High-Pressure Synthesized Lithium Pentazolate Compound Metastable under Ambient Conditions

Abstract

Polynitrogen compounds have been actively pursued driven by their potential as ultra-high-performing propellants or explosives. Despite remarkable breakthroughs over the past two decades, the two figures of merit for a compelling material, namely a large fraction of nitrogen by weight and a bulk stability under ambient conditions, have not yet been achieved. We report the synthesis of a lithium pentazolate solid by compressing and laser-heating lithium embedded in molecular N₂ around 45 GPa along with its recovery under ambient conditions. The observation by Raman spectroscopy of vibrational modes unique to the cyclo-N₅^- anion is the signature of the formation of LiN₅. Mass spectroscopy experiments confirm the presence of the pentazolate anion in the recovered compound. A monoclinic lattice is obtained from X-ray diffraction measurements and the volume of the LiN₅ compound under pressure is in good agreement with the theoretical calculations.