Dielectric relaxations and conduction mechanism in Aurivillius-type Bi4Ti3O12–Bi5Fe0.5Co0.5Ti3O15 solid solution

The structural, multiferroic, dielectric and conductivity properties of Aurivillius-type Bi4Ti3O12–Bi5Fe0.5Co0.5Ti3O15 solid solutions prepared by a modified pechini method are investigated. The magnetic measurements indicate that the double remnant magnetization 2Mris 2.6 memu/g and the ferromagnetic Curie temperature is 599 K. The optical band gap Eg is obtained as 2.31 eV. Meanwhile, four different dielectric relaxations are observed in the temperature ranging from 300 to 1050 K. The corresponding relaxation mechanisms are systematically studied by the measurements of complex dielectric, impedance, electrical modulus and ac conductivity spectra. The low-frequency relaxation with Ea = 0.752 eV is ascribed to the thermal migration of oxygen vacancy, the medium-frequency one with Ea = 0.294 eV is assigned to the localized hole transfer behavior, whereas the high-frequency one with Ea = 0.327 eV is associate with the hopping process of electron. In addition, the dielectric loss relaxation above ~ 800 K exhibits a rather large activation energy of Ea = 2.00 eV. The dc conductivity can be ascribed to the ionic-p-type mixed conduction mechanism.