295 K) and its changes in phase transformations

International Nuclear Information System (INIS)

Merinov, B.V.; Bolotina, N.B.; Baranov, A.I.; Shuvalov, L.A.

1988-01-01

Crystal structure of Cs 3 H(SeO 4 ) 2 3 phase at T=295 K is decoded by X-ray diffraction data. Monoclinic cell parameters are improved: a=10.903(3), b=6.390(8), c=8.452(2)A, β=112.46(1) deg, V=544 A 3 , Z=2, sp. gr. C2/m. Structural peculiarities of 3↔2↔1 phase transitions in Cs 3 H(SeO 4 ) 2 and proton conductivity mechanism in superionic phase are considered

Phase formation and stability of quasicrystal/α-Mg interfaces in the Mg–Cd–Yb system

International Nuclear Information System (INIS)

Ohhashi, S.; Suzuki, K.; Kato, A.; Tsai, A.P.

2014-01-01

Phase formation involving icosahedral quasicrystals (iQc) in the Mg–Cd–Yb system was investigated. The phase diagrams obtained revealed that the iQc is in equilibrium with either (Mg, Cd) 2 Yb or an α-Mg phase over a wide composition range at 673 K. A eutectic reaction, where the melt decomposed to a rod-like lamella structure consisting of iQc and α-Mg phases was observed for Mg 68 Cd 24 Yb 8 at 735 K. High-angle annular dark-field scanning transmission microscopy observation of the iQc in Mg 96 Cd 3 Yb 1 verified the atomic positions of the Yb icosahedra and confirmed that the i-MgCdYb is isostructural to the i-CdYb. The formation of the eutectic structure is responsible for the high stability of the iQc/α-Mg interfaces because of good lattice matching; which is coincident interplanar spacing over several planes for the two phases. This coincidence in interplanar spacing was further confirmed in the real atomic structure, for which the twofold planes of the iQc, and the [0 0 0 2] and [2 −1 −1 0] planes of α-Mg are dominant factors in determining the stability of the interfaces

Determination of complex formation constants by phase sensitive alternating current polarography: Cadmium-polymethacrylic acid and cadmium-polygalacturonic acid.

Science.gov (United States)

Garrigosa, Anna Maria; Gusmão, Rui; Ariño, Cristina; Díaz-Cruz, José Manuel; Esteban, Miquel

2007-10-15

The use of phase sensitive alternating current polarography (ACP) for the evaluation of complex formation constants of systems where electrodic adsorption is present has been proposed. The applicability of the technique implies the previous selection of the phase angle where contribution of capacitive current is minimized. This is made using Multivariate Curve Resolution by Alternating Least Squares (MCR-ALS) in the analysis of ACP measurements at different phase angles. The method is checked by the study of the complexation of Cd by polymethacrylic (PMA) and polygalacturonic (PGA) acids, and the optimal phase angles have been ca. -10 degrees for Cd-PMA and ca. -15 degrees for Cd-PGA systems. The goodness of phase sensitive ACP has been demonstrated comparing the determined complex formation constants with those obtained by reverse pulse polarography, a technique that minimizes the electrode adsorption effects on the measured currents.

Thermal behavior and phase transformation of ZrO{sub 2}–10%SiO{sub 2} precursor powder prepared by a co-precipitation route without adding stability agent

Energy Technology Data Exchange (ETDEWEB)

Chu, Hsueh-Liang [Department of Materials Science and Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan (China); Hwang, Weng-Sing [Department of Materials Science and Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan (China); Institute of Nanotechnology and Microsystems Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan (China); Wang, Cheng-Li [Department of Materials Science and Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan (China); Wang, Moo-Chin, E-mail: mcwang@kmu.edu.tw [Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 80708, Taiwan (China); Lee, Kuen-Chan [Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 80708, Taiwan (China); Huang, Hong-Hsin [Department of Electrical Engineering, Cheng Shiu University, 840 Cheng Ching Road, Niaosong, Kaohsiung 83347, Taiwan (China); Lee, Huey-Er, E-mail: huerle@kmu.edu.tw [School of Dentistry, College of Dental Medicine, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan (China); Department of Dentistry, Kaohsiung Medical University, 100 Tzyou 1st Road, Kaohsiung 807, Taiwan (China)

2014-12-15

Highlights: • The precursor powders contained about 68.3 wt% ZrO{sub 2}, which corresponds to ZrO{sub 2}·1/8 H{sub 2}O. • The exothermic peak temperature of tetragonal ZrO{sub 2} formation occurred at 1014 K. • The activation energy of ZrO{sub 2}–10%SiO{sub 2} precursors crystallization is 993.7 kJ/mol. • Only the tetragonal ZrO{sub 2} formed when the precursor calcined at 1173–1373 K for 2 h. • As calcined at 1473 K for 2 h, tetragonal ZrO{sub 2} fully converted to monoclinic ZrO{sub 2}. - Abstract: Thermal behavior and phase transformation of ZrO{sub 2}–10%SiO{sub 2} precursor powder prepared by a co-precipitation route without adding stability agent has been studied using different thermal analysis/thermogravimetry (DTA/TG), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano beam electron diffraction (NBED), high-resolution TEM (HRTEM) and energy-dispersive X-ray spectrometer (EDS). The TG results show that four weight loss regions were from 298 to 443 K, 443 to 743 K, 743 to 793 K and 793 to 1400 K. The DTA result shows that the ZrO{sub 2} freeze-dried precursor powders crystallization at 1014 K. The activation energy of 993.7 kJ/mol was obtained for tetragonal ZrO{sub 2} crystallization using a non-isothermal process. The XRD result shows that only a single phase of tetragonal ZrO{sub 2} appears when the freeze-dried precursor powders after calcination between 1173 and 1373 K for 2 h. Moreover, when calcined at 1473 K for 2 h, the phase transformation from tetragonal ZrO{sub 2} fully converted to monoclinic ZrO{sub 2} occurred.

Why the Heyd-Scuseria-Ernzerhof hybrid functional description of VO2 phases is not correct

KAUST Repository

Grau-Crespo, Ricardo; Schwingenschlö gl, Udo; Wang, Hao

2012-01-01

In contrast with recent claims that the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid functional can provide a good description of the electronic and magnetic structures of VO2 phases, we show here that the HSE lowest-energy solutions for both the low-temperature monoclinic (M1) phase and the high-temperature rutile (R) phase, which are obtained upon inclusion of spin polarization, are at odds with experimental observations. For the M1 phase the ground state is (but should not be) magnetic, while the ground state of the R phase, which is also spin polarized, is not (but should be) metallic. The energy difference between the low-temperature and high-temperature phases has strong discrepancies with the experimental latent heat.

Why the Heyd-Scuseria-Ernzerhof hybrid functional description of VO2 phases is not correct

KAUST Repository

Grau-Crespo, Ricardo

2012-08-06

In contrast with recent claims that the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid functional can provide a good description of the electronic and magnetic structures of VO2 phases, we show here that the HSE lowest-energy solutions for both the low-temperature monoclinic (M1) phase and the high-temperature rutile (R) phase, which are obtained upon inclusion of spin polarization, are at odds with experimental observations. For the M1 phase the ground state is (but should not be) magnetic, while the ground state of the R phase, which is also spin polarized, is not (but should be) metallic. The energy difference between the low-temperature and high-temperature phases has strong discrepancies with the experimental latent heat.

Tunable Crystal-to-Crystal Phase Transition in a Cadmium Halide Chain Polymer

Directory of Open Access Journals (Sweden)

Ulli Englert

2011-07-01

Full Text Available The chain polymer [{Cd(μ-X2py2}1∞] (X = Cl, Br; py = pyridine undergoes a fully reversible phase transition between a monoclinic low-temperature and an orthorhombic high-temperature phase. The transformation can be directly monitored in single crystals and can be confirmed for the bulk by powder diffraction. The transition temperature can be adjusted by tuning the composition of the mixed-halide phase: Transition temperatures between 175 K up to the decomposition of the material at ca. 350 K are accessible. Elemental analysis, ion chromatography and site occupancy refinements from single-crystal X-ray diffraction agree with respect to the stoichiometric composition of the samples.

Phase-field modeling of microstructural pattern formation during directional solidification of peritectic alloys without morphological instability

International Nuclear Information System (INIS)

Shing Lo, Tak; Karma, Alain; Plapp, Mathis

2001-01-01

During the directional solidification of peritectic alloys, two stable solid phases (parent and peritectic) grow competitively into a metastable liquid phase of larger impurity content than either solid phase. When the parent or both solid phases are morphologically unstable, i.e., for a small temperature gradient/growth rate ratio (G/v p ), one solid phase usually outgrows and covers the other phase, leading to a cellular-dendritic array structure closely analogous to the one formed during monophase solidification of a dilute binary alloy. In contrast, when G/v p is large enough for both phases to be morphologically stable, the formation of the microstructure becomes controlled by a subtle interplay between the nucleation and growth of the two solid phases. The structures that have been observed in this regime (in small samples where convection effects are suppressed) include alternate layers (bands) of the parent and peritectic phases perpendicular to the growth direction, which are formed by alternate nucleation and lateral spreading of one phase onto the other as proposed in a recent model [R. Trivedi, Metall. Mater. Trans. A 26, 1 (1995)], as well as partially filled bands (islands), where the peritectic phase does not fully cover the parent phase which grows continuously. We develop a phase-field model of peritectic solidification that incorporates nucleation processes in order to explore the formation of these structures. Simulations of this model shed light on the morphology transition from islands to bands, the dynamics of spreading of the peritectic phase on the parent phase following nucleation, which turns out to be characterized by a remarkably constant acceleration, and the types of growth morphology that one might expect to observe in large samples under purely diffusive growth conditions

Phase formation in titanium alloys during their quenching from liquid state

International Nuclear Information System (INIS)

Golub, S.Ya.; Kotko, A.V.; Kuz'menko, N.N.; Kulak, L.D.; Firstov, S.A.; Khaenko, B.V.

1992-01-01

Methods of X-ray diffractin analysis, light and electron microscopy were applied to study structural state of titanium base alloys quenched from liquid state by spinning with cooling in inert gas or at the surface of solid heat exchanger. Phase formation under rapid cooling conditions was considered. The morphology of phases and mutual orientation of their crystal lattices were investigated along with the character of crystallization texture. It was revealed that on melt quenching with 10 5 -10 6 K/s cooling rates the growth of columnar branches of degenerated dendrites was accopanied by Si atoms movement of the order of 0.1 μm. Structure and crack resistance of compacted articles produced from rapidly solidified powders were under study

Halo formation in three-dimensional bunches with various phase space distributions

Directory of Open Access Journals (Sweden)

A. V. Fedotov

1999-01-01

Full Text Available A realistic treatment of halo formation must take into account 3D beam bunches and 6D phase space distributions. We recently constructed, analytically and numerically, a new class of self-consistent 6D phase space stationary distributions, which allowed us to study the halo development mechanism without being obscured by the effect of beam redistribution. In this paper we consider nonstationary distributions and study how the halo characteristics compare with those obtained using the stationary distribution. We then discuss the effect of redistribution on the halo development mechanism. In contrast to bunches with a large aspect ratio, we find that the effect of coupling between the r and z planes is especially important as the bunch shape becomes more spherical.

Evaluation of commercial and sulfated ZrO{sub 2} aiming application catalysis; Avaliacao de ZrO{sub 2} comercial e sulfatada visando aplicacao em catalise

Energy Technology Data Exchange (ETDEWEB)

Silva, F.N.; Dantas, J.; Costa, A.C.F.M., E-mail: nilson.s@hotmail.com [Universidade Federal de Campina Grande (UFCG), PB (Brazil). Pos-Graduacao em Engenharia de Materiais; Pallone, E.M.J.A. [Universidade de Sao Paulo (USP), Pirassununga, SP (Brazil). Departamento de Ciencias Basicas; Dutra, R.C.L. [Instituto de Aeronautica e Espaco (AQI/IAE), Sao Jose dos Campos, SP (Brazil). Divisao de Quimica

2014-07-01

This study evaluates the performance of commercial and sulfated ZrO{sub 2} for future application in catalysis. Commercial ZrO{sub 2} was provided by the company Saint-Gobain Zirpro. The sulfation occurred with SO{sub 4}{sup -2} ion content of 30% compared to the mass of ZrO{sub 2}. The samples were characterized by XRD, FTIR, EDX and GD. The results revealed the formation of a monoclinic phase for the commercial sample, and a monoclinic major phase with tetragonal traces for the sulfated sample. The commercial ZrO{sub 2} showed a narrow, bimodal and asymmetric agglomerates distribution, while the sulfated sample showed a narrow, tetramodal and asymmetric agglomerates distribution. The presence of traces of the tetragonal phase in the SO{sub 4}{sup -2}/ZrO{sub 2} XRD, and the presence of SO{sub 3} in the EDX were good indicators for future use in catalysis to provide ester. (author)

Superconductivity optimization and phase formation kinetics study of internal-Sn Nb{sub 3}Sn superconducting wires

Energy Technology Data Exchange (ETDEWEB)

Zhang, Chaowu

2007-07-15

Superconductors Nb{sub 3}Sn wires are one of the most applicable cryogenic superconducting materials and the best choice for high-field magnets exceeding 10 T. One of the most significant utilization is the ITER project which is regarded as the hope of future energy source. The high-Cu composite designs with smaller number of sub-element and non-reactive diffusion barrier, and the RRP (Restacked Rod Process) internal-Sn technology are usually applied for the wire manufacturing. Such designed and processed wires were supplied by MSA/Alstom and WST/NIN in this research. The systematic investigation on internal-Sn superconducting wires includes the optimization of heat treatment (HT) conditions, phase formation and its relation with superconductivity, microstructure analysis, and the phase formation kinetics. Because of the anfractuosity of the configuration design and metallurgical processing, the MF wires are not sufficient for studying a sole factor effect on superconductivity. Therefore, four sets of mono-element (ME) wires with different Sn ratios and different third-element addition were designed and fabricated in order to explore the relationship between phase formation and superconducting performances, particularly the A15 layer growth kinetics. Different characterization technic have been used (magnetization measurements, neutron diffraction and SEM/TEM/EDX analysis). The A15 layer thicknesses of various ME samples were measured and carried out linear and non-linear fits by means of two model equations. The results have clearly demonstrated that the phase formation kinetics of Nb{sub 3}Sn solid-state reaction is in accordance with an n power relation and the n value is increased with the increase of HT temperature and the Sn ratio in the wire composite. (author)

HRTEM investigation of orthorhombic phase in Mg-PSZ

International Nuclear Information System (INIS)

Liu, Z.W.; Spargo, A.E.C.; Hannink, R.H.J.

