New phosphate Fe0.5Nb1.5(PO4)3 with an electrically neutral framework. Synthesis and crystal structure

A new iron-niobium phosphate, Fe_0.5Nb_1.5(PO₄)₃, has been prepared and studied by X-ray diffraction, electron microprobe analysis, IR spectroscopy, and neutron powder diffraction. On the basis of X-ray powder data, it was found that the synthesized phosphate crystallizes into the sp. gr. R $\bar 3$ c and corresponds to the structural type of sodium-zirconium phosphate NaZr₂(PO₄)₃. The structure was refined by the Rietveld method based on a powder neutron diffraction experiment. The obtained phosphate belongs to complex niobium orthophosphates and has a framework structure with a zero framework charge.     

Crystal structures of double cesium zirconium and barium zirconium orthophosphates

Double cesium zirconium and barium zirconium orthophosphates with the compositions CsZr₂(PO₄)₃ and Ba_0.5Zr₂(PO₄)₃, respectively, were prepared by thermal treatment of stoichiometric gels. The samples were characterized by electron-probe microanalysis and powder X-ray diffraction analysis. The crystal structures of both phosphates were refined by the Rietveld method within the space groups R\(\bar 3\)c and R\(\bar 3\), respectively, with isotropic atomic displacement parameters for all atoms.     

Synthesis and crystal chemical characteristics of the structure of <Emphasis Type="Italic">M</Emphasis><Subscript>0.5</Subscript>Zr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> phosphates

Double phosphates of zirconium and metals with an oxidation degree of +2 of the composition M_0.5Zr₂(PO₄)₃ (M = Mg, Ca, Mn, Co, Ni, Cu, Zn, Sr, Cd, and Ba) are synthesized and characterized by X-ray diffraction methods and IR spectroscopy. The crystal structures of all the compounds are based on three-dimensional frameworks of corner-sharing PO₄-tetrahedra and ZrO₆-octahedra. Phosphates with large Cd²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ cations octahedrally coordinated with oxygen atoms form rhombohedral structures (space group R3), whereas phosphates with small tetrahedrally coordinated Mg²⁺, Ni²⁺, Cu²⁺, Co²⁺, Zn ²⁺, and Mn²⁺-cations are monoclinic (space group P2₁/n). The effect of various structure-forming factors on the M_0.5Zr₂(PO₄)₃ compounds with a common structural motif but different symmetries are discussed.     

Calcium thorium phosphate (Whitlockite-type mineral). Synthesis and structure refinement

The crystal structure of a new calcium thorium phosphate has been refined by the full-profile Rietveld method using X-ray powder diffraction data. The sample has been synthesized by the sol-gel technique. The phosphate has been identified by X-ray powder diffraction and IR spectroscopy. The refined composition is represented by the formula Ca_10.26Th_0.12(PO₄)₇. The CaO _n and PO₄ polyhedra are distorted compared to the corresponding polyhedra in the basic compound β-Ca₃(PO₄)₂.     

Crystal structure of tveitite-(Y): Fractionation of rare-earth elements between positions and the variety of defects

The crystal structure of the mineral tveitite-(Y) (Y_0.883Na_0.106) (Ca_0.841 LREE _0.159)(Ca_0.716Na_0.204 HREE _0.080)(Ca_0.092Na_0.074)F_6.952 from amazonite pegmatites of Rov-Gora Mountain (Keivy, Kola Peninsula) is determined using X-ray diffraction (Stoe IPDS diffractometer, λMoK _α, graphite monochromator, 2θ_max = 63.5°, R = 0.051 for 1542 reflections). The main crystal data are as follows: a = 17.020(2) Å, c = 9.679(2) Å, V = 2428.2(4) ų, space group $R\bar 3$ , Z = 18, and ρ_calcd = 4.00 g/cm³. The idealized structural formula of the mineral is represented as (Y,Na)₆(Ca,LREE)₆(Ca,Na,HREE)₆(Ca,Na)F₄₂ (Z = 3). The defect structure of the mineral manifests itself in a mixed occupation of all four independent cation positions and in a randomly disordered distribution of fluorine atoms over the majority of anion positions. It is shown that the crystal structure of tveitite-(Y) fulfills the function of an “Eratosthenes sieve” for yttrium cations and two groups of lanthanide cations, so that these cations are distributed over three different positions.     

