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

Abstract La 2 Zr 2 O 7 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 La 2 Zr 2 O 7 , (La 0.7 Yb 0.3 ) 2 (Zr 0.7 Ce 0.3 ) 2 O 7 and (La 0.2 Yb 0.8 ) 2 (Zr 0.7 Ce 0.3 ) 2 O 7 were synthesized by solid state reaction. The effects of co-doping on the phase structure and thermophysical properties of La 2 Zr 2 O 7 were investigated. The phase structures of these ceramics were identified by X-ray diffraction, showing that the La 2 Zr 2 O 7 ceramic has a pyrochlore structure while the co-doped ceramics (La 0.7 Yb 0.3 ) 2 (Zr 0.7 Ce 0.3 ) 2 O 7 and the (La 0.2 Yb 0.8 ) 2 (Zr 0.7 Ce 0.3 ) 2 O 7 exhibit a defect fluorite structure, which is mainly determined by ionic radius ratio r (A av. 3+ )/ r (B av. 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 (La 0.7 Yb 0.3 ) 2 (Zr 0.7 Ce 0.3 ) 2 O 7 and (La 0.2 Yb 0.8 ) 2 (Zr 0.7 Ce 0.3 ) 2 O 7 have a larger thermal expansion coefficient and a lower thermal conductivity than La 2 Zr 2 O 7 , and the (La 0.2 Yb 0.8 ) 2 (Zr 0.7 Ce 0.3 ) 2 O 7 shows the more excellent thermophysical properties than (La 0.7 Yb 0.3 ) 2 (Zr 0.7 Ce 0.3 ) 2 O 7 due to the increase of Yb 2 O 3 content.