, and Hui-Tian

The physical mechanisms behind the reduction of the bulk modulus of a high-pressure cubic TiO2 phase are confirmed by first-principles calculations. An unusual and abrupt change occurs in the dependence of energy on pressure at 43 GPa, indicating a pressure-induced phase transition from columbite TiO2 to a newly-identified modified fluorite TiO2 with a Pca21 symmetry. Oxygen atom displacement in Pca21 TiO2 unexpectedly reduces the bulk modulus by 34 % relative to fluorite TiO2. This discovering provides a direct evidence for understanding the compressive properties of such groups of homologous materials Titanium dioxide (TiO2) has rich phase diagrams, namely, the rutile (P42/mnm), anatase (I41/amd), brookite (Pbca), columbite (Pbcn), baddeleyite (P21/c), and cotunnite (Pnma) phases [1-6]. Due to its versatile physical and chemical properties, TiO2 is extensively used in many industrial applications, such as high efficiency solar cells, photocatalysis, dynamic random access memory modules, and super-hard materials [7-12]. The rutile and anatase phases of TiO2 are abundant in nature [13,14]