Crystal structures and electrical properties of Sr/Fe-modified KNbO3 ferroelectric semiconductors with narrow bandgap

In the process of exploring ferroelectric semiconductors, a new system of (1− x ) KNbO 3 – x SrFeO 3−δ ( x = 0.00-0.20) was successfully synthesized via solid-state reaction. The crystal structures, ferroelectric, dielectric, optical, and electrical properties were systematically characterized. The orthorhombic phase with Amm2 space group is detected in all the ceramics. In addition, the orthorhombic and tetragonal phases coexist in 0.80KNbO 3 -0.20SrFeO 3-δ ceramic. The decrease in oxygen octahedron distortion induces a weak ferroelectric polarization. The existence of long-range ferroelectric polarization order in all the ceramics is verified and the bandgap of the ceramics can be tuned to ~2.18 eV. The improved short-circuit photocurrent density ( J sc ) and open-circuit voltage ( V oc ) of the poled 0.95KNbO 3 -0.05SrFeO 3−δ ceramic at 30 kV/cm are ~6.90 nA/cm 2 and 0.04 V, respectively. The activation energies for electrical conductivity of the grains and grain boundaries from 0.90KN–0.10SF ceramic are 0.67 and 0.77 eV, respectively, which indicate the doubly ionized oxygen vacancies. This work provides a new way to tune the optical bandgap/ferroelectric properties of KNbO 3 -based ceramics for potential application in ferroelectric photovoltaic and energy fields.