Structure determination of (3D) P2NbS8

Tridimensional P₂NbS₈ crystallizes in P4?n2 tetragonal space group, with $\text{a}\text{= 12.0483(4)}\text{A}\text{?}$, $\text{c}\text{= 7.2070(5)}\text{A}\text{?}$, $\text{V}\text{= 1046.2(1)}\text{A}\text{?}{}^3$ and Z = 4. The structure was anisotropically refined down to R = 2.3% from 468 reflexions and 53 variables. It is built from [Nb₂S₁₂] biprismatic bicapped units (average $\text{d}{}_{\mathrm{Nb?S}}\text{= 2.571}\text{A}\text{?}$) made of S^?II and S^?II₂ anions (dianionic distance of 2.014(3) Å). The niobium atoms are found as isolated Nb^IV ? Nb^IV pairs ($\text{d}{}_{\mathrm{Nb?Nb}}\text{= 2.859(1)}\text{A}\text{?}$) in these niobium group otherwise linked to each other through (PS₄) tetrahedral units (average $\text{d}{}_{\mathrm{P?S}}\text{= 2.051}\text{A}\text{?}$) themselves constituting interbonded [P₄S₁₂] rings. The P₂NbS₈ three-dimensional network thus obtained is compared to the (2D) P₂NbS₈, layered phase already described.     

Copper doped zinc oxide Y2BaZnO5: ERS and optical investigation

In copper doped Y₂BaZnO₅ oxides, copper exhibits a distorted square pyramidal coordination which is consistant with the values of g and A tensors obtained from O band ERS spectrum for a sample containing about 1 % Cu. Three values for g and A are observed, g₁ = 2.049₅, g₂ = 2.051₅, g₃ = 2.275, $\text{¦}\text{A}{}_1\text{¦ = 13 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$, $\text{¦}\text{A}{}_2\text{¦ = 10 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$ and $\text{¦}\text{A}{}_3\text{¦ = 147.5 10}{}^{\mathrm{?4}}\text{cm}{}^{\mathrm{?1}}$. Since $\text{g}{}_1\text{?}\text{g}{}_2$ an approximate C_4v point symmetry can be assumed for copper. The electronic spectrum shows three bands at 11700, 14500 and 20500 cm^?1 which can be assigned to the transitions A₁ → B₁, B₂ → B₁ and E → B₁ respectively. The orbital reduction parameters are calculated and the bonding covalency is discussed.     

CuTa2O6 - crystal growth and characterization

The compound CuTa₂O₆ has been prepared as crystals from a Cu/O melt and found to be tetragonal ($\text{a}\text{= 7.510}\text{A}\text{?}$, $\text{c}\text{= 7.526}\text{A}\text{?}$) rather than cubic as reported in the literature. The coefficient of thermal expansion between room temperature and 1000°C was found to be 8.0 × 10^?6°C^?1. Electrical resistivity measurements on a crystal showed semiconductor behavior between room temperature ($\text{? = 2 × 10}{}^3\text{Ω}\text{cm}$) and 140°K ($\text{? = 7 × 10}{}^6\text{Ω}\text{cm}$) with an activation energy of E_A = 0.2 eV. Magnetic measurements between 4.2°K and room temperature showed Curie-Weiss behavior with a change in μeff at 120°K. For T>120°K, μeff = 1.76μ_B and θ_p = 0°K while for T<120°K μeff = 1.91 μB and θ_p = ?15°K.     

High pressure synthesis of Cu2GeO4 with hausmannite structure

Copper(II)metagermanate, CuGeO₃, decomposes at high pressure to rutile-type GeO₂ and Cu₂GeO₄. Very small single crystals of Cu₂GeO₄ can be obtained by direct high pressure synthesis from CuOGeO₂ mixtures. The compound has a distorted spinel structure (Hausmannite structure, space group $\text{I}\text{4}{}_1\text{amd}$) with $\text{a}\text{= 5.593}\text{A}\text{?}$, $\text{c}\text{= 9.396}\text{A}\text{?}$, Z = 4.     

