Crystal structure of Rb<Subscript>2</Subscript>[Ti(VO<Subscript>2</Subscript>)<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>]

The crystal structure of the new compound Rb₂[Ti(VO₂)₃(PO₄)₃] obtained by hydrothermal synthesis in the RbCl-TiPO₄-V₂O₅-B₂O₃-H₂O system (a = 13.604(2) Å, c = 9.386(2) Å, sp. gr. P6cc, Z = 4, ρ_calcd = 3.32 g/cm³) has been studied by X-ray diffraction (Xcalibur-S-CCD diffractometer, R = 0.038). It is shown that the isotypism of Rb₂[Ti(VO₂)₃(PO₄)₃] and Cs₂[Ti(VO₂)₃(PO₄)₃] is caused by the flexibility of a mixed anionic framework composed of phosphorus tetrahedra, vanadium five-vertex polyhedra, and titanium octahedra (bases of the crystal structures of these compounds). The topological correlations between the structures of titanium-vanadyl phosphates and benitoite and beryl silicates are analyzed.     

Refinement of the crystal structure of rhombohedral KU<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> as a representative of orthophosphates with the NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> structure

The crystal structure of the high-temperature β modification of synthetic orthophosphate KU₂(PO₄)₃ was refined from powder X-ray diffraction data by the Rietveld method: sp. gr. \(R\bar 3c\), the unit-cell parameters a= 9.113(1) Å and c= 24.997(1) Å. The isotropic refinement converged to R _wp = 6.15, R _B = 2.14, R _F = 3.52, and S = 0.42. It was confirmed that β-KU₂(PO₄)₃ belongs to the structure type of sodium zirconium phosphate containing an actinide atom in a sixfold (octahedral) coordination formed by oxygen atoms, which is unusual for orthophosphates. The principal interatomic distances and bond angles in the structure are reported.     

Structure of Cs<Subscript>4</Subscript>(HSO<Subscript>4</Subscript>)<Subscript>3</Subscript>(H<Subscript>2</Subscript>PO<Subscript>4</Subscript>) single crystals

Single crystals of Cs₄(HSO₄)₃(H₂PO₄) are synthesized and studied for the first time. The new compound is found in the course of studies of the phase diagram of the CsHSO₄–CsH₂PO₄–H₂O triple system. Data on the atomic crystal structure of single-crystalline and powder specimens, as well as on structural phase transitions, are obtained.     

Synthesis and crystal structure of bis(malonato)tetra (aqua)barium(II)cobalt(II): [BaCo(C<Subscript>3</Subscript>H<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>]

The title compound [BaCo(C₃H₂O₄)₂(H₂O)₄] was synthesized and its crystal structure was determined. The compound is orthorhombic, space group Pccn with a = 18.974(3) Å, b = 6.783(2) Å, c = 9.394(4) Å. The structure is polymeric and consists of edge-sharing BaO₈ polyhedra and CoO₆ octahedra linked together by the malonate groups. The geometry around the Ba(II) centres is a slightly distorted square-antiprism with Ba–O distances ranging from 2.789(4) to 2.843(4) Å. Around the Co(II) centres, the coordination forms a distorted octahedron with Co–O bonds between 2.040(3) and 2.238(4) Å.     

Crystallization of trigonal (Tb,Er)(Fe,Ga)<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> phases with hantite structure in bismuth trimolybdate-based fluxes

The stability regions of the trigonal (Tb,Er)(Fe,Ga)₃(BO₃)₄ phases are established in (Bi₂Mo₃O₁₂)-based fluxes. The specific features of heterogeneous nucleation and the subsequent phase transformations during transition to the equilibrium are studied in the vicinity of the boundaries. The temperature modes of single crystal growth on seeds are suggested with due regard for the “nonequilibrium effect.”     

Proton-Conducting Composites Based on the Cs<Subscript>4</Subscript>(HSO<Subscript>4</Subscript>)<Subscript>3</Subscript>(H<Subscript>2</Subscript>PO<Subscript>4</Subscript>) Compound

Proton-conducting composites xCs₄(HSO₄)₃(H₂PO₄) + (1–x)AlPO₄ in the composition range x = 0.9–0.5 have been obtained. Their transport properties are studied by impedance spectroscopy. The dependences of the phase composition of the materials on the component ratio are investigated by X-ray diffraction analysis. The spatial phase distribution in the materials is analyzed using scanning electron microscopy.     

