Preparation And Research On Barium Strontium Titanate Based Material Used For Phase Shifter

Ferroclectric phase shifter, as a typical medium phase shifter, because of its excellent advantages, has earned lots of attention. In order to meet the requirence of the design of the phase shifter, moderate dielectric constant, low dielectric loss and high tunability are necessary for the ferroelectric material. Barium strontium titanate(BST) are potential materials for the applications of microware devices due to their high dielectric nonlinearity low leakage current and adjusting Curie temperature.This paper chose BST as the main phase, traditional solid state sintering as the sintering method. The influences of sintering conditions, diferent Ba/Sr ratio, MgO, CuO, MnO2 and CuO-MnO2 codoped on microstructure and dielectric propertie were investigated. The main works are as follows:The sintering conditions have great influence on the structure and properties of BST ceramic materials. The improvement of the sintering temperature can improve the sintering density of ceramics and theirs dielectric performance, but higher sintering temperature can lead to overburning, reduce the density and the dielectric properties of the ceramics. Proper holding time can ensure sintering process completely, but extended holding time has little influence on the density of the ceramic samples. Through the experimental investigation, the best sintering temperature is 1320?, holding time is 2h.The research of different barium strontium ratio has shown that with the increase of barium strontium ratio, the curie temperature of ceramics gradually raise, the dielectric constant of ceramics increase firstly and then reduce, the dielectric loss of ceramics reduced firstly and then increase. The component as Ba0.6Sr0.4TiO3 has the best dielectric properties. The research of MgO doped Ba0.6Sr0.4TiO3 has shown that the incorporation of MgO makes the dielectric constant and dielectric loss of the ceramics both reduced, the main reason is MgO is the ferroelectric phase material, which has the characteristics of low dielectric constant and low loss. When the amount of MgO is 45wt%, the dielectric constant of BST material is down to 174, tan? = 0.018, Tunability= 25%, FOM = 13.88.In order to further reduce the dielectric loss of BST materials, the influences of CuO doping and MnO2 doping on the structure and the dielectric properities of BST-MgO composite ceramics were inversigated. The results show that both of these two kinds of dopant can reduce the dielectric loss of materials, but the modification mechanism of them are different, the former is to improve the sintering properties of ceramics to reduce material dielectric loss, the latter is by inhibiting the change of titanium ion valence to reduce material dielectric loss. After getting the optimal doping ratio of CuO and MnO2, the influence of CuO and MnO2 co-doping on the structure and properties of BST materials was inversigated. This experiment prepared successfully the BST ferroelectric materials with the dielectric constant is about 190, dielectric loss tan? is 0.0022 under 10 kHz and the Tunability is 16%(3 kv/mm), which can satisfies the requirement of the phase shifters basically.