Synthesis and phase formation in M 0.5(1+x) 2+ FexTi2−x (PO4)3 phosphate series

New complex phosphates of titanium, iron, and alkaline-earth metals have been synthesized. X-ray powder diffraction, differential thermal analysis (DTA), and IR spectroscopy are used to study phase formation in the series of M_0.5(1+x)Fe_xTi_2?x (PO₄)₃ (M = Mg, Ca, Sr, Ba) phosphates. Individual compounds and solid solutions are found to crystallize in the NaZr₂(PO₄)₃ and K₂Mg₂(SO₄)₃ structure types. Their crystal parameters are calculated. CaFeTi(PO₄)₃ is studied using Mössbauer spectroscopy. Its structure is refined by the Rietveld method: space group $R\bar 3$ c, Z = 6, a = 8.5172(1), Å, c = 21.7739(4) Å, V = 1367.91(4) ų.     

Phosphates having the NaZr2(PO4)3 structure and containing titanium (or zirconium) and elements in oxidation degree 2+ (calcium or zinc)

Complex phosphates Ca_{0.5 + x} Zn _x E_{2 ? x} (PO₄)₃ (E = Ti, Zr) having NaZr₂(PO₄)₃ (NZP) structure have been prepared and characterized by X-ray diffraction, electron probe microanalysis, IR spectroscopy, and differential thermal analysis (DTA). Their phase formation has been studied by X-ray powder diffraction and DTA. The concentration and temperature fields of existence of these NZP phases have been determined: substitution solid solutions exist in the range of compositions where 0 ≤ x ≤ 0.5. The Ca_0.7Zn_0.2Ti_1.8(PO₄)₃ crystal structure has been refined by the Rietveld method (space group \(R\bar 3\) , a = 8.3636(4) Å, c = 21.9831(8) Å, V = 1331.7(1) ų, Z = 6). The framework in the NZP structure is built of octahedra, which are populated by titanium and zinc atoms, and PO₄ tetrahedra. Calcium atoms occupy extraframework positions. Extensive solid solution formation due to the accommodation of cations(2+) in the interstices within the NZP framework (M) and in the framework-forming octahedra (M′) makes it possible to design a plurality of new M_{0.5 + x} M′ _x E_{2 ? x} (PO₄)₃ phosphates with tailored structures.     

Synthesis and structure of alkali metal zirconium vanadate phosphates

Mixed vanadate phosphates in the systems MZr₂(VO₄) _x (PO₄)_{3 ? x} , where M is an alkali metal, were synthesized and studied by X-ray diffraction, electron probe microanalysis, and IR spectroscopy. Substitutional solid solutions with the structure of the mineral kosnarite (NZP) are formed at the compositions 0 ≤ x ≤ 0.2 for M = Li; 0 ≤ x ≤ 0.4 for M = Na; 0 ≤ x ≤ 0.5 for M = K; 0 ≤ x ≤ 0.3 for M = Rb; and 0 ≤ x ≤ 0.2 for M = Cs. Apart from the high-temperature NZP modification, lithium vanadate phosphates LiZr₂(VO₄) _x (PO₄)_{3 ? x} with 0 ≤ x ≤ 0.8 synthesized at temperatures not exceeding 840°C crystallize in the scandium tungstate type structure. The crystal structures of LiZr₂(VO₄)_0.8(PO₄)_2.2 (space group P2₁/n, a = 8.8447(6) Å, b = 8.9876(7) Å, c = 12.3976(7) Å, β = 90.821(4)○, V = 985.4(1) ų, Z = 4) and NaZr₂(VO₄)_0.4(PO₄)_2.6 (space group $R\bar 3c$ = 8.8182(3) Å, c = 22.7814(6) Å, V = 1534.14(1) ų, Z = 6) were refined by the Rietvield method. The framework of the vanadate phosphate structure is composed of tetrahedra (that are statistically occupied by vanadium and phosphorus atoms) and ZrO₆ octahedra. The alkali metal atoms occupy extra-framework sites.     