1997-01-01

Tetragonal, orthorhombic and monoclinic phases are only slight distortions of the cubic structure. Due to minor differences in unit cell parameters it is difficult to distinguish these phases only by high resolution images. However, using high resolution transmission electron microscopy (HRTEM) observation in combination with image simulation and digital Fourier transformation of HRTEM images, it was found that one tetragonal precipitate can be transformed to several orthorhombic domains with different orientations in MgO-partially-stabilized zirconia (Mg-PSZ). The lattice correspondence between two adjacent orthorhombic domains is such that their b axes are parallel, while their a axes are perpendicular to each other. Also it was found that cubic ZrO 2 could be transformed to orthorhombic ZrO 2 . 8 refs., 1 tab., 4 figs

Modeling of Semiconductors and Correlated Oxides with Point Defects by First Principles Methods

KAUST Repository

Wang, Hao

2014-01-01

Point defects in silicon, vanadium dioxide, and doped ceria are investigated by density functional theory. Defects involving vacancies and interstitial oxygen and carbon in silicon are after formed in outer space and significantly affect device performances. The screened hybrid functional by Heyd-Scuseria-Ernzerhof is used to calculate formation energies, binding energies, and electronic structures of the defective systems because standard density functional theory underestimates the bang gap of silicon. The results indicate for the A-center a −2 charge state. Tin is proposed to be an effective dopant to suppress the formation of A-centers. For the total energy difference between the A- and B-type carbon related G-centers we find close agreement with the experiment. The results indicate that the C-type G-center is more stable than both the A- and B-types. The electronic structures of the monoclinic and rutile phases of vanadium dioxide are also studied using the Heyd-Scuseria-Ernzerhof functional. The ground states of the pure phases obtained by calculations including spin polarization disagree with the experimental observations that the monoclinic phase should not be magnetic, the rutile phase should be metallic, and the monoclinic phase should have a lower total energy than the rutile phase. By tuning the Hartree-Fock fraction α to 10% the agreement with experiments is improved in terms of band gaps and relative energies of the phases. A calculation scheme is proposed to simulate the relationship between the transition temperature of the metal-insulator transition and the dopant concentration in tungsten doped vanadium dioxide. We achieve good agreement with the experimental situation. 18.75% and 25% yttrium, lanthanum, praseodymium, samarium, and gadolinium doped ceria supercells generated by the special quasirandom structure approach are employed to investigate the impact of doping on the O diffusion. The experimental behavior of the conductivity for the

Modeling of Semiconductors and Correlated Oxides with Point Defects by First Principles Methods

KAUST Repository

Wang, Hao

2014-06-15

Point defects in silicon, vanadium dioxide, and doped ceria are investigated by density functional theory. Defects involving vacancies and interstitial oxygen and carbon in silicon are after formed in outer space and significantly affect device performances. The screened hybrid functional by Heyd-Scuseria-Ernzerhof is used to calculate formation energies, binding energies, and electronic structures of the defective systems because standard density functional theory underestimates the bang gap of silicon. The results indicate for the A-center a −2 charge state. Tin is proposed to be an effective dopant to suppress the formation of A-centers. For the total energy difference between the A- and B-type carbon related G-centers we find close agreement with the experiment. The results indicate that the C-type G-center is more stable than both the A- and B-types. The electronic structures of the monoclinic and rutile phases of vanadium dioxide are also studied using the Heyd-Scuseria-Ernzerhof functional. The ground states of the pure phases obtained by calculations including spin polarization disagree with the experimental observations that the monoclinic phase should not be magnetic, the rutile phase should be metallic, and the monoclinic phase should have a lower total energy than the rutile phase. By tuning the Hartree-Fock fraction α to 10% the agreement with experiments is improved in terms of band gaps and relative energies of the phases. A calculation scheme is proposed to simulate the relationship between the transition temperature of the metal-insulator transition and the dopant concentration in tungsten doped vanadium dioxide. We achieve good agreement with the experimental situation. 18.75% and 25% yttrium, lanthanum, praseodymium, samarium, and gadolinium doped ceria supercells generated by the special quasirandom structure approach are employed to investigate the impact of doping on the O diffusion. The experimental behavior of the conductivity for the

Optical evidences for an intermediate phase in relaxor ferroelectric Pb(In1/2Nb1/2O3-Pb(Mg1/3Nb2/3O3-PbTiO3 single crystals

Directory of Open Access Journals (Sweden)

Xiaolong Zhang

2016-02-01

Full Text Available The mechanism of low-temperature structural transformation and evolution of polar nano-structures in relaxor ferroelectric Pb(In1/2Nb1/2O3-Pb(Mg1/3Nb2/3O3-xPbTiO3 (x = 0.33, 0.35, and 0.42 single crystals have been investigated with the aid of temperature dependent low-wavenumber Raman scattering (LWRS and photoluminescence (PL spectra. The E(TO1 phonon mode reveals the characteristic relaxational polarization fluctuations associated with the reorientation of either polar nano-regions or polar nano-domains. It was found that these mechanisms are not independent and they can be ascribed to the phonon localization. In addition, a short-range monoclinic phase (Mc can be found below 250 K in the tetragonal phase region by LWRS, which is always associated with the morphotropic phase boundary (MPB and excellent electromechanical properties. It is interesting that PL spectra confirm these results. The present work indicates that external field modulation and change of composition can result in the monoclinic phase and co-existence of multi-phase.

Analytical model of chemical phase and formation of DSB in chromosomes by ionizing radiation

Czech Academy of Sciences Publication Activity Database

Barilla, J.; Lokajíček, Miloš; Pisaková, Hana; Šimr, P.

2013-01-01

Roč. 36, č. 1 (2013), s. 11-17 ISSN 0158-9938 Institutional support: RVO:68378271 Keywords : radiobiological mechanism * chemical phase * DSB formation * oxygen effect Subject RIV: BF - Elementary Particles and High Energy Physics Impact factor: 0.848, year: 2013

Ultrafast dynamics during the photoinduced phase transition in VO2

Science.gov (United States)

Wegkamp, Daniel; Stähler, Julia

2015-12-01

The phase transition of VO2 from a monoclinic insulator to a rutile metal, which occurs thermally at TC = 340 K, can also be driven by strong photoexcitation. The ultrafast dynamics during this photoinduced phase transition (PIPT) have attracted great scientific attention for decades, as this approach promises to answer the question of whether the insulator-to-metal (IMT) transition is caused by electronic or crystallographic processes through disentanglement of the different contributions in the time domain. We review our recent results achieved by femtosecond time-resolved photoelectron, optical, and coherent phonon spectroscopy and discuss them within the framework of a selection of latest, complementary studies of the ultrafast PIPT in VO2. We show that the population change of electrons and holes caused by photoexcitation launches a highly non-equilibrium plasma phase characterized by enhanced screening due to quasi-free carriers and followed by two branches of non-equilibrium dynamics: (i) an instantaneous (within the time resolution) collapse of the insulating gap that precedes charge carrier relaxation and significant ionic motion and (ii) an instantaneous lattice potential symmetry change that represents the onset of the crystallographic phase transition through ionic motion on longer timescales. We discuss the interconnection between these two non-thermal pathways with particular focus on the meaning of the critical fluence of the PIPT in different types of experiments. Based on this, we conclude that the PIPT threshold identified in optical experiments is most probably determined by the excitation density required to drive the lattice potential change rather than the IMT. These considerations suggest that the IMT can be driven by weaker excitation, predicting a transiently metallic, monoclinic state of VO2 that is not stabilized by the non-thermal structural transition and, thus, decays on ultrafast timescales.

Effects of S/V on secondary phase formation on waste glasses

International Nuclear Information System (INIS)

Feng, X.; Buck, E.C.; Bates, J.K.; Gong, M.; Dietz, N.L.; Pegg, I.L.

1994-01-01

Simulated West Valley high-level nuclear waste glass, WV205, was leached with and without buffered media in both deuterated and ordinary water at glass surface area to solution volumes (S/N) of 200--6000 m -1 . Examination of the glass surface after testing for 14 days indicated that the S/V-induced pH change plays a dominant role in the development of the altered surface layer and the secondary phases formed. The changes due to SN-induced pH determine the rate of surface layer formation, the element distribution in the surface layer, and possibly, the identities of the secondary phases. Changes due to SN-induced elemental concentration also influence glass reaction rate in terms of the layer thickness and the elemental distribution in the surface layers

Third phase formation in the extraction of Th(NO_3)_4 by Tri-sec-butyl phosphate. A comparison with Tri-n-butyl phosphate

International Nuclear Information System (INIS)

Chandrasekar, Aditi; Suresh, A.; Sivaraman, N.

2017-01-01

Earlier studies carried out in our laboratory indicated that Tri-sec-butyl phosphate (TsBP) is a potential extractant for U/Th separation. Also, the third phase formation tendency of TsBP is lower compared to its isomers, Tri-n-butyl-phosphate (TBP) and Tri-iso-butyl phosphate (TiBP). In this context, the extraction and third phase formation behaviour of 1.1 M solutions of TiBP and TsBP in n-dodecane in the extraction of Th(IV) from 1 M HNO_3 at 303 K over a wide range of Th concentrations were investigated in the present study and the results are compared with the literature data on TBP system. Concentrations of Th(IV) and HNO_3 loaded in the organic phase before third phase formation (biphasic region) as well as in third phase and diluent-rich phase after third phase formation (triphasic region) were measured as a function of equilibrium aqueous phase Th(IV) concentration. The density of loaded organic phase was also measured at various Th(IV) concentrations. The extraction profiles in the biphasic region indicated that extraction of Th(IV) by TBP is higher than that of TiBP which in turn is higher than that of TsBP. Extractant concentration in the diluent-rich phase and third phase was measured for the triphasic region.

A first principles study of structural stability, electronic structure and mechanical properties of beryllium alanate BeAlH{sub 5}

Energy Technology Data Exchange (ETDEWEB)

Santhosh, M.; Rajeswarapalanichamy, R., E-mail: rajeswarapalanichamy@gmail.com; Priyanga, G. Sudha; Cinthia, A. Jemmy [Department of physics, N.M.S.S.V.N college, Madurai, Tamilnadu-625019 (India); Kanagaprabha, S. [Department of Physics, Kamaraj College, Tuticorin, Tamil Nadu 628003 (India); Iyakutti, K. [Department of Physics and Nanotechnology, SRM University, Chennai, Tamilnadu-603203 (India)

2015-06-24

Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of BeAlH{sub 5} for monoclinic crystal structures with two different types of space group namely P2{sub 1} and C{sub 2}/c. Among the considered structures monoclinic (P2{sub 1}) phase is found to be the most stable at ambient condition. The structural phase transition from monoclinic (P2{sub 1}) to monoclinic (C{sub 2}/c) phase is observed in BeAlH{sub 5}. The electronic structure reveals that this compound is insulator. The calculated elastic constants indicate that this material is mechanically stable at ambient condition.

Methodology for determination of trace elements in mineral phases of iron banded formation by LA-ICP-MS

International Nuclear Information System (INIS)

Sousa, Denise V.M. de; Nalini Junior, Herminio A.; Sampaio, Geraldo M.S.; Abreu, Adriana T. de; Lana, Cristiano de C.

2015-01-01

The study of the chemical composition of mineral phases of iron formation (FF), especially of trace elements, is an important tool in the understanding of the genesis of these rocks and the contribution of the phases in the composition of whole rock. Low mass fraction of such elements in the mineral phases present in this rock type requires a suitable analytical procedure. The laser ablation technique coupled with ICP-MS (LA-ICP-MS) has been widely used for determination of trace elements in geological samples. Thus, the aim of this study is to develop calibration curves for determination of trace elements (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) in mineral phases of banded iron formations by LA-ICP-MS. Several certified reference materials (CRM) were used for calibrate the equipment. The analytical conditions were checked by CRM NIST SRM 614. The results were satisfactory, since the curves showed good linearity coefficients, good accuracy and precision of results. (author)

Influence of powder pre-annealing on the phase formation and critical current of Bi-2223/Ag tapes

DEFF Research Database (Denmark)

Chen, X.P.; Grivel, Jean-Claude; Li, M.Y.

2004-01-01

. The effects of different precursors were investigated by XRD, SEM/EDS and critical current measurements. It has been found that both the microstructure and phase formation depended strongly on the different lead-rich phases, which determined the reactivity of the precursor. Tapes fabricated using...... the precursor with Ca2PbO4 phase (tape T1) had lower transformation rate of 2223 phase than tapes fabricated using the precursor with 3321 phase (tape T2). SEM results show that a large fraction of secondary phases with big particle size was formed in the tape T1 during the subsequent sintering, which might...

Effect of elemental composition of ion beam on the phase formation and surface strengthening of structural materials

International Nuclear Information System (INIS)

Avdienko, K.I.; Avdienko, A.A.; Kovalenko, I.A.

2001-01-01

The investigation results are reported on the influence of ion beam element composition on phase formation, wear resistance and microhardness of surface layers of titanium alloys VT-4 and VT-16 as well as stainless steel 12Kh18N10T implanted with nitrogen, oxygen and boron. It is stated that ion implantation into structural materials results in surface hardening and is directly dependent on element composition of implanted ion beam. The presence of oxygen in boron or nitrogen ion beams prevents the formation of boride and nitride phases thus decreasing a hardening effect [ru

Phase stabilization in transparent Lu2O3:Eu ceramics by lattice expansion

Science.gov (United States)

Seeley, Z. M.; Dai, Z. R.; Kuntz, J. D.; Cherepy, N. J.; Payne, S. A.

2012-11-01

Gadolinium lutetium oxide transparent ceramics doped with europium (Gd,Lu)2O3:Eu were fabricated via vacuum sintering and hot isostatic pressing (HIP). Nano-scale starting powder with the composition GdxLu1.9-xEu0.1O3 (x = 0, 0.3, 0.6, 0.9, 1.0, and 1.1) were uniaxially pressed and sintered under high vacuum at 1625 °C to obtain ˜97% dense structures with closed porosity. Sintered compacts were then subjected to 200 MPa argon gas at temperatures between 1750 and 1900 °C to reach full density. It was observed that a small portion of the Eu3+ ions were exsolved from the Lu2O3 cubic crystal lattice and concentrated at the grain boundaries, where they precipitated into a secondary monoclinic phase creating optical scattering defects. Addition of Gd3+ ions into the Lu2O3 cubic lattice formed the solid solution (Gd,Lu)2O3:Eu and stretched the lattice parameter allowing the larger Eu3+ ions to stay in solid solution, reducing the secondary phase and improving the transparency of the ceramics. Excess gadolinium, however, resulted in a complete phase transformation to monoclinic at pressures and temperatures sufficient for densification. Light yield performance was measured and all samples show equal amounts of the characteristic Eu3+ luminescence, indicating gadolinium addition had no adverse effect. This material has potential to improve the performance of high energy radiography devices.

The U phase formation in cement-based systems containing high amounts of Na2SO4

International Nuclear Information System (INIS)

Li, G.; Moranville, M.; Le Bescop, P.

