Study On The Abnormal Increase Of The Tunability In Binary Ferroelectric-dielectric Composites

Barium strontium titanate is a material with tunable properties,and has a wide range of applications,such as phase shifters and tunable filters.However,pure barium strontium titanate material has high dielectric constant and high loss tangent,which precluded their use in many fields.Therefore,it is of great significance to study how to reduce the dielectric constant and dielectric loss of barium strontium titanate while maintaining high tunability.Adding linear dielectric materials to barium strontium titanate to form ferroelectric-dielectric composites and changing the sintering process are important ways to optimize dielectric properties.In this dissertation,Ba_0.55Sr_0.45TiO₃-Ce O₂ and Ba_0.45Sr_0.55TiO₃-Ce O₂ composite ceramics were prepared by solid-phase sintering.The microstructure and tunability of composite ceramics are studied.Studies have shown that there are only BST and Ce O₂phases in Ba_0.55Sr_0.45TiO₃-Ce O₂ composite ceramics.The dielectric constant of BST-Ce O₂composite ceramics decreases with the increase of Ce O₂ content,and the tunability of BST-Ce O₂ composite ceramics first increases and then decreases with the increase of Ce O₂content.The Ba_0.5Sr_0.5TiO₃-Mg₂TiO₄ composite ceramic was prepared by spark plasma sintering（SPS）method,and its microstructure and dielectric properties were studied.Research shows that the composite ceramics prepared by SPS technique has highly densified structures.The dielectric constant of Ba_0.5Sr_0.5TiO₃-Mg₂TiO₄ composite ceramics decreases with the increase of Mg₂TiO₄ composition,and its tunability first increases and then decreases with the increase of Mg₂TiO₄ content,and the tunability of composite ceramics is greater than that of pure BST,there is no initial decreasing region,which shows that SPS can effectively suppress the doping effect.Three-dimensional models of Ba_0.55Sr_0.45TiO₃-Ce O₂ composite ceramics and Ba_0.5Sr_0.5TiO₃-Mg₂TiO₄ composite ceramics were constructed by finite element analysis software.The linear dielectric component in the model will redistribute the electric field in the model.The electric field strength of the BST in the enhanced region increases with the increase of the dielectric component content,resulting in an abnormal increase in the tunability of the composite ceramic.In the BST-Mg₂TiO₄ model,the simulation results show that there is no initial decreasing region in the tunability of the model,which is consistent with the experimental results.It proved that the doping effect was effectively suppressed by SPS.