Abstract
We report hafnium nitrides under pressure using first-principles evolutionary calculations. Metallic -HfN (calculated Vickers hardness 23.8 GPa) is found to be more energetically favorable than NaCl-type HfN at zero and high pressure. Moreover, NaCl-type HfN actually undergoes a phase transition to -HfN below 670 K at ambient pressure. , which simultaneously has infinite armchairlike polymeric N chains and molecules in its crystal structure, is discovered to be stable at moderate pressure above 23 GPa and can be preserved as a metastable phase at ambient pressure. At ambient conditions (298 K, 0 GPa), the gravimetric energy densities and the volumetric energy densities of are 2.8 kJ/g and 14.1 kJ/, respectively.
- Received 15 June 2016
DOI:https://doi.org/10.1103/PhysRevB.95.020103
©2017 American Physical Society