Thermal synthesis and structural characterization of the orthorhombic Th2(PO4)(P3O10)

Polycrystalline thorium(IV) phosphate-triphosphate, Th₂(PO₄)(P₃O₁₀) (1), was obtained by (NH₄)₂Th(PO₄)₂·H₂O (2) heating from room temperature to 1,273 K. 1 crystallizes in the orthorhombic space group Pn2₁ a (a = 11.6846(2) Å, b = 7.1746(1) Å, c = 12.9320(3) Å, Z = 4). Combining powder synchrotron X-ray diffraction data and DFT geometry optimization, a structural model is proposed for 1. The structure is built on ThO₈ polyhedral chains along the b-axis. PO₄ ^3? and P₃O₁₀ ^5? groups coexist in the structure and the latter group forms non-linear chains. Cohesion of the structure is made by the linkage of ThO₈ chains by PO₄ and P₃O₁₀ groups. Thermal transformation from 2 to 1 was monitored by thermogravimetric analysis (activation energy as a function of the extent of conversion was obtained from Kissinger–Akahira–Sunose (KAS) isoconversional method) and powder X-ray thermo-diffraction. For 2, the dehydration process takes place in two steps, with the apparition of a layered intermediate phase, (NH₄)₂Th(PO₄)₂·nH₂O (0 < n < 1, d = 6.42 Å), previously to the formation of (NH₄)₂Th(PO₄)₂ (d = 6.31 Å). The condensation process produces an amorphous material that crystallizes to α-ThP₂O₇ (3) when the temperature increases. At 1,273 K, 3 slowly transforms to 1.     

Equilibria of aqueous solutions of isopolyniobotungstates-6 with c Nb : c W = 1 : 5

Complex formation in the Nb₆O ₁₉ ^8? -WO ₄ ^2? -H⁺-H₂O system with c _Nb : c _W = 1 : 5 and varied c _{Nb + W} ⁰ = 10^?2, 5 × 10^?3, 2.5 × 10^?3, and 10^?3 mol/L) has been studied. Distribution diagrams were simulated for individual niobium(V) and tungsten(VI) isopolyanions and mixed isopolyniobotungstates for $Z = \frac{{c_{H^ + }^0 }}{{c_{Nb + W}^0 }} = 0 - 3.0$ in an NaCl background electrolyte. We have shown that isopolyniobotungstates-6 of composition H _x NbW₅O ₁₉ ^{(3 ? x)?} are formed via H _x Nb _n W_6?n O ₁₉ ^{(2 + n ? x)?} (n=2, 3, 5) ions. The concentration formation constants and thermodynamic formation constants of isopolyniobotungstate anions (IPNTAs) in aqueous solution have been calculated. Salt Tl₃NbW₅O₁₉·9H₂O has been synthesized and identified by chemical analysis and IR spectroscopy.     

Synthesis and crystal structure of new sodium oxothiocyanofluoroantimonate(III) Na2Sb5F9O3(NCS)2

Na₂Sb₅F₉O₃(NCS)₂, a new complex, has been synthesized from NaSCN and SbF₃ aqueous solutions and studied by chemical, X-ray diffraction, and thermal analyses and IR, ^121,123Sb NQR, and ¹⁹F NMR spectroscopy. Its layered structure (triclinic symmetry system, a = 6.9998(1) Å, b = 9.4180(1) Å, c = 13.1094(2) Å, α = 74.815(1)°, β = 78.188(1)°, γ = 82.779(1)°, Z = 2, space group P $\bar 1$ ) is built of Na⁺ cations and [Sb₁₀F₁₈O₆(NCS)₄]^4? decanuclear complex anions that consist of two [Sb₅F₉O₃(NCS)₂]^2? pentanuclear complex anions linked by two weak Sb-F ionic bonds (2.529(2) Å). Decanuclear complex anions are linked into layers by secondary Sb…F bonds and Na-F bonds. Van der Waals interactions link these layers into a framework. The complex is stable up to 200°C.     

