Effects of doping on thermal conductivity of pyrochlore oxides for advanced thermal barrier coatings

Pyrochlore oxides of general composition, A2B2O7, where A is a 3+ cation (La to Lu) and B is a 4+ cation (Zr, Hf, Ti, etc.) have high melting point, relatively high coefficient of thermal expansion, and low thermal conductivity which make them suitable for applications as high-temperature thermal barrier coatings. The effect of doping at the A site on the thermal conductivity of a pyrochlore oxide La2Zr2O7, has been investigated. Oxide powders of various compositions La2Zr2O7, La1.7Gd0.3Zr2O7, La1.7Yb0.3Zr2O7 and La1.7Gd0.15Yb0.15Zr2O7 were synthesized by the citric acid sol–gel method. These powders were hot-pressed into discs and used for thermal conductivity measurements using a steady-state laser heat flux test technique. The rare-earth oxide doped pyrochlores La1.7Gd0.3Zr2O7, La1.7Yb0.3Zr2O7 and La1.7Gd0.15Yb0.15Zr2O7 had lower thermal conductivity than the undoped La2Zr2O7. The Gd2O3 and Yb2O3 co-doped composition showed the lowest thermal conductivity.