The alignment of defect dipoles along the direction of spontaneous polarization in polycrystalline samples of these ferroelectric ceramics was demonstrated by using electron paramagnetic resonance techniques. The alignment was revealed by the existence of orientation-dependent paramagnetic centers, and computer modelling of the electron paramagnetic resonance line-shapes. It was shown that defect dipoles could become aligned by O vacancy motion in the octahedron around a negatively charged center, in the case of O vacancy-related dipole complexes, or by defect displacement and domain realignment in the lattice, in the case of isolated defect centers. Such alignment was not observed in non-ferroelectric materials such as SrTiO3, and was destroyed in ferroelectric materials by heating to above the Curie temperature. These results suggested the occurrence of an interplay between distortion of the unit cell and the alignment of defect dipoles; as in the more general case of ferroelectric dipole alignment. Aligned intrinsic Ti and Pb ion displacements were also observed directly in the ferroelectric Pb(Zr,Ti)O3 perovskite unit cell.

W.L.Warren, G.E.Pike, K.Vanheusden, D.Dimos, B.A.Tuttle, J.Robertson: Journal of Applied Physics, 1996, 79[12], 9250-7