Perovskites by Design:  A Toolbox of Solid-State Reactions

In recent years, many soft-chemical reactions of layered perovskites have been reported, and they can be classified into sets of similar reactions. Simple ion-exchange and intercalation reactions replace or modify the interlayer cations of layered perovskites, and more complex metathesis reactions replace interlayer cations with cationic structural units. Topochemical condensation reactions that involve dehydration and reduction provide access to a variety of metastable structural features in three-dimensional perovskites, and similar reactions can be used to convert among higher order layered perovskite homologues. Other techniques, such as high pressure and anion intercalation/deintercalation, also yield interesting metastable phases. When combined, the individual reactions complement each other, and a powerful toolbox of solid-state reactions emerges. By using layered perovskites as templates, it is possible to retrosynthetically design new product perovskites that retain the structural features of the precursor layered phases. The toolbox of reactions was used to synthesize a new Ruddlesden−Popper phase, Na2Sr2Nb2MnO10, and to demonstrate the first example of a complete cycle of reactions of layered perovskites. In addition, topochemical dehydration and reduction were combined to synthesize the new A-site defective cubic perovskite Ca0.67Eu1.33La0.67Ti3O9. It should be possible to extend the toolbox to include more complex systems using layer-by-layer assembly of perovskite thin films, which provide access to “made to order” stacking sequences.