High-Pressure FeN_x: Stability, Phase Transition, and Energetic Characteristic

Abstract

P1̅ -FeN 4 with polymeric nitrogen chains has recently been synthesized by Bykov et al. at a temperature of 2000 K and pressure of 106.8 GPa. Upon pressure release, this material was recoverable until 22.7 GPa at room temperature, which disagreed with the theoretically predicted dynamical stability at ambient pressure. To clarify this discrepancy, we conduct the structure search of highpressure FeN x using CALYPSO and calculate the pressure-dependent phase transition of P1̅ -FeN 4 using a variable-cell double-ended surface walking method. The results show a quantitative trend of decreasing barrier upon pressure release and, more importantly, a switching of phase transition pathways at 15−20 GPa that reduces the barrier by more than one-half. In addition, the energetic characteristics of nitrogen-rich high-pressure FeN x compounds are evaluated. While P1̅ -FeN 4 performs worse than RDX and HMX, P1̅ -FeN 5 , C2/m-FeN 6 , and Pnnm-FeN 8 are found to be promising candidates for high-energy-density materials.

Recent advances in studying the nonnegligible role of noncovalent interactions in various types of energetic molecular crystals

“…Due to the traditional energetic molecules that are primarily composed of CHON atoms, the hydrogen bonding networks make up the majority of intermolecular interactions in energetic molecular crystals, which play an important role in their key performance under different conditions. Different external conditions such as high temperature or pressure, 55,56 phase transition, 57,58 nanoparticle size, 59,60 and crystal defects 61,62 usually accelerate the initiation decomposition of energetic crystals and so increase their potential danger. 63 Therefore, the detailed description of noncovalent interactions in traditional explosive crystals under different conditions should be valuable for clarifying the initiation mechanisms so as to design new high-energy insensitive crystals.…”

Polymerization of nitrogen in two theoretically predicted high-energy compounds ScN6 and ScN7 under modest pressure

“…To expand the scope of research on nitrogen-rich compounds, more and more researchers are focusing on transition metal polynitrogen compounds. In the study of Fe-N [21] system, the energy released when FeN 6 and FeN 8 decompose are 4.34 kJ g −1 and 4.70 kJ g −1 , respectively. And the energy density is almost close to energy released by the decomposition of TNT [26], even higher than TNT, and energy storage of transition metal polynitrogen compounds has begun to make breakthroughs.…”

“…Recent many research results have found that the addition of metal elements to pure nitrogen can induce the formation of new polynitrogen compounds under high pressure. For example, alkali metals (Li [13], Na [14,15], K [16]), alkaline Earth metals (Be [17], Mg [18], Ca [19], Ba [20]) and transition metals (Fe [21], Cu [22,23], Zn [24], Cd [25]). These nitrogen-containing compounds have a variety of configurations, such as isolated nitrogen atoms, a curved chain structure, ring structure, a three-dimensional extended network, those has a high degree of nitrogen polymerization, which is generally related to high energy density.…”

High-Pressure Computational Search of Trivalent Lanthanide Dinitrides

“…The intriguing properties and the potential vast application of transition-metal nitrides have attracted the interest of the scientific community in recent years. − In general, nitrides are much less studied than the corresponding oxygen-based compounds but have been shown to give rise to ultrahard − and superconducting , materials that can find application in modern technologies as field-effect transistors, p–n junctions, and energy-storage devices. , …”