Transparency of K0.5N0.5NbO3-Sr(Mg1/3Nb2/3)O3 lead-free ceramics modulated by relaxor behavior and grain size

High transparency was obtained in (1-x)(K0.5Na0.5)NbO3-xSr(Mg1/3Nb2/3)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(Mg1/3Nb2/3)O-3 content on the microstructure, phase transition, optical properties and electrical properties were studied in detail. The Xray diffraction results showed that the crystal structure of ceramics gradually transformed from orthorhombic phase into pseudo-cubic phase with doping of Sr(Mg1/3Nb2/3)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(Mg1/3Nb2/3)O-3 doping, causing the ceramics become more relaxor-like and transparent. The transmittance and electric properties results indicated that the 0.95(K0.5Na0.5)NbO3-0.05 Sr(Mg1/3Nb2/3)O-3 ceramics exhibited higher transmittance (60% in the near-IR region) accompanied with better electrical properties (epsilon(m)=2104, P-r=5.0 mu C/cm(2), d(33)=92 pC/N).