1996-01-01

Simulated cemented low level wastes containing high amounts of Na 2 SO 4 (10--15%) were examined with respect to the mineralogy of the solid phases, chemical composition of the interstitial aqueous phase and immersion behavior in water. All results reveal the formation of a mineral called U phase, first observed by Dosch and zur Strassen in 1967, and its deleterious effects on the samples immersed in water. It appears that this phase can form only at very high alkaline concentration, not compatible with traditional cement paste. Two possible degradation mechanisms associated with the U phase are proposed which are to be elucidated in further works

Precipitation of Ag{sub 2}Te in the thermoelectric material AgSbTe{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Sugar, Joshua D. [Materials Physics Department, Sandia National Laboratories, Livermore, CA (United States)], E-mail: jdsugar@sandia.gov; Medlin, Douglas L. [Materials Physics Department, Sandia National Laboratories, Livermore, CA (United States)

2009-06-10

The microstructure of AgSbTe{sub 2}, prepared by solidification, is investigated using electron microscopy. During solidification and thermal treatment, the material separates into a two-phase mixture of a rocksalt phase, which is Ag{sub 22}Sb{sub 28}Te{sub 50}, and silver telluride, Ag{sub 2}Te. Ag{sub 2}Te formation results either from eutectic solidification (large lamellar structures), or by solid-state precipitation (fine-scale particles). The crystal structure of the AgSbTe{sub 2} phase determined by electron diffraction is consistent with a rocksalt structure that has a disordered cation sublattice. A preferred crystallographic orientation relationship at the interface between the matrix and the low-temperature monoclinic Ag{sub 2}Te phase is defined and discussed. This orientation relationship is observed for both second-phase morphologies. In both cases, the orientation relationship originates from a topotactic (cube-on-cube) alignment of the Te sublattices in the initially cubic Ag{sub 2}Te and the matrix at elevated temperature. This Te sublattice alignment is retained as the Ag{sub 2}Te undergoes a cubic-to-monoclinic transformation during cooling. This orientation relationship is observed for both second-phase morphologies.

Precipitation of Ag2Te in the thermoelectric material AgSbTe2

International Nuclear Information System (INIS)

Sugar, Joshua D.; Medlin, Douglas L.

2009-01-01

The microstructure of AgSbTe 2 , prepared by solidification, is investigated using electron microscopy. During solidification and thermal treatment, the material separates into a two-phase mixture of a rocksalt phase, which is Ag 22 Sb 28 Te 50 , and silver telluride, Ag 2 Te. Ag 2 Te formation results either from eutectic solidification (large lamellar structures), or by solid-state precipitation (fine-scale particles). The crystal structure of the AgSbTe 2 phase determined by electron diffraction is consistent with a rocksalt structure that has a disordered cation sublattice. A preferred crystallographic orientation relationship at the interface between the matrix and the low-temperature monoclinic Ag 2 Te phase is defined and discussed. This orientation relationship is observed for both second-phase morphologies. In both cases, the orientation relationship originates from a topotactic (cube-on-cube) alignment of the Te sublattices in the initially cubic Ag 2 Te and the matrix at elevated temperature. This Te sublattice alignment is retained as the Ag 2 Te undergoes a cubic-to-monoclinic transformation during cooling. This orientation relationship is observed for both second-phase morphologies.

FORMATION REGULARITIES OF PHASE COMPOSITION, STRUCTURE AND PROPERTIES DURING MECHANICAL ALLOYING OF BINARY ALUMINUM COMPOSITES

Directory of Open Access Journals (Sweden)

F. G. Lovshenko

2015-01-01

Full Text Available The paper presents investigation results pertaining to  ascertainment of formation regularities of phase composition and structure during mechanical alloying of binary aluminium composites/substances. The invetigations have been executed while applying a wide range of methods, devices and equipment used in modern material science. The obtained data complement each other. It has been established that presence of oxide and hydro-oxide films on aluminium powder  and introduction of surface-active substance in the composite have significant effect on mechanically and thermally activated phase transformations and properties of semi-finished products.  Higher fatty acids have been used as a surface active substance.The mechanism of mechanically activated solid solution formation has been identified. Its essence is  a formation of  specific quasi-solutions at the initial stage of processing. Mechanical and chemical interaction between components during formation of other phases has taken place along with dissolution  in aluminium while processing powder composites. Granule basis is formed according to the dynamic recrystallization mechanism and possess submicrocrystal structural type with the granule dimension basis less than 100 nm and the grains are divided in block size of not more than 20 nm with oxide inclusions of 10–20 nm size.All the compounds  with the addition of  surface-active substances including aluminium powder without alloying elements obtained by processing in mechanic reactor are disperse hardened. In some cases disperse hardening is accompanied by dispersive and solid solution hardnening process. Complex hardening predetermines a high temperature of recrystallization in mechanically alloyed compounds,  its value exceeds 400 °C.

Effect of Preparation Method on Phase Formation Process and Structural and Magnetic Properties of Mn2.5Ge Samples

Directory of Open Access Journals (Sweden)

R. Sobhani

2016-12-01

Full Text Available In this paper, the phase formation process of Mn2.5Ge samples, prepared by mechanical alloying of Mn and Ge metal powders and annealing, has been studied. Results showed that in the milled samples the stable phase is Mn11Ge8 compound with orthorhombic structure and Pnam space group. The value of saturation magnetization increases by increasing milling time from 0.2 up to 1.95 (Am2Kg-1. The remanece of the samples increases by increasing the milling time while the coercivity decreases. Annealing of 15-hour milled sample results in disappearance of Mn and Ge and the formation of new phases of Mn3Ge, Mn5Ge2, Mn5Ge3 and Mn2.3Ge. Mn3Ge is the main phase with Do22 tetragonal structure and I4/mmm space group which is stable and dominant. The enhancement of saturation magnetization in the annealed sample is related to the formation of three new magnetic phases and the increase of coercivity is due to the presence of Mn3Ge compound with tetragonal structure. Studies were replicated on samples made by arc melting method to compare the results and to investigate the effect of the preparation method on phase formation and structural and magnetic properties of the materials. In these samples the saturation value was in range of 0.2 up to 1.95 (Am2Kg-1 depending on preparation methods. Rietveld refinement shows that Mn2.3Ge sample prepared from arc melted under 620oC anealing is single phase. Magnetic analysis of this sample show a saturation magnetization of 5.252(Am2Kg-1 and 0.005 T coercive field.

Microstructure Formations in the Two-Phase Region of the Binary Peritectic Organic System TRIS-NPG

Science.gov (United States)

Mogeritsch, Johann; Ludwig, Andreas

2012-01-01

In order to prepare for an onboard experiment on the International Space Station (ISS), systematic directional solidification experiments with transparent hypoperitectic alloys were carried out at different solidification rates around the critical velocity for morphological stability of both solid phases. The investigations were done in the peritectic region of the binary transparent organic TRIS-NPG system where the formation of layered structures is expected to occur. The transparent appearance of the liquid and solid phase enables real time observations of the dynamic of pattern formation during solidification. The investigations show that frequently occurring nucleation events govern the peritectic solidification morphology which occurs at the limit of morphological stability. As a consequence, banded structures lead to coupled growth even if the lateral growth is much faster compared to the growth in pulling direction.

Vacancy enhanced formation and phase transition of Cu-rich precipitates in α - iron under neutron irradiation

Energy Technology Data Exchange (ETDEWEB)

Lv, G. C. [Basic Experimental Center of Natural Science, University of Science and Technology Beijing, Beijing, 100083 (China); Corrosion and Protection Center, Key Laboratory of Environmental Fracture (MOE), University of Science and Technology Beijing, Beijing, 100083 (China); Zhang, H. [Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Canada, T6G2V4 (Canada); He, X. F.; Yang, W. [China Institute of Atomic Energy, Beijing, 102413 (China); Su, Y. J., E-mail: yjsu@ustb.edu.cn [Corrosion and Protection Center, Key Laboratory of Environmental Fracture (MOE), University of Science and Technology Beijing, Beijing, 100083 (China)

2016-04-15

In this paper, we employed both molecular statics and molecular dynamics simulation methods to investigate the role of vacancies in the formation and phase transition of Cu-rich precipitates in α-iron. The results indicated that vacancies promoted the diffusion of Cu atoms to form Cu-rich precipitates. After Cu-rich precipitates formed, they further trapped vacancies. The supersaturated vacancy concentration in the Cu-rich precipitate induced a shear strain, which triggered the phase transition from bcc to fcc structure by transforming the initial bcc (110) plane into fcc (111) plane. In addition, the formation of the fcc-twin structure and the stacking fault structure in the Cu-rich precipitates was observed in dynamics simulations.

Pressure induced phase transitions in ceramic compounds containing tetragonal zirconia

Energy Technology Data Exchange (ETDEWEB)

Sparks, R.G.; Pfeiffer, G.; Paesler, M.A.

1988-12-01

Stabilized tetragonal zirconia compounds exhibit a transformation toughening process in which stress applied to the material induces a crystallographic phase transition. The phase transition is accompanied by a volume expansion in the stressed region thereby dissipating stress and increasing the fracture strength of the material. The hydrostatic component of the stress required to induce the phase transition can be investigated by the use of a high pressure technique in combination with Micro-Raman spectroscopy. The intensity of Raman lines characteristic for the crystallographic phases can be used to calculate the amount of material that has undergone the transition as a function of pressure. It was found that pressures on the order of 2-5 kBar were sufficient to produce an almost complete transition from the original tetragonal to the less dense monoclinic phase; while a further increase in pressure caused a gradual reversal of the transition back to the original tetragonal structure.

Formation and structural phase transition in Co atomic chains on a Cu(775) surface

International Nuclear Information System (INIS)

Syromyatnikov, A. G.; Kabanov, N. S.; Saletsky, A. M.; Klavsyuk, A. L.

2017-01-01

The formation of Co atomic chains on a Cu(775) surface is investigated by the kinetic Monte Carlo method. It is found that the length of Co atomic chains formed as a result of self-organization during epitaxial growth is a random quantity and its mean value depends on the parameters of the experiment. The existence of two structural phases in atomic chains is detected using the density functional theory. In the first phase, the separations between an atom and its two nearest neighbors in a chain are 0.230 and 0.280 nm. In the second phase, an atomic chain has identical atomic spacings of 0.255 nm. It is shown that the temperature of the structural phase transition depends on the length of the atomic chain.

Formation and structural phase transition in Co atomic chains on a Cu(775) surface

Energy Technology Data Exchange (ETDEWEB)

Syromyatnikov, A. G.; Kabanov, N. S.; Saletsky, A. M.; Klavsyuk, A. L., E-mail: klavsyuk@physics.msu.ru [Moscow State University (Russian Federation)

2017-01-15

The formation of Co atomic chains on a Cu(775) surface is investigated by the kinetic Monte Carlo method. It is found that the length of Co atomic chains formed as a result of self-organization during epitaxial growth is a random quantity and its mean value depends on the parameters of the experiment. The existence of two structural phases in atomic chains is detected using the density functional theory. In the first phase, the separations between an atom and its two nearest neighbors in a chain are 0.230 and 0.280 nm. In the second phase, an atomic chain has identical atomic spacings of 0.255 nm. It is shown that the temperature of the structural phase transition depends on the length of the atomic chain.

Theoretical study on phase coexistence in ferroelectric solid solutions near the tricritical point

Energy Technology Data Exchange (ETDEWEB)

Lu, Xiaoyan, E-mail: luxy@hit.edu.cn, E-mail: dzk@psu.edu; Li, Hui [Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education, School of Civil Engineering, Harbin Institute of Technology, Harbin 150001 (China); Zheng, Limei [Condensed Matter Science and Technology Institute, Harbin Institute of Technology, Harbin 150001 (China); Cao, Wenwu [Condensed Matter Science and Technology Institute, Harbin Institute of Technology, Harbin 150001 (China); Department of Mathematics and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States)

2015-04-07

Phase coexistence in ferroelectric solid solutions near the tricritical point has been theoretically analyzed by using the Landau-Devonshire theory. Results revealed that different phases having similar potential wells could coexist in a narrow composition range near the tricritical point in the classical Pb(Zr{sub 1−x}Ti{sub x})O{sub 3} system. The potential barrier between potential wells increases with the decrease of temperature. Coexisting phases or different domains of the same phase can produce adaptive strains to maintain atomic coherency at the interfaces or domain walls. Such compatibility strains have influence on the energy potential as well as the stability of relative phases, leading to the appearance of energetically unfavorable monoclinic phases. Those competing and coexisting phases also construct an easy phase transition path with small energy barrier in between, so that very small stimuli can produce large response in compositions near the morphotropic phase boundary, especially near the tricritical point.

Theoretical study on phase coexistence in ferroelectric solid solutions near the tricritical point

International Nuclear Information System (INIS)

Lu, Xiaoyan; Li, Hui; Zheng, Limei; Cao, Wenwu

2015-01-01

Phase coexistence in ferroelectric solid solutions near the tricritical point has been theoretically analyzed by using the Landau-Devonshire theory. Results revealed that different phases having similar potential wells could coexist in a narrow composition range near the tricritical point in the classical Pb(Zr 1−x Ti x )O 3 system. The potential barrier between potential wells increases with the decrease of temperature. Coexisting phases or different domains of the same phase can produce adaptive strains to maintain atomic coherency at the interfaces or domain walls. Such compatibility strains have influence on the energy potential as well as the stability of relative phases, leading to the appearance of energetically unfavorable monoclinic phases. Those competing and coexisting phases also construct an easy phase transition path with small energy barrier in between, so that very small stimuli can produce large response in compositions near the morphotropic phase boundary, especially near the tricritical point

Effects of degradation on third phase formation in the extraction of Th(NO3)4 by trialkyl phosphates

International Nuclear Information System (INIS)

Benadict Rakesh, K.; Suresh, A.; Vasudeva Rao, P.R.

