Anomalous lattice thermal conductivity in layered materials MNCl (M=Zr, Hf) driven by the lanthanide contraction

TL;DR

This study reveals that replacing Zr with Hf in layered MNCl materials unexpectedly increases lattice thermal conductivity due to enhanced phonon lifetimes caused by lanthanide contraction, offering new insights for thermoelectric material design.

Contribution

It demonstrates that heavy element substitution can increase lattice thermal conductivity via lanthanide contraction, challenging conventional strategies for reducing thermal conductivity.

Findings

Replacing Zr with Hf increases thermal conductivity by 4 times at 300K.

Enhanced phonon lifetimes are due to stronger interatomic bonding from lanthanide contraction.

The microscopic mechanism involves increased phonon lifetimes linked to lanthanide contraction.

Abstract

High performance thermoelectric devices requires materials with low lattice thermal conductivities. Many strategies, such as phonon engineering, have been made to reduce lattice thermal conductivity without simultaneously decrease of the charge transport performance. It is a simple and effective approach to use materials with heavy element to reduce the lattice thermal conductivity. Here, based on the first-principles calculations and phonon Boltzmann transport equations, we find the replacement of Zr with heavy element Hf in ZrNCl doesn't reduce the lattice thermal conductivity, instead, it surprisingly increases by about 4 times at 300K. This unusual lattice thermal conductivity is mainly attributed to the dramatic enhancement in phonon lifetimes in Hf compound, originating from the strong interatomic bonding due to lanthanide contraction. Our findings unveil the microscopic mechanisms of high thermal transport properties in materials with heavy element, providing an alternative strategy in materials design with low lattice thermal conductivity for thermoelectric applications such as power restoration and generation.