A comprehensive review on synthesis, properties, and applications of quaternary transition metal oxychalcogenides

2D layered materials have been the center of attraction for material science researchers after the discovery of graphene. Among the various layered 2D materials, transition metal oxychalcogenide (TMOCh) materials possess a unique position due to their exciting properties and applications. Numerous reported articles are available on these materials, but we realized that a systematic classification of them, along with their general properties and applications, was missing. So, in this review, we attempted to present a systematic approach to study more about these materials conveniently. We have classified these TMOChs based on precursor materials used (i.e., quaternary or more than that) along with the transition metal, oxygen, and chalcogen (S, Se, and Te) into three categories such as TMOChs with 1. Alkaline earth metals, 2. Post transition metals, 3. Rare earth metals. Here, we consider the compounds with fixed compositions of at least one transition metal, oxygen, and chalcogen combined with any other metals from the above three categories. The detailed discussion of various synthesis routes adopted for preparing these materials is discussed thoroughly, along with their crystal structure, electronic structure, and X-ray diffraction (XRD) patterns. The next section of the review covers a broad discussion of different properties exhibited by these materials, like optoelectronic, thermoelectric, magnetic, thermal transport, nonlinear optical, semiconducting, and resistivity. Based on these fascinating properties, TMOCh materials have a wide range of applications in various fields, which are well discussed in the application segment of this review. We have tried to provide the reader with a complete understanding of these layered materials through this review, from their synthesis to applications, with the necessary description, figures, and tables to support it.