Stable xenon nitride at high pressures

Abstract

Nitrides in many ways are fascinating since they often appear as superconductors, high energy density and hard materials. Though there exist a large variety of nitrides, noble gas nitrides are long missing in nature. Pursuit of noble gas nitrides has therefore become the subject of topical interests, but remains as a great challenge since molecular nitrogen (N 2 , a major form of nitrogen) and noble gases are both inert systems and do not interact at normal conditions. We show through a swarm structure searching simulation that high pressure can lift the reactivity of both N 2 and xenon (Xe), making chemical reaction of them possible. The resultant nitride has a peculiar stoichiometry of XeN 6 , possessing a high-energy-density of approximately 2.4 kJg -1 , rivaling that of the modern explosives. Chemically, XeN 6 is more intriguing with the appearance of chaired N 6 hexagons and an emergent 12-fold Xe by acceptance of unprecedentedly 12 Xe-N weak covalent bonds. Our work opens up the possibility of achieving Xe nitrides whose formation is long sought as impossible.PACS numbers: 61.66.fn, 71.15.Mb, 81.40.Vw Nitrogen (N) is the most abundant element in the Earth's atmosphere and is one of most important constituents of our universe. In air, N exists in the form of diatomic N 2 molecules and has the strongest-known triple N≡N bond. As a result, N 2 is chemically inert[1] and hardly interacts with other elements or substances under normal conditions. Syntheses of useful nitrides for industrial applications rely on chemical methods [2] via, e.g., temperature-programmed reaction, thermal decomposition, electrochemical synthesis, or with the aid of catalysts (e.g., the synthesis of NH 3 ). [3] Nitrides have a variety of intriguing properties, such as superconductivity[4], high energy density [5], and high hardness [6], as well as extraordinary chemical and thermal stability [7].Noble gases (e.g., Ar, Kr, and Xe) as typical closed-shell systems are inert prototype examples and where the famous octet rule[8] originated. They are critical elements[9] because their abundances constrain the models for giant planet formation and the origin of their atmospheres. Among noble gases, Xe has the largest atomic core and is polarizable to form Xe fluorides[10] (or Xe noble metal hexafluorides [11]) and Xe oxides [12] in certain circumstances at ambient conditions due to its low ionization energy and large relativistic effect.[13] However, other Xe compounds are only synthesizable by using Xe fluoride precursors, instead of Xe gas, in the reaction with other organics or inorganics.Since both N 2 and Xe are inert, they do not directly interact at ambient conditions. Although Xe and N containing compounds have been seen at ambient pressure in (FXe)[N(SO 2 F) 2 ] salts [14], the syntheses of these salts relied on the precursors of the cationic (FXe) + and anionic Ncontaining ligands, while not the uses of N 2 and Xe gases [13]. All of these as-synthesized complex salts have poor thermal stability, and most of them decompose explosi...

Novel triadius-like N4 specie of iron nitride compounds under high pressure

“…These nitrogen species have various structural forms ranging from single atom (N) to molecular (N 2 , N 3 , N 4 , N 5 , N 6 ) units and polynitrides 13 – 17 . To note, these stable nitrides have a variety of intriguing properties, such as superconductivity (MoN) 13 , high-energy density (LiN 3 , NaN 3 ) 14 , and high hardness (WN 2 ) 15 , as well as extraordinary chemical and thermal stability (Xe-N) 16 . These nitrides aroused our significant interest in the field of exploring new HP nitrogen species and their potential remarkable properties.…”

“…In order to systematically explore the possibility of obtaining new stable N-rich iron nitrides, and especially to examine the possibility of attaining new nitrogen species at HP, we here present extensive structure searches of stoichiometric Fe-N compounds under various pressures ranging from 0 to 300 GPa, using an unbiased particle swarm optimization (PSO) algorithms for crystal structure predictions 18 . This swarm-intelligence high-throughput searching has proven effective in revealing new compositions favorable to form in large sets of multicomponent Ca-H, Li-B, Xe-N, Cs-N systems 16 , 17 , 19 , 20 . The effectiveness has been also demonstrated by recent successes in predicting high-pressure structures of various systems, and their several experimental confirmations 21 – 30 .…”

Formation of xenon-nitrogen compounds at high pressure

“…S5 ) indicating that the molecular N-N bond is weakening. Up to highest pressure studied (180 GPa) we see no evidence of Xe-N bonded compounds predicted by theory 24 . In an attempt to promote synthesis of such compounds, we performed laser heating of the sample to temperatures of 3000 K at 120, 150, 160 and 180 GPa but no transition was observed in either Raman spectroscopy or x-ray diffraction.…”

“…The direct reaction of N 2 and Xe would seem unlikely due to the relative inertness of both materials. Nevertheless, a recent theoretical study predicts the formation of novel xenon nitride compounds above 146 GPa with stoichiometry - XeN 6 24 . Possible interactions between Xe and N 2 have been explored experimentally at low pressures investigating mutual solubility 25 26 .…”

Geoscience material structures prediction via CALYPSO methodology

“…Increased reactivity of the noble gas elements under pressure has been seen in numerous CSP studies [46][47][48][49][50] and for the purpose of this section, xenon was found to react with either iron or nickel at inner core pressure and temperature conditions [46] . Xenon is predicted to form XeM 3 compounds with either metal, which are in parts stabilised by charge transfer from xenon to iron or nickel.…”