The Al–Li–Si System: 1. A New Structure Type Li8Al3Si5 and the Ternary Solid-State Phase Equilibria

Solid-state phase equilibria of the ternary Al–Li–Si system were studied by arc-melted and levitation-melted samples in the ascast state and annealed at 250°C up to 1 month. Phase analysis was done with X-ray powder diffractometry. The ternary phase diagram at 250°C is established. Three virtually stoichiometric ternary phases exist: LiAlSi (1), Li5.3Al0.7Si2 (2), Li8Al3Si5 (3). The phase 3 is a new compound, whereas 1 and 2 have also been reported in previous works. Other phases claimed in the literature do not exist in the stable phase diagram. The single crystals of the new ternary 3 compound were studied to determine their compositions by SEM/EDX. The crystal structure of the 3 compound was resolved using its similarities to LiAlSi structure and refined using Rietveld analysis. It is found that the Li8Al3Si5 compound constitutes a new structure type with space group P 43m and Pearson symbol cP16. Its unique features compared to closely related structure types are discussed.