Anomalous enhancement of tetragonality in PbTiO3 induced by negative pressure

TL;DR

This study uses first-principles calculations to show that applying negative pressure can significantly enhance tetragonality in PbTiO3, revealing a phase transition-like behavior and similar effects in BaTiO3 at higher pressures.

Contribution

It demonstrates that negative hydrostatic pressure induces large tetragonal strain in PbTiO3 and BaTiO3, revealing a novel pressure-induced phase transition mechanism.

Findings

Large tetragonal strain induced by negative pressure in PbTiO3.

Abrupt changes in structural and dielectric properties near crossover pressure.

Similar effects observed in BaTiO3 at higher negative pressures.

Abstract

Using a first-principles approach based on density-functional theory, we find that a large tetragonal strain can be induced in PbTiO3 by application of a negative hydrostatic pressure. The structural parameters and the dielectric and dynamical properties are found to change abruptly near a crossover pressure, displaying a ``kinky'' behavior suggestive of proximity to a phase transition. Analogous calculations for BaTiO3 show that the same effect is also present there, but at much higher negative pressure. We investigate this unexpected behavior of PbTiO3 and discuss an interpretation involving a phenomenological description in terms of a reduced set of relevant degrees of freedom.