Highly transparent lead‐free (1‐x)K0.5Na0.5NbO3–xSr(Zn1/3Nb2/3)O3 (KNN–xSZN) ferroelectric ceramics have been synthesized via a conventional pressureless sintering method. All samples are optically clear, showing high transmittance in the visible and near‐infrared regions (~70% and ~80% at 0.5 mm of thickness, respectively). This exceptionally good transmittance is due to the pseudo‐cubic phase structure as well as the dense and fine‐grained microstructure. In addition, a high energy storage density of 3.0 J/cm3 has been achieved for the 0.94K0.5Na0.5NbO3–0.06Sr(Zn1/3Nb2/3)O3 ceramics with submicron‐sized grains (~136 nm). The main reason is likely to be the typical relaxor‐like behavior characterized by diffuse phase transition, in addition to the dense and fine‐grained microstructure. This study demonstrates that the 0.94K0.5Na0.5NbO3–0.06Sr(Zn1/3Nb2/3)O3 ceramic is a promising candidate of lead‐free transparent ferroelectric ceramics for new areas beyond transparent electronic device applications.

High transparency was obtained in (1-x)(K 0.5 Na 0.5)NbO 3-xSr(Mg 1/3 Nb 2/3)O 3 (x = 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08) lead-free ceramics by pressure-less sintering procedure. The effects of Sr(Mg 1/3 Nb 2/3)O 3 content on the microstructure, phase transition, optical properties and electrical properties were studied in detail. The X-ray diffraction results showed that the crystal structure of ceramics gradually transformed from orthorhombic phase into pseudo-cubic phase with doping of Sr(Mg 1/3 Nb 2/3)O 3 ,. The fine grain microstructure with clear grain boundary was observed in all compositions, while the grain size exhibited significant composition dependence. It was found that a more uniform distribution with smaller grain size was favorable to high optical transmittance, owing to the decreased scattering by grains and grain boundaries. In addition, a strong diffuse phase transformation in KNN-based ceramics induced by Sr(Mg 1/3 Nb 2/3)O 3 doping, causing the ceramics become more relaxor-like and transparent. The transmittance and electric properties results indicated that the 0.95(K 0.5 Na 0.5)NbO 3-0.05Sr(Mg 1/3 Nb 2/3)O 3 ceramics exhibited higher transmittance (60% in the near-IR region) accompanied with better electrical properties ( m = 2104, P r = 5.0 μC/cm 2 , d 33 = 92 pC/N).

Transparent, Sr(Al0.5Nb0.5)O3‐modified K0.5Na0.5NbO3 (KNN) ceramics were successfully fabricated by a solid‐state pressureless sintering method in this work. The obtained microstructure, transmittance, and electrical properties were characterized in detail. Our results indicated that the modification by Sr(Al0.5Nb0.5)O3 significantly limited the grain growth behavior of KNN, resulting in dense ceramics with submicron grain size (<0.5 μm) and small pore size. Consequently, the ceramic with the 0.96K0.5Na0.5NbO3‐0.04Sr(Al0.5Nb0.5)O3 composition showed superior transmittance and electrical properties: T = 55% in the visible region (0.78 μm), d33 = 105 pC/N, εr = 1021, and Pr = 15.1 μC/cm2, which were significantly higher than those of pure KNN. Our findings implied that the addition of Sr(Al0.5Nb0.5)O3 could be a good strategy to obtain superior transmittance and electrical properties in KNN and may shed light on other ferroelectric systems.

Highly transparent lead-free (1 − x)K0.5Na0.5NbO3–xCa(Zn1/3Nb2/3)O3 (abbreviated as KNN–xCZN) piezoceramics were synthesized by a solid state reaction method.