Effect of sintering temperature on nanostructured multiferroic BiFeO/sub 3/ ceramics

Nano structured multiferroic BiFeO/sub 3/ (BFO) powders were synthesized by using the co-precipitation method. Calcination of acquired powder was carried out at 400 deg. C for 3h. Uniaxially pressed pellets were sintered at 500 deg. C, 600 deg. C, 700 deg. and 800 deg. C for 2 hours in air. These samples were characterized for structural, thermal, electrical and magnetic properties. X-ray diffraction (XRD) confirmed the amorphous nature of the as driven powder and phase purity of the calcined BFO sample. The crystallite size varied with the sintering temperature from 52 to 70 nm. Sintering above 500 deg. C induced impure phases due to oxygen vacancies and volumetric strain in crystal structure. Ferroelectric to paraelectric transition temperature T/sub C/ approx. equal to 815 deg. C was verified by the differential scanning calorimetry (DSC). Surface morphology and grain growth was observed using scanning electron microscopy (SEM). Electrical ac measurements were performed in the frequency range from 20 Hz to 3 MHz at room temperature. For a particular sample, capacitance decreased and susceptance increased with the increase of applied frequency signal. These parameters were increased with the increase of sintering temperature. Vibrating sample magnetometer (VSM) revealed the diverse weak ferromagnetic behavior for the samples sintered at different temperatures. Maximum coercivity (H/sub c/ approx. equal to 119.2 Oe) and maximum remnant magnetization (M/sub R /approx. equal to 2.1 X 10/sup -3/ emu/g) were obtained for the sample sintered at 700 deg. C for 2hr. (author)