High-Pressure Metathesis Synthesis and Physical Property Characterization of Cubic Fluorite-Structured CeO₂Cl_0.07

The 4f electron of Ce has long attracted extensive attention due to their unique delocalization mechanism and their influence on atomic structure, phase transformation behavior, and magnetic structure. In this paper, CeO₂Cl_0.07 was synthesized with a cubic fluorite structure by changing the stoichiometry of the precursors (CeCl₃, MgO powder) and regulating the high-pressure solid-state metathesis (HSM) reaction under high temperature and high pressure conditions (1873 K, 5 GPa) provided by a large volume press. Then pressure was provided by a diamond anvil cell (DAC), and the sample was characterized by high-pressure in-situ synchrotron X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and high-pressure Raman spectroscopy. By comparing the obtained pressure-volume (p-V) curve with CeO₂, it is found that CeO₂Cl_0.07 is more compressible. The high-pressure Raman phonon spectrum (F_2g) is obtained, indicating that the pressure-dependent behavior of CeO₂Cl_0.07 exhibits anomalous changes at 0–2 GPa and near 15 GPa under non-hydrostatic pressure. We believe that the doping of Cl elements introduces oxygen vacancies, which increases the concentration of Ce³⁺, thereby causing the delocalization of 4f electron and resulting in the observed phenomenon. This study developed a new high-pressure synthesis pathway for cerium-based compounds and revealed their behavior under high-pressure conditions.