Ge 0.57 Ti 0.43 O 2 : a new high-pressure material with rutile-type crystal structure.

Single crystals of a GeO2 -TiO2 solid solution with the corresponding composition Ge0.57 Ti0.43 O2 (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 P 42 / mnm ), where Ge and Ti share the same position M (site symmetry m.mm ), with occupancy values of 0.57 (3) and 0.43 (3), respectively, and one O-atom position ( m .2 m ). The M site is in a sixfold O-atom coordination and, as in the original TiO2 rutile structure, an elongation of the O- M -O bonds along the c -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.