Effect of Mn2O3 addition on the microstructure and electrical properties of lead-free (Na0.5K0.5)NbO3-Ba(Sn0.02Ti0.98)O3 ceramics

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In this paper, the 0.98(Na0.5K0.5)NbO3–0.02Ba(Sn0.02Ti0.98)O3 ceramics with the addition of 0–4.0 wt % Mn2O3 have been prepared following the conventional mixed oxide process. The disc samples were sintered in alumina crucible at 1100°C for 3 h in air. For 0.98(Na0.5K0.5)NbO3–0.02Ba(Sn0.02Ti0.98)O3 ceramics, the electromechanical coupling coefficients of the planar mode kp and the thickness mode kt reach 0.31 and 0.39, respectively. In the low Mn2O3 content region (≤1 wt %), the decrease of dielectric constant, dielectric loss tangent and planar coupling factor together with the enhancement of mechanical quality factor correspond well to the feature of a hard doping effect on the electrical properties. For 0.98(Na0.5K0.5)NbO3–0.02Ba(Sn0.02Ti0.98)O3 ceramics by doping 1.0 wt % Mn2O3, the electromechanical coupling coefficients of the planar mode kp and the thickness mode kt reach 0.29 and 0.47, respectively, at the sintering of 1100°C for 3 h. The significant rise of dielectric loss tangent and degradation of mechanical quality factor in the high Mn2O3 content region (≥2 wt %) may be attributed to the appearance of distinct pores in the microstructure. With suitable Mn2O3 doping, a dense microstructure and good electrical properties were obtained.
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