ELECTROCHEMICAL EXCITATION METHOD IN KINETIC-STUDY OF AG2S

A steady-state electrochemical method of sinusoidal excitation has been developed in which the chemical diffusion coefficient of an atomic species in a solid is obtained via the determination of the spatial distribution of the phase and amplitude of its chemical potential oscillation. It has been applied to Ag2+deltaS to measure the chemical diffusion coefficient D of Ag in alpha-Ag2+deltaS at 168-degrees-C and in beta-Ag2+deltaS at 220-degrees-C, with a typical precision of 0.2%. The measurements were performed at frequencies from 0.02 to 0. 1 6 Hz, with delta covering the whole nonstoichiometry range. The values of D measured fell between 0.01 and 0. 1 5 cm2/s at 168-degrees-C and between 0.08 and 0.32 cm2/s at 220-degrees-C, changing significantly with delta but slightly with f The component diffusion coefficient of Ag+ was determined for beta-Ag2+deltaS to be in the range of 3.0 to 3.6 x 10(-5) cm2/s, decreasing with a frequency dependence with increasing delta.