Ferroelectric, Optical, and Photovoltaic Properties of Morphotropic Phase Boundary Compositions in the PbTiO3-BiFeO3-Bi(Ni1/2Ti1/2)O3 System

Ferroelectrics can exhibit the bulk photovoltaic effect (BPVE), which enables a switchable photoresponse and above-band-gap open-circuit voltages (V-oc). For these systems a large remnant polarization (P-r) combined with a narrow band gap (E-g) is believed to be critical in optimizing the photovoltaic performance. Here we investigate the PbTiO3-BiFeO3-Bi(Ni1/2Ti1/2)O-3 system which exhibits a large bulk P-r and a tunable narrow E-g. To optimize the ferroelectric polarization, ceramic samples were prepared in the vicinity of the ternary morphotropic phase boundary (MPB), and their photovoltaic properties were characterized over a broad range of optical wavelengths. MPB compositions with a direct optical gap ranging from 2.25 to 2.85 eV and P-r = 32-39 mu C/cm(2) show a BPVE with V-oc = 6 V at room temperature and a wavelength-dependent switchable photoresponse. Under 1 sun AM 1.5 G illumination the short-circuit photocurrent (j(sc)) increased by an order of magnitude as E-g was lowered from 2.85 to 2.25 eV, with, similar to 0.1 mu A/cm(2).