Novel polymerization of nitrogen in zinc nitrides at high pressures

Abstract

Nitrogen-rich compounds containing polynitrogen are attractive candidates for high-energy-density materials. In this work, using first-principles calculations and a particle swarm optimization structural search method, four novel nitrogen-rich structures are predicted at high pressures, i.e., two ZnN3 phases with the same space group P-1 (low-pressure phase LP-ZnN3 and high-pressure phase HP-ZnN3), Cmm2-ZnN5 and Pcc2-ZnN6¬, the energy density are estimated to be 1.41 kJ/g, 1.88 kJ/g, 4.07 kJ/g, and 2.60 kJ/g, respectively. LP-ZnN3 (54~72 GPa) and HP-ZnN3 (above 72 GPa) have the lowest enthalpies in all known ZnN3 phases, and the N6 chains in LP-ZnN3 polymerize into infinite nitrogen chains in HP-ZnN3 at 72 GPa, showing a narrow-band-gap-semiconductor to metallic phase transition. Interestingly, P-1-ZnN3 has a superconducting transition temperature of 6.2 K at 50 GPa and 16.3 K at 100 GPa. In Cmm2-ZnN5 and Pcc2-ZnN6, nitrogen atoms polymerize into three-dimensional network structures and network layers under high pressures. Those predicted structures may enrich the phase diagram of high-pressure zinc nitrides, and provide clues for synthesis and exploration of novel stable polymeric nitrogen.

Polynitrogen clusters interaction with water: experimental and theoretical perspectives

“…Polynitrogen clusters are mainly composed of nitrogen atoms linked together by weak N=N double bonds or single N-N bonds [1][2][3][4]. During combustion and explosion reactions, they can be converted into diatomic nitrogen molecules, and released enormous amounts of energy without generating harmful waste.…”

“…Therefore, polynitrogen clusters are considered to be clean high-energy-density materials (HEDMs) with broad applications in various fields, including aerospace [5][6][7]. While a large number of polynitrogen clusters with size ranging from 3 to 60 have been studied through theoretical calculations [1][2][3][4], only a few species have been identified and synthesized by experiments [8][9][10][11][12]. For instance, the well-known azide ion (N −…”