Effect of Ag doping on the formation and properties of percolative Ag/BiFeO3 composite thin film by sol–gel method

Abstract

The Ag/BiFeO3 thin films were prepared on ITO/glass substrate by in situ sol–gel method. The morphology and formation of the perovskite phase and Ag nanoparticles (NPs) were studied by XRD, SEM, and UV–Vis spectra. The doping of Ag+ ions and the formation of defects were analyzed by XPS measurement. The dielectric and magnetic properties were measured by impedance analyzer and magnetic property measurement system. Results showed that a few Ag+ ions (<7%) were doped into the bismuth ferrite lattice to substitute Bi. In addition, most of the Ag+ ions were reduced to Ag NPs in BiFeO3 thin films and the Ag NPs/BiFeO3 composite thin film was formed. The Ag+ ions doping was beneficial for not only the formation of crystalline phase of bismuth ferrite, but also the preferential orientation growth of (012) lattice plane. The Ag NPs dispersed in the thin film introduced the percolation behavior into composite the thin film, having the theoretical percolation threshold of fc = 0.131. When the volume fraction of Ag NPs is about 0.12 (Ag/Fe = 0.6). The dielectric constant of the Ag NPs/BiFeO3 thin film reached about 173, being three times as large as that of BiFeO3 thin film without Ag NPs. The minimum value of the dielectric loss was about 0.1–0.2. The typical ferromagnetic property was maintained although the magnetizations decreased a little with the increase in Ag content. The coercive force was 111Oe, showing no typical difference between the thin films with and without Ag NPs. They were beneficial to be used as a candidate in devices with both dielectric and ferromagnetic properties at the same time.