LiSi3As6 and Li2SiAs2 with flexible SiAs2 polyanions: Synthesis, structure, bonding, and ionic conductivity
Two novel ternary phases, LiSi3As6 and Li2SiAs2, have been synthesized and characterized. Both phases have an identical Si:As ratio of 1:2 providing insight on how layers of the parent phase SiAs2 accommodate excess electrons from Li cations to form Si-As anionic frameworks. LiSi3As6 exhibits a variety of bonding schemes involving Si-Si and As-As bonds, as well as corner-sharing SiAs4 tetrahedra, while Li2SiAs2 is isostructural to the previously reported Li2SiP2, with adamantane-like Si4As10 units connected into 3D framework. LiSi3As6 and Li2SiAs2 are predicted to be indirect semiconductors which was experimentally confirmed by optical properties characterization. Li2SiAs2 exhibits low thermal conductivity 1.20 W m–1 K–1 at 300 K in combination with a room temperature ionic conductivity of 7x10–6 S cm–1, an order of magnitude greater than that of the phosphide and nitride analogues, indicating its potential as a solid-state Li-ion conductor.