2014-01-01

It is well known that solvents undergo chemical and radiolytic degradation during processing and in general the degradation products affect organic-aqueous phase separation, extraction and stripping behaviour, density, viscosity etc. In the present study, an attempt has been made to understand the effects of irradiation (100 MRad with 60 Co- γ-source) on third phase formation in the extraction of Th(IV) from nitric acid media by 1.1 M solutions of tri-n-butyl phosphate (TBP) and tri-iso-amyl phosphate (TiAP) in n-dodecane (n-DD). Two types of irradiated solvents, namely Type 1 solvents containing only primary degradation products (formed by the degradation of TBP molecules) and Type 2 solvents containing primary as well as secondary degradation products (surfactant type molecules formed by the reaction between the degradation products of extractant and diluent) were prepared by dissolving required amount of irradiated extractant in unirradiated n-DD and irradiating 1.1 M solutions of extractant in n-DD, respectively. These solvents with and without washing with 5 M NaOH solution have been investigated for third phase formation. The variations of limiting organic concentration (LOC) for third phase formation as a function of equilibrium aqueous phase acidity are shown. LOC values for third phase formation by unirradiated solvents reported in our earlier work are also shown. These figures depict that LOC values for Type 1 solvents are lower than the corresponding unirradiated solvents and can be attributed to the decrease in the extractant concentration by degradation. Estimation of extractant in Type 1 solvents by nitric acid equilibration method after the removal of primary degradation products by washing with 5 M NaOH solution revealed that extractant concentrations have been reduced to 1.03 M and 1.05 M for TBP and TiAP, respectively. Estimation of extractant in Type 2 solvents revealed 1.07 M extractant concentration in TBP and TiAP solvents. However, data

Process for obtaining sintered conglomerates with a high density of rare earth oxides and actinides

International Nuclear Information System (INIS)

Pasto, A.E.

1974-01-01

The invention concerns a method to produce agglomerates of actinide and rare earth oxides possessing a cubic-monoclinic transformation in order to obtain high densities close to the theoretical density, and the articles produced by the method. The process is based on the use of a rare earth or actinide oxide, in particular Eu 2 O 3 , with a cubic-monoclinic phase transformation, the oxide being sintered by hot compression at a temperature 50 deg C to 100 deg C above the transformation temperature. The sintered agglomerates obtained can have a purity of at least 99.9% and a density of practically 100%. These agglomerates are suitable in particular for the formation of nuclear reactor control rods [fr

Anisotropy of laser emission in monoclinic, disordered crystal Nd:LYSO.

Science.gov (United States)

Zhao, Yongguang; Zhuang, Shidong; Xu, Xiaodong; Xu, Jun; Yu, Haohai; Wang, Zhengping; Xu, Xinguang

2014-02-10

Multi-wavelength emissions have been demonstrated in many disordered laser crystals. Improving the emission controllability is crucial for their practical applications. However, it is difficult because the closely adjacent laser components cannot be effectively adjusted by the traditional resonator design. In this paper, the anisotropy of laser emission in a monoclinic, disordered crystal Nd:LuYSiO(5) (Nd:LYSO) is reported for the first time. By selecting crystal orientation, high power laser emission with different wavelengths and polarizations were obtained. For X-cut sample, 1076 nm single-wavelength laser output reached 7.56 W, which will be a useful light source for detecting carbonyl-hemoglobin and nitrite after frequency doubling. For Y- and Z-cut samples, 1076, 1079 nm dual-wavelength laser output reached 10.3 W and 7.61 W, with parallel and orthogonal polarizations, respectively, which are convenient to be used as the generation sources of 0.78 THz wave by type-I or type-II difference frequency. The output characteristic is well explained by a theoretical analysis on the stimulated emission cross-section. The present work reveals that the intrinsic anisotropy in disordered laser crystal can be utilized to elevate the emission controllability. Accordantly, the material's application scopes can be extended.

Structure of bayerite-based lithium-aluminum layered double hydroxides (LDHs): observation of monoclinic symmetry.

Science.gov (United States)

Britto, Sylvia; Kamath, P Vishnu

2009-12-21

The double hydroxides of Li with Al, obtained by the imbibition of Li salts into bayerite and gibbsite-Al(OH)(3), are not different polytypes of the same symmetry but actually crystallize in two different symmetries. The bayerite-derived double hydroxides crystallize with monoclinic symmetry, while the gibbsite-derived hydroxides crystallize with hexagonal symmetry. Successive metal hydroxide layers in the bayerite-derived LDHs are translated by the vector ( approximately -1/3, 0, 1) with respect to each other. The exigency of hydrogen bonding drives the intercalated Cl(-) ion to a site with 2-fold coordination, whereas the intercalated water occupies a site with 6-fold coordination having a pseudotrigonal prismatic symmetry. The nonideal nature of the interlayer sites has implications for the observed selectivity of Li-Al LDHs toward anions of different symmetries.

SANS study of Th (IV) third phase formation in HNO3 / DHDECMP-n-dodecane system

International Nuclear Information System (INIS)

Lohithakshan, K.V.; Aggarwal, S.K.; Aswal, V.K.

2009-01-01

Third phase formation taking place during the extraction of Th (IV) from nitric acid medium by DHDECMP in dodecane has been investigated by small angle neutron scattering (SANS) and explained the process with Baxter model. (author)

Vapour phase dehydration of glycerol to acrolein over tungstated zirconia catalysts

Science.gov (United States)

Rao Ginjupalli, Srinivasa; Mugawar, Sowmya; Rajan N., Pethan; Kumar Balla, Putra; Chary Komandur, V. R.

2014-08-01

Tetragonal (TZ) and monoclinic (MZ) polymorphs of zirconia supports were synthesised by sol-gel method followed by variation of the calcination temperature. Tungstated (10 wt% WO3) supported on the zirconia polymorphs were prepared by impregnation method by using ammonium metatungstate precursor. The physico-chemical properties of the calcined catalysts were characterised by X-ray diffraction, UV-vis diffused reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), surface area and pore size distribution measurements to gain insight into the effect of morphology of the catalyst textural properties, and structure. The surface acidic properties have been determined by NH3 TPD method and also with FT-IR spectra of pyridine adsorption. Vapour phase dehydration of glycerol to acrolein was employed to investigate the catalytic functionalities. Glycerol conversion and acrolein selectivity was mainly dependent on the fraction of moderate acid sites with majority of them are due to Brønsted acidic sites. Monoclinic zirconia based catalysts have shown the highest activity and acrolein selectivity compared to the corresponding tetragonal zirconia catalysts.

Vapour phase dehydration of glycerol to acrolein over tungstated zirconia catalysts

International Nuclear Information System (INIS)

Rao Ginjupalli, Srinivasa; Mugawar, Sowmya; Rajan, Pethan N.; Kumar Balla, Putra; Chary Komandur, V.R.

2014-01-01

Tetragonal (TZ) and monoclinic (MZ) polymorphs of zirconia supports were synthesised by sol–gel method followed by variation of the calcination temperature. Tungstated (10 wt% WO 3 ) supported on the zirconia polymorphs were prepared by impregnation method by using ammonium metatungstate precursor. The physico-chemical properties of the calcined catalysts were characterised by X-ray diffraction, UV–vis diffused reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), surface area and pore size distribution measurements to gain insight into the effect of morphology of the catalyst textural properties, and structure. The surface acidic properties have been determined by NH 3 TPD method and also with FT-IR spectra of pyridine adsorption. Vapour phase dehydration of glycerol to acrolein was employed to investigate the catalytic functionalities. Glycerol conversion and acrolein selectivity was mainly dependent on the fraction of moderate acid sites with majority of them are due to Brønsted acidic sites. Monoclinic zirconia based catalysts have shown the highest activity and acrolein selectivity compared to the corresponding tetragonal zirconia catalysts.

Vapour phase dehydration of glycerol to acrolein over tungstated zirconia catalysts

Energy Technology Data Exchange (ETDEWEB)

Rao Ginjupalli, Srinivasa; Mugawar, Sowmya; Rajan, Pethan N.; Kumar Balla, Putra; Chary Komandur, V.R., E-mail: kvrchary@iict.res.in

2014-08-01

Tetragonal (TZ) and monoclinic (MZ) polymorphs of zirconia supports were synthesised by sol–gel method followed by variation of the calcination temperature. Tungstated (10 wt% WO{sub 3}) supported on the zirconia polymorphs were prepared by impregnation method by using ammonium metatungstate precursor. The physico-chemical properties of the calcined catalysts were characterised by X-ray diffraction, UV–vis diffused reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), surface area and pore size distribution measurements to gain insight into the effect of morphology of the catalyst textural properties, and structure. The surface acidic properties have been determined by NH{sub 3} TPD method and also with FT-IR spectra of pyridine adsorption. Vapour phase dehydration of glycerol to acrolein was employed to investigate the catalytic functionalities. Glycerol conversion and acrolein selectivity was mainly dependent on the fraction of moderate acid sites with majority of them are due to Brønsted acidic sites. Monoclinic zirconia based catalysts have shown the highest activity and acrolein selectivity compared to the corresponding tetragonal zirconia catalysts.

Anomalous lattice compressibility of hexagonal Eu{sub 2}O{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Irshad, K.A.; Chandra Shekar, N.V., E-mail: chandru@igcar.gov.in

2017-07-01

Monoclinic Eu{sub 2}O{sub 3} was investigated in a Mao-Bell type diamond anvil cell using angle dispersive x-ray diffraction up to a pressure of 26 GPa. Pressure induced structural phase transition from monoclinic to hexagonal phase was observed at 4.3 GPa with 2% volume collapse. Birch –Murnaghan equation of state fit to the pressure volume data yielded a bulk modulus of 159(9) GPa and 165(6) GPa for the monoclinic and hexagonal phases respectively. Equation of state fitting to the structural parameters yielded an axial compressibility of β{sub a} > β{sub c} > β{sub b} for the parent monoclinic phase, showing the least compressibility along b axis. Contrary to the available reports, an anomalous lattice compressibility behavior is observed for the high pressure hexagonal phase, characterized by pronounced hardening of a axis above 15 GPa. The observed incompressible nature of the hexagonal a axis in the pressure range 15–25 GPa is found to be compensated by doubling the compressibility along the c axis. - Highlights: • Structural phase transition in Eu{sub 2}O{sub 3} from monoclinic to hexagonal phase. • Anomalous lattice compressibility in the hexagonal phase has reported first time. • Quantitative analysis of lattice compressibility.

Influence of the selected alloy additions on limiting the phase formation in Cu-Zn alloys

OpenAIRE

J. Kozana; St. Rzadkosz; M. Piękoś

2010-01-01

Influence of the selected alloy additions into copper and zinc alloys was investigated in order to find out the possibility of limiting the precipitation of unfavourable phase . The observation of microstructures and strength tests were performed. The results of metallographic and strength investigations indicate positive influence of small amounts of nickel, cobalt or tellurium. The precise determination of the influence of the selected alloy additions on limiting the gamma phase formation ...

Pattern Formation During Phase Separation of Polymer-Ionic Liquid Co-Solutions

Science.gov (United States)

Meng, Zhiyong; Osuji, Chinedum

2010-03-01

Co-solutions of polystyrene (PS) with a 1-butyl-3-methylimidazolium based ionic liquid (IL) in DMF phase separated into IL-rich and PS-rich domains on solvent evaporation. Over a limited range of polymer molecular weights and substrate temperatures, a variety of striped and cellular or polygonal structures were found on the resulting film surface, as visualized using bright-field and phase-contrast optical microscopy. This effect appears to be due to a Benard-Marangoni instability at the free surface of the liquid film as it undergoes evaporation, setting up convection rolls inside the fluid which become locked in place as the system vitrifies on solvent removal. Differential scanning calorimetry shows that the IL does not significantly plasticize the polymer, suggesting that the viscosity of the polystyrene solution itself controls the formation of this instability.

On the competition in phase formation during the crystallisation of Al-Ni-Y metallic glasses

International Nuclear Information System (INIS)

Styles, M.J.; Sun, W.W.; East, D.R.; Kimpton, J.A.; Gibson, M.A.; Hutchinson, C.R.

2016-01-01

Glassy metals exhibit a range of interesting properties including high strength and corrosion resistance, but often have poor toughness and tensile ductility in the fully amorphous state. It has been shown that combinations of desirable properties can be achieved by the partial crystallisation of glass-forming alloys, either during controlled solidification or by annealing a fully amorphous glass. The aim of this investigation is to understand the competition in phase formation during the crystallisation of metallic glasses in the Al-Ni-Y system. High-resolution, in situ synchrotron powder diffraction has been used to quantitatively follow the evolution of phases in 5 different alloys between Al 87 Ni 9 Y 4 and Al 75 Ni 15 Y 10 , as they were continuously heated to melting and subsequently cooled back to ambient temperature. Upon heating, the first crystallisation product was found to vary from FCC Al to the intermetallic Al 9 Ni 2 phase with increasing Ni concentration. In addition, the crystallisation sequence also changed from a two-stage to a three-stage process. High number densities of crystallites (∼10 23  m −3 ) were observed initially for both FCC Al and Al 9 Ni 2 . Upon cooling, the partially disordered Al 9 Ni 3 Y phase was found to form preferentially over the intermetallic phases observed during heating. The difference in competition in phase formation during heating and cooling are discussed in terms of nucleation barriers calculated using a recent thermodynamic assessment of the Al-Ni-Y system. The role of compositional heterogeneities in the as-quenched glasses and long-range diffusion on the nucleation process is discussed. - Graphical abstract: High-resolution, in situ synchrotron powder diffraction has been used to quantitatively follow the evolution of phases in 5 different alloys between Al 87 Ni 9 Y 4 and Al 75 Ni 15 Y 10 , as they were continuously heated to melting and subsequently cooled back to ambient temperature. Upon heating, the

Phase transitions of Pb(ZrxTi1-x)O3 ceramics

International Nuclear Information System (INIS)

Frantti, J.; Kakihana, M.; Ivanov, S.; Eriksson, S.; Rundloef, H.; Lantto, V.; Lappalainen, J.

2002-01-01

Recent experimental and theoretical reports on the structure of lead zirconate titanate [Pb(Zr x Ti 1-x )O 3 (PZT)] ceramics with compositions in the vicinity of the morphotropic phase boundary are discussed. There has been ambiguity concerning the low-temperature structure of x=0.52 samples, due to the superlattice reflections which were not explained by the reported monoclinic phase Cm [B. Noheda, D. E. Cox, G. Shirane, R. Guo, B. Jones, and L. E. Cross, Phys. Rev. B 63, 014103 (2001)]. Neutron powder diffraction (NPD) and Rietveld refinement were used to identify the space group symmetries of x=0.52 and x=0.53 samples at 10 K. Both samples had two coexisting phases R3c and Cm at 10 K. At 10 K, monoclinic angles of both samples were larger than at 295 K, as was the octahedral tilt angle of the R3c phase of the x=0.53 sample. We analyzed our previous and current NPD data to study the structural changes in PZT ceramics, 0.20≤x≤0.53, as a function of x and temperature. Bond-valence calculations were carried out to test the models used in Rietveld refinements. Valences of Zr and Ti ions were larger and smaller than their nominal valences, respectively, although the anomaly decreased with increasing x. The composition-weighted-average valence of Zr and Ti ions was close to +4, and the relationship between the positions and valences of Zr and Ti ions explains the main structural features of PZT ceramics as a function of x. The valence of Pb ions was slightly below +2 and decreased with increasing x until it started to slightly increase for x≥0.50. Average oxygen valency was found to be close to -2. Also spontaneous polarization values were computed and found to be reasonable

Rapid formation of the 110 K phase in Bi-Pb-Sr-Ca-Cu-O through freeze-drying powder processing

International Nuclear Information System (INIS)

Song, K.H.; Liu, H.K.; Dou, S.X.; Sorrell, C.C.

