Synthesis and characterization of multiferroic Sm-doped BiFeO3 nanopowders and their bulk dielectric properties

Multiferroic Bi1−xSmxFeO3 (x = 0, 0.05, 0.1, 0.2, and 0.3) nanopowders with particle sizes of 69-22.6 nm were prepared by a simple co-precipitation method. The structure and morphology of the samples were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD patterns confirmed the phase transition from rhombohedral to orthorhombic phases. The results of X-ray absorption spectroscopy (XAS) data indicate that the oxidation state of Fe in the sample was Fe3+. The results of magnetic properties revealed the enhancement of weak ferromagnetic property with increasing Sm doping in BFO nanopowders. SEM images revealed that the average grain size decreased with an increase in Sm concentration. Undoped BFO ceramics exhibited a high dielectric constant ε′ ∼1.1 × 104 and a low loss tangent of tan δ ∼0.5 at room temperature for 1 kHz. The room temperature dielectric constant decreased with increasing concentration of Sm doping and the dielectric relaxation peaks were observed at x ≤ 0.1. The dielectric relaxation peaks which were observed at all frequency ranges were x ≤ 0.1 samples which were attributed to Maxwell-Wagner relaxation. As the temperature increased, great increases in dielectric permittivity were observed in all the Bi1−xSmxFeO3 samples. The effects of grain boundaries on the dielectric properties of Sm-doped BFO ceramics were investigated by measuring the dielectric responds in the frequencies of 100 Hz-1 MHz at room temperature under applied dc bias of 0-20 V. It was found that, with an increase in applied dc bias voltage from 0 to 20 V, the dielectric constant decreases at frequencies below 104 Hz. However, the dielectric properties in the high-frequency region remained unchanged.