Unraveling metastable perovskite oxides insights from structural engineering to synthesis paradigms

Metastable perovskite oxides, with their complex atomic arrangements and nonequilibrium electronic structures, show great potential in fields such as energy conversion, storage, advanced optoelectronics, and intelligent sensing. Compared to conventional perovskites, metastable structures exhibit unique local symmetry breaking and oxygen vacancy modulation, high defect concentrations and tunable electronic structures. These features provide significant advantages in enhancing interfacial catalytic activity, ion transport, and photoelectric performance. However, their nonequilibrium structures tend to transform into more thermodynamically stable phases under typical synthesis conditions, complicating the study of their structure-property relationships and synthesis. This review adopts a structural materials perspective to analyze the unique advantages and structure-performance correlations of metastable perovskite oxides. Key concepts are introduced, categorizing these oxides based on their structural characteristics into four groups: symmetry-distorted type, Heterojunction type, Layered type, and Multivalent-regulated type, focusing on their impact on physicochemical properties. Major synthesis strategies, such as solid-state synthesis, high-pressure synthesis, pulsed laser deposition, salt-assisted method, and wet chemical approach, are systematically reviewed, highlighting their effectiveness in stabilizing metastable phases. The review also summarizes recent advancements in metastable perovskites, encompassing their types, structural features, synthesis methods, and applications, while identifying key challenges and future prospects in energy and information technologies.