Tunneling spectroscopy of heavily underdoped crystals of Bi2Sr2CaCu2O8+δ

International Nuclear Information System (INIS)

Ozyuzer, L.; Zasadzinski, J.F.; Miyakawa, N.; Kendziora, C.; Jian, S.; Hinks, D. G.; Gray, K.E.

2000-01-01

Crystals of Bi 2 Sr 2 CaCu 2 O 8+δ with optimal Tc = 95 K have been underdoped using two different methods and the superconducting gaps have been obtained by tunneling. In some cases, three different tunneling geometries have been utilized: point contact, STM and break junctions. The first doping method involves control of the oxygen content by annealing in various partial pressures of oxygen. These crystals exhibit a narrow spread of gap values over a wide doping range from overdoped (Tc = 56 K) to underdoped with Tc = 70 K. However, for underdoped crystals with Tc midpoints in the range 25 K--63 K, there is a dramatic increase in the spread of gap values which may signal the development of static phase separation of either chemical or electronic origin. To avoid possible chemical phase separation, the authors have explored another doping procedure which incorporates Dy substitution on the Ca site. These crystals exhibit a relatively narrow superconducting transition width and some preliminary tunneling spectra will be presented

U(1) x SU(2) Chern-Simons gauge theory of underdoped cuprate superconductors

International Nuclear Information System (INIS)

Marchetti, P.A.; Su Zhao-Bin; Yu Lu

1998-05-01

The Chern-Simons bosonization with U(1)xSU(2) gauge field is applied to the 2-D t-J model in the limit t>>J, to study the normal state properties of underdoped cuprate superconductors. We prove the existence of an upper bound on the partition function for holons in a spinon background, and we find the optimal spinon configuration saturating the upper bound on average - a coexisting flux phase and s+id-like RVB state. After neglecting the feedback of holon fluctuations on the U(1) field B and spinon fluctuations on the SU(2) field V, the holon field is a fermion and the spinon field is a hard-core boson. Within this approximation we show that the B field produces a π flux phase for the holons, converting them into Dirac-like fermions, while the V field, taking into account the feedback of holons produces a gap for the spinons vanishing in the zero doping limit. The nonlinear σ-model with a mass term describes the crossover from the short-ranged antiferromagnetic (AF) state in doped samples to long range AF order in reference compounds. Moreover, we derive a low-energy effective action in terms of spinons holons and a self-generated U(1) gauge field. Neglecting the gauge fluctuations, the holons are described by the Fermi liquid theory with a Fermi surface consisting of 4 ''half-pockets'' centered at (+-π/2,+-π/2) and one reproduces the results for the electron spectral function obtained in the mean field approximation, in agreement with the photoemission data on underdoped cuprates. The gauge fluctuations are not confining due to coupling to holons, but nevertheless yield an attractive interaction between spinons and holons leading to a bound state with electron quantum numbers. The renormalisation effects due to gauge fluctuations give rise to non-Fermi liquid behaviour for the composite electron, in certain temperature range showing the linear in T resistivity. This formalism provides a new interpretation of the spin gap in the underdoped superconductors

Superconductivity and fluctuations in Ba_1_–_pK_pFe_2As_2 and Ba(Fe_1_–_nCo_n)_2As_2

International Nuclear Information System (INIS)

Böhm, T.; Hosseinian Ahangharnejhad, R.; Technical University of Munich, Garching

2016-01-01

In this paper, we study the interplay of fluctuations and superconductivity in BaFe_2As_2 (Ba-122) compounds with Ba and Fe substituted by K (p doping) and Co (n doping), respectively. To this end, we measured electronic Raman spectra as a function of polarization and temperature. We observe gap excitations and fluctuations for all doping levels studied. The response from fluctuations is much stronger for Co substitution and, according to the selection rules and the temperature dependence, originates from the exchange of two critical spin fluctuations with characteristic wave vectors (±π,0) and (0,±π). At 22% K doping (p = 0.22), we find the same selection rules and spectral shape for the fluctuations but the intensity is smaller by a factor of 5. Since there exists no nematic region above the orthorhombic spin-density-wave (SDW) phase, the identification of the fluctuations via the temperature dependence is not possible. The gap excitations in the superconducting state indicate strongly anisotropic near-nodal gaps for Co substitution which make the observation of collective modes difficult. The variation with doping of the spectral weights of the A_1_g and B_1_g gap features does not support the influence of fluctuations on Cooper pairing. Thus, the observation of Bardasis–Schrieffer modes inside the nearly clean gaps on the K-doped side remains the only experimental evidence for the relevance of fluctuations for pairing.

Tunneling spectroscopy of heavily underdoped crystals of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}

Energy Technology Data Exchange (ETDEWEB)

Ozyuzer, L.; Zasadzinski, J. F.; Miyakawa, N.; Kendziora, C.; Jian, S.; Hinks, D. G.; Gray, K. E.

2000-02-17

Crystals of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} with optimal {Tc} = 95 K have been underdoped using two different methods and the superconducting gaps have been obtained by tunneling. In some cases, three different tunneling geometries have been utilized: point contact, STM and break junctions. The first doping method involves control of the oxygen content by annealing in various partial pressures of oxygen. These crystals exhibit a narrow spread of gap values over a wide doping range from overdoped ({Tc} = 56 K) to underdoped with {Tc} = 70 K. However, for underdoped crystals with {Tc} midpoints in the range 25 K--63 K, there is a dramatic increase in the spread of gap values which may signal the development of static phase separation of either chemical or electronic origin. To avoid possible chemical phase separation, the authors have explored another doping procedure which incorporates Dy substitution on the Ca site. These crystals exhibit a relatively narrow superconducting transition width and some preliminary tunneling spectra will be presented.

Uniaxial-strain mechanical detwinning of CaFe2As2 and BaFe2As2 crystals: Optical and transport study

International Nuclear Information System (INIS)

Tanatar, M.A.; Blomberg, E.C.; Kreyssig, A.; Kim, M.G.; Ni, N.; Thaler, A.; Bud'ko, S.L.; Canfield, P.C.; Goldman, A.I.; Mazin, I.I.; Prozorov, R.

2010-01-01

The parent compounds of iron-arsenide superconductors, AFe 2 As 2 (A=Ca, Sr, Ba), undergo a tetragonal to orthorhombic structural transition at a temperature T TO in the range 135-205 K depending on the alkaline-earth element. Below T TO the free standing crystals split into equally populated structural domains, which mask intrinsic, in-plane, anisotropic properties of the materials. Here we demonstrate a way of mechanically detwinning CaFe 2 As 2 and BaFe 2 As 2 . The detwinning is nearly complete, as demonstrated by polarized light imaging and synchrotron x-ray measurements, and reversible, with twin pattern restored after strain release. Electrical resistivity measurements in the twinned and detwinned states show that resistivity, ρ, decreases along the orthorhombic a o axis but increases along the orthorhombic b o axis in both compounds. Immediately below T TO the ratio ρ bo /ρ ao = 1.2 and 1.5 for Ca and Ba compounds, respectively. Contrary to CaFe 2 As 2 , BaFe 2 As 2 reveals an anisotropy in the nominally tetragonal phase, suggesting that either fluctuations play a larger role above T TO in BaFe 2 As 2 than in CaFe 2 As 2 or that there is a higher temperature crossover or phase transition.

Mass spectrometric determination of stability of gaseous BaMoO2, Ba2MoO4, Ba2MoO5, Ba2Mo2O8 molecules

International Nuclear Information System (INIS)

Kudin, L.S.; Balduchchi, Dzh.; Dzhil'i, G.; Gvido, M.

1982-01-01

During the mass spectrometric investigation of BaCrO 4 evaporation Cr + , Ba + , BaO + main ions are recorded as well as BaMoO 4 + , BaMoO 3 + , BaMoO 2 + , BaMoO + , BaMoO 4 + , Ba 2 MoO 5 + , BaMo 2 O 8 + ions - the products of ionization of three-component (Ba, Mo, M) molecules, forming as a result of substance chemical interaction with the material of an effusion cell (Mo). Heats of formation of BaMoO 2 , Ba 2 MoO 4 , Ba 2 MoO 5 and Ba 2 Mo 2 O 8 molecules which constituted - 577+-70, -1343+-115, -1464+-70, -2393+-90 k J/mol respectively are determined on the base of the analysis of curves of ionisation efficiency and of reaction heats Ba 2 MoO 5 =BaO+BaMoO 4 , ΔH 0 0 =322+-60 kJ/mol Ba 2 Mo 2 O 8 =2BaMoO 4 , ΔH 0 0 =351+-80 kJ/mol calculated with the use of third low of thermodynamics [ru

Accurate projected augmented wave datasets for BaFe2As2

International Nuclear Information System (INIS)

Cao Chao; Wu Yuing; Hamdan, Rashid; Wang, Yunpeng; Cheng Haiping

2010-01-01

By carefully choosing parameters and including more semi-core orbitals as valence electrons, we have constructed a high-quality projected augmented wave dataset that yields results comparable to existing full-potential linearized augmented plane-wave calculations. The dataset was then applied to BaFe 2 As 2 to study the effects of different levels of structure optimization, as well as different choices of exchange-correlation functionals. It was found that the local density approximation exchange-correlation functional fails to find the correct spin-density-wave anti-ferromagnetic (SDW-AFM) ground state under full optimization, while the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional obtains the correct state but significantly overestimates the magnetism. The electronic structure of the SDW-AFM state is not very sensitive to structure optimizations with the PBE exchange-correlation functional because the positions of the As atoms are preserved under optimizations. We further investigated the Ba atom diffusion process on the BaFe 2 As 2 surface using the nudged elastic bands method. The Ba atom was found to be stable above the center of the squares formed by the surface As atoms, and a diffusion barrier of 1.2 eV was found. Our simulated scanning tunneling microscopy image suggests an ordered surface Ba atom structure, in agreement with Massee et al (2009 Phys. Rev. B 80 140507; van Heumen E et al 2010 arXiv:1009.3493v1).

In-plane anisotropy of the electric field gradient in Ba(Fe 1 -xCox)2As2 observed by 75As NMR

Science.gov (United States)

Toyoda, Masayuki; Ichikawa, Akihiro; Kobayashi, Yoshiaki; Sato, Masatoshi; Itoh, Masayuki

2018-05-01

We have performed 75As NMR measurements on single crystals to investigate the nematic behavior via the in-plane anisotropy of the electronic state at the As site far from Co impurities in the representative iron arsenides Ba (Fe1-xCox) 2As2 . From the analysis of the angular dependence of the NMR satellites in the c plane using the binominal distribution, we find that there is the in-plane fourfold symmetry breaking, namely, the orthorhombic-type anisotropy in the electric field gradient (EFG) at the As site with no Co atom at the nearest neighboring Fe sites even in the tetragonal phase of both BaFe2As2 and Ba (Fe1-xCox) 2As2(x ≠0 ) . The NMR spectrum in the antiferromagnetically ordered state of BaFe2As2 is shown not to support a nanotwin model on the basis of the nematic order proposed from the pair-distribution analysis of neutron scattering data. Based on results of the x and temperature T dependences of the in-plane anisotropy in the wide x and T ranges, the symmetry breaking is concluded to come from the local orthorhombic domains induced by disorder such as Co impurities or lattice imperfections. Furthermore, we find that the asymmetry parameter of EFG η obeys the Curie-Weiss law which may be governed by nematic susceptibility, and the Weiss temperature becomes zero at xc˜0.05 in Ba (Fe1-xCox) 2As2 .

Effects of heavy-ion irradiation on the vortex state in Ba(Fe1-xCox)2As2

International Nuclear Information System (INIS)

Tamegai, T.; Tsuchiya, Y.; Taen, T.; Nakajima, Y.; Okayasu, S.; Sasase, M.

2010-01-01

We report effects of heavy-ion irradiation in Ba(Fe 1-x Co x ) 2 As 2 single crystals. The columnar defects with about 40% of the irradiation dose are confirmed by transmission electron microscopy. Magneto-optical imaging and bulk magnetization measurements reveal strong enhancement of the critical current density in the irradiated region. The vortex creep rate is also strongly suppressed by the columnar defects. Effects of heavy-ion irradiation into Ba(Fe 1-x Co x ) 2 As 2 and cuprate superconductors are compared.

Symmetry-Breaking Orbital Anisotropy Observed for Detwinned Ba(Fe1-xCox)2As2 above the Spin Density Wave Transition

International Nuclear Information System (INIS)

Yi, Ming

2011-01-01

Nematicity, defined as broken rotational symmetry, has recently been observed in competing phases proximate to the superconducting phase in the cuprate high temperature superconductors. Similarly, the new iron-based high temperature superconductors exhibit a tetragonal to orthorhombic structural transition (i.e. a broken C 4 symmetry) that either precedes or is coincident with a collinear spin density wave (SDW) transition in undoped parent compounds, and superconductivity arises when both transitions are suppressed via doping. Evidence for strong in-plane anisotropy in the SDW state in this family of compounds has been reported by neutron scattering, scanning tunneling microscopy, and transport measurements. Here we present an angle resolved photoemission spectroscopy study of detwinned single crystals of a representative family of electron-doped iron-arsenide superconductors, Ba(Fe 1-x Co x ) 2 As 2 in the underdoped region. The crystals were detwinned via application of in-plane uniaxial stress, enabling measurements of single domain electronic structure in the orthorhombic state. At low temperatures, our results clearly demonstrate an in-plane electronic anisotropy characterized by a large energy splitting of two orthogonal bands with dominant d xz and d yz character, which is consistent with anisotropy observed by other probes. For compositions x > 0, for which the structural transition (T S ) precedes the magnetic transition (T SDW ), an anisotropic splitting is observed to develop above T SDW , indicating that it is specifically associated with T S . For unstressed crystals, the band splitting is observed close to T S , whereas for stressed crystals the splitting is observed to considerably higher temperatures, revealing the presence of a surprisingly large in-plane nematic susceptibility in the electronic structure.

Competing charge, spin, and superconducting orders in underdoped YBa2Cu3Oy

DEFF Research Database (Denmark)

Hücker, M.; Christensen, Niels Bech; Holmes, A. T.

2014-01-01

order decreases with underdoping to TCDW~90 K in YBa2Cu3O6.44. Together with a weakened order parameter this suggests a competition between CDW and SDW orders. In addition, the CDW order in YBa2Cu3O6.44 shows the same type of competition with superconductivity as a function of temperature and magnetic...

Synthesis and pressure effects on the La doped CaFe{sub 2}As{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Shin, Soo Hyun; Park, Tuson [Dept. of physics, Sungkyunkwan University, Suwon (Korea, Republic of); Shang, T.; Yuan, H. Q. [Dept. of physics, Zhejiang University, Hangzhou (China)

2014-09-15

We have synthesized La doped CaFe2As{sub 2} single crystals with Sn flux in an evacuated quartz ampule. Doping and pressure effects on the magnetic and superconducting properties of the under-doped Ca{sub 1-x}La{sub x}Fe{sub 2}As{sub 2} (x=0.08, 0.1) were studied by measuring electrical resistivity under quasi-hydrostatic pressure up to 21 kbar. Magnetic transition temperatures for all studied concentrations were sharply suppressed with slight amplitude of pressure, less than 3 kbar, while superconducting transition temperatures were robust against pressure. In this communication, we report temperature-pressure phase diagram for the La-doped CaFe{sub 2}As{sub 2} single crystals.

Crystal structure of the mixed-metal trisulfide BaCu1/3Ta2/3S3

Directory of Open Access Journals (Sweden)

Kejun Bu

2017-05-01

Full Text Available The mixed-metal title compound, BaCu1/3Ta2/3S3 [barium copper(II tantalum(V trisulfide], was prepared through solid-state reactions. The crystal structure adopts the BaTaS3 structure type and consists of face-sharing [MS6] (M = Ta,Cu octahedra (point-group symmetry -3m. that are condensed into infinite chains along [001]. Adjacent chains are linked through the barium cations (site symmetry -6m2, which exhibit a coordination number of twelve. The M site is occupied by 2/3 of TaV and 1/3 of CuII, whereby the average M—S distances are slightly longer than those of ordered BaTaS3. The classical charge balance of the title compound can be represented by [Ba2+] [(Ta/Cu4+] [S2−]3.

Vortex pinning in artificially layered Ba(Fe,Co)2As2 film

Science.gov (United States)

Oh, M. J.; Lee, Jongmin; Seo, Sehun; Yoon, Sejun; Seo, M. S.; Park, S. Y.; Kim, Ho-Sup; Ha, Dong-Woo; Lee, Sanghan; Jo, Youn Jung

2018-06-01

Static high critical current densities (Jc) > 1 MA/cm2 with magnetic field parallel or perpendicular to c-axis were realized in Co-doped/undoped multilayerd BaFe2As2 films. We made a current bridge by FIB to allow precise measurements, and confirmed that the boundary quality using FIB was considerably better than the quality achieved using a laser. The presence of a high in-plane Jc suggested the existence of c-axis correlated vortex pinning centers. To clarify the relationship between the Jc performance and superstructures, we investigated the magnetic flux pinning mechanism using scaling theory of the volume pinning force Fp(H). The Jc(H) curves, Fp/Fp,max vs. h = H/Hirr curves, and parameters p and q depended on the characteristics of the flux pinning mechanism. It was found that the dominant pinning mechanism of Co-doped/undoped multilayerd BaFe2As2 films was Δl-pinning and the inserted undoped BaFe2As2 layers remained non-superconducting. The dominant pin geometry varied when the magnetic field direction changed. It was concluded that the artificially layered BaFe2As2 film is a 3-D superconductor due to its long correlation length compared to the thickness of the non-superconducting layer.

Structural and magnetic properties and superconductivity in Ba(Fe_1-xTM_x)₂As₂

Energy Technology Data Exchange (ETDEWEB)

Thaler, Alexander [Iowa State Univ., Ames, IA (United States)

2012-01-01

We studied the effects on structural and magnetic phase transitions and the emergence of superconductivity in transition metal substituted BaFe₂As₂. We grew four series of Ba(Fe_1-xTM₂)₂As₂ (TM=Ru, Mn, Co+Cr and Co+Mn) and characterized them by crystallographic, magnetic and transport measurements. We also subjected Ba(Fe_1-xCr_x)₂As₂ and Ba(Fe_1-xCo_x)₂As₂ to heat treatment to explore what changes might be induced.

Carrier dynamics of Ba(Fe1-xCox)2As2 as a function of doping

International Nuclear Information System (INIS)

Muschler, Bernhard

2012-01-01

In this thesis a systematic light scattering study of the newly discovered iron-based superconductor Ba(Fe 1-x Co x ) 2 As 2 is presented. The main focus is placed on the study of electronic properties in a doping range x in which magnetism and superconductivity are in close proximity. The experiment affords a window into band and momentum-dependent electronic properties. The magnetic order is predominantly itinerant. The structure of the superconducting gap indicates that the coupling potential may result from magnetic fluctuations.

Evidence for a vortex-glass transition in superconducting Ba(Fe0.9Co0.1)2As2.

Science.gov (United States)

Prando, G; Giraud, R; Aswartham, S; Vakaliuk, O; Abdel-Hafiez, M; Hess, C; Wurmehl, S; Wolter, A U B; Büchner, B

2013-12-18

Measurements of magneto-resistivity and magnetic susceptibility were performed on single crystals of superconducting Ba(Fe0.9Co0.1)2As2 close to the conditions of optimal doping. The high quality of the investigated samples allows us to reveal dynamic scaling behaviour associated with a vortex-glass phase transition in the limit of a weak degree of quenched disorder. Accordingly, the dissipative component of the ac susceptibility is reproduced well within the framework of Havriliak-Negami relaxation, assuming a critical power-law divergence for the characteristic correlation time τ of the vortex dynamics. Remarkably, the random disorder introduced by the Fe1-xCox chemical substitution is found to act on the vortices as a much weaker quenched disorder than previously reported for cuprate superconductors such as Y1-xPrxBa2Cu3O7-δ.

Zintl-phases with layer anions: preparation and crystal structures of the isotypic compounds SrSn sub 2 As sub 2 and Sr sub 0. 87 Ba sub 0. 13 Sn sub 2 As sub 2 and a single crystal structure determination of KSnSb. Zintl-Phasen mit Schichtanionen: Darstellung und Kristallstrukturen der isotypen Verbindungen SrSn sub 2 As sub 2 und Sr sub 0,87 Ba sub 0,13 Sn sub 2 As sub 2 sowie eine Einkristallstrukturbestimmung von KSnSb

Energy Technology Data Exchange (ETDEWEB)

Eisenmann, B; Klein, J [Abt. 2 fuer Anorganische Chemie, Technische Hochschule Darmstadt (Germany)

1991-06-01

The metallic reflecting compounds SrSn{sub 2}As{sub 2} and Sr{sub 0.87}Ba{sub 0.13}Sn{sub 2}As{sub 2} were prepared from the melt, they crystallize in the trigonal rhombohedral system (space group R3m, Z = 3) with lattice constants see ''Inhaltsuebersicht''. In the crystal structure of the isotypic compounds threebonded Sn atoms and threebonded As atoms together form puckered layers which are isostructural to grey As. The mean values of the bond lengths Sn -- As are 277.6 pm (SrSn{sub 2}As{sub 2}) and 279.1 pm (Sr{sub 0.87}Ba{sub 0.13}Sn{sub 2}As{sub 2}) resp. Along (001) the alkaline earth atoms occupy the octahedral interstices of As atoms between each second SnAs layer. The single crystal structure determination of KSnSb confirms the results of the X-ray powder analysis, but leads to slightly different values for the bond lengths.

Synthesis, Crystal Structure, and Chemical-Bonding Analysis of BaZn(NCN2

Directory of Open Access Journals (Sweden)

Alex J. Corkett

2017-12-01

Full Text Available The ternary carbodiimide BaZn(NCN2 was prepared by a solid-state metathesis reaction between BaF2, ZnF2, and Li2NCN in a 1:1:2 molar ratio, and its crystal structure was determined from Rietveld refinement of X-ray data. BaZn(NCN2 represents the aristotype of the LiBa2Al(NCN4 structure which is unique to carbodiimide/cyanamide chemistry and is well regarded as being constructed from ZnN4 tetrahedra, sharing edges and vertices through NCN2− units to form corrugated layers with Ba2+ in the interlayer voids. Structural anomalies in the shape of the cyanamide units are addressed via IR spectrometry and DFT calculations, which suggest the presence of slightly bent N=C=N2− carbodiimide units with C2v symmetry. Moreover, chemical-bonding analysis within the framework of crystal orbital Hamilton population (COHP reveals striking similarities between the bonding interactions in BaZn(NCN2 and SrZn(NCN2 despite their contrasting crystal structures. BaZn(NCN2 is only the second example of a ternary post-transition metal carbodiimide, and its realization paves the way for the preparation of analogues featuring divalent transition metals at the tetrahedral Zn2+ site.

Li{sub 4}Ba[BN{sub 2}]{sub 2} - structure and vibrational spectra

Energy Technology Data Exchange (ETDEWEB)

Seidel, Stefan; Rodewald, Ute C.; Poettgen, Rainer [Institut fuer Anorganische und Analytische Chemie, Universitaet Muenster (Germany); Somer, Mehmet; Kiraz, Kamil [Chemistry Department, Koc University, Sariyer-Istanbul (Turkey)

2017-12-13

The nitridoborate Li{sub 4}Ba[BN{sub 2}]{sub 2} was synthesized from a 4:1 molar ratio of Li{sub 3}[BN]{sub 2} and Ba{sub 3}[BN{sub 2}]{sub 2} in an arc-welded niobium ampoule at a maximum annealing temperature of 1173 K. The structure was refined from single-crystal X-ray diffractometer data: new type, P1, a = 533.9(2), b = 585.0(3), c = 860.6(4) pm, α = 80.72(3), β = 73.84(6), γ = 89.87(4) , wR{sub 2} = 0.1196, 1429 F{sup 2} values, 50 variables. The Li{sub 4}Ba[BN{sub 2}]{sub 2} structure contains two crystallographically independent [BN{sub 2}]{sup 3-} units with 134 pm B-N distance, which are slightly bent: 178 for N2-B1-N1 and 175 for N4-B2-N3. Due to the high lithium content both [BN{sub 2}]{sup 3-} units have a strongly distorted coordination by 8Li{sup +} + 3Ba{sup 2+}. The four crystallographically independent lithium cations show distorted tetrahedral coordination by [BN{sub 2}]{sup 3-} units with Li-N distances ranging from 195 to 247 pm. IR and Raman spectra show the typical vibrations of the [BN{sub 2}] unit along with a well-resolved splitting of the ν({sup 10}B) and ν({sup 11}B) frequencies. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Tuning the magnetism of the top-layer FeAs on BaFe2As2 (001): First-principles study

Science.gov (United States)

Zhang, Bing-Jing; Liu, Kai; Lu, Zhong-Yi

2018-04-01

Magnetism may play an important role in inducing the superconductivity in iron-based superconductors. As a prototypical system, the surface of BaFe2As2 provides a good platform for studying related magnetic properties. We have designed systematic first-principles calculations to clarify the surface magnetism of BaFe2As2 (001), which previously has received little attention in comparison with surface structures and electronic states. We find that the surface environment has an important influence on the magnetic properties of the top-layer FeAs. For As-terminated surfaces, the magnetic ground state of the top-layer FeAs is in the staggered dimer antiferromagnetic (AFM) order, distinct from that of the bulk, while for Ba-terminated surfaces the collinear (single-stripe) AFM order is the most stable, the same as that in the bulk. When a certain coverage of Ba or K atoms is deposited onto the As-terminated surface, the calculated energy differences among different AFM orders for the top-layer FeAs on BaFe2As2 (001) can be much reduced, indicating enhanced spin fluctuations. To compare our results with available scanning tunneling microscopy (STM) measurements, we have simulated the STM images of several structural/magnetic terminations. Astonishingly, when the top-layer FeAs is in the staggered dimer AFM order, a stripe pattern appears in the simulated STM image even when the surface Ba atoms adopt a √{2 }×√{2 } structure, while a √{2 }×√{2 } square pattern comes out for the 1 ×1 full As termination. Our results suggest: (i) the magnetic state at the BaFe2As2 (001) surface can be quite different from that in the bulk; (ii) the magnetic properties of the top-layer FeAs can be tuned effectively by surface doping, which may likely induce superconductivity at the surface layer; (iii) both the surface termination and the AFM order in the top-layer FeAs can affect the STM image of BaFe2As2 (001), which needs to be taken into account when identifying the surface

Superconductivity at 108 K in the simplest non-toxic double-layer cuprate of Ba2CaCu2O4(O,F)2

International Nuclear Information System (INIS)

Shirage, P M; Shivagan, D D; Crisan, A; Tanaka, Y; Kodama, Y; Kito, H; Iyo, A

2008-01-01

We report the superconductivity in apical fluorine system of Ba 2 CaCu 2 O 6-y F y : the second member of Ba 2 Ca n-1 Cu n O 2n (O,F) 2 homologous series. The polycrystalline samples of Ba 2 CaCu 2 O 6-y F y (F-0212) were synthesized under high pressure as a parameter of nominal fluorine content (y). Samples with y = 2.0 ∼ 1.2 elucidating the very sharp superconducting transitions in temperature dependence of susceptibility from under doping state to slightly over doping state via optimal doping state. A remarkable highest T c of 108 K has been achieved for the sample synthesized from a nominal composition of Ba 2 CaCu 2 O 4.4 F 1.6 . This T c is highest among the double CuO 2 layered system except for that including toxic elements such as Hg and T1. The T c has been systematically controlled from 57 K to 108 K by controlling the doping state, by designing the starting composition of fluorine and oxygen. The strong dependence of the 'a' and 'c' lattice constants were found on the nominal F content. We propose the Ba 2 CaCu 2 O 4 (O,F) 2 as a promising material for practical use due to its high T c and non-toxicity with a simple crystal structure

Tetragonal To Collapsed Tetragonal Phase Transition In BaFe2As2 and CaFe2As2

International Nuclear Information System (INIS)

Mittal, R.; Mishra, S. K.; Chaplot, S. L.; Ovsyannikov, S. V.; Trots, D. M.; Dubrovinsky, L.; Greenberg, E.; Su, Y.; Brueckel, Th.; Matsuishi, S.; Hosono, H.; Garbarino, G.

2010-01-01

Superconductivity in MFe 2 As 2 (M = Ba, Ca) compounds appears either at a critical doping level at ambient pressure or in the parent compound itself by application of pressure above a critical value. We report high pressure powder x-ray diffractions studies for these compounds at 300 K up to about 56 GPa using membrane diamond anvil cells. The measurements for BaFe 2 As 2 show a new tetragonal to collapsed tetragonal phase transition at about 22 GPa that remains stable upto 56 GPa. CaFe 2 As 2 is already known to transform to collapsed phase at 1.7 GPa at 300 K. Our measurements on CaFe 2 As 2 do not show any post collapsed phase transition on increase of pressure 50 GPa at 300 K. It is important to note that the transition in both compounds occurs when they are compressed to almost the same value of the unit cell volume and attain similar c t /a t ratios. We present a detailed analysis of the pressure dependence and structure phase transitions as well as equation of state in these important FeAs compounds that should be useful in the context of possible superconductivity in the collapsed phase.

Growth and characterizations of Ba2Ti2Fe2As4O single crystals

Directory of Open Access Journals (Sweden)

Yun-Lei Sun, Abduweli Ablimit, Jin-Ke Bao, Hao Jiang, Jie Zhou and Guang-Han Cao

2013-01-01

Full Text Available Single crystals of a new iron-based superconductor Ba2Ti2Fe2As4O have been grown successfully via a Ba2As3-flux method in a sealed evacuated quartz tube. Bulk superconductivity with Tc ~ 21.5 K was demonstrated in resistivity and magnetic susceptibility measurements after the as-grown crystals were annealed at 500 °C in vacuum for a week. X-ray diffraction patterns confirm that the annealed and the as-grown crystals possess the identical crystallographic structure of Ba2Ti2Fe2As4O. Energy-dispersive x-ray spectra indicate that partial Ti/Fe substitution exists in the [Fe2As2] layers and the annealing process redistributes the Ti within the Fe-plane. The ordered Fe-plane stabilized by annealing exhibits superconductivity with magnetic vortex pinned by Ti.

Epitaxial growth and electronic structure of a layered zinc pnictide semiconductor, β-BaZn2As2

International Nuclear Information System (INIS)

Xiao, Zewen; Ran, Fan-Yong; Hiramatsu, Hidenori; Matsuishi, Satoru; Hosono, Hideo; Kamiya, Toshio

2014-01-01

BaZn 2 As 2 is expected for a good p-type semiconductor and has two crystalline phases of an orthorhombic α phase and a higher-symmetry tetragonal β phase. Here, we report that high-quality epitaxial films of the tetragonal β-BaZn 2 As 2 were grown on single-crystal MgO (001) substrates by a reactive solid-phase epitaxy technique. Out-of-plane and in-plane epitaxial relationships between the film and the substrate were BaZn 2 As 2 (00 l)//MgO (001) and BaZn 2 As 2 [200]//MgO [200], respectively. The full-widths at half maximum were 0.082° for a 008 out-of-plane rocking curve and 0.342° for a 200 in-plane rocking curve. A step-and-terrace structure was observed by atomic force microscopy. The band gap of β-BaZn 2 As 2 was evaluated to be around 0.2 eV, which is much smaller than that of a family compound LaZnOAs (1.5 eV). Density functional theory calculation using the Heyd–Scuseria–Ernzerhof hybrid functionals supports the small band gap. - Highlights: • High-quality epitaxial β-BaZn 2 As 2 films were obtained. • The band gap of β-BaZn 2 As 2 was evaluated to around 0.2 eV. • Hybrid Heyd–Scuseria–Ernzerhof calculation supports the small band gap

Perovskites Ba/sub 2/Bsub(1/2)sup(I)Bsub(1/2)sup(III)Usup(VI)O/sub 6/

Energy Technology Data Exchange (ETDEWEB)

Roller, H; Kemmler-Sack, S [Tuebingen Univ. (Germany, F.R.). Inst. fuer Chemie

1978-11-01

Compounds of type Ba/sub 2/Lisub(1/2)Bsub(1/2)sup(III)Usup(VI)O/sub 6/ and Ba/sub 2/Nasub(1/2)Bsub(1/2)sup(III)Usup(VI)O/sub 6/ are formed with Bsup(III) = La, Nd, Sm, Gd, Y, In as red to reddish brown perovskites. They are for Bsup(III) = La, Nd and Sm polymorphic. With Bsup(III) = La both HT-forms crystallize cubic. In the Li series the HT-modifications with Bsup(III) = Nd, Sm are monoclinic (a < c/..sqrt..2 < b) and in the Na series rhombic (c/..sqrt..2 < a < b); the corresponding Gd, Y, and In compounds have the same structure. The transformation HT ..-->.. TT is reversible. The TT modifications crystallize monoclinic (a < b < c/..sqrt..2). Unlike the HT forms an increase of c and a decrease of a and b is observed, the cell volumina rested nearly unchanged. The origin for the transformation are order disorder phenomena.

Thermal annealing and pressure effects on BaFe2-xCoxAs2 single crystals.

Science.gov (United States)

Shin, Dongwon; Jung, Soon-Gil; Prathiba, G; Seo, Soonbeom; Choi, Ki-Young; Kim, Kee Hoon; Park, Tuson

2017-11-26

We investigate the pressure and thermal annealing effects on BaFe_2-xCo_xAs₂ (Co-Ba122) single crystals with x = 0.1 and 0.17 via electrical transport measurements. The thermal annealing treatment not only enhances the superconducting transition temperature (T_c) from 9.6 to 12.7 K for x = 0.1 and from 18.1 to 21.0 K for x = 0.17, but also increases the antiferromagnetic transition temperature (T_N). Simultaneous enhancement of T_c and T_N by the thermal annealing treatment indicates that thermal annealing could substantially improve the quality of the Co-doped Ba122 samples. Interestingly, T_c of the Co-Ba122 compounds shows a scaling behavior with a linear dependence on the resistivity value at 290 K, irrespective of tuning parameters, such as chemical doping, pressure, and thermal annealing. These results not only provide an effective way to access the intrinsic properties of the BaFe₂As₂ system, but also may shed a light on designing new materials with higher superconducting transition temperature. © 2017 IOP Publishing Ltd.

Microstructure and transport properties of [0 0 1]-tilt bicrystal grain boundaries in iron pnictide superconductor, cobalt-doped BaFe2As2

International Nuclear Information System (INIS)

Hiramatsu, Hidenori; Katase, Takayoshi; Ishimaru, Yoshihiro; Tsukamoto, Akira; Kamiya, Toshio; Tanabe, Keiichi; Hosono, Hideo

2012-01-01

Relationships between microstructure and transport properties of bicrystal grain boundary (BGB) junctions were studied in cobalt-doped BaFe 2 As 2 (BaFe 2 As 2 :Co) epitaxial films grown on [0 0 1]-tilt bicrystal substrates of MgO and (La, Sr)(Al, Ta)O 3 with misorientation angles θ GB = 3–45°. The θ GB of BaFe 2 As 2 :Co BGBs were exactly transferred from those of the bicrystal substrates. No segregation of impurities was detected at the BGB junction interfaces, and the chemical compositions of the BGBs were uniform and the same as those in the bulk film regions. A transition from a strongly-coupled GB behavior to a weak-link behavior was observed in current density–voltage characteristics under self-field around θ GB ∼ 9°. The critical current density decreased from (1.2–1.6) × 10 6 A/cm 2 of the intragrain transport to (0.7–1.1) × 10 5 A/cm 2 of θ GB = 45° because supercurrent becomes more governed by Josephson current with increasing θ GB .

Electronic structure of BaFe2As2 as obtained from DFT/ASW first-principles calculations

KAUST Repository

Schwingenschlö gl, Udo; Di Paola, Cono

2010-01-01

We use ab-initio calculations based on the augmented spherical wave method within density functional theory to study the magnetic ordering and Fermi surface of BaFe2As2, the parent compound of the hole-doped iron pnictide superconductors (K,Ba)Fe2As

Radiation Damage in CaF{sub 2}2 and BaF{sub 2} Investigated by the Channeling Technique

Energy Technology Data Exchange (ETDEWEB)

Hellborg, R; Skog, G

1973-04-15

The radiation damage in single crystals of CaF{sub 2} and BaF{sub 2} due to room temperature bombardment with 2.0 MeV helium ions has been studied by the channeling technique. Back scattering spectra for the <111> and <110> axial directions were taken after different doses of random irradiation. A slight in crease of the aligned yield with radiation dose has been found for both crystals at doses below 1017 ions/cm2. For CaF{sub 2} at a dose of about 1.4x1017 ions/cm2 a steep increase is found, after which the aligned yield saturates at a high value. Analyses of spectra measured along different aligned directions indicate that the structures of defects in CaF{sub 2} and BaF{sub 2} differ

Annealing Effects on the Normal-State Resistive Properties of Underdoped Cuprates

Science.gov (United States)

Vovk, R. V.; Khadzhai, G. Ya.; Nazyrov, Z. F.; Kamchatnaya, S. N.; Feher, A.; Dobrovolskiy, O. V.

2018-05-01

The influence of room-temperature annealing on the parameters of the basal-plane electrical resistance of underdoped YBa_2Cu_3O_{7-δ } and HoBa_2Cu_3O_{7-δ } single crystals in the normal and superconducting states is investigated. The form of the derivatives dρ (T)/dT makes it possible to determine the onset temperature of the fluctuation conductivity and indicates a nonuniform distribution of the labile oxygen. Annealing has been revealed to lead to a monotonic decrease in the oxygen deficiency, that primarily manifests itself as a decrease in the residual resistance, an increase of T_c, and a decrease in the Debye temperature.

Ho3+/Yb3+ co-doped TeO2-BaF2-Y2O3 glasses for ∼1.2 μm laser applications

Science.gov (United States)

Wang, Shunbin; Li, Chengzhi; Yao, Chuanfei; Jia, Shijie; Jia, Zhixu; Qin, Guanshi; Qin, Weiping

2017-02-01

Intense ∼1.2 μm fluorescence is observed in Ho3+/Yb3+ co-doped TeO2-BaF2-Y2O3 glasses under 915 nm laser diode excitation. The 1.2 μm emission can be ascribed to the transition 5I6→5I8 of Ho3+. With the introducing of BaF2, the content of OH in the glasses drops markedly, and the 1.2 μm emission intensity increases gradually as increasing the concentration percentage of BaF2. Furthermore, microstructured fibers based on the TeO2-BaF2-Y2O3 glasses are fabricated by using a rod-in-tube method, and a relative positive gain of ∼9.42 dB at 1175.3 nm is obtained in a 5 cm long fiber.

