Investigation of La³⁺ Doped Yb₂Sn₂O₇ as new thermal barrier materials

Low thermal conductivity is one of the key requirements for thermal barrier coating materials. From the consideration of crystal structure and ion radius, La³⁺ Doped Yb₂Sn₂O₇ ceramics with pyrochlore crystal structures were synthesized by sol-gel method as candidates of thermal barrier materials in aero-engines. As La³⁺ and Yb³⁺ ions have the largest radius difference in lanthanoid group, La³⁺ ions were expected to produce significant disorders by replacing Yb³⁺ ions in cation layers of Yb₂Sn₂O₇. Both experimental and computational phase analyses were carried out, and good agreement had been obtained. The lattice constants of solid solution (La_xYb_1-x)₂Sn₂O₇ (x=0.3, 0.5, 0.7) increased linearly when the content of La³⁺ was increased. The thermal properties (thermal conductivity and coefficients of thermal expansion) of the synthesized materials had been compared with traditional 8wt.% yttria stabilized zirconia (8YSZ) and La₂Zr₂O₇ (LZ). It was found that La³⁺ Doped Yb₂Sn₂O₇ exhibited lower thermal conductivities than un-doped stannates. Amongst all compositions studied, (La_0.5Yb_0.5)₂Sn₂O₇ exhibited the lowest thermal conductivity (0.851W·m^-1·K^-1 at room temperature), which was much lower than that of 8YSZ (1.353W·m^-1·K^-1), and possessed a high coefficient of thermal expansion (CTE), 13.530×10^-6K^-1 at 950°C.