Fundamentals of Thermal Transport and Energy Conversion in Ultra‐High Temperature Ceramics: From Microscale Mechanisms to Macroscopic Properties

Ultra-high temperature ceramics (UHTCs) are pivotal materials for applications in extreme environments, such as hypersonic flight, advanced nuclear systems, and next-generation energy conversion, where their thermal transport and radiative properties dictate performance. This review examines the thermal transport and energy conversion fundamentals of UHTCs. It covers the unique characteristics and extreme-condition stability of these materials, alongside the governing heat transfer mechanisms-including phonon-phonon, electron-phonon, and photon-matter interactions. The influence of micro/nanostructure and composition on thermal conductivity and high-temperature radiative properties is analyzed. The review also assesses the potential of UHTCs for thermoelectric energy conversion and highlights the growing role of physics-informed machine learning in accelerating their discovery and optimization, from high-throughput screening to multiscale modeling. Key challenges and future opportunities in predictive design, scalable synthesis, and microstructure control for extreme-environment applications are critically assessed, offering a roadmap for advancing UHTCs toward future technological demands.