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Crystallite size dependence of morphotropic phase boundary in the multiferroic BiFeO3-PbTiO3

The morphotropic phase boundary (MPB) in the magnetoelectric multiferroic BiFeO3-PbTiO3 is shown to be uniquely dependent on crystallite size. The system exhibits the phenomenon of abnormal grain growth (AGG) during sintering with abrupt increase in the grain size from ~ 1 micron to ~ 10 microns. The large sized free crystallites (10 microns) exhibit pure tetragonal phase. Phase coexistence sets in after reducing the size to ~ 1 micron. These results prove that size, and not the internal stress, as the controlling mechanism for stabilizing phase coexistence in this system.