Atomic-Scale Visualization of Thermally Driven Hidden Symmetry Evolution in Layered Bi–Se–Te Compounds

Layered bismuth chalcogenides Bi2Se3–xTex are versatile platforms for topological quantum phenomena and advanced thermoelectric applications, yet the precise correlation between Se–Te solute chemical inhomogeneity and macroscopic transport remains unclear. Herein, we directly visualize temperature-driven atomic rearrangement in Bi2Se2.25Te0.75 nanosheets. As the growth temperature increases, Te atoms progressively redistribute from centrosymmetric mixing at two outer sites (Se/Te–Bi–Se–Bi–Se/Te) to noncentrosymmetric single-side segregation (Se–Bi–Se–Bi–Se/Te) inside quintuple layers, while the central layer remains mostly occupied by Se atoms. This evolution modulates electron–phonon coupling via intrinsic polarization fields and alters carrier mobility. Linear magnetoresistance is observed in this system, resulted from Se–Te solute inhomogeneity induced mobility fluctuations within the Parish–Littlewood model. Angle-dependent magnetoresistance confirms the preservation of significant two-dimensional transport in both configurations. Our findings establish that atomic-scale chemical inhomogeneity is a tunable structural degree of freedom and offer a potential strategy for engineering transport properties in layered bismuth chalcogenides.