Synthesis and an X-ray diffraction study of Rb<Subscript>2</Subscript>[(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>3</Subscript>]

The synthesis and X-ray diffraction study of compound Rb₂[(UO₂)₂(C₂O₄)₃], which crystallizes in the monoclinic crystal system, are performed. The unit cell parameters are as follows: a = 7.9996(6) Å, b = 8.8259(8) Å, c = 11.3220(7) Å, β = 105.394(2)°, and V = 770.7(1) ų; space group P2₁/n, Z = 2, and R ₁ = 0.0271. [(UO₂)₂(C₂O₄)₃]^2? layers belonging to the AK _0.5 ⁰² T ¹¹ crystal chemical group of uranyl complexes (A = UO ₂ ²⁺ , K ⁰² = C₂O ₄ ^2? , and T ¹¹ = C₂O ₄ ^2? ) are uranium-containing structural units of the crystals. The layers are connected with outer-sphere rubidium cations by electrostatic interactions.     

Crystal structure of Rb<Subscript>2</Subscript>Mn<Subscript>3</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>[P<Subscript>2</Subscript>O<Subscript>7</Subscript>]<Subscript>2</Subscript>, a new representative of the family of hydrated diphosphates

The crystal structure of Rb₂Mn₃(H₂O)₂[P₂O₇]₂, a new phase obtained in the form of single crystals under hydrothermal conditions in the MnCl₂–Rb₃PO₄–H₂O system, is determined by X-ray diffraction (Xcalibur-S-CCD diffractometer, R = 0.0270): a = 9.374(2), b = 8.367(2), c = 9.437(2) Å, ß = 99.12(2)°, space group P2₁/c, Z = 2, D_x = 3.27 g/cm³. A correlation between the unit-cell parameters and the size of cations forming the crystal structures of isostructural A₂M₃(H₂O)₂[P₂O₇]₂ diphosphates (A = K, NH₄, Rb, or Na; _M = Mn, Fe, Co, or Ni) is revealed. It is shown that, due to the topological similarity, the structures of diphosphates and orthophosphates of the farringtonite structural type can undergo mutual transformations.     

Flux crystallization of trigonal GdFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> competing with the crystallization of α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

The formation of trigonal GdFe₃(BO₃)₄ crystals in the Bi₂Mo₃O₁₂-B₂O₃-Li₂MoO₄-Gd₂O₃-Fe₂O₃ system was studied. The flux compositions for which GdFe₃(BO₃)₄ is the high-temperature phase with a wide range of crystallization were determined. The features of nucleation of these crystals and their growth near the phase boundary with α-Fe₂O₃ were analyzed. The growth of GdFe₃(BO₃)₄ single crystals involving preliminary nonequilibrium crystallization of α-Fe₂O₃ is described.     

Vibrational modes of hydrogen in (NH<Subscript>4</Subscript>)H<Subscript>5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> (Neutron scattering and simulation)

The vibrational modes of hydrogen in (NH₄)H₅(PO₄)₂ have been investigated by inelastic incoherent neutron scattering at temperatures above (220 K) and below (160 and 5 K) the phase-transition point T _c = 180 K. Computer simulation of vibrational modes has been performed for the low-temperature phase (NH₄)H₅(PO₄)₂ at 5 K. The calculated generalized incoherent dynamic factor and the partial incoherent dynamic factors for all hydrogens make it possible to identify the observed modes from acid hydrogens and hydrogens of ammonium ions.     

Crystal chemistry of KCuMn<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>3</Subscript> in the context of detailed systematics of the alluaudite family

The crystal structure of new manganese potassium copper vanadate KCuMn₃(VO₄)₃, which was prepared by the hydrothermal synthesis in the K₂CO₃–CuO–MnCl₂–V₂O₅–H₂O system, was studied by X-ray diffraction (R = 0.0355): a = 12.396(1) Å, b = 12.944(1) Å, c = 6.9786(5) Å, β = 112.723(1)°, sp. gr. C2/c, Z = 4, ρ_calc = 3.938 g/cm³. A comparative analysis of the crystal-chemical features of the new representative of the alluaudite family and related structures of minerals and synthetic phosphates, arsenates, and vanadates of the general formula A(1)A(1)′A(1)″A(2)A(2)′M(1)M(2)₂(TO₄)₃ (where A are sites in the channels of the framework composed of MО₆ octahedra and TО₄ tetrahedra) was performed. A classification of these structures into subgroups according to the occupancy of A sites is suggested.     

