Thermal conductivity reduction in (Zr$_{0.25}$Ta$_{0.25}$Nb$_{0.25}$Ti$_{0.25}$)C high entropy carbide from extrinsic lattice defects

TL;DR

This study investigates how extrinsic structural defects, introduced via Zr ion implantation, further reduce thermal conductivity in high entropy carbide (Zr,Ta,Nb,Ti)C, highlighting nanoscale defects as effective phonon scatterers.

Contribution

It demonstrates that nanoscale defects, rather than dislocation loops, significantly enhance phonon scattering and reduce thermal conductivity in high entropy carbides.

Findings

Nanoscale defects effectively scatter phonons and reduce thermal conductivity.

Dislocation loops contribute little to phonon scattering.

Implantation temperature influences defect formation and thermal transport.

Abstract

High entropy carbides ceramics with randomly-distributed multiple principal cations have shown high temperature stability, low thermal conductivity, and possible radiation tolerance. While chemical disorder has been shown to suppress thermal conductivity in these materials, little investigation has been made on the effects of additional, extrinsically-generated structural defects on thermal transport. Here, (Zr$_{0.25}$Ta$_{0.25}$Nb$_{0.25}$Ti$_{0.25}$)C is exposed to Zr ions to generate a micron-scale, structural-defect-bearing layer. The reduction in lattice thermal transport is measured using laser thermoreflectance. Conductivity changes from different implantation temperatures suggest dislocation loops contribute little to phonon scattering while nanoscale defects serve as effective scatterers, offering a pathway for thermal engineering.