Impedance Spectroscopy and Photovoltaic Effect of Oxygen Defect Engineering on KNbO3 Ferroelectric Semiconductors

Abstract

Perovskite-oxide (1 − x)KNbO3-xBaCo1/2Nb1/2O3−δ (KN-BCN; x = 0.00–0.20) ferroelectric semiconductor ceramics with oxygen defects are successfully prepared via a conventional solid-state sintering method. X-ray diffraction data indicate that the crystal symmetry evolves from orthogonal to tetragonal at increasing x values. Raman spectroscopic analysis confirms the long-range polarization of all compositions. X-ray photoelectron spectroscopy shows that the detailed chemical formula of 0.90KN-0.10BCN ceramics is 0.90KNbO3-0.10BaCo1/2Nb1/2O2.90. Room-temperature ferroelectricity weakens when the x value increases. The optical band gap narrows from 3.25 eV for x = 0.00 to 1.57 eV for x = 0.20, and the minimum value of ∼ 1.28 eV occurs in the 0.90KN-0.10BCN ceramic. Impedance analysis illustrates that the conduction mechanism of grains is mainly internal electron conduction, and that of the grain boundary is intrinsic conduction. The conducting mechanism of the ceramic system follows ohmic behavior by log I–log U curves. The maximum short-circuit photocurrent density and open-circuit photovoltage are 6.68 nA cm−2 and 0.80 V, and stable output is maintained. The KN-BCN ceramic system can be used in photovoltaic materials.