Magnetic and Dielectric Properties of Nanostructured BiFeO3 Prepared by Sol-Gel Method

Polycrystalline BiFeO3 was synthesized at 400 degrees C-700 degrees C. Distinctive difference in the magnetic and dielectric properties was observed between the samples sintered at 400 degrees C-500 degrees C and those sintered at 600 degrees C-700 degrees C. The former showed ferromagnetic- like hysteresis loops with an increased magnetization of 0.54 emu/g, whereas the later showed linear loops with a small magnetization of 0.065 emu/g. Although X-ray did not identify any secondary phase, the suspected trace of some magnetic phase (Fe3O4) in the samples was conceded by the occurrence of an exchange bias. The difference in dielectric response between the two groups of samples arose mainly from a different conductivity at the grain boundaries. Owing to Fe3O4 coating at grain surface, the 400 degrees C-500 degrees C sintered samples behaved like a single parallel R-C circuit, whereas the dielectric response of the samples sintered at 600 degrees C-700 degrees C was represented by a series of two parallel R-C units for grains and grain boundaries, respectively. Two dielectric relaxation peaks observed at <700 Hz and 0.3 similar to 6 MHz in the high-temperature sintered samples were attributed to the Maxwell-Wagner relaxation and electron hopping, respectively.