SYNTHESIS, STRUCTURE AND CONDUCTIVITY OF AG2ZNSIO4, AG2ZNGEO4 AND AG2BESIO4

The compounds Ag(2)MM'O-4 with MM' = ZnSi, ZnGe and BeSi have been syn thesised by reacting the corresponding Na compounds with molten AgNO3. The crystal structures of Ag2ZnSiO4 and Ag2ZnGeO4 have been refined f rom CuK alpha(1) powder diffractometer data by the Rietveld technique to R(F) = 3.3 and 7.1%, respectively. They are isostructural with mono clinic Na2ZnSiO4. The powder pattern of Ag2BeSiO4 indicates that it is isostructural with orthorhombic Na2BeSiO4. The conductivity of the co mpounds has been determined using ac impedance measurements. Ag2ZnSiO4 and Ag2BeSiO4 are ionic conductors, with conductivities that are very similar to those of their corresponding isostructural Na compounds. A g2ZnGeO4 is an electronic semiconductor with sigma(60 degrees C) = 1.0 X 10(-2) (Omega cm)(-1).