The search for synthesis methods which are simple, green, reliable, scalable and generalizable for functional complex metal oxides such as rare earth hafnates RE2Hf2O7 has been an area of interest for many researchers in recent years. The RE2Hf2O7 series compounds are functional materials that exist in fluorite or pyrochlore phase depending on synthesis method and calcination temperature. In this study, we have investigated the process of synthesis, crystal structure stabilization and phase transition in a series of RE2Hf2O7 compounds, synthesized by the coprecipitation process of a single-source complex hydroxide precursor followed with direct calcination or molten-salt synthesis (MSS) method. Phase pure RE2Hf2O7 (RE = Y, La, Pr, Gd, Er, and Lu) ultrafine nanostructured powders are obtained after calcinating the precursor in a molten salt at 650 °C. Moreover, we have demonstrated that the MSS method can successfully stabilize ideal pyrochlore structured La2Hf2O7 and Pr2Hf2O7 in the nanodomain, which is not possible by direct calcination of the coprecipitated precursor. We have proposed mechanisms to elucidate the differences in these two synthesis methods and highlighted the superiority of the MSS method for the production of RE hafnate nanoparticles.

Molten-salt synthesis of pyrochlore RE2Hf2O7 nanoparticles

2019 Fall National Meeting

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