A new tungsten trioxide hydrate, WO3 · 13H2O: Preparation,characterization, and crystallographic study

A new hydrate of tungsten trioxide, $\text{WO}{}_3\text{·}\text{1}\text{3}\text{H}{}_2\text{O}$ has been obtained by hydrothermal treatment at 120°C of an aqueous suspension of either tungstic acid gel or crystallized dihydrate. This hydrate has been characterized by different methods. A crystallographic study was carried out from X-ray powder diffraction. The hydrate crystallizes in the orthorhombic system: a = 7.359(3) Å, b = 12.513(6) Å, c = 7.704(5) Å, Z = 12. The existence of structural relationships between the hydrate, $\text{WO}{}_3\text{·}\text{1}\text{3}\text{H}{}_2\text{O}$, and the product of dehydration, hexagonal WO₃, has permitted us to propose a structural model in agreement with the experimental data. $\text{WO}{}_3\text{·}\text{1}\text{3}\text{H}{}_2\text{O}$ must be regarded as an interesting compound because its dehydration leads to a new anhydrous tungsten trioxide, hexagonal WO₃.     

An outline of the stucture of 7Bi2O3 · 2WO3 and its solid solutions

This paper gives an outline of the structure of a solid solution based on 7Bi₂O₃ · 2WO₃. The experimental results using X-ray diffraction methods (precession and powder) showed that 7Bi₂O₃ · 2WO₃ crystallizes in the space group $\text{I4}{}_1\text{a}$ with a = 12.5143(5)Å and c = 11.2248(6) Å. The number of formula weights per unit cell is 40, when the formula is considered to be of the oxygen-deficient fluorite-type Bi_0.875W_0.125O_1.6875. The compound has a substructure based on a defect fluorite-type pseudocubic subcell with $\text{a′ ? 5.6}$ Å. The axial relations between the supercell and subcell are $\text{a ? √a′}$ and $\text{c ? 2a′}$. The solid solution was formed over a limited range of WO₃ content between 21.3 mole% and 26.3 mole% at 700°C. The ordering of metal atoms is discussed and an ideal crystal structure is proposed.     

Optical and structural investigation of the lanthanum β-alumina phase doped with europium

The lanthanum β-alumina phase doped with europium was investigated by X-ray diffraction and fluorescence. This nonstoichiometric phase exists over the composition range: $\text{11}\text{Al}{}_2\text{O}{}_3\text{1}\text{La}{}_2\text{O}{}_3$ to $\text{14}\text{Al}{}_2\text{O}{}_3\text{1}\text{La}{}_2\text{O}{}_3$. The unit cell is hexagonal hexagonal with a = 5.560 ± 0.003 Å, c = 22.001 ± 0.003 Å and belongs to the $\text{P6}{}_3\text{mmc}$ space group. X-ray diffraction patterns do not vary between both boundary compositions, but fluorescence spectra show that the structure of the mirror plane in which the lanthanide ions are located is deeply modified. The atomic structure of the mirror plane is of “β-type” (like β(Na) or β(Ag)) for the lower alumina contents; it gradually changes to a “magnetoplumbite type” for higher alumina contents.     

Crystal structures of some niobium and tantalum oxides. VIII. The 5Rb2O:14.6Ta2O5 phase—A tunnel structure

Rb₁₀Ta_29.20O₇₈ crystallizes in the hexagonal system with unit-cell dimensions (from single-crystal data) a = 7.503(4)Å, c = 36.348(4)Å, and space group $\text{P6}{}_3\text{mmc}\text{, z = 1}$. The structure was solved using three-dimensional Patterson and Fourier techniques. Of the 666 unique reflections measured by counter techniques, 515 with I ? 3σ(I) were used in the least-squares refinement of the model to a conventional R of 0.057 (R_ω = 0.039). The structure of Rb₁₀Ta_29.20O₇₈ consists of layers of corner-sharing groups of six edge-shared octahedra separated by layers of single octahedra and double hexagonal tungsten bronze-like layers, these layers being perpendicular to the hexagonal c-axis. Nine-coordinate tricapped trigonal prismatic sites between the hexagonal tungsten bronze-like layers are partially occupied by Ta(V) ions.     

