V.Ya. Markiv

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 optical properties of EuF3 film-forming material

Abstract The crystal structure of europium trifluoride, α-EuF 3 , synthesized by consecutive dissolving was refined. The optical and operational properties of thin film coatings prepared from this material using thermal evaporation were studied. The coatings were shown to contain either single β-EuF 3 or an α-EuF 3 and β-EuF 3 mixture, depending on the preparation conditions.

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.

Crystal structure of a novel cubic pyrophosphate WP2O7

Abstract The crystal structure of a novel pyrophosphate WP 2 O 7 has been studied by X-ray powder diffraction. It was found that the crystal structure of WP 2 O 7 belongs to the well-known MoP 2 O 7 structure type ( a =7.9502 A). The tetravalent state of tungsten in the pyrophosphate has been confirmed by magnetic susceptibility measurements.

The isothermal section of the phase diagram of the ternary system Y–Ge–Ga at 800oC in the region 33.3 to 100 at.% Y

Abstract The isothermal section of the phase diagram of the ternary system Y–Ge–Ga (33.3 at.% Y or more) at 800°C was investigated by X-ray powder diffraction. The section at 800°C consists of six single-phase regions (while excluding binary compounds). Four true ternary phases were found, namely: 1-YGe 0.6 Ga 1.4 (α-ThSi 2 -type structure), 2-YGe 0.7−0.4 Ga 1.1−1.4 (AlB 2 defect), 3-YGe 1.3−1.0 Ga 0.4−0.7 (α-GdSi 2 derivative) and 4-Y 2 Ge 2.3−1.7 Ga 0.7−1.3 (AlB 2 defect). Two other single-phase regions in the section (5-Y 5 Ge 0.4 Ga 2.6 and 6-Y 5 Ge 0.2 Ga 2.8 ) correspond to the high-temperature binary h -Y 5 Ga 3 and M -Y 5 Ga 3 compounds, that are stable above 800°C. A continuous series of solid solution YGe 1− x Ga x ( x =0÷1) and solid solutions, based on the Y 3 Ge 5 , α-Y 2 Ge 3 , Y 11 Ge 10 , Y 5 Ge 3 and YGa 2 binary compounds, were found. The composition ranges of the ternary phases and solid solutions were determined.

Magnetic susceptibility of the phases of YAlxGa4−x series with the structures derived from BaAl4-type structure

Abstract The magnetic susceptibility of the alloys in the concentration region corresponding to five YAl x Ga 4− x compounds was investigated by the Faraday method. The crystal structures of these compounds are related to the BaAl 4 -type structure. It was shown that diamagnetism of the investigated alloys is determined by the existence of 6-, 8-, 10-, 12- and 14-term circuits of Me atoms (Ga+Al statistical mixture) in the crystal structures of the YAl x Ga 4− x compounds. The Me atoms are thought to form π-type interatomic bonds within these circuits. The diamagnetic constituent of the susceptibility calculated on the basis of the above assumption was found to be in a fairly good agreement with the experimental values of the susceptibility of the investigated phases.

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.