Structural origins of ultra-low glass-like thermal conductivity in AgGaGe3Se8

TL;DR

This study reveals that AgGaGe3Se8 exhibits ultra-low, glass-like thermal conductivity due to structural disorder, anharmonicity, and soft bonding, with potential implications for thermoelectric applications.

Contribution

It uncovers the structural origins of ultra-low thermal conductivity in AgGaGe3Se8, linking atomic disorder and anharmonicity to heat transport properties.

Findings

Thermal conductivity as low as 0.2 W/m·K at room temperature.

Glass-like thermal behavior observed from 2 K to 700 K.

Large Ag atomic displacement parameters indicating disorder.

Abstract

Materials with a low thermal conductivity are important for a variety of applications such as thermal barrier coatings and thermoelectrics, and understanding the underlying mechanisms of low heat transport, and relating them to structural features, remains a central goal within material science. Here, we report on the ultra-low thermal conductivity of the quarternary silver chalcogenide AgGaGe3Se8 with a remarkable value of only 0.2 Wm-1K-1 at room temperature, and an unusual glass-like thermal behavior from 2 K to 700 K. The ultra-low thermal conductivity is linked to a disordered nature of Ag in the structure, displaying extremely large Ag atomic displacement parameters obtained from multi-temperature synchrotron powder X-ray scattering measurements, and Ag ionic conductivity at elevated temperatures. Additionally, signs of structural anharmonicity and soft bonding are evident from a low temperature Boson peak in the heat capacity and a low Debye temperature of 147 K.