Session 6-4

Abstract

Thermal transport in crystalline solids is strongly influenced not only by crystallographic long-range order but also by local structural features. Locally distorted coordination environments and dynamical structural fluctuations can significantly suppress lattice thermal conductivity, yielding glass-like behavior. Mixed-anion materials with distorted heteroleptic coordination, where different types of anions are asymmetrically arranged around a cation, have emerged as a platform for ultralow lattice thermal conductivity (Fig. 1) [1,2]. In these compounds, the strong local distortions often produce off-center cations that exhibit rattling behavior. We also observe glass-like temperature dependence of thermal conductivity in crystalline oxides near ferroelectric phase transitions, attributable to dynamical structural fluctuations [3]. I will discuss how local structure and chemical bonding control phonon transport, and outline design strategies for intrinsically low thermal conductivity materials relevant to thermoelectrics and thermal barrier coatings.