Li₁₂P₃N₉ with Non‐Condensed [P₃N₉]¹²⁻‐Rings and its High‐Pressure Polymorph Li₄PN₃ with Infinite Chains of PN₄‐Tetrahedra

Abstract

Li₁₂ P₃ N₉ was synthesized by solid-state reaction of Li₃ N and P₃ N₅ at 790 °C. It is made up of non-condensed [P₃ N₉ ]^12- dreier-rings of PN₄ -tetrahedra. The corresponding high-pressure polymorph, Li₄ PN₃ , was synthesized under high-pressure/high-temperature conditions from Li₁₂ P₃ N₉ or LiPN₂ and Li₇ PN₄ at 6 or 7 GPa, respectively, using the multianvil technique. Li₄ PN₃ is the first lithium catena-nitridophosphate and contains PN₃ zweier-chains of corner sharing PN₄ -tetrahedra. To confirm the structure elucidated from single-crystal X-ray data, Rietveld refinement, ⁶ Li, ⁷ Li, and ³¹ P solid-state NMR spectroscopy, FTIR spectroscopy and EDX measurements were carried out. To examine the phase transition of Li₁₂ P₃ N₉ to Li₄ PN₃ at 6 GPa and to corroborate the latter as the corresponding high-pressure polymorph, DFT calculations were conducted. Electronic band gap and electron localization function (ELF) calculations were carried out to elucidate the electronic properties and bonding behavior of both polymorphs.