Monoclinic morphotropic phase and grain size-induced polarization rotation in Pb(Mg1/3Nb2/3)O-3-PbTiO3

A detailed Rietveld analysis of x-ray data, collected at room temperature, was done on ceramics with controlled grain size between 100 nm and 4 mu m for (PbMg1/3Nb2/3O3)0.80-(PbTiO3)0.20 (PMN-PT20), i.e., a compound at the border of the so-called morphotropic phase boundary. With size reduction the polarization rotates within the monoclinic plane from M-B, i.e., P-x=P-y > P-z to M-A, i.e., P-x=P-y < P-z, and finally reaches a rhombohedral phase, i.e., P-x=P-y=P-z, below a critical value of similar to 200 nm without diminishing the amplitude of the polarization. This study provides an easy way to tailor the direction of polarization of these materials