Study On The Dielectric Properties Of BaTiO₃ Ceramics

Barium titanate with a perovskit e structure?ABO₃?is mostly used to make multilayer ceramic capacitor materials.And it is noteworthy for its excellent electronic performance,such as ferroelectric properties,piezoelectric properties,high dielectric constant and positive temperature coefficient.With the rapid development of electronic industry,the demand for electronic materials becomes more heavily all over the world.In order to optimise the dielectric properties of BaTiO₃ ceramics,it can be altered by doping and improving process for preparing ceramic powder.In this thesis,BaTiO₃ ceramics doping with Al³⁺,Ca²⁺and Nb⁵⁺were prepared by solid traditional phase reaction and Sol-Gel method,and the influence on the properties of ceramics had been discussed.1.The Al-doped BaTiO₃ ceramics were respectively prepared by solid phase reaction and sol-gel method.The results indicate that the ceramic samples prepared by solid phase reaction had uniform grain size and fine bulk density.While the grain size of ceramic samples prepared by sol-gel method decreased as Al³⁺increased,meantime,homogeneity of particle size and bulk density improved.The second phase of samples prepared by two kinds of methods appeared,detected as BaAl₂O₄.What's more,the dielectric constant???peak broadened and the Curie temperature?Tc?shifted to lower temperature.2.The Ca-doped BaTiO₃ ceramics were respectively prepared by solid phase reaction and sol-gel method.The results indicate that the sintering temperature of the samples prepared by solid phase reaction was 1350°C,but the samples prepared by sol-gel method was1300°C.And no second phase appeared in the XRD diagram.At the same amount of Ca²⁺,the samples prepared by sol-gel method had higher?,smaller?_c,narrower hysteresis loop,lower Pr and Ec.3.B-site of BaAl_0.04Ti_0.96O₃ was substituted by Nb⁵⁺.The results indicate that when the content of Nb⁵⁺was less than 0.03,the grain size increased with Nb⁵⁺increased;the grain size decreased with Nb⁵⁺increased,and the second phase appeared on the contrary.With content of Nb⁵⁺increased,?increased first and then decreased,the Tc shifted to lower temperature and the dielectric peak broadened obviously.Dielectric loss increased with the increase of test frequency.When the content of Nb⁵⁺was more than 0.01,ceramic samples showed relaxation ferroelectric phenomenon.4.The dielectric property of BaNb_0.02Ti_0.98O₃ ceramics doped with Al³⁺was investigated.The results indicate that when the content of Al³⁺was more than 0.02,the second phase appeared.And with the content of Al³⁺increased,bulk density increased,Tc shifted to higher tempera-ture,dielectric peak broadened,meanwhile,?decreased at the same frequency.5.The Ca-doped BaTi_0.96Al_0.04O₃ ceramics were prepared by solid phase reaction.The results indicate that when the content of Ca²⁺increased,no second phase appeared,and at the same frequency dielectric peak broadened and decreased,but Tc did not shift.What's more,as Ca²⁺increased,dielectric loss,Pr and Ec increased,but?decreased.6.A-site of BaTi_0.93 Al_0.04Nb_0.03O₃ was substituted by Ca²⁺.The results indicate that the bulk density of samples increased and tended to be stable with content of Ca²⁺increased.At the same frequency,?and dielectric loss increased first and then decreased as Ca²⁺increased.