Thermophysical properties of SmTaO4, Sm3TaO7 and SmTa3O9 ceramics

Abstract

SmTaO _4 , Sm _3 TaO _7 and SmTa _3 O _9 ceramics were prepared via a high temperature solid-state reaction. The results show that the phase structures of the SmTaO _4 ceramics are a monoclinic phase (space group: I2 (5)), the Sm _3 TaO _7 ceramics are an ordered orthorhombic phase (space group: Ccmm), and the SmTa _3 O _9 ceramics are an orthorhombic phase (space group: Cmmm). Macromolecular and crystal structures of Sm _3 TaO _7 and SmTa _3 O _9 are more complex than those of SmTaO _4 , which can enhance phonon scattering and reduce thermal conductivity. Compared with those of SmTaO _4 and SmTa _3 O _9 , Sm _3 TaO _7 has the smallest grain size, indicating that a small grain size has an effect on strength and ensures material stability. Because of a distorted TaO _6 octahedron and a high concentration of cation vacancy in the lattice of SmTa _3 O _9 , its thermal conductivity increases with increasing temperature. Compared with that of 7–8 YSZ, Sm _3 TaO _7 has a low thermal conductivity (1.3–1.7 W·m ^−1 ·K ^−1 at 100 °C–900 °C), and its minimum thermal conductivity is nearly 30% lower than that of YSZ. The Sm _3 TaO _7 ceramics have the highest TECs at approximately 9.82 × 10 ^−6 K ^−1 at 1200 °C, which is close to that of 7–8 YSZ (approximately 10 × 10 ^−6 ). This indicates that Sm _3 TaO _7 has the potential to be employed as a thermal barrier coating.

Keywords

• SmTaO4
• Sm3TaO7 and SmTa3O9 ceramics
• TBCs
• thermophysical properties
• thermal conductivity