Electric Field Assisted Sintering Of Potassium Sodium Niobate-based Lead-free Piezoelectric Ceramics

Potassium sodium niobate(KNN)based lead-free piezoelectric ceramics have attracted much attention because of their high Curie temperature and good piezoelectric properties,and are considered as one of the most promising alternatives to lead-based piezoelectric ceramics.However,due to the narrow sintering interval and high temperature segregation of KNN-based lead-free piezoelectric ceramics,it is difficult to mass-produce ceramic with high density by traditional sintering technology.Electric field sintering technology can promote the sintering of ceramic,improve the performance of ceramics,and derived from the electric field sintering technology flash technology is a recent research focus,and has been confirmed to promote the sintering of various types of functional ceramics.In this paper,the effect of flashover technology and non-contact electric field aided technique on the sintering behavior of KNN-based lead-free piezoelectric ceramics was investigated.The effect of different parameters on sintering behavior of KNN ceramics was studied and discussed systematically by changing the parameters of sintering KNN ceramic by flashover and non-contact electric field aided technique.In this paper,KNN powders were synthesized by solid phase synthesis method.The experimental setup was designed for these two sintering techniques.The effect of current density on the firing of KNN ceramics was studied.The safety current density of KNN flash was 5mA/mm2.The increase of current density accelerated the sintering of the samples.It is found that the electric field strength has a decisive influence on the temperature of the flash,and only the electric field intensity is higher than 70V/cm,and the KNN can generate flash.The higher the electric field intensity,the lower the temperature at which the flashing occurs,the faster the flashing rate is,the flashback temperature of 70V/cm is 1090℃,and the flashback temperature at 450V/cm is 865 ℃.Through the sample temperature calculation,it was found that the electric field reduced the actual sintering temperature of KNN ceramics,from 1120 ℃ at 75V/cm to 1025 ℃ at 450V/cm,which indicated that there was not only Joule thermal effect but also electric field to promote the transport of matter TheIn the KNN ceramic non-contact electric field assisted sintering experiment,through the measurement of the shrinkage and density of the sample and its micro-morphology observation,the study found that non-contact electric field can promote sintering,increase grain size.In particular,when the sintering temperature of pure KNN ceramics reaches 1100 ℃,the effect of electric field becomes very significant.It is effective in accelerating the sintering process by promoting liquid phase formation,which also causes some grains to grow abnormally.In the experiment of KNN-0.2%CuO,it can also be found that the sintering effect of KNN ceramics is very significant at the time of liquid phase sintering.