采用固相反应法制备了K_0.5Na_0.5NbO_3+xCo_2O_3(0≤x≤1%)无铅压电陶瓷,使用XRD、SEM、 Agilent 4294A精密阻抗分析仪等对该体系的相组成、显微结构、压电及介电等性能进行表征.结果表明:Co_2O_3的掺入并没有改变K_0.5Na_0.5NbO_3的晶体结构,该陶瓷材料仍然为正交相钙钛矿结构;Co_2O_3的掺入使材料的晶粒尺寸明显增大,但当x=1%时,晶粒尺寸减小,说明过多的Co_2O_3有抑制晶粒长大的作用;Co_2O_3的掺入使200 ℃附近的正交→四方铁电相变温度TO-T向低温方向移动,居里温度TC向高温方向移动,同时材料的压电常数d_(33)、机电耦合系数k_p均随之先增大后减小,机械品质因数Qm整体增大,1 kHz频率下的介电常数ε_r和介电损耗tanδ降低,密度显著增大.当x=0.5%时,陶瓷性能最佳:d_(33)=103 pC/N,k_p=0.362, tanδ=1.8%,ε_r=234,Qm=182,ρ=4.29 g/cm~3.
The K_0.5Na_0.5NbO_3 +xwt%Co_2O_3(0≤x≤1)lead-free piezoelectric ceramics were fabricated by solid state reaction. The phase, microstructure, electric properties of the samples were characterized by XRD, SEM and Agilent 4294A impedance analyzer. With the increasing of Co_2O_3 content, all samples have an orthorhombic perovskite structure and the grain size of those materials increases obviously with the increase of Co_2O_3 content. However, when x=1, the grain size decreases, which indicates that more Co_2O_3 content can inhibit the grain growth. And the transitional temperature around 200 ℃ (TO-T, from orthorhombic to tetragonal phase) will shift to lower temperature, while the Curie temperature (T_C) will shift to higher temperature. Furthermore, the piezoelectric constant (d_(33)), electromechanical planar coupling coefficients (k_p) increased firstly and decreased subsequently with the increase of content of Co_2O_3. The mechanical quality factor (Q_m) increases evidently. The dielectric constant (ε_r) and dielectric loss (tgδ) decreases, and the density increases. When x equals to 0.5, it exhibits optimal piezoelectric properties: d_(33)=103pC/N, k_p=0.362, tanδ=1.8%, ε_r=234, Q_m=182 and ρ=4.29 g/cm~3.
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