I.P. Studenyak

Electrical conductivity studies in (Ag3AsS3)x(As2S3)1−x superionic glasses and composites

Compositional, frequency, and temperature studies of impedance and electrical conductivity in (Ag3AsS3)x(As2S3)1−x superionic glasses and composites were performed. Frequency range from 10 Hz to 3 × 109 Hz and temperature interval 300–400 K were used for the measurements. Compositional dependences of electrical conductivity and activation energy are analyzed; the most substantial changes are observed with the transition from (Ag3AsS3)0.4(As2S3)0.6 glass to (Ag3AsS3)0.5(As2S3)0.5 composite. With increase of Ag3AsS3 content, the investigated materials are found to have crystalline inclusions and show the two-phase composite nature. Addition of Ag3AsS3 leads to the increase of electrical conductivity whereas the activation energy decreases.

DIELECTRIC PROPERTIES OF Cu6PS5I SINGLE CRYSTALS

ABSTRACT The dielectric properties of Cu6PS5I crystals were investigated in broad frequency (20 Hz–1 GHz) and temperature (25 K–300 K) range. At high temperatures and low frequencies dielectric spectra are highly influenced by very high ionic conductivity. The temperature dependence of the static dielectric permittivity reveals just one phase transition at Tc1 = 156 K. The frequency spectra of conductivity, at low frequencies (20 Hz–1 MHz) obeys the Almond-West power law. The activation energy of conductivity changes at 194 K, which indicates the second phase transition of Cu6PS5I.

Ultrasonic and Piezoelectric Investigations of Phase Transitions in Ferroelastic Cu6PS5(I,Br) Mixed Crystals

The ultrasonic velocity and attenuation anomalies were observed near the elastic phase transitions (PT) in the vicinity of 270 K in Cu 6 PS 5 (I,Br) mixed superionic crystals, where I was partially substituted by Br. We have shown that elastic anomalies at phase transition gradually decrease with increasing of iodine concentration in the material. The critical anomalies were described by relaxational Landau theory, which implies the increase of order parameter relaxation time: τ = τ o /(T c − T). The prefactor τ o increases with increasing iodine content in crystal. The ultrasonic anomalies near low temperature superionic phase transitions were weak. These transitions were observed using piezoelectric detection of ultrasonic waves by surface barrier. The temperature dependencies of detected by surface barrier signal were measured and it was shown that this method is very sensitive for indication of phase transitions in such superionic crystals.

Internal friction in silver-containing (Ag3AsS3) x (As2S3)100 − x superionic glasses

The mechanical properties of glasses in the Ag3AsS3-As2S3 system have been studied by the internal friction method. Measurements of internal friction and shear modulus have been carried out in the temperature interval 80–300 K at deformation frequencies of 10–50 mHz. Relaxation-type maxima of internal friction have been revealed. It has been shown that the concentration-induced variations in the parameters of the mechanical relaxation process in (Ag3AsS3)x(As2S3)100 − x glasses observed in the region of 20 at % Ag3AsS3 are of the threshold character. It has been established that this feature can be associated with the variation in the structural unit, which accounts for the process of mechanical energy dissipation within the temperature interval 150–250 K.

Optical parameters of X-ray irradiated Cu 7 GeS 5 I thin films

51 PACS 78.40.Ha; 77.80.Bh DOI: https://doi.org/10.24144/2415-8038.2016.39.51-56 I.P. Studenyak, A.V. Bendak, V.Yu. Izai, A.M. Solomon, P. Kúš, M. Mikula Uzhhorod National University, 3 Narodna Sq., 88000 Uzhhorod, Ukraine; e-mail: studenyak@dr.com Institute of Electron Physics, 10 Universytetska St., 88000 Uzhhorod, Ukraine; e-mail: asol952@gmail.com Comenius University, Mlynska dolina, 84248 Bratislava, Slovakia; e-mail: kus@fmph.uniba.sk

Internal friction in Cu6PS5Br superionic crystals and related composites

Mechanical properties of Cu6PS5Br single crystals and composites based on them have been investigated by the internal friction method. The measurements of the internal friction and the shear modulus have been performed in the temperature range of 80–300 K at deformation frequencies of 10–100 mHz in a mode of forced torsional vibrations. The maxima caused by the superionic and ferroelastic phase transitions have been found in temperature dependences of the internal friction. It has been shown that a more than two-fold decrease in the shear modulus with increasing temperature in the range of 150–230 K is caused by mobility unfreezing in the cation sublattice of the Cu6PS5Br single crystal during the superionic phase transition. An abrupt (more than threefold) increase in the shear modulus upon heating in the range of 260–270 K is caused by the ferroelastic phase transition of the Cu6PS5Br single crystal. Parameters of the internal friction of this single crystal in the course of mentioned phase transitions have been determined.

Impedance spectroscopy study of Cu6PS5I–As2S3 nanocomposites

Nanocrystalline Cu6PS5I powder has been mixed with As2S3 semiconducting glass to obtain nanocomposite. Surface of the obtained sample has been photographed by scanning electron microscope. Electrical properties of Cu6PS5I–As2S3 nanocomposite have been measured using two- and four-probe methods. The obtained results were analyzed by fitting the experimental data to the equivalent circuit model. Warburg impedance element described Cu6PS5I nanoparticles, and the phase transition of this material was indicated.

Influence of anionic substitution on phase transitions in Cu6PS5I1− x Cl x mixed crystals

Cu6PS5I1  −   x Cl x mixed crystals were grown using chemical vapour transport. Isoabsorption studies of optical absorption edge and optical polarization measurements were performed in the temperature range 77–320 K. The influence of anionic I → Cl substitution on the phase transitions in Cu6PS5I1  −   x Cl x mixed crystals is studied. Compositional dependence of the phase-transition temperatures is obtained and the x,T-diagram for Cu6PS5I1  −   x Cl x mixed crystals is constructed.

Optical absorption and exciton-phonon interaction in solid solutions Cu6PS5I1 − xClx

We have studied the optical absorption edge of solid solutions Cu6PS5I1 − xClx at high absorption levels in the temperature range of 77–320 K. In a superionic state, we have revealed the Urbach behavior of the absorption edge, determined its parameters, and studied their temperature and concentration variations. We consider exciton-phonon interaction as a mechanism by which the Urbach bundle is formed and show that this bundle can be described in terms of the Dow-Redfield model.

Dielectric Investigations of Phase Transitions in Cu6PS5(Ix,Br1-X) Mixed Crystals

The dielectric properties of mixed Cu6PS5(Ix,Br1-x) crystals were investigated in wide frequency (20 Hz – 1 MHz) and temperature regions (120 K–300 K). Similar to the pure Cu6PS5Br and Cu6PS5I, the mixed Cu6PS5(Ix,Br1-x) exhibit two phase transitions - at higher temperatures feroelastic one and at lower temperatures a superionic phase transition. The ferroelastic phase transition temperature in mixed Cu6PS5(Ix,Br1-x) decreases from 273 K to 268 K while the superionic phase transition temperature increases 156 K to 166 K, with increasing bromine concentration. The ionic contribution to the total conductivity was separated from the electronic contribution by calculating the distribution of relaxation times from impedance spectra.