Electrochemical properties of Bi₄Ti_{3 – x} Cr _x O_{12 – 0.5x} (0.4 ≤ x ≤ 1.2) solid solutions with a layered perovskite structure

Abstract

Chromium-containing bismuth titanates Bi₄Ti_3–x Cr _x O_12–δ (0 ≤ x ≤ 1.2) with a layered perovskite structure and with the number of layers in the perovskite-like unit m = 3 at x ≤ 0.5 and m = 4 at 0.5 < x ≤ 1.2 were synthesized by the solid state method. The electrochemical properties of Bi₄Ti_1.8Cr_1.2O_11.38 (m = 4) and Bi₄Ti_2.6Cr_0.4O_11.8 (m = 3) were studied by impedance spectroscopy and DC electric conductivity measurements in different gas media. The oxygen conductivity increased at temperatures (t) of 450–500°C. For the samples with m = 4 at t ≥ 500°C in the frequency range of the order of a few Hz, the imaginary part of impedance was inverted, which was explained by the electrochemical process on electrodes. At t ≥ 600°C a reversible breakdown of the Bi₄Ti_2.6Cr_0.4O_11.8 sample in an electric field of over 30 V/m was observed. It was concluded that the conductivity of Bi₄Ti_3–x Cr _x O_12–δ is of electron-ion type.