【作者】 雷文；

【导师】 吕文中；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2008， 博士

【摘要】 综观微波介质陶瓷材料的发展历史和应用前景,结合当前微波介质陶瓷的研究现状,确定ZnAl₂O₄基陶瓷为本文的研究对象。利用X射线衍射（XRD）、扫描电镜（SEM）、X射线能谱（EDS）、X射线光电子能谱（XPS）、电子探针（EPMA）和网络分析仪等仪器系统地研究了制备方法（常规固相法和熔盐法）、烧结工艺、相成分、微观组织结构和微波介电性能之间的关系。首先研究了（1-x）ZnAl₂O_4-xTiO₂材料的烧结特性、相成分和微波介电性能。结果表明,TiO₂能有效地改善材料的烧结性能和调节材料的谐振频率温度系数,当x=0.21时,（1-x）ZnAl₂O_4-xTiO₂陶瓷具有近零的谐振频率温度系数,体系中包括细小的ZnAl₂O₄尖晶石晶粒和粗大的金红石相晶粒。在此基础上,系统地研究了（1-x）ZnAl₂O_4-xTiO₂ （x=0.21）材料的预烧温度、烧结温度和升温速率,并确定了最佳工艺参数,它们分别为1150℃、1500℃和5℃/min,此时的微波介电性能为:εr=11.6、Q·f=74000GHz、τf=-0.4ppm/℃。利用熔盐法制备了（1-x）ZnAl₂O_4-xTiO₂陶瓷,并探索了材料的烧结性能、微观组织和微波介电性能特点。与常规固相法相比,利用LiCl和ZnCl₂熔盐均能制备出颗粒细小均匀、活性高的（1-x）ZnAl₂O_4-xTiO₂粉末,并能有效降低材料的烧结温度,但同时也降低了材料的密度和微波介电性能。当熔盐为LiCl、预烧温度为900℃时,（1-x）ZnAl₂O_4-xTiO₂（x=0.21）陶瓷的致密化温度为1425℃,微波介电性能分别降到:εr=10.0、Q·f=39970GHz、τf=-21.2ppm/℃。当x=0.25时,（1-x）ZnAl₂O_4-xTiO₂陶瓷的致密化温度降低到1300℃,τf值被调节到-7.1ppm/℃,同时,Q·f值降低到27000GHz,而εr值变化很小。当熔盐为ZnCl2、预烧温度为900℃时,（1-x）ZnAl₂O_4-xTiO₂（x=0.25）陶瓷的致密化温度为1350℃,此时材料的微波介电性能为:εr=10.0、Q·f=56440GHz、τf=-25.4ppm/℃。利用MO（M=Co, Mg, Mn）和TiO₂共同改性ZnAl₂O₄时,比较了（1-x）ZnAl₂O₄- xM2TiO₄（x=0.21）与（1-x）ZnAl₂O_4-xTiO₂（x=0.21）陶瓷的相成分、微观结构和微波介电性能之间的差异。研究表明,Co²⁺离子能促使Ti⁴⁺离子固溶入ZnAl₂O₄尖晶石晶格中形成单一的固溶体相,能将Q·f值从74000GHz提高到94000GHz。Mg²⁺和Mn²⁺离子均不能使Ti⁴⁺离子完全固溶入ZnAl₂O₄晶格中,而在体系中分别出现了MgTi₂O₅和ZnMn3O7相,两者的Q·f值分别为188540GHz和23530GHz。与（1-x）ZnAl₂O₄-xTiO₄ （x=0.21）陶瓷相比,（1-x）ZnAl₂O_4-xM₂TiO₄（x=0.21）陶瓷的εr和τf值均有所降低,但相互之间的差别很小。进一步研究了（1-x）ZnAl₂O_4-xM₂TiO₄（M=Co, Mg）陶瓷的相变过程和微波介电性能特点。结果表明,对于（1-x）ZnAl₂O_4-xMg₂TiO₄体系,当x=0.1时,ZnAl₂O₄能与Mg2TiO₄形成尖晶石固溶体,当x=0.21～0.8时,体系中包括尖晶石相和MgTi2O5相,当x=0.9和1.0时,体系中存在尖晶石相和MgTiO₃相。对于（1-x）ZnAl₂O_4-xCo₂TiO₄体系,当x=0.1～0.3时,ZnAl₂O₄能与Co2TiO₄形成尖晶石固溶体,当x=0.4时,体系中析出少量Co₂TiO₄相,当x=0.5时,体系中同时析出Co₂TiO₄和（Zn, Co）Al₂O₄相,两者相互交替生长在（1-x）ZnAl₂O_4-xCo₂TiO₄基体上。随着M₂TiO₄含量的增加,（1-x）ZnAl₂O_{4- x}M₂TiO₄陶瓷的εr值几乎线性增大,Q·f值先减小然后增大,τf值变化很小。研究了TiO₂、CaTiO₃和SrTiO₃对0.79ZnAl₂O₄-0.21M₂TiO₄（M=Co, Mg）陶瓷谐振频率温度系数的影响。研究发现,TiO₂不能调节0.79ZnAl₂O₄-0.21M₂TiO₄（M=Mg, Co）材料的τf值,因为TiO₂与基体反应生成了具有负温度系数的MTi2O5相。CaTiO₃和SrTiO₃均能有效地调节0.79ZnAl₂O₄-0.21M2TiO₄（M=Co, Mg）材料的τf值。总的来说,随着CaTiO₃（或SrTiO₃）添加量的增多,材料的εr和τf值逐渐增大,而Q?f值具有减小的趋势。研究了ZnB₂O₄和B₂O₃助烧剂对（1-x）（0.79ZnAl₂O₄-0.21Co2TiO₄）-xCaTiO₃（x=0.08） （ZCC）和（1-x）（0.79ZnAl₂O₄-0.21Mg2TiO₄）-xCaTiO₃（x=0.06）（ZMC）材料的烧结特性、相成分和微波介电性能的影响。ZnB₂O₄助烧剂能将ZCC材料的烧结温度降低到1100℃,降幅为300℃,但ZnB₂O₄助烧剂对ZMC材料以及B₂O₃助烧剂对ZCC和ZMC材料的助烧作用均不显著,仅能降低50～100℃。当掺入助烧剂后,材料的εr值均有所降低,但材料的Q?f和τf值的变化趋势与助烧剂的种类和数量有关。一般而言,ZnB₂O₄助烧剂使ZCC和ZMC材料的Q?f值降低幅度较大,而B₂O₃助烧剂对Q?f值的影响相对较小。更多还原

