TlxTi6Se8 and TlxNb6Se8, two phases with filled up Nb3Te4 type of structure showing pronounced cation disorder

The new ternary chalcogenides Tl_xTi₆Se₈ (x= 0.76) and Tl_xNb₆Se₈ (x= 0.70) crystallize with a partially filled up Nb₃Te₄-structure: space group $\text{P}\text{6}{}_3\text{m}$, z= 1 with

$\text{a= 9.882(1) c= 3.590(1)}\text{A}\text{?}\text{(Tl}{}_{0.76}\text{Ti}{}_6\text{Se}{}_8\text{)}$

$\text{a= 10.033(2) c= 3.475(1)}\text{A}\text{?}\text{(Tl}{}_{0.70}\text{TNb}{}_6\text{Se}{}_8\text{)}$

The crystal structures were determined from single crystal diffractometer data and refined to a conventional R-value of 0.077 and 0.055 respectively. The T1 atoms in the octahedral channels cannot be localized. In Tl_xTi₆Se₈ diffuse scattering indicates one-dimensional short range order. A model of the cation distribution in Tl_0.76Ti₆Se₈ is discussed.     

Rutiles of the system Tio2-FeNb2O6-NbO2 : Structural,magnetic and electron transport properties

A wide domain of rutile solid solution has been isolated in the system TiO₂-FeNb₂O₆-NbO₂. The cristallographic parameters, characteristic of the classical rutile cell, have been determined by X-ray diffraction. The Mössbauer and magnetic susceptibility study shows that in the whole domain iron exhibits the divalent state. A second type of site for Fe(II) has been observed on the limit $\text{Ti}{}_{\mathrm{1?x}}{}^{\mathrm{IV}}\text{Fe}{}^{\mathrm{II}}{}_{\mathrm{<mtext>x</mtext><mtext>3</mtext>}}$Nb^V, which has been interpreted by a small loss of oxygen involving the formation of trivalent titanium. The study of the conductivity and the thermoelectric power confirms the classical band model proposed for the rucile structure, involving in this case narrow Π^H bands. The evolution of σ and α as well as that of the c parameter shows that two domains, I and II, must be distinguished, in which the Π^H bands involve the Ti-3d and Nb-4d orbitals, respectively. The first domain is indeed characterized by the presence simultanously of Ti^IV, Ti^III and Nb^V and corresponds to the triangle Ti^IVO₂-Fe^IINb^V₂O₆Ti ^III_0.5Nb^V_0.5O₂ second domain in which all the titanium ions are in the trivalent state is characterized by the presence of Ti^III, Nb^IV and Nb^V simultanously and corresponds to the triangle Nb^IVO₂-Fe^II₂Nb^V₂O₆-Ti^III_0.5Nb^V_0.5O₂.     

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.     

New phase with K2NiF4 structure in the LaLiFeO system

The existence has been proved, for the first time, in the LaLiFeO system of the phase (La_1.75Li_.25) (Fe_.5Li_.5)O_4?x with tetragonal symmetry ($\text{a}{}_{\mathrm{o}}\text{=3.765±0.001}\text{A}\text{?}$; $\text{c}{}_{\mathrm{o}}\text{=12.918±0.01}\text{A}\text{?}$; $\text{c}{}_{\mathrm{o}}\text{a}{}_{\mathrm{o}}\text{=3.43}$) and K₂NiF₄-type structure.This phase gives probably the first example of lithium distribution in both A and B sites of A₂BO₄-type mixed oxides. The high $\text{c}{}_{\mathrm{o}}\text{a}{}_{\mathrm{o}}$ ratio suggests a strong elongation of FeO₆ octahedra induced by a high spin Fe(IV) d⁴ configuration. The results of structural studies and of Mössbauer analysis, confirming the above conclusions, are reported.     

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.     

Electrostriction in Pb (Zn13Nb23)O3

The electrostriction in $\text{Pb (Zn}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)}\text{O}{}_3$ crystals has been investigated using a strain gauge method. In the ferroelectric phase below 140 C, the strain vs the electric field shows a hysteresis, which is ascribed to the effect of ferroelectric domains. A quadratic relation holds between the strain x and the electric polarization P as x = QP² above about 170 C in the paraelectric phase. Values of the electrostrictive Q coefficients are determined from the measurements near 190 C, as Q₁₁ = 1.6·10^?2m⁴/C², Q₁₂ = ?0.86·10^?2m⁴/C², and Q₄₄ = 0.85·10^?2m⁴/C².     

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.     

High pressure synthesis of Gd3InO6, Tb3InO6 and Lu3InO6

Three new compounds, X₃InO₆ (X = Gd, Tb, Lu) were prepared at 1–4 GPa, ～1050°C. They are monoclinic, space group $\text{P}\text{2}{}_1\text{n}$ with $\text{a}\text{? 8.9}\text{A}\text{?}$, $\text{b}\text{? 9.8}\text{A}\text{?}$, $\text{c}\text{? 5.9}\text{A}\text{?}$, β ～ 95° and Z = 4.     

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.     

Synthesis of a new perovskite Pb(Li14Nb34)O3

A high-pressure technique was adopted to obtain perovskite-type $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$. A new perovskite $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$ was characterized to have a cubic symmetry with $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 4.069}\text{A}\text{?}$; Li and Nb ions in the B-site of perovskite lattice may be in a random arrangement.     

