THE EFFECT OF HYDROSTATIC-PRESSURE AND TEMPERATURE ON THE FREQUENCY DEPENDENCIES OF THE A.C. CONDUCTIVITY OF IONIC (AGPO3) AND (AG2S)(0.3)(AGPO3)(0.7) GLASSES

The dielectric properties of vitreous (Ag2S)(x)(AgPO3)(1-x) and AgPO3 have been measured in the radio frequency region under hydrostatic pre ssure up to about 0.2 GPa in the temperature range 293 to 373 K to det ermine the effects of pressure on ionic motion in a conducting glass, Measurements have also been made at atmospheric pressure down to 20 K to extend understanding of the conduction mechanisms. The d.c, conduct ivity increases with temperature and decreases with hydrostatic pressu re. Analysis of the frequency dependencies of the conductivities of bo th glasses indicates the pressure and temperature dependencies of thei r conductivities to be caused by the effects of pressure and temperatu re on their respective ion hopping rates alone. The activation energy and volume for these two glasses have been determined as functions of pressure and temperature. At 293 K, the activation volumes are 4.15 an d 2.52 cm(3)mol(-1) for AgPO, and (Ag2S)(0.3)(AEPO(3))(0.7) glasses, r espectively, and become larger at higher temperatures. In an alternati ve interpretation, deformation potentials of 1.25 and 0.9 eV have been obtained for the two glasses. Results are consistent with the random- walk model but are an order of magnitude smaller than expected from th e free volume theory. Introduction of Ag2S into the glass decreases th e activation energy and volume Delta V, suggesting that the P-S mode v ibration has a weaker pressure dependence than the P-O mode. The fact that the Delta V is less than the molar volume of the corresponding ch arge carrier evidences a higher polarisability of silver ions in this glass. (C) 1998 Elsevier Science B.V. All rights reserved.