Study On The Preparation And Doping Of NKN System Lead-free Piezoelectric Ceramics With Sol-gel Method

Piezoelectric ceramics is a very important functional material which can be used toachieve the mutual conversion of mechanical energy and electrical energy. This material iswidely used in the electronic products, ultrasonic transducer, sensor, non-destructive testingtechnology (NDT), and other technical areas. In recent years, driven by the worldwideenvironmental concern, lead-free piezoelectric ceramics materials became an inevitable trend.Many of the countries increase their government budget on the lead-free ceramic researches inthese years. Among all of the lead-free systems, potassium sodium niobate (NKN)piezoelectric ceramics is thought to be one of the most possible substitute, the researchesabout this system become a front-burner and key issue in the field of piezoelectrics. Tooccupy the high position in the technologies of this domain, this will be a potential sally portof our “corner beyond” strategy.In this research we adopted a sol-gel method，with new-prepared Nb(OH)5as niobateresource, oxalic acid or citric acid as chelating agent, glycol as esterifying agent, rochelle salttaking the place of sodium carbonate and potassium carbonate as sodium and potassiumresource in order to increase the complexing action of the sol-gel system. We successfullyprepared well-performed (Na0.5K0.5)NbO3lead-free piezoelectric ceramics. Further more wedid some exploratory researches about the (Na0.52-xK0.48Ndx)Nb1-xTixO3(NKN-NT) system.In the first chapter, firstly we introduced the history, research background, theperformance parameter and definition of the piezoelectric ceramics, the mechanism ofpiezoelectric effect, the recent research status and development tendency, and the researchbreakthrough of the theoretical study. Further more we particularly pay attention to the dopingtheory of this system. At last we give an introduction of the development tendency of thissystem, include the doping method, texture-growth process and the oriented growth.In the second chapter, the main points is about the needed chemicals and reagents, themeasurement tools, the process flow of the preparation of the NKN ceramics, the influencingfactor and matters needed attention. A modified sol-gel method was used to prepared wellcharacter (K0.5Na0.5)NbO3(NKN) powders. We used the single variable adjustment andcombined with IR (infrared spectrum), X-ray diffraction (XRD), Synchronous hot heavydifferential thermal analyzer (TG-DSC), scanning electron microscope (SEM) and othermeasurement tools, finally confirmed all the influence of various factors on the systemfunction, and do the preliminary work for the next chapter. The main study can be separated in the following sections:(1) the reaction mechanism in the rochelle salt sol-gel system.(2)The technological parameter such as sintering temperature, heating rate, different Na/K rawmaterial such as Rochelle salt and sodium carbonate/potassium carbonate, affect on the phase,crystal structure and microstructure of the powders.(3) The different of the microstructure ofceramics prepared with powders synthesized using different heating rates.(4) Ascertaining theoptimum sintering schedule by measured the property of the ceramics.In the third chapter, we used the sol-gel method to prepare the NKN-NT lead-freepiezoelectric ceramics system. And we also studied the influence of the heating rate, sinteringtemperature, and the doping rate of the Nd/Ti on the ceramic system. The single variableadjustment method was used to explore the optimum sintering schedule and doping rate. Inthe work we find that the piezoelectric constant, the dielectrical property, the density andother properties increased at first then reduced at last with the doping rate increased, andreach a peak at the4%doping rate. But we find no morphotropic phase boundary (MPB)along all the doping rate range. It can draw a conclusion that the doping of the Nd/Ti is a“rigid doping” mechanism.