Tantalum pentoxide and yttrium oxide were used as base materials. By adding alkali metal sintering agent Li₂CO₃, the doped tantalate ceramic samples were prepared by high temperature solid-phase sintering. The effects of alkali metal sintering agent Li₂CO₃ on the physical and chemical properties of rare earth yttrium tantalate coating were studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), laser pulse method (LFA), thermal-mechanical analyzer (TMA) and UV-visive-near-infrared spectrophotometer. The results show that under the sintering system at 1530℃, the ceramic is compact, resulting in Li₃TaO₄ ceramic. With more Li₂CO₃ inclusion, the higher Li₃TaO₄ of the second phase is generated. With a stable thermal expansion coefficient, the range of 8.2-8.6×10^-6K^-1(900℃); The Young's modulus and hardness of the samples decreased with the increase of the added sintering aid dose. When 6% alkali metal sintering agent Li₂O₃ is mixed into the ceramic, the transmittance rate of YTaO₄ ceramic can be stable at more than 80%, which shows that YTaO₄ ceramic has superior potential of optical ceramics.

The function of thermal barrier coating is to protect the hot components of advanced aero-engines from hot corrosion and ensures the hot components service in high-temperature environment safely. In general, a low thermal conductivity and a high fracture toughness are the key performance indexes for the selection of novel thermal barrier coating materials. In this work, a high-entropy rare-earth tantalate ceramic of (Y_0.2Dy_0.2Sm_0.2Yb_0.2Er_0.2)TaO₄ (i.e. (5RE_0.2)TaO₄) with the superior properties was synthesized via solid-state reaction. The results indicate that (5RE_0.2)TaO₄ exhibits a low thermal conductivity (i.e., 1.68 W·m^–1·K^–1 @ 900 ℃) and a high thermal expansion coefficient (i.e., 10.0×10^–6 K^–1 @ 1200 ℃). (5RE_0.2)TaO₄ shows a high fracture toughness (i.e., 2.6 MPa·m^1/2) and a low brittleness index (i.e., 2.1 μm^–1/2) because of the unique ferroelastic toughening effect. In addition, (5RE_0.2)TaO₄ also has a promising application prospect as one of thermal barrier coating materials.