Heteroanionic Tuning of Cooperative Ta Off-Centering in Quasi-One-Dimensional CsTaS3− x Cl x Semiconductors

Abstract The structural behavior of CsTaS3 was investigated alongside that of the new heteroanionic compound CsTaS2.16Cl0.84, synthesized via the reaction of Ta and S in a CsCl flux. Single-crystal X-ray diffraction reveals that both compounds are isostructural, crystallizing in the centrosymmetric hexagonal space group P63/mmc with split Ta positions along the face-sharing octahedral chain direction. Pair distribution function analysis of both compounds, supported by STEM imaging of CsTaS3, identifies the local intrachain displacement motif as cooperative Ta sliding rather than alternating Ta−Ta dimerization. While X-ray absorption near-edge spectroscopy (XANES) confirms the decrease of the average oxidation state in CsTaS2.16Cl0.84, the same structural distortion persists, albeit now with a reduced magnitude. Both materials are semiconducting, and Cl incorporation increases the band gap from ∼1.00 eV in CsTaS3 to ∼1.12 eV in the heteroanionic phase. Single-crystal detectors fabricated from CsTaS2.16Cl0.84 exhibit high resistivity, which effectively suppresses dark current and enhances signal-to-noise performance. These devices deliver an X-ray sensitivity of 7470 μC Gyair−1 cm−2, demonstrating efficient charge generation and collection under irradiation.