Under the extreme conditions of high temperature and high pressure, molecular crystal nitrogen breaks the traditional three-bond mechanism and transforms into a single-bond polymerization state. The unique dissociation mechanism of nitrogen under high pressure makes the research significance of polymeric nitrogen beyond the scope of energetic materials, and also has profound scientific significance in the field of fundamental physics. Following the cubic gauche polymeric nitrogen cg-N (space group I213), the second experimentally discovered layered structure polymeric nitrogen LP-N (space group Pba2) has been controversial. The main problem is that, in addition to not being verified by other high-pressure X-ray diffraction experiments, LP-N structure has the similar synthesis temperature and pressure conditions and synthesis pathways, as well as almost the same Raman spectral characteristics as the subsequently discovered black phosphorus structure polymeric nitrogen BP-N (space group Cmca). The high-temperature and high-pressure synthesis of LP-N is likely to have a unique phase transition kinetic barrier. In this work, we started from the low-temperature solid-state molecular nitrogen λ-N2, used double-sided laser-heated diamond anvil cell (LHDAC) technology, combined with high-pressure X-ray diffraction based on the synchrotron radiation and high-pressure Raman scattering spectroscopy, supplemented by first-principles calculations, and observed the Pba2 structure of polymeric nitrogen LP-N at the conditions of about 141 GPa and about 2600 K. Combined with first-principles calculations, we compared and analyzed its pressure-dependent evolution of the volume per atom (p-V curve) and discussed the kinetic factors of LP-N synthesis at high temperature and high pressure. In addition to a more comprehensive understanding of LP-N, this paper further reveals the high-pressure path-dependent characteristics of polymeric nitrogen.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |