铁电-介电复合物的调谐率反常增加机制研究

Ferroelectric-dielectric composites have potential applications for tunable microwave device such as phase shifters and phased array antennas. However, with the increase of ferroelectrics content (the decrease of dielectric constant), the tunability decreases obviously, so their applications were restricted. Recently, an "anomalous phenomenon" in some ferroelectric-dielectric composites were observed: with the decrease of ferroelectric content, the tunability increases, but it is unclear what the mechanism is. To understand this useful "anomalous increase phenomenon", barium strontium titanate (BST) based ferroelectric-dielectric composites will be prepared by spark plasma sintering (SPS) technology, the influence mechanism of composite effect on the tunable properties will be explored; At the same time, organic ferroelectric materials poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) will be chosen to form composites with inorganic dielectric materials at low temperature, so that doping effect can be eliminated completely, the effects of dielectric materials on the structures and properties of composites will be studied. On the basis of the above works, the relationship of chemical composition-microstructure-dielectric properties and the restricting law of permittivity, loss tangent and tunability will be explored. The effect of linear dielectrics on the dielectric properties of composites will be simulated using COMSOL MULTIPHYSICS. Through the combination of experiment and theory, the mechanism of anomalous increase of the tunability will be proved, solutions to the difficult problem of the decrease of tunability will be provided and new materials with independent intellectual property rights will be obtained.

铁电-介电复合物在移相器和相控阵天线等方面应用前景广阔，但其调谐率随铁电材料含量减少(介电常数降低)而明显降低，严重影响其应用。近来发现了部分铁电-介电复合物中调谐率随铁电材料含量减少而增加的"反常现象"，但其增加机制不明。本项目拟针对这一有利的"反常增加现象"，采用放电等离子体烧结技术制备钛酸锶钡基铁电-介电复合物，探明复合效应对调谐性能的影响机制；与此同时，选择有机铁电材料聚偏氟乙烯-三氟乙烯共聚物与无机介电材料进行低温复合，以便完全消除掺杂效应，揭示介电材料对复合物的介电性能和结构的影响规律。在此基础上，探索复合物的化学组成-微结构-介电性能间的关系及介电常数、介电损耗和调谐率间的制约规律，并采用COMSOL MULTIPHYSICS软件模拟介电材料对复合物介电性能的影响。通过实验与理论相结合，探明调谐率反常增加的机制，为克服调谐率下降难题提供解决方案，获得具有自主知识产权的新材料。

钛酸锶钡(BST)的介电常数能够在偏置直流电场作用下发生改变，因而在移相器和相控阵天线等微波调谐器件中具有广阔的应用前景，然而存在介电常数高，介电损耗大的问题。加入介电材料形成铁电-介电复合物能有效降低介电常数，但其调谐率随铁电材料含量减少明显降低，严重影响其应用。近来发现了部分铁电-介电复合物中调谐率随铁电材料含量减少而增加的"反常现象"，但其增加机制不明。本项目从抑制或消除掺杂效应入手，采用放电等离子烧结(SPS) 工艺制备了BST基铁电-介电复合陶瓷，采用旋涂或直滴法制备了P(VDF-TrFE)基有机-无机复合膜，研究了其介电调谐性能。在SPS技术制备的BST-MgO, BST-Mg2TiO4, BST-MgO-Mg2TiO4和BST-MgO-Mg2SiO4等体系中，均实现了比纯BST低的介电常数和比纯BST高的调谐率，因为掺杂效应的作用，这在传统烧结方法制备的陶瓷中是无法达到的。制备的P(VDF-TrFE)-MgO，P(VDF-TrFE)-Mg2TiO4和P(VDF-TrFE)-Mg2SiO4等复合膜具有比纯P(VDF-TrFE)低的介电常数和高的调谐率，这可归因于掺杂效应的消除。仿真分析表明，铁电-介电复合物中电场集中在介电常数小的介电材料上，虽然铁电材料上的平均电场强度低于外加的电场强度，但随介电材料含量的增加，增强区的平均电场强度增加，导致调谐率增加，尽管铁电性稀释会导致调谐率降低，二者共同作用导致复合物的调谐率随介电材料含量增加先增加后降低。本项目直接证明了掺杂效应引起了BST基复合陶瓷的调谐率的急剧下降，复合效应是调谐率反常增加的原因。通过抑制或消除掺杂效应，消除了调谐率的初始下降区，实现了比纯铁电材料高的调谐率和低的介电常数，解决了BST基铁电-介电复合陶瓷中长期存在的介电常数的降低和调谐率的增加的矛盾，探明了铁电-介电复合物中调谐率反常增加的机理，为探索新的材料体系和寻求新的制备工艺，获得更优性能的铁电材料奠定了基础。另外，根据电场分布特性，提出在P(VDF-TrFE)中加入介电常数高的材料如CeO2, CaTiO3和SrTiO3，提高了铁电材料的调谐率。