Unusual compression behavior ofTiO2polymorphs from first principles

Abstract

The physical mechanisms behind the reduction in the bulk modulus of a high-pressure cubic ${\text{TiO}}_{2}$ phase are revealed 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 ${\text{TiO}}_{2}$ to a modified fluorite ${\text{TiO}}_{2}$ with a $Pca21$ symmetry. Oxygen atom displacement in $Pca21$ ${\text{TiO}}_{2}$ unexpectedly reduces the bulk modulus by 34% relative to fluorite ${\text{TiO}}_{2}$. This discovering provides a direct evidence for understanding the compressive properties of such groups of homologous materials.