锡钛酸钡体系陶瓷的介电、铁电及巨电热性能研究

发布时间：2018-05-09 12:18

本文选题：无铅铁电陶瓷 + 电热效应　；参考：《南京大学》2015年硕士论文

【摘要】：研究低功耗、高能效且环境友好的新型制冷技术,替代传统的压缩制冷,已经成为人们生产生活的迫切需要。在各种各样的替代型制冷技术中,电热制冷备受关注。它利用铁电材料的电热效应进行制冷,具有低成本、高能量转换率等优势。事实上在电热材料研究进程中,铅基化合物的电热性能普遍高于无铅材料,然而日益严苛的环保政策制约着含铅材料的商业化应用,因此提高无铅材料的电热性能已经成为必然趋势。其中,寻找在室温附近具有大电热效应和宽工作温区的无铅铁电材料就是研究热点之一。钛酸钡是目前无铅电热性能研究领域中的重要基体材料,通过离子取代和掺杂改性等方法可以提升材料的电热性能。其中,BaSnxTi1-xO3(简称BST)体系陶瓷具有优异的介电、铁电、热释电等性能,存在多相交界点和准同型相界,且该体系的铁电相变温度接近室温,是潜在的高性能电热制冷材料。本文系统研究了BST体系陶瓷的成分、介电铁电性能、微观结构与电热性能之间的关系,提出增强无铅陶瓷材料在室温下的电热效应的方法。本研究工作采用固相法制备了BaSnxTi1-xO3 (x=0.02,0.06,0.08,0.10,0.12,0.15,0.18)7个组分的陶瓷样品。利用XRD、SEM进行微观结构分析,发现Sn4+对晶粒生长有抑制作用。BST体系的介电温谱研究表明,随着锡含量的增加,陶瓷铁电-顺电相变的弥散程度逐渐明显。室温下的电滞回线体现了多相临界点和准同型相界对材料铁电性能的增强作用。通过测试各组分陶瓷的变温电滞回线,然后基于麦克斯韦方程间接推导其电热性能,并分析BST各组分陶瓷的电热性能与铁电相变之间的关系。根据BST各组分陶瓷电热性能的对比分析,我们得出以下结论：(一)四相临界点处由于多相共存,拥有数目较多且能量接近的极化态,在电场变化时容易引起较大的熵变,从而导致大的电热效应。另外由于此处各极化态之间转变的能量较小,所以在较低的电场下即可引起大电热效应。BST陶瓷体系在准四相临界点附近组分(x=0.12)体现出最优益的电热性能,在10kV/cm时,电热强度为△T/△E=0.027 Kcm/kV和△S/△E=0.0345 Jcmkg-1K-1kV-1。(二)铁电弥散相变会拓宽陶瓷的电热制冷温度区间。与纯钛酸钡的狭窄电热峰不同,由于存在铁电弥散相变,BST(x=0.12)在接近室温的较宽温区(Tspan=55K)中维持高电热效应。而居里温度更低的x=0.18的电热半峰宽更是扩大到70 K,表明其在室温范围内具有稳定的电热性能。(三)准同型相界(MPB)可以提高陶瓷在室温附近的电热效应。BST陶瓷x=0.02在MPB附近的电热强度(△T/△E)高达0.037 Kcm/kV。另外当F-F相变与F-P相变温度接近时,电热效应的衔接有助于拓宽电热材料的工作温区。这使得x=0.08在接近100 K的温区中都有较为出色的制冷温度和熵变输出。
[Abstract]:It has become an urgent need for people to study new refrigeration technology with low power consumption, high energy efficiency and environmental friendliness, instead of traditional compression refrigeration. Among all kinds of alternative refrigeration technologies, electrothermal refrigeration has attracted much attention. It uses the electrothermal effect of ferroelectric materials for refrigeration, which has the advantages of low cost and high energy conversion rate. In fact, in the research process of electrothermal materials, the electrothermal properties of lead-based compounds are generally higher than those of lead-free materials. However, increasingly stringent environmental policies restrict the commercial application of lead-based materials. Therefore, it has become an inevitable trend to improve the electrothermal properties of lead-free materials. Among them, finding lead-free ferroelectric materials with large electrothermal effect and wide working temperature range near room temperature is one of the research hotspots. Barium titanate is an important substrate material in the field of lead-free electrothermal properties. The electrothermal properties of the materials can be improved by ion substitution and doping modification. The ceramics of BaSnxTi1-xO3 (abbreviated as BST) have excellent dielectric, ferroelectric and pyroelectric properties, and there are multiphase junction points and quasi-homogeneous phase boundaries. The ferroelectric phase transition temperature of the system is close to room temperature, so it is a potential high performance electrothermal refrigeration material. In this paper, the relationship among the composition, dielectric ferroelectric properties, microstructure and electrothermal properties of BST ceramics has been systematically studied, and a method to enhance the electrothermal effect of lead-free ceramics at room temperature has been proposed. In this study, the ceramic samples of 7 components of BaSnxTi1-xO3 were prepared by solid state method. The samples were 0.06%, 0.08%, 0.10, 0.12, 0.15, 0.18). The dielectric temperature spectra of Sn4 system show that the dispersion of ferroelectric-paraelectric phase transition becomes more and more obvious with the increase of tin content. The hysteretic loop at room temperature reflects the enhancement of ferroelectric properties by multiphase critical point and quasi-homogeneous phase boundary. By testing the hysteresis loop of each component ceramics, the electrothermal properties of each component ceramics are deduced indirectly based on Maxwell equation, and the relationship between the electrothermal properties and ferroelectric phase transition of BST ceramics is analyzed. Based on the comparative analysis of the electrothermal properties of BST ceramics, we draw the following conclusions: due to the coexistence of multiphase, there are many polarized states with close energy at the critical point of four phases, which can easily cause large entropy change when the electric field changes. This results in a large electrothermal effect. In addition, because the energy of the transition between the polarization states here is small, the large electrothermal effect can be induced at a lower electric field. BST ceramic system shows the optimum electrothermal performance near the quasi four-phase critical point. At 10kV/cm, The electrothermal strength is T / E 0.027 Kcm/kV and S / E 0. 0345 Jcmkg-1K-1kV-1. (2) Ferroelectric dispersion phase transition will widen the temperature range of electrothermal refrigeration of ceramics. Different from the narrow electrothermal peak of pure barium titanate, the high electrothermal effect is maintained in a wide temperature range near room temperature due to the existence of ferroelectric dispersion phase transition (BST) 0.12). The electrothermal half-width of x _ 2O _ 0.18 with lower Curie temperature is increased to 70K, which indicates that it has stable electrothermal performance at room temperature. (3) the quasi-homogenous phase boundary (MPB) can increase the electrothermal effect near room temperature. The electrothermal strength (T / E) of BST ceramics near MPB is as high as 0.037 Kcm / KV. In addition, when the temperature of F-F phase transition and F-P phase transition is close to that of F-P phase transition, the convergence of electrothermal effect is helpful to widen the working temperature range of electrothermal materials. This results in the excellent cooling temperature and entropy output in the temperature range of nearly 100 K.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ174.7

【共引文献】