The Phosphidosilicates AE 2 Li 4 SiP 4 (AE=Ca, Sr, Eu) Ba 4 Li 16 Si 3 P 12 .

The quaternary phosphidosilicates AE 2 Li 4 SiP 4 (AE=Ca, Sr, Eu) and Ba 4 Li 16 Si 3 P 12 were synthesized by heating the elements and Li 3 P under argon atmosphere. Their crystal structures were determined by single crystal X-ray diffraction. AE 2 Li 4 SiP 4 crystallize in a new layered structure type (P2 1 /m, Z=2) with CdI 2 -analoguos layers. Edge sharing CaP 6 octahedra are separated by layers of vertex-sharing SiP 4 and LiP 4 tetrahedra, which contain additional chains of LiP 6 octahedra. Ba 4 Li 16 Si 3 P 12 forms likewise a new structure type (P2 1 /c, Z=16) with a three-dimensional network of SiP 4 , Si 2 P 6 and LiP 4 entities as well as one phosphorus site not bonded to silicon. Barium is located in capped trigonal prisms of phosphorus which form strongly corrugated layers. 31 P and 29 Si solid-state NMR spectra confirm the crystal structures of the compounds AE 2 Li 4 SiP 4 . 7 Li spectra show only one signal in spite of quite different crystallographic positions, which indicate possible Li + mobility. However, this signal is much broader compared to the known Li + conducting phosphidosilicates. Accordingly, electrochemical impedance measurements show low Li + conductivities.