Chalcogenidosilicates: Ba/sub 2/SiTe/sub 4/ and Ba/sub 2/SiSe/sub 4/

Energy Technology Data Exchange (ETDEWEB)

Brinkmann, C; Eisenmann, B; Schaefer, H [Technische Hochschule Darmstadt (Germany, F.R.). Fachbereich Anorganische Chemie und Kernchemie

1985-05-01

The new compounds Ba/sub 2/SiSe/sub 4/ and Ba/sub 2/SiTe/sub 4/ crystallize in the monoclinic system, space group: P2/sub 1//m (No. 11) with the lattice constants Ba/sub 2/SiSe/sub 4/: a = 918.4(5) pm, b = 703.3(3) pm, c = 687.2(3) pm, ..beta.. = 109.2(1)/sup 0/, Ba/sub 2/SiTe/sub 4/: a = 965.0(5) pm, b = 762.6(3) pm, c = 746.6(3) pm, ..beta.. = 108.9(1)/sup 0/. Both compounds are isotypic to the Sr/sub 2/GeS/sub 4/ structure. Ba/sub 2/SiTe/sub 4/ is the first o-telluridosilicate with discrete SiTe/sub 4//sup 4 -/ anions.

H+ irradiation effect in Co-doped BaFe2As2 single crystals

International Nuclear Information System (INIS)

Nakajima, Y.; Tsuchiya, Y.; Taen, T.; Tamegai, T.; Kitamura, H.; Murakami, T.

2011-01-01

The effect of H + irradiation on the suppression of Tc in Co-doped BaFe 2 As 2 . H + irradiation introduces nonmagnetic scattering centers. Critical Scattering rate is much higher than that expected in s±-pairing scenario. We report the suppression of the critical temperature T c in single crystalline Ba(Fe 1-x Co x ) 2 As 2 at under-, optimal-, and over-doping levels by 3 MeV proton irradiation. T c decreases and residual resistivity increases monotonically with increasing the dose. The low-temperature resistivity does not show the upturn in contrast with the α-particle irradiated NdFeAs(O,F), which suggests that proton irradiation introduces nonmagnetic scattering centers. Critical scattering rates for all samples obtained by three different ways are much higher than that expected in s±-pairing scenario based on inter-band scattering due to antiferro-magnetic spin fluctuations.

Effects of Sr2+ substitution on photoluminescence characteristics of Ba1−x−ySryZrSi3O9:xEu2+ phosphors

International Nuclear Information System (INIS)

Chiang, Chung-Hao; Gong, Syuan-Jhih; Lin, Han-Yu; Zhan, Ting-Shi; Chu, Sheng-Yuan

2014-01-01

In this work, single-phase Ba 1−x−y Sr y ZrSi 3 O 9 :xEu 2+ phosphors were synthesized via the solid-state reaction method. The crystal structure and luminescence properties were investigated using X-ray diffraction and photoluminescence measurements, respectively. An increase of the dopant Sr 2+ increased the emission intensity of the phosphors. The peak intensity of the samples was at y = 0.4 under near-ultraviolet light excitation (397 nm). The wavelength of the emission peaks red-shifts slightly from 477 to 483 nm due to the splitting of the 5d energy level. Sr 2+ ions have a smaller ionic radius than that of Ba 2+ ions, and thus the dopant changes the crystal structure, improving the energy transfer efficiency between luminescence centers. More Eu 2+ solid solubility was found in Ba 0.6−x Sr 0.4 ZrSi 3 O 9 :xEu 2+ phosphors (10 mol. %) than in the host BaZrSi 3 O 9 (6 mol. %), which enhanced the emission intensity. In addition, the thermal reliability of the phosphors was studied

Design, synthesis and luminescence properties of Ba2 YB2 O6 Cl- and Ba2 YB2 O6 F-based phosphors.

Science.gov (United States)

Chen, Wanping; Yang, Xin; Liu, Yan; Dai, Xiaoyan

2015-05-01

Using a high-temperature solid-state reaction, the chlorine in Ba2 YB2 O6 Cl is gradually replaced by F, and a new compound with the nominal chemical formula Ba2 YB2 O6 F and two phosphors doped with Ce(3+) and Eu(3+) , respectively, are obtained. X-Ray diffraction and photoluminescence spectroscopy are used to characterize the as-synthesized samples. The as-synthesized Ba2 YB2 O6 Cl exhibits bright blue emission in the spectral range ~ 330-410 nm with a maximum around 363 nm under X-ray or UV excitation. Ba2 YB2 O6 F:0.01Ce(3+) exhibits blue emission in the range ~ 340-570 nm with a maximum around 383 nm. Ba2 YB2 O6 F:0.01Eu(3+) exhibits a predominantly (5) D0 -(7)  F2 emission (~610 nm) and the relative intensities of the (5) D0 -(7)  F0,1,2 emissions are tunable under different wavelength UV excitation. The luminescence behaviors of the two phosphors are explained simply in terms of the host composition and site occupancy probability of Ce(3+) and Eu(3+) , respectively. The results indicate that these phosphors have potential application as a blue phosphor or as a red phosphor. Copyright © 2014 John Wiley & Sons, Ltd.

Luminescence characteristics of Sr{sub 1-x}Ba{sub x}Si{sub 2}O{sub 2}N{sub 2}:Eu{sup 2+} phosphors for white light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Anoop, G.; Cho, I.H.; Suh, D.W.; Yoo, J.S. [Display Materials Laboratory, School of Chemical Engineering and Materials Science, Chung-Ang University, Heukseok-Dong 221, Dongjak-gu, Seoul 156-756 (Korea, Republic of)

2012-12-15

Sr{sub 1-x}Ba{sub x}Si{sub 2}O{sub 2}N{sub 2}:Eu{sup 2+} phosphors were synthesized using high temperature solid state reaction. The effect of Ba incorporation on the structural and luminescence characteristics of SrSi{sub 2}O{sub 2}N{sub 2}:Eu{sup 2+} phosphors were studied. The phosphors were crystallized in triclinic crystal structure and the cell volume increases monotonically with Ba addition. The PL emission peak wavelength red shifts with Ba up to x = 0.50 beyond which no red shift is observed. The XPS analysis shows that nitrogen is being incorporated into the host lattice along with Ba addition up to x = 0.50. The as synthesized phosphors show high thermal stability. Phosphor converted light emitting diodes were realized using Sr{sub 1-x}Ba{sub x}Si{sub 2}O{sub 2}N{sub 2}:Eu{sup 2+} phosphors (x = 0 and x = 0.40) showing luminance efficacies of 108 and 101 lm W{sup -1}. The CIE chromaticity coordinates of Sr{sub 1-x}Ba{sub x}Si{sub 2}O{sub 2}N{sub 2}:Eu (x = 0 and x = 0.40) phosphors. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Two S-wave gap symmetry for single crystals of the superconductor BaFe1.8Co0.2As2

International Nuclear Information System (INIS)

Choi, Ki-Young; Kim, Soo Hyun; Choi, Changho; Jung, Myung-Hwa; Wang, X.F.; Chen, X.H.; Noh, Jae Dong; Lee, Sung-IK

2010-01-01

To clarify the gap structure of the iron-pnictide superconductors, we synthesized optimally doped single crystals of BaFe 1.8 Co 0.2 As 2 , which had a critical temperature, T c , of 23.6 K. The initial M-H curve was used to find the lower critical field, H c1 . The full range of the temperature dependence of H c1 was explained by using a two S-wave gap symmetry. We estimate the two gap as Δ 1 (0) = 1.64 ± 0.2 meV for the small gap and Δ 2 (0) = 6.20 ± 0.2 meV for the large gap.

Crystallisation of Ba1-xSrxZn2Si2O7 from BaO/SrO/ZnO/SiO2 glass with different ZrO2 and TiO2 concentrations

Science.gov (United States)

Vladislavova, Liliya; Kracker, Michael; Zscheckel, Tilman; Thieme, Christian; Rüssel, Christian

2018-04-01

The effect of different nucleation agents such as ZrO2 and TiO2 was investigated for a first time with respect to their crystallisation behaviour in the glass system BaO-SrO-ZnO-SiO2. In all studied glasses, a Ba1-xSrxZn2Si2O7 (0.1 ≤ x ≤ 0.9) solid solution crystallized. This phase was first described in 2015 to possess a similar structure as the high temperature phase of BaZn2Si2O7 and a thermal expansion close to zero or even negative. It may find applications e.g. as cook panels, telescope mirrors, and furnace windows. Kinetic parameters of the crystallisation process were determined by supplying different heating rates in a differential scanning calorimeter (DSC). The results were evaluated using the equations of Ozawa and Kissinger with respect to the activation energies. Furthermore, the Ozawa method was used for the determination of Avrami parameters, which provides further information on the nucleation and crystallisation processes. Scanning electron microscopy including electron backscatter diffraction (EBSD) was used to characterise the microstructure, to determine the crystallite size and the crystal orientation. For the characterisation of the occurring crystalline phases, X-ray diffraction was used.

Surface impedance of BaFe2-xNixAs2 in the radio frequency range

Directory of Open Access Journals (Sweden)

A. Abbassi

2012-08-01

Full Text Available We report measurements of the temperature dependence of the surface impedance in superconducting BaFe1.93Ni0.07As2 crystals using the radiofrequency reflection technique in the 5BaFe2-xNixAs2 has attracted much interest. For a Ni doping level of 7% the superconducting phase transition is found around 20K. The temperature dependence of the superconducting penetration depth was determined.

Anomalous magneto-elastic and charge doping effects in thallium-doped BaFe2As2

Science.gov (United States)

Sefat, Athena S.; Li, Li; Cao, Huibo B.; McGuire, Michael A.; Sales, Brian; Custelcean, Radu; Parker, David S.

2016-01-01

Within the BaFe2As2 crystal lattice, we partially substitute thallium for barium and report the effects of interlayer coupling in Ba1-xTlxFe2As2 crystals. We demonstrate the unusual effects of magneto-elastic coupling and charge doping in this iron-arsenide material, whereby Néel temperature rises with small x, and then falls with additional x. Specifically, we find that Néel and structural transitions in BaFe2As2 (TN = Ts = 133 K) increase for x = 0.05 (TN = 138 K, Ts = 140 K) from magnetization, heat capacity, resistivity, and neutron diffraction measurements. Evidence from single crystal X-ray diffraction and first principles calculations attributes the stronger magnetism in x = 0.05 to magneto-elastic coupling related to the shorter intraplanar Fe-Fe bond distance. With further thallium substitution, the transition temperatures decrease for x = 0.09 (TN = Ts = 131 K), and this is due to charge doping. We illustrate that small changes related to 3d transition-metal state can have profound effects on magnetism. PMID:26867821

Raman spectroscopy of Ba(Fe{sub 1−x}Mn{sub x}){sub 2}As{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Dias, Fabio Teixeira [Universidade Federal de Pelotas (UFPEL), RS (Brazil); Pinheiro, Lincoln Brum Leite Gusmao [Instituto Federal de Educacao, Ciencia e Tecnologia do Rio Grande do Sul (IFRS), Erechim, RS (Brazil); Jurelo, Alcione Roberto, E-mail: arjurelo@uepg.br [Universidade Estadual de Ponta Grossa (UEPG), PR (Brazil). Departamento de Fisica

2015-10-01

Raman scattering measurements on iron–pnictide Mn-doped BaFe{sub 2}As{sub 2} single crystals are reported. Single crystals were grown out of a Fe As self-flux using conventional high-temperature solution growth and characterized by X-ray diffraction, atomic force microscopy, and Raman. Raman spectra were obtained at room temperature and 77 K on ab-and a(b)c-planes. Two of four phonon modes allowed by symmetry were found and identified. It was observed that the scattering intensity of A{sub 1g} mode and the frequencies of the A{sub 1g} and B{sub 1g} phonons are dependent upon doping of Mn. The dependence of scattering intensity and frequency of A{sub 1g} mode on Mn doping might indicate that the Mn ion also occupies the As site. (author)

Superconducting gap symmetry in the superconductor BaFe1.9Ni0.1As2

Science.gov (United States)

Kuzmicheva, T. E.; Kuzmichev, S. A.; Sadakov, A. V.; Gavrilkin, S. Yu.; Tsvetkov, A. Yu.; Lu, X.; Luo, H.; Vasiliev, A. N.; Pudalov, V. M.; Chen, Xiao-Jia; Abdel-Hafiez, Mahmoud

2018-06-01

We report on the Andreev spectroscopy and specific heat of high-quality single crystals of BaFe1.9Ni0.1As2 . The intrinsic multiple Andreev reflection spectroscopy reveals two anisotropic superconducting gaps ΔL≈3.2 -4.5 meV , ΔS≈1.2 -1.6 meV (the ranges correspond to the minimum and maximum value of the coupling energy in the kxky plane). The 25 %-30 % anisotropy shows the absence of nodes in the superconducting gaps. Using a two-band model with s -wave-like gaps ΔL≈3.2 meV and ΔS≈1.6 meV , the temperature dependence of the electronic specific heat can be well described. A linear magnetic field dependence of the low-temperature specific heat offers further support of s -wave type of the order parameter. We find that a d -wave or single-gap BCS theory under the weak-coupling approach cannot describe our experiments.

Decrease in electrical contact resistance of Sb-doped n+-BaSi2 layers and spectral response of an Sb-doped n+-BaSi2/undoped BaSi2 structure for solar cells

Science.gov (United States)

Kodama, Komomo; Takabe, Ryota; Yachi, Suguru; Toko, Kaoru; Suemasu, Takashi

2018-03-01

We investigated how the electron concentration n in a 300-nm-thick Sb-doped n+-BaSi2 layer grown by molecular beam epitaxy affected the contact resistance R C to surface electrodes (Al, indium-tin-oxide). As the n of n-BaSi2 increased, R C decreased and reached a minimum of 0.019 Ω cm2 at n = 2.4 × 1018 cm-3 for the Al electrodes. This value was more than 1 order of magnitude smaller than that obtained for Al/B-doped p-BaSi2. We believe that this significant decrease in R C came from Sb segregation. Furthermore, the internal quantum efficiency (IQE) spectrum was evaluated for an Sb-doped n+-BaSi2 (20 nm)/undoped BaSi2 (500 nm)/n+-Si(111) structure. Its IQE reached as high as ˜50% over a wide wavelength range under a small bias voltage of 0.1 V applied between the top and bottom electrodes.

Electronic structure of BaFe2As2 as obtained from DFT/ASW first-principles calculations

KAUST Repository

Schwingenschlögl, Udo

2010-07-02

We use ab-initio calculations based on the augmented spherical wave method within density functional theory to study the magnetic ordering and Fermi surface of BaFe2As2, the parent compound of the hole-doped iron pnictide superconductors (K,Ba)Fe2As2, for the tetragonal I4/mmm as well as the orthorhombic Fmmm structure. In comparison to full potential linear augmented plane wave calculations, we obtain significantly smaller magnetic energies. This finding is remarkable, since the augmented spherical wave method, in general, is known for a most reliable description of magnetism. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Three new chalcohalides, Ba4Ge2PbS8Br2, Ba4Ge2PbSe8Br2 and Ba4Ge2SnS8Br2: Syntheses, crystal structures, band gaps, and electronic structures

International Nuclear Information System (INIS)

Lin, Zuohong; Feng, Kai; Tu, Heng; Kang, Lei; Lin, Zheshuai; Yao, Jiyong; Wu, Yicheng

2014-01-01

Highlights: • Three new chalcohalides: Ba 4 Ge 2 PbS 8 Br 2 , Ba 4 Ge 2 PbSe 8 Br 2 and Ba 4 Ge 2 SnS 8 Br 2 have been synthesized. • The MQ 5 Br octahedra and GeQ 4 tetrahedra form a three-dimensional framework with Ba 2+ in the channels. • Band Gaps and electronic structures of the three compounds were studied. - Abstract: Single crystals of three new chalcohalides: Ba 4 Ge 2 PbS 8 Br 2 , Ba 4 Ge 2 PbSe 8 Br 2 and Ba 4 Ge 2 SnS 8 Br 2 have been synthesized for the first time. These isostructural compounds crystallize in the orthorhombic space group Pnma. In the structure, the tetra-valent Ge atom is tetrahedrally coordinated with four Q (Q = S, Se) atoms, while the bi-valent M atom (M = Pb, Sn) is coordinated with an obviously distorted octahedron of five Q (Q = S, Se) atoms and one Br atom, showing the stereochemical activity of the ns 2 lone pair electron. The MQ 5 Br (M = Sn, Pb; Q = S, Se) distorted octahedra and the GeQ 4 (Q = S, Se) tetrahedra are connected to each other to form a three-dimensional framework with channels occupied by Ba 2+ cations. Based on UV–vis–NIR spectroscopy measurements and the electronic structure calculations, Ba 4 Ge 2 PbS 8 Br 2 , Ba 4 Ge 2 PbSe 8 Br 2 and Ba 4 Ge 2 SnS 8 Br 2 have indirect band gaps of 2.054, 1.952, and 2.066 eV respectively, which are mainly determined by the orbitals from the Ge, M and Q atoms (M = Pb, Sn; Q = S, Se)

Carrier dynamics of Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} as a function of doping

Energy Technology Data Exchange (ETDEWEB)

Muschler, Bernhard

2012-07-23

In this thesis a systematic light scattering study of the newly discovered iron-based superconductor Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} is presented. The main focus is placed on the study of electronic properties in a doping range x in which magnetism and superconductivity are in close proximity. The experiment affords a window into band and momentum-dependent electronic properties. The magnetic order is predominantly itinerant. The structure of the superconducting gap indicates that the coupling potential may result from magnetic fluctuations.

Structural Distortion Stabilizing the Antiferromagnetic and Semiconducting Ground State of BaMn2As2

Directory of Open Access Journals (Sweden)

Ekkehard Krüger

2016-09-01

Full Text Available We report evidence that the experimentally found antiferromagnetic structure as well as the semiconducting ground state of BaMn 2 As 2 are caused by optimally-localized Wannier states of special symmetry existing at the Fermi level of BaMn 2 As 2 . In addition, we find that a (small tetragonal distortion of the crystal is required to stabilize the antiferromagnetic semiconducting state. To our knowledge, this distortion has not yet been established experimentally.

Ba{sub 2}Cu{sub 2}Te{sub 2}P{sub 2}O{sub 13}: A new telluro-phosphate with S=1/2 Heisenberg chain

Energy Technology Data Exchange (ETDEWEB)

Xia, Mingjun [Beijing Center for Crystal Research and Development, Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China); Shen, Shipeng; Lu, Jun; Sun, Young [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Li, R.K., E-mail: rkli@mail.ipc.ac.cn [Beijing Center for Crystal Research and Development, Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190 (China)

2015-10-15

A new telluro-phosphate compound Ba{sub 2}Cu{sub 2}Te{sub 2}P{sub 2}O{sub 13} with S=1/2 Heisenberg chain has been successfully synthesized by solid state reaction and grown by flux method. Single crystal X-ray diffraction reveals that Ba{sub 2}Cu{sub 2}Te{sub 2}P{sub 2}O{sub 13} crystallizes into a monoclinic space group C2/c and cell parameters of a=17.647(3) Å, b=7.255(2) Å, c=9.191(2) Å and β=100.16 (3)°. In the structure of Ba{sub 2}Cu{sub 2}Te{sub 2}P{sub 2}O{sub 13}, one dimensional [CuTePO{sub 7}]{sup 3−} chains are formed by tetrahedral PO{sub 4} and trigonal bi-pyramidal TeO{sub 4} joining square planar CuO{sub 4} groups. Those [CuTePO{sub 7}]{sup 3−} chains are inter-connected by sharing one oxygen atom from the TeO{sub 4} group to form two dimensional layers. Magnetic susceptibility and specific heat measurements confirm that the title compound is a model one dimensional Heisenberg antiferromagnetic chain system. - Graphical abstract: Ba{sub 2}Cu{sub 2}Te{sub 2}P{sub 2}O{sub 13}, containing (CuTePO{sub 7}){sup 3−} chains formed by PO{sub 4} and TeO{sub 4} joining CuO{sub 4} groups, shows typical 1D Heisenberg antiferromagnetic chain model behavior as confirmed by magnetic measurements. - Highlights: • New telluro-phosphate Ba{sub 2}Cu{sub 2}Te{sub 2}P{sub 2}O{sub 13} has been grown. • It features layered structure composed of [CuTePO{sub 7}]{sup 3−} chains and TeO{sub 4} groups. • It shows the Heisenberg antiferromagnetic chain behavior. • It is transparent in the range of 1000–2500 nm with a UV absorption edge of 393 nm.

Perovskites Ba/sub 2/Bsub(1/2)sup(I)Bsub(1/2)sup(III)Tesup(VI)O/sub 6/

Energy Technology Data Exchange (ETDEWEB)

Roller, H; Kemmler-Sack, S [Tuebingen Univ. (Germany, F.R.). Lehrstuhl fuer Anorganische Chemie 2

1980-07-01

Compounds of composition Ba/sub 2/Bsub(1/2)sup(I)Bsub(1/2)sup(III)Tesup(VI)O/sub 6/ with Bsup(I) = Li, Na; Bsup(III) = La, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Yb, Y, In, Sc crystallize in a cubic 1:1 ordered perovskite structure. The vibrational spectroscopic investigations show, that more species of TeO/sub 6/ octahedra are present in the lattice.

The microscopic structure of charge density waves in underdoped YBa2Cu3O6.54 revealed by X-ray diffraction

DEFF Research Database (Denmark)

Forgan, E.M.; Blackburn, E.; Holmes, A.T.

2015-01-01

Charge density wave (CDW) order appears throughout the underdoped high-temperature cuprate superconductors, but the underlying symmetry breaking and the origin of the CDW remain unclear. We use X-ray diffraction to determine the microscopic structure of the CDWs in an archetypical cuprate YBa2Cu3O6...... oxygen atoms have the largest displacements, perpendicular to the CuO2 planes. Our results allow many electronic properties of the underdoped cuprates to be understood. For instance, the CDWs will lead to local variations in the electronic structure, giving an explicit explanation of density-wave states...

Effect of local environment on crossluminescence kinetics in SrF{sub 2}:Ba and CaF{sub 2}:Ba solid solutions

Energy Technology Data Exchange (ETDEWEB)

Terekhin, M.A. [P.N. Lebedev Physical Institute, Leninskij Prospekt 53, 119991 Moscow (Russian Federation); Makhov, V.N., E-mail: makhov@sci.lebedev.ru [P.N. Lebedev Physical Institute, Leninskij Prospekt 53, 119991 Moscow (Russian Federation); Lebedev, A.I.; Sluchinskaya, I.A. [Lomonosov Moscow State University, Moscow 119991 (Russian Federation)

2015-10-15

Spectral and kinetic properties of extrinsic crossluminescence (CL) in SrF{sub 2}:Ba (1%) and CaF{sub 2}:Ba (1%) are compared with those of intrinsic CL in BaF{sub 2} and are analyzed taking into account EXAFS data obtained at the Ba L{sub III} edge and results of first-principles calculations. The CL decay time was revealed to be longer in SrF{sub 2}:Ba and CaF{sub 2}:Ba compared to BaF{sub 2}. This fact contradicts the expected acceleration of luminescence decay which could result from an increased overlap of wave functions in solid solutions due to shortening of the Ba-F distance obtained in both EXAFS measurements and first-principles calculations. This discrepancy is explained by the effect of migration and subsequent non-radiative decay of the Ba (5p) core holes in BaF{sub 2} and by decreasing of the probability of optical transitions between Ba (5p) states and the valence band in SrF{sub 2}:Ba and CaF{sub 2}:Ba predicted by first-principles calculations. - Highlights: • The crossluminescence kinetics in SrF{sub 2}:Ba and CaF{sub 2}:Ba is slower than in BaF{sub 2}. • Ba{sup 2+} ions substitute for host Ca{sup 2+}(Sr{sup 2+}) ions in the on-center positions. • The nearest Ba-F distances in SrF{sub 2}:Ba and CaF{sub 2}:Ba are shorter than in BaF{sub 2}. • EXAFS data and first-principles calculations of the local structure agree well. • First-principles calculations explain slower luminescence decay in solid solutions.

Impedance and ac conductivity studies of Ba (Pr1/2Nb1/2) O3 ceramic

Indian Academy of Sciences (India)

Home; Journals; Bulletin of Materials Science; Volume 36; Issue 4. Impedance and a.c. conductivity studies of ... Abstract. Impedance and electrical conduction studies of Ba(Pr1/2Nb1/2)O3 ceramic prepared through conventional ceramic fabrication technique are presented. The crystal symmetry, space group and unit cell ...

Surface reconstruction switching induced by tensile stress of DB steps: From Ba/Si(0 0 1)- 2 × 3 to Ba/Si(0 0 1)-4° off- 3 × 2

Science.gov (United States)

Kim, Hidong; Lkhagvasuren, Altaibaatar; Zhang, Rui; Seo, Jae M.

2018-05-01

The alkaline-earth metal adsorption on Si(0 0 1) has attracted much interest for finding a proper template in the growth of high- κ and crystalline films. Up to now on the flat Si(0 0 1) surface with double domains and single-layer steps, the adsorbed Ba atoms are known to induce the 2 × 3 structure through removing two Si dimers and adding a Ba atom per unit cell in each domain. In the present investigation, the Si(0 0 1)-4° off surface with DB steps and single domains has been employed as a substrate and the reconstruction at the initial stage of Ba adsorption has been investigated by scanning tunneling microscopy and synchrotron photoemission spectroscopy. On this vicinal and single domain terrace, a novel 3 × 2 structure rotated by 90° from the 2 × 3 structure has been found. Such a 3 × 2 structure turns out to be formed by adding a Ba atom and a Si dimer per unit cell. This results from the fact that the adsorbed Ba2+ ions with a larger ionic radius relieve tensile stress on the original Si dimers exerted by the rebonded atoms at the DB step.

Relaxor behavior in lead-free Ba(Ti1−xScx/2Nbx/2O3 ceramics

Directory of Open Access Journals (Sweden)

N. Bensemma

2014-06-01

Full Text Available Solid solutions of (1−xBaTiO3-xBaSc1/2Nb1/2O3 (BT-BSN with x = 0.025, 0.05, 0.075, 0.1 and 0.125 were prepared by a high temperature solid-state reaction technique. The effects of the Ba(Sc1/2Nb1/2O3 addition on the phase composition, dielectric properties, as well as polarization-electric field (P-E loops of the BT-BSN solid solution were investigated. The room-temperature X-ray diffraction analyses of all the ceramics revealed a perovskite phase after sintering at 1350 °C with a composition-dependent symmetry. Temperature and frequency dependence of the dielectric permittivity and losses have been explored: ceramics of compositions x ≤ 0.075 showed normal ferroelectric behavior, while ceramics with x ≥ 0.1 were of relaxor type. The degree of diffuseness and the relaxor effect increase while the transition temperature (TC or Tm decreases when both scandium and niobium are introduced in the BaTiO3 lattice. Ceramics of composition x = 0.125 exhibited interesting relaxor characteristics at 10 kHz: ΔTm = 20 K, ɛr = 12,000, and Tm = 140 K. In addition, modeled using Vogel–Fülcher relation, this same composition showed the fitting parameters: Ea = 0.0503 eV, f0 = 1.129 × 1014 Hz and TVF = 166.85 K.

Hydrostatic pressure (8 GPa) dependence of electrical resistivity of BaCo{sub 2}As{sub 2} single crystal

Energy Technology Data Exchange (ETDEWEB)

Ganguli, Chandreyee; Matsubayashi, Kazuyuki; Ohgushi, Kenya [Institute for Solid State Physics, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan); Uwatoko, Yoshiya, E-mail: uwatoko@issp.u-tokyo.ac.jp [Institute for Solid State Physics, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan); Kanagaraj, Moorthi [Centre for High Pressure Research, School of Physics, Bharathidasan University, Tiruchirappalli 620024 (India); Arumugam, Sonachalam, E-mail: sarumugam1963@yahoo.com [Centre for High Pressure Research, School of Physics, Bharathidasan University, Tiruchirappalli 620024 (India)

2013-10-15

Graphical abstract: - Highlights: • Single crystals of BaCo{sub 2}As{sub 2} were grown by CoAs self-flux method. • We have studied pressure effects (8 GPa) on dc electrical resistivity of BaCo{sub 2}As{sub 2}. • On applied external pressure BaCo{sub 2}As{sub 2} remains a metallic state up to 8 GPa. • Superconductivity is absent in BaCo{sub 2}As{sub 2} because of its proximity to ferromagnetism. - Abstract: The pressure dependence of the electrical resistivity of BaCo{sub 2}As{sub 2} single crystal as a function of temperature was measured at ambient and high pressures up to 8 GPa for the first time using cubic anvil high pressure cell. It is observed that at room temperature the resistivity monotonically decreases with increasing pressure and it remains in the metallic state even at an applied pressure of 8 GPa. From the temperature dependence of the resistivity measurements under pressure, we found that superconductivity is absent up to 8 GPa. The value of the electron's scattering factor (A) is found to be large at ambient pressure and it decreases with the application of pressure, indicating that the substantial electron correlation effect of BaCo{sub 2}As{sub 2} is reduced under pressure, revealing a dramatic change of density of states at the Fermi energy.

Transport properties and pinning analysis for Co-doped BaFe2As2 thin films on metal tapes

Science.gov (United States)

Xu, Zhongtang; Yuan, Pusheng; Fan, Fan; Chen, Yimin; Ma, Yanwei

2018-05-01

We report on the transport properties and pinning analysis of BaFe1.84Co0.16As2 (Ba122:Co) thin films on metal tapes by pulsed laser deposition. The thin films exhibit a large in-plane misorientation of 5.6°, close to that of the buffer layer SrTiO3 (5.9°). Activation energy U 0(H) analysis reveals a power law relationship with field, having three different exponents at different field regions, indicative of variation from single-vortex pinning to a collective flux creep regime. The Ba122:Co coated conductors present {{T}{{c}}}{{onset}} = 20.2 K and {{T}{{c}}}{{zero}} = 19.0 K along with a self-field J c of 1.14 MA cm‑2 and an in-field J c as high as 0.98 and 0.86 MA cm‑2 up to 9 T at 4.2 K for both major crystallographic directions of the applied field, promising for high field applications. Pinning force analysis indicates a significant enhancement compared with similar Ba122:Co coated conductors. By using the anisotropic scaling approach, intrinsic pinning associated with coupling between superconducting blocks can be identified as the pinning source in the vicinity of H//ab, while for H//c random point defects are likely to play a role but correlated defects start to be active at high temperatures.

Syntheses, crystal structures and characterizations of BaZn(SeO3)2 and BaZn(TeO3)Cl2

International Nuclear Information System (INIS)

Jiang Hailong; Feng Meiling; Mao Jianggao

2006-01-01

Two new barium zinc selenite and tellurite, namely, BaZn(SeO 3 ) 2 and BaZn(TeO 3 )Cl 2 , have been synthesized by the solid state reaction. The structure of BaZn(SeO 3 ) 2 features double chains of [Zn(SeO 3 ) 2 ] 2- anions composed of four- and eight-member rings which are alternatively along a-axis. The double chains of [Zn 2 (TeO 3 ) 2 Cl 3 ] 3- anions in BaZn(TeO 3 )Cl 2 are formed by Zn 3 Te 3 rings in which each tellurite group connects with three ZnO 3 Cl tetrahedra. BaZn(SeO 3 ) 2 and BaZn(TeO 3 )Cl 2 are wide bandgap semiconductors based on optical diffuse reflectance spectrum measurements. -- Graphical abstract: Two new barium zinc selenite and tellurite, namely, BaZn(SeO 3 ) 2 and BaZn(TeO 3 )Cl 2 , have been synthesized by solid state reaction. The structure of BaZn(SeO 3 ) 2 features 1D double chains of [Zn(SeO 3 ) 2 ] 2- anions composed of four- and eight-member rings which are alternatively along a-axis. The 1D double chains of [Zn 2 (TeO 3 ) 2 Cl 3 ] 3- anions in BaZn(TeO 3 )Cl 2 are formed by Zn 3 Te 3 rings in which each tellurite group connects with one ZnO 3 Cl and two ZnO 2 Cl 2 tetrahedra. BaZn(SeO 3 ) 2 and BaZn(TeO 3 )Cl 2 are wide bandgap semiconductors based on optical diffuse reflectance spectrum measurements

Microscopic description of orbital-selective spin ordering in BaMn2As2

Science.gov (United States)

Craco, L.; Carara, S. S.

2018-05-01

Using generalized gradient approximation+dynamical mean-field theory, we provide a microscopic description of orbital-selective spin ordering in the tetragonal manganese pnictide BaMn2As2 . We demonstrate the coexistence of local moments and small band-gap electronic states in the parent compound. We also explore the role played by electron/hole doping, showing that the Mott insulating state is rather robust to small removal of electron charge carriers similar to cuprate oxide superconductors. Good qualitative accord between theory and angle-resolved photoemission as well as electrical transport provides support to our view of orbital-selective spin ordering in BaMn2As2 . Our proposal is expected to be an important step to understanding the emergent correlated electronic structure of materials with persisting ordered localized moments coexisting with Coulomb reconstructed nonmagnetic electronic states.

Colloidal synthesis of BaF2 nanoparticles and their application as fillers in polymer nanocomposites

Science.gov (United States)

Sathyamurthy, Srivatsan; Tuncer, Enis; More, Karren L.; Gu, Baohua; Sauers, Isidor; Paranthaman, M. Parans

2012-03-01

Nanoparticles of pure and Eu-doped BaF2 have been prepared through sol-gel colloidal synthesis. In addition, BaF2-filled PMMA polymer nanocomposites were fabricated and dielectric properties were measured. The as-synthesized pure and Eu-doped BaF2 nanoparticles were analyzed by both X-ray diffraction and transmission electron microscopy and consisted of crystalline BaF2 particles with an average diameter of 13.6 nm with a standard deviation of about ±2.4 nm. The photoluminescence properties of the pure and Eu-doped (2%, 4% and 8%) nanoparticles showed characteristic emission of Eu3+ (5D0→7F J ( J=1-4) transitions). We also measured significantly enhanced dielectric breakdown strength of up to 30% for BaF2 nanocomposites over the unfilled PMMA polymer. This study thus offers some promise of sol-gel synthesis of nanocomposite dielectrics with great potential for use as electrical insulation materials in cryogenic high-voltage applications.

Colloidal synthesis of BaF2 nanoparticles and their application as fillers in polymer nanocomposites

Energy Technology Data Exchange (ETDEWEB)

Sathyamurthy, Srivatsan [ORNL; Tuncer, Enis [ORNL; More, Karren Leslie [ORNL; Gu, Baohua [ORNL; Sauers, Isidor [ORNL; Paranthaman, Mariappan Parans [ORNL

2012-01-01

Nanoparticles of pure and Eu-doped BaF2 have been prepared through sol-gel colloidal synthesis. In addition, BaF2 filled PMMA polymer nanocomposites were fabricated and dielectric properties were measured. The as-synthesized pure and Eu-doped BaF2 nanoparticles were analyzed by both X-ray diffraction and transmission electron microscopy and consisted of crystalline BaF2 particles with an average diameter of 13.6 nm with a standard deviation of about 2.4 nm. The photoluminescence properties of the pure and Eu-doped (2%, 4% and 8%) nanoparticles showed characteristic emission of Eu3+ (5D0 7FJ (J=1-4) transitions). We also measured significantly enhanced dielectric breakdown strength of up to 30% for BaF2 nanocomposites over the unfilled PMMA polymer. This study thus offers some promise of sol-gel synthesis of nanocomposite dielectrics with great potential for use as electrical insulation materials in cryogenic high voltage applications.

Synthesis, crystal structure and electrical properties of A-site cation ordered BaErMn2O5 and BaErMn2O6

International Nuclear Information System (INIS)

Świerczek, Konrad; Klimkowicz, Alicja; Zheng, Kun; Dabrowski, Bogdan

2013-01-01

In this paper, we report on a synthesis procedure, structural and electrical properties of BaErMn 2 O 5 and BaErMn 2 O 6 , A-site double perovskites having layered arrangement of Ba and Er cations. These materials belong to a family of BaLnMn 2 O 5+δ oxides, which up to now were successfully synthesized for Ln=Y and La–Ho lanthanides. Up to our knowledge, this is the first report on the successful synthesis of BaErMn 2 O 5 and BaErMn 2 O 6 , yielding>95 wt% of the considered compounds. Structural characterization of the materials is given at room temperature, together with in situ XRD studies, performed during oxidation of BaErMn 2 O 5 in air, at elevated temperatures up to 500 °C. A complex structural behavior was observed, with oxidation process of BaErMn 2 O 5 occurring at around 300 °C. The oxidized BaErMn 2 O 6 shows a structural phase transition at about 225 °C. Results of structural studies are supported by thermogravimetric measurements of the oxidation process, performed in air, as well as reduction process, preformed in 5 vol% of H 2 in Ar. Additionally, isothermal oxidation/reduction cycles were measured at 500 °C, showing interesting properties of BaErMn 2 O 5+δ , from a point of view of oxygen storage technology. Electrical conductivity of BaErMn 2 O 5 is of the order of 10 −4 S cm −1 at room temperature and shows activated character on temperature with activation energy E a =0.30(1) eV. Positive sign of Seebeck coefficient for this material indicates holes as dominant charge carriers. Oxidized BaErMn 2 O 6 possesses much higher electrical conductivity, almost 0.2 S cm −1 at room temperature. Additional, about 10-fold increase of electrical conductivity, occurring in the vicinity of 225 °C for this material, can be associated with phase transition from charge/orbital-ordered insulator COI(CE) to paramagnetic metal PM phase. The highest conductivity for BaErMn 2 O 6 was measured near 500 °C and is almost equal to 40 S cm −1 , while

Growth of BaSi2 continuous films on Ge(111) by molecular beam epitaxy and fabrication of p-BaSi2/n-Ge heterojunction solar cells

Science.gov (United States)

Takabe, Ryota; Yachi, Suguru; Tsukahara, Daichi; Toko, Kaoru; Suemasu, Takashi

2017-05-01

We grew BaSi2 films on Ge(111) substrates by various growth methods based on molecular beam epitaxy (MBE). First, we attempted to form BaSi2 films directly on Ge(111) by MBE without templates. We next formed BaSi2 films using BaGe2 templates as commonly used for MBE growth of BaSi2 on Si substrates. Contrary to our prediction, the lateral growth of BaSi2 was not promoted by these two methods; BaSi2 formed not into a continuous film but into islands. Although streaky patterns of reflection high-energy electron diffraction were observed inside the growth chamber, no X-ray diffraction lines of BaSi2 were observed in samples taken out from the growth chamber. Such BaSi2 islands were easily to get oxidized. We finally attempted to form a continuous BaSi2 template layer on Ge(111) by solid phase epitaxy, that is, the deposition of amorphous Ba-Si layers onto MBE-grown BaSi2 epitaxial islands, followed by post annealing. We achieved the formation of an approximately 5-nm-thick BaSi2 continuous layer by this method. Using this BaSi2 layer as a template, we succeeded in forming a-axis-oriented 520-nm-thick BaSi2 epitaxial films on Ge substrates, although (111)-oriented Si grains were included in the grown layer. We next formed a B-doped p-BaSi2(20 nm)/n-Ge(111) heterojunction solar cell. A wide-spectrum response from 400 to 2000 nm was achieved. At an external bias voltage of 1 V, the external quantum efficiency reached as high as 60%, demonstrating the great potential of BaSi2/Ge combination. However, the efficiency of a solar cell under AM1.5 illumination was quite low (0.1%). The origin of such a low efficiency was examined.

