Dresden 2009 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 39: Phase Transitions II

MM 39.2: Vortrag

Donnerstag, 26. März 2009, 12:15–12:30, IFW B

Atomistic simulations on polymeric nitrogen — •Jani Kotakoski and Karsten Albe — Institut für Materialwissenschaft, TU Darmstadt, Germany

Existence of polymeric nitrogen was proposed in 1992 by Mailhiot and co-workers [Phys. Rev. B 46, 14419]. Despite significant effort, the structure was synthesized first time a decade later in 2004 by Eremets et al. [Nature Mater. 3, 558]. Interest in this material is due to its enormous energy capacity (more than 140 kJ/mol or 2.0 MJ/g) - 500 times higher than for TNT, for example. This gives promise for applications such as environmentally safe rocket fuel. The material is obtained by applying high pressure and temperature on the conventional molecular nitrogen.

Even though the cubic gauche structure is considered as a school book example of the predictive power of ab initio calculations, it’s far from the complete answer for high pressure phases for nitrogen. In fact, within the last few years, more than twenty different new structures have been proposed. We present density functional theory calculations for the free energy of different phases at large temperature and pressure ranges (energy minimization and phonon density of states calculations). Also presented are the thermodynamically most stable (and dynamically stable) phases at intermediate (188-320 GPa) and high pressures (>320 GPa) which were found recently. Further, we have developed an analytic bond order potential (and extended it to non-bond interactions) in order to mimic the experimental setup.