Thermal radiation and cycling properties of (Ca, Fe) or (Sr, Mn) co-doped La2Ce2O7 coatings

La2Ce2O7 with low thermal conductivity as a potential candidate of thermal barrier coatings (TBCs) was co-doped with (Ca, Fe) or (Sr, Mn) in order to further improve its thermal radiation at high temperatures. The microstructure, chemical composition, infrared emission properties (reflection and absorption properties) and thermal cycling lifetime of the coatings were respectively investigated. The results revealed that La(2-x)Ca(x)Ce(2-)xFe(x)O(7+)delta and La2-xSrxCe2-xMnxO7+delta coatings had defected fluorite structure and their infrared emittances were much higher than that of the parent La2Ce2O7. The superior infrared emission could be ascribed to the enhancement of the intrinsic absorption (electron transition absorption), free-carrier absorption and impurity absorption as well as lattice vibration absorption. However, the thermal cycling lifetime of La2Ce2O7 coatings presented a reduction after the (Ca, Fe) or (Sr, Mn) substitution, primarily due to the decrease in the fracture toughness and the increase in the thermal conductivity.