Synthesis and crystal structure of novel complex phosphate Li5Cu2Al(PO4)4

A new complex phosphate Li₅Cu₂Al(PO₄)₄ has been obtained by the flux method in the Cs-Li-Cu-V-P-O system. Its crystal structure has been determined by X-ray diffraction (R ₁ = 2.74%) to be as follows: sp. gr. $P\bar 1$ , a = 4.860(5) Å, b = 7.788(5) Å, c = 8.324(5) Å, α = 69.542(5)°, β = 90.016(5)°, γ = 75.318(5)°, Z = 1, and V = 284.2(4) ų. The compound under study has a dense structure and a three-dimensional framework build up of [LiO₅], [AlO₆], [Cu/LiO₅], and [CuO₄] polyhedra and [PO₄] tetrahedra. A comparative crystal-chemical analysis of two isotypic compounds with a general formula Li₅Cu₂ M(PO₄)₄ (M = Fe, Al) has been performed. Topological relations between the Na₂Mg₅(PO₄)₄ and Li₅Cu₂ M(PO₄)₄ crystal structures, which are characterized by different cationic compositions, are revealed.     

Synthesis and structure of zirconium and 3d-transition metal phosphates M 0.5Zr2(PO4)3(M = Mn, Co, Ni, Cu, Zn)

Double zirconium and 3d-transition metal phosphates of the compositions M 0.5Zr2(PO4)3[M = Mn (I), Co (II), Ni (III), Cu (IV), Zn (V)] have been synthesized and the types of their structures have been refined. Compounds I, II, III, IV, and V are all monoclinic (sp. gr. P2₁/n, Z = 4) and have the unit cell parameters a = 12.390(3), 12.389(3), 12.385(3), 12.389(3), 12.389(2) Å; b = 8.931(4), 8.928(3), 8.924(4), 8.925(4), 8.929(3) Å; c = 8.843(3), 8.840(2), 8.840(3), 8.841(3), 8.842(2) Å, β = 90.55(1), 90.54(1), 90.53(1), 90.53(1), 90.54(1)°; V = 978.5, 977.7, 977.0, 977.4, 978.1 ų, respectively. All the structures have the {[Zr₂(PO₄)₃]^?}3_∞-type frameworks. The crystallographic data for 3d-transition and alkali earth metal phosphates described by the general formula M _0.5Zr₂(PO₄)₃ are compared.     

Hole defects in the crystal structure of synthetic lipscombite (Fe 4.7 3+ Fe 2.3 2+ )[PO4]4O2.7(OH)1.3 and genetic crystal chemistry of minerals of the lipscombite-barbosalite series

The crystal structure of a synthetic analog of the mineral lipscombite (Fe _2.3 ²⁺ Fe _4.7 ³⁺ )[PO₄]₄O_2.7(OH)_1.3 obtained under hydrothermal conditions in the LiF-Fe₂O₃-(NH₄)₂HPO₄-H₂O system is resolved (R = 0.040) by X-ray diffraction analysis (Bruker Smart diffractometer with a highly sensitive CCD detector, MoK _α radiation): a = 14.776(3) Å, b = 14.959(3) Å, c = 7.394(1) Å, β = 119.188(4)°, sp. gr. C2/c, Z = 4, ρ_exp = 3.8 g/cm³, ρ_calcd = 3.9 g/cm³. Fe²⁺ and Fe³⁺ cations are statistically distributed in each of four crystallographically independent positions, while occupying the corresponding octahedra with probabilities of 60, 90, 100, and 91%. The ratio Fe²⁺/Fe³⁺ in the composition of the crystals was established by Mössbauer spectroscopy. Lipscombite is interpreted as a mineral of variable composition described by the formula (Fe _x ²⁺ Fe _n?x ³⁺ )[PO₄]₄O_y(OH)_4?y . The field of stability is determined as a function of the iron content and the ratio Fe²⁺/Fe³⁺. It is shown that at n = 6 iron cations are ordered in octahedra and barbosalite structure is formed. An interpretation of genetically and structurally related members of the lipscombite family within a unified polysomatic series is proposed.     

Synthesis and structure of iron zirconium phosphate Fe1/3[Zr2(PO4)3]

Iron zirconium phosphate Fe_1/3 [Zr₂(PO₄)₃] is synthesized by heat treatment of gels with the stoichiometric composition of components. The compound prepared is characterized using electron probe microanalysis, X-ray diffraction, and IR spectroscopy. The crystal structure of the Fe_1/3[Zr₂(PO₄)₃] phosphate is refined in space group P2₁/n by the Rietveld method in the isotropic approximation for atomic displacements of all elements.     

