CRYSTAL-STRUCTURES OF THE ALPHA-FORM AND BETA-FORM OF K2ZNGEO4

The crystal structures of two phases of K2ZnGeO4 have been refined by the Rietveld method using neutron powder diffraction data, at 298 K (a lpha form) and 1153 K (beta form), to R-B = 4.8 and 7.3%, respectively . alpha-K2ZnGeO4 is orthorhombic, a = 11.1131(4) Angstrom, b = 5.5369( 2) Angstrom, c = 15.8629(5) Angstrom, space group Pca2(1), and Z = 8, beta-K2ZnGeO4 is cubic, a = 8.0254(5) Angstrom, space group F (4) over bar 3m, and Z = 4, Phase transition between alpha and beta forms occu rs at 1049 K, Both phases are stuffed cristobalites and correspond to a distortion of the ideal cristobalite structure, Neutron diffraction data show an ordered and alternating arrangement of ZnO4 and GeO4 tetr ahedra in alpha-K2ZnGeO4. The beta phase shows a static or dynamic sup erposition of short-range ordered clusters analogous to SiO2 cristobal ite, (C) 1997 Academic Press.