The crystal structure of topotactically dehydrated copper(II) formate tetrahydrate

Thermal dehydration of copper(II) formate tetrahydrate leads to a modification of the anhydrous salt different from that produced by direct preparation of the latter. As the dehydration is a topotactic process, the known crystal structure of the tetrahydrate and the topotactic orientation relations can be used to deduce the crystal structure of the product. Single-crystal X-ray diffraction patterns of decomposed pseudomorphs yield the following unit cell for the dehydrated formate: monoclinic, a = 8.195 ? 0.006 Å, b = 7.925 ? 0.006 Å, c = 3.620 ? 0.005Å, β = 122.21 ? 0.09°, probable space group $\text{P2}{}_1\text{a}\text{= C}{}^5{}_{\mathrm{2h}}$. The structure contains copper formate layers very similar to those in the tetrahydrate, stacked in such a way that columns of distorted coordination polyhedra, linked by formate bridges, are formed. The topotactic dehydration occurs in such a way that two-dimensional elements of the structure are unaltered but the mode of stacking is changed.     

Crystal chemistry of the BaNbS system: A layer structure of approximate composition Ba2NbS4(S2)0.5

Black platy crystals from the product of a reaction mixture of 6BaS : 3Nb : 7S reacted at 1000°C were hexagonal with a = 6.909(4) Å, c = 49.25(2) Å, $\text{P6}{}_3\text{mmc}\text{, Z = 10}$. A pronounced subcell with a = 6.91Å, c = 5.5 Å indicated that this was a layer structure consisting of stacking of close-packed BaS₃ layers. Three dimensional X-ray diffraction data were collected from a single crystal using monochromatized MoKα radiation. From the 1535 measured reflections, 782 unique structure amplitudes were obtained of which 608 greater than 2σ(F) were used to solve the structure. The final R = 0.1065, ωR = 0.0793; for 91 reflections with l = 9n, R = 0.0397 and for the 517 reflections l ≠ 9n, R = 0.138. The structure is based on the stacking of close-packed BaS₃ layers with the sequence CBDBABDBC BCDCACDCB, where D designates a disordered layer. The disordered layers contain two crystallographically independent Ba with partial site occupancies and disordered S₂ and S ions. Nb occupy octahedral interstices and form two different arrangements; a unit consisting of 3 face-sharing octahedra and a unit of 2 face-sharing octahedra. These octahedral units are separated by the disordered layers. The NbNb distances in the chain of 3 are 3.29 Å and they are 3.57 Å in the double unit.     

Oxygen defect K2NiF4-type oxides: The compounds La2−xSrxCuO4−x2+δ

Oxygen defect K₂NiF₄-type oxides $\text{La}{}_{\mathrm{2?x}}\text{Sr}{}_{\mathrm{x}}\text{CuO}{}_{\mathrm{<mtext>4?</mtext><mtext>x</mtext><mtext>2</mtext><mtext>+\delta </mtext>}}$ have been synthesized for a wide composition range: 0 ≤ x ≤ 1.34. From the X-ray and electron diffraction study three domains have been characterized: orthorhombic compounds with La₂CuO₄ structure for 0 ≤ x < 0.10, tetragonal oxides similar to LaSrCuO₄ for 0.10 ≤ x < 1 and several superstructures derived from the tetragonal cell ( with n = 3, 4, 4.5, 5, 6) for 1 ≤ x ≤ 1.34. The compounds corresponding to 0 < x < 1 differ from the other oxides in that they are characterized by the presence of copper with two oxidation states: + 2 and + 3. A model structure for La_0.8Sr_1.2CuλO_3.4, in which copper has only the + 2 oxidation state, and for which the actual cell is tegragonal—a = 18.80₄ Å and c = 12.94 Å—has been established. The particular structural evolution of these compounds is discussed in terms of a competition between the capability of Cu(II) to be oxidized to Cu(III) and the ordering of oxygen vacancies.     

