Thermal conductivity of (Sm1-xLax)2Zr2O7 (x=0,0.25,0.5,0.75 and 1) oxides for advanced thermal barrier coatings

Pyrochlore oxides of general compositions, A2Zr2O7, where A is a 3+ cation (La to Lu), are promising candidate materials for applications as high temperature thermal barrier coatings because of their high melting points, high thermal expansion coefficients, and low thermal conductivities. In this study, oxides of Sm2Zr2O7, (Sm0.75La0.25)2Zr2O7, (Sm0,5 La0.5)2 Zr2O7, (Sm0.25La0.75)2Zr2O7 and La2Zr2O7 were prepared by solid reactions at 1600 °C for 10 h using Sm2O3, La2O3 and ZrO2 as the reactants. The phase compositions of these ceramic materials were analyzed by X-ray diffractometer (XRD) and fourier transform infrared spectroscopy (FT-IR) methods, respectively. The micro-structure was observed by scanning electronl microscope (SEM). The thermal conductivities of these ceramic materials were measured using laser-flash method. XRD and FT-IR results showed that pure ceramic materials with pyrochlore structure were prepared successfully. SEM results indicated that microstructures of these ceramic materials were dense and grain boundaries were very clean. The La2O3 doped Sm2Zr2O7 pyrochlores (Sm0.75 La0.25)2Zr2O7 and (Sm0.5 La0.5)2 Zr2O7 had lower thermal conductivity than the undoped Sm2Zr2O7. The thermal conductivity of (Sm0.25La0.75)2Zr2O7 was found to be lower than that of La2Zr2O7. The results showed that these ceramic materials had the potential to be used as candidate materials for TBCs.