Cubic gauche polynitrogen(cg-N)is an attractive high-energy density material.However,high-pressure synthesized cg-N will decompose at low pressure and cannot exist under ambient conditions.Here,the stabilities of cg-N...Cubic gauche polynitrogen(cg-N)is an attractive high-energy density material.However,high-pressure synthesized cg-N will decompose at low pressure and cannot exist under ambient conditions.Here,the stabilities of cg-N surfaces with and without saturations at different pressures and temperatures are systematically investigated based on first-principles calculations and molecular dynamics simulations.Pristine surfaces at 0 GPa are very brittle and will decompose at 300 K,especially(110)surface will collapse completely just after structural relaxation,whereas the decompositions of surfaces can be suppressed by applying pressure,indicating that surface instability causes the cg-N decomposition at low pressure.Due to the saturation of dangling bonds and transferring electrons to the surfaces,saturation with H can stabilize surfaces under ambient conditions,while it is impossible for OH saturation to occur solely from obtaining electrons from surfaces.This suggests that polynitrogen is more stable in an acidic environment or when the surface is saturated with less electronegative adsorbates.展开更多
Since the discoveries of polymeric nitrogen, named cg-N (2004), LP-N (2014), HLP-N (2019), another polymorph named black phosphorus nitrogen (BP-N) was synthesized at high-pressure-high-temperature conditions. The nar...Since the discoveries of polymeric nitrogen, named cg-N (2004), LP-N (2014), HLP-N (2019), another polymorph named black phosphorus nitrogen (BP-N) was synthesized at high-pressure-high-temperature conditions. The narrow existing pressure region and similar synthesized pressure of BP-N compared with cg-N indicate that the stable energy and enthalpy of formation of these two structures are close to each other, which was confirmed by our theoretical calculation. In order to obtain the pressure region of BP-N phase, pure N2 and TiN/Pb + N2 precursors were used for laser-heating high pressure experiments in diamond anvil cell (DAC), and the phase identity was examined by Raman and XRD mapping. BP-N can be synthesized in the pressure range of 130 GPa to 140 GPa with the assistance of heating absorber. With the decrease of the pressure, BP-N can be quenched to ~ 40 GPa. The synthesizing pressure–temperature and the stable pressure region of BP-N are important for further exploration of BP-N and its kinetic and thermal dynamic relationship with other polymeric nitrogen, especially cg-N.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.U2030114)CASHIPS Director's Fund(Grant No.YZJJ202207-CX)。
文摘Cubic gauche polynitrogen(cg-N)is an attractive high-energy density material.However,high-pressure synthesized cg-N will decompose at low pressure and cannot exist under ambient conditions.Here,the stabilities of cg-N surfaces with and without saturations at different pressures and temperatures are systematically investigated based on first-principles calculations and molecular dynamics simulations.Pristine surfaces at 0 GPa are very brittle and will decompose at 300 K,especially(110)surface will collapse completely just after structural relaxation,whereas the decompositions of surfaces can be suppressed by applying pressure,indicating that surface instability causes the cg-N decomposition at low pressure.Due to the saturation of dangling bonds and transferring electrons to the surfaces,saturation with H can stabilize surfaces under ambient conditions,while it is impossible for OH saturation to occur solely from obtaining electrons from surfaces.This suggests that polynitrogen is more stable in an acidic environment or when the surface is saturated with less electronegative adsorbates.
基金Project supported by the National Natural Science Foundation of China (Grant No. 11904281).
文摘Since the discoveries of polymeric nitrogen, named cg-N (2004), LP-N (2014), HLP-N (2019), another polymorph named black phosphorus nitrogen (BP-N) was synthesized at high-pressure-high-temperature conditions. The narrow existing pressure region and similar synthesized pressure of BP-N compared with cg-N indicate that the stable energy and enthalpy of formation of these two structures are close to each other, which was confirmed by our theoretical calculation. In order to obtain the pressure region of BP-N phase, pure N2 and TiN/Pb + N2 precursors were used for laser-heating high pressure experiments in diamond anvil cell (DAC), and the phase identity was examined by Raman and XRD mapping. BP-N can be synthesized in the pressure range of 130 GPa to 140 GPa with the assistance of heating absorber. With the decrease of the pressure, BP-N can be quenched to ~ 40 GPa. The synthesizing pressure–temperature and the stable pressure region of BP-N are important for further exploration of BP-N and its kinetic and thermal dynamic relationship with other polymeric nitrogen, especially cg-N.
