Glass-like thermal conductivities in (La 1-x1 Y x1) 2 (Zr 1-x2 Y x2) 2 O 7-x2 (x = x 1 + x 2, 0≤ x ≤ 1.0) solid solutions

The evolution of structure and thermal conductivity (k) has been studied for a range of Y-La 2Zr 2O 7 solid solutions. Within the pyrochlore range (x <0.40) Y 3+ solely substitutes for La 3+ below a critical composition factor (x = 0.15), above which it substitutes for both La 3+ and the Zr 4+. A glass-like k, approaching the amorphous limit, is observed within a certain composition range (0.20 ≤ x <0.40). The glass-like k behaviour is attributed to a phonon localization effect that arises from small and weakly bound Y 3+ cations (rattlers) oscillating locally and independently in oversized anionic cages [(La/Y)O 8]. The ultralow and glassy k makes Y 3+-doped La 2Zr 2O 7 pyrochlores promising candidate materials for high temperature thermal barrier coating topcoats. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.