【作者】 郑克玉；

【导师】 张端明；

【作者基本信息】 华中科技大学 ， 凝聚态物理， 2009， 博士

【摘要】 随着信息时代的到来,现代社会的发展需要越来越多品种各异和性能独特的功能材料。铁电体材料作为一类重要的功能材料,以其优异的介电压电性能、热释电性能和光学性能等得到广泛的关注和研究。掺镧的锆钛酸铅[（Pb,La）（Zr,Ti）O₃,PLZT]和钽铌酸钾（KTN）是重要的铁电陶瓷材料。PLZT不仅具有优越的透光性和电光性,而且具有良好的压电和介电特性,是制备电容器、压电传感器、光转换、光存储和微驱动器等的良好材料。KTN材料具有良好非线性光学效应、热释电效应,在计算机显示、激光全息存储以及光电子等领域展示着良好的应用前景。为了达到实用化的要求,低制备条件和高性能获得仍然是一个具有挑战性的课题。因此,探索和研究纳米尺度铁电材料及所具有的性能,丰富和发展相关制备方法,对于基础研究和开拓新材料应用领域有着重要意义。本文在系统总结和全面分析PLZT、KTN铁电材料研究现状的基础上,对两种铁电材料的设计、超微粉合成和细晶粒陶瓷的制备,以及所获得新材料的铁电压电性能、光学性能等进行了有益的探索。论文主要研究内容如下:1.系统研究了采用原材料为无机盐和有机盐的溶胶-凝胶法（sol-gel）制备出单颗粒尺寸≤50nm、团聚体尺寸≤100nm的PLZT超微粉,这不仅解决了进口原材料问题,也简化了制备工艺,使合成在分子级别上进行,利于制备高质量铁电粉体,利于产业化。探讨了PLZT前躯体溶液的水解、聚合反应机理,并且就合成温度和保温时间对PLZT纳米粉的物相形成、粉体形貌的影响进行了研究。2.以sol-gel方法合成的钙钛矿型PLZT超微粉为原料制备出晶粒尺寸≤500nm亚微米细晶粒陶瓷,比普通固相法烧结的陶瓷粒径（1.56μm）小得多。对制备出的陶瓷试样进行结构、形貌和介电压电性能测试分析,找出最佳制备细晶粒陶瓷的工艺参数:PLZT超微粉合成条件为600℃×1.5h,烧结条件为1150℃×1.5h,得到PLZT陶瓷的介电、压电性能俱佳,陶瓷的压电参数d₃₃=595,室温介电常数ε_r=5108,介电损耗tgδ=0.02347.陶瓷烧结温度也低于普通固相法烧结成瓷温度（1230-1300℃）.3.在PLZT超微粉中掺杂钛酸锶钡（BST）纳米粉,制备PLZT改性陶瓷,其介电、压电性能较佳,BST掺杂量为1mol%时陶瓷的性能最好,压电参数d₃₃=508,室温介电常数ε_r=8315,介电损耗tgδ=0.035.研究发现掺BST后,PLZT材料的电滞回线变窄,矫顽场变小,自发极化和剩余极化减小。4.以超微粉制备的PLZT陶瓷最高介电常数达15404,对应的相变温度为212℃,这与普通固相烧结的情况接近。在PLZT超微粉中掺杂Mg²⁺所制得陶瓷介电温谱曲线较未掺杂时向高温方向移动,PLZT相变温度提高;当掺杂K⁺时,ε最大值对应的温度为150℃,Tc显著变小,而室温介电常数与未掺杂时相差不大。这对PLZT材料在器件方面的应用非常有意义。5.从理论角度进一步研究颗粒尺寸大小对PLZT的介电性能的影响,确立介电常数ε_r与四方度c/a的基本关系式。6.对KTN水热合成工艺作了系统研究,首次对KTN的微电子结构以及光吸收性能和光发射性能进行了表征,讨论工艺条件对KTN陶瓷相结构以及光吸收性能和光发射性能的影响。随KOH的浓度或反应温度的增高,KTN粉体的晶相结构由立方相向铁电四方相转变,并且晶格参数c/a比值增大,四方度增强。获得铁电压电系数高的四方相KTN粉的较佳工艺条件是KOH的浓度为16M、反应温度240℃、反应时间24小时。KOH的浓度大小决定了KTN材料的禁带宽度的大小。随KOH的浓度增加,禁带宽度增大,最大吸收波长向短波方向移动,发生蓝移现象,影响其光响应范围。7.利用KTN中的B位高价离子置换,制备了W⁶⁺掺杂改性的KTN陶瓷样品。研究了W⁶⁺掺杂对KTN材料结构和电性能的影响。实验结果表明,W⁶⁺掺杂量为6mol%时,KTN的电导率较纯KTN下降了一半;在200V时,W⁶⁺掺杂量为8mol%的漏电流为8.71×10^-4A,纯KTN漏电流为5.14×10^-3A,使漏电流减小了5倍。通过掺杂的方式,成功的降低了KTN陶瓷的漏电流,有利于提高陶瓷的铁电压电性能。更多还原

