Multiple relaxation, reversible electrical breakdown and bipolar conductivity of pyrochlore–type Bi2Cu0.5Zn0.5Ta2O9 ceramics

Abstract

Cu-doped bismuth zinc tantalate pyrochlore was synthesized for the first time using standard ceramic technology. Electrical properties were investigated by impedance spectroscopy in a wide frequency range of 10 Hz – 1 MHz and a temperature range of 25–450 °C. As a result of modeling the Nyquist curves, the structure of the equivalent circuit of the ceramic is determined. Two mechanisms of ion-migration polarization caused by ionic transfer of copper and oxygen have been discovered. The activation energy of conduction at temperatures above 200 °C was 0.796 ± 0.009 eV. Current-voltage characteristics were investigated in the potential range 0.1–2 V and temperature 150–450 °C. The calculation of the potential barrier on the electrodes showed that at temperatures above ~250 °C, the potential barrier changes sign and magnitude by an order of magnitude from - 150 mV to +10 mV, which is associated with a change in the nature of charge carriers and activation of oxygen conductivity. In ceramics at 400–450 °C, a reversible effect is observed, which is characteristic of electrochromic materials. When measuring the current in the sample at a fixed potential, a transition from a direct current to an increasing current was detected, and then its sharp drop almost to zero. The instant of the onset of the growing current and electrical breakdown, as well as the recovery time of the electrical characteristics of the sample, depend on the applied potential and the temperature of the sample.