摘要
掺杂是在ABO3钙钛矿结构压电陶瓷中获得大压电效应的重要途径，掺杂造成相不稳定通常是大压电效应的内在来源，如准同型相界(MPB)和多型性相变(PPT)，在ABO3压电陶瓷中是否还有其他获得大压电效应的机制一直受到广泛关注。本文利用固相合成法合成A位施主-受主(Li+-Al3+)共掺杂的BaTiO3与Pb(Zr,Ti)O3体系陶瓷，表征了陶瓷的物相及微观结构，测试陶瓷的介电、铁电与压电性能，探讨掺杂提高压电性能的原因，提出一种获得大压电效应的掺杂路线，阐明了这种掺杂路线的压电机制。
在ABO3结构氧化物的合成过程中有氧空位的产生，氧空位使BaTiO3有从绝缘体向导体转变的趋势。在ABO3体系中施主与受主共掺杂可以有效的降低氧空位缺陷的产生，在Li+与Al3+共掺杂的BaTiO3陶瓷中，X射线衍射(XRD)结果表明Li+与Al3+有占据同一单胞的相邻A位，在[001]pc方向择优取向排列的趋势，通过第一性原理分析证明了这种排列的合理性与可行性。在掺杂后陶瓷的电畴中，发现不同于正常电畴的异形畴，这种异形畴被认为是离子对周围畸变电场造成的，异形畴的发现间接地证明了离子对的存在。离子对作为一种偶极子，在温度场与电场的共同作用下可以发生取向化行为，将离子对进行取向化后，陶瓷出现了自建电场，场强达到2.1 kV/cm。掺杂显著提高了BaTiO3陶瓷的压电性能，1 mol%掺杂量下的陶瓷的压电系数(d33)达到300 pC/N，机械品质因数(Q m)高达2000，退极化温度接近居里温度。
为验证这种掺杂方法在ABO3体系陶瓷中的普适性，系统研究了掺杂对不同相区的PZT陶瓷的铁电与压电性能的影响。XRD结果表明PZT陶瓷中Li+-Al3+的占位方式与BaTiO3陶瓷中相同，掺杂后的PZT陶瓷中发现束腰电滞回线，这种电滞回线来源于离子对产生的电偶极矩对电畴内部自发极化的影响，束腰电滞回线几乎没有弛豫特性。压电性能结果表明掺杂对四方相区附近的PZT陶瓷的压电性能有积极作用，对菱方相区附近的PZT陶瓷压电性能几乎没有影响，掺杂显著拓宽了PZT陶瓷的最优性能区间。
介温谱与高温XRD数据表明掺杂造成四方相陶瓷的四方-立方相变在较宽的温度区间内完成，具有弥散性，利用Landau-Ginzburg-Devonshire理论分析了掺杂应力对T相的BaTiO3、PZT陶瓷和R相的PZT陶瓷中铁电-顺电相的势垒高度的影响，计算发现应力使得T相陶瓷的势垒高度明显降低，但对R 相陶瓷的势垒高度几乎没有影响，基于唯象理论解释了该种掺杂提高压电性能的原因-应力诱导自由能曲面平坦化，最后，计算了可以使不同相结构(四方相，
正交相和菱方相)ABO3体系势垒高度下降的敏感应力方向，为在其他ABO3体系中通过该种掺杂路线获得大压电效应提供理论支持。
关键词：压电陶瓷；离子对；缺陷偶极子；束腰电滞回线；压应力；自由能曲面平坦化
Abstract
Doping is a significant method to obtain large piezoelectric effect in ABO3 perovskite structure piezoelectric ceramics. The pha instability induced by doping is usually the intrinsic source of large piezoelectric effect, such as Morphotropic pha boundary (MPB) and Polymorphic pha transition (PPT), Whether there are other intrinsic mechanisms for obtaining large piezoelectric effects in the ABO3system have been widely concerned. (Li+-Al3+) co-doped BaTiO3and Pb(ZrTi)O3ceramics were synthesized by conventional sintering method. The pha structure and microstructure of the ceramics were characterized. The dielectric, ferroelectric and piezoelectric properties are carried out. The reason for enhanced piezoelectricity related to this doping is discusd. The prent study provides a promising route to the large piezoelectric effect in the ABO3, and reveals the mechansm for the enhanced piezoelectricity.
