Negative and positive photodielectric effects in quantum paraelectric BaFe12O19 single crystals

The effects of light illumination on dielectric properties were investigated in ferrimagnetic quantum paraelectric BaFe12O19 single crystals. The enhancement and reduction of dielectric constants under light illumination, i.e., positive and negative photodielectric (PD) effects, were found in BaFe12O19. The high-temperature positive PD effect depends significantly on the frequency and temperature, which can be ascribed to the photo-excitation accelerated electron hopping process between Fe2+ and Fe3+. The low-temperature negative PD effect is nearly frequency-independent and is associated with non-polar tendency of the FeO5 bipyramids induced by photo-excited carriers. These findings could suggest a promising route to generate large and frequency-independent PD effects for application in photo-sensing devices.