Effect of contact phenomena on the electrical conductivity of reduced lithium niobate

Abstract

Lithium niobate is a ferroelectric material finding a wide range of applications in optical and acoustic engineering. Annealing of lithium niobate crystals in an oxygen-free environment leads to appearance of black coloration and concomitant increasing electrical conductivity due to chemical reduction. There are plenty of literary data on the electrophysical properties of reduced lithium niobate crystals though contact phenomena occurring during electrical conductivity measurement as well as issues of interaction between the electrode material and the test specimens are almost disregarded. The effect of chromium and indium tin oxide electrodes on the results of measurements of electrophysical parameters at room temperature for lithium niobate specimens reduced at 1100 °C has been investigated. It was found that significant nonlinearities in the VACs of the specimens at below 5 V distort the specific resistivity readings for lithium niobate. This requires measurements at higher voltages. Impedance spectroscopy studies have shown that the measurement results are largely affected by capacities including those probably induced near the contacts. It has been shown that the experimental results are described adequately well by a model implying the presence of near-contact capacities that are parallel to the specimen’s own capacity. Possible mechanism of the induction of these capacities has been described and a hypothesis has been proposed of the high density of electron states at the electrode/specimen interface that can trap carriers, the concentration of trapped carriers growing with an increase in annealing duration.