Thermal conductivity of (Sm_1-xLa_x)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, (Sm_0.75La_0.25)₂Zr₂O₇, (Sm_0,5 La_0.5)₂ Zr₂O₇, (Sm_0.25La_0.75)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 microstructure 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 (Sm_0.75 La_0.25)₂Zr₂O₇ and (Sm_0.5 La_0.5)₂ Zr₂O₇ had lower thermal conductivity than the undoped Sm₂Zr₂O₇. The thermal conductivity of (Sm_0.25La_0.75)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.