Polyanionic Frameworks in the Lithium Phosphidogermanates Li 2 GeP 2 and LiGe 3 P 3 – Synthesis, Structure, and Lithium Ion Mobility

Recently fast lithium ion conductors were discovered in compounds containing tetrahedral SiP 4 8– and GeP 4 8– units. In the context of material development for all solid state batteries the ternary Li/Ge/P phase system has been further investigated and two new lithium phosphidogermanates were discovered on the lithium poor side of the ternary composition diagram. Li 2 GeP 2 crystallizes in space group I 4 1 / acd with unit cell parameters of a = 12.3069(1) Å and c = 19.0306(4) Å, consists of a framework of Ge 4 P 10 supratetrahedra, and exhibits an ionic conductivity of 1.5(3)×10 –7 S · cm –1 at 27 °C. LiGe 3 P 3 crystallizes in Pbam with a = 9.8459(5) Å, b = 15.7489(7) Å, and c = 3.5995(2) Å. In LiGe 3 P 3 Ge and P atoms form a two dimensional polyanion. The slabs consist of five‐ and six‐membered heteroatomic rings comprising GeP 4 and Ge(P 3 Ge) tetrahedra including homoatomic Ge–Ge bonds. A semiconducting behavior with an electronic conductivity of ∼10 –4 S · cm –1 and a remarkable stability vs. air and moisture is observed.