1990-01-01

This paper reports three techniques for processing Bi-Pb-Sr-Ca-Cu-O (BPSCCO) powders investigated: dry-mixing, sol-gel formation, and freeze-drying. It was found that sintering for 120 h at 850 degrees C is required to form nearly single-phase (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O 10-y by dry-mixing, whereas sintering for 30 h at 840 degrees C was sufficient to form the 110 K (2223) phase when freeze-drying was used. The sol-gel route was found to be intermediate in efficiency between these two techniques. Freeze-drying provided highly reactive, intimately mixed, and carbon-free precursors. The presence of carbonates in the uncalcined powders was the major cause of phase segregation and sluggishness of the 110 K phase formation

X-ray and neutron single-crystal diffraction on [Rbx(NH4)1-x]3H(SO4)2. I. Refinement of crystal structure of phase II with x=0.11 at 300 K

International Nuclear Information System (INIS)

Loose, A.; Wozniak, K.; Dominiak, P.; Smirnov, L.S.; Natkaniec, I.; Frontas'eva, M.V.; Pomyakushina, E.V.; Baranov, A.I.; Dolbinina, V.V

2006-01-01

The study of [Rb x (NH 4 ) 1-x ] 3 H(SO 4 ) 2 mixed crystals by X-ray single-crystal diffraction is known up to now only for x=0.57 at the temperatures 293 and 180 K. The crystal structures at these temperatures as was determined [1] belong to monoclinic phase II (C2/c sp. gr., Z=4). In accordance with this work, ammonium ions should be considered as deformed tetrahedra. Monoclinic phase II on the x-T phase diagram of [Rb x (NH 4 ) 1-x ] 3 H(SO 4 ) 2 mixed crystals, which has earlier been determined by the dielectric spectroscopy, is stabilized below room temperature if Rb concentration exceeds 9%. The presented results of X-ray and neutron single-crystal diffraction of the [Rb 0.11 (NH 4 ) 0.89 ] 3 H(SO 4 ) 2 mixed crystal at T= 300 K show that ammonium ions could be considered as regular tetrahedra

Formation of secondary phases during the corrosion of vitrified nuclear waste

International Nuclear Information System (INIS)

Zimmer, P.

2003-11-01

The first aim of this work was the examination of the formation and long-term stability of secondary phases that form during an aquatic attack on simulated, vitrified nuclear waste. In the glasses used for the investigations actinides had been replaced by rare earth elements (chemical analogues), other radionuclides by inactive isotopes. For predictions about the long-term safety of nuclear waste disposals it is important to identify secondary phases that have formed during the glass corrosion process and to determine their stability. Two different saline solutions (rich in MgCl 2 and in NaCl, respectively) are relevant as a corrosion medium for waste disposals. It showed that in such an environment sulfates, silicates and molybdates represent the main new formations of minerals after 7.5 years of corrosion. However, the formation, long-term stability and sorption characteristics of those minerals regarding rare earth elements depend to a high degree on the corrosion medium as well as on changes in the geochemical environment in the course of the experiment. By means of SEM/EDX barytes of different morphology with up to 15% w/w Sr ((Ba,Sr)SO 4 ) were identified in both corrosion media; they were capable of binding long-term stable radionuclides like Sr. Furthermore, pure rare earth (RE) sulfates were observed in the saline solution rich in MgCl 2 . This formation of RE-sulfates has not been described in the literature so far. Depending on the saline solution, the secondary silicate and molybdate minerals that formed on the glass surfaces differed noticeably in their sorption characteristics and their stability. Another focus of the work was a more profound understanding of the glass corrosion mechanism in the presence of metallic iron since steel jackets are used as technical barriers for the vitrified nuclear waste in nuclear waste disposals. Another important point in connection with the mobilization and immobilization of radionuclides released during glass

p-type doping efficiency in CdTe: Influence of second phase formation

Science.gov (United States)

McCoy, Jedidiah J.; Swain, Santosh K.; Sieber, John R.; Diercks, David R.; Gorman, Brian P.; Lynn, Kelvin G.

2018-04-01

Cadmium telluride (CdTe) high purity, bulk, crystal ingots doped with phosphorus were grown by the vertical Bridgman melt growth technique to understand and improve dopant solubility and activation. Large net carrier densities have been reproducibly obtained from as-grown ingots, indicating successful incorporation of dopants into the lattice. However, net carrier density values are orders of magnitude lower than the solubility of P in CdTe as reported in literature, 1018/cm3 to 1019/cm3 [J. H. Greenberg, J. Cryst. Growth 161, 1-11 (1996) and R. B. Hall and H. H. Woodbury, J. Appl. Phys. 39(12), 5361-5365 (1968)], despite comparable starting charge dopant densities. Growth conditions, such as melt stoichiometry and post growth cooling, are shown to have significant impacts on dopant solubility. This study demonstrates that a significant portion of the dopant becomes incorporated into second phase defects as compounds of cadmium and phosphorous, such as cadmium phosphide, which inhibits dopant incorporation into the lattice and limits maximum attainable net carrier density in bulk crystals. Here, we present an extensive study on the characteristics of these second phase defects in relation to their composition and formation kinetics while providing a pathway to minimize their formation and enhance solubility.

Formamidinium iodide: crystal structure and phase transitions

Directory of Open Access Journals (Sweden)

Andrey A. Petrov

2017-04-01

Full Text Available At a temperature of 100 K, CH5N2+·I− (I, crystallizes in the monoclinic space group P21/c. The formamidinium cation adopts a planar symmetrical structure [the r.m.s. deviation is 0.002 Å, and the C—N bond lengths are 1.301 (7 and 1.309 (8 Å]. The iodide anion does not lie within the cation plane, but deviates from it by 0.643 (10 Å. The cation and anion of I form a tight ionic pair by a strong N—H...I hydrogen bond. In the crystal of I, the tight ionic pairs form hydrogen-bonded zigzag-like chains propagating toward [20-1] via strong N—H...I hydrogen bonds. The hydrogen-bonded chains are further packed in stacks along [100]. The thermal behaviour of I was studied by different physicochemical methods (thermogravimetry, differential scanning calorimetry and powder diffraction. Differential scanning calorimetry revealed three narrow endothermic peaks at 346, 387 and 525 K, and one broad endothermic peak at ∼605 K. The first and second peaks are related to solid–solid phase transitions, while the third and fourth peaks are attributed to the melting and decomposition of I. The enthalpies of the phase transitions at 346 and 387 K are estimated as 2.60 and 2.75 kJ mol−1, respectively. The X-ray powder diffraction data collected at different temperatures indicate the existence of I as the monoclinic (100–346 K, orthorhombic (346–387 K and cubic (387–525 K polymorphic modifications.

Energy of formation for AgIn liquid binary alloys along the line of phase separation

CERN Document Server

Bhuiyan, G M; Ziauddin-Ahmed, A Z

2003-01-01

We have investigated the energy of formation for AgIn liquid binary alloys along the solid-liquid phase separation line. A microscopic theory based on the first order perturbation has been applied. The interionic interaction and a reference liquid are the fundamental components of the theory. These are described by a local pseudopotential and the hard sphere liquids, respectively. The results of calculations reveal a characteristic feature that the energy of formation becomes minimum at the equiatomic composition, and thus indicates maximal mix-ability at this concentration. The energy of formation at a particular thermodynamic state that is at T 1173 K predicts the experimental trends fairly well.

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)

Phase Transitions in CsSnCl3 and CsPbBr3 An NMR and NQR Study

Science.gov (United States)

Sharma, Surendra; Weiden, Norbert; Weiss, Alarich

1991-04-01

The phase transitions in CsSnCl3 and CsPbBr3 have been studied by X-ray powder diffraction, by 81Br-NQR and by 'H-, 119Sn-, and 113Cs-NMR. At room temperature in air CsSnCl3 forms a hydrate which can be dehydrated to the monoclinic phase II of CsSnCl3. The high temperature phase I has the Perovskite structure, as the X-ray and NMR experiments show. The three phases of CsPbBr3, known from literature, have been corroborated. The results are discussed in the framework of the group ABX3, A = alkalimetal ion, B = IV main group ion, and X = Halogen ion

Selective scanning tunneling microscope light emission from rutile phase of VO2.

Science.gov (United States)

Sakai, Joe; Kuwahara, Masashi; Hotsuki, Masaki; Katano, Satoshi; Uehara, Yoichi

2016-09-28

We observed scanning tunneling microscope light emission (STM-LE) induced by a tunneling current at the gap between an Ag tip and a VO2 thin film, in parallel to scanning tunneling spectroscopy (STS) profiles. The 34 nm thick VO2 film grown on a rutile TiO2 (0 0 1) substrate consisted of both rutile (R)- and monoclinic (M)-structure phases of a few 10 nm-sized domains at room temperature. We found that STM-LE with a certain photon energy of 2.0 eV occurs selectively from R-phase domains of VO2, while no STM-LE was observed from M-phase. The mechanism of STM-LE from R-phase VO2 was determined to be an interband transition process rather than inverse photoemission or inelastic tunneling processes.

Formation of metastable and equilibrium phases in the decomposition of the β solid solution in Zr alloys

International Nuclear Information System (INIS)

Zakharova, M.I.; Kirov, S.A.; Khundzhua, A.G.

1978-01-01

The decomposition of the β solid solution is studied in Zr-Nb alloys with adding Mo, Al, V, Fe by the methods of electron microscopy and X-ray diffraction on single crystals. The intermetallic compounds forming during crystallization of the alloys do not influence the precipitation of the ω- and α-phases during ageing. In the local regions of foils prepared by electropolishing after ageing the formation of the metastable f.c.c. phase and in some cases the inverse transformation of two phase state to the parent phase is observed. (author)

The effect of thermal cycling on tetragonal to monoclinic transformation in ZrO2(2%Y2O3) ceramic studied by high temperature X-ray diffraction

International Nuclear Information System (INIS)

Zhu, W.Z.; Lei, T.C.; Zhou, Y.

1993-01-01

It has been established that brittleness and reliability of ceramics can be improved by a stress-triggered tetragonal (T) to monoclinic (M) transformation in zirconia termed transformation toughening. The T → M transformation is not only influenced by such intrinsic factors as the variety and amount of stabilizers, grain size and morphology of T phase, but can be affected by the cooling rate as well. A previous study by Tsubadin, using a dilation experiment to determine the effect of thermal cycling on the T → M transformation in partially stabilized zirconia suggested that sintering temperature determined the role of thermal cycling, while the underlying cause still remains ambiguous. The intent of the present paper is to reinvestigate the effect of thermal cycling on the T → M transition in a hot pressed ZrO 2 (2%y 2 O 3 ) ceramic, using a high temperature x-ray diffractometer, and rationalize the experimental results from the viewpoint of thermodynamics

TEM investigation of the topotactic reaction of (001) and (111) Ag films and Te

International Nuclear Information System (INIS)

Safran, G.; Geszti, O.; Radnoczi, G.

2002-01-01

The formation, structure and morphology of Ag 2 Te phase developed by the reaction of single crystalline Ag films with subsequently vacuum deposited Te vapour was investigated. Silver films 30-40 nm in thickness were deposited at 85-120 grad C by thermal evaporation in vacuum at a base pressure of 4x10 -5 mbar. The NaCl substrates were cleaved and saw-cut in order to achieve (001) and (111) surfaces, respectively. The surfaces were treated with water and chlorine prior to Ag deposition. This preparation resulted in single crystalline Ag films of (001) and (111) orientation. Tellurium was deposited onto the silver at a rate about 0.1 nm/s at 200 grad C i.e. above the temperature of the polymorphic phase transformation from monoclinic to fcc (T c =150 grad C). The Ag-Te reaction occurred during the Te deposition. The samples were investigated by TEM and SAED in a 200 kV Philips CM 20 electron microscope equipped with a Ge detector Noran EDS system. In the fully tellurized layers, however, the monoclinic (low temperature) Ag 2 Te phase was found. It exhibited large single crystals consisting of strictly oriented mosaic grains of 1-2 mm size. Surprisingly, the orientation of the telluride was identical (010) on both the (001) and (111) Ag parent films. It is suggested that the final orientation appears during the polymorphic phase transition while cooling to room temperature, regardless to Ag orientation, due to the lower surface energy of the (010) orientation of monoclinic phase nuclei. (Authors)

Quasicrystalline phase formation in the mechanically alloyed Al{sub 70}Cu{sub 20}Fe{sub 10}

Energy Technology Data Exchange (ETDEWEB)

Medeiros, S. N. de, E-mail: snm@dfi.uem.br; Cadore, S.; Pereira, H. A.; Santos, I. A.; Colucci, C. C.; Paesano, A. [Universidade Estadual de Maringa, Departamento de Fisica (Brazil)

2010-01-15

In the present work, the formation of the Al{sub 70}Cu{sub 20}Fe{sub 10} icosahedral phase by mechanical alloying the elemental powders in a high-energy planetary mill was investigated by X-ray diffraction and Moessbauer spectroscopy. It was verified that the sample milled for 80 h produces an icosahedral phase besides Al(Cu, Fe) solid solution ({beta}-phase) and Al{sub 2}Cu intermetallic phase. The Moessbauer spectrum for this sample was fitted with a distribution of quadrupole splitting, a doublet and a sextet, revealing the presence of the icosahedral phase, {beta}-phase and {alpha}-Fe, respectively. This compound is not a good hydrogen storage. The results of the X-ray diffraction and Moessbauer spectroscopy of the sample milled for 40 h and annealed at 623 deg. C for 16 h shows essentially single i-phase and tetragonal Al{sub 7}Cu{sub 2} Fe phase.

Mechanism of formation of perovskite phase and dielectric properties of Pb(Zn,Mg)1/3Nb2/3O3 ceramics prepared by columbite precursor routes

International Nuclear Information System (INIS)

Jang, H.M.; Cho, S.R.; Lee, K.M.

