Knlnt Based Lead-free Piezoelectric Ceramic Milling Process And Doped

Piezoelectric ceramics is a kind of function materials which can realize the transform of mechanical energy and electrical energy into each other. These materials are extensively applied in many military affairs, business, medical treatment and other technical fields. Because of the protection of the environment and the health of the human, it is very important to develop lead-free piezoelectric ceramic materials with high properties and good temperature stability.(K,Na)NbO3 (KNN)-based lead-free piezoelectric ceramics have been extensively studied because of their high piezoelectric properties, strong ferroelectric properties, high Curie temperature, etc. However, the piezoelectric properties of KNN ceramics are very sensitive to the preparation conditions. Then it is difficult to obtain the KNN ceramics with dense structure and stable properties by traditional ceramic process. And the electrical properties of KNN-based lead-free piezoelectric ceramics are not stable due to the deliquescent problem.In this paper, in order to find a kind of promising lead-free material system, the effects of milling process parameter and doping on the properties of (K0.46Na0.50Li0.04)(Nb0.85Ta0.15)O3 (KNLNT) ceramics were studied. Through carefully controlling the process parameters, the (1-x)KNLNT-xBF ceramics with dense structure and optimized properties were obtained.(1) Firstly, the effect of milling process parameters (milling time and ball size) on the phase structure, microstructure, density, piezoelectric properties, dielectric properties and ferroelectric properties of KNLNT ceramic were studied. It was found that by using the milling ball ofφ5+φ10 size, the submicron-level could be obtained when the powders were milled for 16 h. The obtained KNLNT ceramics with pure perovskite phase, higher density and better homogenous microstructure showed the optimized properties as follows:d33= 231 pC/N, Kp= 0.47, tanδ= 0.019, Ec= 1.08 kV/cm,Pr= 25.54μC/cm2.(2) Then, for further improve the properties of KNLNT-based ceramics, a small amount of BiFeO3 was introduced to form (K0.46Na0.50Li0.04)(Nb0.85Ta0.15)O3 system. With increasing the BiFeO3 amount, the phase structure changed from tetragonal phase to pseudocubic phase, the grain size decreased, and the density increased firstly and decreased subsequently. The highest density could be obtained at x= 0.004, which was 4.65 g/cm3. d33, Kp, Pr, Ec and strain increased firstly and decreased subsequently with the increase of BiFeO3 content. In addition, with increasing the BiFeO3 content, Tc decreased and To-t moved to lower temperatures, which is benefit to improve temperature stability of the ceramics. When the powders were calcined at 850℃for 9 h and then sintered at 1130℃for 3.5 h, the obtained ceramics with x= 0.004 showed better electrical properties:d33= 261 pC/N, tanδ= 0.016, Kp= 0.58, Tc= 345℃,εr=1116, Pr= 24.23μC/cm2, Ec= 2.3 kV/mm and strain= 902μm. Temperature stability and time stability were both best at x= 0.004 with the values of 5.6% and 4.97%, respectively.(3) Finally, LiBiO2 was doped in the 0.996KNLNT-0.004BF ceramics to further improve the electrical properties. With increasing the LiBiO2 amount, the phase structure changed from tetragonal phase to pseudocubic phase, Tc andεr decreased gradually, while the density, d33, Kp and strain of the ceramics increased firstly and decreased subsequently. The highest density 4.62 g/cm3 could be obtained when LiBiO2 content is 0.2wt.%, and the powders were calcined at 850℃for 9 h and then sintered at 1150℃for 3.5 h. The obtained ceramics also showed better electrical properties:d33= 254 pC/N, Kp= 0.54, stain= 1476μm,εr=1040, Pr= 22.76μC/cm2, Ec= 1.48 kV/mm and strain= 1476μm.