Ge_0.57Ti_0.43O₂: a new high-pressure material with rutile-type crystal structure

Single crystals of a GeO₂-TiO₂ solid solution with the corresponding composition Ge_0.57Ti_0.43O₂ (germanium titanium tetra-oxide) were obtained by devitrification of germania-titania glass at high pressure and temperature. The new compound crystallizes in the rutile structure type (space group <i>P</i>4₂/<i>mnm</i>), where Ge and Ti share the same position <i>M</i> (site symmetry <i>m.mm</i>), with occupancy values of 0.57 (3) and 0.43 (3), respectively, and one O-atom position (<i>m</i>.2<i>m</i>). The <i>M</i> site is in a sixfold O-atom coordination and, as in the original TiO₂ rutile structure, an elongation of the O-<i>M</i>-O bonds along the <i>c</i>-axis direction of the coordination polyhedron and deviation of the angles from 90° lead to a decrease in the coordination symmetry from octa-hedral to tetra-gonal. The Ge and Ti atoms are fully disordered in the structure, which indicates that the rutile structure is surprisingly pliant given the differing sizes of the two cations.