Halide-Driven Stabilization of a Hexagonal Polymorph with a Distinct and Disordered Li Substructure in Li_3.25GeS_3.25Cl_0.75

Here, partial substitution of S^2– by Cl^– in Li₄GeS₄ stabilizes a hexagonal polymorph near the composition Li_3.25GeS_3.25Cl_0.75. Ab initio structure determination by joint refinement of time-of-flight neutron powder diffraction and X-ray diffraction data supports a <i>P</i>6₃<i>mc</i> average structure built on a hexagonal close-packed anion framework.

The resulting framework exhibits a distinct Li-site topology with symmetry-inequivalent Li environments, including a shared tetrahedral framework site and additional tetrahedral and octahedral interstitial sites. Systematic investigation of the Li_4–<i>x</i>GeS_4–<i>x</i>Cl_<i>x</i> series shows that the hexagonal phase is preferentially stabilized near the nominal <i>x</i> = 0.75 composition, for which no secondary crystalline phase was detected by PXRD.