【作者】 李旭东；

【导师】 郑鹏；

【作者基本信息】 杭州电子科技大学 ， 电子与通信工程， 2020， 硕士

【摘要】 压电材料是一类实现机械能与电能相互转换的重要功能材料,广泛应用于制造传感器、驱动器、超声换能器、谐振器、滤波器等多种电子元器件,在国民经济、科学技术、现代国防等各个领域有着重要的应用。近年来,随着航空航天和核工业的快速发展,对于可以在500℃或更高温度下运行,且平均故障时间间隔较长的传感器的需求急剧增加。然而,传统的PZT基压电陶瓷和当前广泛研究的无铅压电陶瓷体系(BCZT、KNN、BNT等)受限于较低的居里温度,无法胜任在高温条件下应用。因此,开发新型的高温压电材料和器件是一项具有迫切现实意义的任务。铋层状结构铁电体(简称BLSFs)是由Aurivillius等人于1949年发现的,其结构是由二维钙钛矿层和铋氧层沿着c轴方向规则的交替间隔排列而成。Bi4Ti3O12(BIT)是一种典型的3层铋层状结构铁电体,它是由(Bi2O2)2+层和伪钙钛矿层(Bi2Ti3O10)2-交错堆积而成。由于本身的结构特性,钛酸铋具有高的铁电相变温度(675℃)以及强的铁电性,在高温压电应用领域得到了广泛的关注和研究。然而,同样受限于其自身的结构特点,铁电极化反转被限制在ab面内,导致其压电性能非常低(利用传统的固相反应法制备的BIT陶瓷的d33在8pC/N左右);其次,受制于组分中较高的铋含量,高温烧结过程中易于产生氧空位,导致材料电阻率很低,影响了高温下的电荷输出的稳定性和灵敏度。基于此背景,本文通过B位掺杂混合价态离子调控氧空位浓度,从而实现BIT基压电陶瓷的压电性能和电性能的优化。本文通过固相反应法制备出BIT基压电陶瓷,通过对混合价态离子掺杂下的离子价态、离子半径、电子组态、电负性等因素对BIT基陶瓷的微观结构、晶格畸变、缺陷状态和导电机制的影响研究,掌握基于混合价态离子掺杂的BIT基陶瓷居里温度、压电活性和电阻率的调控方法。在掌握物性规律的基础上,制备兼具高居里温度(Tc>675℃)、高压电活性(d33>30 pC/N)、高温下具有高电阻率(500℃时电阻率ρ>106 Ω·cm)的高性能陶瓷。1、论文中通过固定低价阳离子Cu2+,制备Cu2+/Nb5+、Cu2+/Ta5+、Cu2+/Sb5+、Cu2+/W6+、Cu2+/Mo6+混合价态离子掺杂的BIT基压电陶瓷,探讨混合价态离子掺杂中高价阳离子对陶瓷压电活性、居里温度和电阻率的影响机制。实验结果表明,B位掺杂混合价态离子显著提高了 BIT基压电陶瓷的压电活性,其中通过Cu2+/Nb5+掺杂改性的BIT基陶瓷的压电性能高达38 pC/N,为当前报道的BIT基陶瓷中的最大值,与未掺杂改性相比,d33提高了 5倍;通过对电阻率与复阻抗的测量分析,证明了氧空位在BIT基压电陶瓷导电行为中占主导作用,且相比未掺杂改性的BIT基压电陶瓷,500℃时电阻率ρ提高了 2～3个数量级,尤其是Cu2+/Sb5+掺杂改性的BIT基陶瓷500℃时电阻率ρ=1.40×107 Ω·cm,为当前报道的BIT基陶瓷中的最大值;掺杂改性后的双向疲劳得到了极大地改善,综合性能的提高,与氧空位浓度的降低有着密不可分的关系;压电性能和电阻率显著提高的同时,居里温度TC均保持在672℃以上,没有出现明显地恶化(纯的BIT陶瓷的 Tc～675℃)。2、取上述BIT基压电陶瓷中综合性能最优方案(Cu2+/Nb5+),固定高价阳离子 Nb5+,制备Ni2+/Nb5+、Mn2+/Nb5+、In3+/Nb5+、Cr3+/Nb5+混合价态离子掺杂的BIT基压电陶瓷,尝试压电性能突破40 pC/N,探讨混合价态离子掺杂中低价阳离子对陶瓷压电活性、居里温度和电阻率的影响机制。研究结果表明,改变低价阳离子后,B位掺杂混合价态离子也可以大幅提高BIT基压电陶瓷的压电活性,Mn2+/Nb5+掺杂改性的BIT基陶瓷的压电性能高达34 pC/N;改变低价阳离子后进行混合价态离子掺杂,500℃时电阻率提升了 1～2个数量级,稍逊于之前的实验方案;在600℃温度下退火,压电性能均能保持在90%以上;B位掺杂混合价态离子对居里温度几乎没有影响。更多还原

