Li3La[PS4]2: The First Lithium Lanthanum Ortho-Thiophosphate

The first lithium-containing lanthanum ortho-thiophosphate(V) with the formula Li3La[PS4](2) crystallizes orthorhombically in the space group Pbca with a=1053.51(6) pm, b=1920.62(11) pm, c=1165.83(7) pm and Z=8. Colorless single crystals were obtained from the reaction of lanthanum trichloride, dilithium sulfide and diphosphorus pentasulfide at 750 degrees C with lithium chloride as by-product. The new structure of Li3La[PS4](2) features characteristic [PS4](3-) anions and a crystallographically unique La3+-cation position, surrounded by eight sulfur atoms from four [PS4](3-) tetrahedra constructing a trigonal dodecahedron. These [LaS8](13-) polyhedra are connected via [PS4](3-) tetrahedra to form strongly corrugated layers (infinity 2 LaPS44/23- ) spreading out parallel to the ac-plane with Li+ cations in between residing in four-, five- and sixfold sulfur coordination. Raman-spectroscopic measurements were performed to visualize further vibrational modes, whereas diffuse reflectance spectroscopy verified the absorption of UV light, owing to the colorless appearance of the crystals. The optical band gap was found to be at 3.25 eV. Energy-dispersive X-ray spectroscopy (EDXS) measurements assured the absence of chlorine in the investigated single crystals. Calculations of Effective Coordination Numbers (ECoN) for each crystallographic position confirm the refined coordination environments for all atoms. Further investigations of the Madelung Parts of the Lattice Energies (MAPLE) point out the strong relationship of Li3La[PS4](2) with the ternary compounds of Li-3[PS4] and La[PS4].

Automated summary

The new Li3La[PS4](2) structure features [PS4](3-) anions and a unique La3+ cation position, surrounded by sulfur atoms constructing a trigonal dodecahedron. Layers of [LaS8](13-) polyhedra connected by [PS4](3-) tetrahedra have Li+ cations in between with different sulfur coordination numbers. Energy-dispersive X-ray spectroscopy confirmed the absence of chlorine in the crystals, while calculations of Effective Coordination Numbers and Madelung Parts of the Lattice Energies highlighted the relationship with other ternary compounds.