K_0.5Na_0.5NbO₃-based lead-free transparent electro-optic ceramics prepared by pressureless sintering

Transparent lead-free electro-optic (EO) ceramics (K0.5Na0.5)0.9Li0.1Nb0.9Bi0.1O3have been fabricated by pressureless sintering. The ceramics have a fine-grained structure and cubic-like symmetry. The comodification with Li and Bi induces a diffuse phase transition, causing the ceramics become relaxor-like and contain polar nanoregions. Our results reveal that excess Bi2O3can further enhance the changes in the crystal structure and dielectric behavior of the ceramics, causing them become more cubic-like and more relaxor-like, respectively. These can reduce the light scattering arisen from birefringence and domain walls, and thus improving the optical properties. For the ceramics added with 4 and 6 mol% excess Bi2O3, the optical transmittance reaches a high value of 60%-70% in the near-infrared region. The ceramics also exhibits a good linear EO response, giving an effective EO coefficient of 30-40 pm/V.