Preparation of YBa2Cu3O7-δ powders by the thermal decomposition of a heteronuclear complex, CuY1/3Ba2/3(dhbaen)(NO3)1/3(H2O)3

International Nuclear Information System (INIS)

Hasegawa, E.; Aono, H.; Sadaoka, Y.; Traversa, E.

1999-01-01

YBa 2 Cu 3 O 7-δ powders were prepared by the thermal decomposition of a heteronuclear complex, CuY 1/3 Ba 2/3 (dhbaen)(NO 3 ) 1/3 (H 2 O) 3 . The products of the complex thermal decomposition were analyzed by TG-DTA, XRD, SEM-Auger and XPS. The decomposition of the CuY 1/3 Ba 2/3 -complex was obtained at about 500 C and the product was a mixture of oxides and carbonates. The formation of YBa 2 Cu 3 O 7-δ proceeded at 800 C, with a gradual decomposition of the carbonates. A homogeneous distribution of each element, Y, Ba, and Cu, was observed for the decomposed CuY 1/3 Ba 2/3 -complex by SEM-Auger analysis. The binding energy values of Ba3d 5/2 and O1s photolines from Ba and O in the superconductive lattice did not shift during the sputtering period. Furthermore, the formation of Ba rich regions on the surface was depressed by using the complex as a starting material for homogeneous 123-oxide, YBa 2 Cu 3 O 7-δ . (orig.)

Nanocomposite dielectrics in PbO-BaO-Na2O-Nb2O5-SiO2 system with high breakdown strength for high voltage capacitor applications.

Science.gov (United States)

Zhang, Qingmeng; Luo, Jun; Tang, Qun; Han, Dongfang; Zhou, Yi; Du, Jun

2012-11-01

Nanocomposite dielectrics in 6PbO-4BaO-20Na2O-40Nb2O5-30SiO2 system were prepared via melt-quenching followed by controlled crystallization. X-ray diffraction studies reveal that Pb2Nb2O7, Ba,NaNb5O15, NaNbO3 and PbNb2O6 phases are formed from the as-quenched glass annealed in temperature range from 700 degrees C to 850 degrees C. Ba2NaNb5O15, Pb2Nb2O7 crystallizes at 700 degrees C and then Pb2Nb2O7 disappears at 850 degrees C, while PbNb2O6 and NaNbO3 are formed at 850 degrees C. Microstructural observation shows that the crystallized particles are nanometer-sized and randomly distributed with glass matrix being often found at grain boundaries. The dielectric constant of the nanocomposites formed at different crystallization temperatures shows good frequency and electric field stability. The breakdown strength is slightly decreased when the glass-ceramics thickness is varied from 1 mm to 4 mm. The corresponding energy density could reach 2.96 J/cm3 with a breakdown strength of 58 kV/mm for thickness of 1 mm.

Polarized-neutron investigation of magnetic ordering and spin dynamics in BaCo2(AsO4)2 frustrated honeycomb-lattice magnet.

Science.gov (United States)

Regnault, L-P; Boullier, C; Lorenzo, J E

2018-01-01

The magnetic properties of the cobaltite BaCo 2 (AsO 4 ) 2 , a good realization of the quasi two-dimensional frustrated honeycomb-lattice system with strong planar anisotropy, have been reinvestigated by means of spherical neutron polarimetry with CRYOPAD. From accurate measurements of polarization matrices both on elastic and inelastic contributions as a function of the scattering vector Q , we have been able to determine the low-temperature magnetic structure of BaCo 2 (AsO 4 ) 2 and reveal its puzzling in-plane spin dynamics. Surprisingly, the ground-state structure (described by an incommensurate propagation vector [Formula: see text], with [Formula: see text] and [Formula: see text]) appears to be a quasi-collinear structure, and not a simple helix, as previously determined. In addition, our results have revealed the existence of a non-negligible out-of-plane moment component [Formula: see text]/Co 2+ , representing about 10% of the in-plane component, as demonstrated by the presence of finite off-diagonal elements [Formula: see text] and [Formula: see text] of the polarization matrix, both on elastic and inelastic magnetic contributions. Despite a clear evidence of the existence of a slightly inelastic contribution of structural origin superimposed to the magnetic excitations at the scattering vectors [Formula: see text] and [Formula: see text] (energy transfer [Formula: see text] meV), no strong inelastic nuclear-magnetic interference terms could be detected so far, meaning that the nuclear and magnetic degrees of freedom have very weak cross-correlations. The strong inelastic [Formula: see text] and [Formula: see text] matrix elements can be understood by assuming that the magnetic excitations in BaCo 2 (AsO 4 ) 2 are spin waves associated with trivial anisotropic precessions of the magnetic moments involved in the canted incommensurate structure.

Quasiparticle mass enhancement close to the quantum critical point in BaFe2(As(1-x)P(x))2.

Science.gov (United States)

Walmsley, P; Putzke, C; Malone, L; Guillamón, I; Vignolles, D; Proust, C; Badoux, S; Coldea, A I; Watson, M D; Kasahara, S; Mizukami, Y; Shibauchi, T; Matsuda, Y; Carrington, A

2013-06-21

We report a combined study of the specific heat and de Haas-van Alphen effect in the iron-pnictide superconductor BaFe2(As(1-x)P(x))2. Our data when combined with results for the magnetic penetration depth give compelling evidence for the existence of a quantum critical point close to x=0.30 which affects the majority of the Fermi surface by enhancing the quasiparticle mass. The results show that the sharp peak in the inverse superfluid density seen in this system results from a strong increase in the quasiparticle mass at the quantum critical point.

Rapid enhancement of nodal quasiparticle mass with heavily underdoping in Bi2212

Science.gov (United States)

Anzai, Hiroaki; Arita, Masashi; Namatame, Hirofumi; Taniguchi, Masaki; Ishikado, Motoyuki; Fujita, Kazuhiro; Ishida, Shigeyuki; Uchida, Shin-ichi; Ino, Akihiro

2018-05-01

We report substantial advance of our low-energy angle-resolved photoemission study of nodal quasiparticles in Bi2Sr2CaCu2O8+δ. The new data cover the samples from underdoped down to heavily underdoped levels. We also present the nodal Fermi velocities that determined by using an excitation-photon energy of hν = 7.0 eV over a wide doping range. The consistency between the results with hν = 8.1 and 7.0 eV allows us to rule out the effect of photoemission matrix elements. In comparison with the data previously reported, the nodal effective mass increases by a factor of ∼ 1.5 in going from optimally doped to heavily underdoped levels. We find a rapid enhancement of the nodal quasiparticle mass at low doping levels near the superconductor-to-insulator transition. The effective coupling spectrum, λ (ω) , is extracted directly from the energy derivatives of the quasiparticle dispersion and scattering rate, as a causal function of the mass enhancement factor. A steplike increase in Reλ (ω) around ∼ 65 meV is demonstrated clearly by the Kramers-Kronig transform of Imλ (ω) . To extract the low-energy renormalization effect, we calculated a simple model for the electron-boson interaction. This model reveals that the contribution of the renormalization at | ω | ≤ 15 meV to the quasiparticle mass is larger than that around 65 meV in underdoped samples.

Crystal and Electronic Structures, Photoluminescence Properties of Eu2+-Doped Novel Oxynitride Ba4Si6O16-3x/2Nx

Directory of Open Access Journals (Sweden)

Takashi Takeda

2010-03-01

Full Text Available The crystal structure and the photoluminescence properties of novel green Ba4-yEuySi6O16-3x/2Nx phosphors were investigated. The electronic structures of the Ba4Si6O16 host were calculated by first principles pseudopotential method based on density functional theory. The results reveal that the top of the valence bands are dominated by O-2p states hybridized with Ba-6s and Si-3p states, while the conduction bands are mainly determined by Ba-6s states for the host, which is an insulator with a direct energy gap of 4.6 eV at Γ. A small amount of nitrogen can be incorporated into the host to replace oxygen and forms Ba4-yEuySi6O16-3x/2Nx solid solutions crystallized in a monoclinic (space group P21/c, Z = 2 having the lattice parameters a = 12.4663(5 Å, b = 4.6829(2 Å, c = 13.9236(6 Å, and β = 93.61(1°, with a maximum solubility of nitrogen at about x = 0.1. Ba4Si6O16-3x/2Nx:Eu2+ exhibits efficient green emission centered at 515–525 nm varying with the Eu2+ concentration when excited under UV to 400 nm. Furthermore, the incorporation of nitrogen can slightly enhance the photoluminescence intensity. Excitation in the UV-blue spectral range (λexc = 375 nm, the absorption and quantum efficiency of Ba4-yEuySi6O16-3x/2Nx (x = 0.1, y = 0.2 reach about 80% and 46%, respectively. Through further improvement of the thermal stability, novel green phosphor of Ba4-yEuySi6O16-3x/2Nx is promising for application in white UV-LEDs.

Dual ferroic properties of hexagonal ferrite ceramics BaFe_1_2O_1_9 and SrFe_1_2O_1_9

International Nuclear Information System (INIS)

Kostishyn, V.G.; Panina, L.V.; Timofeev, A.V.; Kozhitov, L.V.; Kovalev, A.N.; Zyuzin, A.K.

2016-01-01

Dual ferroic properties of a strong magnetism and large ferroelectricity have been observed in barium BaFe_1_2O_1_9 and strontium SrFe_1_2O_1_9 hexaferrite ceramics. The samples were fabricated by a modified ceramic technique from highly purified raw materials with addition of boron oxide allowing the control of grain size and enhancement of bulk resistivity. Whereas the samples of PbFe_1_2O_1_9 fabricated by the same technological method did not have sufficient electric resistivity to support an electric field and did not exhibit the ferroelectric properties. The structure of the samples examined by X-ray diffraction is consistent with a single hexagonal phase. The grains are randomly oriented with the average grain size of 300–400 nm coated with boron oxide. The magnetic properties are characterised by standard ferrimagnetic behavior with the Neel temperature of about 450 °C. Large spontaneous polarization was observed with the maximal values of 45–50 μC/cm"2 under an applied electric field of 100–300 kV/m. A strong coupling between magnetic and electric ordering was confirmed by measuring the magnetoelectric (ME) parameter and magnetodielectric ratio. These ME characteristics are more advanced than those for well-known room temperature multiferroic BiFeO_3. Furthermore, by applying an electric field, the manipulation of magnetization in the range of up to 9% was observed, which is even greater than in some substituted hexaferrites with a non-collinear magnetic structure. The obtained results on electrical polarization are similar to the values reported for the corresponding hexaferrites sintered by polymer precursor technique. This suggests a promising potential of M-type hexaferrite ceramics in devices utilizing magnetoelectric coupling. - Highlights: • Ba(Sr)Fe_1_2O_1_9-hexaferrites show large room-temperature multiferroic properties. • Small addition of B_2O_3 increases the hexaferrite resistivity by 4 orders of magnitude. • Large spontaneous

Electronic structure and transport properties of Ba2Cd2Pn3 (Pn = As and Sb): An efficient materials for energy conversion

International Nuclear Information System (INIS)

Reshak, A.H.

2016-01-01

The full potential method within the recently modified Becke-Johnson potential explore that the Ba 2 Cd 2 Pn 3 (Pn = As and Sb) compounds are narrow band gap semiconductors of about 0.49 and 0.32 eV, which confute the finding of the previous TB-LMTO-ASA calculation that Ba 2 Cd 2 Sb 3 is a poor metal. It has been found that there are subtle difference in band desperations of the two compounds, resulting in significant influence on the electronic and transport properties, taking into account the size and the electro-negativity differences between As and Sb atoms. Calculation show that there exists a strong hybridization between the orbitals which may lead to form covalent bonding which is more favorable for the transport of the carriers than ionic one. The electronic structure, the anisotropy and the inter-atomic interactions are further analyzed by calculating the valence electronic charge density distribution in two crystallographic planes. The semi-classical Boltzmann theory as incorporated in BoltzTraP code was used to calculate the transport properties of Ba 2 Cd 2 As 3 and Ba 2 Cd 2 Sb 3 at different temperatures and chemical potentials to ascertain the influence of temperatures and substituting As by Sb on the transport properties. The carries mobility decreases with increasing the temperature also with increasing the carriers concentration. We have observed that substituting As by Sb lead to increase the carries mobility of Ba 2 Cd 2 Sb 3 along the whole temperature interval and the carries concentration range. It has been found that Ba 2 Cd 2 As 3 exhibit higher carriers concentration, electronic electrical conductivity and Seebeck coefficient than that of Ba 2 Cd 2 Sb 3 along the investigated temperature range. The highest value of Seebeck coefficient occurs at 300 K, which show good agreement with the experimental data. The power factor increases linearly with increasing the temperature and Ba 2 Cd 2 As 3 exhibit a bit higher power factor than that of Ba

An electron diffraction and bond valence sum study of the space group symmetries and structures of the photocatalytic 1:1 ordered A2InNbO6 double perovskites (A=Ca2+, Sr2+, Ba2+)

International Nuclear Information System (INIS)

Ting, V.; Liu, Y.; Withers, R.L.; Krausz, E.

2004-01-01

A careful investigation has been carried out into the space group symmetries, structures and crystal chemistries of the 1:1 B-site ordered double perovskites A 2 InNbO 6 (A=Ca 2+ , Sr 2+ , Ba 2+ ) using a combination of bond valence sum calculations, powder XRD and electron diffraction. A recent investigation of these compounds by Yin et al. reported a random distribution of In 3+ and Nb 5+ ions onto the perovskite B-site positions of these compounds and hence Pm3-barm (a=a p , subscript p for parent perovskite sub-structure) space group symmetry for the A=Ba and Sr compounds and Pnma (a=a p +b p , b=-a p +b p , c=2c p ) space group symmetry for the A=Ca compound. A careful electron diffraction study, however, shows that both the A=Ca and Sr compounds occur at room temperature in P12 1 /n1 (a=a p +b p , b=-a p +b p , c=2c p ) perovskite-related superstructure phases while the A=Ba compound occurs in the Fm3-barm, a=2a p , elpasolite structure type. Bond valence sum calculations are used to explain why this should be so as well as to provide a useful first-order approximation to the structures of each of the compounds

Syntheses, and crystal and electronic structures of the new Zintl phases Na2ACdSb2 and K2ACdSb2 (A=Ca, Sr, Ba, Eu, Yb): Structural relationship with Yb2CdSb2 and the solid solutions Sr2-xAxCdSb2, Ba2-xAxCdSb2 and Eu2-xYbxCdSb2

International Nuclear Information System (INIS)

Saparov, Bayrammurad; Saito, Maia; Bobev, Svilen

2011-01-01

Presented are the details of the syntheses, crystal and electronic structures of a new family of Zintl phases Na 2 ACdSb 2 and K 2 ACdSb 2 (A=Ca, Sr, Ba, Eu, Yb), as well as the solid solutions Sr 2-x A x CdSb 2 , Ba 2-x A x CdSb 2 and Eu 2-x Yb x CdSb 2 . The structures of Na 2 ACdSb 2 and K 2 ACdSb 2 (A=Ca, Sr, Ba, Eu, Yb) were determined to be of a new type with the non-centrosymmetric space group Pmc2 1 (no. 26), Pearson symbol oP12, with lattice parameters a=4.684(1)-4.788(1) A; b=9.099(3)-9.117(2) A; c=7.837(1)-8.057(2) A for the Na 2 ACdSb 2 series, and a=4.6637(9)-5.0368(8) A; b=9.100(2)-9.8183(15) A; and c=7.7954(15)-8.4924(13) A for K 2 ACdSb 2 , respectively. The solid solutions Sr 2-x A x CdSb 2 , Ba 2-x A x CdSb 2 and Eu 2-x Yb x CdSb 2 (x∼1) are isostructural and isoelectronic to the recently reported Yb 2 CdSb 2 (space group Cmc2 1 (no. 36), Pearson symbol cP20). All discussed structures are based upon CdSb 2 4- polyanionic layers, similar to the ones observed in Yb 2 CdSb 2 , with various alkali- and/or alkaline-earth cations coordinated to them. Magnetic susceptibility and Seebeck coefficient measurements on selected Eu 2-x Yb x CdSb 2 samples, taken at low temperatures up to 300 K, are also reported. -- Graphical abstract: The quaternary Zintl phases Na 2 ACdSb 2 and K 2 ACdSb 2 (A=Ca, Sr, Ba, Eu, Yb) with novel layered structures have been synthesized for the first time and structurally characterized by single-crystal X-ray diffraction. Reported as well are the results from crystallographic and property studies of the closely related solid solutions Sr 2-x A x CdSb 2 , Ba 2-x A x CdSb 2 (x∼1), and Eu 2-x Yb x CdSb 2 (1 2 ACdSb 2 and K 2 ACdSb 2 (A=Ca, Sr, Ba, Eu, Yb) are new quaternary Zintl phases. → Sr 2-x A x CdSb 2 , Ba 2-x A x CdSb 2 (x∼1), and Eu 2-x Yb x CdSb 2 (1 4 tetrahedra. → Eu 2-x Yb x CdSb 2 (1< x<2) exhibit high Seebeck coefficient (217 μV/K at RT).

Growing barium hexaferrite (BaFe_1_2O_1_9) thin films using chemical solution deposition

International Nuclear Information System (INIS)

Budiawanti, Sri; Soegijono, Bambang

2016-01-01

Barium hexaferrite (BaFe_1_2O_1_9, or simply known as BaM) thin films has been recognized as a potential candidate for microwave-based devices, magnetic recording media and data storage. To grow BaM thin films, chemical solution deposition is conducted using the aqueous solution of metal nitrates, which involves spin coatings on Si substrates. Furthermore, Thermal Gravimeter Analysis (TGA), X-Ray Diffractometer (XRD), Scanning Electron Microscopy (SEM) and Vibrating Sample Magnetometer (VSM) are applied to evaluate the decomposition behavior, structure, morphology, and magnetic properties of BaM thin films. Additionally, the effects of number of layers variation are also investigated. Finally, magnetic properties analysis indicates the isotropic nature of the films.

Versatility of {l_brace}M(30-crown-10){r_brace} (M = K{sup +}, Ba{sup 2+}) as a guest in UO{sub 2}{sup 2+} complexes of 3.1.3.1 - and 3.3.3 homo-oxa-calixarenes

Energy Technology Data Exchange (ETDEWEB)

Masci, B. [Univ Roma La Sapienza, Dipartimento Chim, I-00185 Rome, (Italy); Thuery, P. [CEA Saclay, DSM/DRECAM/SCM, CNRS-URA 331, F-91191 Gif Sur Yvette, (France)

2007-07-01

The reaction between p-R-[3.1.3.1]- or [3.3.3] homo-oxa-calixarenes and uranyl salts in the presence of 30-crown-10 and the alkali or alkaline-earth metal cations K{sup +} or Ba{sup 2+} gives various supramolecular assemblages characterized by 'complex-within-complex' architectures. These can be of the simple nesting or sandwich types, as in [{l_brace}Ba(30-crown-10){r_brace}{l_brace}UO{sub 2}(L{sup 1}){r_brace}]. 2H{sub 2}O.3CHCl{sub 3} (L{sup 1}H{sub 4} p-tert-butyl[3.1.3.1] homo-oxa-calixarene) and [{l_brace}Ba(30-crown-10){r_brace}{l_brace}UO{sub 2}(L{sup 4}){r_brace}{sub 2}].2CHCl{sub 3} (L{sup 4}H{sub 3} p-bromo[3.3.3]homo-oxa-calixarene), respectively, with the cation held in the cavity of the homo-oxa-calixarene complexes in cone conformation by weak interactions, but more original structures arise when uranyl-cation bonds are present. In [{l_brace}Ba(30-crown-10){r_brace}{l_brace}UO{sub 2}(L{sup 2}){r_brace}] (L{sup 2}H{sub 4} p-phenyl[3.1.3.1] homo-oxa-calixarene), the barium ion included in the crown ether is bound to the uranyl oxo group located out of the calixarene cavity, resulting in the formation of a neutral species which self-organizes to form a columnar assembly by auto-inclusion. In [{l_brace}K(30-crown-10){r_brace}{l_brace}UO{sub 2}K(L{sup 1})(H{sub 2}O){sub 3}{r_brace}]{sub 2}.6H{sub 2}O, the nesting-type subunit dimerizes around two oxo-bound potassium ions. Finally, the use of the coordinating solvent dimethylsulfoxide leads to the neutral complex [UO{sub 2}Ba(L{sup 3})(dmso){sub 2}(MeOH)]{sub 2} (L{sup 3}H{sub 4} = p-methyl[3.1.3.1] homo-oxa-calixarene), in which the crown ether is absent and two oxo-, phenoxo- and ether-bound barium atoms ensure the dimerization of the uranyl complex. (authors)

Electrical and magnetic properties of 0-3 Ba(Fe1/2Nb1/2)O3/PVDF composites

Science.gov (United States)

Ranjan, Hars; Mahto, Uttam K.; Chandra, K. P.; Kulkarni, A. R.; Prasad, A.; Prasad, K.

Lead-free Ba(Fe1/2Nb1/2)O3/PVDF 0-3 composites were fabricated using melt-mixing technique. X-ray diffraction, scanning electron microscopy, dielectric, impedance, ac conductivity, magnetic force microscopy (MFM) and vibrating sample magnetometer studies were undertaken to characterize the samples. Average crystallite size of the Ba(Fe1/2Nb1/2)O3 powder, estimated using Williamson-Hall approach, was found to be ˜42nm. The filler particles of ˜0.5-1μm were found to disperse in the polymer matrix of all the composites. Filler concentration-dependent values of real and imaginary parts of complex permittivity showed increasing trend and were seen to follow Bruggeman and Furukawa equations. The data for ac conductivity exhibited negative temperature coefficient of resistance character of the test materials and were found to obey Jonscher’s power law. The correlated barrier hopping model was found to explain satisfactorily the mechanism of charge transport occurring in the system. MFM confirmed the presence of magnetic phases in the composites. Typical magnetization versus applied field curves indicated the possibility of magnetoelectric coupling in the system. Hence, the present composites have shown themselves as potential multi-functional candidate materials for use in high density data storage applications.

Upper critical field and superconducting anisotropy of BaFe2-xRuxAs2 (x=0.48 and 0.75) single crystals

International Nuclear Information System (INIS)

Jo, Youn Jung; Eom, Man Jin; Kim, Jun Sung; Kang, W.

2014-01-01

The upper critical field (H c 2 ) was determined by applying a magnetic field along the ab plane and c axis for two single crystals of BaFe 2-x Ru x As 2 (x=0.48 and 0.75). The anisotropy of the H c 2 (0), γ(0)=H c 2 ab (0)/H c 2 c (0), was ∼1.6 for x=0.48 and ∼2.3 for x=0.75. The angle-dependent resistance measured below T c allowed perfect scaling features based on anisotropic Ginzburg-Landau theory, leading to consistent anisotropy values. Because only one fitting parameter γ is used in the scaling for each temperature, the validity of the γ value was compared with that determined from γ=H c 2 ab /H c 2 c . The γ obtained at a temperature close to Tc was 3.0 and decreased to 2.0 at low temperatures. Comparing to the anisotropy determined for electron- or hole-doped BaFe 2 As 2 using the same method, the present results point to consistent anisotropy in Ru-doped BaFe 2 As 2 with other electron- or hole-doped BaFe 2 As 2 .

Effect of Sr substitution on superconductivity in Hg2(Ba1-ySry)2YCu2O8-d (part2): bond valence sum approach of the hole distribution

OpenAIRE

Toulemonde, P.; Odier, P.; Bordet, P.; Floch, S. Le; Suard, E.

2004-01-01

The effects of Sr substitution on superconductivity, and more particulary the changes induced in the hole doping mechanism, were investigated in Hg2(Ba1-ySry)2YCu2O8-d by a "bond valence sum" analysis with Sr content from y = 0.0 to y = 1.0. A comparison with CuBa2YCu2O7-d and Cu2Ba2YCu2O8 systems suggests a possible explanation of the Tc enhancement from 0 K for y = 0.0 to 42 K for y = 1.0. The charge distribution among atoms of the unit cell was determined from the refined structure, for y ...

First-principles calculation on electronic structure and optical property of BaSi{sub 2}O{sub 2}N{sub 2}:Eu{sup 2+} phosphor

Energy Technology Data Exchange (ETDEWEB)

Tong, Zhi-Fang, E-mail: tongzhifang1998@126.com; Wei, Zhan-Long; Xiao, Cheng

2017-04-15

The crystal structure, electronic structure and optical properties of BaSi{sub 2}O{sub 2}N{sub 2}:Eu{sup 2+} with varying Eu doping concentrations are computed by the density functional theory (DFT) and compared with experimental results. The results show that the lattice parameters of primitive cells of Ba{sub 1−x}Si{sub 2}O{sub 2}N{sub 2}:Eu{sub x} become smaller and Eu–N bond length shortens as Eu concentration increases. The band structure of Ba{sub 1−x}Si{sub 2}O{sub 2}N{sub 2}:Eu{sub x} exhibits a direct optical band gap and it's propitious to luminescence. The energy differences from the lowest Eu 5d state to the lowest Eu 4f state decrease with increasing Eu concentrations. The analysis of simulative absorption spectra indicates that the electron transition from Eu 4f states to 5d states of both Eu and Ba atoms contributes to the absorption of Ba{sub 1−x}Si{sub 2}O{sub 2}N{sub 2}:Eu{sub x}. Under the coupling effect between Eu and Ba, Ba in BaSi{sub 2}O{sub 2}N{sub 2} exhibits longer wavelength absorption and increases absorption efficiency. The emission wavelength is deduced by measuring energy differences from the lowest Eu 5d state to the lowest Eu 4f state, and the result is in good agreement with experimental value within experimental Eu{sup 2+} doping range. - Graphical abstract: The structure and optical property of BaSi{sub 2}O{sub 2}N{sub 2}:Eu{sup 2+} are computed by DFT and its absorption mechanism is analysed. Results show that absorption peak α is from the host lattice absorption. The absorption peaks β, γ and δ are from Eu 4f to Eu 5d and Ba 6s 5d states. The absorption is attributed to the coupling effect of Eu and Ba atom. - Highlights: • The crystal, electronic structure and optical properties of BaSi{sub 2}O{sub 2}N{sub 2}:Eu{sup 2+} are computed by DFT. • The lattice parameters of primitive cells reduces and Eu–N bond length shortens as Eu{sup 2+} increases. • The energy gap from Eu 5d state to Eu 4f state

High field properties of superconducting BaFe{sub 2-x}Ni{sub x}As{sub 2} thin films

Energy Technology Data Exchange (ETDEWEB)

Richter, Stefan [Institute for Metallic Materials, IFW Dresden (Germany); Technical University Dresden (Germany); Kurth, Fritz; Grinenko, Vadim; Nielsch, Kornelius; Huehne, Ruben [Institute for Metallic Materials, IFW Dresden (Germany); Iida, Kazumasa [Nagoya University (Japan); Pervakov, Kirill [Russian Academy of Sciences (Russian Federation); Tarantini, Chiara; Jaroszynski, Jan [National High Magnetic Field Laboratory (United States); Pukenas, Aurimas; Skrotzki, Werner [Technical University Dresden (Germany)

2016-07-01

Fe based superconductors combine the advantages of cuprates (high upper critical field) with the small Hc{sub 2} anisotropy of classic low temperature superconductors, which makes them suitable candidates for high field applications. The study of Fe-based superconducting thin films is one crucial step to explore this potential in more detail. We present results for epitaxial BaFe{sub 2-x}Ni{sub x}As{sub 2} thin films, which have been successfully grown for the first time using pulsed laser deposition. Superconducting transition temperatures of up to 19 K have been realized in slightly overdoped films, which is in good agreement with results obtained for single crystals. The behavior of the upper critical field and critical current density has been measured in high magnetic fields up to 35 T. The results will be correlated to the observed microstructure and compared to high field data for single crystals with similar composition.

In-plane optical response in underdoped YBCO

Science.gov (United States)

Kakeshita, Teruhisa; Masui, Takahiko; Tajima, Setsuko

2005-03-01

The recent STM experiments demonstrated that the electronic state in CuO2 plane is inhomogeneous [1], which becomes conspicuous in the underdoped regime. In such an inhomogeneous state, it is not obvious whether a superfluid density is correctly estimated by a conventional way. We investigated the in-plane optical response for underdoped YBCO crystal to discuss the relation between inhomogeneity and superfluid density in the pseudo-gapped state. The a-axis optical spectrum shows a larger residual conductivity than that for the optimum doping. The superfluid density estimated from our optical spectrum at the lowest temperature is substantially smaller than that determined by μSR. We discuss this strongly suppressed superfluid density and the large residual conductivity in terms of the inhomogeneity in real- and k-space. This work was supported by the New Energy and Industrial Technology Development Organization(NEDO) through ISTEC as the Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications. [1]K.M.Lang et al., Nature 415, 412 (2002). *present address: Dept. of Physics, Osaka University, Machikaneyama 1-1, Toyonaka, Osaka 560-0043, Japan

Data of evolutionary structure change: 1C7BA-2ZLWD [Confc[Archive

Lifescience Database Archive (English)

Full Text Available 1C7BA-2ZLWD 1C7B 2ZLW A D -MLSPADKTNVKAAWGKVGAHAGEYGAEALERMFLSFPT...R VQLSGEEKAAVLALWDKVN--EEEVGGEALGRLLVVYPWTQRFFDSFGDLSNPGAVMGNPKVKAHGKKVLHSFGEGVHHLDNLKGTFAALSEL.../index> 2ZLW D 2ZLWD

Carbon-14 immobilization via the Ba(OH)2.8H2O process

International Nuclear Information System (INIS)

Haag, G.L.; Nehls, J.W. Jr.; Young, G.C.

1983-03-01

The airborne release of 4 C from varous nuclear facilities has been identified as a potential biohazard due to the long half-life of 14 C (5730 y) and the ease with which it may be assimilated into the biosphere. At ORNL, technology has been developed for the removal and immobilization of this radionuclide. Prior studies have indicated that 14 C will likely exist in the oxidized form as CO 2 and will contribute slightly to the bulk CO 2 concentration of the gas stream, which is airlike in nature (approx. 330 ppmv CO 2 ). The technology that has been developed utilizes the CO 2 -Ba(OH) 2 .8H 2 O gas-solid reaction with the mode of gas-solid contacting being a fixed bed. The product, BaCO 3 , possesses excellent thermal and chemical stability, prerequisites for the long-term disposal of nuclear wastes. For optimal process operation, studies have indicated that an operating window of adequate size does exist. When operating within the window, high CO 2 removal efficiency (effluent concentrations 99%), and an acceptable pressure drop across the bed (3 kPa/m at a superficial velocity of 13 cm/s) are possible. This paper addresses three areas of experimental investigation: (1) microscale studies on 150-mg samples to provide information concerning surface properties, kinetics, and equilibrium vapor pressures; (2) macroscale studies on large fixed beds (4.2 kg of reactant) to determine the effects of humidity, temperature, and gas flow rate upon bed pressure drop and CO 2 breakthrough; and (3) design, construction, and initial operation of a pilot unit capable of continuously processing a 34-m 3 /h (20-ft 3 /min) air-based gas stream

Effect of Sr substitution on superconductivity in Hg2(Ba1-ySry)2YCu2O8-d (part 1): a neutron powder diffraction study

OpenAIRE

Toulemonde, P.; Odier, P.; Bordet, P.; Floch, S. Le; Suard, E.

2002-01-01

The effect of Sr chemical pressure on superconductivity was investigated in Hg2(Ba1-ySry)2YCu2O8-d. The samples were synthesized at high pressure-high temperature from y = 0.0 to full substitution, y = 1.0. These Sr-substituted compounds are superconducting, without Ca doping on the Y site, and show an increasing Tc with Sr, reaching 42 K for y = 1.0. A detailed neutron powder diffraction study compares the structural changes induced by this chemical Sr/Ba substitution and the mechanical pres...

Polarized-neutron investigation of magnetic ordering and spin dynamics in BaCo2(AsO42 frustrated honeycomb-lattice magnet

Directory of Open Access Journals (Sweden)

L.-P. Regnault

2018-01-01

Full Text Available The magnetic properties of the cobaltite BaCo2(AsO42, a good realization of the quasi two-dimensional frustrated honeycomb-lattice system with strong planar anisotropy, have been reinvestigated by means of spherical neutron polarimetry with CRYOPAD. From accurate measurements of polarization matrices both on elastic and inelastic contributions as a function of the scattering vector Q, we have been able to determine the low-temperature magnetic structure of BaCo2(AsO42 and reveal its puzzling in-plane spin dynamics. Surprisingly, the ground-state structure (described by an incommensurate propagation vector k1=(kx,0,kz, with kx=0.270±0.005 and kz≈−1.31 appears to be a quasi-collinear structure, and not a simple helix, as previously determined. In addition, our results have revealed the existence of a non-negligible out-of-plane moment component ≈0.25μB/Co2+, representing about 10% of the in-plane component, as demonstrated by the presence of finite off-diagonal elements Pyz and Pzy of the polarization matrix, both on elastic and inelastic magnetic contributions. Despite a clear evidence of the existence of a slightly inelastic contribution of structural origin superimposed to the magnetic excitations at the scattering vectors Q=(0.27,0,3.1 and Q=(0.73,0,0.8 (energy transfer ΔE≈2.3 meV, no strong inelastic nuclear-magnetic interference terms could be detected so far, meaning that the nuclear and magnetic degrees of freedom have very weak cross-correlations. The strong inelastic Pyz and Pzy matrix elements can be understood by assuming that the magnetic excitations in BaCo2(AsO42 are spin waves associated with trivial anisotropic precessions of the magnetic moments involved in the canted incommensurate structure.

Ca doping of TSMTG-YBa2Cu3O7-δ/Y2BaCuO5 composites

International Nuclear Information System (INIS)

Delorme, F.; Harnois, C.; Monot-Laffez, I.; Marinel, S.

2002-01-01

Calcium doped YBa 2 Cu 3 O 7-δ /Y 2 BaCuO 5 bulk samples have been synthesised by the top-seeding-melt-texture growth (TSMTG) process up to 1 wt.% of CaCO 3 . Calcium additions up to 0.25 wt.% of CaCO 3 do not change the decomposition temperature whereas additions of 1 wt.% of CaCO 3 lead to an increase of the decomposition temperature of about 10 deg. C. This difference is not important enough to change the thermal cycle used to process YBa 2 Cu 3 O 7-δ undoped bulk samples. Microstructure studies show that no precursor or secondary phases containing calcium are present in the samples. Energy dispersive spectroscopy analyses have shown that Ca is present both in the YBa 2 Cu 3 O 7-δ matrix and the Y 2 BaCuO 5 particles. The position of the calcium atoms in the superconducting matrix is discussed. The calcium doped samples present slightly depressed critical temperatures but drastically depressed critical current densities

Polymorphism of perovskite compounds Ba/sub 2/SEsub(0. 67)Wsup(VI)O/sub 6/. 2. The systems Ba/sub 2/Ndsub(0. 67(1-x))Ysub(0. 67x)WO/sub 6/ and Ba/sub 2/Ndsub(0. 67)Wsub(1-x)Usub(x)O/sub 6/

Energy Technology Data Exchange (ETDEWEB)

Schnittenhelm, H J; Kemmler-Sack, S [Tuebingen Univ. (Germany, F.R.). Inst. fuer Chemie

1977-06-01

In the system Ba/sub 2/Ndsub(0.67(1-x))Ysub(0.67x)WO/sub 6/ the formation of a continuous series of mixed crystals with cubic 1:1 ordered perovskite structure is observed. The existence of a hexagonal modification is confined to the Y-rich side (x => 0.9). In the Ba/sub 2/Ndsub(0.67)Wsub(1-x)Usub(x)O/sub 6/ series only for x =< 0.25 homogeneous cubic perovskites are obtained. In contrast to systems with other rare earths the Nd series show uncommon optical properties.

The case for spin-fluctuation induced pairing in Ba{sub 1-x}K{sub x}Fe{sub 2}As{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Boehm, Thomas U.

2017-03-07

The microscopic mechanism and the experimental identification of unconventional superconductivity is one of the most vexing problems of contemporary condensed matter physics. Raman spectroscopy provides a new avenue for this quest by accessing the hierarchy of superconducting pairing propensities. The doping-dependent study of competing pairing channels in Ba{sub 1-x}K{sub x}Fe{sub 2}As{sub 2} for 0.22 ≤ x ≤ 0.70 is one of the main aspects of this thesis. The observations demonstrate the importance of spin fluctuations for Cooper pairing.

NMR/NQR study of the superconductor Y2Ba4Cu7O15

International Nuclear Information System (INIS)

Stern, R.