1995-01-01

The mechanism of formation of the perovskite phase and the dielectric properties of Pb(Zn,Mg) 1/3 Nb 2/3 O 3 (PZMN) ceramics were examined using two different types of columbite precursors, (Mg,Zn)Nb 2 O 6 (MZN) and MgNb 2 O 6 + ZnNb 2 O 6 (MN + ZN). The formation of perovskite phase in the PbO + MN + ZN system is characterized by an initial rapid formation of Mg-rich perovskite phase, followed by a sluggish formation of Zn-rich perovskite phase. On the other hand, due to the formation of pyrochlore phase of mixed divalent cations Pb 2-x (Zn,Mg) y Nb 2-y O 7-x-3y/2 , the pyrochlore/perovskite transformation in the PbO + MZN system proceeded uniformly with a spatial homogeneity. Further analysis suggested that the formation of perovskite phase is a diffusion-controlled process. The degree of diffuseness of the rhombohedral/cubic phase transition (DPT) is higher in the PbO + MN + ZN system than in the PbO + MZN specimen for T > T max (temperature of the dielectric permittivity maximum), indicating a broadened compositional distribution of the B-site cations in the PbO + MN + ZN system

Up-scaling, formative phases, and learning in the historical diffusion of energy technologies

International Nuclear Information System (INIS)

Wilson, Charlie

2012-01-01

The 20th century has witnessed wholesale transformation in the energy system marked by the pervasive diffusion of both energy supply and end-use technologies. Just as whole industries have grown, so too have unit sizes or capacities. Analysed in combination, these unit level and industry level growth patterns reveal some consistencies across very different energy technologies. First, the up-scaling or increase in unit size of an energy technology comes after an often prolonged period of experimentation with many smaller-scale units. Second, the peak growth phase of an industry can lag these increases in unit size by up to 20 years. Third, the rate and timing of up-scaling at the unit level is subject to countervailing influences of scale economies and heterogeneous market demand. These observed patterns have important implications for experience curve analyses based on time series data covering the up-scaling phases of energy technologies, as these are likely to conflate industry level learning effects with unit level scale effects. The historical diffusion of energy technologies also suggests that low carbon technology policies pushing for significant jumps in unit size before a ‘formative phase’ of experimentation with smaller-scale units are risky. - Highlights: ► Comparative analysis of energy technology diffusion. ► Consistent pattern of sequential formative, up-scaling, and growth phases. ► Evidence for conflation of industry level learning effects with unit level up-scaling. ► Implications for experience curve analyses and technology policy.

Effect of calcination routes on phase formation of BaTiO3 and their electronic and magnetic properties

Science.gov (United States)

Majumder, Supriyo; Choudhary, R. J.; Tripathi, M.; Phase, D. M.

2018-05-01

We have investigated the phase formation and correlation between electronic and magnetic properties of oxygen deficient BaTiO3 ceramics, synthesized by solid state reaction method, following different calcination paths. The phase analysis divulge that a higher calcination temperature above 1000° C is favored for tetragonal phase formation than the cubic phase. The core level X-ray photo electron spectroscopy measurements confirm the presence of oxygen vacancies and oxygen vacancy mediated Ti3+ states. As the calcination temperature and calcination time increases these oxygen vacancies and hence Ti3+ concentrations reduce in the sample. The temperature dependent magnetization curves suggest unexpected magnetic ordering, which may be due to the presence of unpaired electron at the t2g state (d1) of nearest-neighbor Ti atoms. In magnetization vs magnetic field isotherms, the regular decrease of saturation moment value with increasing calcination temperature and calcination time, can be discussed considering the amount of oxygen deficiency induced Ti3+ concentrations, present in the sample.

Phase formation in Mg-Sn-Si and Mg-Sn-Si-Ca alloys

Energy Technology Data Exchange (ETDEWEB)

Kozlov, A.; Groebner, J. [Institute of Metallurgy, Clausthal University of Technology, Robert-Koch-Str. 42, D-38678 Clausthal-Zellerfeld (Germany); Schmid-Fetzer, R., E-mail: schmid-fetzer@tu-clausthal.de [Institute of Metallurgy, Clausthal University of Technology, Robert-Koch-Str. 42, D-38678 Clausthal-Zellerfeld (Germany)

2011-02-17

Research highlights: > The solidification paths of ternary and quaternary alloys are analyzed in detail, using the tool of thermodynamic calculations. > The precipitation sequence of phases and their amounts compare well with the microstructure of alloys. > The most efficient comparison to the experimental thermal analysis data is done by calculation of the enthalpy variation with temperature. > The viability of a procedure for the selection of multicomponent key samples is demonstrated for the development of the Mg-Ca-Si-Sn phase diagram. - Abstract: Experimental work is done and combined with the Calphad method to generate a consistent thermodynamic description of the Mg-Ca-Si-Sn quaternary system, validated for Mg-rich alloys. The viability of a procedure for the selection of multicomponent key samples is demonstrated for this multicomponent system. Dedicated thermal analysis with DTA/DSC on sealed samples is performed and the microstructure of slowly solidified alloys is analyzed using SEM/EDX. The thermodynamic description and phase diagram of the ternary Mg-Si-Sn system, developed in detail also in this work, deviates significantly from a previous literature proposal. The phase formation in ternary and quaternary alloys is analyzed using the tool of thermodynamic equilibrium and Scheil calculations for the solidification paths and compared with present experimental data. The significant ternary/quaternary solid solubilities of pertinent intermetallic phases are quantitatively introduced in the quaternary Mg-Ca-Si-Sn phase diagram and validated by experimental data.

Heterogeneity-enhanced gas phase formation in shallow aquifers during leakage of CO2-saturated water from geologic sequestration sites

DEFF Research Database (Denmark)

Plampin, Michael R.; Lassen, Rune Nørbæk; Sakaki, Toshihiro

2014-01-01

sands. Soil moisture sensors were utilized to observe the formation of gas phase near the porous media interfaces. Results indicate that the conditions under which heterogeneity controls gas phase evolution can be successfully predicted through analysis of simple parameters, including the dissolved CO2......, it is important to understand the physical processes that CO2 will undergo as it moves through naturally heterogeneous porous media formations. Previous studies have shown that heterogeneity can enhance the evolution of gas phase CO2 in some cases, but the conditions under which this occurs have not yet been...... quantitatively defined, nor tested through laboratory experiments. This study quantitatively investigates the effects of geologic heterogeneity on the process of gas phase CO2 evolution in shallow aquifers through an extensive set of experiments conducted in a column that was packed with layers of various test...

Zirconium oxide crystal phase: The role of the pH and time to attain the final pH for precipitation of the hydrous oxide

International Nuclear Information System (INIS)

Srinivasan, R.; Harris, M.B.; Simpson, S.F.; De Angelis, R.J.; Davis, B.H.

1988-01-01

Precipitated hydrous zirconium oxide can be calcined to produce either a monoclinic or tetragonal product. It has been observed that the time taken to attain the final pH of the solution in contact with the precipitate plays a dominant role in determining the crystal structure of the zirconium oxide after calcination at 500 0 C. The dependence of crystal structure on the rate of precipitation is observed only in the pH range 7--11. Rapid precipitation in this pH range yields predominately monoclinic zirconia, whereas slow (8 h) precipitation produces the tetragonal phase. At pH of approximately 13.0, only the tetragonal phase is formed from both slowly and rapidly precipitated hydrous oxide. The present results, together with earlier results, show that both the pH of the supernatant liquid and the time taken to attain this pH play dominant roles in determining the crystal structure of zirconia that is formed after calcination of the hydrous oxide. The factors that determine the crystal phase are therefore imparted in a mechanism of precipitation that depends upon the pH, and it is inferred that it is the hydroxyl concentration that is the dominant factor

Influence of the selected alloy additions on limiting the phase formation in Cu-Zn alloys

Directory of Open Access Journals (Sweden)

J. Kozana

2010-01-01

Full Text Available Influence of the selected alloy additions into copper and zinc alloys was investigated in order to find out the possibility of limiting the precipitation of unfavourable phase . The observation of microstructures and strength tests were performed. The results of metallographic and strength investigations indicate positive influence of small amounts of nickel, cobalt or tellurium. The precise determination of the influence of the selected alloy additions on limiting the gamma phase formation will be the subject of further examinations.

The Genealogical Tree of Ethanol: Gas-phase Formation of Glycolaldehyde, Acetic Acid, and Formic Acid

Science.gov (United States)

Skouteris, Dimitrios; Balucani, Nadia; Ceccarelli, Cecilia; Vazart, Fanny; Puzzarini, Cristina; Barone, Vincenzo; Codella, Claudio; Lefloch, Bertrand

2018-02-01

Despite the harsh conditions of the interstellar medium, chemistry thrives in it, especially in star-forming regions where several interstellar complex organic molecules (iCOMs) have been detected. Yet, how these species are synthesized is a mystery. The majority of current models claim that this happens on interstellar grain surfaces. Nevertheless, evidence is mounting that neutral gas-phase chemistry plays an important role. In this paper, we propose a new scheme for the gas-phase synthesis of glycolaldehyde, a species with a prebiotic potential and for which no gas-phase formation route was previously known. In the proposed scheme, the ancestor is ethanol and the glycolaldehyde sister species are acetic acid (another iCOM with unknown gas-phase formation routes) and formic acid. For the reactions of the new scheme with no available data, we have performed electronic structure and kinetics calculations deriving rate coefficients and branching ratios. Furthermore, after a careful review of the chemistry literature, we revised the available chemical networks, adding and correcting several reactions related to glycolaldehyde, acetic acid, and formic acid. The new chemical network has been used in an astrochemical model to predict the abundance of glycolaldehyde, acetic acid, and formic acid. The predicted abundance of glycolaldehyde depends on the ethanol abundance in the gas phase and is in excellent agreement with the measured one in hot corinos and shock sites. Our new model overpredicts the abundance of acetic acid and formic acid by about a factor of 10, which might imply a yet incomplete reaction network.

Structural, electronic and optical properties of monoclinic Na2Ti3O7 from density functional theory calculations: A comparison with XRD and optical absorption measurements

International Nuclear Information System (INIS)

Araújo-Filho, Adailton A.; Silva, Fábio L.R.; Righi, Ariete; Silva, Mauricélio B. da; Silva, Bruno P.; Caetano, Ewerton W.S.; Freire, Valder N.

2017-01-01

Powder samples of bulk monoclinic sodium trititanate Na 2 Ti 3 O 7 were prepared carefully by solid state reaction, and its monoclinic P2 1 /m crystal structure and morphology were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM), respectively. Moreover, the sodium trititanate main energy band gap was estimated as E g =3.51±0.01 eV employing UV–Vis spectroscopy, which is smaller than the measured 3.70 eV energy gap published previously by other authors. Aiming to achieve a better understanding of the experimental data, density functional theory (DFT) computations were performed within the local density and generalized gradient approximations (LDA and GGA, respectively) taking into account dispersion effects through the scheme of Tkatchenko and Scheffler (GGA+TS). Optimal lattice parameters, with deviations relative to measurements Δa=−0.06 Å, Δb=0.02 Å, and Δc=−0.09 Å, were obtained at the GGA level, which was then used to simulate the sodium trititanate electronic and optical properties. Indirect band transitions have led to a theoretical gap energy value of about 3.25 eV. Our results, however, differ from pioneer DFT results with respect to the specific Brillouin zone vectors for which the indirect transition with smallest energy value occurs. Effective masses for electrons and holes were also estimated along a set of directions in reciprocal space. Lastly, our calculations revealed a relatively large degree of optical isotropy for the Na 2 Ti 3 O 7 optical absorption and complex dielectric function. - Graphical abstract: Monoclinic sodium trititanate Na2Ti3O7 was characterized by experiment and dispersion-corrected DFT calculations. An indirect gap of 3.5 eV is predicted, with heavy electrons and anisotropic holes ruling its conductivity. - Highlights: • Monoclinic Na2Ti3O7 was characterized by experiment (XRD, SEM, UV–Vis spectroscopy). • DFT GGA+TS optimized geometry and optoelectronic properties were

Local Cloudiness Development Forecast Based on Simulation of Solid Phase Formation Processes in the Atmosphere

Science.gov (United States)

Barodka, Siarhei; Kliutko, Yauhenia; Krasouski, Alexander; Papko, Iryna; Svetashev, Alexander; Turishev, Leonid

2013-04-01

Nowadays numerical simulation of thundercloud formation processes is of great interest as an actual problem from the practical point of view. Thunderclouds significantly affect airplane flights, and mesoscale weather forecast has much to contribute to facilitate the aviation forecast procedures. An accurate forecast can certainly help to avoid aviation accidents due to weather conditions. The present study focuses on modelling of the convective clouds development and thunder clouds detection on the basis of mesoscale atmospheric processes simulation, aiming at significantly improving the aeronautical forecast. In the analysis, the primary weather radar information has been used to be further adapted for mesoscale forecast systems. Two types of domains have been selected for modelling: an internal one (with radius of 8 km), and an external one (with radius of 300 km). The internal domain has been directly applied to study the local clouds development, and the external domain data has been treated as initial and final conditions for cloud cover formation. The domain height has been chosen according to the civil aviation forecast data (i.e. not exceeding 14 km). Simulations of weather conditions and local clouds development have been made within selected domains with the WRF modelling system. In several cases, thunderclouds are detected within the convective clouds. To specify the given category of clouds, we employ a simulation technique of solid phase formation processes in the atmosphere. Based on modelling results, we construct vertical profiles indicating the amount of solid phase in the atmosphere. Furthermore, we obtain profiles demonstrating the amount of ice particles and large particles (hailstones). While simulating the processes of solid phase formation, we investigate vertical and horizontal air flows. Consequently, we attempt to separate the total amount of solid phase into categories of small ice particles, large ice particles and hailstones. Also, we

Controlling phase formation during aluminium/steel Nd:YAG laser brazing

Directory of Open Access Journals (Sweden)

Rodriguez, L.

2006-12-01

Full Text Available The reduction of fuel consumption of internal combustion motors, imposed by the new anti-pollution and energy saving laws may be attained by reducing the weight of vehicles, introducing, for example, aluminium sections into the main steel car-body. Laser brazing is a process which can be used to perform such a junction. The main problem of welding this kind of materials combination with conventional processes is the potential formation of inter-metallic phases, which reduces the good performance of the joint. Laser brazing allows a very good control of the thermal development of the joint, with a limited precipitation of these brittle phases. This paper presents the results of a feasibility study made with ZnAl-30 as filler metal. The study shows that the type of configuration used for the assembly has a particular influence on the formation of brittle phases and consequently on the mechanical performance of the joint.

La reducción en el consumo de combustibles fósiles y las emergentes leyes mundiales anti-contaminación, obligan a prever una reducción en el peso de los vehículos de transporte. Esta condición se puede cumplir por ejemplo, introduciendo componentes de Aluminio en el cuerpo de la carrocería principal de acero de los mencionados vehículos. El principal problema que se presenta al realizar este tipo de ensamblaje es la formación de fases íntermetálicas frágiles que pueden comprometer el buen desenvolvimiento de la unión. La soldadura con rayo láser permite un buen control de calor aportado y una formación muy limitada de este tipo de fases. Este trabajo presenta los resultados preliminares de los estudios realizados en uniones soldadas con ZnAl-30 como material de aportación. El estudio muestra que el tipo de configuración utilizada para realizar la soldadura tiene una influencia importante sobre la posibilidad de formación de estas fases ínter-metálicas.

