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.     

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.     

The incommensurate solid solution phase Na5−4x Zr1+x(PO4)3:0.04 <x <0.15

The orthophosphate solid solution phase, Na_5?4x Zr_1+x(PO₄)₃:0.04 ? x ? 0.15 has trigonal symmetry with an apparent one dimensional incommensurate superstructure parallel to c_HEX. Using selected area electron diffraction patterns as a guide, an indexing scheme for the powder X-ray data has been devised. The parameter $\text{k = c}{}_{\mathrm{<mtext>supercell</mtext>}}\text{c}{}_{\mathrm{<mtext>subcell</mtext>}}$ varies smoothly with composition from ～ 10.4 at x = 0.04 to ～4.4 at x = 0.11 and is believed to originate in ordering of the extra interstitial Zr⁴⁺ ions. The Na⁺ ion conductivity increases gradually with x and for x = 0.108 varies from ～5×10^?8 ohm^?1 cm^?1 at 25°C to ～1×10^?3 ohm^?1 cm^?1 at 300°C.     

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.     

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.     

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.     

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.     

Preparation and X-ray characterization of CsAlSiO4

A systematic study of the preparation of CsAlSiO₄ using various cesium oxide, alumina, and silica sources and a typical set of firing conditions was performed. The objective was to determine effective methods of preparing phase-pure CsAlSiO₄. The reaction of Cs₂CO₃ with metakaolin at 600°C (decomposition and calcining), 850°C (prefiring) and 1050°C (crystallization) produced the only phase-pure CsAlSiO₄ obtained by these methods. None of the eighteen sets of starting materials yielded a phase-pure CsAlSiO₄ in the 1100°C and 1200°C firings. CsAlSiO₄ was determined to be isomorphous with RbAlSiO₄ as reported by Klaska and Jarchow (1). CsAlSiO₄ is orthorhombic with lattice parameters of $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 8.907 (2)}\text{A}\text{?}\text{,}\text{b}{}_{\mathrm{o}}\text{= 9.435(1)}\text{A}\text{?}\text{,}\text{and}\text{c}{}_{\mathrm{<mtext>o</mtext>}}\text{= 5.435(1)}\text{A}\text{?}$. The space group is Pna2₁, with Z = 4. Single crystals of CsAlSiO₄ were grown hydrothermally from a lCs₂O:1Al₂O₃:2SiO₂ gel in a 3M CsOH solution. The reaction conditions were 770°C and 11, 700 psi. The crystal habit of CsAlSiO₄ is needle-like.     

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.     

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%.     

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.     

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.     

Hydrogen bonding in NH4HSO4. NH4H2PO4

NH₄HSO₄·NH₄H₂PO₄ is monoclinic $\text{P}\text{2}{}_1\text{n}$ with Z = 2 and the following unit cell dimensions : a = 7.723(5), b = 7.540(5), $\text{c}\text{= 7.482(5)}\text{A}\text{?}$, β = 101.32(5)°. Crystal structure of this salt has been solved with a final R value 0.028. As in the corresponding potassium salt PO₄ and SO₄ tetrahedra are randomly distributed.A complete hydrogen bonding pattern is given.     

Thermal expansion of corundum structure Rh2O3

The directional thermal expansion coefficients of the corundum structure form of Rh₂O₃ were determined from room temperature to 850°C by x-ray diffraction methods. Rh₂O₃ has a lower thermal expansion and is less anisotropic in thermal expansion than alumina. The directional thermal expansion coefficients of Rh₂O₃ expressed in second degree polynominal form are: $\text{“α}{}_{\mathrm{<mtext>a</mtext>}}\text{” = 5.350 ×10}{}^{\mathrm{?6}}\text{+ 1.281 ×10}{}^{\mathrm{?9}}\text{T}\text{? 1.133 ×10}{}^{\mathrm{?14}}\text{T}{}^2\text{/°}\text{C}$ and $\text{“α}{}_{\mathrm{<mtext>c</mtext>}}\text{” = 5.246 ×10}{}^{\mathrm{?6}}\text{+ 6.369 ×10}{}^{\mathrm{?9}}\text{T}\text{? 7.480 ×10}{}^{\mathrm{?14}}\text{T}{}^2\text{/°}\text{C}$.     