X-ray analysis of the structural and dynamic properties of BaFe12O19 hexagonal ferrite at room temperature

The room temperature crystal structure of BaFe₁₂O₁₉ hexagonal ferrite has been refined from X-ray single crystal data. This compound is hexagonal, space group $\text{P6}{}_3\text{mmc}$, with two formula units per cell and cell parameters a = 5.8920(1) Å and c = 23.183(1) Å. The crystal structure has been refined to a final R value of 1.6% for 380 independent reflections. Three different models are considered for the structural and dynamic characteristics of the bipyramidal Fe ions: (1) a nondisordered configuration, (2) a static disorder between two adjacent pseudotetrahedral sites, and (3) a dynamical disorder between these sites. The X-ray results show that the bipyramidal Fe ions have a disordered configuration and previous Mössbauer spectroscopy studies prove that, at room temperature, the disorder is a dynamical one. The observed oxygen thermal relaxation, Fourier-difference peaks, and interatomic distances are consistent with a fast diffusional motion of the bipyramidal Fe ions within a quasiharmonic double-well potential.     

Crystal structures of the fluorite-related phases CaHf4O9 and Ca6Hf19O44

Crystal structures for the fluorite-related phases CaHf₄O₉$\text{ф}{}_1$) and Ca₆Hf₁₉O₄₄ ($\text{ф}{}_2$) have been determined from X-ray powder diffraction data. qf₁ is monoclinic, $\text{C2}\text{c}$, with a = 17.698 Å, b = 14.500Å, c = 12.021 Å, β = 119.47° and Z = 16. qf₂ is rhombohedral, $\text{R}\text{3}\text{c}$, with a = 12.058 Å, α = 98.31° and Z = 2.Both phases are superstructures derived from the defect fluorite structure by ordering of the cations and of the anion vacancies. The ordering is such that the calcium ions are always 8-coordinated by oxygen ions, while the hafnium ions may be 6-, 7-, or 8-coordinated. The closest approach of anion vacancies is a $\text{1}\text{2}\text{〈111〉}$ fluorite subcell vector, and in each structure vacancies with this separation form strings.     

The crystal structure of α-SrMnO3

α-SrMnO₃ crystallizes in the hexagonal system with unit-cell dimensions a = 5.454(1) Å, c = 9.092(2)Å, space group $\text{P6}{}_3\text{mmc}\text{, Z = 4}$. The structure was solved by the heavy-atom method; of 404 unique reflections measured by counter method, 203 that obeyed the condition |F₀| ≥ 3σ (|F₀|) were used in the refinement to a conventional R value of 0.043. The structure consists of four close-packed SrO₃ layers in an ABAC stacking sequence along the hexagonal c axis. Oxygen octahedra containing Mn⁴⁺ are grouped into face-sharing pairs linked by corner sharing within the cubically stacked “A” layer.     

A single crystal study of eight-layer barium managanese oxide,BaMnO3

A single crystal study of hydrothermally prepared eight-layer BaMnO₃ has been carried out which confirms the (Zhdanov notation) 121121 layer stacking scheme for the BaO₃ layers. The MnO₆ octahedra share faces in strings of four, and these strings are connected to each other by corner sharing. The compound has an hexagonal unit cell of dimensions a = 5.667 ± 0.003 and c = 18.738 ± 0.009 Å, probable space group $\text{P6}{}_3\text{mmc}\text{, Z = 8}$. Its structure has been determined from 352 independent reflections, of which 242 were considered observed, collected manually by a counter technique and refined to a conventional R value of 0.079.     

