Engineering Phonons in Compositionally Complex Carbide Ceramics

TL;DR

This paper uses ab initio calculations and experiments to explore how compositional complexity in carbide ceramics influences phonon behavior and thermal conductivity, revealing ways to optimize these materials for extreme environment applications.

Contribution

It systematically investigates phonon properties in complex carbides and demonstrates how element selection affects phonon scattering and thermal conductivity, offering new design strategies.

Findings

Phonon band structure can be tuned via element composition.

Five-component carbides can have higher thermal conductivity than simpler alloys.

Unexpectedly, increased cation disorder does not always reduce thermal conductivity.

Abstract

In the pursuit of advanced ceramic materials with exceptional irradiation-resistance and high-temperature tolerance for nuclear applications, compositionally complex carbides (CCCs) have emerged as a highly promising class of candidate materials for extreme environments. In such conditions, critical material properties such as thermal stability, elasticity, thermal conductivity and thermodynamics behavior are predominantly influenced by phonons. In CCCs, pronounced cation disorder can lead to significant phonon scattering due to inherent mass and force constant variations, impacting these critical properties. In this study, we used ab initio calculations to predict the phonon band structures and systematically explore the influence of mass and force constant variance on the phonon spectral function of CCCs with a rock salt structure, ranging from binary to five-metal component carbides. Our findings reveal that the selection and concentration of constituent elements can be strategically utilized to tune the phonon band structure, phonon bandgap and phonon scattering in CCCs, thereby enabling control over phonon-related properties. Additionally, we measured the thermal conductivity of some of these CCCs using the spatial-domain thermoreflectance technique. Interestingly, the measured thermal conductivity of some of these CCCs indicates that five-component ceramics exhibit higher thermal conductivity than certain ternary and binary alloys. This observation contrasts with the expectation that greater cation disorder would result in more scattering and lower thermal conductivity. This intriguing result opens up the possibility of discovering CCCs with better thermal conductivity, presenting new opportunities for their application in extreme environments.