Third phase formation in the extraction of Th(NO{sub 3}){sub 4} by Tri-sec-butyl phosphate. A comparison with Tri-n-butyl phosphate

Energy Technology Data Exchange (ETDEWEB)

Chandrasekar, Aditi; Suresh, A.; Sivaraman, N. [Indira Gandhi Centre for Atomic Research, Kalpakkam (India). Chemistry Group

2017-06-01

Earlier studies carried out in our laboratory indicated that Tri-sec-butyl phosphate (TsBP) is a potential extractant for U/Th separation. Also, the third phase formation tendency of TsBP is lower compared to its isomers, Tri-n-butyl-phosphate (TBP) and Tri-iso-butyl phosphate (TiBP). In this context, the extraction and third phase formation behaviour of 1.1 M solutions of TiBP and TsBP in n-dodecane in the extraction of Th(IV) from 1 M HNO{sub 3} at 303 K over a wide range of Th concentrations were investigated in the present study and the results are compared with the literature data on TBP system. Concentrations of Th(IV) and HNO{sub 3} loaded in the organic phase before third phase formation (biphasic region) as well as in third phase and diluent-rich phase after third phase formation (triphasic region) were measured as a function of equilibrium aqueous phase Th(IV) concentration. The density of loaded organic phase was also measured at various Th(IV) concentrations. The extraction profiles in the biphasic region indicated that extraction of Th(IV) by TBP is higher than that of TiBP which in turn is higher than that of TsBP. Extractant concentration in the diluent-rich phase and third phase was measured for the triphasic region.

Phase recording for formation of holographic optical elements on silver-halide photographic emulsions

Science.gov (United States)

Ganzherli, Nina M.; Gulyaev, Sergey N.; Maurer, Irina A.; Chernykh, Dmitrii F.

2009-05-01

Holographic fabrication methods of regular and nonregular relief-phase structures on silver-halide photographic emulsions are considered. Methods of gelatin photodestruction under short-wave ultra-violet radiation and chemical hardening with the help of dichromated solutions were used as a technique for surface relief formation. The developed techniques permitted us to study specimens of holographic diffusers and microlens rasters with small absorption and high light efficiency.

Altering the cooling rate dependence of phase formation during rapid solidification in the Nd{sub 2}Fe{sub 14}B system

Energy Technology Data Exchange (ETDEWEB)

Branagan, D.J. [USDOE, Ames, IA (United States). Ames Lab.]|[Iowa State Univ. of Science and Technology, Ames, IA (United States). Dept. of Materials Science and Engineering; McCallum, R.W. [USDOE, Ames, IA (United States). Ames Lab.]|[Iowa State Univ. of Science and Technology, Ames, IA (United States). Dept. of Materials Science and Engineering

1995-04-26

In order to evaluate the effects of additions on the solidification behavior of Nd{sub 2}Fe{sub 14}B, a stoichiometric alloy was modified with elemental additions of Ti or C and a compound addition of Ti with C. For each alloy, a series of wheel speed runs was undertaken, from which the optimum wheel speeds and optimum energy products were determined. On the BH{sub max} versus wheel speed plots, regions were identified in order to analyze the changes with cooling rates leading to phase formation brought about by the alloy modifications. The compilation of the regional data of the modified alloys showed their effects on altering the cooling rate dependence of phase formation. It was found that the regions of properitectic iron formation, glass formation, and the optimum cooling rate can be changed by more than a factor of two through appropriate alloying additions. The effects of the alloy modifications can be visualized in a convenient fashion through the use of a model continuous cooling transformation (CCT) diagram which represents phase formation during the solidification process under continuous cooling conditions for a wide range of cooling rates from rapid solidification to equilibrium cooling. ((orig.)).

Investigation on the formation of a third phase in the extraction of Pu(IV) nitrate with tributyl phosphate

International Nuclear Information System (INIS)

Yu Enjiang; Liu Liming; Huang Huaian

1986-01-01

The formation of a third phase is studied in the system Pu(IV) nitratenitric acid-TBP-alkane diluent (or kerosine). The maximum concentration (solubility, S Pu ) of Pu(IV) in the equilibrium organic phase at which still no third phase is formed is measured as a function of the nitric acid concentration in the equilibrium aqueous phase C H , the temperature, and the molecular size of n-alkane duluent. Results show that maxima of S Pu at 6 to 7 M nitric acid are observed at 17 deg C, 26 deg C and 35 deg C while not at 40 deg C. Minima on the S Pu vs. C H curves at 0.5 to 2 M mitric acid have been observed at 17 deg C and 26 deg C. It is found that the molecular size of n-alkane diluents has a very pronounced effect on S Pu . The effect of aqueous equilibrium Pu(IV) concentration on the formation of a third phase is investigated, when the equilibrium HNO 3 concentration is 3.5 M. It is shown that the plutonium concentration of the third phase is increased with increasing aqueous equilibrium Pu(IV) concentration. The effect of the addition of lauryl alcohol on the S Pu is preliminarily studied

Characterisation of iron inclusion during the formation of calcium sulfoaluminate phase

International Nuclear Information System (INIS)

Idrissi, M.; Diouri, A.; Damidot, D.; Greneche, J.M.; Talbi, M. Alami; Taibi, M.

2010-01-01

The iron distribution among the sulfoaluminate clinker phases and its ability to enter the calcium sulfoaluminate lattice in solid solution can have a significant influence on manufacturing process and reactivity of calcium sulfoaluminate (CSA) cements. X-ray diffraction (XRD) analysis, Moessbauer spectroscopy, scanning electron microscopy (SEM) equipped with an energy dispersive X-ray analysis system (EDAX) and infrared spectroscopy were used to identify the mineralogical conditions of iron inclusion during the formation of calcium sulfoaluminate (C 4 A 3 S) phase from different mixtures in the CaO-Al 2 O 3 -Fe 2 O 3 -SO 3 system. The mixtures, heated in a laboratory electric oven, contained stoichiometric amounts of reagent grade CaCO 3 , Al 2 O 3 , Fe 2 O 3 and CaSO 4 .2H 2 O for the synthesis of Ca 4 Al (6- 2x) Fe 2x SO 16 , where x, comprised between 0 and 3, is the mole number of Al 2 O 3 substituted by Fe 2 O 3 . With x increasing from 0 to 1.5, both the iron content of C 4 A 3 S phase and the amounts of side components such as C 2 F and CS increased. For x values included in the range of 1.5-3.0, at temperatures higher than 1200 o C, melting phenomena were observed and, instead of the C 4 A 3 S solid solution, ferritic phases and anhydrite were formed.

Experimental study of the oxide film structural phase state in the E635 and E110 alloys

International Nuclear Information System (INIS)

Shevyakov, A. Yu.; Shishov, V. N.; Novikov, V. V.

2013-01-01

The microstructure, phase and element compositions of oxide films of E110 (Zr-1%Nb) and E635 (Zr-1%Nb-0,35%Fe-1,2%Sn) alloys after autoclave tests in pure water had been studied by the method of transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDS). TEM investigations of oxide film structure were carried on different oxide layers according to their thickness (near interface of “metal-oxide”, in central part of the oxide film and near outer surface) and in cross-section. The results of the tests show that oxide films of the alloys have different microstructure (grain size, fraction of tetragonal phase, content of defects, etc) and the phase compositions. The crystal structure of oxide films is mainly monoclinic, however, at the “metal-oxide” interface there are a significant fraction of the tetragonal phase. Researching of oxides on different stages of oxidation allow us to determine the kinetics of the second phase precipitate structure change: a) in E635 alloy at early oxidation stages of the amorphization process of the Laves phase precipitates begins with decreasing the content of iron and niobium; b) in E110 alloy the amorphization process of β-Nb precipitates begins at a later stage of oxidation. The influence of changes of the crystal structure and the chemical composition of the second phase precipitates on protective properties of the oxides had been determined. Researching of alloying element redistribution in E635 alloy oxide film shows that iron and niobium are concentrated in pores. Increased porosity of the E635 alloy oxide films at a later oxidation stage, in comparison with the E110 alloy, shows the influence of change composition and subsequent dissolution of the Laves phase particles on the pore formation in the oxide. (authors)

Investigation of phase stability in the scandia-zirconia; Investigacao da estabilidade de fases da zirconia-escandia

Energy Technology Data Exchange (ETDEWEB)

Grosso, Robson Lopes

2016-11-01

In this work, the phase stability of scandia-zirconia (ScSZ) system was investigated by the thermodynamic study of nanoparticles, within the range of 0 to 20 mol% Sc{sub 2}O{sub 3}, and by codoping of ZrO{sub 2}-10 mol% Sc{sub 2}O{sub 3} (10ScSZ) with Dy{sub 2}O{sub 3} and Nb{sub 2}O{sub 5}. The phase stability of ScSZ was evaluated based on thermodynamic data collected by water adsorption microcalorimetry and high temperature oxide melt solution. Nanostructured zirconia-scandia solid solutions were synthesized by coprecipitation method. Thermodynamic data were determined for ScSZ polymorph (monoclinic, tetragonal, cubic, rhombohedral β and γ) found by X-ray diffraction. This systemic work resulted in an unprecedented phase diagram at the nanoscale of particle size-composition. The effects of additives on 10ScSZ were investigated aiming to stabilize the cubic (c) structure at room temperature and to suppress the characteristic cubic-rhombohedral β phase transformation. Compositions were prepared by coprecipitation and solid state reaction. Materials were sintered by conventional and spark plasma sintering. Full stabilization of the cubic phase was attained by 1 mol% Dy{sub 2}O{sub 3} and 0.5 mol% Nb{sub 2}O{sub 5} additions. The smallest Nb{sub 2}O{sub 5} content required for cubic phase stabilization was attributed to liquid phase formation during sintering and to small ionic radius of Nb{sup 5+}. Results of high temperature X-ray diffraction and thermal analysis show suppression of the c-β transformation. Samples containing 0.5 mol% Nb{sub 2}O{sub 5} show total ionic conductivity similar to 10ScSZ without additives within a broad temperature range with high stability during 170 h at 600 °C. (author)

Influence of Homogenization and Micro/Nano Source of Starting Powders on Format Ion of the Single YAP Phase

Directory of Open Access Journals (Sweden)

Michalik D.

2016-12-01

Full Text Available Manufacturing high purity polycrystalline YAlO3 (YAP ceramics could replace monocrystalline YAP thus recently it is an interesting task for low cost producers of scintillators. The paper presents influence of different source of initial oxide powders (micro/nano powders of Y2O3 and Al2O3 and the method of their homogenization on the formation of a YAP phase. The solid state reaction method was used to prepare YAP powder or ceramic pellets. After preheating, all samples in the form of powders and pellets were heat-treated in the temperature range of 1050-1650 °C. DTA method was applied for examination of the phase crystallization in the tested system. X-ray diffraction method (XRD was used for characterization of the phase composition. X-ray microanalysis (EDS was used to control homogeneity in the small areas. Morphology of the resultant samples are presented on SEM pictures. The results show a significant influence of the starting powders on the homogeneity, purity and temperature of formation of the main phase.

High-pressure phase transition of alkali metal-transition metal deuteride Li2PdD2

Science.gov (United States)

Yao, Yansun; Stavrou, Elissaios; Goncharov, Alexander F.; Majumdar, Arnab; Wang, Hui; Prakapenka, Vitali B.; Epshteyn, Albert; Purdy, Andrew P.

2017-06-01

A combined theoretical and experimental study of lithium palladium deuteride (Li2PdD2) subjected to pressures up to 50 GPa reveals one structural phase transition near 10 GPa, detected by synchrotron powder x-ray diffraction, and metadynamics simulations. The ambient-pressure tetragonal phase of Li2PdD2 transforms into a monoclinic C2/m phase that is distinct from all known structures of alkali metal-transition metal hydrides/deuterides. The structure of the high-pressure phase was characterized using ab initio computational techniques and from refinement of the powder x-ray diffraction data. In the high-pressure phase, the PdD2 complexes lose molecular integrity and are fused to extended [PdD2]∞ chains. The discovered phase transition and new structure are relevant to the possible hydrogen storage application of Li2PdD2 and alkali metal-transition metal hydrides in general.

Formation of Microcracks During Micro-Arc Oxidation in a Phytic Acid-Containing Solution on Two-Phase AZ91HP

Science.gov (United States)

Zhang, R. F.; Chang, W. H.; Jiang, L. F.; Qu, B.; Zhang, S. F.; Qiao, L. P.; Xiang, J. H.

2016-04-01

Micro-arc oxidation (MAO) is an effective method to produce ceramic coatings on magnesium alloys and can considerably improve their corrosion resistance. The coating properties are closely related with microcracks, which are always inevitably developed on the coating surface. In order to find out the formation and development regularity of microcracks, anodic coatings developed on two-phase AZ91HP after different anodizing times were fabricated in a solution containing environmentally friendly organic electrolyte phytic acid. The results show that anodic film is initially developed on the α phase. At 50 s, anodic coatings begin to develop on the β phase, evidencing the formation of a rough area. Due to the coating successive development, the microcracks initially appear at the boundary between the initially formed coating on the α phase and the subsequently developed coating on the β phase. With the prolonging treatment time, the microcracks near the β phase become evident. After treating for 3 min, the originally rough area on the β phase disappears and the coatings become almost uniform with microcracks randomly distributed on the sample surface. Inorganic phosphates are found in MAO coatings, suggesting that phytate salts are decomposed due to the high instantaneous temperature on the sample surface resulted from spark discharge.

Predictive calculation of phase formation in Al-rich Al-Zn-Mg-Cu-Sc-Zr alloys using a thermodynamic Mg-alloy database

International Nuclear Information System (INIS)

Groebner, J.; Rokhlin, L.L.; Dobatkina, T.V.; Schmid-Fetzer, R.

