Low thermal conductivity and anisotropic thermal expansion of ferroelastic (Gd1−xYx)TaO4 ceramics

Abstract

In this paper, (Gd1−xYx)TaO4 ceramics had been fabricated by solid-phase synthesis reaction. Each sample was found to crystallize in a monoclinic phase by X-ray diffraction (XRD). The properties of (Gd1−xYx)TaO4 were optimized by adjusting the ratio of Gd/Y. (Gd1−xYx)TaO4 had a low high-temperature thermal conductivity (1.37–2.05 W·m−1·K−1), which was regulated by lattice imperfections. The phase transition temperature of the (Gd1−xYx)TaO4 ceramics was higher than 1500 °C. Moreover, the linear thermal expansion coefficients (TECs) were 10.5×10−6 K−1 (1200 °C), which was not inferior to yttria-stabilized zirconia (YSZ) (11×10−6 K−1, 1200 °C). (Gd1−xYx)TaO4 had anisotropic thermal expansion. Therefore, controlling preferred orientation could minimize the TEC mismatch when (Gd1−xYx)TaO4 coatings were deposited on different substrates as thermal barrier coatings (TBCs). Based on their excellent properties, it is believed that the (Gd1−xYx)TaO4 ceramics will become the next generation of high-temperature thermal protective coatings.