Abstract
First principles calculations were performed to investigate the structural, elastic, and electronic properties of for various space groups: cubic and , hexagonal , tetragonal , orthorhombic , , and , and monoclinic . Our calculation indicates that the phase with arsenopyrite-type structure is energetically more stable than the other phases. It is semiconducting (the remaining phases are metallic) and contains diatomic N-N with the bond distance of . These characters are consistent with the experimental facts that is in lower symmetry and nonmetallic. Our conclusion is also in agreement with the recent theoretical studies that the most stable phase of is monoclinic . The calculated bulk modulus of is also the highest among the considered space groups. It matches the recent theoretical values of within 4.3% and of within 7.8%, but smaller than the experimental value of by 14.7%. Chemical bonding and potential displacive phase transitions are discussed for . For , cubic skutterudite structure was assumed. Our calculation indicated that it is also promising to be superhard due to the large bulk modulus of and shear modulus of . The diatomic N-N bond distance is even shorter .
5 More- Received 7 November 2006
- Corrected 23 August 2007
DOI:https://doi.org/10.1103/PhysRevB.76.054115
©2007 American Physical Society
Corrections
23 August 2007