Novel lithium containing compounds with the composition Li 1+3 xSrAl 1 -xP 2 – in a variant of the CaAl 2 Si 2 structure type and a related modification Vincent Daiber , Prof. Dr. Thomas F. Fässler Department of Chemistry, Chair of Inorganic Chemistry with Focus on New Materials, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany Energy storage materials and technologies are of great importance. All solid-state batteries (ASSBs) have been in research’s focus lately as they hold promise for improved efficiency, sustainability, and safety [1]. One method to modify ionic conductivity in solid-state electrolytes is to change the charge of the anionic building units and subsequently change the amount of cationic mobile species contributing to the conduction effect. Recently, two extremely Li rich compounds, namely Li 9 AlP 4 [2] and Li 14 Tt P 6 [3, 4] ( Tt = Si, Ge, Sn) have been presented which exhibit high ionic conductivities. Here, we present investigation on substitution of lithium by earth alkaline metals to yield lithium poorer phases. In this context the compounds of composition Li 1+3 x SrAl 1- x P 2 ( x = 0 – 0.5) were analyzed by means of single crystal and powder X-ray diffraction. The well known CaAl 2 Si 2 structure type (space group P- 3 m 1, No.164) is used as basic model for every structural discussion in this system: For x >0 the respective compound crystallizes in a stuffed variant where formerly empty octahedral voids are successively partially occupied by lithium depending on the overall amount of the alkaline metal. To the best of our knowledge this stuffed variant is unprecedented in literature. Lithium poorer phases ( x = 0), however, do not crystallize in the pristine CaAl 2 Si 2 structure type but in the t3 related subgroup C 2/ m (No. 12). Here, the structural motive found in the trigonal aristotype is slightly distorted, leading to the indicated symmetry degradation. Summing up, inclusion of earth alkaline metals results in a change from a cubic to a hexagonal closed packing of phosphorous atoms. The resulting voids are not occupied evenly in terms of elements and partiality and for alkaline metal poor phases, a further loss of symmetry is observed. References 1. J. Janek, et al . Nat. Energy 1 (2016) 16141
2. T. M. F. Restle et al . Angew. Chem. Int. Ed. 59 (2020) 5665–5674 3. S. Strangmüller, et al . J. Am. Chem. Soc. 141 (2019) 14200–14209 4. S. Strangmüller, et al . Chem. Mater. 32 (2020) 6925–6934
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