Crystallochemical modeling, synthesis, and study of new tantalum and niobium phosphates with a framework structure

A crystallochemical approach is used to model the compositions of phosphates of pentavalent elements with the expected structure. New phosphates with a framework structure of the T ₂ ^I T ₃ ^2/III T ₁ ^2/V (PO₄)₃ type (T ^I = Na or K; T ^III = Al, Cr, or Fe; and T ^V = Nb or Ta) are synthesized and characterized by X-ray diffraction analysis (including high-temperature diffraction) and IR spectroscopy. It is established that, depending on the nature of the alkali cation (Na or K), these compounds are crystallized in two structural modifications: rhombohedral and cubic (sp. gr. R $\bar 3$ c and P2₁3, respectively). The unit-cell parameters and the thermal expansion coefficients of the phosphates under study are determined and the dependences of these characteristics on the nature of cations are established.     

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.     

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.     

Crystal structure of the double magnesium zirconium orthophosphate at temperatures of 298 and 1023 K

Double magnesium zirconium orthophosphate Mg_0.5Zr₂(PO₄)₃ is synthesized by the sol-gel method. The compound prepared is characterized using electron probe microanalysis and X-ray diffraction. The crystal structure of the orthophosphate is refined by the Rietveld method in space group P2₁/n (Z = 4) at temperatures of 298 K [a = 12.4218(2) Å, b = 8.9025(2) Å, c = 8.8218(2) Å, β = 90.466(1)°] and 1023 K [a = 12.4273(5) Å, b = 8.9453(4) Å, c = 8.8405(4) Å, β = 90.320(3)°]. It is demonstrated that an increase in the temperature leads to an anisotropic expansion of the unit cell of the phosphate structure, but the structural type remains unchanged.     

Crystal structures of double vanadates, Ca9 R(VO4)7 ⋅ III. R = Nd, Sm, Gd, or Ce

The crystal structures of Ca₉ R(VO₄)₇ (R = Nd (I), Sm (II), or Gd (III)) were studied by the Rietveld method. The compounds are isostructural to Ca₃(VO₄)₂ and are crystallized in the trigonal system (sp. gr. R3c, Z = 6). The unit-cell parameters are as follows: for I, a = 10.8720(5) Å, c = 38.121(1) Å; for II, a = 10.8652(5) Å, c = 38.098(1) Å; and for III, a = 10.8631(5) Å, c = 38.072(1) Å. In the structures of I and II, the M(1), M(2), and M(3) positions are statistically occupied by the rare-earth cations and calcium anions. In the structure of III, the Gd³⁺ cations occupy the _M(1) and _M(2) positions. The distributions of the R ³⁺ cations over the positions are characteristic of each structure. The composition of the cerium-ontaining compound Ca_9.81Ce_0.42(VO₄)₇ (a = 10.8552(5) Å, c = 38.037(1) Å) was refined and its crystal structure was solved from the X-ray powder data. In this compound, cerium atoms are in the oxidation states +3 and +4.     

Crystal structure and IR spectroscopic study of (CN3H6)2[(UO2)2(C2O4)(CH3COO)4]

Compound (CN₃H₆)₂[(UO₂)₂(C₂O₄)(CH₃COO)₄] is synthesized and characterized by IR spectroscopy and single-crystal X-ray diffraction [a = 8.5264(2) Å, b = 13.8438(4) Å, c = 10.7284(2) Å, β = 103.543(1)°, space group P2₁/n, Z = 2, and R = 0.0258]. The main structural units of the crystals are binuclear [(UO₂)₂C₂O₄(CH₃COO)₄]^2? groups, which belong to the A ₂ K ⁰² B ₄ ⁰¹ crystal chemical group of uranyl complexes (A = UO ₂ ²⁺ , K ⁰² = C₂O ₄ ^2? , and B ⁰¹ = CH₃COO^?). The coordination polyhedron of the uranium atom is the UO₈ hexagonal bipyramid with the oxygen atoms of the uranyl ion at the axial positions. Uranium-containing groups and guanidinium cations are connected by electrostatic interactions and by the hydrogen bond system, which involves hydrogen atoms of guanidinium cations and oxygen atoms of oxalate and acetate anions. The results of the spectroscopic study of the compound agree with the X-ray diffraction data.     

