Alternative TitleMicrostructure Characterizations of Perovskite-based Oxides by Transmission Electron Microscopy
Thesis Advisor马秀良
Degree Grantor中国科学院金属研究所
Place of Conferral金属研究所
Degree Discipline材料物理与化学
Keyword透射电子显微术 钙钛矿型氧化物 显微结构 缺陷
Abstract钙钛矿型氧化物是具有超导、介电、巨磁阻、压电、铁电、光电、非线性光学等丰富物理性能的功能材料,被广泛的应用于人类的社会生产、生活之中。钙钛矿型氧化物之所以具有如此丰富的物理性能是因为其结构复杂多变。现代高分辨透射电子显微术和高空间分辨率分析透射电子显微术的发展,可以使我们在原子尺度研究钙钛矿氧化物的结构和缺陷,加深对结构与性能之间关系的理解。 本文主要利用高分辨透射电子显微术、扫描透射电子显微术和X射线能量色散谱对掺杂BaTiO3块体的晶界结构及BaNb0.3Ti0.7O3、PZT外延薄膜的微观结构进行了深入研究,探讨了微观结构对性能的影响,主要研究结果包括以下几个方面: 用传统的陶瓷工艺制备具有明显异常长大现象的Y掺杂BaTiO3,并利用电子显微术对其晶界结构进行研究。研究结果发现:片状第二相Ba6Ti17O40的小晶粒出现在异常长大晶粒和相邻的基体小晶粒形成的三角晶界处,并与异常长大晶粒的{111}面有特定的外延关系。BaTiO3和Ba6Ti17O40的取向关系确定为(1 )t//(001)m、(1 2)t//(60 )m和[110]t//[0 0]m,其界面结构是由BaTiO3的{110}t和{001}t面形成的规则的原子级的台阶构成的。当晶界一侧为BaTiO3{111}面时,晶界上有一种普遍存在的0.7nm厚的晶间相。此晶间相的结构和Ba6Ti17O40类似,其与BaTiO3{111}面的界面结构和Ba6Ti17O40与BaTiO3{111}面的界面结构一致。 根据BaTiO3异常长大晶界特征指出二维形核侧向生长的长大机理是BaTiO3主要异常长大机理之一。二维形核优先发生在异常长大的{111}面与相邻的基体晶粒形成的三角晶界处。晶核在异常长大的{111}面形成后生长成平台,并沿{111}面侧向长大。当侧向生长的台阶表面为高指数晶面,且其高度在10nm左右时,台阶生长速率较大。 外延生长在(001)SrTiO3基体上的BaNb0.3Ti0.7O3薄膜具有{111}孪晶片层和高密度反相畴两大显微结构特征。反相畴的畴界可以看作1/2<110>层错。由于孪晶界和反相畴界相互作用,一方面使得孪晶界偏离了{111}面,与(001)面形成大约为62o的α角;另一方面使孪晶面沿<112>轴倾转,在<110>取向下孪晶界两侧的晶体相互重叠,出现了三倍于{111}面间距的晶格条纹。孪晶界和反相畴界相互作用的最终结果产生了非对称孪晶结构。 为了阐明MBP(morphotropic phase boundary)处PZT薄膜中的两相共存问题,对外延生长的PbZr0.52Ti0.48O3薄膜的畴结构和位错进行了研究。研究结果发现PbZr0.52Ti0.48O3薄膜中存在畴界位于{110}面的四方相90°铁电畴和畴界位于{100}面的菱方相71°铁电畴,即薄膜中四方相和菱方相共存。另外,通过对薄膜与基体界面上失配位错的分析,发现薄膜中的应变符合理论上预言的两相共存时的应变区间,即实验结果与理论预言一致。薄膜中的穿过位错是柏氏矢量为a<100>的全位错。穿过位错可以有效钉扎四方相90°铁电畴。 为了实现对材料结构和性能的控制,对外延生长的[PZT(20/80)/PZT(40/60)]5 PZT(20/80)/SRO/(001)STO和[PZT(20/80)/PZT(40/60)]10PZT(20/80)/SRO/(001)STO多层薄膜的结构进行了电子显微学研究。研究结果发现:90ºa-c铁电畴和穿过位错均起始于第一个PZT20/80和PZT40/60的界面,但是具有较厚单层的[PZT(20/80)/PZT(40/60)]5薄膜中a畴和穿过位错密度均高于具有较薄单层的[PZT(20/80)/PZT(40/60)]10薄膜,而且前者应变不均匀,有局限于PZT20/80单层的a畴,后者整个多层膜形成了均匀的应变。
Other AbstractPerovskite-based oxides are of vital importance in the modern society due to their excellent properties, such as superconduction, ferroelectricity, colossal magnetic resistance. These properties attribute to their complicated structures. With the development of high resolution transmission electron microscopy and high spatial resolution analytical microscopy, it is highly possible to study the microstructures at atomic scale, thus improve our understanding of the relationships between structures and properties. In this dissertation, microstructures of several perovskite-based oxides were investigated by means of high resolution (scanning) transmission electron microscopy, high-angle annular dark-field imaging, X-ray energy dispersive spectroscopy. The main results are as follows: An intergranular layer was found in 0.4 mol % Y-doped BaTiO3, which was sintered below the eutectic temperature in air. The layer possessed a crystal structure similar to Ba6Ti17O40 and a thickness of 0.7 nm. Plate-like second phases Ba6Ti17O40 were also observed at triple-grain junctions and an orientation relationship of (1 )t // (001)m, (1 2)t // (60 )m and [110]t // [0 0]m was determined between the tetragonal BaTiO3 and the monoclinic