Effect of K_2CO_3 Addition on the Structure and Electrical Properties of Lead-Free (Na_(0.5)K_(0.5))NbO_3-(Na_(0.5)Bi_(0.5))TiO_3 Ceramics

摘要

K_2CO_3-doped 0.98 (Na_(0.5)K_(0.5)) NbO_3-0.02 (Na_(0.5)Bi_(0.5)) TiO_3 [abbreviated as 0.98NKN-0.02NBT] lead-free piezoelectric ceramics were prepared by the conventional mixed oxide process. The effects of K_2CO_3 additions on the crystalline structures and electrical properties of the 0.98NKN-0.02NBT ceramics were investigated. The specimens of 0.98NKN-0.02NBT ceramics added with K_2CO_3 maintain an orthorhombic phase. In the case of low K_2CO_3 content (≤ 0.3 wt%), the grain growth became remarkable. The increase of grain size favors improving the piezoelectric properties, which is known as grain size effect. The grain size effect compensates the decrease of the electromechanical coupling factor due to the hard doping effect. For 0.98NKN-0.02NBT ceramics by doping 0.3 wt% K_2CO_3, the electromechanical coupling coefficients of the thickness mode k_t and the planar mode k_p reach 0.51 and 0.33, respectively, after sintering at 1100°C for 3 h. Our results show that 0.98NKN-0.02NBT with the addition of 0.3 wt% K_2CO_3 is a good lead-free piezoelectric ceramic.