Stability of fluorite-type La2Ce2O7 under extreme conditions

• La2Ce2O7 transforms to a metastable phase at pressure higher than 21 GPa.
• La2Ce2O7 reacts with water at ∼1 GPa and above 200 °C.
• The pressure-induced phase transition is reversible.

The structural stability of fluorite-type La2Ce2O7 was studied at pressure up to ∼40 GPa and under hydrothermal conditions of ∼1 GPa and up to 350 °C, respectively, using synchrotron X-ray diffraction (XRD) and Raman scattering measurements. XRD measurements indicated that the fluorite-type La2Ce2O7 is not stable at pressures greater than 22.6 GPa and gradually transformed to a high-pressure phase. The high-pressure phase is not stable and changeed back to the fluorite-type structure when pressure is released. The La2Ce2O7 fluorite is also not stable under hydrothermal conditions and began to react with water at 200–250 °C. Both Raman and XRD results suggest that lanthanum hydroxide La(OH)3 and La3+-doped CeO2 fluorite are the dominant products after hydrothermal treatment.

The fluorite-type La2Ce2O7 reacted with water at hydrothermal condition (1 GPa, and above 200 °C), and formed rare earth hydroxides.Figure optionsDownload as PowerPoint slide