【作者】 庞旭明；

【导师】 裘进浩；

【作者基本信息】 南京航空航天大学 ， 材料加工工程， 2012， 博士

【摘要】 本论文采用X射线衍射（XRD）、扫描电镜（SEM）、差式量热分析（DSC）、透射电镜（TEM）、拉曼光谱分析等实验手段系统地研究了（K, Na）NbO₃基无铅压电陶瓷的成分、制备工艺、组织结构和性能等之间的关系。首先计算了不同成分K_xNa_1-xNbO₃固溶体的价电子结构，并研究了价电子结构与压电性能的关系。计算结果指出：当x在0.4和0.5之间变化时，压电常数几乎不变。压电常数在所谓的准同型相界附近没有出现显著的增加。实验结果和计算结果也符合的相当好。与典型的准同型相界不同，该体系的准同型相界并未使压电和介电性能显著提高。这意味着传统准同型相界在铌酸钾钠体系中是不存在的。研究了ZnO、CuO和K_5.70Li_4.07Nb_10.23O₃₀作为烧结助剂对陶瓷组织和性能的影响。研究表明，由于ZnO的掺杂，陶瓷的密度、压电和介电性能得到显著的提高。在K_5.70Li_4.07Nb_10.23O₃₀含量低于1mol%时，晶粒出现异常长大。适量的KLN可以减少缺陷的数量，因此可以显著地提高剩余极化强度以及降低矫顽场。陶瓷的烧结特性和压电性能同时提高。CuO掺杂可以大大提高其机械品质因数。当添加量为1.5moL%时，获得了具有最佳性能的压电陶瓷。通过添加Bi₂O₃和Li₂CO₃研究（K）（0.5）Na_0.5)NbO₃压电陶瓷的低温烧结技术。在900oC烧结5h可以制备压电性能良好的陶瓷，其介电常数ε、压电常数d33和机电耦合系数kp分别为877、92pC/N和0.27。综合性能可以与高温烧结的（K）（0.5）Na_0.5)NbO₃压电陶瓷相媲美。研究了（K, Na）NbO₃基固溶体的烧结过程和机理。研究表明，（K, Na）NbO₃基固溶体在400-800℃范围内通过A₂CO₃（A: K、Na、Li）和B2O5（B: Nb、Ta、Sb）固相反应生成。根据固相反应机理，此过程由扩散机制控制。（K, Na）NbO₃基陶瓷的烧结动力学为晶界扩散。研究了烧结温度对(K_0.4425Na_0.52Li_0.0375)(Nb_0.8925Sb_0.07Ta_0.0375)O₃压电陶瓷的显微组织相结构的变化和电性能的影响。当温度低于1130℃时，材料为正交结构，温度继续升高时，其结构为四方相。由于处在类似准同型相界的相界附近，在1120℃烧结无铅压电陶瓷的压电性能最高。对（K, Na）NbO₃基无铅压电陶瓷两步烧结进行研究。实验表明，在最佳的烧结条件下，陶瓷组织致密，晶粒尺寸为5μm，并且陶瓷具有良好的介电和压电性能。此外，随着温度的变化，压电陶瓷具有低的介电损耗。研究了Ta和Sb含量对(K_0.4425Na_0.52Li_0.0375)(Nb_0.9625-xSb_xTa_0.0375)O₃压电陶瓷的相结构、显微组织、介电、压电及铁电性能的影响。随着Sb的量从5mol%逐渐增加到9mol%，所有试样为钙钛矿结构，并且晶粒尺寸逐渐增大。成分为(K_0.4425Na_0.52Li_0.0375)(Nb_0.8925Sb_0.07Ta_0.0375)O₃陶瓷的压电性能最优。随着Ta掺杂量的提高，压电常数d33和平面机电耦合系数kp增大，机械品质因数Q_m减小。Ta含量的增加同时会降低居里温度，减弱铁电性。当x=0.0375时，获得了具有最佳性能的压电陶瓷。更多还原

