The process of isothermal compositional ordering in the Pb2ScNbO6 ferroelectric and Pb2InNbO6 antiferroelectric is studied. Variation in the degree of the compositional long‐range order is brought about by annealing at high temperature and the subsequent quenching and is registered by its effect on dielectric characteristics in the Curie point region. The compositional ordering in oxides studied appeared to proceed most probably via non‐nucleation mechanism. In crystals with non‐homogeneous defect distribution and in ceramics a macroscopically non‐homogeneous process of ordering is observed. A model of the ordering kinetics in ceramics is proposed.

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