Sol–gel synthesis and characterization of a new four-layer K0.5Gd0.5Bi4Ti4O15 Aurivillius phase

Monophasic K0.5Gd0.5Bi4Ti4O15 powders were synthesized via a citrate-based sol–gel route. Rietveld analysis of powder X-ray diffraction data confirmed the composition to be a pure four-layer Aurivillius phase with an orthorhombic structure (space group A21am and unit cell parameters a = 5.42798(52) Å, b = 5.41821(41) Å, and c = 41.2723(33) Å) at room temperature. The chemical composition and the morphology of the sintered pellets were examined by field emission scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS). The dielectric properties were investigated as a function of temperature (27–600 °C) at various frequencies (10 Hz–1 MHz), and the phase transition was observed at 560 °C. Ferroelectric nature of K0.5Gd0.5Bi4Ti4O15 was demonstrated by the polarization–electric field (P–E) hysteresis loop. Equivalent circuit modeling of the complex impedance data was employed to determine the conduction behavior. The temperature dependence of dc conductivity was found to follow the Arrhenius law associated with the activation energy of 1.22 ± 0.02 eV and was attributed to the long-range movement of oxygen vacancies.