Study On The Ferroelectric Material BST Used In The Phase Shifter Of Phased-array Radar

The ferroelectric materials possess excellent dielectric, piezoelectric, ferroelectric, pyroelectric and nonlinear polarization properties and have been widely used in many fields, such as the dynamic random-access memory, the infrared sensor, the tunable microware device. In phased-array antennas, although the ferrite phase-shifters are widely used nowadays, but they have the disadvantage of large volume and weight, high cost which can't been easily conquered. Barium strontium titanate (Ba_xSr_1-xTiO₃, short for BST) are potential materials for the applications of microware devices such as dielectric phase shifters and tunable filters due to their high dielectric nonlinearity low leakage current and adjusting Curie temperature.In this dissertation, we founded the origin of dielectric tenability is that the non-linear polarization under applied DC electric field, the origin of non-linear polarization is the spontaneous polarization of ferroelectric or ferroelectric micro-regions, modified sol-gel method to prepared BaSrTiO₃ was founded , by means of DTA /TG analysis of dried BST gels, the technique of the sol-gel processing was optimized. XRD was used to indicate the phase structure of the BST, energy spectrum analyzed by EDS, and the surface morphology was investigated through field-emission SEM, By means of these modern analyses, the crystallization properties, the microstructure, the chemical composition ,the bonding energy and chemical valence states of elements in BST was analyzed.Besides preparing BST by sol-gel, the other two doping experiment have done, firstly, different weight proportion of MgO-doping BST were prepared by sol-gel. the proportion are 0 , 40% ,50% , 60%.Secondly, MgO and Bi2O3-doping BST were prepared by sol-gel. After referring to a lot of information we have improved and optimized the preparation technique all the while. And last, the samples were tested by AV3618 network-analyzer at frequency sects of 8.2-12.4GHz and 12.4-18.0GHz, calculated the permittivityεand the loss tangentδand got its changing curve. The experimental result indicated that, BST which prepared with sol-gel have good crystallization condition , but dielectric constant and dielectric loss are high. In barium strontium titanate/magnesium titante composite system, the material properties can be dramatically improved by properly controlling the weight of doped MgO and Bi2O3,while doped MgO proportion is 50%,the 0.25% Bi₂O₃ doped sample demonstrates the desirable properties, including low dielectric constant less than...