Research On Doping Mechanism Of BT4/BST High Frequency Dielectric Ceramics

The development of filters, resonators and other telecommunication technology required better dielectric materials . The dielectric materials, used as the resonate body, should be high in dielectric constant, low in dielectric loss and a near zero temperature coefficient of dielectric constant in high frequency band, also could be sintered in a relative low temperature so as to reduce production cost, and what's more, the miniaturization and reliability of materials are also the main aspects in the research work of high frequency band dielectric materials.The thesis mainly investigated the BaTi₄O₉(BT₄), which has the lowest dielectric loss in Ba-Ti system, and (Ba,Sr)TiO₃ , the A position substitute compound of BaTiO₃. The dielectric properties of BT₄/BST with different preparation way and different elements doping were investigated. A Archimedes method, XRD, SEM, impedance analyzer, network analyzer and Hakki-Coleman method were used to investigate the density, phase formation, microstructure, dielectric properties and doping mechanisms. The main results are shown as follows:1.BT₄ doped with CuO could be sintered in a lower temperature, because CuO has a low melting point. There isn't any other phase in the samples. The dielectric properties decreased because CuO was non-crystalloid.2.BT₄ doped with MnO₂ could slightly decrease the sintering temperature, Mn ion can lower the dielectric loss and improve the dielectric constant. 3.A BaZrO₃ phase was formed when BST doped with more ZrO₂, and the grain size increased. Along with the doping content increases, the dielectric constant initially increased and then decreased.The dielectric loss was on the contrary.4.BT₄ doped with Bi₂O₃ or V2O5 got a lower sintering temperature. A BaBi4Ti4O15 phase raised when Bi₂O₃ was doped and the dielectric properties ruined. Compound doping of Bi₂O₃ and V₂O₅, no second phase exists. V ion can restrain the formation of BaBi₄Ti₄O₁₅.5.BST doped with proper amount of La could restrain the largen of grains, improve dielectric constant and decrease dielectric loss, whereas La₄Ba₄Ti₇O₂₄ raised when more La doped, and it was harmful to dielectric properties. No second phase exists when BT₄ doped with Nd and the dielectric properties increased when the doping content is small.