Ba6Ti17O40. Detailed structure of the interface between BaTiO3 and Ba6Ti17O40 was resolved by scanning transmission electron microscopy and high-resolution transmission electron microscopy investigations. The microstructure of abnormal grains in BaTiO3 based ceramics suggests that 2-D nucleation and lateral growth take place in the material. High-resolution transmission electron microscopy investigation reveals that nucleation takes place at triple junctions of abnormal grain and adjacent matrix grains, subsequently form steps and the steps grow laterally along {111} planes of the abnormal grains. The abnormal grain boundaries are faceted in the growth direction, however, the ledges, which possess boundaries deviated from low-index crystallographic planes of the abnormal grains, could provide high mobility necessary for abnormal grain growth. Asymmetrical twin boundaries and highly dense antiphase domains are found by means of transmission electron microscopy in the Perovskite-based BaNb0.3Ti0.7O3 thin film grown by laser molecular beam epitaxy on SrTiO3 (001) substrate. The microstructural characteristic of the BaNb0.3Ti0.7O3 film was clarified in terms of lamellar {111} twins and antiphase domains whose domain boundaries are 1/2 <110> stacking faults. It is proposed that the intersections of (111) twinning with the antiphase domain boundaries result in the asymmetrical twin boundaries. The microstructural characteristics of PbZr0.52Ti0.48O3 thin films grown epitaxially on (001) SrRuO3-buffered (001) SrTiO3 substrates by pulsed laser deposition were analyzed by transmission electron microscopy. Through analysis of the ferroelectric domain structures, tetragonal and rhombohedral phases were found coexisting in the PZT film. In order to affirm the coexisting of tetragonal and rhombohedral phases, the misfit strain status and misfit dislocations of the films were studied. In addition to the phase coexisting, threading dislocations with Burgers vector a<100> also were identified. It is proposed that threading dislocations can pin the domains effectively. Multilayers consisting of two tetragonal compositions PbZr0.2Ti0.8O3 and PbZr0.4Ti0.6O3 were deposited onto a SrRuO3 electrode grown on a (001) SrTiO3 substrate. It has been shown that 90ºa-c ferroelectric domains and threading dislocations formed at the first interface between PbZr0.2Ti0.8O3 and PbZr0.4Ti0.6O3 of the both multilayers. However, the densities of the a-domain and the threading dislocation are highetr in the multilayer with thicker single layers than that in the multilayer with thin single layers. Further more, some a-domains confined to PbZr0.2Ti0.8O3 single layers in the multilayer with thicker single layers and all a-domains propagated the whole film in the multilayer with thinner single layers. This indicates that the strain state of the multilayer with thinner single layers is much more homogenous than that of the multilayer with thicker single layers.
Document Type学位论文
Recommended Citation
GB/T 7714
郑士建. 钙钛矿型氧化物结构与缺陷的透射电子显微学研究[D]. 金属研究所. 中国科学院金属研究所,2009.
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