Dimensional Reduction of Transition Metal Dichalcogenides by Oxide Insertion: Quasi-1D Oxychalcogenide Semiconductors

Heteroanionic solids offer unique levers for tuning structures and properties, but accessing multianion phase space remains challenging due to mismatches in anion reactivity. Here, we describe a new family of A₂Hf₃Q₆O (A = K, Rb, Cs; Q = S, Se) oxychalcogenides, the first reported in the A─Hf─Q─O quaternary space, which are prepared by reacting HfQ₂ with the corresponding alkali carbonate (A₂CO₃). The resulting structures are dimensionally reduced variants of the 1T-HfQ₂ parent phase, where rows of O atoms insert into the transition metal dichalcogenide (TMD) layers. This yields nanometer-wide 1D-[Hf₃Q₆] ribbons that link into step-like sheets through distinctive Hf─O─Hf bridges, which connect heteroleptic HfQ₅O polyhedra at the ribbon edges. UV/Vis and photoluminescence spectra reveal tunable absorption and emission features spanning 1.8-2.6 eV. Calculated band structures show direct-gap transitions and highly dispersive bands along the [Hf₃Q₆] nanoribbons, yielding effective masses more than two orders of magnitude lower than in other crystallographic directions. Charge-density plots further illustrate quasi-1D electronic anisotropy, showing frontier orbitals confined to the nanoribbons due to covalent Hf─Q bonding. We anticipate heteroanion-driven dimensional reduction can be used to engineer anisotropy in semiconductors and offers new routes to synthetically challenging multianion systems.