Preparation And Doping Modification Of KNN-based High Temperature Lead-free Piezoelectric Ceramics

KNN based ceramics have been playing an important role among lead-free piezoelectric ceramics field nowadays.Wiih both good electrical properties and high depolarization temperature in the lead-free piezoelectric ceramics,KNN piezoelectric ceramics have been paid much attention.People always tend to focus on piezoelectric performance boost,but depolarization temperature of KNN based ceramics has a downward trend with piezoelectric performance boost.The purpose of this paper is to prepare a variety of ceramic material with higher depolarization temperature and good piezoelectric properties,satisfying the application of high temperature ceramics.At the same time,it is expected to replace lead-based piezoelectric material in some other piezoelectric areas.Firstly,the process of K substituted partly by Li has been achieved to improve the depolarization temperature of KNN based ceramics.(Na0.5K0.5-xLix)NbO3(x = 0.055～0.07)series of KNN based high temperature ceramic materials were prepared.The optimal content of Li was determined to be =0.065,where the main performance parameters for ceramics at room temperature are:d33 = 205 pC/N,kp＝46.1%,Td～480℃.The effects on preparation process and piezoelectric properties of Na/K ratio and substituting Li for A-site ions have been investigated.(Na0.55K0.45)0.94Li0.06NbO3 ceramic materials were prepared on different process of calcined and sintered.Experiment show that calcined and sintered have effects on piezoelectric properties.The samples prepared at optimal calcined and sintered temperature have a high piezoelectric,d33＝255pC/N,kp =44.9%.Then the effects on preparation process and piezoelectric properties of different metal oxides doped ceramics have been investigated.Through the preparation methods and process optimization,the ceramic material formula with high piezoelectric constant and high depolarization temperature are obtained.By doping Al2O3,KNN-based lead-free piezoelectric ceramic material with depolarization resistant at high temperature is obtained,which make it practical in high temperature ceramic sensors and more promising to replace PZT based ceramics.