Investigations of Diffusion and Nonstoichiometry in Cuprous Sulfide at 400°C

The chemical diffusivity of copper in chalcocite has been determined electrochemically as a function of the copper activity at 400°C, using the cell [formula omitted] A potentiostatic technique involving a CuBr solid electrolyte has been used. The diffusivity changes from a value of 7.3 x 10-3 cm2/sec when the copper activity is 0.78 to a value of 4.2 x 10-3 cm2/sec when the copper activity is 0.23. The copper to sulfur ratio in cuprous sulfide has been determined as a function of the copper activity using a coulometric titration technique. The results of the measurements are consistent with a model involving neutral copper vacancies, VCu, as the predominant defect carrier in cuprous sulfide. Using this model, a value of 1.9992 has been calculated for the Cu/S ratio in cuprous sulfide having unit activity of copper at 400°C.