Li vs. Zn substitution in Li₁₇Si₄ - Li_{17- ϵ - δ}Zn_ϵSi₄ connecting the structures of Li₂₁Si₅ and Li₁₇Si₄

Binary lithium silicides play a crucial role in high energy density anode materials for rechargeable batteries. During charging processes of Si anodes Li₁₅Si₄ is formed as a metastable phase which has been stabilized through Li by Mg, Zn and Al substitution. Here we investigate Li by Zn substitution in the lithium-richest phase Li₁₇Si₄ and report on the particular site preference of Zn atoms since Zn is substituting Li atoms only on one out of 13 possible lithium sites. This site preference shows an interesting relation to the closely related phase Li₂₁Si₅ and thus Li_{17- ϵ - δ}Zn_ϵSi₄ with ϵ = 0.025(1) and δ= 0.033(1) can be considered as the missing link between the structures of Li₂₁Si₅ (= Li_4.20Si) and Li₁₇Si₄ (= Li_4.25Si).