Investigation of La3+ Doped Yb2Sn2O7 as new thermal barrier materials

Abstract

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 synthesised by sol-gel method as candidates of thermal barrier materials in aero-engines. As La3+ and Yb3+ ions have the largest radius difference in lanthanoids group, La3+ ions were expected to produce significant disorders by replacing Yb3+ ions in cation layers of Yb2Sn2O7. Both experimental and computational phase analysis were carried out, and good agreement had been obtained. The lattice constants of solid solution (LaxYb1-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 8 wt.% 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, (La0.5Yb0.5)2Sn2O7 exhibited the lowest thermal conductivity (0.851 W·m-1·K-1 at room temperature), which was much lower than that of 8YSZ (1.353 W·m-1·K-1), and possessed a high coefficient of thermal expansion (CTE), 13.530×10-6 K-1 at 950oC.