Controlling Self-Assembled Perovskite−Spinel Nanostructures

We report a discovery that self-assembled perovskite−spinel nanostructures can be controlled simply by selecting single-crystal substrates with different orientations. In a model BiFeO₃−CoFe₂O₄ system, a (001) substrate results in rectangular-shaped CoFe₂O₄ nanopillars in a BiFeO₃ matrix; in contrast, a (111) substrate leads to triangular-shaped BiFeO₃ nanopillars in a CoFe₂O₄ matrix, irrespective of the volume fraction of the two phases. This dramatic reversal is attributed to the surface energy anisotropy as an intrinsic property of a crystal.