Synthesis of nanostructured La2Zr2O7 by a non-alkoxide sol–gel method: From gel to crystalline powders

Nanocrystalline La2Zr2O7 powders of single prochlore phase were synthesized by a non-alkoxide sol–gel process. Homogeneous sol, free of precipitation, was prepared by addition of citric acid, polyethylene glycol and formamide to aqueous solutions of Zr4+ and La3+ inorganic salt precursors. We found that fluorite structure La2Zr2O7 was crystallized at 1000 °C, and then transformed to pyrochlore structure at 1200 °C. With further increase in temperature, the crystalline degree of pyrochlore La2Zr2O7 powders increased. The particle size of the as-prepared La2Zr2O7 powders at 1200 °C was about 80–200 nm. With temperature increase, sintering of La2Zr2O7 particles resulted in grain size growth. Mechanism of La2Zr2O7 nano-particles as function of temperature during heat treatment was analyzed. The density of the powders sintered at 1600 °C was 96.0% of the theoretical value, and thermal conductivity ranged from 0.65 to 0.85 W·m−1·K−1, which was much lower than that of 7YSZ.