【Abstract】 Piezoelectric material is an important functional material for converting mechanical energy and electrical energy.It is widely used in the manufacture of sensors,actuators,ultrasonic transducers,resonators,filters and other electronic components,and has important applications in national economy,science and technology,modern national defense and other fields.In recent years,with the rapid development of the aerospace and nuclear industries,the demand for sensors that can operate at 500℃ or higher temperature with a long mean time between failures has increased dramatically.However,conventional PZT-based piezoelectric ceramics and currently widely studied lead-free piezoelectric ceramic systems(BCZT,KNN,BNT,etc.)are limited by lower Curie temperatures and are not suitable for use under high temperature conditions.Therefore,the development of new high-temperature piezoelectric materials and devices is an urgent task.Bismuth layer structure ferroelectrics(abbreviated as BLSFs)were discovered by Aurivillius et al.in 1949,and their structures are arranged by regularly alternating intervals of a two-dimensional perovskite layer and a bismuth oxide layer along the c-axis direction.Bi4Ti3O12(BIT)is a typical three-layered bismuth-structured ferroelectric,which is formed by interlacing a(Bi2O2)2+layer and a pseudo-perovskite layer(Bi2Ti3O10)2-.Due to its structural characteristics,bismuth titanate has a high ferroelectric phase transition temperature(675℃)and strong ferroelectricity,which has received extensive attention and research in high temperature piezoelectric applications.However,due to its own structural characteristics,ferroelectric polarization inversion is limited to the ab plane,resulting in very low piezoelectric performance(the d33 of the BIT ceramic prepared by the conventional solid phase reaction method is around 8pC/N);Secondly,subject to the higher content of bismuth in the composition,oxygen vacancies are easily generated during high-temperature sintering,resulting in low material resistivity,affecting the stability and sensitivity of charge output at high temperatures.Based on this background,this thesis regulates the oxygen vacancy concentration by B-site doped mixed valence ions,so as to optimize the piezoelectric properties and electrical properties of BIT-based piezoelectric ceramics.In this thesis,BIT-based piezoelectric ceramics were prepared by solid-phase reaction method.By studying the influence of ion valence state,ion radius,electron configuration,electronegativity and other factors under mixed valence ion doping on the micro structure,lattice distortion,defect state and conductive mechanism of BIT-based ceramics,master the regulation methods of Curie temperature,piezoelectric activity and resistivity of BIT-based ceramic doped with mixed valence ions.Based on mastering the laws of physical properties,the preparation has both high Curie temperature(TC>675℃),high piezoelectric activity(d33>30 pC/N),and high resistivity at high temperature(resistivity ρ>106 Ω·cm at 500℃)of high performance ceramics.1.The BIT-based piezoelectric ceramics doped with Cu2+/Nb5+,Cu2+/Ta5+,Cu2+/Sb5+,Cu2+/W6+,Cu2+/Mo6 mixed valence ions were prepared by immobilizing low-valent cation Cu2+,to explore the influence mechanism of high-priced cations doped with mixed valence ions on the piezoelectric activity,Curie temperature and resistivity of ceramics.The experimental results show that the B-site doped mixed valence ions significantly improve the piezoelectric activity of BIT-based piezoelectric ceramics.The piezoelectric properties of BIT-based ceramics doped by Cu2+/Nb5+ are as high as 38 pC/N,which is the maximum value of the BIT-based ceramic reported at present.Compared with the undoped,d33 increased by 5 times;Based on the analysis of resistivity and complex impedance measurement proved that oxygen vacancy in BIT-based piezoelectric ceramic dominant role in conductive behavior,and compared with the undoped modified BIT-based piezoelectric ceramics,500 ℃ resistivity ρ improved 2～3 orders of magnitude,especially Cu2+/Sb5+ doping modification of BIT-based ceramic 500℃ resistivity when ρp=1.40×107 Ω·cm.The resistivity ρ=1.40×107 Ω·cm is the maximum value of the currently BIT-based ceramics;the bipolar fatigue is greatly improved and the comprehensive performance is improved,which is closed related to the decrease of oxygen vacancy concentration;while the piezoelectric properties and resistivity are significantly improved,the Curie temperature Tc is maintained above 672℃,and there is no significant deterioration(TC～675℃ for pure BIT ceramics).2、Take the optimal performance of the above BIT-based piezoelectric ceramics(Cu2+/Nb5+),fix the high-valent cation Nb5+,and prepare Ni2+/Nb5+,Mn2+/Nb5+,In3+/Nb5+,Cr3+/Nb5+mixed valence ion doped BIT-based piezoceramics,the piezoelectric properties was attempted to break through 40 pC/N,and the influence mechanism of low-valent cation doped with mixed valence ions on the piezoelectric activity,Curie temperature and resistivity of ceramics was investigated.The results show that after changing the low-valent cations,the B-site doped mixed valence ions can also greatly improve the piezoelectric activity of BIT-based piezoelectric ceramics.The piezoelectric properties of Mn2+/Nb5+doped BIT-based ceramics can ce as high as 34 pC/N;After changing the low-valent cations,the mixed valence ion doping is performed.The resistivity at 500℃ is increased by 1～2 orders of magnitude,which is slightly inferior to the previous experimental scheme;When annealing at 600℃,the piezoelectric properties can be maintained above 90%;B-doped mixed valence ions have little effect on Curie temperature.更多还原