Low Temperature Sintering And Acceptor Doping Of Potassium Sodium Niobate Based Lead-free Piezoelectric Ceramics

(K,Na)NbO3(KNN)based lead-free piezoelectric ceramics have recived wide attention because of their high Curie temperature and excellent piezoelectric properties,they also have been considered as one of the most promosing candidates to replace the lead based piezoelectric ceramic materials.This paper focuses on the acceptor doping and the low temperature sintering of KNN ceramics,and try to solve the problems of alkali volatilization,segregation and the narrow sintering temperature range in KNN ceramics by using single oxide.Firstly,it is found that oxides likes as GeO2 can promote sintering of KNN.Further studies showed that(K0.5SNa0.5)NbO3 acceptor doped 0.5mol%Ge4+ could achieve single-phase powders in uniform size and regular morphology when synthesis temperature was 800°C,this temperature was 100? lower than pure KNN powders.Acceptor doping Ge4+ and Ga3+ in KNN ceramics decreased the optimum sintering temperature significantly,the samples maximum piezoelectric constant were 1 1OpC/N and 123pC/N,much higher than the maximum piezoelectric constant of pure(K0.5Na0.5)NbO.3.We also studied the effect of KNN ceramics sintering properties and piezoelectric properties by adding CuO and acceptor doping Cu2+,and found that the addition of copper could not only reduce sintering temperature significantly,but also obviously improve the mechanical quality factor Qm,of KNN ceramics,while the Qm,improvement of Ge4+ and Ga3+ doped KNN ceramics were not obvious.The reason of this phenomenon was that the effective charges of Cu2+,Ga3+,Ge4+ replaced Nb5+were different,so there existed the large difference attractive force between oxygen vacancy,the f-orce between defects of Cu2+ replaced Nb5+ and oxygen vacancy were largest,some associated defects were formed to limit the movement of domain wall,which results in improving mechanical quality factor.The sintering properties and piezoelectric properties of Ge4+,Ga3+,Cu2+ doped(K0.4725Na0.4725Li0.035)(Nbo.8Ta0.2)O3(KNLNT)were also studied in this paper.With the results revealed,the d33 of pure K0.4725Na0.4725Li0.035Nb0.8Ta0.2O3(KNLNT)was around 240pC/N,unfortunately,the sintering temperature range of KNLNT ceramic was very narrow,mostly concentrated in 1080?,this makes the properties very sensitive with the changing of sintering temperature.The 0.2mol%Ge4+,Ga3?,Cu2+doped KNLNT ceramics displayed a wider sintering temperature range,respectively,the sintering temperature could been widen to 1000?,1040? and 1000? at least,the optimal values of d33 were 220pC/N,240pC/N and 200pC/N.