Kagome modes, a new route to ultralow thermal conductivity?

TL;DR

This study identifies kagome lattice vibrations as a key factor in achieving ultralow thermal conductivity in pyrochlore materials, suggesting a new direction for designing efficient thermal insulators.

Contribution

It reveals that kagome modes are responsible for low thermal conductivity in pyrochlores, providing a novel insight into material design for thermal insulation.

Findings

Kagome vibrational modes are highly anharmonic and flat.

These modes correlate with ultralow thermal conductivity.

Kagome compounds are promising candidates for low-$ppa$ materials.

Abstract

From next generation gas turbines to scavenging waste heat from car exhausts, finding new materials with ultra-low thermal conductivity ($\kappa$) has the potential to lead to large gains in device efficiency. Crystal structures with inherently low $\kappa$ are consequently desirable, but candidate materials are rare and often difficult to make. Using first principles calculations and inelastic neutron scattering we have studied the pyrochlore La$_2$Zr$_2$O$_7$ which has been proposed as a next generation thermal barrier. We find that there is a highly anharmonic, approximately flat, vibrational mode associated with the kagome planes. Our results suggest that this mode is responsible for the low thermal conductivity observed in the pyrochlores and that kagome compounds will be a fruitful place to search for other low $\kappa$ materials.