Prepapration And Doping Effects Of Potassium Sodium Niobate Based Piezoelectric Ceramics

Piezoelectric ceramic is a most important functional material, which is applied to the common lives and industry field widely. At present, the piezoelectric ceramics in use are still traditional lead based piezoelectric ceramics containing more than 60 wt.% lead. The toxicity of lead oxide and its high vapor pressure during processing, preparing, using, and discarding pollute the environment. As the concept of environment protection arising, the legislation, law and government instruction on waste electrical electronic equipment have been issued; the use of hazardous substance such as lead in electric parts is prohibited in the international community. The search for alternative piezoelectric material now is focused on the alkaline niobate compounds. In this paper, Sr, Ti, Ta, Cu elements are doped into the potassium sodium niobate ceramic, (1-x)(K_0.5Na_0.5)NbO₃-xSrTiO₃(KNN-STO) and (K_0.5Na_0.5)(Nb_0.95Ta_0.05)O₃-xCu(NO₃)₂ (KNNT-Cu) were prepared by conventional solid reaction sintering method, the effects on properties of the potassium sodium niobate based ceramic were investigated.KNN-STO ceramics were synthesized by traditional sintering process and effects of the SrTiO₃ amounts on crystal structure and dielectric properties of KNN were investigated. The sintering ability of the ceramic was improved by SrTiO₃; the density of the ceramic is above 97% of the theoretical density; The phase structure of KNN based ceramic changed from the orthorhombic to the pseudo-cubic, and dielectric properties of KNN based ceramics were enhanced greatly by SrTiO₃, dielectric loss decreased, frequency stabilization increased, even KNN-STO shown the characterization of relaxor ferroelectricity.In order to improving the mechanical quality factor (Q_m) and keeping electromechanical coupling factor (k_p), less than 1mol.% Cu element were doped in the KNNT. Results shown that with the proper amount of the Cu, the dielectric constant (ε ), the planar mode electromechanical coupling factor (k_p), the piezoelectric coefficient (d₃₃), and the mechanical quality factor (Q_m) of KNNT ceramics with copper additive were 320-450, 0.21-0.41, 70-110 pC/N, 105-979, respectively. According to the dielectric-temperature relationship, we got the cure temperature (T_c) was nearly 400℃, dielectric constant was less than 500, and dielectric loss was less than 1%. Meanwhile, we got both the frequency stabilization and environment stabilization were enhanced by contrasting the dielectric behavior of KNN, KNNT, and KNNT-Cu. Thus, KNNT-Cu based ceramics is a kind of the alternative piezoelectric ceramics for mid-frequency filter and high temperature application.