Oxygen vacancy, as a kind of the defects will appear in the synthesis process of ABO3 structural oxides. The electrical properties of BaTiO3 containing oxygen vacancies are more like conductor, which suggests that the defects have great influence on the electrical properties of BaTiO3. In the ABO3system, the donor and acceptor co-doping can guarantee the local electricity of the lattice, and inhibit the formation of oxygen vacancy defects. The X-ray diffraction (XRD) results show that Li+ an
d Al3+ ions are inclined to occupy the neighboring A-sites (along the [001] pc direction) in the lattice. The DFT analysis proves the rationality and feasibility of this occupation. In the process of investigating domain structure, the abnormal domain structure which is resulted from the electricfield distortion around ionic pairs is found. The discovery of the domain also confirms the ordering distribution of the ionic pair. Besides, the orientation of ionic pair is achieved under the action of temperature- and electric- field. The bias (about 2.1 kV/m) is obrved in the BLAT (1 mol%) ceramics including oriented ionic pairs. BLAT (1 mol%) exhibits largely thermo-stable piezoelectric constant (d33≈300 pC/N) and huge mechanical quality factor (Q m>2000). The depolarization temperature is clo to the Curie temperature.
In order to verify the universality of this doping in ABO3systems, the ferroelectric and piezoelectric properties of PZT ceramics with various symmetries (T, M or R) doped by Li+and Al3+ were systematically studied. Similar XRD results obtained in doped PZT ceramics suggest that the distribution of Li+-Al3+ in PZT is as same as that in BLAT. A contricted hysteresis loop is found in the doped
PZT ceramics, which is derived from the effect of the dipole moment generated by the ionic pair on the spontaneous polarization inside the domain. This constricted hysteresis loop induced by ionic pairs does not exhibit relaxation characteristics. This doping can largely affect the tetragonal crystal symmetry and the corresponding piezoelectric properties. For the rhombohedral lattice, doping has little effect on their structure and properties. The composition range for the optimum properties in doped PZT has the potential to be expanded (0.46≤Ti≤0.51).
The dependence of dielectric properties and in-situ XRD results indicate that the T-C pha transition is completed in a wide temperature range, namely, diffu. Bad on the fact that lattice distorstion is related to the doping stress, the effect of stress on the free energy profiles of BT, PZT(40/60) and PZT(60/40) is analysized in the framework of the Landau-Ginzburg-Devonshire (LGD) theory. The results show that the energy barrier between the ferroelectric and paraelectric phas in the BT and PZT(40/60) will decrea with the compressive stress. The energy barrier of PZT(60/40) is innsitive to this kind of stress. The above analysis explains the reason why the dopant improves the piezoelectric properties of T-pha BT and PZT ceramics. A piezoelectricity enhancement mechanism related to the stress-driven flattening of a free-energy profile is propod. Finally, the nsitive stress direction for the ABO3with the different pha structure can be calculated.
This study provides theoretical support for obtaining the large piezoelectric effect through this doping route in other ABO3 systems.专业英语
赚钱的句子
Keywords: piezoelectric ceramic, ionic pairs, defect dipole, constricted hysteresis loop, compressive stress, flattening of free energy profile
任务栏消失
目录
摘要......................................................................................................................I Abstract ................................................................................................................. I II
胸部护理
第1章绪论 (1)
1.1 课题背景及研究的目的和意义 (1)
1.2 ABO3钙钛矿型压电陶瓷 (1)
1.2.1 ABO3型含铅压电陶瓷 (2)
1.2.2 ABO3型无铅压电陶瓷 (3)
1.3 ABO3钙钛矿型压电陶瓷中的大压电效应 (6)
1.3.1 大压电效应的内在因素 (6)
1.3.2 大压电效应的外在因素 (8)
1.4 A2+B4+O3钙钛矿型压电陶瓷的离子掺杂 (9)
1.4.1 A2+B4+O3压电陶瓷的B-位掺杂 (9)
1.4.2 A2+B4+O3压电陶瓷的A-位掺杂 (11)
1.5 ABO3钙钛矿型压电陶瓷中的缺陷偶极子 (12)
1.5.1 缺陷偶极子的组成与特性 (12)
1.5.2 缺陷偶极子的弛豫与储能 (15)
1.6 本文的研究内容 (17)
第2章试验材料及方法 (19)
2.1 试验材料 (19)
学生手册心得体会2.1.1钛酸钡纳米线与聚合物基体材料 (19)脾湿热
2.1.2钛酸钡陶瓷材料 (19)
2.1.3锆钛酸铅陶瓷材料 (20)
2.2材料制备工艺 (20)
庶妾2.2.1钛酸钡纳米线的制备 (20)
宠物猫价格排行
2.2.2聚合物基复合材料的制备 (20)
2.2.3钛酸钡压电陶瓷的制备 (21)
2.2.4锆钛酸铅压电陶瓷的制备 (23)
2.3材料的结构表征 (23)
2.4 材料的电学性能测量 (24)
