Low thermal conductivity and anisotropic thermal expansion of ferroelastic (Gd_1−xY_x)TaO₄ ceramics

In this paper, (Gd_1−xY_x)TaO₄ ceramics have 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 (Gd_1−xY_x)TaO₄ were optimized by adjusting the ratio of Gd/Y. (Gd_1−xY_x)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 (Gd_1−xY_x)TaO₄ ceramics was higher than 1500 ℃. Moreover, the linear thermal expansion coefficients (TECs) were 10.5×10⁻⁶ K⁻¹ (1200 ℃), which was not inferior to yttria-stabilized zirconia (YSZ) (11×10⁻⁶ K⁻¹, 1200 ℃). (Gd_1−xY_x)TaO₄ had anisotropic thermal expansion. Therefore, controlling preferred orientation could minimize the TEC mismatch when (Gd_1−xY_x)TaO₄ coatings were deposited on different substrates as thermal barrier coatings (TBCs). Based on their excellent properties, it is believed that the (Gd_1−xY_x)TaO₄ ceramics will become the next generation of high-temperature thermal protective coatings.