[en] The physical characteristic and properties of Gd₂Te₃ are presented: M(sub r) = 697.30, orthorhombic, Pnma, a = 12.009(9), b = 4.3012 (6), c = 11.818(2) A, V = 610.4(6) A(sup 3), Z = 4, D sub x = 7.57 gm/cubic cm, MoK(sub alpha), lambda = 0.71069 A, mu = 357/cm, F(000) = 1136, room temperature, R = 0.033,822 observed reflections. The redetermination confirms that Gd₂Te₃ is isostructural with Sb2S3 (stibnite). The reported solid solution series Gd₂Te₃-Gd₃Te₄ does not exist. Gd-Te bond lengths vary from 3.104(1) to 3.240(3) A and Gd is in seven fold co-ordination. Gd₂Te₃ has a power factor S(sup 2)/rho = -.000006V(sup 2 degrees)/C(sup 2)/omega/cm at 1000 C. It is not suitable as a high temperature thermoelectric material because it decomposes to GdTe which is metallic

[en] Platy crystals from the products of a mixture 4 Bas:2 Nb:5 S reacted at 1000⁰C have cell constants a = 13.754(3) angstrom, c = 83.73(2) angstrom, R3m. The reciprocal lattice had a pronounced subcell with dimensions a = 6.877(1) angstrom, c = 41.84(1) angstrom, same space group. Three dimensional X-ray diffraction data were collected using monochromatized MoKα radiation and of 5051 measured intensities 1892 were considered observed. From the set of observed intensities 611 reflections having all even indices were used to refine the crystal structure of the 42 x 7-angstrom subcell. The subcell content based on the ordered structure only is Ba₁₂Nb₉S₃₆. The placement of disordered Ba and S at Z=0, 1/3, and 2/3 levels of the subcell leads to the unlikely composition Ba/sub 16.5/Nb₉S₄₂. The ordered structure most likely has a composition Ba₄Nb₂S₉, Z=36, so that the subcell composition should be Ba₁₈Nb₉S/sub 40.5/. The completely ordered structure has not been solved

[en] The crystal structure of two compounds having the generic formula Ln_4-xA_4+xCo_2+yAl_2-yO₁₅ has been determined. The structure consists of clusters formed by a Co-oxygen octahedron that shares three corners of a triangular face with three separate Co/Al-oxygen tetrahedra leading to a cluster formula [Co^VI(Co/Al)₃^IV]O₁₅. The tetrahedral interstice is randomly occupied by Co³⁺ and Al³⁺ ions. The octahedral interstice is occupied by Co whose valence is 2+ in compound I and 3+ in II. Two such clusters exist in the unit cell and they are joined by rare earth-alkaline earth cations in 6-fold (octahedral), 8-fold (bisdisphenoid), 10-fold (capped trigonal prism), and 12-fold (cubic close packed) coordination to the oxygen ions. The octahedral cation positions are randomly occupied by about equal amounts of Nd-Ba and Y-Sr, respectively. Phase I forms with Pr and Gd but not with La, Y, or Er, restricting its formation to lanthanide ionic radii between 1.14 and 1.06 angstrom

[en] Aluminium calcium cobalt praseodymium oxide, (Ca_0.821(4)Pr_0.179)₂{Co[Co_0.651(16)Al_0.349]}O₅, M_r = 303.0, orthorhombic, Pnma, a = 5.2789(5), b = 14.998(2), c = 5.4868(5) A, V = 434.41(14) A³, Z = 4, D_x = 4.63 g cm^-3, λ(Mo Kα) = 0.71069 A, μ = 102.5 cm^-1, F(000) = 572.4, room temperature, R = 0x0484, wR = 0.0461 for 398 reflections >4σ(F_o). The Co³⁺ occupies the octahedral site, while Co²⁺ and Al³⁺ occupy the tetrahedral site. The octahedron is elongated nearly parallel to the b axis, Co1-O2 2.190(6) A and the equatorial bond lengths to O1 are 1.870(10) and 1.957(10) A respectively. The tetrahedron around Co/Al is severely distorted. The octahedral layers are linded by the tetrahedra as found in brownmillerite. The eight oxygen ions coordinated to Ca²⁺/Pr⁴⁺ form an irregular polyhedron, with Ca/Pr-O bond lengths varying from 2.337(9) to 2.818(10) A. To stabilize the brownmillerite structure in the Ca-Co-O system both Pr and Al are necessary. Single phase material for (Ca_1-xPr_x)₂(Co_1-yAl_y)₂O₅ can be synthesized at 1400 K for 0.15 < x < 0.2 and 0.15 < y < 0.25. The phase decomposes at 1473 K. (orig.)

