Thermal conductivity and expansion coefficient of Ln2LaTaO7 (Ln=Er and Yb) oxides for thermal barrier coating applications

Two kinds of novel Ln2LaTaO7 (Ln=Er and Yb) ceramics were prepared via high-temperature solid reaction method. The phase composition, micro-morphology and thermophysical properties were investigated. Results indicate that pure Ln2LaTaO7 ceramics with single fluorite-type structure are synthesized successfully. The thermal conductivities of Er2LaTaO7 and Yb2LaTaO7 are in the range of 1.22–1.43 W/m K and 1.17–1.51 W/m K, respectively, which are much lower than that of YSZ. The lower thermal conductivity can be attributed to the phonon scattering caused by oxygen vacancies and the substituting atoms. The average thermal expansion coefficients of Yb2LaTaO7 and Er2LaTaO7 are 9.94×10−6/K and 9.63×10−6/K, respectively. As compared with Yb2LaTaO7, the higher thermal expansion coefficient of Er2LaTaO7 can be ascribed to its lower ionic-bond strength between cations at sites A and B.