Phase structure and thermophysical properties of co-doped La2Zr2O7 ceramics for thermal barrier coatings

La2Zr2O7 has high melting point, low thermal conductivity and relatively high thermal expansion which make it suitable for application as high-temperature thermal barrier coatings. Ceramics including La2Zr2O7, (La0.7Yb0.3)2(Zr0.7Ce0.3)2O7 and (La0.2Yb0.8)2(Zr0.7Ce0.3)2O7 were synthesized by solid state reaction. The effects of co-doping on the phase structure and thermophysical properties of La2Zr2O7 were investigated. The phase structures of these ceramics were identified by X-ray diffraction, showing that the La2Zr2O7 ceramic has a pyrochlore structure while the co-doped ceramics (La0.7Yb0.3)2(Zr0.7Ce0.3)2O7 and the (La0.2Yb0.8)2(Zr0.7Ce0.3)2O7 exhibit a defect fluorite structure, which is mainly determined by ionic radius ratio r(Aav.3+)/r(Bav.4+). The measurements for thermal expansion coefficient and thermal conductivity of these ceramics from ambient temperature to 1200 °C show that the co-doped ceramics (La0.7Yb0.3)2(Zr0.7Ce0.3)2O7 and (La0.2Yb0.8)2(Zr0.7Ce0.3)2O7 have a larger thermal expansion coefficient and a lower thermal conductivity than La2Zr2O7, and the (La0.2Yb0.8)2(Zr0.7Ce0.3)2O7 shows the more excellent thermophysical properties than (La0.7Yb0.3)2(Zr0.7Ce0.3)2O7 due to the increase of Yb2O3 content.