Characteristics of ferroelastic domains and thermal transport limits in HfO₂ alloying YTaO₄ ceramics

Low thermal conductivity and a ferroelastic tetragonal-monoclinic phase transition are essential for the use of YTaO₄ in thermal barrier coatings. The phonon scattering mechanism of HfO₂ alloying YTaO₄ is elucidated via the analysis of microstructural characteristics, and a limit thermal conductivity (1.3 W·m⁻¹·K⁻¹) is achieved. Furthermore, a revised model is developed to successfully derive high-temperature phonon thermal conductivity, showing a decrease in the phonon scattering coefficient as strain field fluctuations decrease. This proves that the phonon scattering coefficient is temperature dependent. Atomic weight disorder plays a significant role in thermal conductivity reduction, whereas HfO₂ alloying enhances lattice symmetry and weakens the phonon scattering, and thus mitigates thermal conductivity reduction. Additionally, domain boundary width and spacing mismatch between neighboring domains cause the scattering of phonons and further reduce the thermal conductivity. Finally, evidence of a diffusive domain boundary validates that tetragonal-monoclinic transition is a second-order process.