【作者】 崔斌；

【导师】 田长生；

【作者基本信息】 西北工业大学 ， 材料学， 2002， 博士

【摘要】 本文发展了弛豫铁电陶瓷的制备技术，提出了兼具传统氧化物混合法（CMO法）、二次合成法（CPM法）和湿化学法（CPM法）特点的半化学法（SCH法）；采用SCM法制备了钙钛矿结构的PMN基、PNN基、PFW基和PMW-PNN-PT系陶瓷；系统研究了制备工艺、过量反应物组分、钙钛矿相稳定剂PbTiO₃（PT）和改性剂MnO₂等对陶瓷的相结构、显微组织及介电性能的影响；优化了SCM法制备工艺。分析了SCM法与CMO法、CPM法在工艺上的差别，并提出了SCM法制备PMN-PT和PFW粉体的固态反应机理。同时研究了具有代表性的助烧剂对PMN-PT陶瓷的烧结温度、相组成、显微组织及介电性能的影响规律。将SCM法和“芯-壳”结构法相结合，制备了低烧高介的具有化学成分和结构不均匀的“芯-壳”结构的PMW-PNN-PT陶瓷，并研究了“芯-壳”结构的形成机理及其改善介电温度稳定性的机制，探讨了满足X7R特性陶瓷的制备工艺。 在PMN-PT体系中，研究了反应物前驱体，如Pb（AC）₂、Mg（NO₃）₂、Ti（OC₄H₉）₄分别代替PbO、MgO、TiO₂等对预烧粉体钙钛矿相形成的影响。结果表明：采用可溶性的醋酸镁或硝酸镁溶液代替MgO，可在分子水平上提高MgO的分散性，并且在低温分解形成“新生态”MgO的具有很高的反应活性，能够促进焦绿石相向钙钛矿相转化，且在钛酸丁酯活化TiO₂组分的协同作用下，得到了与化学法相近的结果。SCM法制备PMN-PT粉体的预烧工艺是800℃～850℃，2h～4h，烧结工艺为950℃～1200℃，1h～2h。 在PNN-PT体系中，采用SCM法在不添加稳定剂PT和过量NiO，便可获得纯钙钛矿结构的陶瓷；该体系粉体的预烧工艺为850℃，2h～3h，烧结工艺为1100℃～1200℃，1h～2h。掺锰后，PNN-PT陶瓷样品的介电常数虽然稍有降低，但陶瓷样品的介电损耗明显降低，较合适的掺锰量为0.5（mol）％。 在PFW-PT体系中，粉体的预烧工艺是800℃～850℃，1h～3h，烧结工艺为870℃，2h～3h；添加过量PbO和过量Fe₂O₃都能提高PFW预烧粉体和陶瓷的钙钛矿相含量以及陶瓷的介电常数，但添加过量Fe₂O₃明显增大了介电损耗。掺锰有利于稳定PFW钙钛矿相，且随着掺锰量的增加，陶瓷的介电常数先增加后降低，介电损耗急剧下降，电阻率明显提高，介电性能得到明显改善，较合适的掺锰量为1.0（mol）％；添加PT能够提高PFW的稳定性，随着PT含量的递增，陶瓷的晶粒尺寸略有增大，而且密度也有所增加，陶瓷的居里温度逐渐升高，弥散相变度逐渐下降，介电常数逐渐增大。 SCM法与CPM法的工艺相比，工艺简单，预烧温度和烧结温度低，反应时间短；陶瓷致密，介电性能比CMO法和CPM法明显得到改善，而且在没有PT存在时，仍可制得纯钙钛矿结构的PMN基、PNN基、PFW基陶瓷。在反应机理上，对于PMN-PT陶瓷，在SCM法中生成了不稳定的、缺B位的焦绿石相Pb₃Nb₂O₈，该中间体极易转变成钙钛矿相；CMO法生成稳定的焦绿石相Pb₃Nb₄O₁3，难以转变成钙钛矿相。对于PFW陶瓷，SCM法是在较低的温度下，由PbWO₄直接与“新生态” 崔斌 西北工业大学博士论文的Fe。0。反应形成焦绿石相PbFeWO。。；而删 是在较高的温度下，Pbbo4继续与Pbo反应生成PbW。0。，然后Pbb。0。才能与反应活性差和分散性差的Fe。0。反应形成PbFeFO。。；最后再转化为钙钛矿结构的PFW。在SCM法中，PFW和州N干T的反应机理的区别是，前者形成的中间相为PbFeWO。。，后者的中间相为比。Nb。0。。 在比、Pbo－Bi公、Ph(Cd；／zw；／。川。、Ph（Cll；／。W；；。）0。和“ 作为PW－PT陶瓷助烧剂的研究中发现，Pbo作为助烧剂，属于液相烧结机制，在烧结中后期，Pbo会停留在晶粒表面，因稀释铁电相而恶化介电性能。在比 和Bi。0。作为复合助烧剂，相比单独采用阶 助烧剂的介电性能明显提高；Ph（Cd；／；W；／。）03和盯（Cll；／。W；／。）0。均为钙钛矿结构，前者能够明显降低PWi－PT陶瓷的介电损耗，后者能够明显提高陶瓷样品的致密度。Cdo作为助烧剂，能够进入复合钙钛矿结构的A位而取代铅，因此形成晶格缺陷而促进烧结。添加 2．0（mol）％的比 或 3．0（mol）％的阶（Cd1。zw；。。）0。、Ph(Cll；；ZW；；。川。、Pbo－Bi仙混合助烧剂（摩尔比为1：1：1）都达到了理想的助烧效果，可将烧结温度降低到900oC，且介电性能优良，样品介电常数分别不小于IS000和 22000，介电损耗分别不大于 0．05和 0．15。 在PW－PNN－PT体系中，当烧结温度高于1000oC时，钙钛矿相开始分解，使陶瓷成为“芯－壳”结构，介电常数虽然降低，但介电温度稳定性提高了。制备介电温度稳定性高的陶瓷的合适烧结温度为1100～1150oC；添加过量吨 有利于稳定钙钛矿相和提高陶瓷的介电常数：过量的 和wo。明显使陶瓷的钙钛矿相含量减少，介电常数降低，但有利于陶瓷“芯一壳”结构的形成及其介电温度稳定性的改善；Pbo过量的缺点是导致陶瓷的介电损耗增大。 “芯一壳”结构的形成机制是：在过量WO。和较高的烧结温度下，钙钛矿相分解成钨酸铅液相，从过渡层向晶粒边界（壳层）扩散，其结果使过渡层的W减少，富集Nb、Ti、Ph；壳更多还原

