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)ų, 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.