Fabrication And Field Induced Strain Property Of KNBT Piezoelectric Ceramic Fibers

With the development of piezoelectric fiber composites research, itsperformance and application respect becomes more and more important, which hasthe excellent ferroelectric and piezoelectric properties of piezoelectric ceramic andthe excellent flexibility of polymer. Piezoelectric fiber is as the functional phase ofpiezoelectric composite, which plays a key role on the properties of compositematerials. Piezoelectric fiber composites often work in electric field, temperatureand stress environment in the process of preparing and application, it is important toget the properties of piezoelectric fibers under the effect of external field. On theother hand, looking for the excellent performance of lead free piezoelectric fiber hasbeen the focus research, because the government proposes the environmentalcoordination. Therefore, we put the promising KNBT lead-free piezoelectricmaterial as the research object in this thesis to investigate its piezoelectric propertiesof the response of electric field, temperature and stress. Therefore, specific work andconclusions of the thesis have the following components:1. The lead free0.2K0.5Bi0.5TiO3-0.8Na0.5Bi0.5TiO3(KNBT) piezoelectric fiberswere fabricated by viscous plastic processing and extrusion molding method. Theinfluences of sintering temperature to the structures and properties KNBT fiberswere studied. The results show that, with enough sodium and potassium provisionwhen sintering temperature is1100C, we can get KNBT piezoelectric fibers, whichhas pure perovskite structure, densification, uniform grain size, excellentperformance.2. Getting the performance of piezoelectric fibers is the key to study the effectof external field. According to the small size characteristics of fibers, we proposedand designed a test fixture to test ferroelectric and piezoelectric properties of asingle piezoelectric fiber. The results show that, the performance of singlepiezoelectric fiber has good repeatability and stability.3. The external field responses of KNBT fibers under electric field, pre-stress,temperature have been studied. The results show that, the fiber samples becomesaturated under8kV/mm. The coercive field of KNBT fibers is4.3kV/mm. When the driving frequency is10Hz, the polarization process of KNBT fibers can matchwith the speed of applied electric field. The stress has large influence on electricfield induced strain. And with the increase of stress, the maximum strain increase,when the stress is1MPa, the maximum is0.15%. Temperature has large influenceon ferroelectric and electric field induced strain. With the increase of temperature,the negative strain and remnant polarization decrease. This can be associated withthe anti-ferroelectric phase, and can be demonstrated by Raman spectroscopy,hysteresis loops and field induced strain loops under different temperature.