Of Bnt-based Lead-free Piezoelectric Ceramics Performance Parameters And Process Study

From the importance, classification, development prospect, development trend of the material, the paper focuses on the piezoelectric effect and the necessary condition of forming piezoelectric effect and Briefly bewrites the ferroelectric, ferroelectric domain of lead-free piezoelectric ceramics. The ferroelectric of ceramics with variation of the external electric field and the forming mechanism of domains are in depth probed into. The discourse mainly explains the five familiar forms of polarization. Such as Spontaneous polarization, resonant polarization, space-charge polarization, relaxation-type polarization, polarizability of displacement polarization.And comparing with the similarities and differences between the five forms of polarization, while exploring the formation of these polarization conditions. The thesis carefully analyzes and studies the piezoelectric constant, electromechanical coupling coefficient, frequency constant, dielectric loss, mechanical quality factor and other important performance parameters and the main factors of affecting these parameters. As is well-known, despite lead zirconate titanate (PZT) piezoelectric ceramics and their composites with the more extensive application can satisfy human needs, lead-based piezoelectric ceramics have the following deficiencies:firstly, lead oxide evaporates at about 800℃; secondly, lead-based piezoelectric ceramics are harmful to the human body in the preparation, use and waste disposal process. This paper from research status and outstanding problems of lead-based piezoelectric ceramics set about in order to elicit practical significance of researching environmental friendly lead-free piezoelectric ceramics(environmental friendly fead-free fiezoelectric ceramics is required both to satisfy basic human needs and not pollut environment). Four categories of more active lead-free piezoelectric ceramics are gived an overview, such as barium titanate (BaTiO3), bismuth layer structure, alkali metal niobate structure and the tungsten bronze structure. Do a brief introduction on piezoelectric, dielectric, acoustic performance of four lead-free piezoelectric ceramics.Advantages and disadvantages of four lead-free piezoelectric ceramics are compared. Practical range of each kind of piezoelectric ceramics is made a brief analysis. And its application of in the future are forecasted.The second chapter illustrates Bi0.5Na0.5TiO3 lead-free piezoelectric ceramics is perovskite type ferroelectric of A site composite replication. Structure of BNT lead-free piezoelectric ceramic is carefully studied. Do a detailed reseach of improving Mechanism of Bi0.5Na0.5TiO3 lead-free piezoelectric ceramics, the principle and the methods of replacing, doped channels, tolerance factor of doped materials, the condition of forming morphotropic phase boundary, remnant polarization, morphotropic phase boundary, coercive field, thermal stability and so on. Meanwhile common methods of preparing BNT-based lead-free piezoelectric ceramics are discussed, such as solid-state reaction method, hydrothermal, sol-gel method, melting salt method. The advantages and disadvantages of them are compared. At the same time the basic urgent problem to solve and Lack of Bio.5Na0.5TiO3 lead-free piezoelectric ceramics are concisely expressed.The third chapter researches the way and announcements of preparing BNT-based lead-free piezoelectric ceramics. Philosophy of measurement of a variety of parameters are also introduced, such as philosophy of measurement and the step of density (direct weighing method, law of archimedes law, the proportion of cup), linear shrinkage rate, plane electromechanical coupling coefficient, the dielectric constant, dielectric loss, mechanical quality factor and piezoelectric constant and the other parameters are studied. The Curie temperature obtained by the method of ferroelectric domain observation and by observing sudden change with oscilloscope showing the electric hysteresis loop by SawyerTowe circuit. Its mechanism and measurement procedures are researched. Calcining temperature and sintering temperature of BNBT6 lead-free piezoelectric ceramic materials were explored. It has effect on density, shrinkage rate, piezoelectric, dielectric properties, quality factor, dielectric loss on BNBT6 lead-free piezoelectric ceramics. Considering kinds of factors we believe that calcined temperature is 900℃better on piezoelectric property of BNBT6 lead-free piezoelectric ceramics than at 850℃. Experiments confirmed that Piezoelectric ceramic obtained better piezoelectric, dielectric properties when calcining temperature is 900℃and the sintering temperature is 1160℃. The parameter is d33= 120pC/N, KP=0.202,εr= 625, Qm= 205, tan8= 2.1.Because of the relatively large radius, a formed vacancy easily,chemical stable performance, the high polarization rate and other advantages of rare earth elements,in this paper, Employing rare earth CeO2 with good performance doped BNBT6 lead-free piezoelectric ceramics in possession of better performace.We research that piezoelectric constant, electromechanical coupling coefficient, dielectric loss, quality factor, relative dielectric constant of BNBT6 lead-free piezoelectric ceramics changes with the CeO2 doped amount from 0.2% to 1%, when the calcining temperature is 890℃, the sintering temperature is 1190℃.