1995-01-01

This dissertation concentrates on several important aspects of the high temperature superconductivity research. Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) studies in Y-Ba-O compounds contribute information regarding various aspects, ranging from the direct observation of strong coupling between the adjacent planes in the double plane to conclusions concerning the spatial symmetry of paring state in these cuprates. We report the first results in the 93 K superconductor Y 2 Ba 4 Cu 7 O 15 . This compound turns out to be a structure containing differently doped CuO 2 planes. The planes in the 1-2-3(1-2-4) block are only slightly lower (higher) doped than those in the corresponding parent compounds YBa 2 Cu 3 O 7 and YBa 2 Cu 4 O 8 . The results obtained from measurements on oxygen depleted Y 2 Ba 4 Cu 7 O 15-x show two new features which could explain the dissimilar variation of T c with oxygen content compared to YBa 2 Cu 3 O 7-x : i) the double chains donate charge carriers to the planes and ii) the chain fragments which survive when emptying single chains are longer than in YBa 2 Cu 3 O 7-x . The pressure induced charge transfer from chain to plane in each block of Y 2 Ba 4 Cu 7 O 15 is the same as in the corresponding parent compound. We explore the strong coupling between nonequivalent planes in this compound using the three main NMR/NQR quantities, K spin , 1/T 1 ; and T 2G,ind , and estimate its approximate strength directly from spin-echo double resonance (SEDOR) experiments. We obtain for the ratio of the effective inter- and intraplane exchange-coupling constants the value of 0.3 just above T c . This ratio decreases with increasing temperature. (author) figs., tabs., refs

Magnetic excitations and phase separation in the underdoped La2-xSrxCuO4 superconductor measured by resonant inelastic X-ray scattering.

Science.gov (United States)

Braicovich, L; van den Brink, J; Bisogni, V; Sala, M Moretti; Ament, L J P; Brookes, N B; De Luca, G M; Salluzzo, M; Schmitt, T; Strocov, V N; Ghiringhelli, G

2010-02-19

We probe the collective magnetic modes of La2CuO4 and underdoped La2-xSrxCuO4 (LSCO) by momentum resolved resonant inelastic x-ray scattering (RIXS) at the Cu L3 edge. For the undoped antiferromagnetic sample, we show that the single magnon dispersion measured with RIXS coincides with the one determined by inelastic neutron scattering, thus demonstrating that x rays are an alternative to neutrons in this field. In the spin dynamics of LSCO, we find a branch dispersing up to approximately 400 meV coexisting with one at lower energy. The high-energy branch has never been seen before. It indicates that underdoped LSCO is in a dynamic inhomogeneous spin state.

Ruthenium perovskites of type Ba/sub 2/BRuO/sub 6/ and Ba/sub 3/BRu/sub 2/O/sub 9/ with B = indium, rhodium

Energy Technology Data Exchange (ETDEWEB)

Schaller, H U; Kemmler-Sack, S [Tuebingen Univ. (Germany, F.R.). Lehrstuhl fuer Anorganische Chemie 2

1981-02-01

The black perovskites Ba/sub 2/InRu/sup 5 +/O/sub 6/ and Ba/sub 3/InRu/sub 2/O/sub 9/ (mean oxydation state of ruthenium: +4.5) adopt the hexagonal BaTiO/sub 3/ structure and form a continuous series of mixed crystals. According to the intensity calculations and analysis of the vibrational spectroscopic data an ordered distribution between indium and ruthenium is present: 1:1 order in Ba/sub 2/RuO/sub 6/ (space group P-3m1 respective Dsub(3d)/sup 3/; R' = 5.3%); 1:2 order in Ba/sub 3/InRu/sub 2/O/sub 9/ (space group P6/sub 3//mmc respective Dsub(6h)/sup 4/; R' = 4.6%). The corresponding black Rh compounds, Ba/sub 2/RhRuO/sub 6/ and Ba/sub 3/RhRu/sub 2/O/sub 9/, crystallize in the rhombohedral 9 L type of BaRuO/sub 3/ (author).

Structural feature controlling superconductivity in compressed BaFe2As2

International Nuclear Information System (INIS)

Yang, Wenge; Jia, Feng-Jiang; Tang, Ling-Yun; Tao, Qian; Xu, Zhu-An; Chen, Xiao-Jia

2014-01-01

Superconductivity can be induced with the application of pressure but it disappears eventually upon heavy compression in the iron-based parent compound BaFe 2 As 2 . Structural evolution with pressure is used to understand this behavior. By performing synchrotron X-ray powder diffraction measurements with diamond anvil cells up to 26.1 GPa, we find an anomalous behavior of the lattice parameter with a S shape along the a axis but a monotonic decrease in the c-axis lattice parameter with increasing pressure. The close relationship between the axial ratio c/a and the superconducting transition temperature T c is established for this parent compound. The c/a ratio is suggested to be a measure of the spin fluctuation strength. The reduction of T c with the further increase of pressure is a result of the pressure-driven weakness of the spin-fluctuation strength in this material

Growth and characterization of acentric BaHf(BO{sub 3}){sub 2} and BaZr(BO{sub 3}){sub 2}

Energy Technology Data Exchange (ETDEWEB)

Mączka, Mirosław, E-mail: m.maczka@int.pan.wroc.pl [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wrocław 2 (Poland); Szymborska-Małek, Katarzyna; Gągor, Anna [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wrocław 2 (Poland); Majchrowski, Andrzej [Institute of Applied Physics, Military University of Technology, 2 Kaliskiego Str., 00-908 Warszawa (Poland)

2015-05-15

Growth, single crystal X-ray diffraction, polarized Raman and infrared (IR) studies of BaHf(BO{sub 3}){sub 2} are presented. Raman and IR spectra of polycrystalline BaZr(BO{sub 3}){sub 2} are also reported to facilitate assignment of modes. BaHf(BO{sub 3}){sub 2} borate crystallizes in trigonal system, space group R3c, with lattice parameters: a=5.1540(4) Å, c=33.901(3) Å. It accommodates dolomite-like structure doubled in the c direction, which is built of alternating layers of HfO{sub 6} octahedra and BaO{sub 6} distorted trigonal prisms that are connected through borate groups. The obtained structural as well as spectroscopic data show that BaHf(BO{sub 3}){sub 2} is isostructural with BaZr(BO{sub 3}){sub 2} and the deviations from centrosymmetry is small. - Graphical abstract: Arrangement of BO{sub 3} groups in BaHf(BO{sub 3}){sub 2} along the c direction in one unit cell. Dark and light blue denote different borate groups. - Highlights: • BaHf(BO{sub 3}){sub 2} single crystals were grown. • X-ray diffraction showed that this borate crystallizes in the acentric R3c structure. • Raman and IR spectra were measured for BaHf(BO{sub 3}){sub 2} and BaZr(BO{sub 3}){sub 2}, respectively. • Assignment of modes is proposed.

Photoluminescence and thermoluminescence properties of Eu2+ doped and Eu2+ ,Dy3+ co-doped Ba2 MgSi2 O7 phosphors.

Science.gov (United States)

Sao, Sanjay Kumar; Brahme, Nameeta; Bisen, D P; Tiwari, Geetanjali

2016-11-01

In this work, we report the preparation, characterization, comparison and luminescence mechanisms of Eu 2 + -doped and Eu 2 + ,Dy 3 + -co-doped Ba 2 MgSi 2 O 7 (BMSO) phosphors. Prepared phosphors were synthesized via a high temperature solid-state reaction method. All prepared phosphors appeared white. The phase structure, particle size, and elemental analysis were analyzed using X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) analysis. The luminescence properties of the phosphors were investigated by thermoluminescence (TL) and photoluminescence (PL). The PL excitation and emission spectra of Ba 2 MgSi 2 O 7 :Eu 2 + showed the peak to be around 381 nm and 490 nm respectively. The PL excitation spectrum of Ba 2 MgSi 2 O 7 :Eu 2 + Dy 3 + showed the peak to be around 341 nm and 388 nm, and the emission spectrum had a broad band around 488 nm. These emissions originated from the 4f 6 5d 1 to 4f 7 transition of Eu 2 + . TL analysis revealed that the maximum TL intensity was found at 5 mol% of Eu 2 + doping in Ba 2 MgSi 2 O 7 phosphors after 15 min of ultraviolet (UV) light exposure. TL intensity was increased when Dy 3 + ions were co-doped in Ba 2 MgSi 2 O 7 :Eu 2 + and maximum TL intensity was observed for 2 mol% of Dy 3 + . TL emission spectra of Ba 1.95 MgSi 2 O 7 :0.05Eu 2 + and Ba 1.93 MgSi 2 O 7 :0.05Eu 2 + ,0.02Dy 3 + phosphors were found at 500 nm. TL intensity increased with UV exposure time up to 15 min, then decreased for the higher UV radiation dose for both Eu doping and Eu,Dy co-doping. The trap depths were calculated to be 0.54 eV for Ba 1.95 MgSi 2 O 7 :0.05Eu 2 + and 0.54 eV and 0.75 eV for Ba 1.93 MgSi 2 O 7 :0.05Eu 2 + ,0.02Dy 3 + phosphors. It was observed that co-doping with small amounts of Dy 3 + enhanced the thermoluminescence properties of Ba 2 MgSi 2 O 7 phosphor. Copyright © 2016 John Wiley & Sons, Ltd. [Correction added on 5 April 2016, after first online publication: The

Magnetic-Field-Enhanced Incommensurate Magnetic Order in the Underdoped High-Temperature Superconductor YBa2Cu3O6.45

DEFF Research Database (Denmark)

Haug, D.; Hinkov, V.; Suchaneck, A.

2009-01-01

We present a neutron-scattering study of the static and dynamic spin correlations in the underdoped high-temperature superconductor YBa2Cu3O6.45 in magnetic fields up to 15 T. The field strongly enhances static incommensurate magnetic order at low temperatures and induces a spectral-weight shift...

Phase relationships in the BaO-Ga2O3-Ta2O5 system and the structure of Ba6Ga21TaO40.

Science.gov (United States)

Cao, Jiang; Yu, Xiaodi; Kuang, Xiaojun; Su, Qiang

2012-07-16

Phase relationships in the BaO-Ga(2)O(3)-Ta(2)O(5) ternary system at 1200 °C were determined. The A(6)B(10)O(30) tetragonal tungsten bronze (TTB) related solution in the BaO-Ta(2)O(5) subsystem dissolved up to ~11 mol % Ga(2)O(3), forming a ternary trapezoid-shaped TTB-related solid solution region defined by the BaTa(2)O(6), Ba(1.1)Ta(5)O(13.6), Ba(1.58)Ga(0.92)Ta(4.08)O(13.16), and Ba(6)GaTa(9)O(30) compositions in the BaO-Ga(2)O(3)-Ta(2)O(5) system. Two ternary phases Ba(6)Ga(21)TaO(40) and eight-layer twinned hexagonal perovskite solid solution Ba(8)Ga(4-x)Ta(4+0.6x)O(24) were confirmed in the BaO-Ga(2)O(3)-Ta(2)O(5) system. Ba(6)Ga(21)TaO(40) crystallized in a monoclinic cell of a = 15.9130(2) Å, b = 11.7309(1) Å, c = 5.13593(6) Å, β = 107.7893(9)°, and Z = 1 in space group C2/m. The structure of Ba(6)Ga(21)TaO(40) was solved by the charge flipping method, and it represents a three-dimensional (3D) mixed GaO(4) tetrahedral and GaO(6)/TaO(6) octahedral framework, forming mixed 1D 5/6-fold tunnels that accommodate the Ba cations along the c axis. The electrical property of Ba(6)Ga(21)TaO(40) was characterized by using ac impedance spectroscopy.

Characterization of quasi-one-dimensional S=1/2 Heisenberg antiferromagnets Sr2Cu(PO4)2 and Ba2Cu(PO4)2 with magnetic susceptibility, specific heat, and thermal analysis

International Nuclear Information System (INIS)

Belik, A.A.; Azuma, M.; Takano, M.

2004-01-01

Properties of Sr 2 Cu(PO 4 ) 2 and Ba 2 Cu(PO 4 ) 2 having [Cu(PO 4 ) 2 ] ∞ linear chains in their structures with Cu-O-P-O-Cu linkages were studied by magnetic susceptibility (T=2-400 K, H=100 Oe) and specific heat measurements (T=0.45-21 K). Magnetic susceptibility versus temperature curves, χ(T), showed broad maxima at T M =92 K for Sr 2 Cu(PO 4 ) 2 and T M =82 K for Ba 2 Cu(PO 4 ) 2 characteristic of quasi-one-dimensional systems. The χ(T) data were excellently fitted by the spin susceptibility curve for the uniform S=1/2 chain (plus temperature-independent and Curie-Weiss terms) with g=2.153(4) and J/k B =143.6(2) K for Sr 2 Cu(PO 4 ) 2 and g=2.073(4) and J/k B =132.16(9) K for Ba 2 Cu(PO 4 ) 2 (Hamiltonian H=JΣS i S i+1 ). The similar J/k B values were obtained from the specific heat data. No anomaly was observed on the specific heat from 0.45 to 21 K for both compounds indicating that the temperatures of long-range magnetic ordering, T N , were below 0.45 K. Sr 2 Cu(PO 4 ) 2 and Ba 2 Cu(PO 4 ) 2 are an excellent physical realization of the S=1/2 linear chain Heisenberg antiferromagnet with k B T N /J 2 CuO 3 (k B T N /J∼0.25%) and γ-LiV 2 O 5 (k B T N /J 2 Cu(PO 4 ) 2 and Ba 2 Cu(PO 4 ) 2 were stable in air up to 1280 and 1150 K, respectively

Weak doping dependence of the antiferromagnetic coupling between nearest-neighbor Mn2 + spins in (Ba1 -xKx) (Zn1-yMny) 2As2

Science.gov (United States)

Surmach, M. A.; Chen, B. J.; Deng, Z.; Jin, C. Q.; Glasbrenner, J. K.; Mazin, I. I.; Ivanov, A.; Inosov, D. S.

2018-03-01

Dilute magnetic semiconductors (DMS) are nonmagnetic semiconductors doped with magnetic transition metals. The recently discovered DMS material (Ba1 -xKx) (Zn1-yMny) 2As2 offers a unique and versatile control of the Curie temperature TC by decoupling the spin (Mn2 +, S =5 /2 ) and charge (K+) doping in different crystallographic layers. In an attempt to describe from first-principles calculations the role of hole doping in stabilizing ferromagnetic order, it was recently suggested that the antiferromagnetic exchange coupling J between the nearest-neighbor Mn ions would experience a nearly twofold suppression upon doping 20% of holes by potassium substitution. At the same time, further-neighbor interactions become increasingly ferromagnetic upon doping, leading to a rapid increase of TC. Using inelastic neutron scattering, we have observed a localized magnetic excitation at about 13 meV associated with the destruction of the nearest-neighbor Mn-Mn singlet ground state. Hole doping results in a notable broadening of this peak, evidencing significant particle-hole damping, but with only a minor change in the peak position. We argue that this unexpected result can be explained by a combined effect of superexchange and double-exchange interactions.

Unusually high critical current of P-doped BaFe{sub 2}As{sub 2} single crystalline thin film

Energy Technology Data Exchange (ETDEWEB)

Kurth, Fritz; Engelmann, Jan; Schultz, Ludwig [IMW, IFW Dresden, Dresden (Germany); TU Dresden, Dresden (Germany); Tarantini, Chiara; Jaroszynski, Jan [ASC, NHMFL, Florida (United States); Grinenko, Vadim; Reich, Elke; Huehne, Ruben [IMW, IFW Dresden, Dresden (Germany); Haenisch, Jens [IMW, IFW Dresden, Dresden (Germany); ITEP, KIT, Karlsruhe (Germany); Mori, Yasohiro; Sakagami, Akihiro; Kawaguchi, Takahiko; Ikuta, Hiroshi [Department of Crystalline Materials Science, Nagoya University, Nagoya (Japan); Holzapfel, Bernhard [ITEP, KIT, Karlsruhe (Germany); Iida, Kazumasa [IMW, IFW Dresden, Dresden (Germany); Department of Crystalline Materials Science, Nagoya University, Nagoya (Japan)

2015-07-01

Microstructurally clean, isovalently P-doped BaFe{sub 2}As{sub 2} single crystalline thin films have been prepared by molecular beam epitaxy. These films show a superconducting transition temperature (T{sub c}) of over 30 K and high transport self-field critical current densities (J{sub c}) of over 6 MA/cm{sup 2} at 4.2 K, which are among the highest for Fe based superconductors. In-field J{sub c} exceeds 0.1 MA/cm{sup 2} at μ{sub 0}H = 35 T for H parallel ab and μ{sub 0}H = 18 T for H parallel c, respectively, in spite of moderate upper critical fields compared to other FeSCs with similar T{sub c}. This unusually high J{sub c} makes P-doped Ba-122 very favorable for high-field magnet applications.

A temperature-dependent structural investigation of electrical transitions in A 3conb2o9 perovskites (A=Ca2+, Sr2+, Ba2+)

International Nuclear Information System (INIS)

Ting, V.; Liu, Y.; Withers, R.L.

2006-01-01

Upon heating, the 1:2 triple perovskites A 3 CoNb 2 O 9 (A=Ca, Sr or Ba) each undergo well-defined insulator to conductor phase transitions at ∼8, ∼126 and ∼325 deg. C, respectively. As the trend in the transition temperatures for these materials does not correlate with the size of the reported band gaps, neutron powder diffraction has been used to investigate if this change in electrical behaviour of the materials was due to a structural phase change. It was found that in the regions of the suspected phase transitions there were only slight perturbations of the structures, namely thermal expansion of the lattices and an apparent muting of the amplitude of the octahedral rotations in the A=Ca and Sr compound at higher temperatures

Er3+ infrared fluorescence affected by spatial distribution synchronicity of Ba2+ and Er3+ in Er3+-doped BaO–SiO2 glasses

Directory of Open Access Journals (Sweden)

Atsunobu Masuno

2016-02-01

Full Text Available Glasses with the composition xBaO–(99.9 − xSiO2–0.1ErO3/2 (0 ≤x ≤ 34.9 were fabricated by a levitation technique. The glasses in the immiscibility region were opaque due to chemical inhomogeneity, while the other glasses were colorless and transparent. The scanning electron microscope observations and electron probe microanalysis scan profiles revealed that more Er3+ ions were preferentially distributed in the regions where more Ba2+ ions existed in the chemically inhomogeneous glasses. The synchronicity of the spatial distributions of the two ions initially increased with increasing x and then decreased when the Ba2+ concentration exceeded a certain value. The peak shape and lifetime of the fluorescence at 1.55 μm depended on x as well as the spatial distribution of both ions. These results indicate that although ErOn polyhedra are preferentially coordinated with Ba2+ ions and their local structure is affected by the coordination of Ba2+, there is a maximum in the amount of Ba2+ ions that can coordinate ErOn polyhedra since the available space for Ba2+ ions is limited. These findings provide us with efficient ways to design the chemical composition of glasses with superior Er3+ fluorescence properties for optical communication network systems.

Emergence of high-mobility minority holes in the electrical transport of the Ba (Fe1 -xMnxAs )2 iron pnictides

Science.gov (United States)

Urata, T.; Tanabe, Y.; Huynh, K. K.; Heguri, S.; Oguro, H.; Watanabe, K.; Tanigaki, K.

2015-05-01

In Fe pnictide (Pn) superconducting materials, neither Mn nor Cr doping to the Fe site induces superconductivity, even though hole carriers are generated. This is in strong contrast with the superconductivity appearing when holes are introduced by alkali-metal substitution on the insulating blocking layers. We investigate in detail the effects of Mn doping on magnetotransport properties in Ba (Fe1 -xMnxAs )2 for elucidating the intrinsic reason. The negative Hall coefficient for x =0 estimated in the low magnetic field (B ) regime gradually increases as x increases, and its sign changes to a positive one at x =0.020 . Hall resistivities as well as simultaneous interpretation using the magnetoconductivity tensor including both longitudinal and transverse transport components clarify that minority holes with high mobility are generated by the Mn doping via spin-density wave transition at low temperatures, while original majority electrons and holes residing in the paraboliclike Fermi surfaces of the semimetallic Ba (FeAs )2 are negligibly affected. Present results indicate that the mechanism of hole doping in Ba (Fe1 -xMnxAs )2 is greatly different from that of the other superconducting FePn family.

A Semimetal Model of the Normal State Susceptibility and Transport Properties of Ba(Fe1-xCox)2As2 Superconductors

Science.gov (United States)

Sales, Brian; Sefat, Athena; McGuire, Michael; Mandrus, David

2010-03-01

A simple two-band 3D model of a semimetal is constructed to see which normal state features of the Ba(Fe1-xCox)2As2 superconductors can be qualitatively understood within this framework. The model is able to account in a semiquantitative fashion for the measured magnetic susceptibility, Hall, and Seebeck data, and the low temperature Sommerfeld coefficient for 0 general conclusion from the model is that the magnetic susceptibility of most semimetals should increase with temperatures. This is indeed found to be the case for two well-known semimetals Bi and TiSe2. Research supported by the US DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

Separation of Sr from Ca, Ba and Ra by means of Ca(OH)2 and Ba(Ra)Cl2 or Ba(Ra)SO4 for the determination of radiostrontium

DEFF Research Database (Denmark)

Chen, Q.J.; Hou, Xiaolin; Yu, Y.X.

2002-01-01

be completed. The new separation procedure has been successfully used for the determination of Sr-90 in samples with high Ca content, such as 451 of seawater and 2001 of drinking water. The analytical quality of the results is comparable to that of the traditional method using fuming nitric acid and BaCrO4......A simple procedure is developed to separate Sr from a large amount of Ca, which relies on the insolubility of Ca(OH)(2) in alkaline solution. Calcium is quantitatively separated from Sr and more than 95% of Sr is recovered from a sample with as much as 50 g of Ca and a Ca/Sr mole ratio of 250....... A new procedure for the separation of Sr from Ba and Ra is also investigated, which is based on the difference in solubility of the chlorides of Sr, Ba and Ra in HCl media. In 9.5 mol 1(-1) HCl or 7.5 mol 1(-1) HCl-10% acetone media, >97% of Ba and Ra can be removed by Ba(Ra)Cl-2 precipitation, and >94...

Thermodynamic model for the solubility of BaSeO4(cr) in the aqueous Ba2+-SeO42--Na+-H+-OH--H2O system. Extending to high selenate concentrations

International Nuclear Information System (INIS)

Rai, Dhanpat; Felmy, Andrew R.; Kitamura, Akira; Yoshikawa, Hideki; Doi, Reisuke; Yoshida, Yasushi; Moore, Dean A.

2014-01-01

The aqueous solubility of BaSeO 4 (cr) was studied at 23 ± 2 C as a function of Na 2 SeO 4 concentrations (0.0001 to 4.1 mol kg -1 ) and equilibration periods (3 to 596 d). The equilibrium, approached from both the under- and over-saturation directions, in this system was reached rather rapidly (≤ 3d). The SIT and Pitzer's ion-interaction models were used to interpret these data and the predictions based on both of these models agreed closely with the experimental data. Thermodynamic analyses of the data show that BaSeO 4 (cr) is the solubility-controlling phase for Na 2 SeO 4 concentrations -1 . The log 10 K 0 value for the BaSeO 4 (cr) solubility product (BaSeO 4 (cr) ↔ Ba 2+ + SeO 4 2- ) calculated by the SIT and Pitzer models were very similar (-7.32 ± 0.07 with Pitzer and -7.25 ± 0.11 with SIT). Although the BaSeO 4 (cr) solubility product and Ba concentrations as a function of Na 2 SeO 4 concentrations predicted by both the SIT and Pitzer models are similar, the models required different sets of fitting parameters. For examples, (1) interpretations using the SIT model required the inclusion of Ba(SeO 4 ) 2 2- species with log 10 K 0 = 3.44 ± 0.12 for the reaction (Ba 2+ + 2SeO 4 2- ↔ Ba(SeO 4 ) 2 2- ), whereas these species are not needed for Pitzer model, and (2) at Na 2 SeO 4 concentrations > 0.59 mol kg -1 it was also possible to calculate the value for log 10 K 0 for the solubility product of a proposed double salt (Na 2 Ba(SeO 4 ) 2 (s) ↔ 2Na + + Ba 2+ + 2SeO 4 2- ) which for the SIT model is -(8.70 ± 0.29) whereas for the Pitzer model it is -(9.19 ± 0.19). The ion-interaction/ion-association parameters hitherto unavailable for both the SIT and Pitzer models required to fit these extensive data extending to as high ionic strengths as 12.3 mol kg -1 were determined. The model developed in this study is consistent with all of the reliable literature data, which was also used to extend the model to barium concentrations as high as 0.22 mol kg

Crystallization kinetics of BaO-Al2O3-SiO2 glasses

Science.gov (United States)

Bansal, Narottam P.; Hyatt, Mark J.

1989-01-01

Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt percent) 10BaO-38Al2O3-51SiO2-1MoO3 (glass A) and 39BaO-25Al2O3-35SiO2-1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3-2SiO2) and hexacelsian (BaO-Al2O3-2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 C. It undergoes structural transformation into the orthorhombic form at approximately 300 C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.

X-ray photoelectron spectroscopy study of BaWO{sub 4} and Ba{sub 2}CaWO{sub 6}

Energy Technology Data Exchange (ETDEWEB)

Capece, Angela M., E-mail: acapece@pppl.gov [California Institute of Technology, Pasadena, CA (United States); Polk, James E. [Jet Propulsion Laboratory, Pasadena, CA (United States); Shepherd, Joseph E. [California Institute of Technology, Pasadena, CA (United States)

2014-12-15

Highlights: • XPS reference spectra for Ba{sub 2}CaWO{sub 6} and BaWO{sub 4} are presented. • Binding energies of Ba 3d and W 4f lines are 0.7 eV higher for BaWO{sub 4} than Ba{sub 2}CaWO{sub 6}. • Ca 2p spectrum contains two sets of Ca 2p doublets attributed to Ba{sub 2}CaWO{sub 6} and CaCO{sub 3}. - Abstract: XPS reference spectra for Ba{sub 2}CaWO{sub 6} and BaWO{sub 4} are presented, including high resolution spectra of the Ba 3d, W 4f, C 1s, Ca 2p, and O 1s lines. The peak locations and full widths at half maximum are also given. The binding energies of the Ba 3d and W 4f lines are 0.7 eV higher for BaWO{sub 4} than for Ba{sub 2}CaWO{sub 6}. The Ca 2p spectrum contains two sets of Ca 2p doublets that were attributed to Ba{sub 2}CaWO{sub 6} and CaCO{sub 3}.

IR-spectroscopic study and electrical properties of glasses in the Ba(PO3)2-Ba(Hal)2 systems

International Nuclear Information System (INIS)

Sokolov, I.A.; Tarlakov, Yu.P.; Murin, I.V.; Pronkin, A.A.

2000-01-01

Temperature-concentration dependence of electric conductivity of glasses in the systems Ba(PO 3 ) 2 -Ba(Hal) 2 , where Hal = Cl, Br, I, is studied by the method of conductometry, the numbers of iodide-ions transfer are determined and their concentration dependence is found. Data of IR spectroscopy permitted ascertained participation of halide ions in formation of anionic constituent of the glass structure at the expense of bridge bonds formation, as well as formation of structural-chemical units of [(Hal) - Ba 2+ O - POO 2/2 ] type, their dissociation giving rise to formation of halide ions their dissociation giving rise to formation of halide ions taking part in electric current transfer [ru

Quantum criticality in electron-doped BaFe2-xNixAs2.

Science.gov (United States)

Zhou, R; Li, Z; Yang, J; Sun, D L; Lin, C T; Zheng, Guo-qing

2013-01-01

A quantum critical point is a point in a system's phase diagram at which an order is completely suppressed at absolute zero temperature (T). The presence of a quantum critical point manifests itself in the finite-T physical properties, and often gives rise to new states of matter. Superconductivity in the cuprates and in heavy fermion materials is believed by many to be mediated by fluctuations associated with a quantum critical point. In the recently discovered iron-pnictide superconductors, we report transport and NMR measurements on BaFe(2-x)Ni(x)As₂ (0≤x≤0.17). We find two critical points at x(c1)=0.10 and x(c2)=0.14. The electrical resistivity follows ρ=ρ₀+AT(n), with n=1 around x(c1) and another minimal n=1.1 at x(c2). By NMR measurements, we identity x(c1) to be a magnetic quantum critical point and suggest that x(c2) is a new type of quantum critical point associated with a nematic structural phase transition. Our results suggest that the superconductivity in carrier-doped pnictides is closely linked to the quantum criticality.

Crystal structures of the double perovskites Ba2Sr1-x Ca x WO6

International Nuclear Information System (INIS)

Fu, W.T.; Akerboom, S.; IJdo, D.J.W.

2007-01-01

Structures of the double perovskites Ba 2 Sr 1- x Ca x WO 6 have been studied by the profile analysis of X-ray diffraction data. The end members, Ba 2 SrWO 6 and Ba 2 CaWO 6 , have the space group I2/m (tilt system a 0 b - b - ) and Fm3-barm (tilt system a 0 a 0 a 0 ), respectively. By increasing the Ca concentration, the monoclinic structure transforms to the cubic one via the rhombohedral R3-bar phase (tilt system a - a - a - ) instead of the tetragonal I4/m phase (tilt system a 0 a 0 c - ). This observation supports the idea that the rhombohedral structure is favoured by increasing the covalency of the octahedral cations in Ba 2 MM'O 6 -type double perovskites, and disagrees with a recent proposal that the formation of the π-bonding, e.g., d 0 -ion, determines the tetragonal symmetry in preference to the rhombohedral one. - Graphical abstract: Enlarged sections showing the evolution of the basic (222) and (400) reflections in Ba 2 Sr 1- x Ca x WO 6 . Tick marks below are the positions of Bragg's reflections calculated using the space groups I2/m (x=0), R3-bar (x=0.25, 0.5 and 0.75) and Fm3-barm (x=1), respectively

Investigations on the local structures of Cu2+ at various BaO concentrations in 59B2O3-10K2O-(30-x)ZnO-xBaO-1CuO glasses

Science.gov (United States)

Jin, Jia-Rui; Wu, Shao-Yi; Hong, Jian; Liu, Shi-Nan; Song, Min-Xian; Teng, Bao-Hua; Wu, Ming-He

2017-11-01

The local structures and electron paramagnetic resonance (EPR) parameters for Cu2+ in 59B2O3-10K2O-(30-x)ZnO-xBaO-1CuO (BKZBC) glasses are theoretically investigated with distinct modifier BaO concentrations x (= 0, 6, 12, 18, 24 and 30 mol %). The ? clusters are found to undergo the relative tetragonal elongations of about 13.5 and 5.0% at zero and higher BaO concentrations. The concentration dependences of the measured d-d transition bands, g factors and A// are suitably reproduced from the Fourier type functions or sign functions of the relevant quantities with x by using only six adjustable parameters. The features of the EPR parameters and the local structures of Cu2+ are analysed in a consistent way by considering the differences in the local ligand field strength and electronic cloud admixtures around Cu2+ under addition of Ba2+ with the highest ionicity and polarisability. The present theoretical studies would be helpful to the researches on the structures, optical and EPR properties for the similar potassium barium zinc borate glasses containing copper with variation concentration of modifier BaO.

Mercury nonstoichiometry of the Hg1-xBa2CuO4+δ superconductor and the P(Hg)-P(O2)-T phase diagram of the Hg-Ba-Cu-O system

International Nuclear Information System (INIS)

Alyoshin, V.A.; Mikhailova, D.A.; Rudnyi, E.B.; Antipov, E.V.

2002-01-01

The P(Hg)-P(O 2 )-T phase diagram of the Hg-Ba-Cu-O system for the Ba:Cu=2:1 ratio was experimentally studied and followed by means of the thermodynamic modeling. It was shown that the Hg 1-x Ba 2 CuO 4+δ (Hg-1201) superconductor possesses a significant range of Hg-nonstoichiometry and exists in a certain P(Hg), P(O 2 ) and T range. Mercury nonstoichiometry of Hg-1201 was investigated in the 923≤T≤1095 K; 2.0≤P(Hg)≤8.4 atm; 0.09≤P(O 2 )≤0.86 atm ranges. It was found that the mercury content varies in the range of 0.80-0.94 under these conditions. The Gibbs energy of the Hg-1201 phase was estimated as a function of temperature and mercury concentration. The obtained results allow optimizing the synthesis conditions of Hg-1201 with a given Hg-content including preparation of the Hg-stoichiometric phase

Carbon-14 immobilization via the CO2-Ba(OH)2 hydrate gas-solid reaction

International Nuclear Information System (INIS)

Haag, G.L.

1981-08-01

For the treatment of an air-based off-gas stream, the use of packed beds of Ba(OH) 2 .8H 2 O flakes to remove CO 2 has been demonstrated. However, the operating conditions must be maintained between certain upper and lower limits with respect to the partial pressure of water. If the water vapor pressure in the gas is less than the dissociation vapor pressure of Ba(OH) 2 .8H 2 O, the bed will deactivate. If the vapor pressure is considerably greater, pressure drop problems will increase with increaseing humidity as the particles curl and degrade. Results have indicted that when operated in the proper regime, the bulk of the increase in pressure drop results from the conversion of Ba(OH) 2 .8H 2 O to BaCO 3 and not from the hydration of the commercial Ba(OH) 2 .8H 2 O (i.e., Ba(OH) 2 .7.50H 2 O) to Ba(OH) 2 .8H 2 O

Structure and physical properties for a new layered pnictide-oxide: BaTi2As2O

International Nuclear Information System (INIS)

Wang, X F; Yan, Y J; Ying, J J; Li, Q J; Zhang, M; Xu, N; Chen, X H

2010-01-01

We have successfully synthesized a new layered pnictide-oxide: BaTi 2 As 2 O. It shares similar characteristics with Na 2 Ti 2 Sb 2 O. The crystal has a layered structure with a tetragonal P4/nmm group (a = 4.047(3) A, c = 7.275(4) A). The resistivity shows an anomaly at 200 K, which should be ascribed to an SDW or structural transition. The SDW or structural transition is confirmed by magnetic susceptibility and heat capacity measurements. These behaviors are very similar to those observed in parent compounds of high-T c iron-based pnictide superconductors, in which the superconductivity shows up when the anomaly due to the SDW or structural transition is suppressed. Therefore, the new layered pnictide-oxide, BaTi 2 As 2 O, could be a potential parent compound for superconductivity. It is found that Li + doping significantly suppresses the anomaly, but no superconductivity emerges so far.

Depairing current density of Ba0.5K0.5Fe1.95Co0.05As2 microbridges with nanoscale thickness

International Nuclear Information System (INIS)

Li, Jun; Yuan, Jie; Ge, Jun-Yi; Ji, Min; Feng, Hai-Luke; Yuan, Ya-Hua; Hatano, Takeshi; Vanacken, Johan; Yamaura, Kazunari; Wang, Hua-Bing

2014-01-01

Highlights: • The critical current density of Ba 0.5 K 0.5 Fe 1.95 Co 0.05 As 2 microbridges is 7.9 MA/cm 2 at 21 K. • The critical current is in consistence with the Ginzburg–Landau depairing limit. • The depairing current density is less than that of impurity-free crystal. - Abstract: We investigated the depairing current density of Ba 0.5 K 0.5 Fe 1.95 Co 0.05 As 2 microbridges with width of 2 μm and thickness of 150 nm. The current vs. voltage characteristics of the microbridges show a Josephson-like behavior with the obvious hysteresis. The critical current density was observed as J c = 7.9 MA/cm 2 at temperature 21 K, which is consistent with the Ginzburg–Landau depairing limit. However, the depairing current density is less than that of impurity-free crystal, although the Co ions provide additional pinning centers within the superconducting Fe 2 As 2 layers. The Co impurity also enhances the anisotropic factor of the critical current density by 1.3 (1 T) or 1.7 (3 T)

Characterization and dielectric properties of BaTiO3 prepared from Ba(NO3)2-TiO2 mixture

International Nuclear Information System (INIS)

Othman, K.I.; Hassan, A.A.; Ali, M.E.; Abdelal, O.A.; Salah El Dien, F.E.; El-Raghy, S.M.; Abdel-Karim, R.

2012-01-01

BaTiO 3 powder was prepared through a solid-state reaction between the Ba(NO 3 ) 2 and TiO 2 . The thermal analysis and XRD techniques were used to study its formation. A single phase BaTiO 3 was formed after calcination at 600 degree C for 6 hrs. The dielectric properties of the sintered BaTiO 3 were determined in the temperature range from room temperature to 20 degree C at a frequency ranging from 500 Hz to 100 khz. The relative permittivity and the dielectric loss of the sintered pellets at 1 khz, measured at room temperature,were 1805 and 0.419 respectively.

Emission characteristics of Y1Ba2Cu3O7-δ cathode

International Nuclear Information System (INIS)

Korenev, S.A.

1988-01-01

The results are presented of experimental investigation of the electron beam in diode with cathode on the base of Y 1 Ba 2 Cu 3 O 7-δ . After corresponding cathode training, the cathode made from Y 1 Ba 2 Cu 3 O 7-δ material may be practicable of stable current electron beam yeild. It is shown experimentally that the voltage of diode of about 100-300 kV there exists an evident possibility of forming the electron beams with the current density of 70 A-380 A/cm 2 . The motion velicity of cathode plasma in the direction of anode for this material of a cathode amounts to (1-3)x 10 6 cm/s

Hydrostatic pressure dependence of the superconducting transition temperature of HgBa2CaCu2O6+δ and HgBa2Ca2Cu3O8+δ

International Nuclear Information System (INIS)

Klehe, A.K.; Schilling, J.S.

1994-02-01

The dependence of the superconducting transition temperature T c (P) on purely hydrostatic pressure to 0.9 GPa has been determined in ac susceptibility studies in a He-gas pressure system for optimally doped ceramic samples of HgBa 2 CaCu 2 O 6+δ and HgBa 2 Ca 2 Cu 3 O 8+δ with superconducting transitions at T c (0) ≅ 126.6 K and 133.9 K, respectively. T c increases reversibly under hydrostatic pressure at the rates, d T c /dP ≅ +1.80 ± 0.06 K/GPa and +1.71 ± 0.05 K/GPa, respectively. Within experimental error, these values are the same as found previously for optimally doped single-layered HgBa 2 CuO 4+δ , where d T c /dP ≅ +1.72 ± 0.05 K/GPa. Remarkably, the logarithmic volume derivative of T c is nearly identical for all three compounds, dln T c /dlnV ≅ -1.20 ± 0.05, even though the bulk modulus differs by more than 30%. This provides strong evidence that a common mechanism is responsible for the pressure dependence of the superconducting state in all three compounds

Structural phase transitions in Iron - based superconductors BaFe2-xCrxAs2 under high pressure

International Nuclear Information System (INIS)

Uhoya, W.O.; Montgomery, J.M.; Samudrala, G.K.; Tsoi, G.M.; Vohra, Y.K.; Sefar, A.S.

