| Piezoelectric ceramics is a kind of highly technical content of functional materials, which in international competition is extremely fierce, Its development is at the leading position in the entire electronic technology domain. In order to protect the environment and ensure the sustainable development of human society, developing high-property and temperature stability of lead-free piezoelectric ceramic materials has become the major trends of the materials research.KNbO3-NaNbO3 (for short KNN)-based lead-free piezoelectric ceramics with high piezoelectric properties, strong ferroelectric properties, high Curie temperature, etc. have attracted much attention, and become the research focus of nowadays materials area. The KNN base piezoelectric ceramics was considered that is the most hopeful substitution lead base piezoelectric ceramics which is a new lead-free piezoelectric ceramics system, however, due to the piezoelectric properties of KNN ceramics have a strong sensitivity to preparation conditions, It is difficult to obtain the KNN ceramics of dense structure and stable properties with traditional ceramic process.This paper choice the system of (K0.46Na0.50Li0.04)(Nb0.85Ta0.15)O3(abbreviated KNLNT) ceramics as the basic object of study, research a series of milling, calcining, sintering, polarization and other conditions. Then add the new group of CaTiO3 to KNLNT ceramics, to expect to improving the temperature stability and maintain the high electrical properties of ceramics. Main contents as following:(1) Study its phase structure, microstructure, piezoelectric properties, dielectric properties and ferroelectric properties of KNLNT ceramic on the effect of milling time. The results show that:In the milling time range for the 5-25 h, the calcined powders have reached the submicron-level, samples of calcined powders and ceramics are pure perovskite phase structure. With the increase of milling time, the degree of uniformization of ceramic crystals grains enhance. When the milling time was 20 h, the ceramic crystals developed well and the size distribution, apparent density of the samples reached the maximum.Ceramic samples obtained hysteresis loops are more saturated; The best milling time is 20 h, at this time, integrated electrical properties of the material is the best, their values are:d33=248 pC/N, Kp=0.50, Qm=70,εr=1130, tanδ=0.019,Ec=14.31 kV/cm,Pr=28.38μC/cm2.(2) Study of the calcining temperature, soaking time, sintering temperature and polarization process (voltage, time, and temperature) and other conditions on the phase structure, microstructure, piezoelectric properties, dielectric properties and ferroelectric properties of KNLNT ceramics. The results show that:When the scope of calcining temperature is 750-950℃, KNLNT ceramics are pure tetragonal perovskite phase structure. With calcining temperature increasing,d33, Kp,εr and Pr of ceramics increase and then reduce, Qm and tanδreduce and then increase, and Ec have little change. The best calcining temperature of ceramics is 850℃, at this time, ceramic crystals are in a full state, and the apparent density of ceramics reached the maximum, piezoelectric properties, dielectric properties and ferroelectric properties of KNLNT ceramics reached best. Under the different calcining time, ceramics are pure tetragonal perovskite phase structure. With the increase of milling time, d33, Kp, andεr of ceramics increase and then reduce, Qm and tanδreduce and then increase. The best calcining time of ceramics is 9 h, at this time, ceramic crystals are in a more full state and its growth is uniform, the apparent density of ceramics reached the maximum, and the electrical properties reached best. When the calcining time is 9h, and range of the test temperature is 25-50℃, Pr and Ec gradually increasing.Under the different sintering temperature, ceramics are pure tetragonal perovskite phase structure. With sintering temperature increasing, d33, Kp, andεr of ceramics increase and then reduce, Qm and tanδreduce and then increase. When the sintering temperature is 1135℃, ceramic crystals are in a full state and its growth is uniform, the apparent density of ceramics reached the maximum, piezoelectric properties, dielectric properties and ferroelectric properties of the ceramics reached best. Polarization voltage, polarization time and polarization temperature on the piezoelectric properties of KNLNT ceramic sample has a great influence, the best conditions is:polarization voltage is 3.5kV, polarization time is 15min and polarization temperature is 80℃.Under these conditions, the properties of ceramics were:p=4.35 g/cm3,d33=262 pC/N, Kp=0.54,Qm=74,εr=1130, tanδ=0.019, Pr=28.38μC/cm2,Ec=14.31 kV/cm.(3) In the best preparation conditions, study its phase structure, microstructure, piezoelectric properties, dielectric properties, ferroelectric properties and temperature stability of KNLNT ceramic add the components of CaTiO3. The results show that:Different compositions of ceramic samples are pure perovskite structure. With the increase of the content of CaTiO3, the apparent density of ceramics is decreasing, uniformity of ceramics crystal is reducing, d33, Kp, and Qm of ceramics are reduce, e, reduce and tanδis increasing. With the accession of CaTiO3, the orthogonal sample-tetragonal phase transition temperature from room temperature, and improve the temperature stability of samples. Considering electrical properties in room temperature and temperature stability of 0.992KNLNT-0.008CT ceramic sample, its properties is best. Its electrical properties are:d33=232 pC/N,Kp=0.43,Qm=62,εr=1062, tanδ=0.024.Through this research, we obtain a better ceramic components:0.992(K0.46Na0.50Li0.04)- (Nb0.85Ta0.15)O3-0.008CaTiO3. Temperature stability and electrical properties of the ceramics is better, and the ceramics has great potential practical value. |
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