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A topochemical route to nondefect, three-dimensional perovskites from lamellar Dion−Jacobson and Ruddlesden−Popper precursors was demonstrated. The method involves reduction of one of the ions (in this case Eu3+) in the precursor phase and concomitant loss of oxygen. CsEu2Ti2NbO10, a three-layer Dion−Jacobson compound, was ion-exchanged to AEu2Ti2NbO10 (A = Na, Li) and reduced in hydrogen to form the SrTiO3-type perovskites AEu2Ti2NbO9. Similarly, K2Eu2Ti3O10, a three-layer Ruddlesden−Popper compound, underwent divalent ion exchange to form the Dion−Jacobson compounds AIIEu2Ti3O10 (AII = Ca, Sr) and MIIEu2Ti3O10 (MII = Ni, Cu, Zn), which were reduced in hydrogen to perovskite-type AIIEu2Ti3O9 and MIIEu2Ti3O9, respectively. The AII and Eu2+ ions of AIIEu2Ti3O9 remain ordered, while A-site disordering occurs in the other perovskites. In all cases, the anisotropic texture of the layered precursors is retained in the product perovskite phase.
Schaak et al. (Wed,) studied this question.