The Preparation And Performance Characterization Of (Sb, Ta, Li) Modified Alkali Metal-Containing Niobate-Based Piezoceramics

The Sb, Ta and Li modified sodium-potassium niobate system has been a research focus in the lead-free piezoelectric ceramics field nowadays. Because the electronegativity of Sb is higher than that of Nb, it can strengthen the covalency of the system, improve the piezoelectric performances, and thus the amount of Sb is fixed at a high value in this thesis (6mol %). Considering that volatilization of Na is more serious than that of K in the sintering process, the amount of Na is used slightly more than that of K. On the basis of this composition, (Na_0.52K_0.48)(Nb_0.96Sb_0.04)O₃, Li and Ta in equal molar ratio are added to form an morphotropic phase boundary (MPB) in the hope of improved performances. Then, the sintering process is optimized, and the influence of CuO-doping on the performances is investigated.Complete and homogeneous solid solutions can form between Li⁺, Ta⁺, Sb⁺ ions and sodium-potassium niobate within the studied scope. The addition of lithium tantalate (TL) improves the sintering performances, while the particle size distribution is not uniform. With increasing the amount of TL, the phase structure at room temperature is changed from an orthorhombic phase to a tetragonal phase such that an MPB is formed within 0.035o-t) moves to room temperature such that the performances are improved. Excellent performances are present in the composition with x=0.04, d₃₃=335 pC/N, k_P=53%,ε₃₃^T =2063, Q_m=41, T_c=291℃, showing the potential for practical application. The result shows that the performances can be improved in the way that the more amount of Sb is added and the component is designed near the MPB.It is found that the influence of the sintering process on the performances is great. The lower sintering temperature, the shorter soaking time and Na excesses in the initial composition tend to cause abnormal grain growth. With increasing sintering temperature and soaking time, the grain grows better, and the density increases and reaches its maximum at 1100 oC. With further increasing the sintering temperature and soaking time, alkali metal ions volatilize seriously, the density decreases, and To-t moves to lower temperature. Moreover, the concentration of oxygen vacancy increases, Tc decreases slightly, the coercive field (E_c) enlarges, and then the electrical properties are influenced. It is shown that comprehensive properties are excellent for those samples sintered at 1100 oC for 3 hours.The (0-1.5) mol% CuO is doped and incorporated into the matrix. The CuO-doping decreases the sintering temperature of the system. The samples doped with 1mol% CuO can be sintered at 1020 oC for 3 hours and their densities are comparable with that of undoped samples sintered at 1100 oC for 3 hours. In addition, the CuO-doping decreases the value of c/a slightly, weakens the tetragonality of this system, and further influences the ferroelectricity. While the doping content of CuO is within (0-0.5) mol%, Cu²⁺ ions are incorporated into A-site of the perovskite structure, the value of E_c and c/a decreases, the tetragonality is weakened, the remnant polarization (P_r) decreases. However, as the content of CuO is within (0.5-1.5) mol%, Cu²⁺ ions are incorporated into B site of the perovskite, the value of Ec increases, while the value of Pr increases due to the well-developed grains. With doping a small quantity of CuO (0.125mol %), both d33 and kp increase and the mechanical quality factory (Q_m) decreases, as the content of CuO is more than 0.5mol%, both d₃₃ and k_p decreases, and the Q_m value increases.