Study On Preparation And Doping Modification Of Perovskite Phase Barium Strontium Titanate (Ba_0.7Sr_0.3TiO₃)

At present, perovskite phase barium strontium titanate electronic ceramics is one ofthe most important research subjects in electronic material field, because of its excellentelectrical properties and its wide range of applications in electronic components. Nowscientists are focus on research barium strontium titanate powder of good morphologyand the ceramics which has excellent dielectric properties.The Ba_0.7Sr_0.3TiO₃nano powder of perovskite structure was prepared by sol-gelmethod, it was pressed into tablets and then was sintered into a ceramic. The dielectricproperty of the pure BST ceramic was researched and it was doped with A-bit and B-bit.We investigated the change on structure, morphology and dielectric properties of thedoped BST material.The barium strontium titanate was produced by sol-gel method; we used thethermo gravimetric analysis （TGA）, differential scanning calorimetry （DSC） analysis,infrared spectroscopy （IR）, X-ray diffraction （XRD） and scanning electron microscopy（SEM） to analysis the in-depth research on heat treatment process, crystallizationprocess and morphology. The results showed that, stable precursor sol could be obtainedunder the reaction conditions: pH=6.0, molar ratio of citric acid and metal ion greaterthan1.5, appropriate content of water. After dehydration sol became gel.Perovskite-type Ba_0.7Sr_0.3TiO₃nano-powders of high purity were prepared by950℃calcination, morphology looked like small cubes and the average particle size was110nm. Mi_xed the powders with PVA, tabletted molding at6MPa, calcined at differenttemperature and silvered can got the BST ceramic electrodes. Detect the dielectricproperties at1KHZ, the results showed that it can got good dielectric properties after 1330℃calcination.The influence on structure, morphology and dielectric properties of the BSTceramic doped by Bi、Ce、 Ni、Mg were studied by the single factor variable method.Results showed that in the beginning, dielectric constant raised because the Bi³⁺wasdoped in the A sit, with the increase of Bi³⁺, it entered into the B-bit, the oxygenvacancies appeared and made the dielectric constant decreased gradually, and the Bi³⁺could lower dielectric constant peak, made it moved from high temperature zone to thelow temperature zone. Improved the dielectric loss of BST; doping of Ce³⁺was theA-bit and Ce³⁺reduced the dielectric constant, when content of Ce³⁺was0.015, thedielectric loss reached to the lowest. And with the change of temperature the change ofdielectric loss was very stable; When Mg²⁺entered into B-bit, dielectric constant anddielectric loss continued to decline, dielectric constant peak gradually moved toward thelow-temperature region and with the changed of temperature the dielectric loss changedlargely; With the doping of Ni²⁺, only a little Ni²⁺entered into the B-bit and substituteTi⁴⁺, it caused the increased of lattice parameters, then it gathered around the grainboundary as NiO and form a composite NiO/BST. The increase of Ni²⁺leaded toreduce of dielectric constant and dielectric loss. Dielectric temperature spectrumshowed that the BST with Ni²⁺hade diffuse phase transition characteristics and with theincrease of Ni²⁺it was more and more obvious. This is also improved the dielectrictemperature spectrum.The permittivity and dielectric loss of BST ceramic could be changed through thedifferent elements of the doping, and made the change of dielectric properties verystable. When the content of Bi³⁺was0.015or the content of Ni²⁺was0.02，we can getthe BST ceramic materials which with high dielectric constant, low dielectric loss andstable temperature performance of dielectric properties.