M. A. Petrova

Crystal structures of Ln2TiO5 (Ln = Gd, Dy) polymorphs

Single crystals of four Ln2TiO5 polymorphs have been grown, and their structures have been determined: orthorhombic (Gd2TiO5, a = 10.460(5), b = 11.317(6), c = 3.750(3) Å, Pnam, Z = 4), hexagonal (Gd1.8Lu0.2TiO5, a = 3.663(3), c = 11.98(1) Å, P63/mmc, Z = 1.2), cubic (Dy2TiO5, a = 10.28(1) Å, Fd3m, Z = 10.4), and monoclinic (Dy2TiO5, a = 10.33(1), b = 3.653(5), c = 7.306(6) Å, β = 90.00(7)°, B2/m, Z = 2.4). The last polymorph has been identified for the first time.

Crystal Structures of Na2ZnP2O7, K2ZnP2O7, and LiKZnP2O7 Phases in the M2O–ZnO–P2O5 Glass-Forming System (M = Li, Na, and K)

The crystal structures of Na2ZnP2O7 and K2ZnP2O7 are determined from X-ray powder diffraction data. The structure of LiKZnP2O7 is determined using a single-crystal sample. In the alkali zinc phosphates studied, the Zn2+ cation is coordinated by four oxygen atoms of the phosphate tetrahedra. In the first two compounds, the [ZnP2O7]2– anion has the form of a sheet consisting of Zn and P oxygen-containing tetrahedra that involves only five-membered rings. In the LiKZnP2O7 structure, the zinc phosphate anion of the same composition has the form of a three-dimensional skeleton with a three-dimensional system of channels. These channels are linked via six-membered, eight-membered, and ten-membered rings. The atomic coordinates and interatomic distances are reported.

Specific features of the phase formation in the titanate systems Ln2TiO5-Ln′2TiO5 (Ln = La, Gd, Tb, Er; Ln′ = Tb, Lu)

The specific features in the crystal chemistry and phase formation of the systems Ln2TiO5-Ln′2TiO5 (Ln = La, Gd, Tb, Er; Ln′ = Tb, Lu) are established. The relation between the topology of the phase diagrams and the structure of the Ln2TiO5 compound is investigated as a function of the ionic radius of the rare-earth cation.

Synthesis and crystal structure of the low-temperature modification of lithium potassium zinc diphosphate LiKZnP2O7

A new polymorphic modification, α-LiKZnP2O7, has been synthesized, which is a low-temperature modification of the LiKZnP2O7 compound. The crystal structure is determined by the Rietveld method from the X-ray powder diffraction data. The compound crystallizes in the monoclinic system (space group Pc, a = 12.3621(3) Å, b = 5.0655(1) Å, c = 10.2365(3) Å, β = 90.88(1)°, Z = 2) and has a framework structure similar to that of the high-temperature β phase. The framework is formed by the diphosphate groups and the oxygen tetrahedra of the zinc and lithium atoms, which statistically uniformly occupy equivalent positions in the structure.

Crystal structure of the K2(Zn3P4O14) compound

Single crystals of potassium zinc phosphate, namely, K2(Zn3P4O14), are grown by crystallization of a glass of the related compound. The crystal structure of the compound is determined using single-crystal X-ray diffraction.

Mixed alkali-zinc diphosphates: Synthesis, structure, and properties

A series of mixed alkali-zinc diphosphates in the form of poly- and single crystals have been synthesized. Their physical-chemical, structural, and thermal characteristics have been determined. The compounds Na2ZnP2O7 and K2ZnP2O7 have a layered structural type, whereas LiNaZnP2O7, LiKZnP2O7, NaKZnP2O7, Li12Zn4(P2O7)5, and K2Zn3(P2O7)2 have a framework structural type.

Structures of two high-temperature Dy2TiO5 modifications

Single crystals of two structural modifications of high-temperature dysprosium titanate Dy2TiO were grown. Using X-ray diffraction, the crystal structure of the cubic modification (space group Fd3m, a = 10.28(1)Å, Z = 10.4) was refined and the structure of a new monoclinic modification (space group B2/m, a = 10.33(1)Å, b = 3.653(5)Å, c = 7.306(6)Å, β = 90.00(7)°, Z = 2.4), which crystallizes in minor amounts together with the cubic phase, was determined. The lowering of symmetry from cubic to monoclinic is due to different distributions of the Dy3+ and Ti4+ cations over the sites present in the cubic cell.

Synthesis and crystal structure of the low-temperature modification of Li12Zn4(P2O7)5

The crystal structure of a low-temperature modification of the Li12Zn4(P2O7)5 compound has been determined by full-profile analysis from the X-ray powder diffraction data. The compound crystallizes in the monoclinic crystal system (a = 5.130(1) Å, b = 13.454(1) Å, c = 8.205(1) Å, β = 90.36(1)°, space group P21/n, Z = 4) and has a framework structure in which the zinc and lithium atoms statistically occupy equivalent positions.

New solid solutions of mixed alkali-zinc diphosphates LiNa1 − xKxZnP2O7

Phase relationships in the LiNaZnP2O7-LiKZnP2O7 system have been studied. For the first time a vast region of solid solutions of the rhombic syngony LiNa1 − xKxZnP2O7 containing simultaneously three alkali cations was found. The miscibility is broken at the temperature of the polymorphous transformations LiKZnP2O7 (270°C) and below, with the formation of the two-phase region of the solid solution with the rhombic and monoclinic structures (0.85 ≤ x ≤ 1 at 25°C).

Phase relationships in the Na2ZnP2O7–LiKZnP2O7 system

The phase relationships in the Na2ZnP2O7–LiKZnP2O7 system are studied. They are represented by a mixture of the starting components in the subsolidus region. The eutectic was found at a temperature of 640°C and composition of 0.5LiKZnP2O7. The phase formation of this system is compared with the previously studied NaKZnP2O7–LiKZnP2O7 system. It is shown that a structural factor affects the geometry of the state diagrams.