Study Of Sintering Characteristics And Ferroelectric Properties Of KNN Doped BCZT-based Lead-free Ceramics

Piezoelectric ceramics are widely used in sensors,transducers,transformers and medical imaging due to their excellent ferroelectricity and piezoelectricity.However,traditional Pb?Zr,Ti?O₃?PZT?ceramics contain a large amount of lead,this ceramics polluting the environment and harmful to human health.Therefore,research on lead-free and leadless piezoelectric ceramics has become very important.In this paper,Ba Ti O₃?BT?material is used as the matrix,and the first-principles calculation and doping modification are studied.Firstly,the first principle of Ba Ti O₃cells doped with A and B sites is calculated.The results show that the incorporation of Ca atoms increases the Ba-O bond length,shortens the Ti-O bond length,and the introduction of Zr atoms has the opposite effect.The co-doping of Ca and Zr atoms increases the Ba-O bond length and the shortening of the Ti-O bond length.Using density functional theory,the bandgap width of pure square phase barium titanate is smaller than the experimental value,which is about 1.781e V.As the doping of Ca and Zr atoms increases the bandgap width and the total density of states increases,the conductivity decreases.From the point of view of the imaginary part and the loss function of the dielectric function,the addition of Ca and Zr atoms reduces the loss of the mediumSecondly,the effect of sintering time on crystal structure and electrical properties of BCZT ceramics was studied with(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃?BCZT?as matrix.The experimental results showed that with the extension of sintering time,the grain size increased from 2?m to 22?m,and the average width of electric domains within it varied from 200nm to 400nm.The XRD test results show that the characteristic peaks of the samples become sharp with the increase of sintering time,indicating that the crystallinity is getting better and better.The piezoelectric test results show that d₃₃,k_pand Q_mof ceramic samples show a trend of rising and then falling with the increase of sintering time,indicating that too long insulation time will reduce the piezoelectric performance of the material at room temperature.The optimal sintering time was 4h,the average grain size of the sample was 9?m,and the optimal piezoelectric parameters were d₃₃=240p C/N?k_p=17.06%and Q_m=245respectively.At last,(K_0.5Na_0.5)Nb O₃?KNN?doped(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃?BCZT?ceramics??1-x?BCZT-x KNN?and(K_0.44Na_0.52Li_0.04)(Nb_0.8Ta_0.2)O₃?KNLNT?doped(Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃?BCZT?ceramics??1-x?BCZT-x KNLNT?were prepared by traditional solid phase method.The effects of KNN and KNLNT doping on the phase structure,grain growth and electrical properties of BCZT were studied.It was found that both?1-x?BCZT-x KNN and?1-x?BCZT-x KNLNT formed solid solutions with pure perovskite structure,and Ba²⁺in A position was partly replaced by Na⁺,K⁺and Li⁺.Ti⁴⁺in B position was partly replaced by Nb⁵⁺.Ion substitution distorts lattice structure and forms oxygen vacancy,segregation occurs at grain boundary,reduces sintering temperature and affects piezoelectric and dielectric properties.When the content of KNN and KNLNT is 2%,the relaxation is obvious and the dielectric constant is maximal.In addition,it was found that the doping of Li element can further reduce the sintering temperature,and the single or co-doping of Li and Ta elements can reduce the O-T transition temperature to the vicinity of room temperature,so as to obtain the O-T coexistence structure at room temperature.In this paper,the first-principles calculation and doping modification of BT-based materials is carried out,which provides guidance for the research of high-performance lead-free piezoelectric ceramics.