Mapping Cation Disorder in Copper Zinc Tin Sulfide via Atomic‐Resolution Electron Energy‐Loss Spectroscopy

ABSTRACT Disorder in multinary crystals is often the hidden degree of freedom that governs phase stability, interfacial bonding, and functional performance. Here we establish an electron‐crystallographic strategy that converts atomic‐resolution electron energy‐loss spectroscopy (AR‐EELS) acquired along multiple zone axes into quantitative, site‐specific occupancies, enabling 3D decoding of cation disorder in complex solids. Applying this approach to polytypic Cu–Zn–Sn–S (CZTS) nanocrystals, we directly resolve the cation sublattices in both zincblende‐ and wurtzite‐derived polymorphs. We find reproducible Cu/Zn mixed occupancy without detectable site preference in both phases, whereas Sn remains fully ordered in the zincblende‐derived polymorph but is partially replaced by Zn (∼35%) in the wurtzite‐derived counterpart, consistent with its Zn‐rich/Sn‐poor composition. These experimentally constrained occupancies, together with reciprocal‐lattice reconstruction, support average structural models consistent with I‐42m and Pmn2 1 symmetry. Density functional theory further compares the energetics of candidate ordered and disordered structures at fixed compositions and supports the energetic plausibility of the experimentally constrained models. This AR‐EELS electron‐crystallography workflow provides a potentially transferable framework for occupancy‐resolved analysis of multinary materials under suitable experimental and crystallographic conditions.