Suppressing Second-Order Jahn–Teller Distortion of Bi3+ by Smaller Y3+-Substitution in Bi3O4Cl

Abstract Controlling local coordination environments of second-order Jahn–Teller (SOJT)-active post-transition metal cations remains a significant challenge due to their inherent preference for asymmetric environments. Previously, we reported that the high-symmetry Y3+ site in layered Bi2YO4Cl can serve as a structural template to stabilize a centrosymmetric coordination environment for Bi3+ (up to 40% replacement), effectively suppressing the SOJT distortion. In this study, we re-examined the synthesis process of Bi2(Y1–xBix)O4Cl and successfully increased the Bi occupancy at the high-symmetry site to x = 0.8, approximately doubling the previously accessible composition range. At this high substitution level, the system is practically better described as a Y-substituted Bi3O4Cl rather than a Bi-substituted Bi2YO4Cl. First-principles calculations, together with comparative experiments using other trivalent cation dopants of different ionic radii, reveal that chemical pressure is a key factor governing the suppression of the SOJT distortion and the resulting band gap narrowing. These findings provide insight into the stabilization of unusually high-symmetry coordination environments in SOJT-active post-transition-metal compounds for tuning their electronic structures.