Macle et structure cristalline de Mn0,75Ga2,17S4

Twins of $\text{Mn}{}_{\mathrm{<mtext>1?</mtext><mtext>x</mtext>}}\text{Ga}{}_{\mathrm{<mtext>2+</mtext><mtext>2</mtext><mtext>3</mtext><mtext>x</mtext>}}\text{S}{}_4$ were used for crystal structure determination. Twinning is explained by a reticular pseudomerihedry. Axis, plane and obliquity of the twin have been determined. Cell dimensions are: $\text{a = b}\text{= 5.456(2)}\text{A}\text{?}$; $\text{c}\text{= 10.220(4)}\text{A}\text{?}$; α = β = γ = 90°; space group 14; Z = 2. The final R value is 0.059. The material is isostructural with CdGa₂S₄.     

Structure cristalline et proprietes physiques de Cu0.75 VS2

A new compound with composition Cu_0.75 VS₂ has been prepared. Its preparation, X-Ray structure, electrical and magnetic properties are reported. The structure is related to the CdI₂-type, as in the case of the previously described Cu_xTiS₂ (1); in Cu_0.75 VS₂, Cu atoms are ordered in tetrahedral sites between the CdI₂-type subunits, whereas in Cu_xTiS₂ Cu atoms are disordered in two independent sites. The vanadium atoms are shifted with respect to the titanium sites which leads a monoclinic distortion of the hexagonal cell. The relation between the CdI₂ unit cell and the true monoclinic cell of Cu_0.75 VS₂ is:

$\text{a}{}_{\mathrm{<mtext>mono</mtext>}}\text{= 2}\text{a}{}_{\mathrm{<mtext>hex</mtext>}}\text{3}\text{;}\text{b}{}_{\mathrm{<mtext>mono</mtext>}}\text{=}\text{4}\text{3}\text{a}{}^2{}_{\mathrm{<mtext>hex</mtext>}}\text{+}\text{c}{}^2{}_{\mathrm{<mtext>hex</mtext>}}\text{9}\text{;}\text{c}{}_{\mathrm{<mtext>mono</mtext>}}\text{= 2}\text{a}{}_{\mathrm{<mtext>hex</mtext>}}$

In Cu_0.75 VS₂, vanadium atoms occupy two independent sites, three vanadium atoms forming a triangular cluster (V₂—V₃ distances are 2.91 Å and V₃—V₃ are 2.92 Å) while one vanadium atom is isolated ($\text{V}{}_1\text{?}\text{V}{}_2\text{= 3.36}\text{A}\text{?}$ and $\text{V}{}_1\text{?}\text{V}{}_3\text{= 3.37}\text{A}\text{?}$. The physical properties exhibit a transition at 50°K approximately, the magnetic susceptibility being temperature-independent above and temperature dependent below the transition (Curie-Weiss behavior). Resistivity and Hall measurements confirm the metallic nature of the compound and show the existence of the low temperature transition. The observed properties could be interpreted as a result of the low temperature localisation of the 3d electron of V₁.     

Syntheses and magnetic properties of Eu3B2O6 and Sr3B2O6

Europium orthoborate and strontium orthoborate crystallize in the rhombohedral system with two formula units in a cell of dimensions $\text{a}{}_{\mathrm{R}}\text{=6.697}\text{A}\text{?}$, α_R=85.17° for Eu₃B₂O₆, and $\text{a}{}_{\mathrm{R}}\text{=6.695}\text{A}\text{?}$, α_R=85.00° for Sr₃B₂O₆. The equivalent hexagonal lattice parameters are $\text{a}{}_{\mathrm{H}}\text{=9.069}\text{A}\text{?}$, $\text{c}{}_{\mathrm{H}}\text{=12.542}\text{A}\text{?}$, and $\text{a}{}_{\mathrm{H}}\text{=9.046}\text{A}\text{?}$, $\text{c}{}_{\mathrm{H}}\text{=12.566}\text{A}\text{?}$ respectively. Eu₃B₂O₆ appears to be ferromagnetic below 7.5K.     

Ionic conductivity of Li4GeO4, Li2GeO3 and Li2Ge7O15

The ionic conductivity of polycrystalline samples of three lithium germanates: Li₄GeO₄, Li₂GeO₃, and Li₂Ge₇O₁₅, has been determined using a c techniques and complex plane analysis. Conductivities at 400°C are 8.7 × 10^?5, 1.5 × 10^?5, and $\text{1.4 × 10}{}^{\mathrm{?7}}\text{(Ω·}\text{cm}\text{)}{}^{\mathrm{?1}}$ respectively. The conductivity of Li₄GeO₄ rises appreciably in the range 700–750°C.     