【Abstract】 In this dissertation, the relationship among composition, manufacturing process, microstructureand properties of fine grained （K, Na）NbO₃-based piezoelectric ceramics have been systematicallyinvestigated by X-ray diffraction （XRD）, scanning and transmission electron microscopy （SEM andTEM）, differential scanning calorimeter（DSC）, and Raman Spectroscopic Analysis.The valence-electron structures （VES） of sodium-potassium niobat(eK_xNa_1-xNbO₃)were calculated,and the relationship between the VES and the piezoelectric properties was determined. The resultsindicate that the piezoelectric constants are continuous and equal in the composition range of0.4≤x≤0.5. The piezoelectric properties do not dramatically improved at the so-called MPB. Theexperimental results show that the change trend of the piezoelectric constants is in good agreementwith the calculation results. Contrary to traditional MPB, the so-called morphotropic phase boundaryof sodium-potassium niobate has no significant influence on the piezoelectric and ferroelectricproperties. In other words, it was speculated that the existence of the traditional morphotropic phaseboundary was possibly controvertible in the KNN system.The influence of the ZnO, CuO, and K_5.70Li_4.07Nb_10.23O₃₀（KLN） as sintering aids on themicrostructure and properties has been studied. Our results reveal that a small amount of ZnO canimprove the density of the ceramics effectively. Because of the high density and ZnO doping effects,the piezoelectric and dielectric properties of the ceramics are improved considerably. Some abnormalcoarse grains were formed in a matrix when the content of KLN was relatively low1mol%. Propercontent of KLN decreased the amount of defects, thus the remnant polarization increased and thecoercive field decreased markedly, and the sinterability of the KNN ceramics was simultaneouslyimproved with significant increase of piezoelectric properties. The mechanical quality factor Qmcouldsignificantly be improved for “hardening” effect of the Cu2+-doped. For the ceramics with1.5mol%,the best performance of piezoelectric ceramic was obtained.Low temperature sintering of （K）（0.5）Na_0.5)NbO₃was investigated using Bi₂O₃and Li₂CO₃assintering aids. The optimal piezoelectric properties are obtained for the ceramics sintered at900oC for5h. The dielectric constant （ε）, piezoelectric coefficient （d33）, and electromechanical couplingcoefficient （kp） show peak values of877,92pC/N, and0.27, respectively. These values arecomparable to the values obtained for （K）（0.5）Na_0.5)NbO₃ceramics sintered above1100oC.The sintering process and mechanism of （K, Na, Li）（Nb, Ta, Sb）O3（KNLNTS） solid solution were investigated. The results show that the KNLNTS forms via the reaction of A₂CO₃（A: K、Na、Li） andB2O5（B: Nb、Ta、Sb） at400-800℃. Based on the reaction kinetic isothermal analysis, KNLNTSformation is corroborated as being controlled by diffusion mechanism. The sintering process in theKNLNTS solid solutions may be explained by the grain boundary diffusion model.Microstructure characteristics, phase transition, and electrical properties of (K_0.4425Na_0.52Li_0.0375)(Nb_0.8925Sb_0.07Ta_0.0375)O₃（KNLNST） lead-free piezoelectric ceramics were investigated with anemphasis on the influence of sintering temperature. Orthorhombic phases mainly exist in the ceramicssintered at1100–1130℃, whereas the tetragonal phase becomes dominant when sintering temperatureis above1130℃. Because of the existence of MPB-like transitional behavior, the piezoelectricproperties show peak values at1120℃.Two-step sintering was investigated to manufacture (K_0.5Na_0.5)NbO₃-based lead-free piezoelectricceramics. Under the optimal condition, dense specimens have an average grain size of approximately5μm, and show good dielectric and piezoelectric properties. Furthermore, the (K_0.5Na_0.5)NbO₃-basedceramics maintain relatively low dielectric loss over wide temperature ranges.The effects of the Ta and Sb content on the phase structure, microstructure, dielectric, piezoelectric,and ferroelectric properties of the (K_0.4425Na_0.52Li_0.0375)(Nb_0.9625-xSb_xTa_0.0375)O₃ceramics wereinvestigated. By increasing x from0.05to0.09, all samples exhibit a single perovskite structure withan orthorhombic phase over the whole compositional range. The grain growth of the ceramics wasimproved by substituting Sb5+for Nb5+. The (K_0.4425Na_0.52Li_0.0375)(Nb_0.8925Sb_0.07Ta_0.0375)O₃ceramicsshow the peak values of the piezoelectric properties. By increasing x from0.03to0.0675, thepiezoelectric performance appears regular change over the whole compositional range, owing toimprovements in d33, kpand a decease in Q_m. Curie temperature TCshift toward lower-temperatureregions by increasing the content of Ta, and Ta would weaken the ferroelectricity of the ceramics. Theoptimal performance of piezoelectric ceramic was obtained at x=0.0375.更多还原