Low-thermal-conductivity rare-earth zirconates for potential thermal-barrier-coating applications

Rare-earth zirconates have been identified as a class of low-thermal-conductivity ceramics for possible use in thermal barrier coatings (TBCs) for gas-turbine engine applications. To document and compare the thermal conductivities of important rare-earth zirconates, we have measured the thermal conductivities of the following hot-pressed ceramics: (i) Gd2Zr2O7 (pyrochlore phase), (ii) Gd2Zr2O7 (fluorite phase), (iii) Gd2.58Zr1.57O7 (fluorite phase), (iv) Nd2Zr2O7 (pyrochlore phase), and (v) Sm2Zr2O7 (pyrochlore phase). We have also measured the thermal conductivity of pressureless-sintered 7 wt% yttria-stabilized zirconia (7YSZ)-the commonly used composition in current TBCs. All rare-earth zirconates investigated here showed nearly identical thermal conductivities, all of which were similar to30% lower than the thermal conductivity of 7YSZ in the temperature range 25degrees-700degreesC. This finding is discussed qualitatively with reference to thermal-conductivity theory.