2011-01-01

Pure BaFe 2 As 2 with the ThCr 2 Si 2 -type crystal structure under ambient conditions is known to superconduct under high pressure and undergo an isostructural phase transition from tetragonal to collapsed tetragonal phase which is accompanied by anomalous compressibility effects. Presently, there is no reported work on the crystal structure on any of the chemically doped 122- iron based superconductors under high pressure. We have carried out the electrical resistance measurements and high pressure X-ray diffraction studies on Chromium doped samples of BaFe 2-x Cr x As 2 (x = 0, 0.05, 0.15, 0.4, 0.61) to a pressure of 75 GPa and a temperature of 10K using a synchrotron source and designer diamond anvils, so as to investigate the influence of chemical doping and high pressure on crystal structure and superconductivity

Investigation on pseudosymmetry, twinning and disorder in crystal structure determinations: Ba(H2O)M2III[PO3(OH)]4 (M=Fe, V) as examples

International Nuclear Information System (INIS)

Sun Wei; Huang Yaxi; Pan Yuanming; Mi Jinxiao

2012-01-01

Twinning commonly occurs in monoclinic crystals with dimensionally similar a and c axes and results in pseudo-orthorhombic symmetries with overlapping diffractions. For example, twinning in the new synthetic compound Ba(H 2 O)Fe 2 [PO 3 (OH)] 4 , which varies in space group from P2 1 to P2 1 /c with approximately equal a and c axial lengths, gives rise to a pseudosymmetry of C222 1 . Similarly, the related compound Ba(H 2 O)V 2 [PO 3 (OH)] 4 is commonly twinned and varies in space groups as well, arising from ordered to disordered distributions of the barium cations and water molecules in the cavities. Moreover, analyses of these and other twinned structures show that the small average standard uncertainty of bond distances is a sensitive criterion for structure determinations, especially for those involving crystal twinning as well as order–disorder. A proper structure determination leads to small standard uncertainties of the atomic displacement parameters, which further result in the small standard uncertainties of bond distances. - Graphical abstract: Ba(H 2 O)M 2 III [PO 3 (OH)] 4 (M=Fe, V) varies in space group from P2 1 to P2 1 /c, arising from ordered to disordered distributions of Ba 2+ and H 2 O in the cavities. Highlights: ► Twinning commonly occurs in monoclinic crystals with a≈c. ► Overlapping diffractions from twin domains hamper with the determination of real space groups. ► Conventional criteria for evaluating the real space groups are not effective in this case. ► Small standard uncertainty of bond distances is proposed as a sensitive criterion. ► Using this criterion we determined the order–disorder structures of Ba(H 2 O)M 2 III [PO 3 (OH)] 4 (M=Fe, V) from twinned crystals.

Competing superconducting and magnetic order parameters and field-induced magnetism in electron doped Ba(Fe1-xCox)2As2

DEFF Research Database (Denmark)

Larsen, Jacob; Uranga, B. Mencia; Stieber, G.

2015-01-01

We have studied the magnetic and superconducting properties of Ba(Fe1-xCox)2As2 as a function of temperature and external magnetic field using neutron scattering and muon spin rotation. Below the superconducting transition temperature the magnetic and superconducting order parameters coexist...... and compete. A magnetic field can significantly enhance the magnetic scattering in the superconducting state, roughly doubling the Bragg intensity at 13.5 T. We perform a microscopic modelling of the data by use of a five-band Hamiltonian relevant to iron pnictides. In the superconducting state, vortices can...... slow down and freeze spin fluctuations locally. When such regions couple they result in a long-range ordered antiferromagnetic phase producing the enhanced magnetic elastic scattering in agreement with experiments....

Surface properties of Co-doped BaFe{sub 2}As{sub 2} thin films deposited on MgO with Fe buffer layer and CaF{sub 2} substrates

Energy Technology Data Exchange (ETDEWEB)

Sobota, R. [Department of Experimental Physics, FMPI, Comenius University, 842 48 Bratislava (Slovakia); Plecenik, T., E-mail: tomas.plecenik@fmph.uniba.sk [Department of Experimental Physics, FMPI, Comenius University, 842 48 Bratislava (Slovakia); Gregor, M.; Truchly, M.; Satrapinskyy, L.; Vidis, M.; Secianska, K. [Department of Experimental Physics, FMPI, Comenius University, 842 48 Bratislava (Slovakia); Kurth, F.; Holzapfel, B.; Iida, K. [Institute for Metallic Materials, IFW Dresden, PO Box 270116, D-01171 Dresden (Germany); Kus, P.; Plecenik, A. [Department of Experimental Physics, FMPI, Comenius University, 842 48 Bratislava (Slovakia)

2014-09-01

Highlights: • Surfaces of Co-doped Ba-122 films on various substrates were studied. • Substrate influences topography and surface conductivity distribution of the films. • Surface conductivity of Co-doped Ba-122 is highly inhomogeneous. • Point contact spectroscopy results can be affected by the surface differences. - Abstract: Surface properties of Co-doped BaFe{sub 2}As{sub 2} (Ba-122) thin films prepared by pulsed laser deposition on MgO with Fe buffer layer and CaF{sub 2} substrates were inspected by atomic force microscopy, scanning spreading resistance microscopy, scanning tunneling microscopy, X-ray photoelectron spectroscopy, auger electron spectroscopy/microscopy and point contact spectroscopy (PCS). Selected PCS spectra were fitted by extended 1D BTK model. The measurements were done on as-received as well as ion beam etched surfaces. Our results show that the substrate is considerably influencing the surface properties of the films, particularly the topography and surface conductivity distribution, what can affect results obtained by surface-sensitive techniques like PCS.

Synthesis and photoluminescence properties of Ba2CaZn2Si6O17:Eu3+ red phosphors for white LED applications

International Nuclear Information System (INIS)

Annadurai, G.; Kennedy, S. Masilla Moses

2016-01-01

Novel pellyite type Ba 2 CaZn 2 Si 6 O 17 :Eu 3+ red emitting phosphors with different Eu 3+ contents were synthesized by the solid state reaction method. The crystal structure, photoluminescence properties and concentration quenching of Ba 2 CaZn 2 Si 6 O 17 :Eu 3+ phosphors were investigated. Powder X-ray diffraction measurements confirmed the structure of the samples. The photoluminescence emission (PL) and excitation (PLE) spectra were measured. The results showed that the dominant hypersensitive red emission peak of the phosphors Ba 2 CaZn 2 Si 6 O 17 :Eu 3+ was located at 613 nm attributed to the Eu 3+ transition ( 5 D 0 → 7 F 2 ) which could be effectively excited by 395 nm (near-UV). The latter band matched well with the emission from the near-UV LED chips. The intensity ratio of 5 D 0 → 7 F 2 to 5 D 0 → 7 F 1 transition showed slight variation with Eu 3+ concentrations. The Eu 3+ emission intensity was maximum for 9 mol%. The luminescence quantum efficiency was determined and also the decay profiles were obtained and analyzed. In addition, the Commission International del'Eclairage (CIE) chromaticity coordinates of Ba 2 CaZn 2 Si 6 O 17 :0.09Eu 3+ phosphor were calculated to be 0.637 and 0.362. The experimental results demonstrated that the Ba 2 CaZn 2 Si 6 O 17 :Eu 3+ red emitting phosphor is a potential candidate for white light emitting diodes (WLEDs) pumped by near-UV chip. - Highlights: • A novel Ba 2 CaZn 2 Si 6 O 17 :Eu 3+ red phosphor was synthesized. • The samples yielded a dominant PL emission of Eu 3+ at 613 nm. • Eu 3+ concentration was optimized to be 9 mol% in Ba 2 CaZn 2 Si 6 O 17. • CIE chromaticity coordinates were estimated from the emission spectrum.

Theoretical investigation on thermoelectric properties of (Ca,Sr,Ba)Fe2(As/Bi)2 compounds under temperature

Science.gov (United States)

Jayalakshmi, D. S.; Sundareswari, M.; Viswanathan, E.; Das, Abhijeet

2018-04-01

The electrical conductivity, resistivity and Seebeck coefficient, Pauli magnetic susceptibility and power factor are computed under temperature (100 K - 800 K) in steps of 100 K for the theoretically designed compounds namely (Ca,Sr,Ba)Fe2Bi2 and their parent compounds namely (Ca,Sr,Ba)Fe2As2 by using Boltzmann transport theory interfaced to the Wien2k program. The Bulk modulus, electron phonon coupling constant, thermoelectric figure of merit (ZT) and transition temperature are calculated for the optimized anti ferromagnetic phase of the proposed compounds. The results are discussed for the novel compounds in view of their superconductivity existence and compared with their parent unconventional superconducting compounds.

On the electronic phase diagram of Ba{sub 1-x}K{sub x}(Fe{sub 1-y}Co{sub y}){sub 2}As{sub 2} and EuFe{sub 2}(As{sub 1-x}P{sub x}){sub 2} superconductors. A local probe study using Moessbauer spectroscopy and muon spin relaxation

Energy Technology Data Exchange (ETDEWEB)

Goltz, Til

2015-10-28

In this thesis, I study the electronic and structural phase diagrams of the superconducting 122 iron pnictides systems Ba{sub 1-x}K{sub x}(Fe{sub 1-y}Co{sub y}){sub 2}As{sub 2} and EuFe{sub 2}(As{sub 1-x}P{sub x}){sub 2} by means of the local probe techniques {sup 57}Fe Moessbauer spectroscopy (MS) and muon spin relaxation (μSR). For both isovalent substitution strategies - Co/K for Fe/Ba and P for As, respectively - the antiferromagnetic Fe ordering and orthorhombic distortion of the parent compounds BaFe{sub 2}As{sub 2} and EuFe{sub 2}As{sub 2} are subsequently suppressed with increasing chemical substitution and superconductivity arises, once long-range and coherent Fe magnetic order is sufficiently but not entirely suppressed. For Ba{sub 1-x}K{sub x}(Fe{sub 1-y}Co{sub y}){sub 2}As{sub 2} in the charge compensated state (x/2 ∼ y), a remarkably similar suppression of both, the orthorhombic distortion and Fe magnetic ordering, as a function of increasing substitution is observed and a linear relationship between the structural and the magnetic order parameter is found. Superconductivity is evidenced at intermediate substitution with a maximum T{sub SC} of 15 K coexisting with static magnetic order on a microscopic length scale. The appearance of superconductivity within the antiferromagnetic state can by explained by the introduction of disorder due to nonmagnetic impurities to a system with a constant charge carrier density. Within this model, the experimental findings are compatible with the predicted s{sup ±} pairing symmetry. For EuFe{sub 2}(As{sub 1-x}P{sub x}){sub 2}, the results from {sup 57}Fe MS and ZF-μSR reveal an intriguing interplay of the local Eu{sup 2+} magnetic moments and the itinerant magnetic Fe moments due to the competing structures of the iron and europium magnetic subsystems. For the investigated single crystals with x = 0.19 and 0.28, {sup 57}Fe MS evidences the interplay of Fe and Eu magnetism by the observation of a transferred

Determination of the UO2-ZrO2-BaO equilibrium diagram

International Nuclear Information System (INIS)

Paschoal, J.O.A.; Kleykanp, H.; Thuemmler, F.

1984-01-01

It is determined the equilibrium diagram of UO 2 - ZrO 2 - BaO to interpret and predict changes in the chemical properties of ceramic (oxide) nuclear fuels during irradiation. The isothermal section of the system at 1700 0 C was determined experimentally, utilizing the techniques of ceramography, X-ray diffraction analysis, microprobe analysis and differential thermal analysis. The solid solubility limits at 1700 0 C between UO 2 and ZrO 2 , UO 2 and BaO, ZrO 2 and BaO, ZrO 2 and BaO and BaUO 3 and BaZrO 3 is presented. The influence of oxygen potential in relation to the different phases is discussed and the phase diagram of the system presented. (M.C.K.) [pt

Experimental study on Ra2+ uptake by barite (BaSO{sub 4}). Kinetics of solid solution formation via BaSO{sub 4} dissolution and Ra{sub x}Ba{sub 1-x}SO{sub 4} (re) precipitation

Energy Technology Data Exchange (ETDEWEB)

Bosbach, Dirk; Boettle, Melanie; Metz, Volker (Karlsruher Inst. fuer Technologie, Inst fuer Nukleare Entsorgung (INE), Karlsruhe (Germany))

2010-03-15

226Ra2+ and 133Ba2+ uptake by barite in aqueous solution is studied on the basis of batch type experiments with two different barite powders with different specific surface area (0.5 m2/g and 3.2 m2/g, respectively). The uptake of 226Ra2+ and 133Ba2+ is not only limited to adsorption reactions but proceeds significantly into the bulk of the barite crystals. 133Ba2+ uptake kinetics is affected by various parameters, such as amount of sample, specific surface area, sample type and solution composition. In the case of 133Ba2+, complete isotopic equilibration of the 133Ba2+ spiked solution with the barite powder occurs within 50 to 600 days. This information is derived by monitoring the aqueous 133Ba2+ concentration combined with simple mass balance calculations. In the case of 226Ra2+ a Ra{sub x}Ba{sub 1-x}SO{sub 4} solid solution forms and the uptake rate drops significantly within 400 days. The observed 226Ra2+ concentration in solution is controlled by the solubility of a Ra{sub x}Ba{sub 1-x}SO{sub 4} solid solution and several orders of magnitude below the Ra2+ solubility with respect to a pure RaSO{sub 4}(s) end member. It cannot be demonstrated unambiguously that a zero exchange rate and therefore thermodynamic equilibrium has been established within the observation period. The observed concentrations may be interpreted either as (1) a partial equilibration of 20 to 50% of the barite crystals with 226Ra2+ or (2) as complete equilibration of a Ra{sub 0.000128}Ba{sub 0.999872}SO{sub 4} solid solution with 226Ra2+ with no pure barite left. In both cases it is concluded that equilibration between aqueous Ra2+ and barite involves the replacement of a substantial fraction of the initial barite and proceeds significantly beyond pure surface adsorption processes

Valence determination as a function of doping in $PrBa_{2} Cu_{3} O_{7}$

CERN Document Server

Staub, U; Wasserman, S R; Conner, A G O; Kramer, M J; Patterson, B D; Shi, M; Knapp, M P

2000-01-01

We present results of X-ray absorption near edge spectra (XANES), neutron powder diffraction, and resonant X-ray diffraction on samples of PrBa/sub 2/Cu/sub 3/O/sub 7- delta / and Pr/sub 1-x/Ca/sub x/Ba /sub 2/Cu/sub 3/O/sub 7/. The data are obtained as a function of the doping levels of oxygen and Ca. There are significant changes in the Pr L/sub 3/ XANES spectra with changes in oxygen or Ca concentrations, indicating that the Pr electronic properties are affected by doping. The resonant X-ray scattering experiments show that the changes observed occur on Pr ions incorporated in the PrBa /sub 2/Cu/sub 3/O/sub 7- delta / structure, and are not the result of changes to a Pr-containing impurity phase. A quantitative model, based on literature precedent, is used to extract Pr valences from the data, although the XANES cannot distinguish between models involving charge transfer and those involving hybridization. The results are compared with data obtained from Pb/sub 2/Sr/sub 2/Pr/sub 1-x/Ca/sub x/Cu/sub 3/O/sub ...

High-pressure effects on isotropic superconductivity in the iron-free layered pnictide superconductor BaPd2As2

Science.gov (United States)

Abdel-Hafiez, M.; Zhao, Y.; Huang, Z.; Cho, C.-w.; Wong, C. H.; Hassen, A.; Ohkuma, M.; Fang, Y.-W.; Pan, B.-J.; Ren, Z.-A.; Sadakov, A.; Usoltsev, A.; Pudalov, V.; Mito, M.; Lortz, R.; Krellner, C.; Yang, W.

2018-04-01

While the layered 122 iron arsenide superconductors are highly anisotropic, unconventional, and exhibit several forms of electronic orders that coexist or compete with superconductivity in different regions of their phase diagrams, we find in the absence of iron in the structure that the superconducting characteristics of the end member BaPd2As2 are surprisingly conventional. Here we report on complementary measurements of specific heat, magnetic susceptibility, resistivity measurements, Andreev spectroscopy, and synchrotron high pressure x-ray diffraction measurements supplemented with theoretical calculations for BaPd2As2 . Its superconducting properties are completely isotropic as demonstrated by the critical fields, which do not depend on the direction of the applied field. Under the application of high pressure, Tc is linearly suppressed, which is the typical behavior of classical phonon-mediated superconductors with some additional effect of a pressure-induced decrease in the electronic density of states and the electron-phonon coupling parameters. Structural changes in the layered BaPd2As2 have been studied by means of angle-dispersive diffraction in a diamond-anvil cell. At 12 GPa and 24.2 GPa we observed pressure induced lattice distortions manifesting as the discontinuity and, hence discontinuity in the Birch-Murnaghan equation of state. The bulk modulus is B0=40 (6 ) GPa below 12 GPa and B0=142 (3 ) GPa below 27.2 GPa.

Muon spin rotation study of magnetism and superconductivity in Ba(Fe₁-_xCo_x)₂As₂ single crystals

DEFF Research Database (Denmark)

Bernhard, C.; Wang, C. N.; Nuccio, L.

2012-01-01

Using muon spin rotation (μSR) we investigated the magnetic and superconducting properties of a series of Ba(Fe1−xCox)2As2 single crystals with 0 ≤x ≤0.15. Our study details how the antiferromagnetic order is suppressed upon Co substitution and how it coexists with superconductivity. In the nonsu......Using muon spin rotation (μSR) we investigated the magnetic and superconducting properties of a series of Ba(Fe1−xCox)2As2 single crystals with 0 ≤x ≤0.15. Our study details how the antiferromagnetic order is suppressed upon Co substitution and how it coexists with superconductivity....... In the nonsuperconducting samples at 0 demonstrated by μSR at x = 0.055 [P. Marsik et al., Phys. Rev. Lett. 105...

Charge/orbital ordering structure in ordered perovskite Sm sub 1 sub / sub 2 Ba sub 1 sub / sub 2 MnO sub 3

CERN Document Server

Uchida, M; Akahoshi, D; Kumai, R; Tomioka, Y; Tokura, Y; Arima, T H

2002-01-01

In an A-site ordered perovskite manganite Sm sub 1 sub / sub 2 Ba sub 1 sub / sub 2 MnO sub 3 , a new charge/orbital ordering pattern was found at room temperature. Electron diffraction studies revealed a series of superlattice reflections with modulation vectors at q sub 2 =(1/2, 1/2, 1/2) as well as at q sub 1 =(1/4, 1/4, 0) in the tetragonal setting (a sub p x a sub p x 2a sub p , a sub p being the cubic perovskite lattice parameter). Together with the results of the resonant X-ray scattering and the charge-transport and magnetization measurements, a new model for the three-dimensional charge/orbital ordering in the ordered perovskite is proposed. (author)

Carbon-14 immobilization via the CO2-Ba(OH)2 hydrate gas-solid reaction

International Nuclear Information System (INIS)

Haag, G.L.

1980-01-01

Although no restrictions have been placed on the release of carbon-14, it has been identified as a potential health hazard due to the ease in which it may be assimilated into the biosphere. The intent of the Carbon-14 Immobilization Program, funded through the Airborne Waste Program Management Office, is to develop and demonstrate a novel process for restricting off-gas releases of carbon-14 from various nuclear facilities. The process utilizes the CO 2 -Ba(OH) 2 hydrate gas-solid reaction to directly remove and immobilize carbon-14. The reaction product, BaCO 3 , possesses both the thermal and chemical stability desired for long-term waste disposal. The process is capable of providing decontamination factors in excess of 1000 and reactant utilization of greater than 99% in the treatment of high volumetric, airlike (330 ppM CO 2 ) gas streams. For the treatment of an air-based off-gas stream, the use of packed beds of Ba(OH) 2 .8H 2 O flakes to remove CO 2 has been demonstrated. However, the operating conditions must be maintained between certain upper and lower limits with respect to the partial pressure of water. If the water vapor pressure in the gas is less than the dissociation vapor pressure of Ba(OH) 2 .8H 2 O, the bed will deactivate. If the vapor pressure is considerably greater, pressure drop problems will increase with increasing humidity as the particles curl and degrade. Results have indicated that when operated in the proper regime, the bulk of the increase in pressure drop results from the conversion of Ba(OH) 2 .8H 2 O to BaCO 3 and not from the hydration of the commercial Ba(OH) 2 .8H 2 O (i.e. Ba(OH) 2 .7.50H 2 O) to Ba(OH) 2 .8H 2 O

Polarizabilities of Ba and Ba2: Comparison of molecular beam experiments with relativistic quantum chemistry

International Nuclear Information System (INIS)

Schaefer, Sascha; Mehring, Max; Schaefer, Rolf; Schwerdtfeger, Peter

2007-01-01

The dielectric response to an inhomogeneous electric field has been investigated for Ba and Ba 2 within a molecular beam experiment. The ratio of the polarizabilities per atom of Ba 2 and Ba is determined to be 1.30±0.13. The experimental result is compared to a high level ab initio quantum chemical coupled cluster calculation with an energy-consistent scalar relativistic small-core pseudopotential for Ba. For the barium atom a polarizability of 40.82 A 3 is obtained and the isotropic value of the polarizability calculated for Ba 2 is 97.88 A 3 , which is in good agreement with the experimental results, demonstrating that a quantitative understanding of the interaction between two closed-shell heavy element metal atoms has been achieved

Synthesis, band structure, and optical properties of Ba2ZnV2O8

International Nuclear Information System (INIS)

Chen, D.-G.; Cheng, W.-D.; Wu, D.-S.; Zhang, H.; Zhang, Y.-C.; Gong, Y.-J.; Kan, Z.-G.

2004-01-01

A novel compound Ba 2 ZnV 2 O 8 has been synthesized in high temperature solution reaction and its crystal structure has been characterized by means of single crystal X-ray diffraction analysis. It crystallizes in monoclinic system and belongs to space group P2 1 /c with a=7.9050(16), b=16.149(3), c=6.1580(12)A, β=90.49(3). It builds up from 1-D branchy chains of [ZnV 2 O 8 4- ] ∞ , and the Ba 2+ cations are located in the space among these chains. The IR spectrum, ultraviolet-visible diffuse reflection integral spectrum and fluorescent spectra of this compound have been investigated. The calculated results of energy band structure by the density functional theory method show that the solid-state compound of Ba 2 ZnV 2 O 8 is an insulator with direct band gap of 3.48eV. The calculated total and partial density of states indicate that the top valence bands are contributions from the mixings of O-2p, V-3d, and Zn-3d states and low conduction bands mostly originate from unoccupied antibonding states between the V-3d and O-2p states. The V-O bonds are mostly covalence characters and Zn-O bonds are mostly ionic interactions, and the ionic interaction strength is stronger between the Ba-O than between the Zn-O. The refractive index of n x , n y , and n z is estimated to be 1.7453, 1.7469, and 1.7126, respectively, at wavelength of 1060nm for Ba 2 ZnV 2 O 8 crystal

A low-fluorine solution with a 2:1 F/Ba mole ratio for the fabrication of YBCO films

DEFF Research Database (Denmark)

Wu, Wei; Feng, Feng; Yue, Zhao

2014-01-01

must be at least 2 for full conversion of the Ba-precursor to BaF2 to avoid the formation of BaCO3, which is detrimental to the superconducting performance of YBCO films. In this study, a solution with a 2:1 F/Ba mole ratio was developed, and the fluorine content of this solution was approximately only...... 10.3% of that used in the conventional TFA-MOD method. Attenuated total reflectance-Fourier transform-infrared spectra (ATR-FT-IR) revealed that BaCO3 was remarkably suppressed in the as-pyrolyzed film—and eliminated at 700 °C. Thus, YBCO films with a critical current density (Jc) of over 5 MA cm−2...... (77 K, 0 T, 200 nm thickness) could be obtained on lanthanum aluminate single-crystal substrates. In situ FT-IR spectra showed that no obvious fluorinated gaseous by-products were detected in the pyrolysis step, which indicated that all F atoms might remain in the film as fluorides. X-ray diffraction...

Variations of force constants, M-O distances and bond order in solid solutions between Ba/sub 2/MgUO/sub 6/ and Ba/sub 2/MgWO/sub 6/

Energy Technology Data Exchange (ETDEWEB)

Kemmler-Sack, S; Fadini, A [Tuebingen Univ. (Germany, F.R.). Inst. fuer Chemie

1977-12-01

In solid solutions between the 1:1 ordered perovskites Ba/sub 2/MgUO/sub 6/ and Ba/sub 2/MgWO/sub 6/ (system Ba/sub 2/MgUsub(1-x)Wsub(x)O/sub 6/) the force constants of the UO/sub 6/ and WO/sub 6/ octahedras are variied. The valence force constants fsub(MO) tend to adjust for each x. The bond order and the M-O distances are reported as well.

Chemical interaction between Ba{sub 2}YCu{sub 3}O{sub 6+x} and CeO{sub 2} at pO{sub 2}=100 Pa

Energy Technology Data Exchange (ETDEWEB)

Wong-Ng, W.; Yang, Z.; Cook, L.P.; Huang, Q.; Frank, J. [Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD (United States); Kaduk, J.A. [BP-Amoco Research, Naperville, IL (United States)

2005-07-01

Chemical interaction between the Ba{sub 2}YCu{sub 3}O{sub 6+x} superconductor and the CeO{sub 2} buffer layers employed in coated conductor architectures has been modeled experimentally by investigating phase equilibria on the Ba{sub 2}YCu{sub 3}O{sub 6+x}-CeO{sub 2} join at pO{sub 2}=100 Pa. This join is actually a non-binary join within the BaOY{sub 2}O{sub 3}CeO{sub 2}CuO{sub x} quaternary system. At an approximate mole ratio of Ba{sub 2}YCu{sub 3}O{sub 6+x}:CeO{sub 2} = 40:60, a phase boundary was found to separate two four-phase regions. At the Ba{sub 2}YCu{sub 3}O{sub 6+x}-rich side of the join, the four-phase region consists of Ba{sub 2}YCu{sub 3}O{sub 6+x}, Ba(Ce{sub 1-z}Y{sub z})O{sub 3-x}, BaY{sub 2}CuO{sub 5}, and Cu{sub 2}O; at the CeO{sub 2} rich side, the four phases were determined to be Ba(Ce{sub 1-z}Y{sub z})O{sub 3-x}, BaY{sub 2}CuO{sub 5}, Cu{sub 2}O and CeO{sub 2}. At 810 C and pO{sub 2}=100 Pa, there appears to be negligible solid solution formation of the types Y{sub 1-z}Ce{sub z}O{sub 3-x} and Ce{sub 1-z}Y{sub z}O{sub 2-x}. The minimum melting temperature along the Ba{sub 2}YCu{sub 3}O{sub 6+x}-CeO{sub 2} join was determined to be {approx} 860 C. As part of this study, phase diagrams of the subsystems CeO{sub 2}-Y{sub 2}O{sub 3}-CuO{sub x}, BaO-CeO{sub 2}-CuO{sub x}, and BaO-Y{sub 2}O{sub 3}-CeO{sub 2} were also determined at 810 C under 100 Pa pO{sub 2}. The Y{sub 2}O{sub 3}-CeO{sub 2}-CuO{sub x} diagram does not contain ternary phases and shows a tie-line from Y{sub 2}O{sub 3} to the binary phase Y{sub 2}Cu{sub 2}O{sub 5-x}. Similarly, the BaO-CeO{sub 2}-CuO{sub x} diagram contains no ternary phases, but has four tie-lines originating from BaCeO{sub 3} to Ba{sub 2}CuO{sub 3+x}, BaCuO{sub 2+x}, BaCu{sub 2}O{sub 2+x} and CuO{sub x}. The BaO-Y{sub 2}O{sub 3}-CeO{sub 2} system contains one ternary phase, the solid solution Ba(Ce{sub 1-z}Y{sub z})O{sub 3-x} (0{<=}z{<=}0.13), which crystallizes with the orthorhombic space group Pmcn (No. 62

Doping dependence of magnetic and transport properties in single crystalline Co-doped BaFe2As2

International Nuclear Information System (INIS)

Nakajima, Yasuyuki; Taen, Toshihiro; Tamegai, Tsuyoshi

2010-01-01

We report the doping dependence of transport and magnetic properties in Co-doped BaFe 2 As 2 . With increasing Co concentration x, structural and magnetic transitions are suppressed and superconductivity emerges in the range of 0.3 c at low temperatures and low fields obtained from bulk magnetization is reasonably large and the doping dependence shows a maximum at x∼0.07 similar to T c . The values of J c at low temperatures reach about 1x10 6 A/cm 2 around the optimally doped region, which is potentially attractive for technological applications.

Optical characteristics of BaGa2S4:Ho3+ and BaGa2Se4:Ho3+ single crystals

International Nuclear Information System (INIS)

Choe, Sung-Hyu; Jin, Moon-Seog; Kim, Wha-Tek

2005-01-01

BaGa 2 S 4 , BaGa 2 S 4 :Ho 3+ , BaGa 2 Se 4 , and BaGa 2 Se 4 :Ho 3+ single crystals were grown by using the chemical transport reaction method. The optical energy gaps of the single crystals were investigated in the temperature region from 11 K to 300 K. The temperature dependence of the optical energy gap was well fitted by the Varshni equation. Two broad emission bands were observed in the photoluminescence spectra of the single crystals. These bands were attributed to donor-acceptor pair recombinations. Sharp emission peaks were observed in the BaGa 2 S 4 :Ho 3+ and the BaGa 2 Se 4 :Ho 3+ single crystals and were assigned to radiation recombination between split Stark levels of Ho 3+ .

Effect of ion irradiation on surface morphology and superconductivity of BaFe{sub 2}(As{sub 1−x}P{sub x}){sub 2} films

Energy Technology Data Exchange (ETDEWEB)

Daghero, D., E-mail: dario.daghero@polito.it [Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Tortello, M. [Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Gozzelino, L. [Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Torino, 10125 Torino (Italy); Gonnelli, R.S. [Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Hatano, T.; Kawaguchi, T.; Ikuta, H. [Department of Crystalline Materials Science, Nagoya University, Nagoya 464-8603 (Japan)

2017-02-15

Highlights: • Epitaxial films of BaFe{sub 2}(As,P){sub 2} at optimal doping on MgO substrate have been irradiated by 250 MeV Au ions with different fluences. • Irradiation induces a partial relaxation of the in-plane tensile stress typical of the pristine films. • The residual resistivity increases less than linearly with fluence, tending to saturate; the overall increase is about 60%, but the critical temperature decreases by only 2%. • These results indicate that the substrate and the reduced dimensionality of the films (as compared to the case of single crystals) play an important role in their response to irradiation. - Abstract: We have irradiated epitaxial thin films of BaFe{sub 2}(As{sub 1−x}P{sub x}){sub 2} with x ≃ 0.2 (optimal doping) with Au ions having an energy of 250 MeV. We have used two different fluences, Φ{sub 1} = 2.4 × 10{sup 11} cm{sup −2} and Φ{sub 2} = 7.3 × 10{sup 11} cm{sup −2}, and we have studied the effects of irradiation on the surface morphology, on the resistivity and on the critical temperature. We have found that irradiation progressively destroys the very clear and interconnected growth terraces typical of the pristine surface, leading first to their smoothening – accompanied by the appearance of localized defects – and then to a completely disordered surface. The residual resistivity increases by almost 60%, but the critical temperature decreases very little (i.e. by about 2%) on going from the pristine film to the most irradiated one. The possible role of the substrate in these results is discussed.

Host composition dependent tunable multicolor emission in the single-phase Ba2(Ln1-zTbz)(BO3)2Cl:Eu phosphors

NARCIS (Netherlands)

Xia, Z.; Zhuang, J.; Meijerink, A.; Jing, X.

2013-01-01

A new strategy based on the host composition design has been adopted to obtain efficient color-tunable emission from Ba2Ln0.97−zTbz(BO3)2Cl:0.03Eu (Ln = Y, Gd and Lu, z = 0–0.97) phosphors. This study reveals that the single-phase Ba2Ln1−zTbz(BO3)2Cl compounds can be applied to use allowed Eu2+

Synthesis and structural characterization of the ternary Zintl phases AE3Al2Pn4 and AE3Ga2Pn4 (AE=Ca, Sr, Ba, Eu; Pn=P, As)

International Nuclear Information System (INIS)

He, Hua; Tyson, Chauntae; Saito, Maia; Bobev, Svilen

2012-01-01

Ten new ternary phosphides and arsenides with empirical formulae AE 3 Al 2 Pn 4 and AE 3 Ga 2 Pn 4 (AE=Ca, Sr, Ba, Eu; Pn=P, As) have been synthesized using molten Ga, Al, and Pb fluxes. They have been structurally characterized by single-crystal and powder X-ray diffraction to form with two different structures—Ca 3 Al 2 P 4 , Sr 3 Al 2 As 4 , Eu 3 Al 2 P 4 , Eu 3 Al 2 As 4 , Ca 3 Ga 2 P 4 , Sr 3 Ga 2 P 4 , Sr 3 Ga 2 As 4 , and Eu 3 Ga 2 As 4 crystallize with the Ca 3 Al 2 As 4 structure type (space group C2/c, Z=4); Ba 3 Al 2 P 4 and Ba 3 Al 2 As 4 adopt the Na 3 Fe 2 S 4 structure type (space group Pnma, Z=4). The polyanions in both structures are made up of TrPn 4 tetrahedra, which share common corners and edges to form 2 ∞ [TrPn 2 ] 3– layers in the phases with the Ca 3 Al 2 As 4 structure, and 1 ∞ [TrPn 2 ] 3– chains in Ba 3 Al 2 P 4 and Ba 3 Al 2 As 4 with the Na 3 Fe 2 S 4 structure type. The valence electron count for all of these compounds follows the Zintl–Klemm rules. Electronic band structure calculations confirm them to be semiconductors. - Graphical abstract: AE 3 Al 2 Pn 4 and AE 3 Ga 2 Pn 4 (AE=Ca, Sr, Ba, Eu; Pn=P, As) crystallize in two different structures—Ca 3 Al 2 P 4 , Sr 3 Al 2 As 4 , Eu 3 Al 2 P 4 , Eu 3 Al 2 As 4 , Ca 3 Ga 2 P 4 , Sr 3 Ga 2 P 4 , Sr 3 Ga 2 As 4 , and Eu 3 Ga 2 As 4 , are isotypic with the previously reported Ca 3 Al 2 As 4 (space group C2/c (No. 15)), while Ba 3 Al 2 P 4 and Ba 3 Al 2 As 4 adopt a different structure known for Na 3 Fe 2 S 4 (space group Pnma (No. 62). The polyanions in both structures are made up of TrPn 4 tetrahedra, which by sharing common corners and edges, form 2 ∞ [TrPn 2 ] 3– layers in the former and 1 ∞ [TrPn 2 ] 3– chains in Ba 3 Al 2 P 4 and Ba 3 Al 2 As 4 . Highlights: ► AE 3 Ga 2 Pn 4 (AE=Ca, Sr, Ba, Eu; Pn=P, As) are new ternary pnictides. ► Ba 3 Al 2 P 4 and Ba 3 Al 2 As 4 adopt the Na 3 Fe 2 S 4 structure type. ► The Sr- and Ca-compounds crystallize with the Ca 3

The interaction of NO2 with BaO: from cooperative adsorption to Ba(NO3)2 formation

International Nuclear Information System (INIS)

Yi, Cheol-Woo W.; Kwak, Ja Hun H.; Szanyi, Janos

2007-01-01

The effect of water on the morphology of BaO/Al2O3-based NOx storage materials was investigated using Fourier transform infrared spectroscopy, temperature programmed desorption, and time-resolved synchrotron X-ray diffraction techniques. The results of this multi-spectroscopy study reveal that, in the presence of water, surface Ba-nitrates convert to bulk nitrates, and water facilitates the formation of large Ba(NO3)2 particles. The conversion of surface to bulk Ba-nitrates is completely reversible, i.e. after the removal of water from the storage material a significant fraction of the bulk nitrates re-convert to surface nitrates. NO2 exposure of a H2O-containing (wet) BaO/Al2O3 sample results in the formation of nitrites and bulk nitrates exclusively, i.e. no surface nitrates form. After further exposure to NO2, the nitrites completely convert to bulk nitrates. The amount of NOx taken up by the storage material is, however, essentially unaffected by the presence of water, regardless of whether the water was dosed prior to or after NO2 exposure. Based on the results of this study we are now able to explain most of the observations reported in the literature on the effect of water on NOx uptake on similar storage materials

Formation pathways in the synthesis and properties of (Tl0.5Pb0.5)(Sr0.9Ba0.1)2Ca2Cu3Oz and (Tl0.5Pb0.5)(Sr0.8Ba0.2)2Ca2Cu3Oz-1223 superconductors

International Nuclear Information System (INIS)

Auinger, M; Gritzner, G; Bertrand, Ch; Galez, Ph; Soubeyroux, J-L

2007-01-01

The formation pathway of (Tl 0.5 Pb 0.5 )(Sr 0.9 Ba 0.1 ) 2 Ca 2 Cu 3 O z and (Tl 0.5 Pb 0.5 )(Sr 0.8 Ba 0.2 ) 2 Ca 2 Cu 3 O z was studied by neutron and x-ray diffraction. The following reaction pathway was proposed: thallium oxide and lead oxide react with Sr-rich (Sr 1-x Ca x )CuO 2 and Ca-rich (Ca x Sr 1-x )O to form Sr 4 Tl 2 O 7 and (Ca x Sr 1-x )PbO 3 , respectively. The thallate and the plumbate compounds then form the (Tl 0.5 Pb 0.5 )-1212 phase starting at a temperature of 600 deg. C. Finally, between 850 and 900 deg. C, the 1223 phase is formed from (Tl 0.5 Pb 0.5 )-1212 (Ca x Sr 1-x ) 2 CuO 3 and CuO. Parallel experiments to fabricate the (Tl, Pb)-1223 superconductor resulted in specimens with critical temperatures of 117.5 K and 116 K, respectively, and transition widths of 2 K. Differences between the pathways for the formation of Pb-doped, Sr-rich and Pb-free, Ba-rich Tl-1223 superconductors are discussed

Cubic Re6+ (5d1) Double Perovskites, Ba2MgReO6, Ba2ZnReO6, and Ba2Y2/3ReO6: Magnetism, Heat Capacity, μSR, and Neutron Scattering Studies and Comparison with Theory.

