Na 0:5 K 0:5 )NbO 3 with Ba(Sn x Ti 1Àx )O 3 with x < 0:1 has been prepared by the conventional mixed oxide process. X-ray diffraction analysis revealed that, during sintering, all the Ba(Sn x Ti 1Àx )O 3 diffuses into the lattice of (Na 0:5 K 0:5 )NbO 3 to form a solid solution and the orthorhombic phase with a perovskite structure. The highest planar coupling factor of 0.98(Na 0:5 K 0:5 )NbO 3 -0.02Ba(Sn 0:02 Ti 0:98 )O 3 ceramics is 0.31 after sintering at 1100 C for 3 h. The samples with a low content of Ba(Sn 0:06 Ti 0:94 )O 3 exhibit relatively good physical and electrical properties. For 0.98(Na 0:5 K 0:5 )NbO 3 -0.02Ba(Sn 0:06 Ti 0:94 )O 3 ceramics, the electromechanical coupling coefficients of the planar mode k p and the thickness mode k t reach 0.18 and 0.46, respectively, after sintering at 1100 C for 3 h. The ratio of the thickness coupling coefficient to the planar coupling coefficient is 2.56. With suitable Ba(Sn x Ti 1Àx )O 3 concentration and sintering conditions, a dense microstructure and good electrical properties are obtained. Our results show that (Na 0:5 K 0:5 )NbO 3 -Ba(Sn 0:06 Ti 0:94 )O 3 solid solution ceramics are promising lead-free ceramics for high-frequency electromechanical transducer applications.

In this paper, the 0.98(Na 0.5 K 0.5 )NbO 3 0.02Ba(Sn 0.02 Ti 0.98 )O 3 ceramics with the addition of 04.0 wt % Mn 2 O 3 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(Na 0.5 K 0.5 )NbO 3 0.02Ba(Sn 0.02 Ti 0.98 )O 3 ceramics, the electromechanical coupling coefficients of the planar mode k p and the thickness mode k t reach 0.31 and 0.39, respectively. In the low Mn 2 O 3 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(Na 0.5 K 0.5 )NbO 3 0.02Ba(Sn 0.02 Ti 0.98 )O 3 ceramics by doping 1.0 wt % Mn 2 O 3 , the electromechanical coupling coefficients of the planar mode k p and the thickness mode k t 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 Mn 2 O 3 content region (²2 wt %) may be attributed to the appearance of distinct pores in the microstructure. With suitable Mn 2 O 3 doping, a dense microstructure and good electrical properties were obtained.