2007-01-01

Three series of Al-rich alloys in the system Al-Zn-Mg-Cu-Sc-Zr and the subsystems Al-Zn-Mg-Cu-Sc and Al-Zn-Mg-Sc were studied by thermodynamic calculations. Phase formation was compared with experimental data obtained by DTA and microstructural analysis. Calculated phase diagrams, phase amount charts and enthalpy charts together with non-equilibrium calculations under Scheil conditions reveal significant details of the complex phase formation. This enables consistent and correct interpretation of thermal analysis data. Especially the interpretation of liquidus temperature and primary phase is prone to be wrong without using this tool of computational thermodynamics. All data are predictions from a thermodynamic database developed for Mg-alloys and not a specialized Al-alloy database. That provides support for a reasonable application of this database for advanced Mg-alloys beyond the conventional composition ranges

Predictive calculation of phase formation in Al-rich Al-Zn-Mg-Cu-Sc-Zr alloys using a thermodynamic Mg-alloy database

Energy Technology Data Exchange (ETDEWEB)

Groebner, J. [Institute of Metallurgy, Clausthal University of Technology, Robert-Koch Strasse 42, D-38678 Clausthal-Zellerfeld (Germany); Rokhlin, L.L. [Baikov Institute of Metallurgy and Materials Science, Leninsky prosp. 49, 119991 GSP-1, Moscow (Russian Federation); Dobatkina, T.V. [Baikov Institute of Metallurgy and Materials Science, Leninsky prosp. 49, 119991 GSP-1, Moscow (Russian Federation); Schmid-Fetzer, R. [Institute of Metallurgy, Clausthal University of Technology, Robert-Koch Strasse 42, D-38678 Clausthal-Zellerfeld (Germany)]. E-mail: schmid-fetzer@tu-clausthal.de

2007-05-16

Three series of Al-rich alloys in the system Al-Zn-Mg-Cu-Sc-Zr and the subsystems Al-Zn-Mg-Cu-Sc and Al-Zn-Mg-Sc were studied by thermodynamic calculations. Phase formation was compared with experimental data obtained by DTA and microstructural analysis. Calculated phase diagrams, phase amount charts and enthalpy charts together with non-equilibrium calculations under Scheil conditions reveal significant details of the complex phase formation. This enables consistent and correct interpretation of thermal analysis data. Especially the interpretation of liquidus temperature and primary phase is prone to be wrong without using this tool of computational thermodynamics. All data are predictions from a thermodynamic database developed for Mg-alloys and not a specialized Al-alloy database. That provides support for a reasonable application of this database for advanced Mg-alloys beyond the conventional composition ranges.

The gas chimney formation during the steam explosion premixing phase

International Nuclear Information System (INIS)

Leskovar, M.

2001-01-01

The crucial part in isothermal premixing experiment simulation is the correct prediction of the gas chimney, which forms when the spheres penetrate into water. The first simulation results with the developed original combined multiphase model showed that the gas chimney starts to close at the wrong place at the top of the chimney and not in the middle, like it was observed in the experiments. To find the physical explanation for this identified weakness of our numerical model a comprehensive parametric analysis (mesh size, initial water-air surface thickness, water density, momentum coupling starting position) has been performed. It was established that the reason for the unphysical gas chimney closing at the top could be the gradual air-water density transition in the experiment model, since there is due to the finite differences description always a transition layer with intermediate phases density over the pure water phase. It was shown that this difference between our numerical model and the experiment can be somewhat compensated if the spheres interfacial drag coefficient at the upmost mesh plane of the unphysical air-water transition layer is artificially risen. On this way a more correct gas chimney formation can be obtained.(author)

Kaempferol Inhibits the Primary Attachment Phase of Biofilm Formation in Staphylococcus aureus.

Science.gov (United States)

Ming, Di; Wang, Dacheng; Cao, Fengjiao; Xiang, Hua; Mu, Dan; Cao, Junjie; Li, Bangbang; Zhong, Ling; Dong, Xiaoyun; Zhong, Xiaobo; Wang, Lin; Wang, Tiedong

2017-01-01

The ability to form biofilms on surfaces makes Staphylococcus aureus the main pathogenic factor in implanted medical device infections. The aim of this study was to discover a biofilm inhibitor distinct from the antibiotics used to prevent infections resulting from S. aureus biofilms. Here, we describe kaempferol, a small molecule with anti-biofilm activity that specifically inhibited the formation of S. aureus biofilms. Crystal violet (CV) staining and fluorescence microscopy clearly showed that 64 μg/ml kaempferol inhibited biofilm formation by 80%. Meanwhile, the minimum inhibitory concentration (MIC) and growth curve results indicated that kaempferol had no antibacterial activity against the tested bacterial strain. Kaempferol inhibited the primary attachment phase of biofilm formation, as determined by a fibrinogen-binding assay. Moreover, a fluorescence resonance energy transfer (FRET) assay and quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) analyses revealed that kaempferol reduced the activity of S. aureus sortaseA (SrtA) and the expression of adhesion-related genes. Based on these results, kaempferol provides a starting point for the development of novel anti-biofilm drugs, which may decrease the risk of bacterial drug resistance, to prevent S. aureus biofilm-related infections.

Formation of {1 0 0} textured columnar grain structure in a non-oriented electrical steel by phase transformation

Energy Technology Data Exchange (ETDEWEB)

Xie, Li; Yang, Ping, E-mail: yangp@mater.ustb.edu.cn; Zhang, Ning; Zong, Cui; Xia, Dongsheng; Mao, Weimin

2014-04-01

This study confirms the effect of anisotropic strain energy on the formation of {1 0 0} textured columnar grain structure induced by temperature gradient during γ to α phase transformation in pure hydrogen atmosphere. Results indicate that high temperature gradient in pure hydrogen atmosphere induces a significant strain energy difference across grain boundaries during γ to α phase transformation, leading to the formation of {1 0 0} texture with columnar grains. Given its simplicity in processing and its ability to obtain good texture-related magnetic properties, the proposed approach is helpful to the development of new types of non-oriented electrical steel. - Highlights: • A strong {1 0 0} texture with columnar grains was obtained. • Good texture and magnetic properties are attributed to the anisotropic strain energy. • The anisotropy in elastic strain energy was induced by the temperature gradient. • The phase transformation rate affects columnar grain morphology.

L1{sub 0} phase formation in ternary FePdNi alloys

Energy Technology Data Exchange (ETDEWEB)

Montes-Arango, A.M. [Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA 02115 (United States); Bordeaux, N.C. [Department of Chemical Engineering, Northeastern University, Boston, MA 02115 (United States); Liu, J.; Barmak, K. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027 (United States); Lewis, L.H., E-mail: lhlewis@neu.edu [Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA 02115 (United States); Department of Chemical Engineering, Northeastern University, Boston, MA 02115 (United States)

2015-11-05

Metallurgical routes to highly metastable phases are required to access new materials with new functionalities. To this end, the stability of the tetragonal chemically ordered L1{sub 0} phase in the ternary Fe–Pd–Ni system is quantified to provide enabling information concerning synthesis of L1{sub 0}-type FeNi, a highly attractive yet highly elusive advanced permanent magnet candidate. Fe{sub 50}Pd{sub 50−x}Ni{sub x} (x = 0–7 at%) samples were arc-melted and annealed at 773 K (500 °C) for 100 h to induce formation of the chemically ordered L1{sub 0} phase. Coupled calorimetry, structural and magnetic investigations allow determination of an isothermal section of the ternary Fe–Pd–Ni phase diagram featuring a single phase L1{sub 0} region near the FePd boundary for x < 6 at%. It is demonstrated that increased Ni content in Fe{sub 50}Pd{sub 50−x}Ni{sub x} alloys systematically decreases the order-disorder transition temperature, resulting in a lower thermodynamic driving force for the ordering phase transformation. The Fe{sub 50}Pd{sub 50−x}Ni{sub x} L1{sub 0} → fcc disordering transformation is determined to occur via a two-step process, with compositionally-dependent enthalpies and transition temperatures. These results highlight the need to investigate ternary alloys with higher Ni content to determine the stability range of the L1{sub 0} phase near the FeNi boundary, thereby facilitating kinetic access to the important L1{sub 0} FeNi ferromagnetic phase. - Highlights: • Chemical ordering in FePdNi enhances intrinsic and extrinsic magnetic properties. • 773 K annealed FePdNi alloys studied show a stable L1{sub 0} phase for Ni ≤ 5.2 at%. • Chemical disordering in FePdNi occurs by a previously unreported two-step process. • Ni additions to FePd dramatically decrease the chemical order-disorder temperature. • The chemical-ordering transformation kinetics are greatly affected by Ni content.

Organic charge transfer phase formation in thin films of the BEDT-TTF/TCNQ donor-acceptor system

DEFF Research Database (Denmark)

Solovyeva, Vita; Keller, K.; Huth, M.

2009-01-01

We have performed charge transfer phase formation studies on the donor/acceptor system bis-(ethylendithio)tetrathiafulvalene (BEDT-TTF)/tetracyanoquinodimethane,(TCNQ) by means of physical vapor deposition. We prepared donor/acceptor bilayer structures on glass and Si(100)/SiO substrates held...

Cement Formation

DEFF Research Database (Denmark)

Telschow, Samira; Jappe Frandsen, Flemming; Theisen, Kirsten

2012-01-01

Cement production has been subject to several technological changes, each of which requires detailed knowledge about the high multiplicity of processes, especially the high temperature process involved in the rotary kiln. This article gives an introduction to the topic of cement, including...... an overview of cement production, selected cement properties, and clinker phase relations. An extended summary of laboratory-scale investigations on clinkerization reactions, the most important reactions in cement production, is provided. Clinker formations by solid state reactions, solid−liquid and liquid......−liquid reactions are discussed, as are the influences of particles sizes on clinker phase formation. Furthermore, a mechanism for clinker phase formation in an industrial rotary kiln reactor is outlined....

Crystal structure, equation of state, and elasticity of hydrous aluminosilicate phase, topaz-OH (Al2SiO4(OH)2) at high pressures

Science.gov (United States)

Mookherjee, Mainak; Tsuchiya, Jun; Hariharan, Anant

2016-02-01

We examined the equation of state and high-pressure elasticity of the hydrous aluminosilicate mineral topaz-OH (Al2SiO4(OH)2) using first principles simulation. Topaz-OH is a hydrous phase in the Al2O3-SiO2-H2O (ASH) ternary system, which is relevant for the mineral phase relations in the hydrated sedimentary layer of subducting slabs. Based on recent neutron diffraction experiments, it is known that the protons in the topaz-OH exhibit positional disorder with half occupancy over two distinct crystallographic sites. In order to adequately depict the proton environment in the topaz-OH, we examined five crystal structure models with distinct configuration for the protons in topaz-OH. Upon full geometry optimization we find two distinct space group, an orthorhombic Pbnm and a monoclinic P21/c for topaz-OH. The topaz-OH with the monoclinic P21/c space group has a lower energy compared to the orthorhombic Pbmn space group symmetry. The pressure-volume results for the monoclinic topaz-OH is well represented by a third order Birch-Murnaghan formulation, with V0mon = 348.63 (±0.04) Å3, K0mon = 164.7 (±0.04) GPa, and K0mon = 4.24 (±0.05). The pressure-volume results for the orthorhombic topaz-OH is well represented by a third order Birch-Murnaghan formulation, with V0orth = 352.47 (±0.04) Å3, K0orth = 166.4 (±0.06) GPa, and K0orth = 4.03 (±0.04). While the bulk moduli are very similar for both the monoclinic and orthorhombic topaz-OH, the shear elastic constants and the shear moduli are very sensitive to the position of the proton, orientation of the O-H dipole, and the space group symmetry. The S-wave anisotropy for the orthorhombic and monoclinic topaz-OH are also quite distinct. In the hydrated sedimentary layer of subducting slabs, transformation of a mineral assemblage consisting of coesite (SiO2) and diaspore (AlOOH) to topaz-OH (Al2SiO4(OH)2) is likely to be accompanied by an increase in density, compressional velocity, and shear wave velocity. However

Effect of the Heusler phase formation on the magnetic behavior of the Cu–10 wt.%Mn alloy with Al and Ag additions

Energy Technology Data Exchange (ETDEWEB)

Carvalho, T.M., E-mail: thaisa.mary@gmail.com [Instituto de Química – UNESP, Caixa Postal 355, 14801-970 Araraquara, SP (Brazil); Adorno, A.T.; Santos, C.M.A. [Instituto de Química – UNESP, Caixa Postal 355, 14801-970 Araraquara, SP (Brazil); Silva, R.A.G. [Departamento de Ciências Exatas e da Terra – UNIFESP, 09972-270 Diadema, SP (Brazil); Magnani, M. [Instituto de Química – UNESP, Caixa Postal 355, 14801-970 Araraquara, SP (Brazil)

2015-09-15

Highlights: • The presence of the Cu{sub 2}MnAl phase was observed in annealed alloys. • Al and Ag additions shift the equilibrium concentration to higher Al values. • There is a correlation between the Ag-rich phase and the Cu{sub 2}MnAl phase. - Abstract: In this work, the formation of the Cu{sub 2}AlMn Heusler phase and its influence on the magnetic behavior of the Cu–Mn–Al–Ag alloys in the range of 8–10 wt.% of aluminum and 2–4 wt.% of silver were studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and saturation magnetization measurements at 4 K. The results showed that there is a correlation between the presence of the Ag-rich phase and the formation of the Cu{sub 2}MnAl phase.

Ab initio molecular dynamics study of pressure-induced phase transition in ZnS

International Nuclear Information System (INIS)

Martinez, Israel; Durandurdu, Murat

2006-01-01

The pressure-induced phase transition in zinc sulfide is studied using a constant-pressure ab initio technique. The reversible phase transition from the zinc-blende structure to a rock-salt structure is successfully reproduced through the simulations. The transformation mechanism at the atomistic level is characterized and found to be due to a monoclinic modification of the simulation cell, similar to that obtained in SiC. This observation supports the universal transition state of high-pressure zinc-blende to rock-salt transition in semiconductor compounds. We also study the role of stress deviations on the transformation mechanism and find that the system follows the same transition pathway under nonhydrostatic compressions as well

High-pressure high-temperature phase diagram of organic crystal paracetamol

Science.gov (United States)

Smith, Spencer J.; Montgomery, Jeffrey M.; Vohra, Yogesh K.

2016-01-01

High-pressure high-temperature (HPHT) Raman spectroscopy studies have been performed on the organic crystal paracetamol in a diamond anvil cell utilizing boron-doped heating diamond anvil. Isobaric measurements were conducted at pressures up to 8.5 GPa and temperature up to 520 K in five different experiments. Solid state phase transitions from monoclinic Form I  →  orthorhombic Form II were observed at various pressures and temperatures as well as transitions from Form II  →  unknown Form IV. The melting temperature for paracetamol was observed to increase with increasing pressures to 8.5 GPa. This new data is combined with previous ambient temperature high-pressure Raman and x-ray diffraction data to create the first HPHT phase diagram of paracetamol.

High-pressure high-temperature phase diagram of organic crystal paracetamol

International Nuclear Information System (INIS)

Smith, Spencer J; Montgomery, Jeffrey M; Vohra, Yogesh K

2016-01-01

High-pressure high-temperature (HPHT) Raman spectroscopy studies have been performed on the organic crystal paracetamol in a diamond anvil cell utilizing boron-doped heating diamond anvil. Isobaric measurements were conducted at pressures up to 8.5 GPa and temperature up to 520 K in five different experiments. Solid state phase transitions from monoclinic Form I  →  orthorhombic Form II were observed at various pressures and temperatures as well as transitions from Form II  →  unknown Form IV. The melting temperature for paracetamol was observed to increase with increasing pressures to 8.5 GPa. This new data is combined with previous ambient temperature high-pressure Raman and x-ray diffraction data to create the first HPHT phase diagram of paracetamol. (paper)