Supercritical hydrothermal synthesis of highly crystalline lanthanum zirconate nanoparticles

Pyrochlore La₂Zr₂O₇ nanoparticles were synthesised in supercritical water at 450 °C under a relatively short reaction time. Compared to traditional methods, e.g. solid-state reactions, hydrothermal methods, highly crystalline pyrochlore La₂Zr₂O₇ nanoparticles were obtained even under such mild conditions. Furthermore, the supercritical hydrothermal synthesis of La₂Zr₂O₇ nanoparticles was highly sensitive to the solution pH employed, as La(OH)₃ and ZrO₂ were formed instead of La₂Zr₂O₇ at pH 10 or lower. pH-controlled dissolution of La(OH)₃ and ZrO₂ thus regulated the formation and growth of La₂Zr₂O₇. This environmentally benign supercritical hydrothermal process will serve as a novel synthetic method for the preparation of La₂Zr₂O₇ with replacing conventional processes.