A series of rare earth silicates RE3+2M3+[SiO4]2 (OH)

A series of isotypic silicates of composition RE₂M[SiO₄]₂ (OH) with RE = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, and M = Al³⁺, Fe³⁺ has been synthesized under hydrothermal conditions. Lattice constants of two members as determined from single crystal X-ray diffraction data are: La₂Al[SiO₄]₂ (OH) (La₂Fe[SiO₄]₂ (OH)) $\text{a}{}_{\mathrm{o}}\text{= 7.401 (7.346)}\text{A}\text{?}$, $\text{b}{}_{\mathrm{o}}\text{= 5.702 (5.862)}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 17.072 (97.196)}\text{A}\text{?}$, gb = 112.4 (112.5°), $\text{P}\text{2}{}_1\text{c}$, Z=4.     

An outline of the crystal-structure of Bi2Mo2O9

An outline of the structure of the catalyser component Bi₂Mo₂O₉ has been determined from X-ray powder diffractometer diagrams. The space group is $\text{P}{}^2\text{l}\text{n}$ ($\text{=}\text{P}{}^2\text{l}\text{c}$) with cell constants: $\text{a}\text{= 11.946 (2)}\text{A}\text{?}$, $\text{b}\text{= 10.795 (2)}\text{A}\text{?}$, $\text{c}\text{= 11.876 (2)}\text{A}\text{?}$ and β = 90.15 (2)°. There are eight formula units per cell. The positions of the metal-ions could directly be derived from the intensities of the strongest reflexions. With difference terms calculated from 19 strong reflexions a Δ F-synthesis was calculated, which revealed the approximate positions of the O^2?-ions. From packing considerations it was apparent that of 9 0^2?-ions one is only coordinated by Bi³⁺ and that Mo⁶⁺ must be tetrahedrally surrounded by 0^2?. These tetrahedra may be strongly distorted. The structure is not related to the scheelite-structure as has been assumed by some authors.     

Pressure induced phase transformation in BaWO4

A new dense form of BaWO₄(BaWO₄-II) was prepared under high pressure. The phase boundary between the normal pressure form (BaWO₄-I, scheelite structure) and BaWO₄-II was determined as P(kb) = 26.₇+0.26₅T(°C), (T=600–1000 °(C). Crystallographic data were obtained from the single crystal and powder X-ray analyses. BaWO₄-II is monoclinic with 8 formula units in the unit cell. The possible space group is $\text{P}\text{2}{}_{\mathrm{<mtext>1</mtext><mtext>n</mtext>}}$ and the cell parameters are; $\text{a}\text{= 13.159}\text{A}\text{?}\text{,}\text{b}\text{= 7.161}\text{A}\text{?}\text{,}\text{c}\text{= 7.499}\text{A}\text{?}\text{, β = 93.76°}$ and the cell $\text{volume}\text{= 705}\text{A}\text{?}{}^3$. The volume decrease upon transformation is estimated to be 12.1%.     

Preferential oxygen sputtering from Nb2O5

The bombardment of Nb₂O₅ with Kr⁺ or O⁺₂ ions leads to the development of a surface layer NbO. The layer begins to form at (2–4) × 10¹⁵ ions cm^-2 as random nuclei which can be resolved by transmission electron microscopy. It is half complete at (4–8) × 10¹⁶ ions cm^?2, a much higher dose than that required for sputter equilibrium to be half complete. The final thickness is roughly 31 nm. These features, together with the further result that the layer forms independently of the bombarding current provided beam heating is avoided, can be understood from a model which combines preferential oxygen sputtering at the surface, diffusion of the relevant point defects, and random nucleation of a phase with lower stoichiometry. The governing equation is an extended form of the diffusion equation

$\text{?C}\text{?t}\text{=}\text{D?}{}^2\text{C}\text{?x}{}^2\text{+}\text{υ?C}\text{?x}\text{?}\text{DC}\text{L}{}^2$

where υ is the velocity of the surface recession due to sputtering and L is the diffusion length for trapping. Appropriate solution of the equation suggests that the altered layer will have a mean thickness similar to L, will be formed with a half-dose given by $\text{0.693LN}\text{S}$ where S is the sputtering coefficient, and will involve a total amount given by $\text{DC}{}_0\text{υ}$ atoms cm^?2, where C₀ is the stoichiometry at the outer surface. Current independence follows if the diffusion is bombardment enhanced, so that D is approximately proportional to υ. The main difficulty with the model is that it is strictly valid only for low concentrations.     

