A modified coulometric titration technique is described for the investigation of nonstoichiometric phases at low temperatures. It allows to obtain titration curves at temperatures where the conventional coulometric titration technique fails because of too small chemical diffusion coefficients of the mobile component. This method for indirect coulometric titration is applied to silver selenide between - 100 and 100 degreesC. The titration curves are analyzed on the basis of a defect chemical model and provide thermodynamic data of the alpha-silver selenide phase. The boundaries of the homogeneous phase field are determined. (C) 2004 Elsevier B.V. All rights reserved.