Estimation of the intensity of near-electrode electrochemical processes on the surface of polar crystal cuts based on the temperature dependencies of short-circuit currents: selection of a conductive coating

Active elements of polar cuts of ionic dielectric crystals of polar and polar-neutral classes with applied on their surface conductive coatings are used to create modern devices of piezo-, acousto-, optoelectronics operating in a wide temperature range. Conductive coatings are applied to the surface of polar slices, which leads to degradation of the crystal elements up to their destruction. However, the nature of such degradation has not yet been established. The mechanisms of electromotive force generation and ion transport in the «ionic dielectric-metal conductive coating» system have been theoretically substantiated. The main factor in the degradation of active elements is the electrochemical decomposition of polar cuts in contact with a metal conductive coating, which is caused by the difference in properties between the opposite sides of the polar cuts. Upon contact of the surface of the polar cuts of crystals, even with the same conductive coating, different products of electrochemical reactions or the same products of different concentrations are formed. This leads to a potential difference and an electromotive force, which induces short-circuit currents. The determination of the presence of short-circuit currents, their values and temperature dependences makes it possible to estimate the intensity of near-electrode electrochemical processes: the lower the strength of short-circuit currents, the weaker the electrochemical processes. This paper summarizes the results of long-term studies of short-circuit currents in a number of crystals obtained by the authors of this article. Measurements of electric currents of model lithium iodate crystals on the previously created SKIP test complex are described within the framework of the author's measurement methodology using a standard sample of high-resistance (100 mOhm). The main unit of the complex is a thermal chamber in the form of a tubular electric furnace. The successful application of the method of measuring the temperature dependences of short-circuit currents for the selection of conductive coatings of polar cuts of functional langatate crystals grown in different atmospheres with different conductive coatings is shown. It was found that as the temperature in the thermal chamber increases, the values and direction of the short-circuit currents may change due to the intensification of phase formation processes, which is confirmed by the results of phase analysis. The material of the conductive coatings that exhibited the lowest short-circuit currents and the fewest changes in current polarity was iridium.

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