Abstract
The evolution of structure and thermal conductivity (k) has been studied for a range of Y–La2Zr2O7 solid solutions. Within the pyrochlore range (x<0.40) Y3+ solely substitutes for La3+ below a critical composition factor (x=0.15), above which it substitutes for both La3+ and the Zr4+. 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 Y3+ cations (rattlers) oscillating locally and independently in oversized anionic cages [(La/Y)O8]. The ultralow and glassy k makes Y3+-doped La2Zr2O7 pyrochlores promising candidate materials for high temperature thermal barrier coating topcoats.
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