Effect of point defects on the thermal transport properties of (LaxGd1-x)2Zr2O7 : Experiment and theoretical model

Thermal transport properties of solid solution (La_xGd_1-x)₂Zr₂O₇ have been investigated for thermal barrier coatings (TBCs) application. The introduction of point defects was intended to provide extra phonon scattering, and much lower thermal conductivity for the solid solution has been obtained compared with La₂Zr₂O₇ and Gd₂Zr₂O₇ . The phonon mean free paths of the solid solution were estimated and discussed with respect to the point defect scattering effect. Young’s modulus and heat capacity of the solid solution, which determine the mean velocity and the carried energy of the phonons, respectively, were measured and both showed suppression compared with the end materials, possibly due to the lattice relaxation aroused by point defects. A theoretical model, which contains no adjustable parameters, was present to accurately describe the thermal conductivities of the solid solution by taking account of the mass and strain field fluctuations induced by the point defects.