Impact of quartic anharmonicity on lattice thermal transport in EuTiO$_3$: A comparative theoretical and experimental investigation

Abstract

We investigate the role of the quartic anharmonicity in the lattice dynamics and thermal transport of the cubic EuTiO3 by combining ab initio self-consistent phonon theory with compressive sensing techniques and experimental thermal conductivity determination measurement. The antiferromagnetic G-type magnetic structure is used to mimic the para-magnetic EuTiO3. We find that the strong quartic anharmonicity of oxygen atoms plays an important role in the phonon quasiparticles free from imaginary frequencies in EuTiO3 and causes the hardening of vibrational frequencies of soft modes. Based on these results, the lattice thermal transport properties are predicted through the Boltzmann transport equation within the relaxation time approximation. The hardened modes thereby affect calculated lattice thermal conductivity significantly, resulting in an improved agreement with experimental results, including the deviation from $ąppa$L ∝ T−1 at high temperatures. The calculated thermal conductivity of 8.2 W/mK at 300 K matched the experimental value of 6.1 W/mK. When considering the boundary scattering, the calculated thermal conductivity is reduced to 6.9 W/mK at 300 K, which agrees better with the experiment.

Terumasa Tadano

Researcher of Materials Science

My research interests include development of computational methods and softwares for predicting thermal properties of solids, and application of machine-learning methods to material science study