Low-thermal conduction mechanisms in cation-deficient perovskite type oxides

Cation-deficient perovskite type oxides of the form LnTa₃O₉ (Ln: lanthanoid) are receiving considerable attention as new thermal barrier coating materials because of their extremely low thermal conductivities. In this study we synthesized LnTa₃O₉ (Ln: Y, La, and Yb) powders by a urea hydrolysis method, followed by pressureless sintering, and investigated the mechanisms behind their low thermal conductivities by performing microstructure analyses using transmission electron microscopy and first-principles molecular dynamics calculations. Thermal conductivity behavior was found to vary with the atomic weight and ion radius of the Ln species. Formation of nano-sized domains, together with the high concentration of intrinsic Ln vacancies, appears to be largely responsible for the very low thermal conductivities of YbTa₃O₉ and YTa₃O₉. The nanodomains correspond to regions with different orientations of Ta-O₆ octahedral tilting, and tend to form in crystals with smaller Ln ion radii.