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Features of the diffuse phase transition in lead barium niobate (PbxBa1−xNb2O6–PBN) ferroelectric ceramics are presented and discussed. Ceramics were prepared near to the morphotropic phase boundary (x∼0.63) and the dielectric properties were investigated. The character of the ferroelectric phase transition was carefully analyzed, indicating that the diffuseness coefficient decreases as the lead concentration increases. This effect is attributed to the increase of the unit-cell polarization with the morphotropic phase boundary proximity. The polarization enhancement induces the formation and interaction between the polar microregions in PBN samples at temperatures higher than Tm. The appearance of dilatation centers, which act as strong oscillating random-field sources and are naturally created due to the peculiar A-site vacancy distribution in PBN structure, increases the maximum dielectric permittivity by the polarization mobility enhancement. On the other hand, the temperature of maximum dielectric permittivity is decreased due to the action of the random fields.

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