Crystal structure of (C2H7N4O)2[UO2(C2O4)2(H2O)]

The single crystals of (C₂H₇N₄O)₂[UO₂(C₂O₄)₂(H₂O)] were studied by X-ray diffraction. The crystals are monoclinic, space group Pn, Z = 2, unit cell parameters: a = 9.4123(2) Å, b = 8.4591(2) Å, c = 11.8740(3) Å, β = 105.500(10)°, V = 911.02(4) ų. The main structural units of the crystals of I are islet complex groups [UO₂(C₂O₄)₂(H₂O)]^2? corresponding to the crystal chemical group AB ₂ ⁰¹ M¹ (A = UO UO ₂ ²⁺ , B⁰¹ = C₂O ₄ ^2? , M = H₂O) of uranyl complexes. Uranium-containing mononuclear complexes are connected into a three-dimensional framework through the electrostatic interactions and hydrogen bonding system involving carbamyolguanidinium ions.     

Crystal structure of (C2H7N4O)2[(UO2)2)(OH)2(C2O4)(CHO2)2]

An X-ray diffraction study of the single crystals of (C₂H₇N₄O)₂[(UO₂)₂(OH)₂(C₂O₄)(CHO₂)₂] was carried out. The compound crystallizes in the triclinic system, space group $P\bar 1$ , Z = 2, a = 5.5621(8) Å, b = 8.1489(10) Å, c = 11.8757(16) Å, α = 88.866(7)°, β = 82.204(6)°, γ = 87.378(6)°, V = 532.7(1) ų, ρ_calcd = 2.988 g/cm³. The main structural units in the crystal are the [(UO₂)₂(OH)₂(C₂O₄)(CHO₂)₂)]^2? chains corresponding to the crystal chemical group A₂M ₂ ² K⁰²M ₂ ¹ (A = UO ₂ ²⁺ , M² = OH^?, K⁰² = C₂O ₄ ^2? , M¹ = CHO ₂ ^? ) of uranyl complexes. The chains are united into a three-dimensional framework through the electrostatic interaction and hydrogen bonds involving uranyl, oxalate, and hydroxyl groups, formate ions, and 1-carbamoylguanidinium cations.     

Cationic mobility in Li3?2xNbxFe2?x(PO4)3 complex phosphates

Synthesis and ionic conductivity of Li_3−2x Nb _x Fe_2−x (PO₄)₃ complex phosphates were studied by X-ray powder diffraction and impedance spectroscopy. These phosphates are formed only at 900–1000°C. Variations in their thermal expansivity and unit cell parameters induced by aliovalent doping were characterized. The conductivity of these materials increases monotonically in the series Li_0.5Nb_1.25Fe_0.75(PO₄)₃-LiNbFe(PO₄)₃ and Li_1.2Nb_0.9Fe_1.1(PO₄)₃-Li₃Fe₂(PO₄)₃, which is explained by consecutive occupation of the Li(1) and Li(2) positions in their structures. Original Russian Text ? A.R. Shaikhlislamova, I.A. Stenina, A.B. Yaroslavtsev, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 12, pp. 1957–1962.     

Synthesis and characterization of phosphates in molten systems Cs2O-P2O5-CaO-M2O3 (M—Al, Fe, Cr)

The crystallization of complex phosphates from the melts of Cs₂O-P₂O₅-CaO-M^III₂O₃ (M^III—Al, Fe, Cr) systems have been investigated at fixed value Cs/P molar ratios equal to 0.7, 1.0 and 1.3 and Са/Р=0.2 and Ca/М^III=1. The fields of crystallization of CsCaP₃O₉, β-Ca₂P₂O₇, Cs₂CaP₂O₇, Cs₃CaFe(P₂O₇)₂, Ca₉M^III(PO₄)₇ (M^III—Fe, Cr), Cs_0.63Ca_9.63Fe_0.37(PO₄)₇ and CsCa₁₀(PO₄)₇ were determined. Obtained phosphates were investigated using powder X-ray diffraction and FTIR spectroscopy. Novel whitlockite-related phases CsCa₁₀(PO₄)₇ and Cs_0.63Ca_9.63Fe_0.37(PO₄)₇ have been characterized by single crystal X-ray diffraction: space group R3c, a=10.5536(5) and 10.5221(4) Å, с=37.2283(19) and 37.2405(17) Å, respectively.     

