Investigation of La3 + Doped Yb2Sn2O7 as new thermal barrier materials. (15th November 2015) - Wang, Jing
Abstract: Low thermal conductivity is one of the key requirements for thermal barrier coating materials. From the consideration of crystal structure and ion radius, La 3 + Doped Yb2 Sn2 O7 ceramics with pyrochlore crystal structures were synthesized by sol–gel method as candidates of thermal barrier materials in aero-engines. As La 3 + and Yb 3 + ions have the largest radius difference in lanthanoid group, La 3 + ions were expected to produce significant disorders by replacing Yb 3 + ions in cation layers of Yb2 Sn2 O7 . Both experimental and computational phase analyses were carried out, and good agreement had been obtained. The lattice constants of solid solution (La x Yb1 − x )2 Sn2 O7 ( x = 0.3, 0.5, 0.7) increased linearly when the content of La 3 + 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 La2 Zr2 O7 (LZ). It was found that La 3 + Doped Yb2 Sn2 O7 exhibited lower thermal conductivities than un-doped stannates. Amongst all compositions studied, (La0.5 Yb0.5 )2 Sn2 O7 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 950 °C. Graphical abstract: Highlights: La ions were introduced to create crystal disorders by replacing Yb in Yb2 Sn2 O7 . Experimental and computational phase analyses showed good agreement. High coefficients of thermal expansion were obtained from the doped ceramics. Low thermal conductivities were achieved from the doped ceramics.