Silver ion conducting composites of the general formula xAgl : (1 - x)alpha-Al2O3, where 0.2 <= x <= 0.8 (vol fraction) were prepared using a high-pressure synthesis route (T=400 degrees C, p = 7.5 GPa). The microstructure of as-received rigid, non-brittle and dense samples was investigated by SEM. Other studies - DSC, XRD and impedance spectroscopy, were done as a function of temperature in the 20-200 degrees C temperature range. Close correlations were observed between the temperature dependences of the XRD patterns, the electrical conductivity and events seen on DSC traces. It was found out that the electrical conductivity at room temperature of all as-received composite materials was higher (by a factor between 7 and 100, depending on composition) than that measured after the heating-cooling cycle. This effect and other observed correlations were explained referring to the residual stress concept. (C) 2010 Elsevier B.V. All rights reserved.