Homogeneity regions of double molybdates in the Na2MoO4-MgMoO4 system and structures of triclinic Na1.51Mg2.245(MoO4)3 and Na1.66Mn2.17(MoO4)3

In the samples of the Na₂MoO₄-MgMoO₄ system quenched in the air at above 600°C, by powder X-ray diffraction two double molybdates of variable composition are detected: monoclinic alluaudite-like Na_4?2x Mg_1+x (MoO₄)₃ (0.05 ≤ x ≤ 0.35) and triclinic Na_2?2y Mg_2+y (MoO₄)₃ (0.10 ≤ y ≤ 0.40) isostructural to previously studied Na₂Mg₅(MoO₄)₆. Sodium-magnesium molybdate of the Li₃Fe(MoO₄)₃ structure type is not revealed in this system. By spontaneous flux crystallization, the crystals are obtained and the structures of two triclinic double molybdates of the Na₂Mg₅(MoO₄)₆ structure type (space group $P\bar 1$ , Z = 1) containing magnesium and manganese are determined. The results of the refinement of site occupancies made it possible to determine the composition of the studied crystals: for the compound with magnesium (Na)_0.5(Na_0.255□_0.745)(Na_0.755Mg_0.245)Mg₂(MoO₄)₃ or Na_1.51Mg_2.245(MoO₄)₃ (a = 6.9577(1) Å, b = 8.6330(2) Å, c = 10.2571(2) Å, α = 106.933(1)°, β = 104.864(1)°, γ = 103.453(1)°, R = 0.0188); for the compound with manganese (Na)_0.5(Na_0.33□_0.67)(Na_0.83Mn_0.17)Mn₂(MoO₄)₃ or Na_1.64Mn_2.17(MoO₄)₃ (a = 7.0778(2) Å, b = 8.8115(2) Å, c = 10.4256(2) Å, α = 106.521(1)°, β = 105.639(3)°, Γ = 103.233(1)°, R = 0.0175). The Na₂Mg₅(MoO₄)₆ structure is redetermined and it is shown that actually it corresponds to the composition Na_1.40Mg_2.30(MoO₄)₃.     

Hydrothermal synthesis and characterization of (Na,K)Ti2(PO4)3 solid solutions

Na_1?x K_xTi₂(PO₄)₃ (0 ≤ x ≤ 1) solid solutions are synthesized through ion exchange under hydrothermal conditions and a sol-gel process. The unit cell parameters are calculated for (Na,K) titanium phosphates. Cation-exchange reactions in the NaTi₂(PO₄)₃-KTi₂(PO₄)₃-NaCl-KCl-H₂O system are studied at T = 973 K and p = 200 MPa. The solid phase with compositions in the range 0 ≤ x ≤ 0.7 is enriched with sodium; in the range 0.7 ≤ x ≤ 1.0, it is enriched with potassium. The excess functions of mixing for the solid solutions are described in terms of the Margules model. Titanium phosphates Na_1?x K_xTi₂(PO₄)₃ show greater nonideality than zirconium phosphates Na_1?x K_xZr₂(PO₄)₃ and lower thermodynamic stability in decay into pure components at high pressures and temperatures.     

Sol-gel synthesis and structure of MZr2(AsO4)3 arsenates and MZr2(AsO4) x (PO4)3 − x arsenate phosphates (M = K,Rb, Cs)

