Electronic transition, ferroelectric and thermoelectric properties of bismuth pyrostannate Bi-2(Sn0.85Cr0.15)(2)O-7

The ferroelectric properties of bismuth pyrostannate Bi₂(Sn_0.85Cr_0.15)₂O₇ in the high-temperature region are established. The linear thermal expansion coefficient, electrical resistance, impedance, I−V characteristics, capacitance, loss-angle tangent, charge, and thermopower of the investigated material are measured in the temperature range of 300−700 K at frequencies of 10²−10⁶ Hz. Anomalies of the thermal expansion coefficient and hodograph spectrum variation in the region of polymorphic phase transitions are observed. The high resistance and change of the hopping conductivity for the tunnel-emission are found. The hysteresis in the electric field dependence of polarization is established. The change in the thermopower sign with temperature is revealed. The obtained experimental data are explained in the framework of the model of migration polarization by charged chromium ions.