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In Pb(Sc0.5Ta0.5)O3 it has been shown that the degree of order in the B-site Sc3+, Ta5+ cations can be controlled by suitable thermal annealing. For samples which have been well-ordered by long annealing, dielectric measurements on single crystals show a normal first-order ferroelectric phase change at 13 °C and a maximum low-temperature spontaneous polarization of 23.0 μc/cm2. With increasing disorder, the crystals begin to exhibit the classical diffuse phase transition of a ferroelectric relaxor, with a broad Curie range and strong low-frequency dielectric dispersion in the transition range. X-ray diffraction measurements of the size of the ordered microregions suggest that ordering proceeds by different mechanisms in single-crystal versus ceramic samples, though the resulting effects upon the dielectric behavior are very similar.
Setter et al. (Fri,) studied this question.