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.

Platinum-group metals (PGMs) nitrides represent a new class of super incompressible superhard materials, typically synthesized under extreme conditions (above 45 GPa, 2000 K) using laser-heated diamond anvil cell (LHDAC) technology via monatomic elemental chemosynthesis (A+B=AB). Exploring non-conventional synthesis methods that significantly reduce the required pressures is crucial for advancing the development and application of PGMs nitrides. In this work, OsN_x (0.16≤x≤0.38) was synthesized for the first time via a novel high-pressure coupling (HPC) reaction, using Fe₂O₃/Co₂O₃, h-BN, and Os powders as precursors under high-temperature and high-pressure conditions (15 GPa, 1800−2100 K) in a large-volume press. The HPC-synthesized metal bulk products primarily consist of OsN_x alloyed with iron-based nitrides. Phase composition and structural characterization via X-ray powder diffraction (XRD) and scanning electron microscope (SEM) confirm the formation of hexagonal OsN₂ (space group P6₃/mmc), as theoretically predicted, at pressures well below the 50 GPa threshold typically required for high-pressure monatomic elemental combination reactions. The nitrogen atoms partially occupy interstitial sites within the Os crystal structure. This study demonstrates that the HPC reaction effectively lowers the energy barrier for Os nitration, facilitating the formation of non-stoichiometric OsN_x compounds. These findings open a new synthetic route for bulk PGM nitride materials under significantly reduced pressure conditions.