Single-bonded cubic form of nitrogen

Abstract

Nitrogen usually consists of molecules where two atoms are strongly triple-bonded. Here, we report on an allotropic form of nitrogen where all atoms are connected with single covalent bonds, similar to carbon atoms in diamond. The compound was synthesized directly from molecular nitrogen at temperatures above 2,000 K and pressures above 110 GPa using a laser-heated diamond cell. From X-ray and Raman scattering we have identified this as the long-sought-after polymeric nitrogen with the theoretically predicted cubic gauche structure (cg-N). This cubic phase has not been observed previously in any element. The phase is a stiff substance with bulk modulus >or=300 GPa, characteristic of strong covalent solids. The polymeric nitrogen is metastable, and contrasts with previously reported amorphous non-molecular nitrogen, which is most likely a mixture of small clusters of non-molecular phases. The cg-N represents a new class of single-bonded nitrogen materials with unique properties such as energy capacity: more than five times that of the most powerfully energetic materials.

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].…”

Electronic and structural properties of dense liquid and amorphous nitrogen

“…At high pressures (P ) and temperatures (T ) these materials often undergo dissociation and/or polymerization transitions to new phases with interesting properties. 1,2 In particular, polymeric nitrogen has become a subject of intense research in recent years. If meta-stable under ambient conditions, polymeric nitrogen could be important as a high-energy-density material.…”

“…This phase was predicted 7 over a decade before its experimental verification. 1 Recently, there have been many studies on the thermodynamic stability of other polymeric crystalline phases of nitrogen, with some possessing lower enthalpy than cg-N at higher pressures, though none have been observed experimentally. [8][9][10][11][12][13][14][15][16][17] Previous shock-wave experiments have shown that molecular liquid nitrogen undergoes a continuous transformation to a conducting atomic liquid at high-P and T .…”

Controlling the Bonding and Band Gaps of Solid Carbon Monoxide with Pressure

“…CO is one of the most extensively studied molecular crystals [3][4][5][6][7][8][9][10][11][12]. Studies of polymerization of CO are motivated by the desire to understand the fundamental physics and chemistry of geological and planetary processes, where CO is present, and to search for new materials [13] exhibiting properties such as ''high energy density'' [10] and ''superhardness'' [14,15].…”