Li+ Ion Conductors with Adamantane-Type Nitridophosphate Anions beta-Li10P4N10 and Li13P4N10X3 with X=Cl, Br

beta-Li10P4N10 and Li13P4N10X3 with X=Cl, Br have been synthesized from mixtures of P3N5, Li3N, LiX, LiPN2, and Li7PN4 at temperatures below 850 degrees C. beta-Li10P4N10 is the low-temperature polymorph of alpha-Li10P4N10 and crystallizes in the trigonal space group R3. It is made up of non-condensed [P4N10](10-) T2 supertetrahedra, which are arranged in sphalerite-analogous packing. Li13P4N10X3 (X=Cl, Br) crystallizes in the cubic space group Fm (3) over barm. Both isomorphic compounds comprise adamantane-type [P4N10](10-), Li+ ions, and halides, which form octahedra. These octahedra build up a face-centered cubic packing, whose tetrahedral voids are occupied by the [P4N10](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 alpha- and beta-Li10P4N10. 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.