Ferroelectric phase transition in relaxor ferroelectric single crystals 0.76PMN-0.24PT

The features of the single crystals 0.76PMN-0.24PT in dielectric, ferroelectric, pyroelectric properties and domain structures indicate that they are located between typical ferroelectrics and normal ones. The unpoled crystals present a transitional domain configuration between microdomains and typical macrodomains while the crystals on (001) cuts undergo field-induced phase transition under poling, showing two special temperature points T-d and T-m during the succedent heating procedure. The dielectric constant starts to decrease drastically at T-d during cooling, or the transformation from induced macrodomain to transitional domain takes place at T-d during heating. Ferroelectric-paraelectric phase transition or depolarization continues within the whole temperature range of T-d-T-m, where ferroelectric phase in the form of transitional macrodomains coexists with paraelectric phase. Then the crystals macroscopically transoform into paraelectric phase containing ferroelectric microdomains at a temperature above T-m. However, owing to the influence of crystallite orientation on field-induced phase transition, the temperature Td does not appear in the same temperature-electric field history in multicrystal ceramics with the same composition as the above single crystals.