Unconventional photo-dielectric effect of Bi0.5Na0.5Ti0.98Nb0.02O3+δ lead-free ceramics: Enhanced dielectric constant with unchanged dielectric loss and low photoconductivity by light irradiation

Abstract

Dense lead-free ceramics Bi_0.5Na_0.5Ti_0.98Nb_0.02O_3+δ were successfully prepared using a conventional solid-state sintering method. The effect of light irradiation on dielectric and ferroelectric properties of the ceramics was investigated systematically. Under the light irradiation, dielectric constant increases significantly in the frequency range between 20 Hz and 1 MHz, while the dielectric loss remains nearly unchanged, exhibiting obvious unconventional photo-dielectric effect. As the light was switched on and off periodically, dielectric constant exhibits periodic variation, and the increased magnitude of dielectric constant is positively correlated with light intensity and light wavelength. The light irradiation caused decrease in coercive field and slight increase in polarization. The band structure was analyzed via density functional theory. The mechanism for the unconventional photo-dielectric effect of the ceramics was also discussed. The study provides a guidance for regulating dielectric properties of lead-free ferroelectric ceramics by using light.