448 / 2019-03-07 21:14:21

Computational Design of High-Energy Density Materials at High Pressure

high pressure,First-principles calculation,structure prediction,high-energy density

全体主题 > High Pressure Physics and Materials Science

The pressure-induced transformation of nitrogen with N≡N bonds into polymeric phases with N-N bond may produce potentially useful high-energy-density materials. Previous experiments have shown that molecular nitrogen can only be transformed into polymeric phase at pressures greater than 100 GPa, and polymeric N has never been formed at ambient pressure, precluding its practical applicability. Using first-principles calculations with structure searching method CALYPSO，we have predicted a new class of nitrogen-rich boron nitrides with a stoichiometry of B3N5 that are stable or metastable relative to solid N2 and h-BN at ambient pressure. The formation of single N-N bonds in B3N5 was found to be 15 GPa, much lower than that required for triple-to-single bond transformation in pure solid nitrogen (110 GPa). We have also predicted a new compound with stoichiometry HeN4 that are energetically stable relative to a mixture of solid He and N2 above 8.5 GPa. The high-pressure phase of HeN4 comprises a polymeric channel-like nitrogen framework filled with linearly-arranged helium atoms. The nitrogen framework persists to ambient pressure on decompression after removal of helium, forming pure polymeric nitrogen, t-N. More importantly, calculations show both polymeric B3N5 and t-N are metastable, and can be recovered under ambient conditions. The energy density of polymeric B3N5 and t-N were estimated to be ~3.44 kJ/g and ~11.31 kJ/g, respectively, making them potential high-energy density materials.