Liquid-crystal composites with controlled photoluminescence of CdSe/ZnS semiconductor quantum rods

Liquid-crystal (LC) composites based on a combination of different acrylates and pentylcyanobiphenyl and containing CdSe/ZnS semiconductor quantum nanorods have been investigated. Samples of electro-optical cells with planar or homeotropic structures (depending on the acrylate type) have been obtained. The morphology of LC composite formation has been studied using luminescence techniques. It is shown that these composites are gel-like LC media, where the formation of dispersed and network structures in the cells plays a stabilizing role. The role of the electron transfer reactions during polymerization and the features of the kinetics of the Freedericksz effect (reorientation in an electric field) are discussed.     

Temperature variation of the structural and thermal characteristics of YBa2Cu3O7−x in the range from 90 to 400 K

The X-ray studies of the tetragonal YBa₂Cu₃O_7−x compound are performed at different temperatures from 400 to 90 K and the temperature variation of the thermal expansion coefficients and the Debye characteristic temperature is determined. The anisotropy of thermal expansion is investigated. It is found that the two dynamical characteristics monotonously decrease with temperature lowering whereas for the superconducting orthorhombic modification their temperature dependences are anomalous. The mean thermal expansion coefficient as well as the overall Debye temperature for the tetragonal phase are smaller than those for the orthorhombic one.     

Lattice Thermal Expansion in CuGaT2 and CuInTe2 Compounds over the Temperature Range 80 to 650 K from X-ray Diffracion Data

The lattice parameters a and c as well as the thermal expansion coefficients α⟂ and α∥ in the two principal direction for CuGaTe2 and CuInTe 2 chalcopyrite-type compounds have been determined as a function of temperature in the range from 80 to 650 K by the X-ray diffraction method. It is found for both the compounds the coefficient of expansion along the α axis (α⟂) is larger than that along the c axis (α∥) over the whole investigated tem-perature range. When comparing the results for a series of the CuB^IIIC compounds (B Ga, In; C S, Se, Te) it is shown that the thermal expansion anisotropy increases strongly when the Ga atom replaces the In atom while it changes a little when the Te atom replaces the Se atom or the S atom.     

Crystal Growth and Properties of the Compounds CuGa3Se5 and CuIn3Se5

CuIn₃Se₅ and CuGa₃Se₅ uniform single crystals 12 mm in diameter and 40 mm in length with the chalcopyrite‐related structure were prepared by directed crystallization of the melt. The melting points of these compounds were defined by means of the differential thermal analysis (DTA). The lattice parameters a and c as well as the axial thermal expansion coefficients α_a and α_c were determined as a function of temperature in the range from 90 to 650 K by the X‐ray diffraction method (XRD). It is found that for both the compounds the coefficients of expansion along the a ‐axis are larger than those along the c ‐axis over the entire temperature range studied.     

Compressibility in the Orthorhombic Phase of AgInS2 from the X-ray diffraction data under high pressure

The compressibilities for different crystallographic directions in the orthorhombic modification of the ternary AgInS₂ compound were studied as a function of pressure up to 4.5 GPa by the X-ray poweder diffraction method under high pressure. The anisotropy of compressibility was found to exist and between the principal components of compressibility tensor the relation χ_c > χ_a > χ_b was observed. For the orthorhombic modification the bulk modulus is smaller than that for tetragonal one.     

X-Ray Study of the Structure and Thermal Properties of Ba1–xKxBiO3 at Different Temperatures

The crystal structure as well as the temperature and composition dependences of the lattice parameters, the thermal expansion coefficients in the high-temperature superconducting Ba_1–xBiO₃ system were determined by an X-ray powder diffraction method at temperatures between 80 and 650 K. The character of variation of intensity, profiles, and line widths of the diffraction lines for different perovskite structures as a function of the content x and temperatures was found. The correlation between the behaviour of the thermal expansion coefficients and potassium content was revealed at different temperatures. It is shown that the thermal expansion coefficients vary inversely with rising x at any temperature in the range from 80 to 400 K.     

Thermal Expansion and Oxygen Nonstoichiometry in High-Tc YBa2Cu3Ox Superconductor

The lattice parameters as well as the axial thermal expansion coefficients for YBa₂Cu₃O_x superconducting oxide ceramics with different oxygen content ranging from × = 6.14 to × = 6.95 are determined as a function of temperature between 80 and 400 K using X-ray powder diffractometry technique. The effect of oxygen concentration on the thermal expansion behaviour is regarded. The values of α are found to decrease with the oxygen content reducing and depend on the condition of heat treatment. The essential anisotropy of thermal expansion is shown to exist, with α_c being larger than α_a and α_b. The relationship between α_a and α_b depends both on the sample preparation conditions and temperature.