Investigation On The Barium Strontium Titanate Microwave Ferroelectric Materials With Modifying Elements

As a microwave ferroelectric material, Barium strontium titanate (BST) hascharacteristics such as proper dielectric constant, small dielectric loss and goodtunability. BST has the potential applications in the fields of photoelectricityinformation and microwave communication. In order to meet the requirements ofdifferent applications, the microwave dielectric properties of BST should beimproved. Recently, investigation of BST doped with oxides has been developedfast.The two doping methods were direct mixture and the equal-mole mixture.Microwave ferroelectric ceramic Ba_0.6Sr_0.4TiO₃ doped with different amount ofAl₂O₃ and La₂O₃ were prepared by two different doping methods. The microscopicstructure characteristic and phase distribution of the composites were investigated bymeans of SEM and XRD, and the dielectric properties of the samples were tested.The mechanism of the improvement of those oxide doped BST was also discussed.The measurement results showed that, when we used the doping method ofmixing directly, Al₂O₃ and La₂O₃ appear in the BST crystal domain by substituting.Meanwhile, the dielectric constant and dielectric loss of material were both reduced.The main reason is that those doped-oxide are not a ferroelectric material and haslow dielectric properties; When we used the doping method of the equal-molemixture, it could find that the Al₂O₃ and La₂O₃ also appear in the BST crystaldomain by substituting, but the dopant of La₂O₃ has affected the crystal boundarysegregation. But we also found a new compound appearing in that segregation and itapproached the (Ba, Sr)TiO₄ of cubic on the structure. With the amounts of dopantsincreasing, the dielectric constant of samples that we fabricated by the mean of theequal-mole mixture was reduced, but the dielectric loss showed fluctuation. Theenhancement of loss could be explained as that the new compound caused thestructure of ceramics to get bad such as the density reduced, the hole and the lacunaincreased.From the experimented results of the two methods, it was found that the doping of Al₂O₃ and La₂O₃ also influence BST ceramic's crystalline structure and dielectricperformance. The results, such as the phase distribution, microscopic structurecharacteristic and dielectric performance, gained from the equal-mole mixturemethed were better than the other methed.