Synthese et structure cristalline d'un nouvel oxyde mixte “FeV3O8” (FexV1−xO2; x ⋍ 0.25)

Single crystals of a new oxide “FeV₃O₈” ($\text{Fe}{}_{\mathrm{x}}\text{V}{}_{\mathrm{1?x}}\text{O}{}_2\text{: x ? 0.25}$) have been synthesized by slowly cooling a melted mixture with the composition, 8VO₂, 3V₂O₅, Fe₂O₃. The chemical formula has been determined by electron microprobe analysis. The compound, isostructural with AlNbO₄ and VO₂(B), has a monoclinic symmetry, space group $\text{C2}\text{m}$; the unit cell dimensions are a = 12.13Å, b = 3.679 Å, c = 6.547 Å, β = 106.85°. A structural refinement based on single crystal data has been carried out. It gave an R-factor of 1.9%. This refinement indicated that the iron and vanadium cations are partially ordered, although the average cation-oxygen distances for the two six-coordinated cations were exactly the same (1.961 Å). This conjecture was supported by the calculation of the cation valences.     

Bronzes with a tunnel structure KxP4O8(WO3)2m: The tenth member of the series—KP8W40O136

The crystal structure of KP₈W₄₀O₁₃₆, the tenth member of the series K_xP₄O₈(WO₃)_2m, has been resolved by three-dimensional single-crystal X-ray analysis. The space group is $\text{P2}{}_1\text{c}$ and the cell parameters are a = 19.589(3) Å, b = 7.5362(4) Å, c = 16.970(3) Å and β = 91.864(14)°. The framework is built up from ReO₃-type slabs connected through pyrophosphate groups. The structure is compared to those of the other members of the series: although the ReO₃-type slabs show a different type of tilting of the WO₆ octahedra, the dispersion of WO distances is always higher for the octahedra linked to one or two P₂O₇ groups and decreases in proportion as W is farther from these groups. The perovskite cages of the slabs are described and compared to those encountered in the structures of WO₃ and of the bronzes A_xWO₃.     

The structures of fluorides X. Neutron powder diffraction profile studies of UF6 at 193°K and 293°K

Neutron diffraction studies on polycrystalline UF₆ have been carried out at 193°K and 293°K. At both temperatures, UF₆ is orthorhombic with the space group Pnma (D¹⁶_2h) and Z = 4. Measured lattice parameters are a = 9.924 (10) Å, b = 8.954 (9) Å, c = 5.198 (5)Å at 293°K and a = 9.843 (11), b = 8.920 (10), c = 5.173 (6) Å at 193°K. The neutron diffraction patterns were analyzed by the least-squares profile-fitting technique. The final values of $\text{R =}\text{∑}\text{i}\text{(|I}{}_{\mathrm{<mtext>o</mtext><mtext>i</mtext>}}\text{? I}{}_{\mathrm{<mtext>o</mtext><mtext>i</mtext>}}\text{|)/∑ I}{}_{\mathrm{<mtext>o</mtext><mtext>i</mtext>}}$ over the pattern points, where I_oi is a background corrected measured intensity, were 0.081 at 193°K and 0.133 at 293°K.On cooling, the hexagonal close-packing tends to become more regular, and the FF distances external to a UF₆ octahedron contract. The octahedra are nearly regular with a mean UF distance of 1.98 Å, a mean FF edge of 2.80 Å, and a FUF angle of 90.0° at 193°K.     

The crystal structure of Rb-β-alumina

The crystal structure of Rb₂O·11Al₂O₃ has been determined from three-dimensional X-ray data. The compound forms hexagonal crystals with a = 5.600, c = 22.87 Å, and Z = 1 in space group $\text{P6}{}_3\text{mmc}$. The structure has been refined by least-squares methods with anisotropic temperature factors to an R value of 0.079 for 331 independent reflections collected by diffractometry. The mobile ion sites and their occupation percentages are discussed in relation to other β-alumina compounds. The covalently bonded corner-sharing O₃AlOAlO₃ tetrahedra are discussed in relation to the ionic conduction phenomena.     

