Effect of electric field on the smeared phase transition in crystals PbIn1/2Nb1/2O3-28PbTiO3 and PbIn1/2Nb1/2O3-37PbTiO3

The effect of a direct-current electric field (0 < E < 3 kV/cm) on the smearing of the phase transition and the Curie-Weiss exponent (gamma) for two PbIn1/2Nb1/2O3-28PbTiO(3) and PbIn1/2Nb1/2O3-37PbTiO(3) crystals lying at different distances from the morphotropic phase boundary has been investigated. The universal Curie-Weiss law has been used to approximate the temperature dependences of the dielectric permittivity. It has been shown that the more remote is the crystal from the morphotropic phase boundary, the larger is the exponent gamma and, consequently, the more smeared is the phase transition (in the zero field, gamma = 1.67 and 1.49 for PbIn1/2Nb1/2O3-28PbTiO(3) and PbIn1/2Nb1/2O3-37PbTiO(3), respectively). It has been found that a weak electric field (no greater than 2-3 kV/cm) in the case of the more smeared phase transition almost does not affect the Curie-Weiss exponent, whereas for the PbIn1/2Nb1/2O3-37PbTiO(3) crystal, this exponent decreases with increasing electric field strength and approaches gamma = 1, which is characteristic of the conventional ferroelectric.