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Shaldin Yu.V.,RAS Shubnikov Institute of Crystallography | Zaleski A.,International Laboratory of Strong Magnetic Fields and Low Temperatures | Matyjasik S.,Polish Academy of Sciences | Bagdasarov Ch.S.,RAS Shubnikov Institute of Crystallography
Doklady Physics | Year: 2012

The data of experiments that characterize the dependences of the unit cell volume, heat capacity, and spontaneous polarization of a nonstoichiometric KTiOPO4 sample are presented for the low-temperature region. It is shown that the influence of the electric field leads to variation in the sample nonstoichiometry, which is characterized by the appearance of anomalous behavior of spontaneous polarization in the region below 30 K. This experimental fact is associated with the appearance of the donor-acceptor pairs possessing the dipole moment. As the temperature increases, they gradually dissociate with the subsequent appearance of the cationic component of conduction. © 2012 Pleiades Publishing, Ltd.

Shaldin Yu.V.,RAS Shubnikov Institute of Crystallography | Matyjasik S.,International Laboratory of Strong Magnetic Fields and Low Temperatures | Novikova N.E.,RAS Shubnikov Institute of Crystallography | Tseitlin M.,Ariel University | And 2 more authors.
Crystallography Reports | Year: 2010

The temperature dependences of the pyroelectric coefficients of KTiOAsO4 and RbTiOAsO4 single crystals grown by flux crystallization have been investigated in the temperature range of 4.2-300 K. With an increase in temperature, superionic conductivity first arises in KTiOAsO4 (at T > 200 K) and then (at T > 270 K) in RbTiOAsO4. This conductivity is much higher in the samples polarized at T = 4.2 K. An exponential change in the crystal resistivity along the polar direction is simultaneously observed. The results of measurements in the range of 4.2-200 K indicate larger values of pyroelectric coefficients when compared with potassium and rubidium titanyl-phosphate crystals. A correlation between the pyroelectric coefficients and a change in the lattice constants at isomorphic substitutions of K atoms for Rb and P atoms for As has been revealed within the symmetry approach. © 2010 Pleiades Publishing, Ltd.

Mikhailov B.P.,RAS Institute of Metallurgy | Ivanov L.I.,RAS Institute of Metallurgy | Shamrai V.F.,RAS Institute of Metallurgy | Nikulin V.Y.,Russian Academy of Sciences | And 4 more authors.
Inorganic Materials: Applied Research | Year: 2010

The effect of pulse high-power nonlinear shock waves generated at the Plasma Focus installation, which was created according to the nuclear fusion program, on some characteristics of multilayered hightemperature superconducting (HTSC) Bi-2223 tape is demonstrated. The tape is produced using the technique of HTSC powder rolling in a silver coating. A more than a twofold increase in the critical current in zero magnetic fields and external magnetic fields from 0.5 to 6 T at a temperature of 77 K is shown to take place under the action of shock waves at room temperature. The volt-ampere characteristics (VACs) of HTSC tape samples exposed to the effect of shock waves are found to drastically differ from the characteristics of the initial tapes. The shock waves suppress the "gear"-type VAC character of unprocessed plasma samples, their jump amplitudes increasing with an increase in the applied magnetic field intensity. © Pleiades Publishing, Ltd., 2010.

Druzhinin A.A.,Lviv Polytechnic | Druzhinin A.A.,International Laboratory of Strong Magnetic Fields and Low Temperatures | Ostrovskii I.P.,Lviv Polytechnic | Khoverko Y.M.,Lviv Polytechnic | And 3 more authors.
Materials Science in Semiconductor Processing | Year: 2011

The aim of this paper is to study the strain-induced low-temperature behavior of Si1-xGex whiskers magnetoresistance and to estimate the prospects for the creation of physical values and sensing elements on the basis operating in strong magnetic fields. We have investigated the magnetoresistance and piezomagnetoresistance of low germanium fraction Si 1-xGex solid solution whiskers under the uniaxial strain (-4.3×10-3 to 4.7×10-4 rel. un.) at 4.2 K in a wide range of magnetic fields up to 14 T. Whiskers have been doped to the impurity concentration corresponding to both the insulator and the metal side of metalinsulator transition (MIT). It has been shown that magnetoresistance substantially depends on the doping level, the type and magnitude of samples strain. The hopping conductivity with Δ2 and Δ3 activation energies at strain effect has been observed. The exponential character of magnetoresistance field dependencies has been obtained for heavily doped "metallic type" Si1-xGex whiskers, while for weakly doped samples at the insulator side of MIT a square-law field dependencies of magnetoresistance have been observed at 4.2 K. A non-monotonic magnetoresistance change depending on the doping level of Si and Si1-xGex whiskers in the vicinity of MIT. © 2010 Elsevier Ltd. All rights reserved.

Nikolaeva A.A.,Moldova Academy of Sciences | Nikolaeva A.A.,International Laboratory of Strong Magnetic Fields and Low Temperatures | Konopko L.A.,Moldova Academy of Sciences | Konopko L.A.,International Laboratory of Strong Magnetic Fields and Low Temperatures | And 2 more authors.
Surface Engineering and Applied Electrochemistry | Year: 2016

This paper reports the results of an experimental study of electronic topological transitions in bismuth glass-covered wires doped with acceptor (Sn) and donor (Te) impurities. The temperature dependences of the thermoelectric power and resistance are measured within the temperature range from 1.5 to 300 K and magnetic fields up to 14T. The position of the Fermi level εF and the concentration of charge carriers at doping are estimated from the Shubnikov de Haas (SdH) oscillations which are clearly visible from both L electrons and L and T holes in all crystallographic directions. We demonstrate anomalies in the temperature dependences of the thermopower in Bi wires doped with acceptor (Sn) and donor (Te) impurities in the form of a triple (doping by Sn) and double (doping by Te) change in the sign of the thermopower. The effect is interpreted with relation to the manifestation of impurity Lifshitz topological transitions. The SdH oscillation method was used to determine the energy position of the Σ band by doping Bi wires with the acceptor impurity Sn and the T band conduction by doping with Te. It is shown that the appearance of the Σ and T bands in Bi wires doped with the acceptor and donor impurities is responsible for the anomalies in the diffusive thermoelectric power, which gives a good conform with to the theoretical models and predictions. © 2016, Allerton Press, Inc.

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