Order-Disorder Transition and Unconventional Thermal Conductivities of the (Sm_(1-x)Yb_x)_2Zr_2O_7 Series

摘要

Low-thermal-conductivity rare earth zirconates (Re_2Zr_2O_7) have recently been identified as promising thermal barrier coating materials. We observed an order-disorder transition in the (Sm_(1-x)Yb_x)_2Zr_2O_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)_2Zr_2O_7series 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)_2Zr_2O_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))_2Zr_2O_7, which possibly arises from the enhanced phonon scattering due to the lattice softening.