Order–Disorder Transition and Unconventional Thermal Conductivities of the (Sm _1−x Yb _x ) ₂ Zr ₂ O ₇ Series

Abstract

Low‐thermal‐conductivity rare earth zirconates ( Re 2 Zr 2 O 7 ) have recently been identified as promising thermal barrier coating materials. We observed an order–disorder transition in the (Sm 1− x Yb x ) 2 Zr 2 O 7 series with the changing x value and investigated the thermal conductivity variation. Structural analysis by X‐ray diffraction and Raman spectroscopy shows that the (Sm 1− x Yb x ) 2 Zr 2 O 7 series undergo a discontinuous phase transition from an ordered pyrochlore phase to a disordered fluorite one between the x =1/6 and x =1/3 compositions. Meanwhile, both of the sound velocity and Young's modulus reveal a dramatic reduction, indicating the lattice softening accompanying the order–disorder transition. The thermal conductivities of the (Sm 1− x Yb x ) 2 Zr 2 O 7 series are different from the conventional behavior of a simple alloying system and show a minimum thermal conductivity value at the transition composition (Sm 2/3 Yb 1/3 ) 2 Zr 2 O 7 , which possibly arises from the enhanced phonon scattering due to the lattice softening.