Investigation of zirconium phosphate Zr<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>4</Subscript> during heating

Zirconium phosphate Zr₃(PO₄)₄ has been synthesized by the sol-gel technique and investigated using X-ray powder diffraction, IR spectroscopy, and differential scanning calorimetry. It has been established that the symmetry of the unit cell, R \(\bar 3\) c, which is characteristic of the NaZr₂(PO₄)₃ (NZP) family, is lowered to P \(\bar 3\) c. The behavior of the zirconium phosphate during heating has been examined using high-temperature X-ray diffraction at temperatures ranging from 25 to 575°C. It has been revealed that the structure of the zirconium phosphate is hardly subjected to expansion due to heating in the temperature ranges 25–125°C (α _a < 1 × 10^?6 K^?1, α _c < 1 × 10^?6 K^?1, Δα < 1 × 10^?6 K^?1) and 325–575°C (α _a = ?1.4 × 10^?6 K^?1, α _c < 1 × 10^?6 K^?1, Δα < ?2.4 × 10^?6 K^?1). In the temperature range 125–325°C, the synthesized compound undergoes a second-order phase transition (upon heating), which is accompanied by the contraction of the structure along all crystallographic directions. Upon cooling in the range from 75 to 25°C, the phase transition is accompanied by the expansion of the structure.     

Hydrothermal Synthesis and Structure of Fe<Subscript>6.36</Subscript>Mn<Subscript>0.64</Subscript>(PO<Subscript>3</Subscript>(OH))<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Abstract  

Single crystals of iron and manganese phosphate Fe_6.36Mn_0.64(PO₃(OH))₄(PO₄)₂ was synthesized by hydrothermal method. The compound crystallizes in the Fe₇(PO₄)₆ structure type and is isotypic with the solid solution \textM_{7 - \textx} \textM_\textx^￠ ( \textHPO₄ )₄ ( \textPO₄ )₂ {\text{M}}_{{7 - {\text{x}}}} {\text{M}}_{\text{x}}^{\prime} \left( {{\text{HPO}}_{4} } \right)_{4} \left( {{\text{PO}}_{4} } \right)_{2} where M is Fe, Co, Mg, Mn. The compound is triclinic, P-1, a = 6.571(5), b = 7.993(3), c = 9.547(2) Ǻ, α = 103.97(1)°, β = 109.29(2)°, γ = 101.57(3)°. The structure is based on a three-dimensional framework of distorted edge-sharing MO₆ and MO₅ polyhedra, forming infinite chains, which are interlinked by corner-sharing with PO₄ tetrahedra. The formula unit is centrosymmetric, with all atoms in general positions except for one Fe atom, which has site symmetry −1.     

Crystal structure of a new synthetic Ca,Li pentaborate: CaLi<Subscript>4</Subscript>[B<Subscript>5</Subscript>O<Subscript>8</Subscript>(OH)<Subscript>2</Subscript>]<Subscript>2</Subscript>

When studying the phase formation in the CaO-Li₂O-B₂O₃-H₂O system, a new Ca,Li pentaborate was synthesized under hydrothermal conditions. The structure of a new compound with the crystallochemical formula CaLi₄[B₅O₈(OH)₂]₂ (sp. gr. Pb2n, a = 8.807(7), b = 9.372(7), c = 8.265(6) Å, V = 682.2(9) ų, Z = 2, d_calcd = 2.43 g/cm³, automated SYNTEX-\(P\bar 1\) diffractometer, 2690 reflections, 2θ/θ scan, λMo) is refined up to R_hkl = 0.0557 in the anisotropic approximation of atomic thermal vibrations with allowance for the localized H atoms. The structure of the Ca,Li pentaborate is formed by (010) open boron—oxygen layers formed by two independent [B₅O₈(OH)₂]^3? pentagroups, with each of them being formed by three B tetrahedra and two B triangles. The structure framework consists of the above boron—oxygen layers bound by isolated Li tetrahedra. The Ca cations are localized in the centers of eight-vertex polyhedra located in the [001] channels of the Li,B,O framework. Comparative crystallochemical analysis of the new Ca,Li pentaborate and Li pentaborate of the composition Li₃[B₅O₈(OH)₂]-II showed that the anionic matrices of both compounds are completely identical, whereas some of the cationic positions are different.     