Science.gov (United States)

Marjerrison, Casey A; Thompson, Corey M; Sala, Gabrielle; Maharaj, Dalini D; Kermarrec, Edwin; Cai, Yipeng; Hallas, Alannah M; Wilson, Murray N; Munsie, Timothy J S; Granroth, Garrett E; Flacau, Roxana; Greedan, John E; Gaulin, Bruce D; Luke, Graeme M

2016-10-04

Double perovskites (DP) of the general formula Ba 2 MReO 6 , where M = Mg, Zn, and Y 2/3 , all based on Re 6+ (5d 1 , t 2g 1 ), were synthesized and studied using magnetization, heat capacity, muon spin relaxation, and neutron-scattering techniques. All are cubic, Fm3̅m, at ambient temperature to within the resolution of the X-ray and neutron diffraction data, although the muon data suggest the possibility of a local distortion for M = Mg. The M = Mg DP is a ferromagnet, T c = 18 K, with a saturation moment ∼0.3 bohr magnetons at 3 K. There are two anomalies in the heat capacity: a sharp feature at 18 K and a broad maximum centered near 33 K. The total entropy loss below 45 K is 9.68 e.u., which approaches R ln 4 (11.52 e.u.) supporting a j = 3/2 ground state. The unit cell constants of Ba 2 MgReO 6 and the isostructural, isoelectronic analogue, Ba 2 LiOsO 6 , differ by only 0.1%, yet the latter is an anti-ferromagnet. The M = Zn DP also appears to be a ferromagnet, T c = 11 K, μ sat (Re) = 0.1 μ B . In this case the heat capacity shows a somewhat broad peak near 10 K and a broader maximum at ∼33 K, behavior that can be traced to a smaller particle size, ∼30 nm, for this sample. For both M = Mg and Zn, the low-temperature magnetic heat capacity follows a T 3/2 behavior, consistent with a ferromagnetic spin wave. An attempt to attribute the broad 33 K heat capacity anomalies to a splitting of the j = 3/2 state by a crystal distortion is not supported by inelastic neutron scattering, which shows no transition at the expected energy of ∼7 meV nor any transition up to 100 meV. However, the results for the two ferromagnets are compared to the theory of Chen, Pereira, and Balents, and the computed heat capacity predicts the two maxima observed experimentally. The M = Y 2/3 DP, with a significantly larger cell constant (3%) than the ferromagnets, shows predominantly anti-ferromagnetic correlations, and the ground state is complex with a spin frozen component T

Magnetocaloric effect in (La1-xAx)2/3Ba1/3Mn1.05O3-δ

DEFF Research Database (Denmark)

Ancona-Torres, Carlos Eugenio; Menon, Mohan; Bahl, Christian Robert Haffenden

Recently, a large magnetocaloric effect has been reported in La2/3Ba1/3MnO3-δ at about 300 K. In this paper, we investigate the effect of the ion size distribution at the A site on the magnetocaloric effect of this perovskite material. This is accomplished by replacing the lanthanum by Ce, Pr......, and Nd, which allows us to study the effect of both the average size, , and the distribution, σrA, on the magnetic properties of the system. Using magnetization and heat capacity measurements, we determine the important magnetocaloric parameters ΔSM and ΔTad of (La1-xAx)2/3Ba1/3Mn1.05O3-δ powders...

Scintillation and radiation damage of doped BaF2 crystals

International Nuclear Information System (INIS)

Gong Zufang; Xu Zizong; Chang Jin

1992-01-01

The emission spectra and the radiation damage of BaF 2 crystals doped Ce and Dy have been studied. The results indicate that the doped BaF 2 crystals have the intrinsic spectra of impurity besides the intrinsic spectra of BaF 2 crystals. The crystals colored and the transmissions decrease with the concentration of impurity in BaF 2 crystals after radiation by γ-ray of 60 Co. The doped Ce BaF 2 irradiated by ultraviolet has faster recover of transmissions but for doped Dy the effect is not obvious. The radiation resistance is not good as pure BaF 2 crystals

Shell model for BaTiO3-Bi(Zn1/2Ti1/2)O3 perovskite solid solutions

Science.gov (United States)

Vielma, J.; Jackson, D.; Roundy, D.; Schneider, G.

2010-03-01

Even though the composition of BaTiO3-Bi(Zn1/2Ti1/2)O3 perovskite solid solutions is similar to other ferroelectric compounds, the dielectric response is unusual. Results of permittivity measurements as a function of temperature show a diffuse phase transition indicative of a weakly coupled relaxor behavior.footnotetextC. C. Huang and D. P. Cann, J. Appl. Phys. 104, 024117 (2008) To investigate the weakly coupled relaxor behavior in these materials at intermediate length scales we are developing a newly calibrated shell model based on first-principles supercell calculations of both the solid solution and its compositional endpoints. Initial results for its phase diagram will presented.

X-ray photoelectron spectrometry and binding energies of Be 1s and O 1s core levels in clinobarylite, BaBe2Si2O7, from Khibiny massif, Kola peninsula

International Nuclear Information System (INIS)

Atuchin, V.V.; Kesler, V.G.; Sapozhnikov, V.K.; Yakovenchuk, V.N.

2008-01-01

The electronic structure of BaBe 2 Si 2 O 7 , clinobarylite, has been investigated by means of X-ray photoelectron spectroscopy (XPS). The valence band of the crystal is mainly formed by Ba 5p, Ba 3s and O 2s states. At higher binding energies the emission lines related to the Si 2p, Be 1s, Si 2s, O 1s and numerous Ba-related states were analyzed in the photoemission spectrum. The Si KLL Auger line has been measured under excitation by the bremsstrahlung X-rays from the Al anode. Chemical bonding effects for Be 1s core level have been considered by comparison with electronic parameters measured for other beryllium containing oxides

Magnetic and electrical properties in BaNiS2-type solid solutions

International Nuclear Information System (INIS)

Irizawa, Akinori; Yoshimura, Kazuyoshi; Kosuge, Koji

2000-01-01

The magnetic and electrical properties are reported in the new solid solutions BaCo 1-x Cu x S 2 and BaNi 1-x Fe x S 2 . Both compounds show spin-glass-like behavior, although the type of spin frustrations is different with each other. BaCo 1-x Cu x S 2 shows a competition type spin-glass behavior with reentrant phenomenon from antiferromagnetic to spin-glass at low temperatures. BaNi 1-x Fe x S 2 shows a dilute type spin-glass behavior together with super-paramagnetic properties. The temperature variation of 57 Fe Moessbauer spectra in BaNi 0.8 Fe 0.2 S 2 is explicable in a framework of cluster-glass. (author)

BaO-Nd2O3-CuOx subsolidus equilibria under carbonate-free conditions at pO2=100 Pa and at pO2=21 kPa

International Nuclear Information System (INIS)

Wong-Ng, W.; Cook, L.P.; Suh, J.; Coutts, R.; Stalick, J.K.; Levin, I.; Huang, Q.

2003-01-01

Subsolidus phase equilibria of the BaO-Nd 2 O 3 -CuO x system at pO 2 =100 Pa (0.1% O 2 volume fraction, 810 deg. C) and at pO 2 =21 kPa (21% O 2 volume fraction, 930 deg. C) have been investigated by applying controlled-atmosphere methods to minimize the presence of carbonate and CO 2 and H 2 O contamination. Under carbonate-free conditions, the BaO-Nd 2 O 3 -CuO x phase diagrams at pO 2 =100 Pa and at pO 2 =21 kPa are similar to one another except for differences in the extent of the solid solutions. Apart from the limiting binary phases, the ternary system consists of three solid solutions and one stoichiometric ternary compound. The first solid solution is the high T c series, Ba 2-x Nd 1+x Cu 3 O 6+z (0.3≥x≥0 at pO 2 =100 Pa; 0.95≥x≥ 0 at pO 2 =21 kPa). At pO 2 =21 kPa, a compositionally dependent phase change was detected, from tetragonal (0.7>x≥0) to orthorhombic (0.95≥x≥0.7). The second solid solution series, the 'brown-phase' Ba 1+x Nd 2-x CuO z , has a narrow homogeneity region (0.10>x≥0 at pO 2 =100 Pa; 0.15>x≥0 at pO 2 =21 kPa). In the high BaO part of the phase diagram, a third solid solution (Ba 2-x Nd x )CuO 3+z (x=0 to ∼ 0.3 at pO 2 =100 Pa; x=0-0.45 at pO 2 =21 kPa) was confirmed, as well as a nominally stoichiometric phase, Ba 4 Nd 2 Cu 2 O z . The latter phase is an insulator, with a structure comprised of unusual CuO 5 linear chains. A significant difference in tie line distribution involving the Ba 2-x Nd 1+x Cu 3 O 6+z superconductor was found under carbonate-free conditions relative to literature studies completed in air. Instead of the BaCuO 2+x -Ba 2+x Nd 4-x Cu 2 O z tie line normally encountered in air, a Ba 2-x Nd 1+x Cu 3 O 6+z -(Ba,Nd) 2 CuO 3+x tie line was established. This tie line substantially expands the field of stability of the Ba 2-x Nd 1+x Cu 3 O 6+z superconductor phase into the BaO-rich region of the phase diagram. Implications for the processing of materials based on the Ba 2-x Nd 1+x Cu 3 O 6+z

A semimetal model of the normal state magnetic susceptibility and transport properties of Ba(Fe1-xCox)2As2

International Nuclear Information System (INIS)

Sales, B.C.; McGuire, M.A.; Sefat, A.S.; Mandrus, D.

2010-01-01

A simple two-band 3D model of a semimetal is constructed to determine which normal state features of the Ba(Fe 1-x Co x ) 2 As 2 superconductors can be qualitatively understood within this framework. The model is able to account in a semiquantitative fashion for the measured magnetic susceptibility, Hall, and Seebeck data, and the low temperature Sommerfeld coefficient for 0 < x < 0.3 with only three parameters for all x. The purpose of the model is not to fit the data but to provide a simple starting point for thinking about the physics of these interesting materials. Although many of the static magnetic properties, such as the increase of the magnetic susceptibility with temperature, are reproduced by the model, none of the spin-fluctuation dynamics are addressed. A general conclusion from the model is that the magnetic susceptibility of most semimetals should increase with temperatures.

Investigation of the Na2(H2PO2)2 - Ba(H2PO2)2 - H2O Water-Salt Ternary System at Room Temperature

OpenAIRE

Erge, Hasan; Turan, Hakan; Kul, Ali Riza

2016-01-01

Objective: In this study, the solubility, density, conductivity and phase equilibria of the Na2(H2PO2)2-Ba(H2PO2)2-H2O ternary system located in the structure of the Na+, Ba2+, (H2PO2)-//H2O quaternary reciprocal water-salt system were investigated using physicochemical analysis methods. Material and Methods: Riedel-de Haen and Merck salts were used to investigate the solubility and phase equilibria of the Na2(H2PO2)2 -Ba(H2PO2)2-H2O ternary water–salt system at room temperature Res...

Properties of half metallic (Ba0.8Sr0.2)2-x La2x/3x/3FeMoO6 double perovskites

International Nuclear Information System (INIS)

Serrate, D.; De Teresa, J.M.; Blasco, J.; Morellon, L.; Ibarra, M.R.

2005-01-01

Previous work in (Ba 0.8 Sr 0.2 ) 2- x La x FeMoO 6 and Ba 1+ x Sr 1-3 x La 2 x FeMoO 6 have stated electron doping as the most important parameter in terms of T c enhancement. Here we report complementary structural, magnetic and transport properties, say a series where there is no doping and only structural parameters are changed: (Ba 0.8 Sr 0.2 ) 2- x La 2 x /3 x /3 FeMoO 6 . We propose a complete phase diagram where structural and bandfilling impact on the Curie temperature is clearly evidenced

Defect chemistry of ''BaCuO2''. Pt. 1. Oxygen non-stoichiometry, cation molecularity and X-ray diffraction determinations

International Nuclear Information System (INIS)

Spinolo, G.; Consiglio Nazionale delle Ricerche, Pavia; Anselmi-Tamburini, U.; Consiglio Nazionale delle Ricerche, Pavia; Arimondi, M.; Consiglio Nazionale delle Ricerche, Pavia; Ghigna, P.; Consiglio Nazionale delle Ricerche, Pavia; Flor, G.; Consiglio Nazionale delle Ricerche, Pavia

1995-01-01

''BaCuO 2 '' is the key intermediate in the synthesis of the Ba 2 YCu 3 O 7-δ superconductor. Its very complex crystal structure is able to accommodate a large change in oxygen content. Oxygen non-stoichiometry of ''BaCuO 2 '' materials with 1:1 and 88:90 (Ba:Cu) molecularity has been investigated by polythermal X-ray powder diffraction coupled with isobaric-isothermal gravimetry determinations under different temperature and oxygen partial pressure conditions [300 ≤ T ≤ 820 C, 1 ≥ P(O 2 ) ≥3 . 10 -3 atm]. The 1:1 composition does not give well reproducible results, thus suggesting its polyphasic nature, at least in part of the investigated range. The results for the 88:90 ≅ 0.98 (Ba:Cu) composition are well reproducible and show that the material is single phase. Ba 0.98 CuO 1.98 + δ is oxygen over-stoichiometric in the whole investigated [T, P(O 2 )] range, with a maximum value δ ∼ 0.21. A Rietveld X-ray profile fitting is in agreement with previous single-crystal data. The trend of δ vs. P(O 2 ) is consistent with the presence of oxygen interstitial defects on (possibly different) crystallographic sites. (orig.)

Enhanced 77 K vortex-pinning in Y Ba2Cu3O7−x films with Ba2Y TaO6 and mixed Ba2Y TaO6 + Ba2Y NbO6 nano-columnar inclusions with irreversibility field to 11 T

Directory of Open Access Journals (Sweden)

F. Rizzo

2016-06-01

Full Text Available Pulsed laser deposited thin Y Ba2Cu3O7−x (YBCO films with pinning additions of 5 at. % Ba2Y TaO6 (BYTO were compared to films with 2.5 at. % Ba2Y TaO6 + 2.5 at. % Ba2Y NbO6 (BYNTO additions. Excellent magnetic flux-pinning at 77 K was obtained with remarkably high irreversibility fields greater than 10 T (YBCO-BYTO and 11 T (YBCO-BYNTO, representing the highest ever achieved values in YBCO films.

System Ba/sub 2/Gdsub(2/3)vacantsub(1/3)Usub(1-x)Wsub(x)O/sub 6/ and hexagonal perovskites of an 18-layer type

Energy Technology Data Exchange (ETDEWEB)

Wischert, W; Schittenhelm, H J; Kemmler-Sack, S [Tuebingen Univ. (Germany, F.R.). Inst. fuer Chemie

1978-04-01

In the system Ba/sub 2/Gdsub(2/3)vacantsub(1/3)Usub(1-x)Wsub(x)O/sub 6/ the formation of a continuous solid solution series is observed. With x <= 0.9 the mixed crystals have a cubic 1:1 ordered perovskite structure. With x >= 0.95 the compounds are polymorphic: besides an cubic 1:1 ordered perovskite type for x = 0.95; 0.99 and 1.00 one hexagonal layer structure exists. This lattice is in all cases rhombohedral (space group R3m) and represents an 18 L-type. Likewise the compounds Ba/sub 2/Bsub(2/3)sup(III)vacantsub(1/3)Wsup(VI)O/sub 6/ with Bsup(III) Tb-Lu and Y belong to the 18 L-type.

In situ screen-printed BaZr{sub 0.1}Ce{sub 0.7}Y{sub 0.2}O{sub 3-{delta}} electrolyte-based protonic ceramic membrane fuel cells with layered SmBaCo{sub 2}O{sub 5+x} cathode

Energy Technology Data Exchange (ETDEWEB)

Lin, Bin; Dong, Yingchao; Zhang, Shangquan; Hu, Mingjun; Zhou, Yang; Meng, Guangyao [Department of Materials Science and Engineering, University of Science and Technology of China (USTC), Hefei, Anhui 230026 (China); Yan, Ruiqiang [Department of Materials Engineering, Taizhou University, Linhai, Zhejiang 317000 (China)

2009-01-15

In order to develop a simple and cost-effective route to fabricate protonic ceramic membrane fuel cells (PCMFCs) with layered SmBaCo{sub 2}O{sub 5+x} (SBCO) cathode, a dense BaZr{sub 0.1}Ce{sub 0.7}Y{sub 0.2}O{sub 3-{delta}} (BZCY) electrolyte was fabricated on a porous anode by in situ screen printing. The porous NiO-BaZr{sub 0.1}Ce{sub 0.7}Y{sub 0.2}O{sub 3-{delta}} (NiO-BZCY) anode was directly prepared from metal oxide (NiO, BaCO{sub 3}, ZrO{sub 2}, CeO{sub 2} and Y{sub 2}O{sub 3}) by a simple gel-casting process. An ink of metal oxide (BaCO{sub 3}, ZrO{sub 2}, CeO{sub 2} and Y{sub 2}O{sub 3}) powders was then employed to deposit BaZr{sub 0.1}Ce{sub 0.7}Y{sub 0.2}O{sub 3-{delta}} (BZCY) thin layer by an in situ reaction-sintering screen printing process on NiO-BZCY anode. The bi-layer with 25 {mu}m dense BZCY electrolyte was obtained by co-sintering at 1400 C for 5 h. With layered SBCO cathode synthesized by gel-casting on the bi-layer, single cells were assembled and tested with H{sub 2} as fuel and the static air as oxidant. A high open-circuit potential of 1.01 V, a maximum power density of 382 mW cm{sup -2}, and a low polarization resistance of the electrodes of 0.15 {omega} cm{sup 2} was achieved at 700 C. (author)

In-plane optical spectral weight redistribution in the optimally doped Ba0.6 K0.4Fe2As2 superconductor

International Nuclear Information System (INIS)

Xu Bing; Dai Yao-Min; Xiao Hong; Qiu Xiang-Gang; Lobo, R. P. S. M.

2014-01-01

We performed detailed temperature-dependent optical measurements on optimally doped Ba 0.6 K 0.4 Fe 2 As 2 single crystal. We examine the changes of the in-plane optical conductivity spectral weight in the normal state and the evolution of the superconducting condensate in the superconducting state. In the normal state, the low-frequency spectral weight shows a metallic response with an arctan (T) dependence, indicating a T-linear scattering rate behavior for the carriers. A high energy spectral weight transfer associated with the Hund's coupling occurs from the low frequencies below 4000 cm −1 ∼ 5000 cm −1 to higher frequencies up to at least 10 cm −1 . Its temperature dependence analysis suggests that the Hund's coupling strength is continuously enhanced as the temperature is reduced. In the superconducting state, the FGT sum rule is conserved according to the spectral weight estimation within the conduction bands, only about 40% of the conduction bands participates in the superconducting condensate indicating that Ba 0.6 K 0.4 Fe 2 As 2 is in dirty limit. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Critical current density in (YBa2Cu3O7-δ)1-x-(PrBa2Cu3O7-δ)x melt-textured composites

Science.gov (United States)

Opata, Yuri Aparecido; Monteiro, João Frederico Haas Leandro; Jurelo, Alcione Roberto; Siqueira, Ezequiel Costa

2018-06-01

Melt textured (YBa2Cu3O7-δ)1-x-(PrBa2Cu3O7-δ)x composites (x = 0.00 and x = 0.05) were grown using the top seeding method. The effect of the PrBa2Cu3O7-δ phase on the growth process and the modification of the microstructure as well as on the physical properties was analyzed. X-ray analyses indicated that both pure and Pr-doped samples present an orthorhombic superconducting phase. From resistivity measurements for YBa2Cu3O7-δ and (YBa2Cu3O7-δ)0.95-(PrBa2Cu3O7-δ)0.05 samples, the Tcab did not change and was around 90.5 K. However, from magnetic measurements, the superconductivity was observed in critical temperatures TC = 92.9 K and 92.4 K for YBa2Cu3O7-δ and (YBa2Cu3O7-δ)0.95-(PrBa2Cu3O7-δ)0.05 samples, respectively. The YBa2Cu3O7-δ sample showed higher critical current densities than those shown by the (YBa2Cu3O7-δ)0.95-(PrBa2Cu3O7-δ)0.05 sample, with values of JC = 5.85 × 105 A/cm2 and 4.72 × 105 A/cm2, respectively. This paper also discusses the importance of Pr substitution on nano- and micro-meter scales to enhance JC(H).

Structure refinement of Ba{sub 0.5}Sr{sub 0.5}Co{sub 0.8}Fe{sub 0.2}O{sub 3-d} as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFC)

Energy Technology Data Exchange (ETDEWEB)

Zakaria, Nurhamidah, E-mail: nurhamidahzakaria@yahoo.com; Idris, Mohd Sobri, E-mail: sobri@unimap.edu.my [Centre of Excellence for Frontier Materials Research, School of Materials Engineering, Universiti Malaysia Perlis (UniMAP), Taman Muhibbah, Jejawi 02600, Arau, Perlis (Malaysia); Osman, Rozana A. M., E-mail: rozana@unimap.edu.my [School of Microelectronics Engineering, Universiti Malaysia Perlis (UniMAP), Pauh Putra, 02600, Arau, Perlis (Malaysia)

2016-07-19

Ba{sub 0.5}Sr{sub 0.5}Co{sub 0.8}Fe{sub 0.2}O{sub 3-δ} was successfully prepared using modified solid-state synthesis routes. The lowest temperature to obtained single phase of Ba{sub 0.5}Sr{sub 0.5}Co{sub 0.8}Fe{sub 0.2}O{sub 3-δ} is about 900°C for 15 hours. Longer period of time are required compared to only 5 hours at 950°C as established in literatures. The X-ray Diffraction (XRD) data confirmed that Ba{sub 0.5}Sr{sub 0.5}Co{sub 0.8}Fe{sub 0.2}O{sub 3-δ} is formed a cubic perovskite with the space group of Pm-3m. The lattice parameters of Ba{sub 0.5}Sr{sub 0.5}Co{sub 0.8}Fe{sub 0.2}O{sub 3-δ} are a = 3.990 (1) Å and unit cell volume is V = 63.5 (1) Å{sup 3}. The Rietveld refinement of XRD data revealed that the crystal structure of Ba{sub 0.5}Sr{sub 0.5}Co{sub 0.8}Fe{sub 0.2}O{sub 3-δ} slightly changes as a function of temperature.

Host composition dependent tunable multicolor emission in the single-phase Ba2(Ln(1-z)Tb(z))(BO3)2Cl:Eu phosphors.

Science.gov (United States)

Xia, Zhiguo; Zhuang, Jiaqing; Meijerink, Andries; Jing, Xiping

2013-05-14

A new strategy based on the host composition design has been adopted to obtain efficient color-tunable emission from Ba2Ln(0.97-z)Tb(z)(BO3)2Cl:0.03Eu (Ln = Y, Gd and Lu, z = 0-0.97) phosphors. This study reveals that the single-phase Ba2Ln(1-z)Tb(z)(BO3)2Cl compounds can be applied to use allowed Eu(2+) absorption transitions to sensitize Eu(3+) emission via the energy transfer Eu(2+) → (Tb(3+))n → Eu(3+). The powder X-ray diffraction (XRD) and Rietveld refinement analysis shows single-phase Ba2Ln(1-z)Tb(z)(BO3)2Cl. As-prepared Ba2Ln(0.97-z)Tb(z)(BO3)2Cl:0.03Eu phosphors show intense green, yellow, orange and red emission under 377 nm near ultraviolet (n-UV) excitation due to a variation in the relative intensities of the Eu(2+), Tb(3+) and Eu(3+) emission depending on the Tb content (z) in the host composition, allowing color tuning. The variation in emission color is explained by energy transfer and has been investigated by photoluminescence and lifetime measurements and is further characterized by the Commission Internationale de l'éclairage (CIE) chromaticity indexes. The quantum efficiencies of the phosphors are high, up to 74%, and show good thermal stabilities up to 150 °C. This investigation demonstrates the possibility to sensitize Eu(3+) line emission by Eu(2+)via energy migration over Tb(3+) resulting in efficient color tunable phosphors which are promising for use in solid-state white light-emitting diodes (w-LEDs).

Hexagonal perovskites with cationic vacancies. 26. Ba/sub 12/Ba/sub 2//sub 2/3/M/sub 7//sup V//sub 1/3/vacant/sub 2/O/sub 33/vacant/sub 3/ (Msup(V) =Nb, Ta) - the first stacking polytypes of a rhombohedral 36 L-type

Energy Technology Data Exchange (ETDEWEB)

Kemmler-Sack, S [Tuebingen Univ. (Germany, F.R.). Lehrstuhl fuer Anorganische Chemie 2

1981-05-01

In the systems BaO-M/sub 2//sup V/O/sub 5/ (M/sup V/ = Nb, Ta) for a Ba:M/sup V/ ratio of 2:1 polymorphism is observed. Here the low temperature modifications are described. They crystallize in a rhombohedral 36 L structure with three formula units Ba/sub 12/Ba/sub 2//sub 2/3/M/sub 7//sup V//sub 1/3/vacant/sub 2/O/sub 33/vacant/sub 3/ for the trigonal setting (M/sup V/ = Nb: a = 5.92/sub 2/ A; c = 93./sub 25/ A; Ta: a = 5.92/sub 2/ A; c = 93.4 A).

Tailoring the piezoelectric and relaxor properties of (Bi1/2 Na1/2) TiO3- BaTiO3 via zirconium doping

DEFF Research Database (Denmark)

Glaum, Julia; Simons, Hugh; Acosta, Matias

2013-01-01

This article details the influence of zirconium doping on the piezoelectric properties and relaxor characteristics of 94(Bi1/2Na1/2)TiO3-6Ba(ZrxTi1-x)O3 (BNT-6BZT) bulk ceramics. Neutron diffraction measurements of BNT-6BZT doped with 0%-15% Zr revealed an electric-field-induced transition...

Tunnelling spectroscopy of BaFe{sub 2}As{sub 2}/Au/PbIn thin film junctions

Energy Technology Data Exchange (ETDEWEB)

Doering, Sebastian; Schmidt, Stefan; Schmidl, Frank; Tympel, Volker; Grosse, Veit; Seidel, Paul [Institut fuer Festkoerperphysik, Friedrich-Schiller-Universitaet Jena (Germany); Haindl, Silvia; Iida, Kazumasa; Kurth, Fritz; Holzapfel, Bernhard [IFW Dresden, Institut fuer Metallische Werkstoffe, Dresden (Germany)

2011-07-01

Tunnelling spectroscopy is an important tool to investigate the properties of iron-based superconductors. In contrast to commonly used point contact Andreev reflection (PCAR) technique, we fabricated hybrid superconductor / normal metal / superconductor (SNS) thin film structures, with tunable barrier thickness and area. For the base electrode we use Ba(Fe{sub 0.9}Co{sub 0.1}){sub 2}As{sub 2} thin films, produced via pulsed laser deposition (PLD). A gold layer was sputtered to form the barrier, while the counter electrode material is the conventional superconductor PbIn with a T{sub c} of 7.2 K. For temperatures below 7.2 K the spectrum shows a subharmonic gap structure (SGS), described by an extended model of Octavio, Tinkham, Blonder and Klapwijk (OTBK), while at higher temperatures the SGS vanishes and an SN-like behaviour can be observed.

Strain induced enhancement of magnetization in Ba{sub 2}FeMoO{sub 6} based heterostructure with (Ba{sub x}Sr{sub 1-x})TiO{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Kim, Kyeong-Won; Norton, David P. [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States); Ghosh, Siddhartha, E-mail: ghoshsid@gmail.com; Buvaev, Sanal; Hebard, Arthur F. [Department of Physics, University of Florida, Gainesville, Florida 32611 (United States)

2016-05-14

High quality epitaxial Ba{sub 2}FeMoO{sub 6} thin films and Ba{sub 2}FeMoO{sub 6}–(Ba{sub x}Sr{sub 1−x})TiO{sub 3} bi-layer (BL) and superlattice (SL) structures were grown via pulsed laser deposition under low oxygen pressure, and their structural, magnetic, and magneto-transport properties were examined. Superlattice and bi-layer structures were confirmed by X-ray diffraction patterns. Low temperature magnetic measurement shows that the saturation magnetization (M{sub S}) is significantly higher for SLs and almost similar or lower for BLs, when compared to phase pure Ba{sub 2}FeMoO{sub 6} thin films. The variation of the coercive field (H{sub C}) follows exact opposite trend, where BL samples have higher H{sub C} and SL samples have lower H{sub C} than pure Ba{sub 2}FeMoO{sub 6} thin films. Also, a significant decrease of the Curie temperature is found in both BL and SL structures compared to pure Ba{sub 2}FeMoO{sub 6} thin films. Negative magneto-resistance is seen in all the BL and SL structures as well as in pure Ba{sub 2}FeMoO{sub 6} thin films. In contrast to the magnetic properties, the magneto-transport properties do not show much variation with induced strain.

Ba(OH)2.8H2O process for the removal and immobilization of carbon-14. Final report

International Nuclear Information System (INIS)

Haag, G.L.; Holladay, D.W.; Pitt, W.W. Jr.; Young, G.C.

1986-01-01

The airborne release of 14 C from various nuclear facilities has been identified as a potential biohazard due to the long half-life of 14 C (5730 years) and the ease with which it may be assimilated into the biosphere. At ORNL, technology has been developed for the removal and immobilization of this radionuclide. Prior studies have indicated that 14 C will likely exist in the oxidized form as CO 2 and will contribute slightly to the bulk CO 2 concentration of the gas stream, which is air-like in nature (approx.300 ppM/sub v/ CO 2 ). The technology that has been developed utilizes the CO 2 -Ba(OH) 2 .8H 2 O gas-solid reaction with the mode of gas-solid contacting being a fixed bed. The product, BaCO 3 , possesses excellent thermal and chemical stability, prerequisites for the long-term disposal of nuclear wastes. For optimal process operation, studies have indicated that an operating window of adequate size does exist. When operating within the window, high CO 2 removal efficiency (effluent concentrations 99%), and an acceptable pressure drop across the bed (3 kPa/m at a superficial velocity of 13 cm/s) are possible. Three areas of experimental investigation are reported: (1) microscale studies on 150-mg samples to provide information concerning surface properties, kinetics, and equilibrium vapor pressures; (2) macroscale studies on large fixed beds (4.2 kg of reactant) to determine the effects of humidity, temperature, and gas flow rate upon bed pressure drop and CO 2 breakthrough; and (3) design, construction, and operation of a pilot unit capable of continuously processing a 34-m 3 /h (20-ft 3 /min) air-based gas stream

Raman study of HgBa 2Ca n-1 Cu nO 2 n+2+ δ ( n=1,2,3,4 and 5) superconductors

Science.gov (United States)

Zhou, Xingjiang; Cardona, M.; Chu, C. W.; Lin, Q. M.; Loureiro, S. M.; Marezio, M.

1996-02-01

Polarized micro-Raman scattering measurements have been performed on the five members of the HgBa 2Ca n-1 Cu nO 2 n+2+ δ ( n=1,2,3,4 and 5) high- Tc superconductor family using different laser frequencies. Local laser annealing measurements were carried out to investigate the variation of the Raman spectra with the excess oxygen content, δ. A systematic evolution of the spectra, which display mainly peaks near 590, 570, 540 and 470 cm -1, with increasing number of CuO 2 layers has been observed; its origin has been shown to lie in the variation of the interstitial oxygen content. In addition to confirming that the 590 cm -1 mode represents vibration of apical oxygens in the absence of neighboring excess oxygen, the 570 cm -1 mode, which may be composed of some finer structures, has been assigned to the vibration of the apical oxygen modified by the presence of the neighboring excess oxygens. The 540 and 470 cm -1 modes may represent the direct vibration of excess oxygens. The implication of possible different distribution sites of excess oxygens is discussed. All other observed lower-frequency modes are also assigned.

Carbon-14 immobilization via the Ba(OH)28H2O process

International Nuclear Information System (INIS)

Haag, G.L.; Nehls, J.W. Jr.; Young, G.C.

1982-01-01

The airborne release of 14 C from various nuclear facilities has been identified as a potential biohazard due to the long half-life of 14 C (5730 yrs) and the ease in which it may be assimilated into the biosphere. At Oak Ridge National Laboratory, technology is under development, as part of the Airborne Waste Management Program, for the removal and immobilization of this radionuclide. Prior studies have indicated that the 14 C will likely exist in the oxidized form as CO 2 and will contribute slightly to the bulk CO 2 concentration of the gas stream, which is airlike in nature (approx. 330 ppMv CO 2 ). The technology under development utilizes the CO 2 - Ba(OH) 2 8H 2 O gas-solid reaction with the mode of gas-solid contacting being a fixed bed. The product, BaCO 3 , possessing excellent thermal and chemical stability, prerequisites for the long-term disposal of nuclear wastes. For optimal process operation, studies have indicated that an operating window of adequate size does exist. When operating within the window, high CO 2 removal efficiency (effluent concentrations 99%), and an acceptable pressure drop across the bed (3 kPa/m at 13 cm/s superficial velocity) are possible. This paper will address three areas of experimental investigation. These areas are (1) micro-scale studies on 150-mg samples to provide information concerning surface properties, kinetics, and equilibrium vapor pressures, (2) macro-scale studies on large fixed beds (4.2 kg reactant) to determine the effects of humidity, temperature, and gas flow-rate upon bed pressure drop and CO 2 breakthrough, and (3) the design, construction, and initial operation of a pilot unit capable of continuously processing a 34 m 3 /h (20 ft 3 /min) air-based gas stream

Structural, electronic and optical characteristics of SrGe{sub 2} and BaGe{sub 2}: A combined experimental and computational study

Energy Technology Data Exchange (ETDEWEB)

Kumar, Mukesh, E-mail: mkgarg79@gmail.com [Environmental Remediation Materials Unit, National Institute for Materials Science, Ibaraki 305-0044 (Japan); Umezawa, Naoto [Environmental Remediation Materials Unit, National Institute for Materials Science, Ibaraki 305-0044 (Japan); Imai, Motoharu [Superconducting Properties Unit, National Institute for Materials Science, Ibaraki 305-0047 (Japan)

2015-05-05

Highlights: • Charge transfer between cation and anion atoms observed first time in digermandies. • Study yields a band gap of ∼1 eV and ∼0.85 eV for SrGe{sub 2} and BaGe{sub 2}, respectively. • Band gap decrease with the application of hydrostatic pressure. • Localized cation d states lead to a large absorption coefficient (>7.5 × 10{sup 4} cm{sup −1}). - Abstract: SrGe{sub 2} and BaGe{sub 2} were characterized for structural, electronic and optical properties by means of diffuse reflectance and first-principles density functional theory. These two germanides crystallize in the BaSi{sub 2}-type structure, in which Ge atoms are arranged in tetrahedral configuration. The calculation indicates a charge transfer from Sr (or Ba) atoms to Ge atoms along with the formation of covalent bonds among Ge atoms in Ge tetrahedral. The computational results confirm that these two germanies are Zintl phase described as Sr{sub 2}Ge{sub 4} (or Ba{sub 2}Ge{sub 4}), which are characterized by positively charged [Sr{sub 2} (or Ba{sub 2})]{sup 2.59+} and negatively charged [Ge{sub 4}]{sup 2.59−} units acting as cation and anion, respectively. These compounds are indirect gap semiconductors with band gap estimated to be E{sub g} = 1.02 eV for BaGe{sub 2} and E{sub g} = 0.89 eV for SrGe{sub 2} which are in good agreement with our experimental measured values (E{sub g} = 0.97 eV for BaGe{sub 2} and E{sub g} = 0.82 eV for SrGe{sub 2}). Our calculations demonstrate that the band gaps are narrowed by application of hydrostatic pressure; the pressure coefficients are estimated to be −10.54 for SrGe{sub 2} and −10.06 meV/GPa for BaGe{sub 2}. Optical properties reveal that these compounds have large absorption coefficient (∼7.5 × 10{sup 4} cm{sup −1} at 1.5 eV) and the estimated high frequency (static) dielectric constant are, ε{sub ∞}(ε{sub 0}) ≈ 12.8(20.97) for BaGe{sub 2} and ε{sub ∞}(ε{sub 0}) ≈ 14.27(22.87) for SrGe{sub 2}.

Determination of the hydrogen positions in the novel barium boroarsenate Ba[B{sub 2}As{sub 2}O{sub 8}(OH){sub 2}] by combined single crystal X-ray and powder neutron investigations

Energy Technology Data Exchange (ETDEWEB)

Lieb, Alexandra [School of Chemistry, University of Southampton (United Kingdom); Fakultaet fuer Verfahrens- und Systemtechnik, Lehrstuhl fuer Technische Chemie, Otto-von-Guericke-Universitaet, Magdeburg (Germany); Weller, Mark T. [School of Chemistry, University of Southampton (United Kingdom); Department of Chemistry, University of Bath (United Kingdom)

2017-11-17

The boroarsenate Ba[B{sub 2}As{sub 2}O{sub 8}(OH){sub 2}] was obtained by the reaction of NH{sub 4}H{sub 2}AsO{sub 4}, B(OH){sub 3} and BaBr{sub 2}.2H{sub 2}O in the melt. Ba[B{sub 2}As{sub 2}O{sub 8}(OH){sub 2}] was obtained as thin colorless needles, together with spherical crystals of BAsO{sub 4} as by-product, grown on a pellet of Ba[BAsO{sub 5}]. The products could be separated mechanically. For neutron scattering experiments a sample was prepared with {sup 11}B(OH){sub 3} as a starting material. The crystal structure of Ba[B{sub 2}As{sub 2}O{sub 8}(OH){sub 2}] was determined by single-crystal X-ray diffraction and exhibits a layer structure with an unprecedented layer topology. The exact positions of the hydrogen atoms were determined using combined single-crystal X-ray and powder neutron diffraction investigations. Ba[B{sub 2}As{sub 2}O{sub 8}(OH){sub 2}] was further characterized by IR spectroscopy and EDX analysis. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Phase formations in the KOH-BaO2-KI(I2)-Bi2O3 system

International Nuclear Information System (INIS)

Klinkova, L.A.; Barkovskij, N.V.; Nikolajchik, V.I.

