3.4.2. Different structures between precursors and products
A material with a different crystal structure from the objective material can be used as a precursor, when the material has a topotactic relation to the objective material. Typical examples are the conversion of the layered perovskite to perovskite (Schaak & Mallouk, 2000) and the preservation of the packing direction of closed-packed layers. The former example is the formation of SrTiO3 from Sr3Ti2O7 and the latter of MFe2O4 (M = Zn, Ni, Mn, etc.) from α-Fe2O3 and of BaTiO3 from Ba6Ti17O40.