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

Pyrochlore oxides of general composition, A 2B 2O 7, 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 La 2Zr 2O 7, has been investigated. Oxide powders of various compositions La 2Zr 2O 7, La 1.7Gd 0.3Zr 2O 7, La 1.7Yb 0.3Zr 2O 7 and La 1.7Gd 0.15Yb 0.15Zr 2O 7 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 La 1.7Gd 0.3Zr 2O 7, La 1.7Yb 0.3Zr 2O 7 and La 1.7Gd 0.15Yb 0.15Zr 2O 7 had lower thermal conductivity than the undoped La 2Zr 2O 7. The Gd 2O 3 and Yb 2O 3 co-doped composition showed the lowest thermal conductivity.