Nanocrystalline yttria‐stabilized hafnia ceramics with low thermal conductivity and enhanced mechanical properties

ABSTRACT Hafnia‐based materials have become promising materials for thermal barrier applications above 1200°C. In this study, a series of yttria‐stabilized hafnia (YSH) ceramics (0‒20 mol% Y 2 O 3 ) were prepared by spark plasma sintering under 100 MPa. In addition, the effects of dopant content and sintering temperature on mechanical properties and thermal conductivity were investigated. YSH ceramics consisted of monoclinic and cubic phases when Y 2 O 3 dopant content ranged from 2 to 10 mol%. The 10 mol% Y 2 O 3 ‐doped HfO 2 ceramic sintered at 1300°C exhibited ultrafine grains of 370 nm, high hardness of 11.31 GPa, high fracture toughness of 2.89 MPa m 1/2 , and low thermal conductivity of 1.52 W m −1  K −1 at 1200°C. Ultrafine microstructures, lattice distortion, and interface defects largely contributed to high mechanical properties and low thermal conductivity.