BST/Mg2TiO4/MgO Ferroelectric Composite For Accelerator Application

Ferroelectric ceramics of BST solid solutions with various additives are the basic ceramic materials to design microwave devices operated by the electric field, namely modulators, filters, phase shifters, and other. Moreover, an interest appeared recently towards the use of bulk ferroelectrics as control elements of high-power phase-shifters and switches for linear colliders. Ferroelectric layers can be also used as control elements for accelerating structures with dielectric loading. The main requirement for the electrical properties of ceramic materials to be used in such devices is a combination of relatively low dielectric constant is below500at the electric field tunability not worse than10-20%(electric field magnitude (2-5)kV/mm) and low dielectric losses at the microwaverange (tan δ≤0.005).The effect of the proportion of Ba/Sr, BST and (Mg2TiO4+MgO), Mg2Ti04and MgO on the dielectric properties of BST/Mg2TiO4/MgO were studied. The effect of La2O3, ZrO2, MnCO3, Co(NO)3·6H2O, CuO, Li2CO3and ZnO doping on the phase structure and dielectric properties of BST/Mg2TiO4/MgO were studied. The impurity phase BaMg6Ti6O19disappeared with reducing the proportion of Ba/Sr or MgO doping.MnCO3, ZnO and a small amount of ZrO2doping can increase the Qxf value and tunability of40Ba0.55Sr0.45TiO3/12Mg2TiO4/48MgO ceramics.0.5mol%MnCO3and0.5wt%ZnO doped40Ba0.55Sr0.45TiO3/12Mg2TiO4/48MgO ceramics show better dielectric properties:the dielectric constant were87.1and131.2at microwave frequency, the Qxf value were387GHz and470GHz and the tunability at2kV/mm were12.5%and11.7%, respectively. With La2O3content exceeding2wt%, the tunabity of40Ba0.55Sr0.45TiO3/12Mg2TiO4/48MgO ceramics abnormal increases with the increase of electric fields. The tunabity is a negative value. With the increase of La2O3content, the absolute value of tunabity increases. Li2CO3doping can reduce the sintering temperature of BST/Mg2Ti04/MgO ceramics from1370℃to1250℃The preparation technology has no obvious effect on the dielectric properties of ZrO2doped40Ba0.55Sr0.45TiO3/12Mg2TiO4/48MgO ceramics.Compared with the40Ba0.55Sr0.45TiO3/12Mg2TiO4/48MgO ceramics, MnCO3, ZnO and a small amount of ZrO2doping can increase the Qxf value and tunability and the composite ceramics are promising materials for tunable microwave application.The thesis is supported by Natural Science Foundation of China under grant No.10975055.