Sintering behavior and thermal conductivity of Y₂O₃ fully stabilized HfO₂ ceramics

A series of Y₂O₃ fully stabilized HfO₂ ceramics (Hf_1−xY_xO_2−0.5x, x = 0.20, 0.24, 0.28, 0.32, 0.36 and 0.40) were synthesized by solid-state reaction at 1500 °C. The phase composition, thermal conductivity and sintering behavior at 1400 °C of the ceramic bulks were studied. The Hf_1−xY_xO_2−0.5x ceramics were comprised of pure cubic phase with disordered fluorite structure. No phase transformation occurred in the ceramics with Y³⁺ doping concentration ranging from 0.24 to 0.36. Both Hf_0.64Y_0.36O_1.82 and Hf_0.6Y_0.4O_1.8 samples revealed the lowest grain growth rate when sintered at 1400 °C, indicating good resistance to sintering. However, the Vicker’s hardness and Young’s modulus after annealed for 96 h at 1400 °C for the Hf_0.64Y_0.36O_1.82 sample were 8.97 and 200 GPa, respectively, much lower than those of the Hf_0.6Y_0.4O_1.8 (14.51 and 237 GPa, respectively). The thermal conductivity of Hf_1−xY_xO_2−0.5x first decreased and then increased slowly as the Y³⁺ content increased, and the associated mechanism was discussed.