【Abstract】 Based on the development, application and research actuality of microwave dielectric ceramics, ZnAl₂O₄-based ceramics are chosen as research objective in this dissertation. The relationships among preparing methods （including solid-state reaction and molten salt method） and processes, phase compositions, microstructures and microwave dielectric properties have been investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDS）, X-ray photoelectron spectroscopy （XPS）, electron-probe microanalysis （EPMA） and network analyzer, etc.Sintering characteristic, phase compositions and microwave dielectric properties of （1-x）ZnAl₂O_4-xTiO₂ ceramics had been studied. It shows that TiO2 can effectively improve the sintering characteristic and control the temperature coefficient of resonant frequency （τf）. （1-x）ZnAl₂O_4-xTiO₂ （x=0.21） ceramics with near-zeroτf value includes smaller ZnAl₂O₄ spinel grains and larger rutile grains. And then, the sintering processes such as calcining temperature, sintering temperature and heating rate of the （1-x）ZnAl₂O_4-xTiO₂ （x=0.21） system have been researched systematically, and the optimal sintering process parameters have been determined which are 1150℃, 1500℃and 5℃/min, respectively, in which sintering conditions the microwave dielectric properties are as follows:εr=11.6, Q·f=74000GHz,τf=-0.4ppm/℃.Sintering characteristic, microstructures and microwave dielectric properties of （1-x）ZnAl₂O_4-xTiO₂ ceramics synthesized by molten salt method had been explored. In contrast to the solid-state reaction, smaller size, more homogenous and higher activity powder can be synthesized by LiCl and ZnCl₂ molten salt, which lowers the sintering temperature, at the same time, also deteriorates the density and microwave dielectric properties of the （1-x）ZnAl₂O_4-xTiO₂ ceramics. （1-x）ZnAl₂O_4-xTiO₂ （x=0.21） calcined at 900℃in LiCl molten salt can be fully densified at 1425℃, and the microwave dielectric properties withεr=10.0, Q·f=39970GHz andτf=-21.2ppm/℃can be obtained. When x is equal to 0.25, the densification temperature reduces to 1300℃, andτf value is adjusted to -7.1ppm/℃and theεr value nearly doesn’t change, however, the Q·f value reduces to 27000GHz. （1-x）ZnAl₂O_4-xTiO₂ （x=0.25） calcined at 900℃in ZnCl2 molten salt can be fully densified at 1350℃and the ceramics exhibits the microwave dielectric properties withε_r=10.0, Q·f=56440GHz andτf=-25.4ppm/℃.When MO（M=Co, Mg, Mn） and TiO₂ were added to ZnAl₂O₄, the phase compositions, microstructures and microwave dielectric properties of （1-x）ZnAl₂O_4-xM₂TiO₄ （x=0.21） ceramics were compared with those of （1-x）ZnAl₂O_4-xTiO₂ （x=0.21） ceramics. It is found that the single phase solid solution appears in the （1-x）ZnAl₂O_4-xCo₂TiO₄ （x=0.21） ceramics because Co²⁺ ion can promote Ti⁴⁺ ion to diffuse into the ZnAl₂O₄ crystal lattice which increases the Q·f value from 74000 to 94000GHz. However, the MgTi₂O₅ and ZnMn₃O₇ phase can be observed in the （1-x）ZnAl₂O_4-xMg₂TiO₄ （x=0.21） and （1-x）ZnAl₂O_4-xMn₂TiO₄ （x=0.21） ceramics, whose Q·f value is 188540GHz and 23530GHz, respectively. Theεr andτf values of the （1-x）ZnAl₂O_4-xM₂TiO₄ （x=0.21） are lower than those of （1-x）ZnAl₂O_4-xTiO₂ （x=0.21） ceramics, whereas theεr andτf values are weakly dependent on the M element and are equal to about 9.7 and -65ppm/℃, respectively.Phase transition and microwave dielectric properties of （1-x）ZnAl₂O_4-xM₂TiO₄ （M=Co, Mg） ceramics had been further studied. In the （1-x）ZnAl₂O_4-xMg₂TiO₄ system, ZnAl₂O₄ can form a spinel solid solution with Mg2TiO₄ for x=0.1, while the MgTi2O5 and MgTiO₃ second phase exists in the systems for 0.21≤x≤0.8 and 0.9≤x≤1.0, respectively. In the （1-x）ZnAl₂O_4-xCo₂TiO₄ system, ZnAl₂O₄ can also form a spinel solid solution with Co2TiO₄ for 0.1≤x≤0.3, however, the Co2TiO₄ second phase appears in the ceramics for x=0.4. When x is equal to 0.5, Co2TiO₄ and （Zn, Co）Al₂O₄ phase coexist and grow alternately in the （1-x）ZnAl₂O_4-xCo₂TiO₄ matrix. As the content of M2TiO₄ increases in the （1-x）ZnAl₂O_4-xM₂TiO₄ system, theεr value takes on a tendency of linear increase, and the Q·f value increases initially and then decreases, while theτf value only changes slightly.The effects of TiO₂, CaTiO₃ and SrTiO₃ additions on theτf value of the 0.79ZnAl₂O₄-0.21M2TiO₄ （M=Mg, Co） ceramics had been investigated. TiO₂ cannot control theτf value of the 0.79ZnAl₂O₄-0.21M2TiO₄ （M=Mg, Co） ceramics due to the MTi2O5, formed by the reaction of TiO₂ with the matrix, with relative high negativeτf value, however, CaTiO₃ and SrTiO₃ can adjust effectively theτf value. In general, with the increasing amount of CaTiO₃ （or SrTiO₃）, bothεr andτf values increase gradually, while, the Q?f value has a tendency of decrease.The influences of ZnB₂O₄ and B₂O₃ sintering aids on the sintering characteristic, phase compositions, microwave dielectric properties of （1-x）（0.79ZnAl₂O₄-0.21Co2TiO₄）- xCaTiO₃（x=0.08）（ZCC） and （1-x）（0.79ZnAl₂O₄-0.21Mg₂TiO₄）-xCaTiO₃（x=0.06）（ZMC） ceramics had been studied. When ZnB₂O₄ is added to ZCC system, the sintering temperature is reduced to 1100℃, which is 300℃lower than the sintering temperature of undoped ZCC. When B₂O₃ is added to ZCC system, or ZnB₂O₄ （or B₂O₃ ） is added to ZMC system, the sintering temperature only lowers 50～100℃. In comparison with the undoped ZCC （or ZMC）, theεr values of the doped system all reduce, and the Q-f andτf values are dependent on the category and amount of additions. On the whole, ZnB₂O₄ addition greatly reduces the Q-f value of the ZCC （or ZMC） ceramics, while B₂O₃ addition does not affect obviously on the Q-f value.更多还原