Functional Indium Vacancies in Indium Phosphors Chalcogenides

Layered Indium phosphorus trichalcogenides (In_4/3P₂X₆) have received significant attention due to their ordered indium vacancies and stacking-dependent properties, enabling applications in electronics, catalysis, and energy storage. However, the vacancy-governed stacking polytypes and atomic structures in In_4/3P₂X₆ remain elusive. Moreover, the facile reconstruction of the indium vacancies upon external stimulus makes their direct visualization challenging. Here, a low-dose aberration-corrected scanning transmission electron microscopy (STEM), four-dimensional STEM (4D-STEM) techniques, and density functional theory (DFT) are employed to systematically explore the atomic structure of In_4/3P₂X₆ and the magnetic properties of doped In_4/3P₂X₆. The indium vacancies with glide-reflection symmetric ordering in In_4/3P₂X₆ are resolved at the atomic scale, driving armchair-type interlayer gliding with an unconventional step in In_4/3P₂Se₆ and zigzag-type gliding in In_4/3P₂S₆, yielding ABC and nearly-ABC stacking polytypes, respectively. DFT calculations reveal that both gliding modes are energetically favorable, with their distinctions arising from the ligand-modulated interlayer charge distributions. Besides, filling the indium vacancies with magnetic dopants induces tunable magnetic ordering in In_4/3P₂X₆, and also drives a structural transition to an MPX₃-like phase and a non-magnetic paramagnetic (PM)-FM transition. This study sheds light on vacancy-governed structure in In_4/3P₂X₆ and highlights it as an excellent matrix for designing novel functional 2D magnets via doping engineering.