Simultaneously achieving high transparency and applicable piezoelectricity in Sm-modified KNN-based lead-free ceramics

Transparent piezoelectric ceramics have drawn extensive concerns in recent years because of their electro-optical applications. However, it's challenging to achieve both high piezoelectricity and transparency simultaneously because of their intrinsic trade-off, especially for lead-free ceramics. In this work, the rare-earth element Sm is introduced into (K,Na)NbO3-based lead-free ceramics for improving transparency while keeping relatively high piezoelectricity. Ceramics with nominal compositions of [(Na0.57K0.43)0.94Li0.06][(Nb0.94Sb0.06-xSmx)0.95Ta0.05]O3 (x = 0 ∼ 0.005) are fabricated via the conventional solid-state reaction method. Even with pressureless sintering, the ceramic with Sm substitution content x = 0.004 possesses high transmittance of T = 63% in the visible light region (without anti-reflection coatings) and good piezoelectricity (d33 = 158 pC/N). The high transparency can be attributed to the presence of a pseudocubic phase and the significant elimination of domain walls by the Sm modification, while a coexistent orthorhombic-tetragonal phase structure at room temperature is responsible for its superior piezoelectric performance which outperforms other reported KNN-based transparent ceramics. Our results demonstrate that the as-fabricated ceramics are promising lead-free ferroelectric materials for transparent electronic device applications and this work provides insights for the further development of transparent piezoelectric ceramics.