Designer-Defective Titanium and Bismuth Chalcogenides: Insights into Structure–Property Relationships and Device Fabrication via Vacancy Engineering and Extrinsic Atom Incorporation

Titanium and bismuth chalcogenides exhibit a wide range of intriguing optical, electronic, and magnetic properties governed by their crystal structure and electronic configurations. These properties can be fine-tuned by deliberately manipulating defects and incorporating extrinsic atoms within their frameworks. Such structural and electronic modifications not only influence the intrinsic behavior of these materials but also offer alternative pathways for optimizing their performance for advanced applications. A comprehensive understanding of the interplay between size constraints, defects, and extrinsic atom integration is essential for the continued development of these systems and their use in functional devices. This review focuses on our synthetic strategies to engineer defects and incorporate extrinsic chalcogen atoms into low-dimensional metal chalcogenides, specifically in bismuth- and titanium-based chalcogenides. Precise structural and compositional modifications to these compounds lead to significant changes in their electronic and crystal properties, providing valuable insights into defect chemistry and its impact on material behavior. These findings are particularly relevant given the natural applicability of low-dimensional metal chalcogenides in various functional devices, including optoelectronics, thermoelectrics, and energy storage systems. Herein, we aim to establish a detailed correlation between the fundamental structure-property relationships and the resulting device performance, emphasizing the critical role of defects and extrinsic atomic engineering in unlocking the full potential of metal chalcogenide systems. This review not only underscores the versatility of these materials but also serves as a foundation for future efforts to design and optimize next-generation devices based on tailored low-dimensional compounds.