High transmittance in lead-free lanthanum modified potassium-sodium niobate ceramics

Compared to lead lanthanum zirconate titanate (PLZT), potassium-sodium niobate shows good advances because of its excellent photoelectric response frequency and holographic storage. However, its low transmittance limits its application in photoelectrical controllers. To address this issue, lanthanum was introduced as a dopant, and the properties of the resulting ceramics were evaluated using both experimental and theoretical approaches. The (1-x)(K_0.5Na_0.5)NbO₃-xLa₂O₃ (KNN-xL; x = 0.005, 0.010, 0.015, 0.020) transmittance ceramics were prepared by traditional low-pressure sintering process. Among the ceramics examined, KNN-0.015L achieved the widest band gap (Eg) of 3.108 eV and the highest transparency of 74%; both values are higher than those of PLZT (band gap = 3.10 eV, transparency = 70%) prepared by hot-press sintering. The transition rule was evaluated by density functional theory (DFT) to validate the experimental results obtained. Additionally, the related mechanism of transparency variation induced by electronic structure and grain size modulation was discussed thoroughly.