Yu. A. Kovalevskaya

Optical and structural proper tees of ZnS and ZnS:Mn films prepared by CVD method

Abstract Films of ZnS and ZnS:Mn 0.1 to 5.0 μm thick were prepared by the CVD method using new volatile complex compounds belonging to dithiocarbamates and xanthates. Their chemical composition, density, structural and optical properties were studied. It is shown that at relatively low temperatures (T ≈ 220 °C) monophase doped ZnS:Mn films can be fabricated with uniform distribution of Mn over the film thickness. Depending on selection of precursors and presence of dopant, ZnS and ZnS:Mn films can be of sphalerite or wurtzite structure. The refractive index of the films was determined at 0.633 and 20.0 μm wavelength.

Low-temperature heat capacity of α and γ polymorphs of glycine

Low-temperature heat capacity of two polymorphs of glycine (α and γ) was measured from 5.5 to 304 K and thermodynamic functions were calculated. Difference in heat capacity between polymorphs ranges from +26% at 10 K to -3% at 300 K. The difference indicates the contribution into the heat capacity of piezoelectric γ polymorph, probably connected with phase transition and ferroelectricity. Thermodynamic evaluations show that at ambient conditions γ polymorph is stable and α polymorph is metastable.

Synthesis and properties of ZnS-EuS films grown from volatile complex compounds

Deposition and characterization of films of ZnS, EuS and ZnS:Eu are described. The films have been prepared by chemical vapor deposition using new volatile complex compounds, dithiocarbamates of Zn and Eu, as precursors. Characterization includes X-ray diffraction, chemical analysis of the film composition, Raman spectroscopy, ellipsometry, and spectrophotometry. The spatial chemical homogeneity of the films has been determined using a recently developed method of differential dissolution and found to be uniform. Doping of ZnS by Eu with dopant concentration up to 0.3 at.% has been achieved. Effects of Eu doping on structural and optical properties of the films are presented.

Low temperature heat capacity of the coordination compound: Nickel(II) nitrate with 4-amine-1,2,4-triazole at temperatures from 11 to 317 K

Low-temperature heat capacity of the coordination compound of nickel(II) nitrate with 4-amine-1,2,4-triazole was measured in the temperature range from 11 to 317 K using a computerized vacuum adiabatic calorimeter. The thermodynamic functions have been derived from the smoothed experimental data over the whole temperature interval covered and at standard conditions. At 298.15 K, the heat capacity is 574.7±1.2 J K-1 mol-1, the entropy is 599.2±1.2 J K-1 mol-1, the enthalpy is 91070±200 J mol-1, and the reduced Gibbs energy is 293.7±1.2 J K-1 mol-1. The results on Cp(T) were compared with those for Cu(NH2trz)3(NO3)2·0.5H2O. It was revealed that the slope of the curve dCp/dT (T) changes essentially for both compounds at 110-120 K. It implies that additional degrees of freedom appear in the heat capacity at these temperatures.

Boundary line of the transition into the pseudogap state in thulium cuprates

Precision measurements of the heat capacity of 1-2-3 thulium cuprates with oxygen content ranging from 6.3 to 6.92 were performed in the temperature range 6–300 K. Analysis of the experimentl data showed anomalies in the temperature dependence of the electronic heat capacity. It is conjectured that the anomalies are due to a transition from the normal metallic into the pseudogap state.

Anomalies of the electronic heat capacity of thulium cuprates in the pseudogap phase region

Precision measurements of the heat capacity of thulium 1-2-3 cuprate with oxygen concentrations x=6.92 and x=6.7 are made in the temperature range 6–300 K. After the lattice components of the heat capacity of the samples are subtracted off, a comparison of the results makes it possible to determine the contribution to the heat capacity due to the formation of the pseudogap phase for the sample with x=6.7. The temperature dependence of this contribution has an anomaly near the boundary of the transition from the pseudogap phase to the normal metallic phase. The experimental results correlate with the theoretical ideas about the rearrangement of the electronic structure upon the transition of the system to the pseudogap phase region.

Temperature dependence of the thermodynamic parameters of cobalt(II) clathrochelate: X-ray diffraction and calorimetric characteristics of the low temperature structural phase transition

The temperature dependence of heat capacity of the polycrystalline sample of cobalt(II) clathrochelate in a range of 6–300 K is studied. Based on the smoothed dependence Cp(T), the entropy and enthalpy values in a temperature range of 8–300 K and their standard values at 298.15 K are calculated. In the Cp(T) curve in a range of 50–70 K, a process is recorded whose entropy and enthalpy are 1.2 J·(K·mol−1) and 68 J·mol−1 respectively. A comparison of the results with the data of a multitemperature X-ray diffraction study makes it possible to attribute this process to the structural phase transition.