Research On Preparation And Dielectric Properties Of BaTiO₃ Based Ceramics Doped By Sol-gel Method

BaTiO₃ is one of the most dynamic and the most widely used advanced ceramic materials.The excellent dielectric properties of BaTiO₃ make it a significant base material for the application of capacitors.However,the change of dielectric constant with temperature for pure barium titanate is large,and the dielectric constant of room temperature is low.It is difficult to be used for capacitor materials directly.Therefore,doping routes should be adopted to improve the temperature stability and the dielectric constant.For the traditional solid-state method of preparing electronic powders and ceramics,there are many disadvantages,e.g.the inhomogenous distribution of dopants and powder size and the limit of thin dielectric layers,which are in disagreement with the requirements of small size and high reliability in electronic devices;but via sol-gel method,nanopowders can be achieved with high purity,homogenous distribution of dopants,and good sintering activity.In this paper,sol-gel method was used to prepare Sm³⁺-Sr²⁺and Tm³⁺-Sr²⁺co-doped BaTiO₃ nanopowders and ceramics for the first time and the composition and properties of the materials were investigated.1.Experimental results showed that it was essential to get transparent light yellow sol and to avoid mixed phase in samples.It was necessary to satisfy several conditions as follows:Citric acid:metal ions=4:1,adding CH₃CH₂OH solution to Ti?C₄H₉O?₄ solution;H₂O:CH₃CH₂OH=32:1;pH value 5⁶;seasoning time 4 hour,and it showed that 900?was the optimum heat treatment temperature at the same time.2.It was considered that Sm³⁺?Sr²⁺entered the crystal lattice of BaTiO₃.When x=0.006,the grain size had the minimum value.Heat treatment and holding time had an effect on the dielectric properties of Ba_0.7-1.5xSm_xSr_0.3TiO₃ ceramics,the optimum ceramics were kept for 4 hour at 1340?.Temperature dielectric constant curves indicated that the addition of Sm led to downward shift of Curie temperature?T_C?.When x=0.006,T_C was about 20?,the dielectric constant was 50394,it also had the best performance about stability of dielectric properties.3.It was indicated that Tm³⁺and Sr²⁺entered the crystal lattice of BaTiO₃ systematicly.The grain size decreased first then increased as the concentrations of Tm increased.With the increase of frequency,the dielectric constant of all dielectric ceramics decreased;the dielectric loss of BaTiO₃?Ba_0.7Sr_0.3O₃ declined gradually but the dielectric loss of Ba_0.7Sr_0.3Ti_1-3/4yTm_y O₃ dielectric ceramics decreased first and then increased rapidly at room temperature.The addition of Tm and Sr led to the fall of the Curie temperature,which moved to room temperature.The influence of Tm³⁺concentration on degree of the Curie temperature was small,yet the stability of dielectric properties were enhanced significantly.The best dielectric properties were observed when y=0.004 and the dielectric constant reached to 33089,and the range of application was broaden availably.