Preparation Of The BST Powders And Dielectric Property Of BST-MT Ceramic

The nanometer barium strontium titanate(BST)powders were prepared by chemical coprecipitation method with butyl titanate,barium nitrate and strontium nitrate as starting materials, oxalic acid as precipitator; absolute ethyl alcohol as solvent. The effects of process conditions, such as pH values, agitation, washing and the preparation method of (C4H9O)4Ti solution on the properties of BST powders were studied and the best process conditions of BST powders were introduced. Then, BST-MT(BaSrTiO3-MgTiO3) ceramics were prepared by the BST powders and magnesium titanate(MT) powders.The effects of doping of manganese and neodymium on dielectric properties of BST-MT ceramics were investigated.The peferable composition of the BST-MT ceramic was introduced at last.The coprecipitation reaction was more completed at pH=3 and stirred at 4000r/min. The BST phase was transformed by calcinated the precursors at less than 800℃, while the synthesize temperature of BST by solid reaction is above 1200℃. The average grain size of BST powders was less than 100 nanometers with narrow distribution.The average grain size of BST ceramic prepared by the above powders was about 1μm, which is more decreased than the ceramic prepared by solid reaction. The dielectric constant and dielectric loss of sintered sample was 1588.00 and 44×10-4 at room temperature and 1MHz. Adding of nonferroelectric phase MT decreased the variance ratio of dielectric constant and dielectric loss by the stretching effect. The BST-MT ceramic was sintered at 1250℃.At this temperature, sintered body was dense, crystalline grain was full-grown. Doping Mn can decrease the dielectric loss. It was 6.66×10-4 at room temperature by adding 1.5 mol % Mn. The dielectric loss could further decrease when doping with Mn and Nd, which was 4.33×10-4 at room temperature by adding 1.2 mol % Mn and 0.5 mol % Nd.