Stable nitrogen-rich yttrium nitrides under high pressure

Polynitrides have excellent physical and chemical properties as well as have drawn wide attention. Through the first-principles calculations and CALYPSO structure searching approach, we calculated the overall structure of YN components (from 0.5 to 10) and established the pressure versus composition diagram and pressure versus structure phase diagram of the YN system. This paper focuses on the YN2 structure (space group P21) which can be stable at 0 GPa and the YN10 structure with the highest nitrogen content (space group Imm2) with the intriguing chain-like N10 cage structure appears. Under ambient conditions, the YN10 structure has a high energy density (9.33 kJ g−1). By calculating the phonon dispersion curve, the structure has better dynamic stability at 250 GPa. Seven structures (Y2N, YN, YN2, YN3, YN5, YN8, YN10) that appear on convex hull graphs in all YN systems are also calculated. Their dynamics, mechanics and related electronic properties are described in the appendix. We hope that our theoretical research can facilitate future experimental realization and help to advance the research on nitrogen chains.