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The possibility of the existence of a spontaneous relaxor-normal ferroelectric transition was proposed and examined using Pb(Ni1/3Nb2/3)O3-PbTiO3-PbZrO3 (PNN-PT-PZ) pseudoternary system across the morphotropic phase boundary (MPB). On cooling, the PNN-PT-PZ system in the tetragonal-rich side of the MPB underwent a spontaneous transition from a relaxor to a normal ferroelectric state. This observation was explained in terms of a thermally driven transformation from an ensemble of polar microregions to normal long-range ferroelectric domains (micro-macrodomain switching). The relaxor-normal ferroelectric transition was further correlated with the rhombohedral-tetragonal first-order phase transition. Increasing the relative content of PbZrO3 enhanced dielectric dispersion characteristics but weakened the extent of relaxor-normal transition. This observation was explained by the enhanced 1:1 Nb-Zr short-range ordering and the breaking of the translational invariance of the ferroelectrically active BO6 octahedra with increasing content of PbZrO3.

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