A. U. Sheleg

Crystal structure and phase transitions in the new crystals of [(CH3)2NH2]2CuCl4[(CH3)2NH2]Cl

Crystals grown from a solution of dimethylammonium and copper chlorides are studied using electron paramagnetic resonance (EPR) and X-ray diffraction. The dielectric properties of the crystals grown are measured. It is established that the crystals have the composition [(CH3)2NH2]2CuCl4[(CH3)2NH2]Cl and, in phase I at room temperature, are described by the orthorhombic space group Pna21 with the unit cell parameters a = 11.338 Å, b = 9.981 Å, and c = 15.675 Å. At temperatures of 279 K and 253 K, the crystals undergo jumpwise phase transitions into the incommensurate modulated ferroelectric phase II and commensurate modulated phase III, respectively.

X-ray diffraction study of (TlInSe2)1−x(TlGaTe2)x crystal system

The crystallographic and dynamic characteristics of TlInSe2 and TlGaTe2 crystals have been studied by X-ray diffraction in the temperature range of 85–320 K. The temperature dependences of the unit-cell parameters a of TlInSe2 and TlGaTe2 crystals, as well as their coefficients of thermal expansion along the [100] direction, are determined. The concentration dependences of the unit-cell parameters a and c for (TlInSe2)1 − x(TlGaTe2)x crystals are measured. Anomalies are found in the temperature dependences of the unit-cell parameters a and, correspondingly, the coefficient of thermal expansion, indicating the existence of phase transitions in TlInSe2 and TlGaTe2 crystals.

Growth and dielectric properties of KTiOPO4 and K1 − xRbxTiOPO4 crystals

Methods of growth of KTiOPO4 and K1 − xRbxTiOPO4 crystals of high optical quality have been optimized. The dielectric properties (permittivity and conductivity) of the crystals grown have been investigated at frequencies from 102 to 106 Hz in the temperature range from 100 to 350 K, along the [001] crystallographic direction. It is established that partial substitution of K+ ions with Rb+ ions leads to a decrease in the permittivity and conductivity.

Dilatometric and ultrasound study of [NH2(CH3)2]MnCl3 · 2H2O crystals

The unit-cell parameters of [NH2(CH3)2]MnCl3 · 2H2O crystals are determined by X-ray diffraction analysis and the velocities of longitudinal ultrasonic waves in these crystals are measured by the echo-pulse method in the temperature range 100–315 K. The coefficients of thermal expansion along the principal crystallographic axes are derived from the temperature dependences of the unit-cell parameters. The temperature dependences of the characteristics studied reveal kink anomalies at temperatures of ∼125, 179, 203, 260, and 303 K. These anomalies are indicative of structural transformations in the [NH2(CH3)2]MnCl3 · 2H2O crystals, which may be related to the dynamics of dimethylammonium cations.

Low-temperature X-ray studies of crystal-lattice parameters and thermal expansion of KTiOPO4 crystals

The unit-cell parameters a, b, and c of KTiOPO4 crystals have been measured by the X-ray diffraction method in the temperature range 80–320 K. The parameters obtained were used to determine the thermal expansion coefficients α[100], α[010], and α[001] along the principal crystallographic axes. It was established that thermal expansion in the crystals is essentially anisotropic and that α[010] > α [100], whereas α[001] is close to zero.

Structural study of [(CH3)2NH2]2CoCl4 single crystals at room temperature

The structure of the crystals grown from a solution of dimethylammonium and cobalt chlorides is determined. It is found that the crystals have the composition [(CH3)2NH2]2CoCl4. At room temperature, the crystals are monoclinic (space group P21/c, Z = 4) and the unit cell parameters are as follows: a = 8.545(2) Å, b = 11.447(2) Å, c = 13.313(3) Å, and β = 90.10°. Cations and anions form simple and bifurcated hydrogen bonds N-H⋯Cl.

Low-temperature X-ray diffraction studies of [(CH3)2NH2]5Cd3Cl11 crystals

Abstract[(CH3)2NH2]5Cd3Cl11 crystals are grown by the method of isothermal evaporation from saturated aqueous solutions containing dimethylamine and cadmium chlorides, [(CH3)2NH2]Cl and CdCl2.5H2O. The crystal grown are studied by the X-ray diffraction method. It is established that the crystals are orthorhombic with the unit-cell parameters at room temperature a = 18.115 ± 0.004 Å, b = 11.432 ± 0.002 Å, and c = 15.821 ± 0.003 Å. The unit-cell parameters a, b, and c of the [(CH3)2NH2]5Cd3Cl11 crystals are measured as functions of temperature in the temperature range 100–320 K. The data obtained were used to determine the thermal expansion coefficients along the main crystallographic axes. The temperature curves of the unit-cell parameters and thermal expansion coefficients showed pronounced anomalies in the vicinity of the temperatures T1 = 120, T2 = 150, and T3 = 180 K corresponding to the phase transitions in the [(CH3)2NH2]5Cd3Cl11 crystals. The crystals are also characterized by a pronounced anisotropy of thermal expansion.[(CH{sub 3}){sub 2}NH{sub 2}]{sub 5}Cd{sub 3}Cl{sub 11} crystals are grown by the method of isothermal evaporation from saturated aqueous solutions containing dimethylamine and cadmium chlorides, [(CH{sub 3})2NH{sub 2}]Cl and CdCl{sub 2.5}H{sub 2}O. The crystal grown are studied by the X-ray diffraction method. It is established that the crystals are orthorhombic with the unit-cell parameters at room temperature a = 18.115 {+-} 0.004 A, b = 11.432 {+-} 0.002 A, and c = 15.821 {+-} 0.003 A. The unit-cell parameters a, b, and c of the [(CH{sub 3}){sub 2}NH{sub 2}]{sub 5}Cd{sub 3}Cl{sub 11} crystals are measured as functions of temperature in the temperature range 100-320 K. The data obtained were used to determine the thermal expansion coefficients along the main crystallographic axes. The temperature curves of the unit-cell parameters and thermal expansion coefficients showed pronounced anomalies in the vicinity of the temperatures T{sub 1} = 120, T{sub 2} = 150, and T{sub 3} = 180 K corresponding to the phase transitions in the [(CH{sub 3}){sub 2}NH{sub 2}]{sub 5}Cd{sub 3}Cl{sub 11} crystals. The crystals are also characterized by a pronounced anisotropy of thermal expansion.