MZr₂(AsO₄)₃ arsenates and MZr₂(AsO₄) _x (PO₄)_{3 ? x} arsenate phosphates (M = K, Rb, Cs) have been obtained by sol-gel synthesis followed by heat treatment and have been characterized by X-ray diffraction, electron probe microanalysis, and IR spectroscopy. Continuous series of substitutional solid solutions form in the MZr₂(AsO₄) _x (PO₄)_{3 ? x} systems (0 ≤ x ≤ 3). The solid solutions have a kosnarite structure (KZr₂(PO₄)₃, space group \(R\bar 3c\) ). The crystal structures of MZr₂(AsO₄)₃ and MZr₂(AsO₄)_1.5(PO₄)_1.5 have been refined by full-profile analysis. The structural frameworks of these phases are built from ZrO₆ octahedra and AsO₄ tetrahedra or (As,P)O₄ tetrahedra statistically populated by arsenic and phosphorus atoms. The alkali metal atoms occupy extraframework sites. The effect of the crystal chemical properties of alkali metals on the formation of the structures of MZr₂(AsO₄)₃ arsenates (M = Li-Cs) and MZr₂(AsO₄) _x (PO₄)_{3 ? x} solid solutions is discussed.     

Phase formation, crystal structure, and electrical conductivity of triple phosphates of alkali metals and titanium

For triple phosphates of composition A′_0.5A_0.5 Ti₂(PO₄)₃ (A?A′=Li?Na, Na?K, K?Rb), phase formation is studied, the crystal structure is refined, and the electrical conductivity is measured. The compounds are classified with the NaZr₂(PO₄)₃ structure type (NZP, space group R $\bar 3$ c). The phosphate frameworks are built of TiO₆ octahedra and PO₄ tetrahedra. Extraframework positions M1 are fully occupied by randomly distributed alkali cations. Positions M2 are vacant. Correlations are found between the structural distortion and electrical conductivity of the phosphates, on one hand, and the alkali cation size, on the other.     

Synthesis,structure, and thermal expansion of sodium zirconium arsenate phosphates

Sodium zirconium arsenate phosphates NaZr₂(AsO₄) _x (PO₄)_3?x were synthesized by precipitation technique and studied by X-ray diffraction and IR spectroscopy. In the series of NaZr₂(AsO₄) _x (PO₄)_3?x , continuous substitution solid solutions are formed (0 ≤ x ≤ 3) with the mineral kosnarite structure. The crystal structure of NaZr₂(AsO₄)_1.5(PO₄)_1.5 was refined by full-profile analysis: space group R \(\bar 3\) c, a = 8.9600(4)Å, c = 22.9770(9) Å, V = 1597.5(1) ų, R _wp = 4.55. The thermal expansion of the arsenate-phosphate NaZr₂(AsO₄)_1.5(PO₄)_1.5 and the arsenate NaZr₂(AsO₄)₃ was studied by thermal X-ray diffraction in the temperature range of 20–800°C. The average linear thermal expansion coefficients (α_av = 2.45 × 10^?6 and 3.91 × 10^?6 K^?1, respectively) indicate that these salts are medium expansion compounds.     

On the intersecting tunnel structure of the monophosphates A3(V,W)4O9(PO4)2 with A = Rb,Tl, Cs

The structure determination of a single crystal with composition Rb₃V_1.63W_2.37O₉(PO₄)₂ shows that this phase belongs to the ‘KNbW’ type (K₃Nb₃WO₉(PO₄)₂). This intersecting tunnel structure which consists of octahedral [MO₃]_∞ chains interconnected with ‘MPO₉’ units is closely related to the ‘KVW’-type (K₃V₂W₂O₉(PO₄)₂), and differs only from the latter by the relative orientation of the [MO₃]_∞ chains. In the same way, the X-ray powder diffraction study of the phosphates A₃V₂W₂O₉(PO₄)₂ with A = Rb, Tl, Cs and Rb₃V_xW_{4 − x} O₉(PO₄)₂ (1.5 ≤ x ≤ 3), shows that they all belong to the same structural ‘KNbW’-type and not to the ‘KVW’-type. These results demonstrate the great flexibility of the ‘KNbW’ structure with regard to the ‘KVW’-structure only observed for one compound.     

