SINGLE-CRYSTAL STRUCTURE REFINEMENT OF HIGH-PRESSURE ZNGEO3 ILMENITE

Single crystals of Zn Geo3 ilmenite have been synthesized at 180kbar and 1500°Cu singauni axial split-sphere apparatus. The crystal structure of ZnGeo3 ilmenite has been determined with 588counter-measured intensities refined by the least-squares method to R=0.020 and Rw=0.021. Zn Geo3 ilmenitei strigonal with a=4.9568(8)Å, c=13.860(2)Å, V=294.91(11)Å3, space group R3 and Z=6. Zinc and germaniumatoms are completely ordered in the structure;the average Zn—O and Ge—O distances are 2.144Å and 1.898Å, respectively. The ZnO6 octahedra in Zn Ge03 ilmenite display one of the largest quadratice longationand bondang levariance values among compounds with the ilmenites tructure. The distortion and height of the GeO6 octahedra in ZnGeO3 ilmeniteare comparable with those observed in other germanateilmenites, consistent with the trend that distortion of the B4+O6 octa hedra changes little upon substitution of different A2+ cations in the structure. Analysis of c/a systematics shows that c/a increases linearly among the germanate and titanateilmenites as the‘size mismatch’(i. e. difference in ionic radii)between the A2+ and B4+ cations increases. The differentsl opesofthe two different groups shows that c/a is less affected by substitution of larger A2+ cations in titanateilmenitesth an germanateilmenites where the ‘size mismatch’ is greater. © by R. Oldenbourg Verlag