【Abstract】 With the advent of information society, more and more functional materials withnovel properties are needed. Ferroelectric materials as extremely important functionalmaterials have received considerable attention due to their excellent ferroelectric,piezoelectric, pyroelectric, and electro-optic properties. （Pb, La）（Zr, Ti）O₃ （PLZT） andKTN are very important ferroelectrics. PLZT is considered to be the promising candidatefor capacitors, transducers, micro-actuator as well as optical storage devices because of itsexcellent ferroelectric, dielectric and electro-optic properties. KTN with attractivequadratic and nonlinear electrooptic properties, as well as a high dielectric permittivityand large piezoelectric and pyroelectric coefficients can be used in many important fieldssuch as volume phase holographic storage, real time optical information processing, andIR detectors electro-optic devices. For the purpose of application, challenge still exists inreducing the synthesis cost and improving the properties of the materials. Therefore,finding new synthesis strategies and investigating their new properties are very importantnot only for fundamental research but also for applied research of the materials.This thesis gives a brief review of the latest development of PLZT and KTN, andthen a description of the synthesis of PLZT and KTN ultrafine powders and fine-grainedceramics. The ferroelectric, dielectric and the optical properties have also beeninvestigated. The main content is described as follows:1. PLZT ultrafine powders in sizes of < 50 run were synthesized by sol-gel method.The new synthesis method not only reduced the cost of the raw materials but alsosimplified the preparing process. The improvement made the synthesis reaction occuramong the molecules which is very helpful for improving the properties and realizingindustrialization. The mechanisms of precursor hydrolysis and polymerization have beendiscussed.The preparing parameters such as reaction temperature and reaction time havealso been investigated in detail.2. Using the ultrafine powder, PLZT fine-grained ceramics with grain size of≤500nm were prepared. The grain size of the as-prepared ceramics is much smaller than that ofthe ceramics （1.56μm） derived from traditional solid state reaction. The optimizedsintering time and temperatures were obtained. The powders were annealed at 600℃for1.5 h and the ceramics were sintered at 1150℃for 1.5 h. The electric measurements revealed that the d₃₃= 595,ε_r= 5108, tgδ= 0.02347. The sintering temperature ofceramics fabricated by ultrafine powders was lower 50-80℃than that of traditional solidstate reaction.3. The modified PLZT ceramics were fabricated by doping BST nanopowders intoPLZT ultrafine powders. The ceramics with lmol% BST doping show good piezoelectricand dielectric properties: d₃₃= 508,ε_r= 8315, tgδ= 0.035. With the increase of the dopingcontent of BST, the PLZT ceramics exhibit lower spontaneous polarization and lowercoercive field comparing to the pure PLZT ceramics.4. The Curie temperature of the PLZT ceramics derived ultrafine powders is 212℃.Dielectric constant of those is up to 15404. The Curie temperature of the ceramics bydoping with Mg²⁺ shifts to high temperature. While it shifts to low temperature by dopingwith K⁺. These characters of PLZT materials are useful for its application.5. The grain size dependence of dielectric properties were investigated, and therelationship ofε_r and cla were obtained in theory.6. KTN nanomaterials were prepared by using hydrothermal method. The electronstructure, UV-Vis absorption and photoluminescence properties have been investigated.The phase structure of the KTN nanopowders transferred from cubic to tetragonal phasewith the increase of the KOH content. The cla value increases too. The precursors with 16M KOH were treated at 240℃for 24 h and KTN nanopowders of tetragonal structure canbe obtained. The band gaps of the KTN nanopowders increase with the increase of theKOH content. The KTN ceramics were prepared by the hydrothermal derived powdersand their optical properties were also investigated.7. The effects on the microstructures and electric properties of KTN by doping withW⁶⁺ ions have been investigated. The KTN conductivity decresed a half compared withthat of pure KTN by doping with 6mol% W⁶⁺ ions. The leakage current of KTN ceramicswhich were doped 8mol% W⁶⁺ions is 8.71×10^-4A. It is one-sixth times of that of pureKTN ceramis (5.14×10^-3A). It is clear that W⁶⁺ doping can reduce the leakage current ofthe KTN materials and improve their ferroelectric and piezoelectric properties.更多还原