Li⁺ Ion Conductors with Adamantane‐Type Nitridophosphate Anions β‐Li₁₀P₄N₁₀ and Li₁₃P₄N₁₀<i>X</i>₃ with <i>X</i>=Cl, Br

Abstract

β-Li₁₀ P₄ N₁₀ and Li₁₃ P₄ N₁₀ X₃ with X=Cl, Br have been synthesized from mixtures of P₃ N₅ , Li₃ N, LiX, LiPN₂ , and Li₇ PN₄ at temperatures below 850 °C. β-Li₁₀ P₄ N₁₀ is the low-temperature polymorph of α-Li₁₀ P₄ N₁₀ and crystallizes in the trigonal space group R3. It is made up of non-condensed [P₄ N₁₀ ]^10- T2 supertetrahedra, which are arranged in sphalerite-analogous packing. Li₁₃ P₄ N₁₀ X₃ (X=Cl, Br) crystallizes in the cubic space group Fm3‾m . Both isomorphic compounds comprise adamantane-type [P₄ N₁₀ ]^10- , Li⁺ ions, and halides, which form octahedra. These octahedra build up a face-centered cubic packing, whose tetrahedral voids are occupied by the [P₄ N₁₀ ]^10- ions. The crystal structures have been elucidated from X-ray powder diffraction data and corroborated by EDX measurements, solid-state NMR, and FTIR spectroscopy. Furthermore, we have examined the phase transition between α- and β-Li₁₀ P₄ N₁₀ . To confirm the ionic character, the migration pathways of the Li⁺ ions have been evaluated and the ion conductivity and its temperature dependence have been determined by impedance spectroscopy. XPS measurements have been carried out to analyze the stability with respect to Li metal.