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Uzhhorod, Ukraine

Macutkevic J.,Lithuanian Academy of Sciences | Banys J.,Vilnius University | Vysochanskii Y.,Uzhgorod University
Physica Status Solidi (B) Basic Research | Year: 2015

Investigations of the electrical conductivity of mixed CuInP2(SxSe1-x)6 crystals were carried out in the frequency range of 20-1MHz. Anomalies in dc conductivity were observed close to the ferroelectric phase-transition temperature. However, these anomalies are different in selenium- and sulfur-rich compounds. While in the selenium-rich crystals group the anomaly of conductivity is sharp, in the sulfur-rich crystals group it is less expressed. These results indicate that the copper ions contribution to the total conductivity is not vanishing down to the lowest temperatures in sulfur-rich crystals. Moreover, in paraelectric phase the dc conductivity activation energy correlate with the pre-exponential factor according to the Meyer-Neldel law. No conductivity anomaly was observed in mixed CuInP2(SxSe1-x)6 crystals with the dipolar glass or relaxor behavior. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Salazar A.,University of the Basque Country | Oleaga A.,University of the Basque Country | Shvalya V.,University of the Basque Country | Shvalya V.,Uzhgorod University | Apinaniz E.,University of the Basque Country
International Journal of Thermal Sciences | Year: 2016

The photopyroelectric (PPE) technique in the front configuration consists of illuminating one surface of a pyroelectric slab while the other surface is in contact with the test sample. This method has been widely used to measure the thermal effusivity of liquids. However, in the case of solid samples the PPE signal is affected by the thin coupling fluid layer used to guarantee the thermal contact. Recently, a thickness scan of the coupling fluid layer has been proposed to extract the thermal effusivity of the solid. However, this method is delicate since it needs absolute values of the fluid thickness. In this work, we propose a classical frequency scan of the PPE signal in the front configuration, which only depends on two parameters: the effusivity of the solid and the thickness of the coupling fluid layer. It is demonstrated that both quantities are not correlated and that the sensitivity to the thermal effusivity of the solid is very high. PPE measurements performed on a set of calibrated solids covering a wide range of effusivity values (from polymers to metals) confirm the ability of the method to obtain the thermal effusivity of solids accurately. Moreover, this method is specially suited to measure the temperature dependence of the thermal effusivity across phase transitions. © 2015 Elsevier Masson SAS. Source

Dziaugys A.,Vilnius University | Banys J.,Vilnius University | Vysochanskii Y.,Uzhgorod University
Zeitschrift fur Kristallographie | Year: 2011

Results on dielectric properties of layered indium rich CuIn 1+δP2S6 crystals are presented. At low frequencies and high temperatures, the dielectric spectra are strongly influenced by the high ionic conductivity with the activation energy corresponding to 6815 K (0.587 eV). The high-frequency part of the dielectric spectra is determined by the relaxational soft mode. The critical slowing down and Debye-type dispersion show an order-disorder type of the ferrielectric phase transition at 330 K, which is substantially higher than for pure CuInP 2S6. The high ferroelectric phase transition temperature suggests an idea that a frustrated ordering should appears in indium sublattice at low temperatures. Indeed, at low temperatures the complex dielectric permittivity exhibits behaviour typical for dipolar glasses. © by Oldenbourg Wissenschaftsverlag, München. Source

Oleaga A.,University of the Basque Country | Salazar A.,University of the Basque Country | Kohutych A.A.,Uzhgorod University | Vysochanskii Yu.M.,Uzhgorod University
Journal of Physics Condensed Matter | Year: 2011

The thermal diffusivity of the ferroelectric family Sn2P 2(SexS1-x)6 (0 ≤ x ≤ 1) has been measured by a high-resolution ac photopyroelectric technique, using single crystals, with the aim of studying the evolution of the ferroelectric transition with Se doping. Its change from second order character to first order while passing the Lifshitz point (x ≈ 0.28) has been evaluated, as well as the splitting of the transition at high Se concentrations. The critical behavior of the ferroelectric transition in terms of the different universality classes and their underlying physical dominant effects (tricriticality, long-range dipole interactions, Lifshitz point) has been discussed using thermal diffusivity measurements in the very close vicinity of the critical temperature. This study reveals that for Se concentrations around the Lifshitz point, long-range dipole interactions do not play a significant role and that the critical parameters are close to those predicted for the Lifshitz universality class. © 2011 IOP Publishing Ltd. Source

Kleemann W.,University of Duisburg - Essen | Shvartsman V.V.,University of Duisburg - Essen | Borisov P.,University of Duisburg - Essen | Borisov P.,University of Liverpool | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

The lamellar antiferromagnet CuCr1-xInxP 2S6 (TN 32 K) rapidly loses magnetic percolation upon diamagnetically diluting the triangular Cu-Cr-P2 planar network with In3+ ions. For 0 ≤ x < 0.3 anti-ferroelectricity (Tc ≤ 150 K) and antiferromagnetic spin order (TN ≤ 32 K) coexist. Both orders are superposed by ferroic fluctuations. Dynamic polar clustering with glasslike polydispersive dielectric susceptibility emerges for x > 0 at T ≤ Tc, while for x < 0.3 pseudocritical planar 2D ferromagnetic fluctuations are encountered. They give rise to Langevin-type magnetization saturation and large quasimolecular magnetic anisotropy. Third-order magnetoelectric coupling is observed in collinear field configuration. © 2011 American Physical Society. Source

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