Excellent Transmittance Induced Phase Transition and Grain Size Modulation in Lead-Free (1-x)(K_0.5Na_0.5)NbO₃-xLaBiO₃ Ceramics

A novel lead-free excellent transmittance electro-optic ceramics (1-x)(K_0.5Na_0.5)NbO₃-xLaBiO₃ (KNN-LB, x = 0.000, 0.005, 0.010, 0.015, 0.020, 0.025, 0.040, 0.060) were fabricated by traditional pressureless ceramics processing procedure. The effects of LaBiO₃ dopant concentration x on the microstructure, phase transition, optical property, and electrical properties were studied systematically. The X-ray diffraction results indicated that the KNN-LB ceramics with x ≥ 0.025 have the pseudocubic phase. The morphology, density, and microstructure of the KNN-LB ceramics were characterized by scanning electronic microscopy and optical microscopy. In particular, the KNN-LB ceramics (0.05 mm thickness) with x = 0.025 exhibited the highest transmittance of 74.00% in the visible spectrum comparable to the 72.00% transmittance of the lead lanthanum zirconate titanate (PLZT 9/65/35 of 0.127 mm thickness). In addition, the related mechanism of transparency variation induced by phase transition and grain size modulation were discussed thoroughly. Finally, the dielectric and ferroelectric properties of as-prepared KNN-LB ceramics were also investigated to further clarify the relationship between transparency and relaxor behavior.