The effect of contact phenomena on the measurement of electrical conductivity of reduced lithium niobate

Abstract

Lithium niobate (LN) is a ferroelectric material with a wide range of applications in optics and acoustics. Annealing of LN crystals in an oxygen-free environment leads to the appearance of black coloration and the concomitant increase in electrical conductivity due to chemical reduction. The literature presents many works on the study of the electrophysical properties of reduced crystals of LN, however, the contact phenomena arising during the measurement of electrical conductivity, as well as the interaction of the electrode material with the samples under study, are practically ignored. In this paper, the effect of chromium and indium tin oxide (ITO) electrodes on the results of measurements at room temperature of electrophysical parameters of LN samples recovered at 1100 °C is investigated. It was found that significant non-linearities in the voltage characteristics (I-V curve.) at voltages less than 5V do not allow to obtain the correct values of the resistivity of NL. This leads to the need to carry out measurements at higher voltages. By the method of pulse spectroscopy, it is shown that capacitances, including those formed, probably, in the contact areas, have a strong influence on the measurement results. It is shown that the results obtained are adequately described by a model assuming the presence of contactless tanks connected in parallel to the sample’s own capacity. A possible mechanism for the formation of such containers is described, and an assumption is made about the existence of a significant density of electronic states at the “electrode - sample” interface capable of capturing charge carriers, and with increasing annealing time, the concentration of captured carriers increases.