[en] It is evident that the promise of the new high temperature ceramic superconductors will not be realized without an intense materials science and engineering effort focused on converting these oxide powders into useful bulk forms. The general limitations of the conventional press and sinter ceramic processing approach are likely to be amplified by the sensitivity of the superconductivity transitions of YBa₂Cu₃O/sub 7-x/ to oxygen content. The crystal structure of the superconducting phase has been determined from Rietveld refinement of powder neutron diffraction data and the tetragonal crystal structure of YBa₂Cu₃O₆ has been determined from single crystal x-ray diffraction data. The two structures are illustrated and the respective calculated x-ray powder diffraction patterns are shown. The extent of the orthorhombic and tetragonal phase fields are reported as a function of the oxygen composition

[en] Diyttrium dibarium copper platinum oxide, M_r=839.11, orthorhombic, Pnma, a=13.191(2), b=5.680(1), c=10.301(2) A, V=771.9(3) A³, Z=4, D_x=7.227 g cm^-3, λ(Mo Kα)=0.71069 A, μ=460.42 cm^-1, F(000)=1444, T=298 K, R=0.05, wR=0.053 for 1026 unique reflections, F₀≥5σ(F₀). Y and Ba have sevenfold oxygen coordination. Y-O bond lengths vary from 2.22(1)-2.40(2) A. Ba-O bond distances vary from 2.60(1) to 2.92(1) A. The coordination about Pt is octahedral while that of Cu is square pyramidal. The average Pt-O distance is 2.04(1) A. The apical Cu-O distance is 2.12(1) A, and the average basal Cu-O distance is 1.99(1) A. The various polyhedra share edges and corners to create a three-dimensional framework. (orig.)

[en] Gd₂Te₃, M_r=697.30, orthorhombic, Pnma, a=12.009(9), b=4.3012(6), c=11.818(2) A, V=610.4(6) A³, Z=4, D_m=7.384, D_x=7.59 g cm^-3, Mo Kα, λ=0.71069 A, μ=357 cm^-1, F(000)=1136, room temperature, R=0.033, 822 observed reflections. The redetermination confirms that Gd₂Te₃ is isostructural with Sb₂S₃ (stibnite). The reported solid-solution series Gd₂Te₃-Gd₃Te₄ does not exist. Gd-Te bound lengths vary from 3.104(1) to 3.240(3) A and Gd is in sevenfold coordination. Gd₂Te₃ has a power factor S²/ρ=0.6x10^-6V ²K^-2Ω^-1 cm^-1 at 1273 K. It is not suitable as a high-temperature thermoelectric material because it decomposes to GdTe which is metallic. (orig.)

[en] The consolidation response of powders of the superconducting compound YBa₂Cu₃O_7-δ by itself and admixed with metal powders is reported. The processing approach relies on short duration (< Is),high current density (10⁴A/cm²), pulse resistive heating of powders under applied pressures of 200 MPa to 400 MPa. Powders and fabricated disk concepts were characterized by X-ray diffraction, optical and scanning electron microscopy

[en] Crystals of Ba₁/sub -//sub x/K/sub x/Bi₂O₃ were obtained from a melt of a mixture of Ba(OH)₂x8H₂O, Bi₂O₃ (0.6Ba:1Bi), and excess KOH heated at 360 ⁰C in air. Single-crystal x-ray diffraction data show that the crystals are cubic a = 4.3223(5) A, space group Pm3m. The 55 unique reflections resulting from averaging 1364 measured intensities were used to refine the structure by least squares to R = 0.0089, wR = 0.0076. The atomic positional parameters are fixed by symmetry; the refinement of the Ba occupancy factor yields the value 0.872(6). The thermal vibration parameters for the cations are constrained to be spherical; the oblate vibration ellipsoid for oxygen yields rms displacements of 0.258(5) A perpendicular to the Bi-Bi distance and 0.12(1) A parallel to it. A prolate ellipsoid for the oxygen anisotropic thermal displacement parameters would have indicated a softening of ''breathing'' modes at the bismuth atoms. Instead, an oblate spheroid locks the oxygen atoms at mid-bismuth positions with enhanced vibrations perpendicular to the Bi-Bi distance. The potassium substitution suppresses the Bi(III)-Bi(V) disproportionation observed in BaBiO₃

[en] SnMo₆S₆S_1.9O_0.1(1), M_r=949.24 rhombohedral, Ranti 3, a=9.175(2), c=11.367(2) A, V=828.7(2) A³, Z=3, D_χ=5.71 g cm^-3, MoKα, λ=0.71069 A, μ=100.9 cm^-1, F(000)=1287.6, room temperature, R=0.0437 for 403 reflections. Ni_2.5-Mo₆S₈(2), M_r=978.93, hexagonal, Ranti 3, a=9.508(2), c=10.237(2) A, V=801.5(2) A³, Z=3, D_χ=6.09 g cm^-3, MoKα, λ=0.71069 A, μ=124.4 cm^-1, F(000)=1350, room temperature, R=0.0421 for 255 reflections. The structure analysis of a crystal grown from a mixture to yield the stoichiometry SnMo₆S₆O₂ led to composition (1). The crystal was twinned across (1anti 100) and refinement showed that 0.12(4) oxygen substituted for sulfur on the anti 3 axis while 0.2(1) tin was displaced from the origin along anti 3 to form Sn-O bond of 2.05(20) A. Oxygen substitution was confirmed by X-ray fluorescence and Auger spectroscopy. A crystal grown by vapor-phase transport, using NH₄Cl, from a reaction mixture to yield hypothetical Ni₂Mo₆S₆O₂, had the composition (2). No oxygen substitution was detected either from the X-ray structure refinement or by spectroscopic techniques. (orig.)