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).     

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).     

On a new structural type of fluorine compounds : Crystal and magnetic structures of a high pressure form of PdF2

A new structural type of MF₂ fluorine compounds has been studied using neutron diffraction. The structure of the high pressure form of Pd difluoride has been shown to derive from the fluorite type by a rhombohedral distortion of the cubic environment of the cations. The coordination number of the cations is VI + II : the six nearest neighbor fluorine atoms form a distorted octahedron with $\text{M}\text{?}\text{F}{}_1\text{? 2.18}\text{A}\text{?}$, while two further anions correspond to $\text{M}\text{?}\text{F}{}_2\text{? 3.17}\text{A}\text{?}$. Distances and angles have been compared with those of other Pd compounds. The structure of the high pressure form of PdF₂ has been refined via neutron diffraction ($\text{a}\text{= 5.329}\text{A}\text{?}$, space group Pa3 or P2₁3). This phase orders antiferromagnetically below 190 ± 5 K and the magnetic structure has been determined on the basis of both collinear and noncollinear models. The magnetic data have been compared with results obtained for other d⁸ or d⁹ difluorides.     

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.     

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.     

Sr2Mn2O5, an oxygen-defect perovskite with Mn(III) in square pyramidal coordination

An oxygen-defect perovskite Sr₂Mn₂O₅ was isolated by reduction of SrMnO_3?x perovskites in the presence of zirconium. Its structure, similar to that of Ca₂Mn₂O₅, has been determined by X-ray powder diffraction and HREM. The orthorhombic cell has the parameters : $\text{a}\text{= 5.523(1)}\text{A}\text{?}$, $\text{b}\text{= 10.761(5)}\text{A}\text{?}$, $\text{c}\text{= 3.811(1)}\text{A}\text{?}$. The possible space groups are Pbam and Pba2. The framework is built up from corner-sharing MnO₄ pyramids forming pseudo-hexagonal tunne$\text{l}$s running along 〈001〉 and perovskite tunnels running along 〈110〉 and 〈110〉. This oxide is antiferromagnetic with $\text{T}{}_{\mathrm{N}}\text{? 380 ± 10}\text{K}$ and $\text{θ}{}_{\mathrm{<mtext>P</mtext>}}\text{? 300 ± 10}\text{K}$.     

Electrical properties of ferromagnetic Gd3−xS4 near its Curie temperature

Nonstoichiometric $\text{Gd}{}_{\mathrm{<mtext>3?</mtext><mtext>x</mtext>}}\text{S}{}_4\text{(0 <}\text{x}\text{<}\text{1}\text{3}\text{)}$, which exhibits a metallic behavior, was obtained by heating an insulating Gd₂S₃ at various temperatures under a vacuum. Electrical and magnetic properties of the samples obtained have been investigated from 4.2 K to 300 K. A maximum in resistivity was observed in the curve of resistivity vs. temperature. The temperature T_P, at which the maximum emerged, was very close to the Curie temperature T_C for the sample. An increase in resistivity at T_P, Δ_?, is proportional to ?_P exp ($\text{E}\text{k}{}_{\mathrm{B}}\text{T}{}_{\mathrm{P}}$), where ?_P is the resistivity obtained by the extrapolation from the linear portion to T_P in the ? vs. T curve. Using the relationship obtained, a model based on the formation of magnetic polaron was proposed for this system.     

Preparation and structure of EuIINb4O11

The occurrence of compound in the system has been studied by means of X-ray powder diffraction. A compound, Eu^IINb₄O₁₁, was found. The X-ray powder diffraction data for Eu^IINb₄O₁₁ could be indexed on a tetragonal cell with $\text{a}\text{=52.52}\text{A}\text{?}$, $\text{C}\text{=7.69}\text{A}\text{?}$. The temperature dependence of the magnetic susceptibility for this compound is expressed by the equation, $\text{X}{}_{\mathrm{M}}\text{=}\text{7.10}\text{(}\text{T}\text{+0.20)}$. This compound is oxidized at about 290°C or above in air.     

Ordering of interstitial nitrogen and oxygen in vanadium near to V8N and V8O

The ordered structure of the V₈N subnitride was studied by X-rays, electron diffraction and electron microscopy. V₈N exists in two different modifications (α′ and α″). The vanadium sublattice of both phases is pseudo-tetragonal, in reality triclinic, with lattice parameters: $\text{α}{}_{\mathrm{<mtext>o</mtext>}}\text{=}\text{b}{}_{\mathrm{o}}\text{= 3.114}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 2.994}\text{A}\text{?}$, α_o = β_o = 90.5^o ± 0.1^o, γ_o = 90^o. The proposed unit cell of α′-V₈N has dimensions: a = 2√2 a_o, c = 2c_o and corresponds to V₃₂N₄. Doublets of nitrogen atoms occupy two sets of octahedral cavities whose shortest axes are aligned along the x and y directions of the sublattice in an ordered fashion. The α″-V₈N phase is a periodically twinned modification of the α′-V₈N, the twin plane being of the (001) type. The V₈O suboxide has the same structure as the α″-V₈N, the sublattice parameters being: $\text{a}{}_{\mathrm{o}}\text{=}\text{b}{}_{\mathrm{o}}\text{= 3.11}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 2.994}\text{A}\text{?}$, α_o = β_o = 90.3^o ± 0.1^o, γ_o = 90^o.     

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.