On the ϵ-ζ transition of nitrogen

Abstract

Group theory analysis and synchrotron x-ray diffraction measurements show that the recently proposed crystal structure of ζ-nitrogen is inconsistent with the available experimental data for that phase.

Genetic algorithm and first-principles DFT study of the high-pressure molecularζphase of nitrogen

“…Interestingly, the optimized B1 structure was found to be closely related to a recently reported Immm phase 33 of polynitrogen, which those authors obtained by optimizing coordinates of the recently solved phase of high-pressure To explore the space-group discrepancy further and reinforce the notion that we had explored the region of the potential-energy surface with Pmma symmetry, we modified our structure searching algorithm to exclusively generate initial structures with Pmma symmetry by placing the atoms on Wyckoff sites of the Pmma space group in a 2/1/1 distribution, as explained in Ref. 9.…”

“…This allows for only two Raman bands in the molecular vibration region of the spectrum, whereas five Raman bands were clearly identified for cell B. 9 Alternatively, structure B8 only lies 0.019 eV/atom higher in enthalpy than B1 at 90 GPa and has the desired 16 atom unit cell. Furthermore, its Pnma symmetry is close to the experimentally identified Pmma symmetry.…”

“…This is highlighted by the recent identification or confirmation of the structures of the elusive and molecular oxygen phases using single-crystal x-ray diffraction data [1][2][3][4] and an ongoing debate over the nature of high-pressure phases of molecular nitrogen. [5][6][7][8][9][10][11][12][13] These solid molecular structures are sought because they are typically intermediates to even more interesting high-pressure phases, such as the superconducting high-pressure phase of oxygen 14 or the high-energy-density polymeric form of nitrogen. 15 The phase diagram of high-pressure molecular nitrogen has been studied extensively but attempts to elucidate the correct molecular crystal structures have proven difficult.…”

“…However, questions were raised if this space group could be one of candidates for the -phase structure based on the number of measured Raman active vibronic and lattice modes. 9 It is the goal of this study to computationally investigate the discrepancy in the reported experimental cells and explore the structure of the phase by performing an exhaustive ab initio search of the molecular nitrogen potentialenergy surface within both cells using search algorithms inspired by the genetic algorithm. 17,18 We identify structures compatible with each of the experimental cells and report possible phase structures, including stability analyses.…”

High-pressure studies with x-rays using diamond anvil cells

“…Unexpectedly at higher pressures, along with the NaCl→CsCl transition, a reentrant Eu transition into a lower valence state (nearly Eu 2+ ) becomes obvious from both the XANES and NFS measurements. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 pressure induces bonding changes [587,588], amorphization [589], changes in quencheability [74,590], metallization [591], and novel structures [393,[592][593][594][595][596][597][598][599]. Many exotic nitrides have been synthesized under HP [22, [600][601][602][603][604], including new durable noble Ir, Pt, and Os metal nitrides synthesized at HP coupled with laser heating [605][606][607].…”