Vanadate phosphates LiZr2(VO4)x(PO4)3 –x are synthesized by the sol-gel technique with subsequent annealing and studied using X-ray diffraction analysis, IR spectroscopy, synchronous differential scanning calorimetry, thermogravimetric analysis, and impedance spectroscopy. In the LiZr2(VO4)x(PO4)3 –x system, a limited series of solid solutions (0 ≤ х ≤ 0.8) with the NASICON (Sc2(WO4)3) structure forms. An increase in the vanadium content in the LiZr2(VO4)x(PO4)3 –x system leads to an increase in the lithium-ionic conductivity which reaches 6.3 × 10–3 S/cm for LiZr2(VO4)0.6(PO4)2.4 at 570 K. At elevated temperature, the temperature dependences of conductivity of samples with x = 0.4–0.8 demonstrate kinks associated with dissolution of silver from electrodes in these materials.

Mg0.5Zr2(AsO4)x(PO4)3 − x arsenate phosphates have been prepared by a sol–gel process and characterized by X-ray diffraction, IR spectroscopy, and impedance spectroscopy. The results indicate the formation of a continuous series of solid solutions with the Sc2(WO4)3 structure (sp. gr. P21/n) in the composition range 0 < x < 3. The unit-cell parameters of the solid solutions increase linearly with composition, as a consequence of arsenic substitution for phosphorus, which has a smaller ionic radius. The number of observed stretching and bending bands of the AsO 4 3- and PO 4 3- ions in the IR spectra of the solid solutions agrees with that predicted by factor group analysis for space group P21/n. The observed gradual shift of the absorption bands of the AsO4 tetrahedra to lower frequencies with increasing arsenic content on the tetrahedral site supports the X-ray diffraction evidence of the formation of substitutional solid solutions. The cation conductivity of Mg0.5Zr2(AsO4)x(PO4)3 − x with 0 ≤ х ≤ 1 has been shown to exceed the conductivity of the parent magnesium zirconium arsenate.

The temperature dependence of heat capacity C ° p = f ( T ) of crystalline arsenate Mg 0.5 Zr 2 (AsO 4 ) 3 was studied by precision adiabatic vacuum and differential scanning calorimetry in the temperature range 8−670 K. The standard thermodynamic functions C ° p ( T ), H °( T )– H °(0), S °( T ), and G °( T )– H °(0) of the arsenate for the range from Т → 0 to 670 K and the standard formation entropy at Т = 298.15 K were calculated from the obtained experimental data. Based on the low-temperature capacity data (30–50 K) the fractal dimension D of the arsenate was determined, and the topology of its structure was characterized. The results were compared with the thermodynamic data for the structurally related crystalline phosphates M 0.5 Zr 2 (PO 4 ) 3 (M = Mg, Ca, Sr, Ba, Ni) and arsenate NaZr 2 (AsO 4 ) 3 .

Arsenates A0.5Zr2(AsO4)3 (A = Mg, Ca, Sr, Ba), synthesized through sol–gel route with subsequent heat treatment, have been studied by X-ray diffraction, electron probe microanalysis, and IR spectroscopy. Mg0.5Zr2(AsO4)3 crystallizes in the Sc2(WO4)3 structure type (space group P21/n). A0.5Zr2(AsO4)3 (A = Ca, Sr, Ba) crystallize in the NaZr2(PO4)3 structure type (space group \(R\bar 3\)). The Ca0.5Zr2(AsO4)3 and Ba0.5Zr2(AsO4)3 structures have been refined by the full-profile analysis. The structure frameworks are composed of ZrO6 octahedra and AsO4 tetrahedra. The alkaline earth metal atoms occupy one of the two extraframework positions inside the structure columns. The internal vibrational frequencies of the AsO4 3- tetrahedron have been assigned. The number of the observed bands corresponds to the number predicted by the factor group analysis of vibrations for space groups \(R\bar 3\) and P21/n.

The catalytic activity of framework phosphates of the general formula LiZr2(VO4) x (PO4)3–x with different degrees of phosphorus replacement (x = 0, 0.1, 0.3, 0.4, 0.6, and 0.8) was studied in methanol transformations in an inert atmosphere. It was shown that the ratio between the activity and selectivity of the catalysts in dehydration and dehydrogenation reactions is determined by their vanadium content and the process temperature.

The thermal expansion parameters of the MZr 2 (AsO 4 ) 3 (M = Li, Na, K, Rb, Cs) arsenates and MZr 2 (TO 4 ) x (PO 4 ) 3– x (T = As, V) arsenate phosphate and vanadate phosphate solid solutions with the NaZr 2 (PO 4 ) 3 (NZP) structure have been determined by high-temperature X-ray diffraction. The effects of the size of the alkali metal cation and arsenic or vanadium substitution for phosphorus on the thermal expansion of the arsenates and solid solutions have been studied systematically. The potassium-, rubidium-, and cesium-containing arsenates, arsenate phosphates, and vanadate phosphates are low-expansion materials (αav < 2 × 10 –6 °C –1 ); sodium zirconium arsenate and sodium zirconium and lithium zirconium arsenate phosphates and vanadate phosphates have intermediate thermal expansion (3 × 10 –6 °C –1 < αav < 7 × 10 –6 °C –1 ); and lithium zirconium arsenate is a high-expansion material (αav = 9.9 × 10 –6 °C –1 ). The present results demonstrate that, increasing the size of the alkali metal cation in the arsenates and varying the composition of the solid solutions, one can produce NZP materials with controlled linear thermal expansion coefficients and extremely low thermal expansion anisotropy.

The LiZr2(AsO4)(3) arsenate and LiZr2(AsO4) (x) (PO4)(3 - x) solid solutions have been prepared through precipitation followed by heat treatment, and characterized by X-ray diffraction, X-ray structure analysis, IR spectroscopy, and impedance spectroscopy. We have established conditions for the crystallization of the arsenate and a continuous series of arsenate phosphate solid solutions (0 a parts per thousand currency sign x a parts per thousand currency sign 3), which have been obtained as two polymorphs: monoclinic and hexagonal. Using the Rietveld method, we have refined the crystal structures of the polymorphs of LiZr2(AsO4)(3) (sp. gr. P2(1)/n, a = 9.1064(2), b = 9.1906(2), c = 12.7269(3) , beta = 90.844(2)A degrees, V =1065.03(5) (3), Z = 4; sp. gr. R c, a = 9.1600(4), c = 22.9059(13) , V = 1664.44(14) , Z = 6) and LiZr2(AsO4)(1.5)(PO4)(1.5). Their structural frameworks are built up of AsO4 tetrahedra-or (As,P)O-4 tetrahedra occupied by arsenic and phosphorus atoms at random-and ZrO6 octahedra, with the lithium atoms in between. The ionic conductivity of the materials has been measured. The cation conductivity of monoclinic LiZr2(AsO4) (x) (PO4)(3 - x) with 0 a parts per thousand currency sign x a parts per thousand currency sign 1 has been shown to exceed the conductivity of lithium zirconium phosphate.

The LiZr2(AsO4)3 arsenate and LiZr2(AsO4) x (PO4)3 − x solid solutions have been prepared through precipitation followed by heat treatment, and characterized by X-ray diffraction, X-ray structure analysis, IR spectroscopy, and impedance spectroscopy. We have established conditions for the crystallization of the arsenate and a continuous series of arsenate phosphate solid solutions (0 ≤ x ≤ 3), which have been obtained as two polymorphs: monoclinic and hexagonal. Using the Rietveld method, we have refined the crystal structures of the polymorphs of LiZr2(AsO4)3 (sp. gr. P21/n, a = 9.1064(2), b = 9.1906(2), c = 12.7269(3) Å, β = 90.844(2)°, V =1065.03(5) Å3, Z = 4; sp. gr. R \(\bar 3\) c, a = 9.1600(4), c = 22.9059(13) Å, V = 1664.44(14) Å, Z = 6) and LiZr2(AsO4)1.5(PO4)1.5. Their structural frameworks are built up of AsO4 tetrahedra—or (As,P)O4 tetrahedra occupied by arsenic and phosphorus atoms at random—and ZrO6 octahedra, with the lithium atoms in between. The ionic conductivity of the materials has been measured. The cation conductivity of monoclinic LiZr2(AsO4) x (PO4)3 − x with 0 ≤ x ≤ 1 has been shown to exceed the conductivity of lithium zirconium phosphate.

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.

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) Å3, 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) Å3, 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.