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.

Improved wear resistance and low thermal radiative conductivity of a middle‐entropy tantalate Y0.5Gd0.5Ta0.5Nb0.5O4

“…Thermal properties of YGTN ceramics compared with other ceramics 22,34,35 : (A) specific heat; (B) thermal diffusivity; (C) thermal conductivity; (D) phonon mean free path…”

“…Thermal properties of YGTN ceramics compared with the GdTaO 4 , YTaO 4 , GdNbO 4 , and YNbO 4 34,35 : (A) inverse of thermal diffusivity; (B) phonon thermal conductivity; (C) photon thermal conductivity; (D) experimental, theoretical, and limit thermal conductivities of YGTN…”

“…The temperature dependence of thermal expansion properties of YGTN ceramics compared with the GdTaO 4 , YTaO 4 , GdNbO 4 , and YNbO 4 34,35 : (A) thermal expansion rate (Δ L / L 0 ); (B) thermal expansion coefficients (TECs)…”

“…Variation of E and H measured by nanoindentation of YGTN and comparison with other thermal barrier coatings (TBCs) materials: (A) H and E as a function of indentation load; (B) E and H for YGTN and other TBCs materials 34,35,45,47,55,56 …”

“…where F(h) refers to the function of the loading curve. Elastic work (W e ) is obtained by integrating the unloading 34,35,45,47,55,56 curve, and the corresponding expression is…”