Structure of stoichiometric USi2

Stoichiometric USi_2.00±0.05 which was thought to be “ord USi_1.88” so far was prepared by immersing USi_1.88 in 1:1 HCl solution, which led to a selective dissolution of excess uranium into the acid. The uranium disilicide thus prepared has two-dimensional platy shapes and tends to align its tetragonal basal planes (00l) parallel to the plane of the sample holder for X-ray diffraction. The orientation effects made it impossible to apply the standard powder pattern technique for the structure analysis of USi₂. The difficulty, however, was eliminated with the aid of a texture pattern technique which has been developed with X-ray diffraction.The uranium disilicide is of the ThSi₂ type ($\text{I4}{}_1\text{amd}$) with a = 3.922 ± 0.001 Å and c = 14.154 ± 0.002 Å, and z = 0.410 ± 0.002. A structural configuration of the compound is essentially the same as that of USi_1.88, except that it has no deficiency of Si.     

The structures of fluorides. XV. Neutron diffraction-kubic harmonic profile analysis of the body-centered cubic phase of sulfur hexafluoride at 193°K

Sulfur hexafluoride has a body-centered cubic phase (a = 5.915(3) Å) between its melting point (222.4°K) and 93°K, below which a lower symmetry phase exists. NMR studies show that in both phases there is rapid reorientation of the sulfur hexafluoride molecules. From a neutron diffraction pattern collected at 193°K with λ = 1.086 Å, the data were not satisfied by a model with a spherically symmetrical fluorine density nor by a refinement with conventional ellipsoidal-shaped atoms. The latter gave systematically low S-F distances and abnormally high β_ij thermal factors. Good agreement was obtained by a combination of Kubic Harmonics with full-matrix least-squares analysis of the neutron profile pattern. The refinement was made with one variable Kubic Harmonic coefficient a₂ = 5.94(11), with $\text{R}{}_{\mathrm{w}}\text{= {}\text{∑ w[y}{}_0\text{? (}\text{1}\text{s}\text{)y}{}_{\mathrm{c}}\text{]}{}^2\text{∑ wy}{}_0{}^2\text{}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 0.079}$ and $\text{χ}{}^2\text{=}\text{∑ w[y}{}_0\text{? (}\text{1}\text{s}\text{)y}{}_{\mathrm{c}}\text{]}{}^2\text{(NO-NV)}\text{= = 1.2}$. Only four least-squares variables were required with 225 observations in the range of one or more hkl reflections to 2θ = 58.3°. AS-F distance of 1.542(4) Å, obtained from the neutron diffraction data, is in good agreement with the reported value of 1.564(10) Å found from electron diffraction measurements of the vapor. The disordered fluorine distribution has broad maxima on the cell edges similar to those found in the plastic cubic phases of MoF₆ and WF₆.     

Crystal structure of the 6H BaCrO3 polytype

A product from the reaction between CrO₂ and Ba₂CrO₄ at 900°C under 60–65 kbar was found to be the six-layer polytype of BaCrO₃ from powder diffraction studies. A hexagonal black crystal obtained from this reaction was isolated for single crystal studies and structure determination. The crystal was found to possess a six-layer stacking sequence of BaO₃ layers with space group $\text{P6}{}_3\text{mmc}$ and had unit cell parameters a = 5.629(2), c = 13.698(6)Å, and Z = 6. The structure was determined from 936 independent reflections of which 693 were considered observed. Averaging equivalent reflections yielded 163 unique, observed reflections. Refinement of the structure by least-squares methods gave a conventional R value of 4.8% (R_w = 6.2%). The structure consists of a six-layer stacking sequence of close-packed BaO₃ layers containing tetravalent chromium in all the octahedral oxygen interstices. The compound was found to be isostructural with previously reported BaMO₃ phases.