Pressure-Stabilized New Phase of CaN4**Supported by the National Key Technology Research and Development Program of China under Grant No. 2018YFA0305900, the National Natural Science Foundation of China under Grant Nos. 11634004, 51320105007, 11604116 and 51602124, and the Program for Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China under Grant No. IRT1132.

Abstract

We propose a new CaN4 high pressure structure with the P21/m space group. The P21/m-CaN4 structure is constituted by the infinite armchair N-chain. The dynamical stability and mechanical stability are verified by the calculations of phonon dispersion curves and elastic constants. The enthalpy difference calculation shows that the P21/m phase is more stable than the reported P41212 phase. The advantaged properties of P21/m-CaN4, such as high nitrogen content (58.3%) and low polymerization pressure (18.3 GPa), allow it to be a potential high energy material. Band structure calculation shows that the P21/m-CaN4 structure is a metallic phase. The nonpolar covalent single N–N bond is a sigma bond. The charge transfer between the Ca and N atoms results in an ionic bond interaction.