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

The magnetization hysteresis loop, structure, and grain morphology of (Bi
_0.85
Ca
_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 BiFeO
₃
(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 Bi
³⁺
to Ca
²⁺
. 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.