CRYSTAL-CHEMISTRY OF LITHIUM GALLIUM SILICATE, LI4-3XGAXSIO4, SOLID ELECTROLYTES

The crystal structure of the lithium ion conductor alpha-Li3.00 Ga0.33SiO4 has been determined from Rietveld refinement of time-of-flight high-resolution powder neutron diffraction data. It is orthorhombic, with space group C222(1), and has an oxygen arrangement that is a distortion of primitive tetragonal packing. Si, Ga and Li atoms occupy tetrahedral and octahedral sites within this oxygen framework. Li and Ga sites are fractionally occupied but certain pairs of face-sharing sites have combined occupancies of unity. The relationship between this structure and those of rutile, Li4SiO4, Li3.4Ga0.2SiO4, Li5GaSi2O8 and gamma-LiAlO2 is discussed. The nature of the Li4SiO4 (s.s.)-alpha(s.s.) phase transition is also discussed.