Rare Earth Oxide Doped Bst-mgo Composite Ceramics Dielectric Nonlinear

Investigation of paraelectric barium strontium titanate(BST) has been continued growth of interest for tunable microwave device applications, such as, electronically tunable mixers, delay lines, filters and phase shifters. Recently, BST thin films becomes the best candidate of dielectric materials for cell capacitor of the dynamic random access memory devices(DRAMs) having gigabit densities. The effects of rare earth oxides such as La₂O₃ and CeO₂ on the properties of barium strontium titanate/magnesia (BSTO/MgO) compound ferroelectric material for improving properties of phase shift, including permittivity, loss tangent and tunability both at low and high frequency, were studied. The mechanism was also presented and discussed. The relations among the composition, microstructure and dielectric properties are also discussed. The principal results are listed as follows:1. La₂O₃ is impaction on sintered properties, phase structure, microstructure and dielectric properties of BSTO/MgO ceramic composites, temperature reduce about 50℃by dopping the trace La₂O₃ and can improve the dielectric properties of ceramics.the temperature range from 1400 to 1550℃, there are two kinds of BST and MgO phase in all samples without other phase was detected. Dielectric loss of BST/MgO composite material is reduced by dopping proper La₂O₃, at the same time dielectric constant can be guaranteed. Tunability of composite ceramic is reduced by dopping La₂O₃, there is a significant role in the improvement in dielectric loss of composite ceramic of BSTO/MgO.2. The effect of doping CeO₂ on the Ba_0.6Sr_0.4TiO₃(BST) mixed with magnesium oxide (wt=56%) composites was investigated. Results of with increasing of CeO₂ contant, the grain size of the composite ceramic is decreased. The XRD,SEM and EDS shows that the composite ceramic consists of BST and MgO phase without other phase was detected. The phase transition of composite ceramic shifts to low temperature with an increase of CeO₂ content, and the dialect constant, loss tangent, dielectric tunability also varies little. The K-factor of the sample increases initially, and then decreases with the CeO₂ dopant increasing. The 0.2% wt% CeO₂ doped samples have the best properties among these samples.