Un compose a structure feuilietee (LaO)4Ag1,5Ga1,5S5

The compound (LaO)₄Ag_{1 · 5}Ga_{1 · 5}S₅ belongs to the quasi-binary La₂O₂SAgGaS₂ system. It undergoes a peritectic decomposition at 1040°C and a order-disorder transition at 750°C. The high temperature variety is tetragonal, with $\text{a}{}_0\text{= 4.18}\text{A}\text{?}$; $\text{c}{}_0\text{= 18.74}\text{A}\text{?}$; Z = 1; space group 1422; it has the same structural type as (CeO)₄Ga₂S₅. The low temperature variety is an orthorhombic superstructure of the preceding one. with a = 17.58 (3 a₀√2); b = 5.90 (a₀√2) and $\text{c}\text{= 18.66}\text{A}\text{?}$ (c₀). The electrical conductivity is mainly of ionic nature. The e.m.f. measurements of a cell Ag/(LaO)₄Ag_{1 · 5}Ga_{1 · 5}S₅/S.C./Pt support this conclusion.     

The spinels CoRh2O4 and Co2RhO4

Polycrystalline CoRh₂O₄ and Co₂RhO₄ are cubic, spinel-type double oxides, S.G. Fd3m (No. 227), Z = 8. For CoRh₂O₄, $\text{a}\text{= 8.4992(1)}\text{A}\text{?}$, $\text{U = 613.95(3)}\text{A}\text{?}{}^3$, D_X = 7.11 Mgm^?3, $\text{x}\text{= 0.257}$, Co in 8(a) positions, R = 0.043. For Co₂RhO₄, $\text{a}\text{= 8.299(2)}\text{A}\text{?}$, $\text{U = 517.6(5)}\text{A}\text{?}{}^3$. D_X = 6.62 Mgm^?3, $\text{x}\text{= 0.261}$, half the Co content in 8(a) positions, R = 0.041. IR absorption band frequencies for both spinels are included.     

A mixed valence compound in the two dimensional MPS3 family: V0.78PS3 structure and physical properties

The non stoichiometric compound V_0.78PS₃ has been obtained as single crystals from a preparation corresponding to the atomic ratio V/P/S = 1/1/3. It cristallizes with monoclinic symmetry, space group C2/m, with the unit cell parameters $\text{a}\text{= 5.867(1)}\text{A}\text{?}\text{,}\text{b}\text{= 10.160(2)}\text{A}\text{?}\text{,}\text{c}\text{= 6.657(1)}\text{A}\text{?}\text{, β = 107.08(2)°,}\text{V}\text{= 379.3(1)}\text{A}\text{?}{}^3$ and Z =4. The structure refinement was made down to a reliability factor value R = 3.3% from 445 reflexions (I > 3 σ (I)) and 31 variables. The material has same layer structure as FePS₃ with the occurrence of the thiophosphate anion (P₂S₆)^4?-including a P₂ pair. In V_0.78PS₃, the charge equilibrium implies the following developped formula : V_0.34^II V_0.44^III □_0.22 P^IV S₃^?II. The phase is a semi-conductor with a small activation energy of 0.24 eV, in accord with a vanadium mixed valence, and it presents, at low temperature, an antiferromagnetic order (T_N = 62 K).     

