STRUCTURE AND IONIC-CONDUCTIVITY OF NA2BEGEO4

The crystal structure of Na2BeGeO4 has been determined from CuK alpha(1) powder diffractometer data and refined by the Rietveld technique to R(F) = 0.047. It is monoclinic, a = 7.2155(4), b = 5.0214(3), c = 10.1380(6) Angstrom, beta = 90.289(5)degrees, space group P2(1)/c, z = 2, and is isostructural with monoclinic Na2BeSiO4. The structure exhibits BeGeO42- layers formed by binuclear Be2O6 groups, containing two edge-sharing BeO4 tetrahedra, which in turn are interconnected by GeO4 tetrahedra. The Na atoms are located between the BeGeO42- layers and are octahedrally coordinated by oxygen atoms. The ionic conductivity of Na2BeGeO4 was determined by impedance measurements and found to be 6.7 x 10(-6) (Omega cm>(-1) at 773 K with an activation energy of E(a) = 0.82 eV. (C) 1995 Academic Press, Inc.