Continuously controllable optical band gap in orthorhombic ferroelectric KNbO3-BiFeO3 ceramics

The optical band gap of orthorhombic ferroelectric KNbO3 is shown to be continuously controllable via Bi and Fe co-substitution according to a K1-xBixNb1-xFexO3 doping mechanism. Room temperature X-ray diffraction data combined with Raman spectroscopy analysis show the polar orthorhombic crystal structure to persist up to x=0.25, while the bandgap narrows monotonically by 1 eV (~33%). In-situ Raman spectroscopy corroborates the polar nature of all compositions in the temperature range -100 to 200 C. The ability to control the band gap while maintaining the spontaneous polarisation makes the K1-xBixNb1-xFexO3 system interesting for photoinduced processes in a wide temperature range.