A. M. Sych

Crystal structure of the high-pressure modification of NdTaO4

Abstract The crystal structure of the metastable NdTaO 4 high-pressure modification (HPM) has been studied by X-ray powder diffraction. It was found that the crystal structure of HPM NdTaO 4 belongs to the monoclinic LaTaO 4 -type structure (space group P2 1 /c , a =7.5920(7) A, b =5.4673(5) A, c =7.7022(7) A, β =100.032(6)°, Z =4). The difference in structure between LnTaO 4 with Ln=Nd–Lu (fergusonite-type structure) and that with Ln=La–Pr (monoclinic LaTaO 4 -type structure) is most likely due to the difference in size of the rare-earth cations.

Synthesis, structure and ferroelectric properties of heteroblock slab phases in La2Ti2O7–LaTaO4 system

Abstract The succession of phase transformations in the La 2 Ti 2 O 7 –LaTaO 4 system on heat treatment of the co-precipitated crystallized hydroxides has been studied. We have studied the possibility of the formation of a number of heteroblock polar slab phases La 4p+2 q Ti 4 p Ta 2 q O 14 p +8 q ( p =1, q =1, 2, 3, 5) having an ordered arrangement of alternating perovskite-type blocks of two and four BO 6 octahedron slabs. The crystal structure has been determined and the spontaneous polarization has been estimated.

Peculiarities of polymorphic transformations in YbTaO4 and crystal structure of its modifications

Abstract The succession of phase transformations upon YbTaO 4 synthesis from a mixture of co-precipitated hydroxides has been determined. Some peculiarities of the polymorphic transformations in YbTaO 4 ( M - and M I -fergusonite structure types) have been studied. Details of the crystal structure of the M - and M I -modifications of YbTaO 4 have been determined using X-ray powder diffraction.

High-pressure polymorph of LaNbO4

A new polymorph of LaNbO4 with a BaMnF4-type structure(a = 0.3938(2) nm,b = 1.442(1) nm,c = 0.5682(3) nm,Z = 4) and octahedral oxygen coordination of Nb was prepared at high pressures and temperatures (8 GPa, 1570 K). At normal pressure, the reverse transformation, from high-pressure LaNbO4 to theM-fergusonite form, occurs at temperatures above 870 K and is close to a second-order phase transition. The spontaneous polarization in high-pressure LaNbO4, evaluated from the second-order nonlinear optical response, is about 2 ώC/cm2.

Synthesis and Properties of Ln3Ti2TaO11Mixed-Layer Perovskite-like Compounds

The Ln3Ti2TaO11(Ln = La, Pr) compounds (AnBnO3n+ 2family) with noncentrosymmetric layered perovskite-like structures were prepared by heat-treating coprecipitated hydroxides, and their lattice parameters and density were determined. The structural changes accompanying the formation of these compounds were studied. Analysis of x-ray diffraction data indicated that, in the structures of Ln3Ti2TaO11 , the LnTaO4and Ln2Ti2O7perovskite layers are stacked in an ordered manner. The spontaneous polarization in Ln3Ti2TaO11was evaluated.

Crystal structure of the high-pressure modification of LaNbO4

Abstract The crystal structure of the metastable LaNbO4 high-pressure modification (HPM) has been studied by X-ray powder diffraction. It was found that the crystal structure of HPM LaNbO4 belongs to- the room temperature BaMCF4 -type structure (space group Cmc21, a = 3,941(1)Å, b= 14,460(4) Å, c = 5,681(2) Å, Z = 4).

Formation, condition of existence and peculiarities of Sr2LaTa3O11 slab perovskite-like structure

Abstract The succession of phase transformations with heat treatment of co-precipitated hydroxy-carbonates with the ratio Sr/La/Ta=2:1:3 has been established. The possibility has been shown to obtain Sr2LaTa3O11. It is the first representative of a series of slab perovskite-like compounds of the AnBnO3n+2-type with n=3. Sr2LaTa3O11 belongs to a new (own) structure type. The formation mechanism and the existence conditions have been investigated. Also the peculiarities of the Sr2LaTa3O11 slab perovskite-like structure have been determined.

The electronic structure of the Ln2Ti2O7 oxides with pyrochlore type structure

Abstract The objects of investigation were pyrochlore type Ln2Ti2O7 oxides (Ln = Sm—Lu) and ferroelectric La2Ti2O7 with layered perovskite-like structure. X-ray OKα TiKβ5, Kα1,2, Lα-emission spectra and X-ray photoelectron spectra of the valence and core states were obtained for pyrochlore oxides. For La2Ti2O7 X-ray photoelectron spectra have been measured. The cluster (Xα-Scattering Waves) and band structure calculations (LMTO-ASA) have been carried out to study valence band structure and the charge states of atoms. As a result the valence band (VB) parameters of the La2Ti2O7 series were defined. The Ln atomic number (ZLn) influence on the La2Ti2O7 (Ln = La; Sm-Lu) electronic structure was disclosed. The atomic charge states and their dependence on ZLn have been determined in mentioned oxides. The La2Ti2O7 electronic structure genesis has been defined