Magnetic and Photovoltaic Properties of Calcium-Doped ${\hbox {BiFeO}}_{3}$ Ceramic

The magnetization hysteresis loop, structure, and grain morphology of (Bi_0.85Ca_0.15)FeO_2.925 (15%Ca-BFO) ceramic, prepared by the solid state reaction, have been studied at room temperature and were compared with BiFeO₃ (BFO) ceramic. The 15%Ca-BFO ceramic exhibits a pseudo-cubic structure and a linear antiferromagnetic magnetization loop with magnetic susceptibility of 4.5×10^-6 emu/gOe, which is slightly less than 6.7×10^-6 emu/gOe observed in BFO due to the heterovalent substitution from Bi³⁺ to Ca²⁺. The 15%Ca-BFO with electrodes of indium tin oxide (ITO) and Au films shows significant photovoltaic effects under near-ultraviolet light of λ = 405 nm. The open-circuit voltage (V_oc) and short-circuit current density (J_sc) under illumination can be described by the exponential equations V_oc = V_b[1-exp(-I/α)] and J_sc = J_b[1-exp(-I/β)] as a function of light intensity (I). V_b and J_b are the balance open-circuit voltage and short-circuit current density, respectively. α and β are characteristic constants. The maximal power-conversion efficiency (η) can reach η ~ 0.0034%, which is larger than η ~ 0.0025% found in graphene/ polycrystalline BFO/ Pt films. The characteristic curve of current versus bias voltage at dark suggests a p-n junction-like depletion region in the interface between ITO film and 15%Ca-BFO ceramic.