Hot-pressed K0.48Na0.52Nb1−xBixO3 (x = 0.05–0.15) lead-free ceramics for electro-optic applications

Bismuth-modified potassium sodium niobate K0.48Na0.52Nb1−xBixO3 (x = 0.05–0.15) transparent lead-free ceramics were fabricated by a hot-pressing method. Both hot-pressing conditions (pressure, temperature and duration) and Bi-content were found to have strong influences on the density, transparency, electro-optical coefficient, and electrical properties of the ceramics. Under the typical hot-pressing conditions of 1060 °C for 5 h at 5.5 MPa, the optimum Bi-content was found at 7.5 at.% in the system under study. These ceramics display good optical transmission in the visible and particularly in the infrared regions. For visible light, the highest transmission value of a polished 0.5-mm thick plates is about 60% at a wavelength of 800 nm; while for infrared, the transmission value is about 80% at 4000 nm. The effective linear electro-optic coefficient of the ceramics was found to be 42 pV m−1. The dielectric permittivity and loss tangent of the KNNB (x = 0.075) ceramics were found to be 716 and 0.031 at room temperature.