Investigating High Temperature Thermal Properties of Rare Earth Oxides for Thermal Barrier Coatings

Rare earth oxides (REOs) show promising thermal properties required of next generation thermal barrier coatings (TBCs) for ultrahigh temperature applications (1500 ^oC+). TBCs mitigate conductive heating between hot components by reducing thermal conductivity through increased phonon-phonon scattering. New research aims to explore the fundamental mechanisms for this reduction and explore other properties of interest such as melting temperature and emissivity.<br/><br/>In this work, we perform a series of thermal and optical studies via pump-probe thermoreflectance, laser radiometry, and spectroscopic ellipsometry to elucidate temperature-dependent thermal properties of REOs. With a novel laser-based metrology, thermal conductivities, melting temperatures and emissivities of ceramics over 2000 ^oC can be measured nondestructively. Understanding these trends is of utmost importance in choosing REOs that can endure cycling to operating temperatures. Additionally, through ellipsometry, the lifetimes of optical phonons can be understood. Anharmonic scattering dominates thermal transport at high temperatures so measuring lifetimes with changing temperature is important to understand fundamental energy transport in REOs. By investigating pertinent physical scattering mechanisms at relevant temperatures, we deconvolute key design considerations for next generation TBCs.