The Structure And Properties Of Lead-free Piezoelectric Ceramics Of The Excess Sodium Niobate Potassium And Sodium

Piezoelectric ceramic is a kind of important functional material, which is widely used in people's daily life. At present, most of them contain about 60 wt% Lead. Lead is volatile and toxic during the fabrication and dispose, so it can cause a crucial environmental pollution to our life and production. With the increasing of environmental protection, the research of Lead-free ceramics drew people's attention. Potassium sodium niobate [(Na, K) NbO3, NKN] lead-free ceramics have great potential application and widely used in high frequency ultrasonic transducer. [(Na, K) NbO3, NKN] is a combination of ferroelectric KNbO3 and antiferroelectric NaNbO3 the crystal lattice of which is still perovskite structure when the ratio (Na: K) vary in any range.In this paper, Bi, Fe and Ta are doped into the potassium sodium niobate ceramic, NKN (Na/K 0.535:0.48 and 0.525:0.49) were prepared by conventional ceramic process. The X-ray diffraction (XRD) was carried out to determine the structure of the sample. The doped Bi and Fe had a significant effect to the grains by means of scanning electron microscope. In this system, the improvement of microstructure is helpful to reduce the dielectric loss. And potassium sodium niobate (Na/K 0.535:0.48) doped a small Ta were also discussed deeply.Results show that small amount of Bi2O3·Fe2O3 is helpful for the sintering of ceramics. The sintering samples are basically perovskite structure, and the grains present massive. The dielectric loss decreases with the increasing of Bi₂O₃·Fe₂O₃, and it increases when the content is more 2%. The conductivity of ceramics increases with the doping content. UV-Visual absorption spectrum is affected by doping Bi³⁺ and Fe³⁺. The mechanism of conductivity is discussed with respect to energy of band-gap in the system.In this paper, the factors that influence the dielectric and conductivity properties of ferroelectrics are discussed, which are references of manufacturing the ferroelectric ceramics that have low dielectric loss, low dielectric constant and low conductance ratio in future. And the optical properties were researched by infrared absorption spectroscope and UV-Vis spectrum together in this work. Their relationship between spectral and conductivity has been discussed.