Growth rate of equilibrium-like-shaped single crystals of superionic conductor cuprous selenide

Abstract

The equilibrium-like-shaped single crystals of nonstoichiometric cuprous selenide were grown in their high-temperature phase from 480 to 530°C using Ohachi's method. The method had been developed for ionic–electronic mixed conductors, involving macroscopic transport of mobile metal atoms through the polycrystalline bulk, due to a fixed chemical potential difference, and utilising capillary narrowing for single-crystal selection. In the solid-state crystallisation mode several large equilibrium-like spherical single crystals were grown on the capillaries tips. Using the real geometry of the polycrystalline bulk and the growing crystal the chemical potential distribution along metal atoms diffusion path was calculated following Yokota's theory of mixed conduction. The model calculations predict and experiments confirm that under stationary conditions the volume of a growing crystal is linear function of time. Also, the volume growth rate was shown to be inversely proportional to the total path resistance (or geometrical factor) for metal atom flow. The calculated and experimental growth rates are compared and discussed within constraints of the particular geometry.