Structure refinement of cadmium cerium(IV) phosphate Cd<Subscript>0.5</Subscript>Ce<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Cadmium cerium orthophosphate Cd_0.5Ce₂(PO₄)₃ is synthesized by precipitation from aqueous solutions. The structure refinement from powder X-ray diffraction data is preceded by the sample preparation and structure solution. The refinement is carried out by the Rietveld method (ADP-2 diffractometer, Cu _Kα radiation, Ni filter, 15° < 2θ < 120°, 2θ-scan step 0.02°, counting time 10 s per step). All calculations are carried out using the WYRIET program (version 3.3) within the sp. gr. P2₁/n. The structure is refined with anisotropic displacement parameters for cations and isotropic displacement parameters for oxygen atoms.     

Two types of structural domains in Pb<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The conditions of the formation of suborientation states in multidomain and single-domain Pb₃(PO₄)₂ crystals are analyzed. It is shown that suborientation states belong to sets of two structurally different types of domains differing in the angle sign and the orientation of the axis of rotation with respect to the coordinate system of the paraelastic phase. These structural differences are proposed to be described by the Gibbs vector. It is concluded that this macroscopic parameter corresponds to cooperative displacement of some groups of atoms with respect to other groups, with the crystal matrix being at rest. It is found that the modulus of the Gibbs vector is proportional to the spontaneous-strain components and depends linearly on the crystallographic parameter c in the ferroelastic phase.     

Na(H<Subscript>2</Subscript>O)[Mn(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>(BP<Subscript>2</Subscript>O<Subscript>8</Subscript>)]: Crystal structure refinement

The crystal structure of synthetic manganese sodium borophosphate hydrate Na(H₂O)[Mn(H₂O)₂(BP₂O₈)] was refined based on X-ray diffraction data. The compound was prepared by soft hydrothermal synthesis in the MnCl₂-Na₃PO₄-B₂O₃-H₂O system. The unit-cell parameters are a= 9.602(1) Å, c= 16.037(3) Å, sp. gr. P6₅22, Z= 6, D _x = 2.57 g/cm³. The water molecules were found to be statistically distributed in the channels of the mixed anionic paraframework consisting of (BO₄) and (PO₄) tetrahedra and [MnO₄(H₂O)₂] octahedra. The hydrogen atoms of the water molecules coordinated to the Mn²⁺ cations were located and their positional and thermal parameters were refined. The crystal-chemical features of borophosphates of the general formula A _x M(H₂O)₂(BP₂O₈)(H₂O) are considered.     

Athermal Directions in KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> Crystal

All orientations of the phase normal, at which the phase of a light wave propagating through a crystal is independent of its temperature (athermal phase directions), have been numerically found for a KGd(WO₄)₂ crystal. There are two sets of such directions for each isonormal wave. Their intersection with the main planes of the optical indicatrix of the crystal yields four athermal directions in the planes orthogonal to the axes with the minimum and intermediate refractive indices and two directions in the plane orthogonal to the axis with the maximum refractive index.     

Synthesis and structure of new framework phosphates Li<Subscript>1/4</Subscript><Subscript>M</Subscript><Subscript>7/4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>(<Emphasis Type="Italic">M</Emphasis> = Nb,Ta)

New lithium-niobium and lithium-tantalum phosphates Li_1/4 M _7/4(PO₄)₃(M = Nb, Ta) are synthesized by the solid-phase method. The compounds prepared are characterized using electron microprobe analysis, X-ray powder diffraction, and IR spectroscopy. The crystal structure of the Li_1/4Ta_7/4(PO₄)₃ phosphate is determined from the X-ray powder diffraction data (the Rietveld method) and belongs to the framework type. The framework of the structure consists of TaO₆ and LiO₆ vertex-shared octahedra and PO₄ tetrahedra. The isostructural phosphates Li_1/4 M _7/4(PO₄)₃ crystallize in the trigonal crystal system (space group R \(\bar 3\) c, Z = 6) and belong to the NaZr₂(PO₄)₃ structure type.