Electronic structure and electrochemical properties of La-doped BiFeO₃ nanoparticles

We investigated the effect of La substitutional ions on the structural, optical, and electrochemical properties of bismuth ferrite (BiFeO₃) and used them as electrode materials for high performance supercapacitors. The compositions of ^1.05Bi_1-xLa_xFeO₃ (0.0 < x <0.10) nanoparticles were prepared through sol-gel conventional route and denoted as ^1.05BiFeO₃: BF0; ^1.05Bi_0.95La_0.05FeO₃: BF5; ^1.05Bi_0.90La_0.10FeO₃: BF10. The Rietveld refinement results of XRD patterns suggested the formation of rhombohedrally distorted perovskite structure (space group: R3c) with negligible secondary phase. The crystallite sizes determined using Scherrer's formula were found to be in the 59−48 nm range and observed to decrease with an increase in La content. The bandgap measured using UV absorption spectroscopy was found to decrease with an increase in La content in BiFeO₃. The SEM micrographs revealed that the prepared samples were composed of nanocrystalline grains with particle sizes ranging from 25 to 40 nm. The electronic structural modification has been confirmed by the XAS analysis of Fe L_3,2 and O K edge spectra as a result of La doping. Electrochemical measurements showed that 5% La-doped BFO (BF5) as an electrode demonstrated excellent performance for supercapacitors with a specific capacitance of 328 F g⁻¹ measured with a scan rate of 10 mV s⁻¹. It also exhibited tremendous cyclic stability with capacitance retention of >97 % for 1000 cycles measured at 1A g⁻¹.