铌酸钾钠基无铅陶瓷的压电及其稳定性研究

发布时间：2018-07-15 10:15

【摘要】：随着人们对环境问题关注度的增加,压电材料的无铅化是未来发展的方向。(K,Na)NbO_3基无铅压电陶瓷被认为是最有潜力替代传统锆钛酸铅(PZT)的材料之一,引起了人们的广泛关注。本文从压电材料实用化的要求出发,围绕(K,Na)NbO_3基压电陶瓷的电学性能及其稳定性的表征与增强开展了系统的研究。首先,利用Mn掺杂及极化调控的方法提高了(K,Na)NbO_3基陶瓷的压电性能。发现在(K,Na)NbO_3基陶瓷中掺入适量的MnO2可显著提高压电性能,压电常数d33由214提高至351 pC/N,增幅达64%,并深入研究了Mn离子在ABO_3钙钛矿结构的占位机制;同时,通过优化极化温度也可将其压电性能提高约15%,基于对不同极化温度下电滞回线的深入分析,提出了一种基于畴翻转与空间电荷聚集竞争的极化理论模型。其次,提出了一种基于压电常数-电场d33(E)曲线原位表征压电常数温度稳定性的方法。有别于传统的退火-测试非原位表征途径,该方法可原位、实时地测量压电常数随温度的变化。采用d33(E)曲线原位研究了Li/Ta/Sb共掺杂(K,Na)NbO_3陶瓷压电常数d33的温度稳定性,并发现随温度升高,其d33呈单调递减趋势,至120oC时降低约40%,这与高温偏离其多晶型相变区有关。为提高(K,Na)NbO_3基陶瓷的温度稳定性,在基体中引入CaZrO_3以减小正交、四方两相的差异,实现多晶型相变的平稳过渡。结果表明5%mol CaZr O_3掺杂(K,Na)NbO_3基陶瓷不仅具有很好的压电性(d33=357pC/N),且其场致应变表现出优异的温度稳定性,可与商业化的PZT相媲美。结合原位变温变电场同步X射线衍射、压电力显微镜等实验手段与第一性原理计算,发现CaZrO_3掺杂(K,Na)NbO_3基陶瓷良好的温度稳定性来源于场致弥散相变。最后,研究了CaZrO_3掺杂(K,Na)NbO_3基压电陶瓷的抗疲劳性能,包括单极、双极及倍半极电场循环模式。该材料在三种电场循环模式下,均表现出优异的抗疲劳特性。深入研究表明抗单极疲劳性能的提高与疲劳过程中存在软化效应与空间电荷聚集的竞争有关;CaZrO_3的引入可降低陶瓷的c/a比,从而有利于其抗双极疲劳性能的增强;倍半极模式介于单极与双极之间,因此样品也表现出很好的抗倍半极疲劳性能。在此基础上,研究了温度及电场强度对其单极疲劳特性的影响,揭示温度较电场强度更加影响(K,Na)NbO_3基陶瓷的单极疲劳性能。
[Abstract]:With the increasing attention to environmental problems, lead-free piezoelectric materials are the future development direction. (Knna) NbO3-based lead-free piezoelectric ceramics are considered as one of the most potential materials to replace the traditional lead zirconate titanate (PZT), which has attracted wide attention. Based on the practical requirements of piezoelectric materials, the electrical properties and their stability of (Knna) NbO3-based piezoelectric ceramics have been systematically studied in this paper. Firstly, the piezoelectric properties of (Knna) NbO3-based ceramics were improved by mn doping and polarization control. It is found that the piezoelectric properties of (Knna) NbO3-based ceramics can be improved by adding a proper amount of MnO2. The piezoelectric constant d33 is increased from 214 to 351pC / N, an increase of 64. The occupation mechanism of mn ions in ABO3 perovskite structure is also studied. By optimizing the polarization temperature, the piezoelectric properties can also be improved by about 15%. Based on the in-depth analysis of the hysteresis loop at different polarization temperatures, a polarization theoretical model based on the competition between domain flipping and space charge aggregation is proposed. Secondly, a method of in-situ characterization of temperature stability of piezoelectric constant based on piezoelectric constant and electric field d 33 (E) curve is proposed. This method can be used to measure the change of piezoelectric constant with temperature in situ, which is different from the traditional non-in-situ method of annealing and testing. The temperature stability of the piezoelectric constant d33 of Li / Ta-Sb co-doped (Knna) NbO3 ceramics was studied by using d33 (E) curve in situ. It was found that the D33 decreased monotonously with increasing temperature, and decreased by about 40% at 120oC, which was related to the deviation of high temperature from its polycrystalline phase transition region. In order to improve the temperature stability of (Knna) NbO _ 3 based ceramics, CaZrO _ 3 was introduced into the matrix to reduce the difference between the orthogonal and tetragonal phases and to realize the smooth transition of the polycrystalline phase transition. The results show that 5%mol CaZr O 3 doped NbO 3 ceramics not only have good piezoelectric properties (d337pC / N), but also show excellent temperature stability in field-induced strain, which can be compared with commercial PZT ceramics. In combination with in-situ thermoelectric field synchronous X-ray diffraction, pressure-power microscopy and first-principle calculation, it is found that the good temperature stability of CaZrO3-doped (Knna) NbO3-based ceramics originates from field-induced dispersion phase transition. Finally, the fatigue resistance of CaZrO3-doped (Knna) NbO _ 3 based piezoelectric ceramics was investigated, including unipolar, bipolar and double hemipolar electric field cycling modes. The material exhibits excellent fatigue resistance under three electric field cycling modes. The further study shows that the improvement of the anti-unipolar fatigue property is related to the softening effect and the competition of space charge accumulation in the fatigue process. The introduction of CaZrO _ 3 can reduce the c / a ratio of the ceramics, which is beneficial to the enhancement of the anti-bipolar fatigue performance of the ceramics. The double haptic mode is between the unipolar and the bipolar, so the sample also shows good fatigue resistance. On this basis, the effects of temperature and electric field strength on the unipolar fatigue properties of (Knna) NbO3-based ceramics were studied. It was revealed that the temperature had more influence on the unipolar fatigue properties of (Knna) NbO3-based ceramics than the electric field strength.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ174.1

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