Unusual Compression Behavior of Columbite TiO2 via First-Principles Calculations

TL;DR

This study uses first-principles calculations to reveal an unusual compression behavior and a pressure-induced phase transition in TiO2, highlighting the role of oxygen displacement in reducing bulk modulus.

Contribution

It identifies a new phase of TiO2 with Pca21 symmetry and explains the mechanisms behind its compression behavior, advancing understanding of high-pressure TiO2 properties.

Findings

Abrupt energy change at 43 GPa indicating phase transition

Displacement of oxygen atoms reduces bulk modulus by 34%

Confirmation of pressure-induced phase transition from cubic to Pca21 TiO2

Abstract

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