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Abstract
A theoretical model is proposed to calculate the spontaneous polarization in PMN relaxor. It is supposed that the Nb ions in the ordered microregions displace cooperatively due to the structure homogeneity, giving rise to the polarization below Td (600 K). The results agree with the polarization deduced from the electro-optic and electrostrictive effects. The ordered microregions have been proved to be the locations of the polar clusters at Tf ≪ T < Td , where Tf is the freezing temperature (near 210 K). The spontaneous polarization process in the ordered microregions is suggested to be similar to that of normal ferroelectrics. The dipole glass model of relaxors is discussed.