Thermal conductivity of ceramics in the ZrO₂-GdO_1.5system

Low thermal conductivity ceramics in the ZrO₂–GdO_1.5 system have potential in structural (refractories, thermal barrier coatings, thermal protection) and nuclear applications. To that end, the thermal conductivities of hot-pressed xGdO_1.5 ·(1 – x)ZrO₂ (where x = 0.05, 0.15, 0.31, 0.50, 0.62, 0.75, 0.89, and 1.00) solid solutions were measured, for the first time, as a function of temperature in the range 25 to 700 °C. On the ZrO₂-rich side, the thermal conductivity first decreased rapidly with increasing concentration of GdO_1.5 and then reached a plateau. On the GdO_1.5-rich side, the decrease in the thermal conductivity with increasing concentration of ZrO₂ was less pronounced. The thermal conductivity was less sensitive to the composition with increasing temperature. The thermal conductivity of pyrochlore Gd₂Zr₂O₇ (x = 0.5) was higher than that of surrounding compositions at all temperatures. A semiempirical phonon-scattering theory was used to analyze the experimental thermal conductivity data. In the case of pure ZrO₂ and GdO_1.5, the dependence of the thermal conductivity to the absolute temperature (T) was less than 1/T. Therefore, the minimum thermal conductivity theory was applied, which better described the temperature dependence of the thermal conductivity of pure ZrO₂ and GdO_1.5. In the case of solid solutions, phonon scattering by cation mass fluctuations and additional scattering by oxygen vacancies on the ZrO₂-rich side and by gadolinium vacancies on the GdO_1.5-side seemed to account for the composition and temperature dependence of the thermal conductivity.