The single crystal growth of α-Ag 2S and α-Ag 2Se controlled by the diffusion of silver atoms at the solid/vapour interface

Abstract

The growth of single crystal α-Ag 2X(X = S and Se) (high-temperature phases) by solid-state crystallization which is rate controlled by the diffusion of silver atoms through solid α-Ag 2X was analyzed by a onedimensional model using a knowledge of irreversible thermodynamics and solid-state ionics (or solid-state electrochemistry). The equivalent electrical circuit of this growth mode is proposed. The growth rate is determined by the diffusion flux of excess Ag. The driving forces for the diffusion of excess Ag atoms are the temperature gradient and the concentration gradient formed by the thermal decomposition of α-Ag 2X. The maximum growth rates were 5.6 and 3.7 mm/hr for α-Ag 2S (δ T = 300°C at T d=600°C) and α-Ag 2Se (δ T = 300°C at T d = 750°C) respectively. The α-Ag 2X experienced lattice distortion when it cooled in the quartz ampoule due probably to the difference of the thermal expansion coefficients of α-Ag 2X and quartz. This distortion could be reduced by annealing.