Pressure-temperature phase diagram of SrTiO3 up to 53 GPa

TL;DR

This study maps the pressure-temperature phase diagram of SrTiO3 up to 53 GPa, revealing a pressure-induced cubic to tetragonal transition consistent across temperatures and proposing a new theoretical model for this transition.

Contribution

The paper provides the first comprehensive pressure-temperature phase diagram of SrTiO3 and introduces a revised Landau theory model for its pressure-induced phase transition.

Findings

Pressure induces a cubic to tetragonal transition at all investigated temperatures.

No other phase transitions observed up to 53 GPa at room temperature.

A new linear phase boundary and Landau potential are proposed.

Abstract

We investigate the cubic to tetragonal phase transition in the pressure-temperature phase diagram of strontium titanate SrTiO3 (STO) by means of Raman spectroscopy and X-ray diffraction on single crystal samples. X-ray diffraction experiments are performed at room temperature, 381 and 467 K up to 53 GPa, 30 GPa and 26 GPa respectively. The observation of the superstructure reflections in the X-ray patterns provides evidence that the crystal undergoes at all investigated temperatures a pressure-induced transition from cubic to the tetragonal I4/mcm phase, identical to the low-temperature phase. No other phase transition is observed at room temperature up to 53 GPa. Together with previously published data, our results allow us to propose a new linear phase boundary in the pressure-temperature phase diagram. The data are analyzed in the framework of the Landau theory of phase transitions. With a revised value of the coupling coefficient between the order parameter and the volume spontaneous strain, the model built from pressure-independent coefficients reproduces satisfactorily the boundary in the phase diagram, but fails at reflecting the more pronounced second-order character of the pressure-induced phase transition as compared to the temperature-induced transition. We propose a new Landau potential suitable for the description of the pressure-induced phase transition. Finally, we show that particular attention has to be paid to hydrostatic conditions in the study of the high-pressure phase transition in STO.