Effect of TiO2 and SrO additions on some physical properties of 33Na2O–xSrO–xTiO2–(50 − 2x)B2O3–17P2O5 glasses

By means of the conventional quenching route, the glass series 33Na₂O–xSrO–xTiO₂–(50 ? 2x)B₂O₃–17P₂O₅ (x = 0–12.5 mol%) were prepared. The amorphous state of samples was verified by X-ray diffraction (XRD). Density, molar volume, micro-hardness, glass transition temperature (T _g), and crystallization temperature (T _c) parameters are determined for each glass. The results show that they depend strongly on the chemical compositions. The structure approach of the glasses is determined by Infrared spectroscopy (IR). This investigation highlights that the glassy-matrix contains various phosphate and borate structural units. The crystallization of the high-TiO₂ glasses by heat-treatments favors the formation of titanate phosphate Na₄TiO(PO₄)₂ or Sr_0.5Ti₂(PO₄)₃ along with Sr₃(PO₄)₂ inside the glass-matrix.     

Phase formation in the Ag2MoO4-CoMoO4-Al2(MoO4)3 system

The subsolidus region of the Ag₂MoO₄-CoMoO₄-Al₂(MoO₄)₃ ternary salt system was studied by X-ray powder diffraction analysis. New compounds Ag_1?x Co_1?x Al_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.4) and AgCo₃Al(MoO₄)₅ were detected to form. The variable-composition phase Ag_1?x Co_1?x Al_{1 + x} (MoO₄)₃ is of the NASICON structure type (space group \(R\bar 3c\) ). AgCo₃Al(MoO₄)₅ crystallizes in the triclinic symmetry (space group \(P\bar 1\) Z = 2) with the unit cell parameters a = 6.9101(6), b = 17.519(1), c = 6.8241(6) Å, α = 87.356(7)°, β = 101.078(7)°, and γ = 91.985(9)°. The compounds are thermally stable until 770–780 and 760°C, respectively.     

Ferrites YbSrFe2O5.5 and YbBaFe2O5.5: Synthesis and X-ray diffraction, thermodynamic, and electrophysical properties

Ferrites YbSrFe₂O_5.5 and YbBaFe₂O_5.5 are prepared by reacting ytterbium(III) oxide and iron(III) oxide with strontium or barium carbonate in the solid phase. The ferrites crystallize in the orthorhombic system as shown by indexing of their X-ray diffraction patterns with homology modeling: for YbSrFe₂O_5.5, a = 10.74 ± 0.006 Å, b = 10.93 ± 0.006 Å, c = 16.64 ± 0.046 Å, V ⁰ = 1953.3 ų, Z = 16, V _subcell ⁰ = 122.08 ų, ρ_X-ray = 6.26 g/cm³, ρ_pycn = 6.18 ± 0.9 g/cm³; for YbaBaFe₂O_5.5, a = 10.74 ± 0.013 Å, b = 10.99 ± 0.004 Å, c = 17.16 ± 0.017 Å, V ⁰ = 2025.4 ų, Z = 16, V _subcell ⁰ = 126.59 ų, ρ_X-ray = 6.69 g/cm³, ρ_pycn = 6.40 ± 0.32 g/cm³. The calorimetric heat capacities of the ferrites are studied from 298.15 to 673 K. The C _p ^o ～ f(T) curves show λ peaks at 448 K for YbSrFe₂O_5.5 and at 373 K for YbBaFe₂O_5.5, likely, due to second-order phase transitions. The dielectric constants and electrical resistances of the ferrites are studied as functions of temperature from 293 to 493 K.     

Synthesis and characterization of a NASICON phase of variable composition Na1 − x Ni1 − x Sc1 + x (MoO4)3 (0 ≤ x ≤ 0.5)

Subsolidus phase ratios in the Na₂MoO₄-NiMoO₄-Sc₂(MoO₄)₃ system have been studied using X-ray diffraction, differential thermal analysis, and vibrational spectroscopy. A phase of variable composition Na_{1 ? x} Ni_{1 ? x} Sc_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.5) having NASICON structure (space group \(R\bar 3c\) ) and a triple molybdate crystallizing in triclinic system (space group \(P\bar 1\) ) have been obtained. The high conductivity of Na_{1 ? x} Ni_{1 ? x} Sc_{1 + x} (MoO₄)₃ allows the phase of variable composition to be regarded as a promising sodiumion-conductive solid electrolyte.