High-pressure investigations of CaTiO3 up to 60 GPa using X-ray diffraction and Raman spectroscopy

TL;DR

This study explores the structural stability and compression behavior of calcium titanate (CaTiO3) under high pressure up to 60 GPa using X-ray diffraction and Raman spectroscopy, revealing stability of the orthorhombic phase and detailed vibrational mode analysis.

Contribution

It provides experimental evidence contradicting ab-initio predictions about phase stability and offers detailed insights into the Raman modes and compression mechanisms of CaTiO3 under high pressure.

Findings

Orthorhombic Pnma structure remains stable up to 60 GPa.

Bulk modulus K0 is 181.0 GPa from compression data.

Raman spectra clarify mode assignments and compression effects.

Abstract

In this work, we investigate calcium titanate (CaTiO3 - CTO) using X-ray diffraction and Raman spectroscopy up to 60 and 55 GPa respectively. Both experiments show that the orthorhombic Pnma structure remains stable up to the highest pressures measured, in contradiction to ab-initio predictions. A fit of the compression data with a second-order Birch-Murnaghan equation of state yields a bulk modulus K0 of 181.0(6) GPa. The orthorhombic distortion is found to increase slightly with pressure, in agreement with previous experiments at lower pressures and the general rules for the evolution of perovskites under pressure. High-pressure polarized Raman spectra also enable us to clarify the Raman mode assignment of CTO and identify the modes corresponding to rigid rotation of the octahedra, A-cation shifts and Ti-O bond stretching. The Raman signature is then discussed in terms of compression mechanisms.