Perovskite Materials: Crystal Chemistry, Synthesis, and Selected Functional Applications

Perovskites provide a flexible structural platform for tailoring electronic, optical, ferroic, catalytic, and transport properties. Their performance depends on composition, octahedral connectivity, defects, microstructure, and interfaces, but the effects of these variables differ between oxide and halide systems. This review examines selected advances in these material families, with emphasis on the links between crystal chemistry and device behavior. It first introduces the ideal perovskite structure, the scope and limitations of geometric stability descriptors, and the distinction between compositional and structural classifications. It then discusses synthesis routes and representative applications in photovoltaics, light emission, radiation detection, gas sensing, electrocatalysis, and electrochemical energy storage. The review also discusses the trade-offs associated with compositional substitution, dimensional reduction, and defect control. Computational methods and machine learning are considered as complementary tools for exploring these relationships. Across the reviewed applications, improved performance in a laboratory test does not necessarily establish operational stability or scalability; meaningful comparisons require consistent measurement conditions and a clear distinction between materials, electrodes, and complete devices. The review identifies priorities for more reliable reporting and for integrating structural characterization, computational predictions, and experimental validation.