Enhanced dielectric, magnetic and optical properties of Cr-doped BiFeO3 multiferroic nanoparticles synthesized by sol-gel route

Chromium-doped multiferroic bismuth ferrite BiFe1-xCrxO3 (x = 0.00, 0.01, 0.03, 0.05 and 0.07) nanoparticles (NPs) were synthesized by an ethylene glycol-based sol-gel technique and annealed at relatively low temperature of 550 degrees C. X-ray diffraction (XRD) confirmed the phase purity of pristine BiFeO3 and 1% Cr-doped BiFeO3 NPs. However, a slight impurity phase started to appear in 3% Cr-doped BFO which became significant in 5% and 7% Cr-doped samples. The crystallite sizes as determined by Scherrer equation were found to be 46 nm, 44 nm, 39 nm, 37 nm, and 34 nm respectively for pristine BiFeO3, BiFe0.99Cr0.01O3, BiFe0.97Cr0.03O3, BiFe0.95Cr0.05O3 and BiFe0.93Cr0.07O3 (referred to as BFO, BFC1O, BFC3O, BFC5O, and BFC7O respectively) NPs. In close agreement to this, the sizes determined by HRTEM was found to be 48 and 46 nm for BFO and BFC1O NPs, respectively. In the low frequency region, the dielectric constant (epsilon e') shows a maximum decrease by 93% on 1% Cr-doping concomitant with 50% decrease in dielectric loss (tan delta) which indicates substantial reduction in leakage current density. Further, the pristine BFO shows a well-defined dielectric loss peak at 40 Hz (tan d= 0.4) which shifts to 400 Hz for 1%, 3% and 7% Cr-doped NPs. Above 133 Hz, the 1%-Cr-doped NPs show greater loss as compared to pristine BFO NPs. The oxidation state of iron was found to be + 3 by X-ray photoelectron spectroscopy (XPS), which was further corroborated by Mossbauer spectroscopy (MS). These nanocrystals with reduced leakage current and enhanced magnetic properties are well-suited for device applications.