On the origin of supertetragonality in BaTiO$_3$

TL;DR

This study uses first-principles calculations to explore how negative pressure induces a supertetragonal phase in BaTiO$_3$, revealing electron bonding changes as the key mechanism, which guides future material design.

Contribution

It uncovers the microscopic origin of supertetragonality in BaTiO$_3$ under negative pressure through detailed first-principles analysis.

Findings

Identification of a phase transition to supertetragonal BaTiO$_3$ with high c/a ratio.

Discovery of covalent $ ext{π}$-bond electron changes as the transition mechanism.

Guidance for designing new supertetragonal and multiferroic materials.

Abstract

Understanding ferroelectricity is of both fundamental and technological importance to further stimulate the development of new materials designs and manipulations. Here, we perform an in-depth first-principle study on the well-known ferroelectric barium titanate BaTiO$_{3}$ under a hydrostatic negative pressure, showing an isosymmetric phase transition to a supertetragonal phase with high $c/a$ ratio of $\sim1.3$. The microscopic origin and driving mechanisms of this phase transition are identified as a drastic change of the covalently $\pi$-bonded electrons. These findings provide guidance in the search for new supertetragonal phases, with great opportunities for novel multiferroic materials; and can be generalized in the understanding of other isosymmetric phase transitions.