The crystal structures of Ba2LaRuO6 and Ca2LaRuO6

Neutron diffraction experiments have been performed to determine the structures of Ba₂LaRuO₆ and Ca₂LaRuO₆. Both are ordered, distorted perovskites. Ba₂LaRuO₆ is monoclinic, space group $\text{P}\text{2}{}_{\mathrm{<mtext>1</mtext>}}\text{n}$ with $\text{a}{}_0\text{=6.0285(7)}\text{A}\text{?}$, $\text{b}{}_0\text{=6.0430(7)}\text{A}\text{?}$, $\text{c}{}_0\text{=8.5409(6)}\text{A}\text{?}$, β=90.44(1)^o. The A sites are occupied by barium and the B sites by an ordered arrangement of lanthanum and ruthenium. Ca₂LaRuO₆ is triclinic, space group P1 with a₀=5.6179(5), b₀=5.8350(5), c⁰=8.0667(4), α=90.0^o, β=89.76(1)^o, γ=90.0^o. The A sites are occupied by calcium and lanthanum in a disordered manner, and the B sites are occupied by an ordered arrangement of calcium and ruthenium. The results reported in this paper thus contradict those of previous workers. The low-temperature magnetic structures are discussed briefly.     

Contribution a l'etude de la conductivite ionique de l'orthophosphate Na3PO4

The present work is concerned with the ionic conductivity of pure trisodium orthophosphate Na₃PO₄, devoid of any trace of hydroxide NaOH. At the allotropic transition (330°C), we observe a jump of the ionic conductivity and a slight decrease in the activation energy (ΔE = 0,70 ± 0,02 eV for the quadratic variety and ΔE = 0,60 ± 0,04 eV for cubic γ-Na₃PO₄). Na₃PO₄ can be considered to be an electrolytic solid with medium conductivity ($\text{σ = 1.10}{}^{\mathrm{?4}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ at 370°C).     

New tetrahedrally coordinated A2CdBr4 compounds (A = Cs,CH3NH3)

(CH₃NH₃)₂CdBr₄ and Cs₂CdBr₄ are two compounds with a tetrahedral CdBr₄-coordination. Their room temperature structures are determined. (CH₃NH₃)₂CdBr₄: monoclinic, $\text{P}\text{2}{}_1\text{c}$, $\text{a}\text{= 8.1227(13)}\text{A}\text{?}$, $\text{b}\text{= 13.4355(16)}\text{A}\text{?}$, $\text{c}\text{= 11.4194(13)}\text{A}\text{?}$, β = 96.194(11) °, z = 4. Cs₂CdBr₄: orthorhombic, Pnma, $\text{a}\text{= 10.235(5)}\text{A}\text{?}$, $\text{b}\text{= 7.946(3)}\text{A}\text{?}$, $\text{c}\text{= 13.977(5)}\text{A}\text{?}$, z = 4.     

Determination de la structure cristalline de la variete a des hydroxycarbonates de terres rares LnOHCO3 (Ln = Na)

A probable model for the structure of the orthorhombic A - type neodymium hydroxycarbonate is presented. It relies on an optical determination of the site symmetry of OH^?, CO^2?₃, and Nd³⁺ atoms from infrared and visible absorption spectra, together with a computation of 50 X-ray diffraction lines intensities of a high resolution Guinier orthorhombic powder pattern ($\text{a}\text{= 4,953}\text{A}\text{?}$, $\text{b}\text{= 8,477}\text{A}\text{?}$, $\text{c}\text{= 7,210}\text{A}\text{?}$; space group Pmcn (n^o62)). The CO^2?₃ groups lies flat between mettalic planes as in the aragonite type of structure and are linked to OH^? by hydrogen bond ($\text{d(CO}{}^{\mathrm{2?}}{}_3\text{?}\text{OH}{}^{\mathrm{?}}\text{) = 2,52}\text{A}\text{?}$). The rare earth coordination is nine fold: two OH^? groups being closer (2,58 Å) than the seven oxygen from the CO^2?₃ groups (2,58 to 2,70 Å).     

The oxygen defect perovskite BaLa4Cu5O13.4, a metallic conductor

A new oxygen defect perovskite BaLa₄Cu₅O_13.4, characterized by a mixed valence of copper has been isolated; the parameters of the tetragonal cell are closely related to that of the cubic perovskite:a = 8.644(4)$\text{A}\text{?}\text{=}\text{a}{}_{\mathrm{p}}\text{5√}$ and c = 3.867(3) $\text{A}\text{?}\text{=}\text{a}{}_{\mathrm{p}}$. The X-ray diffraction study shows that the atoms are displaced from their ideal positions in the cubic cell, owing to the presence of ordered oxygen vacancies. The study of conductivity, magnetic susceptibility and thermoelectric power versus temperature shows that this oxide is a very good metallic conductor.