The cubic structure of Li3As stabilized by substitution – Li8TtAs4 (Tt = Si, Ge) and Li14TtAs6 (Tt = Si, Ge, Sn) and their lithium ion conductivity

Abstract

The new lithium arsenidotetrelates Li₈SiAs₄, Li₈GeAs₄, Li₁₄SiAs₆, Li₁₄GeAs₆ and Li₁₄SnAs₆ were synthesized via ball milling and structurally characterized by Rietveld analysis of X-ray powder diffraction data. The aliovalent substitution of lithium in hexagonal Li₃As by introducing a tetravalent tetrel cation stabilizes cubic structures for Li₈TtAs₄ (Tt = Si, Ge) in the space group Pa and for the lithium richer compound Li₁₄TtAs₆ (Tt = Si, Ge, Sn) in the higher symmetrical space group Fmm (no. 225). Thermal properties of the arsenidotetrelates were investigated via high temperature powder diffraction and differential thermal analysis revealing a decomposition process of the lithium richer arsenidotetrelate (Li₁₄TtAs₆ → Li₈TtAs₄ + 2Li₃As) into the lithium poorer arsenidotetrelates and lithium arsenide at moderate temperatures. Impedance spectroscopy shows moderate to good lithium ion conductivity for the lithium arsenidotetrelates.