Crystal structure of [Rb0.24(H2O)0.76]VO(H2O)(PO4), a new monoclinic variety in the series of layered vanadyl phosphates

The crystal structure of a new monoclinic variety of hydrous rubidium vanadyl phosphate [Rb_0.24(H₂O)_0.76]VO(H₂O)(PO₄) doped with Al³⁺ ions is studied by X-ray (R = 0.054) diffraction: a = 6.2655(4) Å, b = 6.2712(3) Å, c = 6.8569(5) Å, β = 107.805(7)°, space group P2₁/m, Z = 2, and D _x = 2.792 g/cm³. The new phase obtained by the hydrothermal synthesis in the V₂O₅-Rb₂CO₃-AlPO₄-H₂O system has a layer-type structure in which Rb atoms and water molecules are located between layers of vertexsharing [VO₅(H₂O)] octahedra and [PO₄] tetrahedra. Rb intercalates based on VOPO₄ · 2H₂O are described by general formula [Rb _x (H₂O)_{1 ? x} ]V _1?x ^V V _x ^IV O(H₂O)(PO₄), where x ≤ 0.5, and the amount of reduced vanadium and interlayer water molecules is determined by the amount of introduced rubidium atoms.     

Search for compounds of the NaBaR(BO3)2 family (R = La, Nd, Gd, and Yb) and the new NaBaYb(BO3)2 orthoborate

A search for compounds of the NaBaR(BO₃)₂ composition (where R = La³⁺, Nd³⁺, Gd³⁺, or Yb³⁺) is performed by solid state synthesis and spontaneous crystallization. A new compound, NaBaYb(BO₃)₂, is found in this series. It crystallizes in space group $R\bar 3$ and belongs to the family of sublayer complex orthoborates with isolated BO₃ groups NaBaR(BO₃)₂ (R = Y, Sc, and Yb). Theoretical X-ray powder diffraction patterns of NaBaY(BO₃)₂, NaBaSc(BO₃)₂, and NaBaYb(BO₃)₂ are calculated based on single-crystal data.     

Crystal structure of magnesioferrikatophorite

The crystal structure of the Na,Ca-amphibole magnesioferrikatophorite found in carbonatites from the Turiy Cape (Kola Peninsula) was refined (Siemens P4 diffractometer, λMoK _α radiation, 1481 independent reflections with |F|>4σ(F), anisotropic refinement, R(F) = 0.039). The parameters of the monoclinic unit cell are a = 9.875(5) Å, b = 18.010(8) Å, c = 5.309(3) Å, β = 104.39(5)°, sp. gr. C2/m, Z = 2. The distribution of the cations over the crystallographically nonequivalent M(1–4)-positions was revealed by Mössbauer spectroscopy and X-ray diffraction analysis. The character of splitting of the A-position correlates with the characteristic features of the magnesioferrikatophorite composition. The resulting structural formula (Na_0.87K_0.13)_{Σ = 1} · (Na_1.18Ca_0.82)_{Σ = 2}(Mg_1.41Fe _0.42 ³⁺ Ti _0.17 ⁴⁺ )_{Σ= 2} Fe _1.31 ³⁺ Mg_0.69)_{Σ = 2}(Mg_0.60Fe _0.38 ²⁺ Mn_0.02)_{Σ = 1}(Si_3.16Al_0.84)_{Σ = 4} · Si₄O₂₂(O_1.05OH_0.66F_0.29)_{Σ= 2} agrees well with the electron microprobe analysis data. Based on the zonal character of the crystal and high Fe ³⁺ content, the conditions of crystallogenesis are defined as oxidative against the background of a decrease in the Na potential in the course of the evolution of a mineral-forming system.     

Cation distribution in the structure of titanium-containing ludwigite

The crystal structure of natural titanium-containing ludwigite has been refined. The unit-cell parameters are a = 9.260 ± 0.002 Å, b = 12.294± 0.002 Å, c = 3.0236± 0.0005 Å, sp. gr. Pbam, and R = 0.0288. The observed cation distribution over the M1-M4 positions corresponds to the structural formula (Mg_0.5)(Mg_1.0)(Mg_0.338Fe _0.162 ²⁺ )(Fe _0.47 ³⁺ Ti _0.21 ⁴⁺ Mg _0.15 ²⁺ Al _0.10 ³⁺ Fe _0.07 ²⁺ (BO₃)O₂. Highly charged titanium ions in the M4 position are balanced mainly with magnesium and not with divalent iron ions.