2004-01-01

Phase composition of electrochemical synthesis products in the system KOH-BaO 2 -KI(I 2 )-Bi 2 O 3 and its influence on superconducting properties of bismuth-containing oxides are studied by the methods of X-ray phase and elementary analyses, electron diffraction in transmission electron microscope and by measuring temperature dependence of magnetic susceptibility. It was been ascertained that in the presence of iodine introduced as KI or I 2 oxoiodides KBi 6 O 9 I and Bi 5 O 7 I are formed in the system above, giving rise to a change in the composition of synthesis products in KOH-BaO 2 -Bi 2 O 3 matrix system towards formation of superconducting oxides K n Ba m Bi m+n O y rich in bismuth, which are characterized by low values of superconducting transition point [ru

Fluorine dynamics in BaF2 superionic conductors investigated by NMR

International Nuclear Information System (INIS)

Gumann, Patryk

2008-01-01

In this work the dynamics of fluorine in solid-state electrolytes having BaF 2 -structure was investigated using three different NMR-methods: field cycling relaxometry, lineshape analysis, and static field gradient NMR. For this purpose a pure BaF 2 crystal, as well as crystals doped with trivalent impurities (LaF 3 ), were studied as a function of temperature. Using MAS NMR it was possible to identify two lines in Ba 0.9 La 0.1 F 2.1 having different chemical shift, and to refer them to the modified crystal structure. On this basis a model for the fluorine lineshape has been developed, taking into account three motional processes characterized by their correlation times. It includes jump diffusion of the fluorine ions among equivalent sites within two crystallographically distinct sublattices, and inter-lattice exchange processes. By measuring frequency and temperature-dependent spin lattice relaxation times, it was possible to gain information about fluorine dynamics on microscopic length scales. An attempt was also made to analyze the data for pure BaF 2 and low admixture concentration samples with a non-exponential correlation function. (orig.)

Analysis of (Ba,Ca,Sr)3MgSi2O8:Eu2+, Mn2+ phosphors for application in solid state lighting

International Nuclear Information System (INIS)

Han, J.K.; Piqutte, A.; Hannah, M.E.; Hirata, G.A.; Talbot, J.B.; Mishra, K.C.; McKittrick, J.

2014-01-01

The luminescence properties of Eu 2+ and Mn 2+ co-activated (Ba,Ca,Sr) 3 MgSi 2 O 8 phosphors prepared by combustion synthesis were studied. Eu 2+ -activated (Ba,Ca,Sr) 3 MgSi 2 O 8 has a broad blue emission band centered at 450–485 nm and Eu 2+ –Mn 2+ -activated (Ba,Ca,Sr) 3 MgSi 2 O 8 exhibits a red emission around 620–703 nm, depending on the relative concentrations of Ba, Ca and Sr. The particle size of Eu 2+ and Mn 2+ co-activated (Ba,Ca) 3 MgSi 2 O 8 ranges from 300 nm to 1 μm depending on the metal ion and are agglomerated due to post-synthesis, high temperature annealing. The green emission of Ba 3 MgSi 2 O 8 originates from secondary phases (Ba 2 SiO 4 and BaMgSiO 4 ) confirmed by emission spectra and X-ray diffraction patterns. The secondary phases of Ba 3 MgSi 2 O 8 are removed by the addition of Sr. The quantum efficiencies range from 45% to 70% under 400 nm excitation and the lifetime of red emission of Ba 3 MgSi 2 O 8 decreases significantly with increasing temperature, which is 54% at 400 K of that at 80 K compared to that of blue emission (90% at 400 K of that at 80 K). -- highlights: • (Ba,Ca,Sr) 3 MgSi 2 O 8 :Eu 2+ , Mn 2+ phosphors were prepared by a combustion synthesis method. • The emission spectra consist of broad blue-emission band and red-emission band. • The quantum efficiencies range between 45% and 70%, depending on the relative concentrations of Ba, Ca and Sr. • The secondary phases were eliminated by additions of Sr. • Lifetime of the red-emission decreases with increasing temperature, suggesting that these phosphors are not useful for solid state lighting applications

Evaluation of GdBaCo{sub 2}O{sub 5+{delta}} as cathode material for doped lanthanum gallate electrolyte IT-SOFCs

Energy Technology Data Exchange (ETDEWEB)

Tarancon, A. [Department of Inorganic Chemistry, University of La Laguna, La Laguna, Tenerife (Spain); EME/XaRMAE/IN, Department of Electronics, University of Barcelona (Spain); Marrero-Lopez, D.; Ruiz-Morales, J.C.; Nunez, P. [Department of Inorganic Chemistry, University of La Laguna, La Laguna, Tenerife (Spain); Pena-Martinez, J.

2008-10-15

The layered perovskite GdBaCo{sub 2}O{sub 5+{delta}} (GBCO), recently proposed for intermediate temperature solid oxide fuel cell applications, was investigated and compared with Ba{sub 0.5}Sr{sub 0.5}Co{sub 0.8}Fe{sub 0.2}O{sub 3-{delta}} (BSCF) cathode material using La{sub 0.9}A{sub 0.1}Ga{sub 0.8}Mg{sub 0.2}O{sub 2.85} (A=Sr,Ba) as electrolytes. Area-specific resistance was measured by impendance spectroscopy in symmetrical cells. The cobaltites were prepared by a modified citrate sol-gel route and tested as cathode materials for doped lanthanum gallate-based cells using dry H{sub 2} as fuel and air as oxidant, rendering power density values of 180 and 240 mW cm {sup -2} at 1,073 K (1 mm thick pellets) for GBCO and BSCF fuel cells, respectively. (Abstract Copyright [2008], Wiley Periodicals, Inc.)

Luminescent properties of BaCl2-Eu microcrystals embedded in a CsI matrix

International Nuclear Information System (INIS)

Pushak, A.; Vistovskyy, V.; Voloshinovskii, A.; Savchyn, P.; Antonyak, O.; Demkiv, T.; Dacyuk, Yu.; Myagkota, S.; Gektin, A.

2013-01-01

The spectral-luminescent properties of CsI-BaCl 2 (1 mol%)-Eu(0.02 mol%) crystalline system are studied. Europium ion doped BaCl 2 microcrystals embedded in a CsI matrix are revealed on CsI-BaCl 2 (1 mol%)-Eu(0.02 mol%) freshly cleaved surface by the scanning electron microscopy. The size of microcrystals is shown to be within 0.5–5 microns. The luminescent parameters of the BaCl 2 -Eu 2+ microcrystals are shown to be similar to ones of a single crystal analogue. The 4f → 5d absorption transitions in europium ions and the reabsorption of the intrinsic emission of the CsI host are the main excitation mechanisms of europium luminescence in the BaCl 2 microcrystals. -- Highlights: ► The formation of chloride BaCl 2 :Eu microcrystals in the case of BaCl 2 doped CsI crystal has been revealed. ► The observed size of microcrystals at BaCl 2 concentration of 1% is about 0.5–5 μm. ► Majority of Eu 2+ ions in CsI-BaCl 2 -EuCl 3 crystalline system enters into BaCl 2 microcrystals. ► The luminescent parameters of the BaCl 2 :Eu 2+ microcrystals and its bulk analogue are similar

Mechanism of a strong rise of Tc due to the calcium doping in Y1-xCaxBa2Cu2.8Zn0.2Oy

International Nuclear Information System (INIS)

Martynova, O.A.; Potapov, D.V.; Gasumyants, V.E.; Vladimirskaya, E.V.

2011-01-01

Highlights: → Calcium is observed to restore superconductivity in Y 1-x Ca x Ba 2 Cu 2.8 Zn 0.2 O y . → Parameters of the band spectrum and charge-carrier system are determined. → The calcium doping is shown to give a noticeable contribution to the DOS function. → The mechanism of calcium effect on T c in doped YBa 2 Cu 3 O y is discussed. - Abstract: The normal-state transport properties and the critical temperature, T c , for three series of Y 1-x Ca x Ba 2 Cu 2.8 Zn 0.2 O y (x = 0-0.2) samples with different oxygen content have been investigated and discussed in comparison with results for other calcium-doped YBa 2 Cu 3 O y . We have observed the calcium doping to restore the superconductivity in the YBa 2 Cu 3 O y system even in case of the preliminary T c suppression by the direct destruction of the CuO 2 planes due to a preliminary doping by zinc. The T c value rises strongly with increasing calcium content and this rise becomes faster for the oxygen-reduced series. Based on a narrow-band model, the parameters of the band spectrum structure and the charge-carrier system in the normal state were determined from the analysis of the thermopower temperature dependences in order to reveal the mechanism of the T c rise under the Ca influence. It is shown that the T c increase in Y 1-x Ca x Ba 2 Cu 2.8 Zn 0.2 O y is related to the direct Ca ions effect. The mechanism of the calcium influence on the T c value is discussed with respect to the Ca-induced conduction band modification. The calcium doping in Y 1-x Ca x Ba 2 Cu 2.8 Zn 0.2 O y is shown to give a noticeable contribution to the density-of-states function leading to a strong rise in its value at the Fermi level that results in a restoration of the superconducting properties.

A Double Layer Sensing Electrode “BaTi(1-XRhxO3/Al-Doped TiO2” for NO2 Detection above 600 °C

Directory of Open Access Journals (Sweden)

Bilge Saruhan

2016-04-01

Full Text Available NO2 emission is mostly related to combustion processes, where gas temperatures exceed far beyond 500 °C. The detection of NO2 in combustion and exhaust gases at elevated temperatures requires sensors with high NO2 selectivity. The thermodynamic equilibrium for NO2/NO ≥ 500 °C lies on the NO side. High temperature stability of TiO2 makes it a promising material for elevated temperature towards CO, H2, and NO2. The doping of TiO2 with Al3+ (Al:TiO2 increases the sensitivity and selectivity of sensors to NO2 and results in a relatively low cross-sensitivity towards CO. The results indicate that NO2 exposure results in a resistance decrease of the sensors with the single Al:TiO2 layers at 600 °C, with a resistance increase at 800 °C. This alteration in the sensor response in the temperature range of 600 °C and 800 °C may be due to the mentioned thermodynamic equilibrium changes between NO and NO2. This work investigates the NO2-sensing behavior of duplex layers consisting of Al:TiO2 and BaTi(1-xRhxO3 catalysts in the temperature range of 600 °C and 900 °C. Al:TiO2 layers were deposited by reactive magnetron sputtering on interdigitated sensor platforms, while a catalytic layer, which was synthesized by wet chemistry in the form of BaTi(1-xRhxO3 powders, were screen-printed as thick layers on the Al:TiO2-layers. The use of Rh-incorporated BaTiO3 perovskite (BaTi(1-xRhxO3 as a catalytic filter stabilizes the sensor response of Al-doped TiO2 layers yielding more reliable sensor signal throughout the temperature range.

Elastic, electronic properties and intra-atomic bonding in orthorhombic and tetragonal polymorphs of BaZn2As2 from first-principles calculations

International Nuclear Information System (INIS)

Shein, I.R.; Ivanovskii, A.L.

2014-01-01

Highlights: • α and β polymorphs of BaZn 2 As 2 as a parent phase of the new DMSs are examined. • Structural, elastic, electronic properties are evaluated from first principles. • Inter-atomic bonding picture is discussed. -- Abstract: Very recently, on the example of hole- and spin-doped BaZn 2 As 2 , quite an unexpected area of potential applications of 122-like phases was proposed as a promising platform for searching the new diluted magnetic semiconductors (DMSs) (2013; K. Zhao, et al, Nature Commun. 4:1442). Herein, by means of the first-principles calculations, we have examined in detail the basic structural, elastic, electronic properties and the peculiarities of the inter-atomic bonding in α and β polymorphs of 122-like BaZn 2 As 2 – a parent phase of the new DMSs. Our characterization of these materials covers the optimized structural parameters, the main elastic parameters (elastic constants, bulk, shear, and Young’s moduli, Poisson’s ratio, anisotropy indexes, and Pugh’s criterion), as well as electronic bands and densities of electronic states

A high performance BaZr0.1Ce0.7Y0.2O3-δ-based solid oxide fuel cell with a cobalt-free Ba0.5Sr0.5FeO3-δ–Ce0.8Sm0.2O2-δ composite cathode

NARCIS (Netherlands)

Sun, Wenping; Shi, Zhen; Fang, S.; Yan, Litao; Zhu, Zhiwen; Liu, Wei

2010-01-01

A cobalt-free Ba0.5Sr0.5FeO3-δ–Ce0.8Sm0.2O2-δ (BSF–SDC) composite is employed as a cathode for an anode-supported proton-conducting solid oxide fuel cells (H-SOFCs) using BaZr0.1Ce0.7Y0.2O3-δ (BZCY) as the electrolyte. The chemical compatibility between BSF and SDC is evaluated. The XRD results show

Observation of a remarkable reduction of correlation effects in BaCr2As2 by ARPES.

Science.gov (United States)

Nayak, Jayita; Filsinger, Kai; Fecher, Gerhard H; Chadov, Stanislav; Minár, Ján; Rienks, Emile D L; Büchner, Bernd; Parkin, Stuart P; Fink, Jörg; Felser, Claudia

2017-11-21

The superconducting phase in iron-based high-[Formula: see text] superconductors (FeSC), as in other unconventional superconductors such as the cuprates, neighbors a magnetically ordered one in the phase diagram. This proximity hints at the importance of electron correlation effects in these materials, and Hund's exchange interaction has been suggested to be the dominant correlation effect in FeSCs because of their multiband nature. By this reasoning, correlation should be strongest for materials closest to a half-filled [Formula: see text] electron shell (Mn compounds, hole-doped FeSCs) and decrease for systems with both higher (electron-doped FeSCs) and lower (Cr-pnictides) [Formula: see text] counts. Here we address the strength of correlation effects in nonsuperconducting antiferromagnetic BaCr 2 As 2 by means of angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. This combination provides us with two handles on the strength of correlation: First, a comparison of the experimental and calculated effective masses yields the correlation-induced mass renormalization. In addition, the lifetime broadening of the experimentally observed dispersions provides another measure of the correlation strength. Both approaches reveal a reduction of electron correlation in BaCr 2 As 2 with respect to systems with a [Formula: see text] count closer to five. Our results thereby support the theoretical predictions that Hund's exchange interaction is important in these materials.

Investigation of the spin-1 honeycomb antiferromagnet BaNi2V2O8 with easy-plane anisotropy

Science.gov (United States)

Klyushina, E. S.; Lake, B.; Islam, A. T. M. N.; Park, J. T.; Schneidewind, A.; Guidi, T.; Goremychkin, E. A.; Klemke, B.; Mânsson, M.

2017-12-01

The magnetic properties of the two-dimensional, S =1 honeycomb antiferromagnet BaNi2V2O8 have been comprehensively studied using dc susceptibility measurements and inelastic neutron scattering techniques. The magnetic excitation spectrum is found to be dispersionless within experimental resolution between the honeycomb layers, while it disperses strongly within the honeycomb plane where it consists of two gapped spin-wave modes. The magnetic excitations are compared to linear spin-wave theory allowing the Hamiltonian to be determined. The first- and second-neighbor magnetic exchange interactions are antiferromagnetic and lie within the ranges 10.90 meV ≤Jn≤13.35 meV and 0.85 meV ≤Jn n≤1.65 meV, respectively. The interplane coupling Jout is four orders of magnitude weaker than the intraplane interactions, confirming the highly two-dimensional magnetic behavior of this compound. The sizes of the energy gaps are used to extract the magnetic anisotropies and reveal substantial easy-plane anisotropy and a very weak in-plane easy-axis anisotropy. Together these results reveal that BaNi2V2O8 is a candidate compound for the investigation of vortex excitations and Berezinsky-Kosterliz-Thouless phenomenon.

Tc dependence on the number of CuO2 planes in multilayered Ba2Can-1CunO2n(O, F)2 superconductors

International Nuclear Information System (INIS)

Iyo, A; Tanaka, Y; Kodama, Y; Kito, H; Tokiwa, K; Watanabe, T

2006-01-01

Multilayered cuprates of Ba 2 Ca n-1 Cu n O 2n (O, F) 2 (F-02(n-1)n) with n = 5 - 9 have been synthesized by using high pressure synthesis method in order to investigate the variation of T c . The temperature dependence of susceptibility showed that the T c (about 80 K) does not depend on n for n 5 - 9. This result can be explained using the carrier imbalance model in multilayered cuprates. Charge reservoir layers supply most of the carriers to adjacent CuO 2 planes (OP) and the OP keeps the T c constant even for large n

Effect of mixing RE elements (Nd, Sm, Gd, Eu, Y, Yb) on the RE2BaCuO5/Nd4-2xBa2+2xCu2-xO10-2x phases in RE cuprate high-Tc superconductors

International Nuclear Information System (INIS)

Langhorn, J.B.; Black, M.A.; McGinn, P.J.

1999-01-01

The phases RE 2 BaCuO 5 /RE 4 Ba 2 Cu 2 O 10 phases (where RE is a mixture of Nd, Sm, Gd, Eu, Y and Yb) have been synthesized in an oxygen atmosphere and subsequently characterized. The mixing of RE elements which inherently form the RE 2 BaCuO 5 phase through the peritectic decomposition of REBa 2 Cu 3 O 7-x (RE123) (i.e. Sm, Gd, Eu, Y, Yb), was observed to give homogeneous mixing of the elements in the 211 phase. In contrast it was found that on mixing Nd with other RE elements a mixture of the Nd 4-2x Ba 2+2x Cu 2-x O 10-2x (Nd422) and RE 2 BaCuO 5 (RE211) phases resulted. It was also observed that on mixing Nd with other REs a finite amount of the RE is substituted into the Nd422 phase and Nd into the RE211. (author)

Precipitation method for barium metaborate (BaB2O4) synthesis from borax solution

International Nuclear Information System (INIS)

Akşener, Eymen; Figen, Aysel Kantürk; Pişkin, Sabriye

2013-01-01

In this study, barium metaborate (BaB 2 O 4 , BMB) synthesis from the borax solution was carried out. BMB currently is used in production of ceramic glazes, luminophors, oxide cathodes as well as additives to pigments for aqueous emulsion paints and also β−BaB 2 O 4 single crystals are the best candidate for fabrication of solid-state UV lasers operating at a wavelength of 200 nm due to excellent nonlinear optical properties. In the present study, synthesis was carried out from the borax solution (Na 2 B 4 O 7⋅ 10H 2 O, BDH) and barium chloride (BaCI 2⋅ 2H 2 O, Ba) in the glass-batch reactor with stirring. The effect of, times (5-15 min), molar ratio [stoich.ration (1.0:2.0), 1.25:2.0, 1.5:2.0, 2.5:2:0, 3.0:2.0, 3.5:2.0,4.0:2.0, 5.0:2.0] and also crystallization time (2-6 hour) on the BMB yield (%) was investigated at 80 °C reaction temperature. It is found that, BMB precipitation synthesis with 90 % yield can be performed from 0.50 molar ration (BDH:Ba), under 80 °C, 15 minute, and 6 hours crystallization time. The structural properties of BMB powders were characterized by using XRD, FT-IR and DTA-TG instrumental analysis technique

Precipitation method for barium metaborate (BaB2O4) synthesis from borax solution

Science.gov (United States)

Akşener, Eymen; Figen, Aysel Kantürk; Pişkin, Sabriye

2013-12-01

In this study, barium metaborate (BaB2O4, BMB) synthesis from the borax solution was carried out. BMB currently is used in production of ceramic glazes, luminophors, oxide cathodes as well as additives to pigments for aqueous emulsion paints and also β-BaB2O4 single crystals are the best candidate for fabrication of solid-state UV lasers operating at a wavelength of 200 nm due to excellent nonlinear optical properties. In the present study, synthesis was carried out from the borax solution (Na2B4O7ṡ10H2O, BDH) and barium chloride (BaCI2ṡ2H2O, Ba) in the glass-batch reactor with stirring. The effect of, times (5-15 min), molar ratio [stoich.ration (1.0:2.0), 1.25:2.0, 1.5:2.0, 2.5:2:0, 3.0:2.0, 3.5:2.0,4.0:2.0, 5.0:2.0] and also crystallization time (2-6 hour) on the BMB yield (%) was investigated at 80 °C reaction temperature. It is found that, BMB precipitation synthesis with 90 % yield can be performed from 0.50 molar ration (BDH:Ba), under 80 °C, 15 minute, and 6 hours crystallization time. The structural properties of BMB powders were characterized by using XRD, FT-IR and DTA-TG instrumental analysis technique.

17 CFR 249.1100 - Form MSD, application for registration as a municipal securities dealer pursuant to rule 15Ba2-1...

Science.gov (United States)

2010-04-01

... 17 Commodity and Securities Exchanges 3 2010-04-01 2010-04-01 false Form MSD, application for registration as a municipal securities dealer pursuant to rule 15Ba2-1 under the Securities Exchange Act of 1934 or amendment to such application. 249.1100 Section 249.1100 Commodity and Securities Exchanges SECURITIES AND EXCHANGE COMMISSION (CONTINUED...

High transport current superconductivity in powder-in-tube Ba0.6K0.4Fe2As2 tapes at 27 T

Science.gov (United States)

Huang, He; Yao, Chao; Dong, Chiheng; Zhang, Xianping; Wang, Dongliang; Cheng, Zhe; Li, Jianqi; Awaji, Satoshi; Wen, Haihu; Ma, Yanwei

2018-01-01

The high upper critical field and low anisotropy of iron-based superconductors (IBS) make them particularly attractive for high-field applications, especially for the construction of next-generation nuclear magnetic resonance spectrometers, particle accelerators and high-field magnets. However, for practical use it is essential to make IBS materials into wire and tape conductors with sufficient current carrying capability, which is limited by misaligned grains inside the conductors. Here, based on a simple and low-cost powder-in-tube (PIT) method, we demonstrate a high transport critical current density (J c) reaching 1.5 × 105 A cm-2 (I c = 437 A) at 4.2 K and 10 T in Ba0.6K0.4Fe2As2 (Ba-122) tapes by texturing the grain orientation with optimized hot-press technique. The transport J c measured at 4.2 K under high magnetic fields of 27 T is still on the level of 5.5 × 104 A cm-2. Moreover, at 20 K and 5 T the transport J c is also as high as 5.4 × 104 A cm-2, showing a promising application potential in moderate temperature range which can be reached by liquid hydrogen or cryogenic cooling. All these J c values are the highest ever reported for IBS wires and tapes. The high-performance PIT Ba-122 tapes in this work suggest IBS to be a strong potential competitor of cuprate superconductors for the race of high-field applications in the future.

Ba/ZrO2 nanoparticles as efficient heterogeneous base catalyst for ...

Indian Academy of Sciences (India)

activity of the Ba/ZrO2 catalyst was evaluated for synthesis of β-nitro alcohols and ... for base catalyzed reactions.10–17 The Ca2+ ions sub- .... by gold sputtering for three minutes. ..... Jain S R, Adiga K C and Verneker V R 1981 Combust.

Synthesis and optical properties of turquoise- and green-colored brownmillerite- type Ba2In2-x-yMnxAlyO5+x codoped with manganese and aluminum

Institute of Scientific and Technical Information of China (English)

Peng Jiang; Wen-hui Yang; Yun-cheng Zhou; Jian-lei Kuang; Yong Li; Ting Xiao

2016-01-01

Brownmillerite-type oxides Ba2In2−x−yMnxAlyO5+x (0≤x≤ 0.6, 0≤y≤ 0.5) were prepared at 1300°C through solid-state reaction. X-ray diffraction (XRD) analysis showed that the structure symmetry evolved from orthorhombic to cubic with increasing Mn and Al con-tents. Wheny was greater than 0.3, peaks associated with small amounts of BaAl2O4 and Ba2InAlO5 impurities were observed in the XRD patterns. When substituted with a small amount of Mn (x≤ 0.3), the Ba2In2−x−yMnxAlyO5+x samples exhibited an intense turquoise color. The color changed to green and dark-green with increasing Mn concentration. UV–vis absorbance spectra revealed that the color changed only slightly upon Al doping. The valence state of Mn ions in Ba2In2−x−yMnxAlyO5+x was confirmed to be +5 on the basis of X-ray photoelectron spectroscopic analysis. According to this analysis, the intense turquoise color of the Ba2In2−x−yMnxAlyO5+x samples is rooted in the existence of Mn5+; thus, the introduction of Al does not affect the optical properties of the compounds.

Dependence of optical properties on the composition of (Ba{sub 1−x−y}Sr{sub x}Eu{sub y})Si{sub 2}O{sub 2}N{sub 2} phosphors for white light emitting diodes

Energy Technology Data Exchange (ETDEWEB)

Zhang, Mei, E-mail: zmjenny@163.com; He, Xin; Luo, Jianyi; Zeng, Qingguang

2014-10-15

BaSi{sub 2}O{sub 2}N{sub 2}: Eu{sup 2+} is an efficient phosphor because of its high quantum yield and quenching temperature. Partial substitution of Ba{sup 2+} by Sr{sup 2+} is the most promising approach to tune the color of phosphors. In this study, a series of (Ba{sub 1−x−y}Sr{sub x}Eu{sub y})Si{sub 2}O{sub 2}N{sub 2} (x = 0.0–0.97, y = 0.00–0.10) phosphors are synthesized via high-temperature solid-state reactions. Intense green to yellow phosphors can be obtained by the partial substitution of the host lattice cation Ba{sup 2+} by either Sr{sup 2+} or Eu{sup 2+}. The luminescent properties and the relationships among the lowest 5d absorption bands, Stokes shifts, centroid shifts, and the splitting of Eu{sup 2+} are studied systematically. Then, based on (Ba{sub 1−x−y}Sr{sub x}Eu{sub y})Si{sub 2}O{sub 2}N{sub 2} phosphors and near-ultraviolet (∼395 nm)/blue (460 nm) InGaN chips, intense green–yellow light emitting diodes (LEDs) and white LEDs are fabricated. (Ba{sub 0.37}Sr{sub 0.60})Si{sub 2}O{sub 2}N{sub 2}: 0.03Eu{sup 2+} phosphors present the highest efficiency, and the luminous efficiency of white LEDs can reach 17 lm/w. These results indicate that (Ba{sub 1−x−y}Sr{sub x}Eu{sub y})Si{sub 2}O{sub 2}N{sub 2} phosphors are promising candidates for solid-state lighting. - Highlights: • The optical properties of Eu{sup 2+} in the (Ba, Sr)Si{sub 2}O{sub 2}N{sub 2} solid-solutions are studied systematically. • The relationship among the lowest 5d absorption bands, Stocks shifts etc.of Eu{sup 2+} are also studied. • The electroluminescent properties of pc-LEDs are studied in details.

From Ba3Ta5O14N to LaBa2Ta5O13N2: Decreasing the optical band gap of a photocatalyst

International Nuclear Information System (INIS)

Anke, B.; Bredow, T.; Pilarski, M.; Wark, M.; Lerch, M.

2017-01-01

Yellow LaBa 2 Ta 5 O 13 N 2 was successfully synthesized as phase-pure material crystallizing isostructurally to previously reported Ba 3 Ta 5 O 14 N and mixed-valence Ba 3 Ta V 4 Ta IV O 15 . The electronic structure of LaBa 2 Ta 5 O 13 N 2 was studied theoretically with the range-separated hybrid method HSE06. The most stable structure was obtained when lanthanum was placed on 2a and nitrogen on 4h sites confirming Pauling's second rule. By incorporating nitrogen, the measured band gap decreases from ∼3.8 eV for the oxide via 2.74 eV for Ba 3 Ta 5 O 14 N to 2.63 eV for the new oxide nitride, giving rise to an absorption band well in the visible-light region. Calculated fundamental band gaps confirm the experimental trend. The atom-projected density of states has large contributions from N2p orbitals close to the valence band edge. These are responsible for the observed band gap reduction. Photocatalytic hydrogen formation was investigated and compared with that of Ba 3 Ta 5 O 14 N revealing significantly higher activity for LaBa 2 Ta 5 O 13 N 2 under UV-light. - Graphical abstract: X-ray powder diffraction pattern of LaBa 2 Ta 5 O 13 N 2 with the results of the Rietveld refinements. Inset: Unit cell of LaBa 2 Ta 5 O 13 N 2 and polyhedral representation of the crystal structure. - Highlights: • Synthesis of a new oxide nitride LaBa 2 Ta 5 O 13 N 2 . • Refinement of the crystal structure. • Quantum chemical calculations provided band gap close to the measured value. • New phase shows a higher photocatalytic H 2 evolution rate compared to prior tested Ba 3 Ta 5 O 14 N.

Study of critical current density from ac susceptibility measurements in (La1-xYx)2Ba2CaCu5O2 superconductors

International Nuclear Information System (INIS)

Nayak, P.K.; Ravi, S. . sravi@iitg.ernet.in

2008-01-01

We have prepared a series of compounds (La 1-x Y x ) 2 Ba 2 CaCu 5 O 2 for x = 0 to 0.5 by adding a CaCuO 2 layer to the parent compound La 2 Ba 2 Cu 4 O 2 and by doping Y in place of La. These materials are also prepared by adding 5 wt% of Ag to enhance the intergranular coupling and critical current density. X-ray diffraction measurements show that all the samples are essentially in single phase form and the patterns could be refined using P4/mmm space group in tetragonal cell. The typical lattice parameters are found to be a = b 3.856 A, c = 11.576 A for x = 0.5 sample. Temperature variations of dc electrical resistivity measured on the above samples show that they exhibit superconductivity with T c ranging from 60 to 75 K. Temperature and ac field amplitude variation of ac susceptibility have been measured on the above samples. The field variation of ac susceptibility data has been analyzed by using Bean critical state model. Using both temperature and field variations of ac susceptibility data, the material dependent parameters, such as critical current density as a function of temperature and effective volume fraction grains have been estimated. The Ag doped samples show relatively large critical current density compared to pure samples due to improved intergranular coupling. (author)

Luminescence of BaCl2:Eu2+ particles dispersed in the NaCl host excited by synchrotron radiation

International Nuclear Information System (INIS)

Pushak, A.S.; Savchyn, P.V.; Vistovskyy, V.V.; Demkiv, T.M.; Dacyuk, J.R.; Myagkota, S.V.; Voloshinovskii, A.S.

2013-01-01

BaCl 2 :Eu 2+ microcrystals embedded in the NaCl host have been obtained in the NaCl–BaCl 2 (1 mol%)–EuCl 3 (0.02 mol%) crystalline system. The influence of the annealing conditions on the formation of such particles has been studied. In particular, long-term annealing (at 200 °S during 100 h) promotes the microcrystals formation in the NaCl–BaCl 2 –Eu crystalline system. The subsequent heat treatment (annealed at 600 °S during 72 h and quenched to room temperature) is shown to lead to the destruction of the majority of these particles. The luminescent-kinetic properties of BaCl 2 :Eu 2+ microcrystals have been studied upon the ultra-violet excitation by the synchrotron radiation. The X-ray excited luminescence has been measured in order to estimate the distribution of europium ions between microcrystals and the NaCl host. The excitation mechanisms of Eu 2+ ions in the NaCl–BaCl 2 –Eu crystalline system are discussed. - Highlights: ► The formation of BaCl 2 :Eu 2+ microcrystals of 1–100 μm size embedded in the NaCl host is revealed. ► Annealing at 600 °C leads to the destruction of significant number of embedded microcrystals. ► The luminescent parameters of microcrystals is similar to ones of single crystal analogs.

Study on the equilibrium in the MBr2-CH3OH-H2O system (M = Sr2+, Ba2+) at 25 0C

International Nuclear Information System (INIS)

Zlateva, I.; Stoev, M.

1985-01-01

The dehydration processes in the three-component system MBr 2 -CH 3 OH-H 2 O (M = Sr 2+ , Ba 2+ ) have been studied at 25 0 C by physio-chemical analyses. Crystallization fields for the lower crystal hydrates SrBr 2 x H 2 O and BaBr 2 x H 2 O have been found. The solubility curves exhibit complex-formation processes. The dehydration and solvation processes in three-component system such as MBr 2 -CH 3 OH-H 2 O at 25 0 C with M = Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ have been discussed in general terms. (author)

Progress toward measuring the 6S1/2 5D3/2 magnetic-dipole transition moment in Ba+

Science.gov (United States)

Williams, Spencer; Jayakumar, Anupriya; Hoffman, Matthew; Blinov, Boris; Fortson, Norval

2015-05-01

We report the latest results from our effort to measure the magnetic-dipole transition moment (M1) between the 6S1 / 2 and 5D3 / 2 manifolds in Ba+. We describe a new technique for calibrating view-port birefringence and how we will use it to enhance the M1 signal. To access the transition moment we use a variation of a previously proposed technique that allows us to isolate the magnetic-dipole coupling from the much larger electric-quadrupole coupling in the transition rates between particular Zeeman sub-levels. Knowledge of M1 is crucial for a parity-nonconservation experiment in the ion where M1 will be a leading source of systematic errors. No measurement of this M1 has been made in Ba+, however, there are three calculations that predict it to be 80 ×10-5μB, 22 ×10-5μB, and 17 ×10-5μB. A precise measurement may help resolve this theoretical discrepancy which originates from their different estimations of many-body effects. Supported by NSF Grant No. 09-06494F.

Ordered perovskites with cationic vacancies. 11. System Ba/sub 2/Gd/sub 2/3/vacant/sub 1/3/U/sub 1-x/W/sub x/O/sub 6/

Energy Technology Data Exchange (ETDEWEB)

Wischert, W; Oelkrug, D; Schittenhelm, H J; Kemmler-Sack, S [Tuebingen Univ. (Germany, F.R.). Lehrstuhl fuer Anorganische Chemie 2

1982-12-01

The cation deficient polymorphic perovskites Ba/sub 2/Gd/sub 2/3/vacant/sub 1/3/UO/sub 6/ and Ba/sub 2/Gd/sub 2/3/vacant/sub 1/3/WO/sub 6/ form a continuous series of mixed crystals, which crystallize over a wide range (x = 0.1 up to 0.99) in a cubic 1:1 ordered perovskite lattice. According to the investigations of the vibrational spectra, the diffuse reflectance spectra, and the photoluminescence - opposite to isostructural perovskites wihout vacancies - different species of UO/sub 6/ and WO/sub 6/ octahedra are present. Numerous differences in properties - e.g. an orange emission colour in comparison with a green one by absence of vacancies - are based upon that.

Synthesis, crystal structure, optical, and electronic study of the new ternary thorium selenide Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2}

Energy Technology Data Exchange (ETDEWEB)

Prakash, Jai [Department of Chemistry, Northwestern University, Evanston, IL 60208-3113 (United States); Mesbah, Adel [Department of Chemistry, Northwestern University, Evanston, IL 60208-3113 (United States); ICSM, UMR 5257 CEA/CNRS/UM2/ENSCM, Site de Marcoule-Bât. 426, BP 17171, 30207 Bagnols-sur-Cèze cedex (France); Beard, Jessica [Department of Chemistry, Northwestern University, Evanston, IL 60208-3113 (United States); Lebègue, Sébastien [Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2, UMR CNRS 7036), Institut Jean Barriol, Université de Lorraine, BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-lès-Nancy (France); Malliakas, Christos D. [Department of Chemistry, Northwestern University, Evanston, IL 60208-3113 (United States); Ibers, James A., E-mail: ibers@chem.northwestern.edu [Department of Chemistry, Northwestern University, Evanston, IL 60208-3113 (United States)

2015-11-15

The compound Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} has been synthesized by solid-state methods at 1173 K. Its crystal structure features one-dimensional chains of {sup 1}{sub ∞}[Th(Se){sub 3}(Se{sub 2}){sub 2}{sup 6−}] separated by Ba{sup 2+} cations. Each Th atom in these chains is coordinated to two Se–Se single-bonded pairs and four Se atoms to give rise to a pseudooctahedral geometry around Th. The Th–Se distances are consistent with Th{sup 4+} and hence charge balance of Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} is achieved as 3×Ba{sup 2+}, 1×Th{sup 4+}, 3×Se{sup 2−}, and 2×Se{sub 2}{sup 2−}. From optical measurements the band gap of Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} is 1.96(2) eV. DFT calculations indicate that the compound is a semiconductor. - Graphical abstract: Local coordination environment of Th atoms in the Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} structure. - Highlights: • Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} has been synthesized by solid-state methods at 1173 K. • The structure features chains of {sup 1}{sub ∞}[Th(Se){sub 3}(Se{sub 2}){sub 2}{sup 6−}] separated by Ba{sup 2+} cations. • Ba{sub 3}ThSe{sub 3}(Se{sub 2}){sub 2} is a semiconductor with a band gap of 1.96(2) eV.

Improved the lithium storage capability of BaLi2Ti6O14 by electroless silver coating

International Nuclear Information System (INIS)

Lin, Xiaoting; Wang, Pengfei; Li, Peng; Yu, Haoxiang; Qian, Shangshu; Shui, Miao; Wang, Dongjie; Long, Nengbing; Shu, Jie

2015-01-01

Highlights: • BaLi 2 Ti 6 O 14 /Ag is fabricated via a facile electroless deposition. • Highly dispersed Ag nanoparticles are successively coated on BaLi 2 Ti 6 O 14 . • BaLi 2 Ti 6 O 14 /Ag is used as anode material for lithium storage. • BaLi 2 Ti 6 O 14 /Ag exhibits improved lithium storage capability. - Abstract: To form BaLi 2 Ti 6 O 14 /Ag, highly dispersed Ag nanoparticles are successfully deposited on the surface of BaLi 2 Ti 6 O 14 by a simple chemical deposition method. The morphology, quantity and size of Ag nanoparticles in BaLi 2 Ti 6 O 14 /Ag composites are significantly influenced by the Ag coating contents. Electrochemical results show that Ag nanoparticles play a positive role in reducing redox polarization and improving electrical conductivity of BaLi 2 Ti 6 O 14 during lithiation/delithiation processes. Among all the as-obtained products, 6 wt.% Ag coated BaLi 2 Ti 6 O 14 shows the highest initial charge specific capacity of 160 mAh g −1 at the current density of 100 mA g −1 (1C), which is much higher than the 149.1 mAh g −1 for bare BaLi 2 Ti 6 O 14 . After 100 charge/discharge cycles, the reversible capacity can be maintained at 117.0 mAh g −1 . Moreover, this sample also shows excellent rate performance with high reversible charge capacities of 147.5, 139.7, 132.6, and 126.7 mAh g −1 at the rates of 2C, 3C, 4C and 5C, respectively. Compared with bare BaLi 2 Ti 6 O 14 , the superior electrochemical performance indicates that BaLi 2 Ti 6 O 14 /Ag can be a good anode material in lithium ion batteries.

