Thermophysical properties research progress of ferroelastic RETaO₄ ceramics

Working temperature is essential for the gas efficiency and energy conversion efficiency of multifarious aero engines, gas turbines, and hypersonic vehicle engines. Thermal barrier coatings （TBCs） are used in the high-temperature alloy components of aforementioned machines to provide thermal insulation and increase their working temperature. The most applied TBC is yttria stabilized zirconia （YSZ）, but it can no longer meet the demands of current industry due to its high thermal conductivity, mismatching thermal expansion coefficients （TECs）, and insufficient working temperature. It is urgent for scholars to investigate the next-generation TBC materials having low thermal conductivity, long lifetime, and high working temperature. The low fracture toughness, low TECs, weak high-temperature phase stability, and other weaknesses inhibit RE₂Zr₂O₇, REPO₄, RE₂SiO₅, RE₂Ce₂O₇, and RE–Al–O oxides from being applied as TBCs. Ferroelastic rare earth tantalates （RETaO₄） are considered as the next-generation TBCs with ultra-high working temperature based on their unique ferroelastic toughening, low thermal conductivity, high TECs, and low Young’s modulus. This paper reviews the thermophysical properties of RETaO₄ ceramics, including their crystal structures, microstructures, and mechanical/thermal properties （hardness, acoustic velocity, modulus, thermal conductivity, TECs, phase stability, and so on）. It is believed that RETaO₄ ceramics are candidate TBCs with high working temperature, and this paper provides scholars with some suggestions and future investigation directions on these series ceramics.