Temperature-Dependent Crystal Structure and Physical Properties of BiFeO3 Bulk Ceramics.

BiFeO₃ bulk ceramics were prepared by sol-gel auto-combustion method at the temperature of 725 °C、750 °C、775 °C、800 °C、825 °C respectively (abbreviated as C725, C750, C775, C800 and C825). XRD patterns confirm the phase stability of BFO ceramics in a large temperature range from 725 °C to 825 °C. Almost no pores were observed in the compact C775 ceramic which has the highest density (8.05 g/cm³, 96.83% of the theoretical one) compared to that of other samples. The average grain sizes of the BFO ceramics increased with the increasing of sintering temperature. The highest electric resistance (538KΩ at 50 Hz) and lowest dielectric constant (689.01 at 1 kHz) were obtained in C775. All BFO bulk ceramics exhibit strong optical absorption in the visible range with two absorption peaks at 520-538 nm and 670 nm. Band gaps of the as-prepared BFO ceramics were slightly affected by sintering temperature, since the band gaps of C725, C750, C775, C800, C825 are 2.74 eV, 2.78 eV, 2.76 eV, 2.63 eV, 2.75 eV, respectively. The weakest photoluminescence signal with largest red shift can be observed in C775. [ABSTRACT FROM AUTHOR]