Role of octahedral tilting induced acoustic softening on limiting thermal transport in SrSnO3

TL;DR

This study reveals that octahedral tilting in SrSnO3 causes acoustic phonon softening, significantly reducing thermal conductivity and highlighting a new mechanism for controlling heat transport in perovskite oxides.

Contribution

It uncovers the opposite effect of octahedral tilting on thermal conductivity in SrSnO3 compared to SrTiO3, demonstrating tilting-induced acoustic softening as a key factor.

Findings

Octahedral tilting triggers acoustic phonon softening in SrSnO3.

Thermal conductivity decreases with increased tilting angle.

Anisotropic suppression of heat transport along the c-axis.

Abstract

Octahedral tilting is a fundamental structural distortion in perovskites, governing key phenomena such as lattice stabilizing, soft phonon dynamics, group-theoretical analysis, phase transitions, ferroelectricity, and even for tunable electronic band gap. However, its influence on lattice thermal conductivity (kL) remains poorly understood. In the archetypal perovskite SrTiO3, tilting in the low-temperature tetragonal phase is known to enhance kL by suppressing specific phonon scattering channels around 200 cm-1. Here, we investigate the thermal transport in strontium stannate (SrSnO3), another perovskite oxide that undergoes temperature-driven phase transitions, and reveal a completely opposite effect. Through a systematic study across its orthorhombic, tetragonal, and cubic phases, we demonstrate that octahedral tilting in the tetragonal phase of SrSnO3 anomalously triggers acoustic phonon softening. This softening manifests as reduced frequencies and group velocities in low-frequency (<3 THz) acoustic modes, creating a large decrease for heat transport, particularly along the c-axis. Consequently, kL is significantly suppressed, decreasing from 7.48 W m-1 K-1 to 6.06 W m-1 K-1 as the tilting angle increases by a mere 1 degree. These findings identify tilting-induced acoustic softening as a pivotal mechanism for limiting and controlling anisotropic thermal transport in SrSnO3, presenting a stark contrast to the established behavior in SrTiO3.