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 Ag_2+δS to measure the chemical diffusion coefficient D̃ of Ag in α-Ag_2+δS at 168°C and in β-Ag_2+δS at 220°C, with a typical precision of 0.2%. The measurements were performed at frequencies from 0.02 to 0.16 Hz, with δ covering the whole nonstoichiometry range. The values of D̃ measured fell between 0.01 and 0.15 cm²/s at 168°C and between 0.08 and 0.32 cm²/s at 220°C, changing significantly with f but slightly with f. The component diffusion coefficient of Ag⁺ was determined for β-Ag_2+δS to be in the range of 3.0 to 3.6×10^-5cm²/s, decreasing with a frequency dependence with increasing δ.