The equation of state of anatase ${\mathrm{TiO}}_2$ has been determined experimentally—using polycrystalline as well as single-crystal material—and compared with theoretical calculations using the ab initio perturbed ion model. The results are highly consistent, the zero-pressure bulk modulus being 179(2) GPa from experiment and 189 GPa from theory. Single-crystal tetragonal anatase transforms to the orthorhombic $\alpha -{\mathrm{PbO}}_2$ structure at about 4.5 GPa. This transition is suppressed in the polycrystalline material at room temperature, probably due to the presence of grain boundaries and other crystal defects. Polycrystalline anatase is found to transform to the monoclinic baddeleyite structure at about 13 GPa. Upon decompression, the baddeleyite phase transforms to the $\alpha -{\mathrm{PbO}}_2$ phase at about 7 GPa. The experimental zero-pressure bulk moduli are 258(8) GPa for the $\alpha -{\mathrm{PbO}}_2$ phase and 290(10) GPa for the baddeleyite phase.

• Received 16 November 1999

DOI:https://doi.org/10.1103/PhysRevB.61.14414