Photoresponse of KNbO3-AFeO3 (A = Bi3+ or La3+) ceramics and its relationship with bandgap narrowing

The crystal structure of (1-x)KNbO3-xBiFeO3 (KNBF) and (1-x)KNbO3-LaFeO3 (KNLF) (where x = 0.00; 0.01; 0.02; 0.04; 0.08; 0.16; 0.32) was evaluated by XRD and Raman spectroscopy. XRD data show the crystal symmetry to evolve from orthorhombic to tetragonal with increasing x. The optical bandgap was found to narrow systematically with increasing x. Raman spectroscopy analysis corroborated long-range polar order in all compositions. The photoresponse of x = 0.32 shows a typical diode-like behaviour, with current and voltage of 0.115 µA and 0.075 V for KNBF and 0.19 µA and 0.035 V for KNLF, respectively. To our knowledge these represent the largest values among KNbO3-based ceramics, making them promising for photovoltaic applications.