The thermophysical properties and defect chemistry of HfO2–Sm3TaO7 ceramics

HfO 2 –Sm 3 TaO 7 ceramics are prepared through a solid-state reaction method. The X-ray diffraction and structural refinement show that the phase structures of HfO 2 –Sm 3 TaO 7 ceramics are an ordered orthorhombic phase and the space groups are belonging to Ccmm . The degree of the structural disorder increases with increasing HfO 2 content. The solid solution mechanism reveals that Hf 4+ exists in the form of interstitial ions that cause crystal expansion when the doping content is less than 4 mol%. When the doping concentration of HfO 2 ≥ 4 mol%, the Hf 4+ ions can substitute an equal number of Sm 3+ and Ta 5+ ions. The phase transition of Sm 3 TaO 7 ceramics is removed with increasing HfO 2 content, and the 8 mol% HfO 2 –Sm 3 TaO 7 ceramics have a high thermal expansion coefficient of 10.2 × 10 −6 K −1 at 1200 °C. The 2 mol% HfO 2 –Sm 3 TaO 7 ceramics have the lowest thermal conductivity (1.03 W/m K at 900 °C), which is lower than previous research of the 7–8 YSZ. The outstanding thermophysical properties of HfO 2 –Sm 3 TaO 7 ceramics indicate that they are potential thermal-barrier coating materials.