E. Černošková

Raman scattering in GeS2 glass and its crystalline polymorphs compared

Abstract Raman spectrum of glassy GeS 2 and low-resolution ones of polycrystalline α- and β-GeS 2 were studied. It was shown that the medium range structure of glassy GeS 2 is similar to the three-dimensional structure of β-GeS 2 . Our conclusion of similarity of medium range order of glassy GeS 2 and β-GeS 2 was also confirmed by detection of β-GeS 2 microcrystals grown from glassy GeS 2 at annealing temperature sufficiently below glass transition temperature.

Structural relaxation near the glass transition temperature

Abstract Enthalpy relaxation processes on a model bulk glass, As 2 Se 3 , were studied below the glass transition temperature, T g , as well as at temperatures close to the glass transition overshoot. Extents of relaxation processes below T g were measured by enthalpy of endothermic relaxation peak. Relaxation processes above T g were determined by melting enthalpies of partly crystallized glass during relaxation. We found an exponential temperature dependence of physical aging. Completely annealed glasses reach the equilibrium having excess of enthalpy compared to the equilibrium supercooled liquid at the same temperature. Using the Tool–Narayanaswamy–Moynihan (TNM) model, we found that the fictive temperature, T f , decreased during isothermal annealling toward aging temperature, T a , and at equilibrium is equal to annealing temperature, T a . When the glass comes to equilibrium the distribution of relaxation times decreases. The description of relaxation processes at the temperatures slightly above T g is more complicated. The nuclei are created in the first step. In the second one these nuclei can create thermodynamically non-equilibrium agglomerates, which consequently can decrease their energy by becoming amorphous.

Non-isothermal structural relaxation and the glass transition temperature

Abstract The glass transition was studied by a new stepwise differential scanning calorimetry (DSC) technique on the model glasses As 2 Se 3 and As 2 S 3 . The glass transition was separated to the two components: a reversible (thermodynamic) one, reflecting temperature changing of the vibrational amplitude, and an irreversible (kinetic) one, bears on structural relaxation. The value of the glass transition temperature, T g , determined from the thermodynamic part of the glass transition was found to be independent both on the heating/cooling rate and the thermal history of glass. The value of T g depends only on the chemical composition of the glass and thus it could be regarded as a material constant. The heating/cooling rate dependence of T g , known from DSC or DTA measurements, is due to kinetic part of the glass transition.

Thermoelectric Properties of Cu2HgSnSe4-Cu2HgSnTe4 Solid Solution

Copper-based semiconductors from the family Cu2-II-IV-VI4 have recently attracted a great deal of attention because of their promising thermoelectric (TE) properties. Polycrystalline samples from the Cu2HgSnSexTe4−x (x = 0, 0.8, 2, 3.2, 4) solid solution were prepared and structurally characterized by powder x-ray diffraction. The samples from this solid solution crystallize in the stannite structure (space group

Crystalline arsenic trisulfide: preparation, differential scanning calorimetry and Raman scattering measurements

I\bar{4}2m

StepScan DSC: The useful tool for the study of the glass transition phenomenon

I4¯2m). Transport, TE, and thermal properties of hot-pressed samples are reported. About a 20 % reduction in calculated lattice thermal conductivities, compared to the lattice thermal conductivities of pure components of the alloys (i.e. Cu2HgSnSe4 and Cu2HgSnTe4), was observed for Cu2HgSnSe2Te2 alloy. The maximum ZT of the Cu2HgSnSe2Te2 sample reaches 0.6 at 575 K.

An X-ray Crystallographic Study of New Monoclinic Selenium Allotrope δ-Se8

Isothermal crystallization of bulk As2Se3 glass was studied in temperature range 270-360°C. Johnson-Mehl-Avrami (JMA) equation describes the crystallization process in the whole temperature range. By means of analysis of JMA equation the temperature dependence of kinetic exponent n was found, its value changes from 3.8 to 1.9 with increasing temperature. The relationship between the value of n and crystal morphology was briefly discussed. Furthermore the value of apparent activation energy E was determined as well as melting enthalpy. Temperature dependence of crystal growth rate was also determined.

Isothermal structural relaxation: temperature and time dependencies of relaxation parameters

Abstract Fully crystalline samples of high-purity arsenic trisulfide have been prepared for the first time. Comparison of X-ray diffraction spectrum (XRD) of prepared crystals with XRD spectrum of natural orpiment, as well as Raman scattering experiments, confirmed the crystallinity of the prepared sample. Using differential scanning calorimetry, the melting enthalpy (78 J/g) and apparent activation energy of the melting process (306 kJ/mol) were found. A kinetic analysis of the peaks, as the melting process took place, showed that melting can be described well by the Johnson–Mehl–Avrami equation with a kinetic exponent slightly more than 1. A detailed computer fit of Raman spectrum is described.