Redetermination of clinobarylite, BaBe2Si2O7

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Adrien J. Di Domizio

2012-10-01

Full Text Available Clinobarylite, ideally BaBe2Si2O7 (chemical name barium diberyllium disilicate, is a sorosilicate mineral and dimorphic with barylite. It belongs to a group of compounds characterized by the general formula BaM2+2Si2O7, with M2+ = Be, Mg, Fe, Mn, Zn, Co, or Cu, among which the Be-, Fe-, and Cu-members have been found in nature. The crystal structure of clinobarylite has been re-examined in this study based on single-crystal X-ray diffraction data collected from a natural sample from the type locality (Khibiny Massif, Kola Peninsula, Russia. The structure of clinobarylite can be considered as a framework of BeO4 and SiO4 tetrahedra, with one of the O atoms coordinated to two Be and one Si, one coordinated to two Si, and two O atoms coordinated to one Si and one Be atom. The BeO4 tetrahedra share corners, forming chains parallel to the c axis, which are interlinked by the Si2O7 units oriented parallel to the a axis. The Ba2+ cations (site symmetry m.. are in the framework channels and are coordinated by eleven O atoms in form of an irregular polyhedron. The Si—Obr (bridging O atom, at site symmetry m.. bond length, the Si—Onbr (non-bridging O atoms bond lengths, and the Si—O—Si angle within the Si2O7 unit are in marked contrast to the corresponding values determined in the previous study [Krivovichev et al. (2004. N. Jb. Miner. Mh. pp. 373–384].

Observation of superconductivity in BaNb2S5

Science.gov (United States)

Smith, M. G.; Neumeier, J. J.

2018-06-01

Bulk superconductivity is reported in BaNb2S5 at the transition temperature Tc = 0.85(1) K. The electrical resistivity ρ versus T is metallic with ρ(2 K) = 42.4 μΩ cm. The magnetic susceptibility is paramagnetic, with temperature-independent contributions due to diamagnetism, Pauli paramagnetism, and Van Vleck paramagnetism; a Curie-Weiss contribution appears to be impurity related. Hall effect measurements show that the majority charge carriers are electrons with charge-carrier concentration n(3 K) = 2.40(2) × 1021 cm-3. Specific heat measurements reveal an electronic specific heat coefficient γ = 11.2(1) mJ/mol K2, a Debye temperature ΘD = 126.4(8) K, and an energy gap associated with the superconducting state of Eg = 0.184(4) meV. Measurements of ρ(T) in magnetic field provide the upper critical magnetic field of about 3055(74) Oe as T → 0 K, which was used to estimate the coherence length ξ = 6.21(15) nm. The results allow classification of BaNb2S5 as a Type II, BCS superconductor in the dirty limit.

Studies on compensating valency substituted BaTi (Mnx/2Nbx/2O3 ...

Indian Academy of Sciences (India)

Studies on compensating valency substituted BaTi(1-)Mn/2Nb/2O3 ceramics ... Annealing is observed to improve quality factor `' of the materials with a ... material engineering efforts are required to improve the material properties.

High-pressure BaCrO_3 polytypes and the 5H–BaCrO_2_._8 phase

International Nuclear Information System (INIS)

Arévalo-López, Angel M.; Paul Attfield, J.

2015-01-01

Polytypism of BaCrO_3 perovskites has been investigated at 900–1100 °C and pressures up to 22 GPa. Hexagonal 5H, 4H, and 6H perovskites are observed with increasing pressure, and the cubic 3C perovskite (a=3.99503(1) Å) is observed in bulk form for the first time at 19–22 GPa. An oxygen-deficient material with limiting composition 5H–BaCrO_2_._8 is synthesised at 1200 °C under ambient pressure. This contains double tetrahedral Cr"4"+ layers and orders antiferromagnetically below 260 K with a (0 0 1/2) magnetic structure. - Graphical abstract: Hexagonal 5H, 4H, and 6H perovskites polytypes of BaCrO_3 are observed with increasing pressure and the cubic 3C perovskite is stabilised in bulk form for the first time at 19–22 GPa. Oxygen-deficient 5H–BaCrO_2_._8 synthesised at ambient pressure contains double tetrahedral Cr"4"+ layers and orders antiferromagnetically below 260 K with a (0 0 1/2) magnetic structure.

The isotypic family of the diarsenates MM'As{sub 2}O{sub 7} (M = Sr, Ba; M' = Cd, Hg)

Energy Technology Data Exchange (ETDEWEB)

Weil, Matthias [Technische Univ. Wien (Austria). Inst. for Chemical Technologies and Analytics

2016-08-01

The diarsenates MM'As{sub 2}O{sub 7} (M = Sr, Ba; M' = Cd, Hg) were prepared under hydrothermal conditions (∝200 C, autogenous pressure), starting from As{sub 2}O{sub 5} and the corresponding metal oxides or precursor compounds thereof in aqueous solutions. Structure analyses on the basis of single crystal X-ray data revealed the four structures to be isotypic. They are the first diarsenates to crystallize in the triclinic BaZnP{sub 2}O{sub 7} structure type (space group P anti 1, Z = 2, a ∼ 5.8 Aa, b ∼ 7.3 Aa, c ∼ 7.6 Aa, α ∼ 101 , β ∼ 91 , γ ∼ 98 ). All related MM'As{sub 2}O{sub 7} diarsenates reported so far (M = Sr, Ba, Pb; M' = Mg, Co, Cu, Zn) crystallize in the monoclinic α-Ca{sub 2}P{sub 2}O{sub 7} structure type (P2{sub 1}/n, Z = 4). Hence, the size of the divalent M' cation determines which of the two structure types is adopted.

Superconducting Tl2Ba2CaCu2O8 thin films prepared by post-annealing in a flow-through multiple-zone furnace

International Nuclear Information System (INIS)

Pluym, T.C.; Muenchausen, R.E.; Arendt, P.N.

1994-01-01

Tl 2 Ba 2 CaCu 2 O 8 thin films were prepared for the first time by use of a multiple-zone flow-through thallination process. Thallous oxide was volatilized from condensed thallium oxide in a low temperature source zone and convectively transported to a higher temperature thallination zone in which initially amorphous Ba 2 CaCu 2 O 5 precursor films were located. By careful control of the source temperature, film temperature, flow rate, anneal time, and rates of heat up and cool down, smooth Tl 2 Ba 2 CaCu 2 O 8 thin films were prepared on (100) LaAlO 3 with the following properties: inductive T c of 107.6 K and 80% transition width of 1.3 K, transport J c at 75 K of 1.3 x 10 5 A/cm 2 , and R s at 10 GHz and 80 K of 1.3 mΩ. The scalability of the process to large area film processing was demonstrated by the preparation of Tl 2 Ba 2 CaCu 2 O 8 thin films on LaAlO 3 three-inch diameter wafers

Fluorine dynamics in BaF{sub 2} superionic conductors investigated by NMR

Energy Technology Data Exchange (ETDEWEB)

Gumann, Patryk

2008-07-01

In this work the dynamics of fluorine in solid-state electrolytes having BaF{sub 2}-structure was investigated using three different NMR-methods: field cycling relaxometry, lineshape analysis, and static field gradient NMR. For this purpose a pure BaF{sub 2} crystal, as well as crystals doped with trivalent impurities (LaF{sub 3}), were studied as a function of temperature. Using MAS NMR it was possible to identify two lines in Ba{sub 0.9}La{sub 0.1}F{sub 2.1} having different chemical shift, and to refer them to the modified crystal structure. On this basis a model for the fluorine lineshape has been developed, taking into account three motional processes characterized by their correlation times. It includes jump diffusion of the fluorine ions among equivalent sites within two crystallographically distinct sublattices, and inter-lattice exchange processes. By measuring frequency and temperature-dependent spin lattice relaxation times, it was possible to gain information about fluorine dynamics on microscopic length scales. An attempt was also made to analyze the data for pure BaF{sub 2} and low admixture concentration samples with a non-exponential correlation function. (orig.)

Structure of the new Tl(Ba sub 1.0 Sr sub 1.0) PrCu sub 2 O sub 7-x by Rietveld analysis

International Nuclear Information System (INIS)

Yang, P.; Fun, H. K.; Lee, T.J.; Ku, H.C.; Lai, C.C.

1994-01-01

The crystalline structure of Tl(Ba sub 1.0 Sr sub 1.0)PrCu sub 2 O sub 7-x was obtained at room temperature from x-ray powder diffraction with CuK sub α radiation using Rietveld analysis. Tl(Ba sub 1.0 Sr sub 1.0)PrCu sub 2 O sub 7-x isomorphous at both room temperature (300 K) and low temperature (100 K) with TlBa sub 2 ca Cu sub 2 O sub 7-x type (1212) structure, crystallized with space group P4/mmm and one formula in the unit cell. At 300 K, cell parameters a=3.8892(2) A, c=12.3099(6) A, the structure was refined with 25 parameters to R sub WP = 6.30%, R sub P = 4.38% for 3551 step intensities and R sub b = 5.01%, R sub f = 4.20% for 156 reflections. The goodness of fitting S=3.18. At 100K, cell parameters a=3.8866(4) A, c= 12.289(1) A, the structure was refined with 26 parameters to R sub WP = 8.42%, R sub P = 6.21% for 2676 step intensities and R sub b = 6.72%, R sub f = 5.28% for 120 reflections. The goodness of fitting S=2.32. Reasonable anisotropic thermal parameters were obtained. The compositions of Ba and Sr atoms were refined to about Ba sub 1.1 Sr sub 0.9 compared with the stoichiometric Ba sub 1.0 Sr sub 1.0

Alkaline earth lead and tin compounds Ae2Pb, Ae2Sn, Ae = Ca, Sr, Ba, as thermoelectric materials

Science.gov (United States)

Parker, David; Singh, David J

2013-01-01

We present a detailed theoretical study of three alkaline earth compounds Ca2Pb, Sr2Pb and Ba2Pb, which have undergone little previous study, calculating electronic band structures and Boltzmann transport and bulk moduli using density functional theory. We also study the corresponding tin compounds Ca2Sn, Sr2Sn and Ba2Sn. We find that these are all narrow band gap semiconductors with an electronic structure favorable for thermoelectric performance, with substantial thermopowers for the lead compounds at temperature ranges from 300 to 800 K. For the lead compounds, we further find very low calculated bulk moduli—roughly half of the values for the lead chalcogenides, suggestive of soft phonons and hence low lattice thermal conductivity. All these facts indicate that these materials merit experimental investigation as potential high performance thermoelectrics. We find good potential for thermoelectric performance in the environmentally friendly stannide materials, particularly at high temperature. PMID:27877610

Alkaline earth lead and tin compounds Ae2Pb, Ae2Sn, Ae = Ca, Sr, Ba, as thermoelectric materials

Directory of Open Access Journals (Sweden)

David Parker and David J Singh

2013-01-01

Full Text Available We present a detailed theoretical study of three alkaline earth compounds Ca2Pb, Sr2Pb and Ba2Pb, which have undergone little previous study, calculating electronic band structures and Boltzmann transport and bulk moduli using density functional theory. We also study the corresponding tin compounds Ca2Sn, Sr2Sn and Ba2Sn. We find that these are all narrow band gap semiconductors with an electronic structure favorable for thermoelectric performance, with substantial thermopowers for the lead compounds at temperature ranges from 300 to 800 K. For the lead compounds, we further find very low calculated bulk moduli—roughly half of the values for the lead chalcogenides, suggestive of soft phonons and hence low lattice thermal conductivity. All these facts indicate that these materials merit experimental investigation as potential high performance thermoelectrics. We find good potential for thermoelectric performance in the environmentally friendly stannide materials, particularly at high temperature.

Longitudinal Spin Excitations and Magnetic Anisotropy in Antiferromagnetically Ordered BaFe_{2}As_{2}

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Chong Wang

2013-12-01

Full Text Available We report on a spin-polarized inelastic neutron-scattering study of spin waves in the antiferromagnetically ordered state of BaFe_{2}As_{2}. Three distinct excitation components are identified, with spins fluctuating along the c axis, perpendicular to the ordering direction in the ab plane and parallel to the ordering direction. While the first two “transverse” components can be described by a linear spin-wave theory with magnetic anisotropy and interlayer coupling, the third “longitudinal” component is generically incompatible with the local-moment picture. It points toward a contribution of itinerant electrons to the magnetism that is already in the parent compound of this family of Fe-based superconductors.

Investigations of the solid solution in the system SrI2-BaI2 at ambient pressures and at 2.0 GPa

International Nuclear Information System (INIS)

Beck, H.P.; Holley, C.; Limmer, A.

1984-01-01

The P,T,x-diagram of the system SrI 2 -BaI 2 has been investigated at ambient pressures and at 2.0 GPa. The amount of solid solution in the four structure types occuring in this system (SrI 2 - or PbCl 2 -ZrAs 2 -type with SrI 2 and PbCl 2 - or anti-Fe 2 P-type with BaI 2 ) differs considerably. Structural geometries belonging to the same PbCl 2 structure family show marked differences in their toleration to cation substitution. Solid solution is especially pronounced in the BaI 2 -rich phases which incorporate up to 60 mol-% Sr 2+ in the high pressure phase of BaI 2 . (author)

Ba2+ Doped CH3NH3PbI3 to Tune the Energy State and Improve the Performance of Perovskite Solar Cells

International Nuclear Information System (INIS)

Zhang, Hanbing; Shang, Ming-hui; Zheng, Xiaoying; Zeng, Zhaobing; Chen, Renjie; Zhang, Ying; Zhang, Jing; Zhu, Yuejin

2017-01-01

Highlights: •Ba doping enlarges the energy band gap of MAPb 1-x Ba x I 3 . •Voc and Jsc are enhanced in perovskite solar cells. •DFT calculation proves the experiment results. -- Abstract: Elements substitution and doping in perovskite CH 3 NH 3 PbI 3 exhibit versatile tunability of energy band structure and opto-electric properties. Ba 2+ is chosen to substitute Pb 2+ for its similar valence state and ionic radius with Pb 2+ . Ba 2+ doping in perovskite (mol% <5) slightly enlarges the optic energy gap by conduction band minimum(CBM) upshifting to vacuum energy level, which is due to the smaller electronegativity of Ba than Pb. The enlarged band gap is also verified by density function theory calculations. In n-i-p structure perovskite solar cells (PSCs), because of the higher CBM of doped perovskite, the Fermi energy difference between n and p side is enlarged and the electron injection from the perovskite to TiO 2 is improved. Thus, both the photovoltage and photocurrent are improved by small amount Ba 2+ doping, resulting optimized 17.4% efficiency under AM1.5. This work reveals the relationship between the doping element property and the energy band structure of the perovskite, and highlights the doping method to improve the performance of PSCs.

Optical Properties of the Fresnoite Ba2TiSi2O8 Single Crystal

Directory of Open Access Journals (Sweden)

Chuanying Shen

2017-02-01

Full Text Available In this work, using large-sized single crystals of high optical quality, the optical properties of Ba2TiSi2O8 were systematically investigated, including transmission spectra, refractive indices and nonlinear absorption properties. The crystal exhibits a high transmittance (>84% over a wide wavelength range from 340 to 2500 nm. The refractive indices in the range from 0.31256 to 1.01398 μm were measured, and Sellmeier’s equations were fitted by the least squares method. The nonlinear absorption properties were studied by using the open-aperture Z-scan technique, with a nonlinear absorption coefficient measured to be on the order of 0.257 cm/GW at the peak power density of 16.4 GW/cm2. Such high transmittance and wide transparency indicate that optical devices using the Ba2TiSi2O8crystal can be applied over a wide wavelength range. Furthermore, the small nonlinear absorption observed in Ba2TiSi2O8 will effectively increase the optical conversion efficiency, decreasing the generation of laser damage of the optical device.

Effect of BaSi2 template growth duration on the generation of defects and performance of p-BaSi2/n-Si heterojunction solar cells

Science.gov (United States)

Yachi, Suguru; Takabe, Ryota; Deng, Tianguo; Toko, Kaoru; Suemasu, Takashi

2018-04-01

We investigated the effect of BaSi2 template growth duration (t RDE = 0-20 min) on the defect generation and performance of p-BaSi2/n-Si heterojunction solar cells. The p-BaSi2 layer grown by molecular beam epitaxy (MBE) was 15 nm thick with a hole concentration of 2 × 1018 cm-3. The conversion efficiency η increased for films grown at long t RDE, owing to improvements of the open-circuit voltage (V OC) and fill factor (FF), reaching a maximum of η = 8.9% at t RDE = 7.5 min. However, η decreased at longer and shorter t RDE owing to lower V OC and FF. Using deep-level transient spectroscopy, we detected a hole trap level 190 meV above the valence band maximum for the sample grown without the template (t RDE = 0 min). An electron trap level 106 meV below the conduction band minimum was detected for a sample grown with t RDE = 20 min. The trap densities for both films were (1-2) × 1013 cm-3. The former originated from the diffusion of Ba into the n-Si region; the latter originated from defects in the template layer. The crystalline qualities of the template and MBE-grown layers were discussed. The root-mean-square surface roughness of the template reached a minimum of 0.51 nm at t RDE = 7.5 min. The a-axis orientation of p-BaSi2 thin films degraded as t RDE exceeded 10 min. In terms of p-BaSi2 crystalline quality and solar cell performance, the optimum t RDE was determined to be 7.5 min, corresponding to approximately 4 nm in thickness.

Structural and luminescence properties of Ca{sub x}Ba{sub 1−x}Ga{sub 2}S{sub 4}:Eu{sup 2+} chalcogenide semiconductor solid solutions

Energy Technology Data Exchange (ETDEWEB)

Tagiyev, B.G. [Institute of Physics of Azerbaijan National Academy of Sciences, 131 H.Javid ave., Baku Az-1143 (Azerbaijan); Tagiyev, O.B. [Institute of Physics of Azerbaijan National Academy of Sciences, 131 H.Javid ave., Baku Az-1143 (Azerbaijan); Baku Branch of M.V. Lomonosov Moscow State University, Baku AZ-1143 (Azerbaijan); Mammadov, A.I. [Institute of Physics of Azerbaijan National Academy of Sciences, 131 H.Javid ave., Baku Az-1143 (Azerbaijan); Quang, Vu Xuan [Institute of Research and Development, Duy Tan University, 550000 Da Nang (Viet Nam); Naghiyev, T.G., E-mail: tural@nagiyev.net [Institute of Physics of Azerbaijan National Academy of Sciences, 131 H.Javid ave., Baku Az-1143 (Azerbaijan); Jabarov, S.H. [Institute of Physics of Azerbaijan National Academy of Sciences, 131 H.Javid ave., Baku Az-1143 (Azerbaijan); Bayerisches Geoinstitute, University Bayreuth, d-95440 Bayreuth (Germany); Leonenya, M.S.; Yablonskii, G.P. [Institute of Physics of National Academy Sciences of Belarus, 220072 Minsk (Belarus); Dang, N.T. [Institute of Research and Development, Duy Tan University, 550000 Da Nang (Viet Nam)

2015-12-01

The structural and luminescence properties of chalcogenide semiconductor Ca{sub x}Ba{sub 1−x}Ga{sub 2}S{sub 4} solid solutions (x=0.1–0.9) doped with 7 at% of Eu{sup 2+} ions were studied at room temperature. It was found, that the crystal structure of Ca{sub x}Ba{sub 1−x}Ga{sub 2}S{sub 4} solid solutions varies with the amount of Ca{sup 2+} cations and phase transition from cubic to orthorhombic takes place with increase of x value. Ca{sub x}Ba{sub 1−x}Ga{sub 2}S{sub 4}:Eu{sup 2+} solid solutions exhibit intense photoluminescence in cyan to yellow spectral region depending on x due to 5d→4f electron–dipole transitions in Eu{sup 2+} ions. The peak position of the emission band shifts from 506 nm for x=0.1 to 555 nm for x=0.9 and the full width at half maximum of the emission band varies from 62 nm to 72 nm depending on the symmetry of the crystal lattice. The PL excitation spectrum of Ca{sub x}Ba{sub 1−x}Ga{sub 2}S{sub 4}:Eu{sup 2+} covers the range at half maximum from 310 nm to 480 nm for x=0.1 and to 520 nm for x=0.9. It was shown that long-wavelength shift is caused by influence of the growing crystal field strength on Eu{sup 2+} ions.

Persistence of slow fluctuations in the overdoped regime of Ba(Fe_1-xRh_x)₂As₂ superconductors

Energy Technology Data Exchange (ETDEWEB)

Bossoni, L. [Univ. of Pavia (Italy); Leiden Univ. (Netherlands); Moroni, M. [Univ. of Pavia (Italy); Julien, M. H. [Leiden Univ. (Netherlands); Canfield, Paul C. [Ames Lab. and Iowa State Univ., Ames, IA (United States); Mayaffre, H. [Leiden Univ. (Netherlands); Reyes, A. [National High Magnetic Field Lab., Tallahassee, FL (United States); Halperin, W. P. [Northwestern Univ., Evanston, IL (United States); Carretta, P. [Univ. of Pavia (Italy)

2016-04-15

We present nuclear magnetic resonance evidence that very slow (1 MHz) spin fluctuations persist into the overdoped regime of Ba(Fe_1-xRh_x)₂As₂ superconductors. Measurements of the ⁷⁵As spin echo decay rate, obtained both with Hahn Echo and Carr Purcell Meiboom Gill pulse sequences, show that the slowing down of spin uctuations can be described by short-range diffusive dynamics, likely involving domain walls motions separating (π/a, 0) from (0, π/a) correlated regions. This slowing down of the fluctuations is weakly sensitive to the external magnetic field and, although fading away with doping, it extends deeply into the overdoped regime.

Optical properties of BaO added bioactive Na2O-CaO-P2O5 glasses

Science.gov (United States)

Edathazhe, Akhila B.; Shashikala, H. D.

2018-04-01

This paper deals with the effect of BaO addition on the optical properties of bioactive Na2O-CaO-P2O5 glasses for biomedical optics applications. The phosphate glasses with composition (26-x)Na2O-xBaO-29CaO-45P2O5 (x = 0, 5, 10, 15 mol%) have been prepared by melt-quenching technique at 1100°C. The refractive index of glasses increased with BaO content. The optical band gap and Urbach energy of synthesized glasses were derived from the optical absorption spectra by using UV-Visible spectrometer. The addition of 5 mol% of BaO increased the band gap energy of glasses due to the formation of ionic cross-links in the glass structure. The defect and interstitial bonds formation in theglasses decreased with BaO additions as indicated by reductions in the Urbach energy values. No such variations in the band gap and Urbach energy values of glasses were observed with BaO content from 5 to 15 mol%. The molar and oxide ion polarizability values were calculated from the band gap and molar volume of glasses. The increase in the calculated optical basicity and metallization criteria of glasses supported the rise in band gap energy values with BaO additions. As the melting temperature of glasses decreased from 1200 to 1100°C, the refractive index increased as supported by the measured density values. The band gap energy is not changed with melting temperature. The Urbach energy decreased with decrease in melting temperature in case of BaO-free Na2O-CaO-P2O5 glasses, whereas it increased in case of BaO added glasses due to the role of BaO as modifying oxide.

Anisotropy and dimensional characteristics in CVD route Y1Ba2Cu3O7-δ

International Nuclear Information System (INIS)

Watanabe, K.; Kobayashi, N.; Awaji, S.; Yamane, H.; Hirai, T.; Muto, Y.

1993-01-01

The anisotropic behaviors of the upper critical field B c2 and the critical current density J c were investigated in Y 1 Ba 2 Cu 3 O 7-δ films prepared by a chemical vapor deposition (CVD) route. The angular dependence of J c at fixed temperature, the field dependence of J c at fixed angle, and the temperature dependence of J c at fixed field were measured. The obtained results were explored in terms of the dimensional superconducting characteristics. The important information on the anisotropic behaviors of J c in CVD-Y 1 Ba 2 Cu 3 O 7-δ was discussed from a viewpoint of the flux pinning. (orig.)

Direct observation of in-plane anisotropy of the superconducting critical current density in Ba (Fe1-xCox) 2As2 crystals

Science.gov (United States)

Hecher, J.; Ishida, S.; Song, D.; Ogino, H.; Iyo, A.; Eisaki, H.; Nakajima, M.; Kagerbauer, D.; Eisterer, M.

2018-01-01

The phase diagram of iron-based superconductors exhibits structural transitions, electronic nematicity, and magnetic ordering, which are often accompanied by an electronic in-plane anisotropy and a sharp maximum of the superconducting critical current density (Jc) near the phase boundary of the tetragonal and the antiferromagnetic-orthorhombic phase. We utilized scanning Hall-probe microscopy to visualize the Jc of twinned and detwinned Ba (Fe1-xCox) 2As2 (x =5 %-8 % ) crystals to compare the electronic normal state properties with superconducting properties. We find that the electronic in-plane anisotropy continues into the superconducting state. The observed correlation between the electronic and the Jc anisotropy agrees qualitatively with basic models, however, the Jc anisotropy is larger than predicted from the resistivity data. Furthermore, our measurements show that the maximum of Jc at the phase boundary does not vanish when the crystals are detwinned. This shows that twin boundaries are not responsible for the large Jc, suggesting an exotic pinning mechanism.

FT-IR and thermoluminescence investigation of P2O5-BaO-K2O glass system

Science.gov (United States)

Ivascu, C.; Timar-Gabor, A.; Cozar, O.

2013-11-01

The 0.5P2O5ṡxBaOṡ(0.5-x)K2O glass system (0≤x≤0.5mol%) is investigated by FT-IR and thermoluminescence as a possible dosimetic material. FT-IR spectra show structural network modifications with the composition variations of the studied glasses. The predominant absorption bands are characterized by two broad peaks near 500 cm-1, two weak peaks around 740 cm-1 and three peaks in the 900-1270 cm-1 region. The shift in the position of the band assigned to asymmetric stretching of PO2- group, υas(PO2-) modes from ˜1100 cm-1 to 1085 cm-1 and the decrease in its relative intensity with the increasing of K2O content shows a network modifier role of this oxide.. Luminescence investigations show that by adding modifier oxides in the phosphate glass a dose dependent TL signals result upon irradiation. Thus P2O5-BaO-K2O glass system is a possible candidate material for dosimetry in the dose 0 - 50 Gy range.

YBa2Cu3O7-δ/NdBa2(Cu1-xNix)3O7-δ double layers by liquid-phase epitaxial growth

International Nuclear Information System (INIS)

Yao, X.; Izumi, Toru; Hobara, Natsuro; Nakamura, Yuichi; Izumi, Teruo; Shiohara, Yuh

2001-01-01

Our present investigation has answered questions pertaining to the REBa 2 Cu 3 O 7-δ (RE123, RE=rare-earth elements)-coated conductor application when NdBa 2 (Cu 1-x Ni x ) 3 O 7-δ (Ni-NdBCO) solid solution is used as a buffer layer by the liquid-phase epitaxy(LPE) process. The NiO/Ni substrate has no substantial reaction in the Ni-saturated Nd-Ba-Cu-O liquid. There is no essential Ni interdiffusion between YBa 2 Cu 3 O 7-δ (YBCO) and Ni-NdBCO LPE thick films as evident from T c values of 90 K obtained from multilayer YBCO/Ni-NdBCO samples. (author)

Investigation of the effect of Zn impurities and magnetic field on the spin dynamics in underdoped YBa2(Cu1-yZny)3Ox

International Nuclear Information System (INIS)

Suchaneck, Anton

2009-01-01

This work employs neutron scattering to examine the changes in the spin excitation spectrum of the underdoped high-temperature superconductor YBa 2 Cu 3 O x which is doped with zinc or subject to a strong magnetic field. Doping levels of x=6.6 and x=6.45 are used with an optional zinc substitution of 2% zinc per copper atom. A detwinning procedure is an important factor in order to reorient all twinning domains of the orthorhombic crystal cell in the same direction. Numerous single crystals were oriented and assembled to create a sample of total mass 2 g neccessary for neutron scattering experiments. The experiments were performed on triple axis neutron scattering spectrometers to measure spin excitations around the antiferromagnetic wave vector at energies up to 50 meV. Zinc substitution and magnetic field influence the spin excitations, which in the pure compound feature the resonance mode, a spin gap and an hour-glass dispersion. Upon zinc substitution the spectrum of YBa 2 (Cu 0.98 Zn 0.02 ) 3 O 6.6 is quantitatively unchanged around the resonance energy, however its marked temperature onset disappears. At lower energies new induced quasi-static excitations emerge. Similar finding have been observed in other cuprate compounds. The induced excitation exhibit a strong anisotropy in the copper planes. All these results are compared to other experimental techniques which provide comparable experimental evidence. Another compounds examined in this work is the more strongly oxygen underdoped YBa 2 (Cu 0.98 Zn 0.02 ) 3 O 6.45 . The common bilayer related signal remains unchanged with zinc substitution, however a new inter-plane correlated signal is induced indicating ordering between copper planes. A comparison with other experimental techniques indicated that the superconducting critical temperature is the sole determining factor of the qualitative spin excitation spectrum, no matter what factor are responsible for it. Additional examinations have been devoted to the

Terahertz conductivity measurement of FeSe0.5Te0.5 and Co-doped BaFe2As2 thin films

International Nuclear Information System (INIS)

Nakamura, D.; Akiike, T.; Takahashi, H.; Nabeshima, F.; Imai, Y.; Maeda, A.; Katase, T.; Hiramatsu, H.; Hosono, H.; Komiya, S.; Tsukada, I.

2011-01-01

We investigated the THz conductivity of FeSe 0.5 Te 0.5 and Ba (Fe 2-x Co x )As 2 thin films. We estimated the superconducting gap energy values. We found anomolous conductivity spectrum in the antiferromagnetic phase. The terahertz (THz) conductivity of FeSe 0.5 Te 0.5 ('11'-type) and Co-doped BaFe 2 As 2 ('122'-type) thin films are investigated. For '11'-type, the frequency dependence of the complex conductivity can be understood as that of BCS-type superconductor near the superconducting gap energy, and we estimated the superconducting gap energy to be 0.6 meV. For '122'-type, we estimated the superconducting gap energy to be 2.8 meV, which is considered to be the superconducting gap opened at the electron-type Fermi surface near the M point.

A{sub 2}Zn{sub 3}As{sub 2}O{sub 2}(A = Ba, Sr): a rare example of square planar zinc

Energy Technology Data Exchange (ETDEWEB)

Keane, P.M. [Chicago Univ., IL (United States). Dept. of Chemistry][Argonne National Lab., IL (United States); Burdett, J.K. [Chicago Univ., IL (United States). Dept. of Chemistry

1994-06-01

Purpose of this study was to explore synthesis of novel solid-state compounds that could potentially exhibit interesting or useful physical properties. Goal was to extend the classes of compounds A{sub 2}Mn{sub 3}Pn{sub 2}O{sub 2} (A=Sr,Ba; Pn=P,As,Sb,Bi) to include a transition metal other than Mn. High-temperature fluxes were used to produce these new compounds.

On Ba2Ge2Te5, a new telluridogermanate(III) with chain structure

International Nuclear Information System (INIS)

Brinkmann, C.; Eisenmann, B.; Schaefer, H.

1984-01-01

The new compound Ba 2 Ge 2 Te 5 crystallizes in the orthorhombic system (space group: Pna2 1 (No. 33)). The lattice constants are given. In the structure distorted Ge 2 Te 6 -trigonal prisms are connected by common corners to infinite chains. (author)

Glassy and Metastable Crystalline BaTi2O5 by Containerless Processing

Science.gov (United States)

Yoda, Shinichi; Kentei Yu, Yu; Kumar, Vijaya; Kameko, Masashi

Many efforts have been devoted to forming bulk glass from the melt of ferroelectric crystalline materials without adding any network-forming oxides such as SiO2 due to the potential for producing transparent glass ceramics with high dielectric constant and enhanced piezoelectric, pyroelectric and electro-optic use. The containerless processing is an attractive synthesis tech-nique as it can prevent melt contamination, minimize heterogeneous nucleation, and allow melt to achieve deep undercooling for forming metastable and glassy materials. We have fabricated a new ferroelectric materiel BaTi2 O5 [1] as bulk glass from melt by us-ing containerless processing and studied the phase relationship between microstructure and ferroelectric properties of BaTi2 O5 [2]. The structures of glassy and metastable crystalline BaTi2 O5 fabricated by the containerless pro-cessing were comprehensively investigated by combined X-ray and neutron diffractions, XANES analyses and computer simulations [3]. The 3-dimensional atomic structure of glassy BaTi2 O5 (g-BaTi2 O5 ), simulated by Reverse Monte Carlo (RMC) modelling on diffraction data, shows that extremely distorted TiO5 polyhedra interconnected with both corner-and edge-shared oxy-gen, formed a higher packing density structure than that of conventional silicate glass linked with only corner-sharing of SiO4 polyhedra. In addition, XANES measurement reveales that five-coordinated TiO5 polyhedra were formable in the crystallized metastable a-and b-BaTi2 O5 phases. The structure of metastable b-BaTi2 O5 was solved by ab initio calculation, and refined by Rietveld refinement as group Pnma with unit lattices a = 10.23784 ˚, b = 3.92715 ˚, c A A = 10.92757 A ˚. Our results show that the glass-forming ability enhanced by containerless pro-cessing, not by `strong glass former', fabricated new bulk oxide glasses with peculiar structures and properties. The intermediate-range structure of g-BaTi2 O5 and the crystalline structure of

Controlled Confinement of Half-metallic 2D Electron Gas in BaTiO3/Ba2FeReO6/BaTiO3 Heterostructures: A First-principles Study

Science.gov (United States)

Saha-Dasgupta, Tanusri; Baidya, Santu; Waghmare, Umesh; Paramekanti, Arun

Using density functional theory calculations, we establish that the half-metallicity of bulk Ba2FeReO6 survives down i to 1 nm thickness in BaTiO3/Ba2FeReO6/BaTiO3 heterostructures grown along the (001) and (111) directions. The confinement of the two-dimensional (2D) electron gas in this quantum well structure arises from the suppressed hybridization between Re/Fe d states and unoccupied Ti d states, and it is further strengthened by polar fields for the (111) direction. This mechanism, distinct from the polar catastrophe, leads to an order of magnitude stronger confinement of the 2D electron gas than that at the LaAlO3/SrTiO3 interface. We further show low-energy bands of (111) heterostructure display nontrivial topological character. Our work opens up the possibility of realizing ultra-thin spintronic devices. Journal Ref: Phys. Rev. B 92, 161106(R) (2015) S.B. and T.S.D thank Department of Science and Technology, India for the support through Thematic Unit of Excellence. AP was supported by NSERC (Canada).

Characterization of BaBi2Ta2O9 prepared through amorphous precursor

International Nuclear Information System (INIS)

Maczka, M.; Kepinski, L.; Hermanowicz, K.; Dacko, S.; Czapla, Z.; Hanuza, J.

2011-01-01

Research highlights: → Formation of Bi-layered BaBi 2 Ta 2 O 9 proceeds via an intermediate fluorite phase. → Mechanochemical activation lowers the synthesis temperature by 150-200 deg. C. → The lateral size of the synthesized plate-like crystallites is about 100-200 nm. → Properties of the synthesized crystallites are different from the bulk material. - Abstract: Formation of ferroelectric BaBi 2 Ta 2 O 9 by annealing of an amorphous precursor prepared by high energy milling in ball mill has been studied by X-ray, scanning electron microscopy (SEM), Raman, infrared spectroscopy (IR), diffuse reflectivity and dielectric measurements. Our results show that formation of Bi-layered BaBi 2 Ta 2 O 9 proceeds via an intermediate fluorite phase. Mechanochemical activation allows obtaining BaBi 2 Ta 2 O 9 at short time and much lower temperatures than those required in a conventional solid state reaction. The lateral size of the plate-like crystallites is about 100-200 nm and properties of the synthesized particles are different compared to the bulk material.

Hexagonal perovskites with cationic vacancies. 7. Vibrational spectroscopic investigations on the rhombohedral 12 L-stacking polytypes Ba/sub 4/Bsup(II)(Re/sub 2/vacantO/sub 12/) and Ba/sub 4/Bsub(2/3)sup(III)vacantsub(1/3)(Re/sub 2/vacantO/sub 12/)

Energy Technology Data Exchange (ETDEWEB)

Fadini, A; Kemmler-Sack, S; Schittenhelm, H J; Rother, H J; Treiber, U [Tuebingen Univ. (Germany, F.R.). Lehrstuhl fuer Anorganische Chemie 2

1979-07-01

For the rhombohedral 12 L stacking polytypes Ba/sub 4/Bsup(II)(Re/sub 2/vacantO/sub 12/) and Ba/sub 4/Bsub(2/3)sup(III)vacantsub(1/3)(Re/sub 2/vacantO/sub 12/), space group R3m, sequence (3)(1), the lattice consists of groups of three face sharing octahedra with the composition Re/sub 2/vacantO/sub 12/. They are isolated from each other by the Ba and B ions. The vibrational spectra are interpreted according to the factor group analysis. For the Re/sub 2/vacantO/sub 12/ unit (symmetry Dsub(3d) the results of a complete vibrational analysis and the calculation of the force constants are reported.

Smooth surfaces in very thin GdBa2Cu3O7−δ films for application in superconducting tunnel junctions

International Nuclear Information System (INIS)

Navarro, H.; Sirena, M.; Kim, Jeehoon; Haberkorn, N.

2015-01-01

Highlights: • A detailed study of the morphological properties of GdBa 2 Cu 3 O 7−δ thin films was realized. • The inclusion of a very thin SrTiO 3 buffer layer modifies the surface of the SrTiO 3 substrates. • The inclusion of the buffer layer suppress the three dimensional nucleation in the GdBa 2 Cu 3 O 7−δ film. • GdBa 2 Cu 3 O 7−δ films with large areas free of topological defects and T c close to liquid nitrogen can be obtained. - Abstract: This paper provides a systematic analysis of the morphology and the superconducting critical temperature obtained in very thin GdBa 2 Cu 3 O 7−δ films grown on (0 0 1) SrTiO 3 substrates by DC sputtering. We find that the use of a very thin SrTiO 3 buffer layer (≈2 nm) modify the nucleation of GdBa 2 Cu 3 O 7−δ on the surface of the substrate reducing the formation of 3 dimensional clusters. Our results demonstrate that 16 nm thick GdBa 2 Cu 3 O 7−δ films with an average root-mean-square (RMS) smaller than 1 nm and large surface areas (up 10 μm 2 ) free of 3 dimensional topological defects can be obtained. In films thinner than 24 nm the onset (zero resistance) of superconducting transition of the films is reduced, being close to liquid nitrogen. This fact can be associated with stress reducing the orthorhombicity and slightly drop in oxygen stoichiometry