Novel high-pressure phases with superconductivity and superhardness in cerium nitrides predicted from first-principles calculations

First-principles calculations were performed on Ce-N system at high pressures. A series of Ce-N compounds were investigated including electronic band, phonon spectra,elastic properties and electron–phonon couplings. It is worth noting that R3¯m-CeN6 is stable above the pressure of 50 GPa, and its hardness reaches 25.57 GPa. When the condensation of N atoms further increases, we found a novel composition of R3¯-CeN8, with a hardness of 43.97 GPa. Furthermore, R3¯-CeN8 emerges superconductivity with an estimated critical temperature Tc of 31.72 K at 180 GPa. The calculated elastic properties of R3¯-CeN8 show that its gravimetric energy density reaches 3.81 kJ/g, which is higher than that of traditional energy materials. This work enriches the theoretical study of the Ce-N system and is expected to provide theoretical guidance for the experimental synthesis of cerium nitrides compounds.