Structure de PbU2Se5

PbU₂Se₅ crystallizes in a monoclinic unit cell $\text{a}\text{= 8,605}\text{A}\text{?}$; $\text{b}\text{= 7,788}\text{A}\text{?}$; $\text{c}\text{= 12,27}\text{A}\text{?}$; β = 90° of space group $\text{P}\text{2}{}_1\text{c}$, Z = 4. The crystal structure has been determined for 1251 independant reflections and refined to a final R value of 0,068. Two kinds of uranium sites are found; the average U-Se distances are 2,97 Å for eight-coordination and 2,88 Å in seven-coordination. The average Pb-Se distance for eight-coordination is 3,20 Å. This structure explains the solid solution between PbU₂Se₅ and U₃Se₅.     

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.     

Single crystals of In2Te5

Single crystals of semiconducting compound In₂Te₅ were grown by chemical transport employing iodine as a transport agent. The crystals had a plate-like habit with the [100] direction perpendicular to the flat surface of the platelets. Nominal dimensions are 10 × 1 × 0.05 mm. In₂Te₅ has a monoclinic structure with dimensions of the base centered cell: $\text{a}\text{= 13.47}\text{A}\text{?}$, $\text{b}\text{= 16.51}\text{A}\text{?}$, $\text{c}\text{= 4.365}\text{A}\text{?}$, β = 92°5′. The space group is $\text{C}{}_{\mathrm{<mtext>2</mtext><mtext>c</mtext>}}$. Pycnometric density is 5.96 g/cm³. The single crystals were all p-type. The conductivity, thermoelectric power and hardness were about 10^?5Ω^?1cm^?1, 650 mkV/°C, and 30 kg/mm², respectively. The minimum energy gap is 1.26 eV.     

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 $\text{θ}{}_{\mathrm{<mtext>P</mtext>}}\text{? 300 ± 10}\text{K}$.     

New Li+ ion conductors in the system,Li4GeO4-Li3VO4

New Li⁺ ion conducting solid electrolytes have been found in the system Li₄GeO₄-Li₃VO₄. Of the compositions studied, Li_3.6Ge_0.6V_0.4O₄ has the highest conductivity with σ ～ 4 × 10^?5 ohm^?1cm^?1 at 18°C rising to ～ 10^?2 ohm^?1 cm^?1 at 190°C. The activation energy is ～0.44 eV. These conductivity values are among the highest yet found for Li⁺ ion conductors; the room temperature value is much higher than in LISICON, Li_3.5Zn_0.25GeO₄, or in Li_3.4Si_0.4P_0.6O₄ and is comparable to that in $\text{LiI/A}\text{l}{}_2\text{O}{}_3$ mixtures. These solid electrolytes are easy to synthesize, thermodynamically stable and insensitive to atmospheric attack. Structurally, they are solid solutions based on γ_II Li₃VO₄, a γ tetrahedral structure; high conductivity is due to the interstitial Li⁺ ions which are created during solid solution formation.     

Stable Po2-region of ordered perovskites Ca2FeMoO6 and Sr2FeMoO6 at 1200°C

Stable Po₂-region of the title compounds at 1200°C has been determined via an isothermal gravimetry. Ca₂FeMoO₆ was stable within the region $\text{?8.9 ≧}\text{log Po}{}_2\text{≧ ?12.5}$, decomposed by reduction into a triphasic mixture of CaO + Mo + ε-Fe₃Mo₂, and by oxidation into a biphasic mixture of CaMoO₄ (Scheelite structure) + CaFeO_2.5 (Brownmillerite structure). Sr₂FeMoO₆ was stable within the region $\text{?9.8 ≧}\text{log Po}{}_2\text{≧ ?13.5}$, decomposed by reduction into SrO + Mo + ε-Fe₃Mo₂ and by oxidation into SrMoO₄ (Scheelite structure) + SrMoO_3?x (non-stoichiometric perovskite structure).