【Abstract】 Semichemical Method(SCM),which have characteristics of both Chemical Method (CM) and Conventional Milled Oxides(CMO),as a new preparation method of Lead based relaxor ferroelectrics was proposed in this paper. Some ceramics(i.e. PMN,PNN,PFW-PT,PMN-PNN-PT) were prepared by the Method. The effects of technological parameters (such as calcining temperature,sintering temperature and soaking time),PbTiO3,excess of some reactants and additives on the phase content,microstructure and dielectric properties were investigated systematically. The difference of Semichemical Method with CMO and CPM was compared. The formation mechanism of PMN-PT and PFW calcined powders prepared by SCM was investigated by means of XRD and DTA DSC techniques. Combined Core-Shell method with SCM,PMW-PNN-PT ceramics with core-shell structure,which have excellent dielectric temperature stability,were successfully prepared. The new mechanism of improving temperature stability of dielectric properties was put forward. The main contents are listed as bellows:In the systems of PMN-PT,the effects of the chemical reactivities of the starting materials such as soluble Mg-salts instead of MgO,Pb-salts instead of PbO and Ti(OC4H9)4 instead of TiO2 respectively on the formation of perovskite phase were investigated in detail. The results show that Mg-salts are effective for the formation of perovskite phase,especially Mg(NO3)2 and/or Mg(AC)2 instead of MgO in a molecular grade. Almost pure perovskite phase were obtained by using Mg-salts and Ti(C4H9O)4 instead of MgO and TiO2 respectively. The optimum preparation parameters are:the calcining condition of 800C-85(rC,2h-4h and the sintering condition of 950-1200,lh-2h.In the systems of PNN-PT,the content of perovskite phase increased rapidly from 800 C to 850 C. The formation of perovskite phase for PNN-PT was more effective than that of PMN-PT system prepared by SCM. Almost pure perovskite phase were prepared without excess NiO or adding PT. The optimum technological parameters are listed:the calcining condition of 850C,2h-3h and the sintering condition of 1100C - 1200C,lh-2h. With the increment of MnO2 content,dielectric loss decreased drastically,but the dielectric constant decreased slightly. When the excess content of MnO2 was 0.5(mol)%,the above properties are optimum.In the systems of PFW-PT,the effects of excess PbO,and Fe2O3,the content PT on the phase structure,microstructure and dielectric properties of PFW ceramics were investigated respectively in detail. The results revealed that by adding excess PbO and Fe2O3,not only the content of perovskite phase in calcined powders and sintered ceramics increased,but also the dielectric constant increased,especially. However,the dielectric loss decreased clearly by adding excess Fe2O3. The dopped MnO2 were effective for stabilization of perovskite phase. With increasing of MnO2 content,the dielectric constant increased gradually at first,then decreased with more MnO2 content,and the dielectric loss greatly decreased and resistivity increased clearly. When the excess content of MnO2 was 1.0(mol)%,the above properties are optimum. With increasing of PT content,grain size,density,Curie temperature and increased slightly,and the diffuse phase transition 6 decreased.Compared with CMO and CPM,SCM had many advantages not only simpling preparation process,lowing calcining and sintering temperatures,shorting reacting time,but also preparing ceramics with excellent dielectric properties. With identical calcining conditions,the content of perovskite phase in calcined powders prepared by SCM was much higher than that by CMO,what’s more,by SCM,the sintered ceramics had clear crystal boundaries,large-sized crystal grains and high density. Without PT as stabling perovskite phase,pure perovskite phase of PMN,PNN and PFW ceramics were successfully prepared by SCM.By analyzing the XRD and DTA or DSC data,the reaction mechanism of SCM in the systems of PMN-PT and PFW ceramics are described as follows. As for PMN-PT systems,unstable and B-site vacant pyroch更多还原