Molten salt synthesis of La2Zr2O7 ultrafine powders

Ultrafine powders of pyrochlore-type La2Zr2O7 were synthesized via a simple molten salt mediated process using zirconium oxide and lanthanum oxide as raw materials, and sodium chloride, potassium chloride and sodium fluoride to form a reaction medium. The effects of reaction temperature, salt/reactant ratio and salt type on the La2Zr2O7 formation were investigated. Among the three attempted salt assemblies (KCl-LiCl, Na2CO3-K2CO3, and NaCl-KCl-NaF), NaCl-KCl-NaF showed the best accelerating effect on the La2Zr2O7 formation. At a given temperature, the La2Zr2O7 content in the final products increased with the increase in the salt amount. Phase pure submicron sized La2Zr2O7 ultrafine powders were obtained after 3 h firing at 1100 °C with the salt/reactant weight ratio of 5:1 or at 1200 °C with salt/reactant weight ratio of 3:1. The synthesis temperature (1100 °C) was much lower than that required by the conventional solid-state mixing method or a wet chemical method. The “dissolution-precipitation” mechanism had dominated the synthesis process.