Site-Specific Substitution Preferences in the Solid Solutions Li₁₂Si_7–xGe_x, Li_12–yNa_ySi₇, Na₇LiSi_8–zGe_z, and Li₃NaSi_6–vGe_v

The mixed silicide-germanides Li₁₂Si_7–xGe_x, Na₇LiSi_8–zGe_z, and Li₃NaSi_6–vGe_vwhich could serve as potential precursors for Si_1–xGe_xmaterials were synthesized and characterized by X-ray diffraction methods. The full solid solution series Li₁₂Si_7–xGe_x(0 ≤ x ≤ 7) is easily accessible from the elements and features preferential occupation of the more negatively charged crystallographic tetrel positions by Ge, which is the more electronegative element. In case of Na₇LiSi_8–zGe_za broad solid solution range of 1.3 ≤ x ≤ 8 is available but the ternary silicide Na₇LiSi₈could not be obtained by the tested methods of synthesis. The solubility of Ge in Li₃NaSi_6–vGe_vis highly limited to a maximum of v ≈ 0.5, and again the formally more negatively charged tetrel positions are preferred by Ge. Additionally, the two crystallographic Li positions in Li₁₂Si₇with unusually large displacement parameters can be partially substituted by Na in Li_12–yNa_ySi₇with 0 ≤ y ≤ 0.6. The statistical mixing of Li and Na in this solid solution contrasts the typical ordering of Li and Na in most ternary tetrelides.