Photo-dielectric response enhancement and switching behavior of (1-x)(K0.5Na0.5)NbO3-xCa(Ni0.5Nb0.5)O3-δ ceramics by semiconduction method

Highlights: • The semiconductive (K_0.5Na_0.5)NbO₃ ceramics were obtained by introducing Ca(Ni_0.5Nb_0.5)O_3-δ component with low valent Ni. • The semiconduction method of KNN-based ferroelectric ceramics and its relationship with photo-dielectric response are studied. • A dielectric tunability of up to 387% under ultraviolet light irradiation was obtained. • The switching behavior of ceramics was also studied. -- Abstract: The lead-free ferroelectric ceramics with high photo-dielectric response will contribute to developing new contactless photoelectric devices. The (1-x)(K_0.5Na_0.5)NbO₃-xCa(Ni_0.5Nb_0.5)O_3-δ (KNN-xCNN) ferroelectric semiconductive ceramics prepared by solid-phase sintering were used to investigate photo-dielectric behavior. After introducing the CNN component, the hysteresis loops of KNN-xCNN ceramics changed from the normal P-E loops to the pinched P-E loops, and the relaxation behavior was enhanced by the increase of diffusion coefficient from 1.16 to 1.85. The phase structure transformed from the orthogonal phase to the tetragonal phase. The grain size decreasing from 360 nm to 170 nm was refined. The bandgap decreased significantly from 2.29 eV to 1.40 eV. An obvious enhanced photo-dielectric response was achieved under ultraviolet light irradiation, which shows high dielectric tunability of ~387% at x = 0.015. Meanwhile, the switching behavior was analyzed by the capacitive ratio under light on and off state, which is about 5. These results pave the way for new photoelectric coupling devices such as photo-adjustable capacitor and capacitive switching.