Thermal conductivity of ceramics in the ZrO 2 -GdO 1.5 system

Low thermal conductivity ceramics in the ZrO 2 –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 x GdO 1.5 ·(1 – x )ZrO 2 (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 ZrO 2 -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 ZrO 2 was less pronounced. The thermal conductivity was less sensitive to the composition with increasing temperature. The thermal conductivity of pyrochlore Gd 2 Zr 2 O 7 ( 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 ZrO 2 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 ZrO 2 and GdO 1.5 . In the case of solid solutions, phonon scattering by cation mass fluctuations and additional scattering by oxygen vacancies on the ZrO 2 -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.