【作者】 张旭；

【导师】 薛冬峰；

【作者基本信息】 大连理工大学 ， 化学工艺， 2010， 博士

【摘要】 随着科学技术的不断发展,人们广泛研究晶体组成、结构与晶体生长和性能之间的关系,旨在探索、设计、合成出新型功能无机晶体材料。化学键方法作为一种行之有效的研究晶体结构与性能关系的理论工具,被广泛应用于功能无机晶体的结构评价和性能预测中。本论文以铌酸锂(LiNbO3, LN)和磷酸二氢钾(KH2PO4, KDP)这两种功能无机晶体为研究主体,以化学键方法为理论基础,从晶体的微观结构出发,致力于晶体材料的结构与性能和生长关系的研究。铌酸锂晶体因其自身具有的多种优异性能和巨大的应用前景而受到人们的广泛关注,但生长出满足不同要求的高质量晶体比较困难,所以迫切需要理论方法的提出来指导铌酸锂晶体的生长。论文基于铌酸锂晶体的结晶学特征,利用布拉维法则和鲍林第三规则研究晶体结构与其生长行为之间的关系,发现八面体堆积方式和化学键行为都对铌酸锂晶体生长起着至关重要的影响。同时,计算结果显示面网密度和键合能最大的铌酸锂晶面生长速度最慢并容易最终显露。这些研究表明,从组成化学键和多面体的微观角度出发,晶体的结构分析可以帮助人们深入理解铌酸锂晶体的生长过程,进而搭建起连接晶体结构与晶体生长的桥梁,为实现铌酸锂晶体的可控化生长提供重要的理论指导。铌酸锂的居里温度(Tc)与晶体组成密切相关,可用于确定晶体的组成,进而判定铌酸锂晶体的质量。论文基于铌酸锂晶体的结晶学数据,提出化学键能的方法用于预测铌酸锂晶体的居里温度和自发极化率(Ps)。结果表明,铌酸锂晶体的居里温度和自发极化率都强烈地依赖于晶体结构中的锂格位。因此,在铌酸锂结晶学结构中,锂位才是能够有效影响铌酸锂晶体铁电性质的敏感格位。此外,还利用化学键方法研究了铌酸锂晶体±Z面的微畴形貌、反转过程和蚀刻速度。铌酸锂晶体的微畴特征密切相关于组成原子各向异性的化学键行为,可以看作是铌酸锂晶体组成化学键行为的微观表现。综上所述,化学键方法不仅为人们更好地理解铌酸锂晶体的铁电行为提供帮助,而且对于探索铌酸锂这类晶体的铁电性质具有重要的指导意义。因为晶体的许多物理和化学性质都与其形貌密切相关,所以控制晶体生长并得到期望的形貌就具有十分重要的意义。论文基于磷酸二氢钾晶体表面结构的分析,提出晶体生长动力学模型,用于不同过饱和度下磷酸二氢钾晶体的生长研究。根据定量计算的相对生长速度能够预测磷酸二氢钾晶体的形貌演变规律。目前的方法结合具体实验对于未来晶体形貌调控的发展具有潜在的促进作用。更多还原

【Abstract】 With the continuous development of science and technology, the complex relationship between the constituent, structure, crystal growth and property of crystals has been widely investigated in order to explore, design and synthesize new functional inorganic crystal materials. The chemical bond method provides an important theoretical tool for studying the relationship between the crystal structure and property, which is widely applied to the structural evaluation and property prediction of functional inorganic crystals. Starting from the microscopic structure of lithium niobate (LN) and potassium dihydrogen phosphate (KDP) crystals, study on the structure, growth and property of these functional inorganic crystals was carried out on the basis of the chemical bond method.LN crystals have attracted much attention due to their excellent physical properties and potential applications in the modern science and technology. However, it is very difficult to grow LN crystals with a high quality and large size, which can match different kinds of practical needs. The theoretical development is thus necessary for directing the growth of LN crystals. Therefore, on the basis of the crystallographic characteristics of LN crystals, Law of Bravais and Pauling’s third rule were employed with the aim to find the relationship between the crystal structure and growth behaviors of LN crystals. It can be found that both octahedra linking and chemical bond behaviors of constituent elements within the crystallographic frame play dramatic roles in affecting the crystal growth. In addition, the calculated results indicated that the crystal plane with the highest reticular density and bonding energy in the LN crystal has the slowest growth rate, and is the most influential face for the LN crystal growth. The current work showed starting from the viewpoint of the microscopic behaviors of constituent chemical bonds and polyhedra in the crystallographic frame, we may comprehensively understand the crystallization process, and build up a link between the crystal structure and growth behaviors of LN crystals, which provides a theoretical tool for us to control the LN crystal growth.Curie temperature (Tc) of LN crystals is a composition-dependent property, which may be applied to determine the crystal composition and estimate the crystal quanlity. A general expression of Tc and spontaneous polarization (Ps) of LN crystals was energetically proposed by employing the viewpoint of the bond energy of constituent chemical bonds within the LN crystallographic frame. The present work showed Tc and Ps of LN crystals are strongly dependent on the Li site within the LN crystallographic structure. Therefore, the Li site is a sensitive lattice position to dominate the ferroelectricity of LN crystals. In addition, domain characteristics (such as the domain shape, domain switching, and etching rate) at±Z surfaces of LN single crystals were comprehensively studied from the chemical bond viewpoint. The present work indicated that domain characteristics are closely correlated to anisotropic bond behaviors of constituent atoms, which may be regarded as a microscopic reflection of the chemical bond behaviors in the LN crystallographic frame. Chemcial bond method provides us a good understanding of ferroelectric behaviors of LN crystals, which may be very helpful to the estimation of ferroelectric behaviors of LN-type solids.Controlling the crystal morphology has become increasingly important, since many of their physical and chemical properties are highly shape dependent. Here we proposed a kinetic model that was applied to the cases of KDP crystals grown from the solution with different surpersaturation on the basis of the structural analysis of the crystal surface. Then, we can predict the growth behaviors of KDP crystals according to the relative growth rate that is quantitatively calculated by using the kinetic model. Seeding experiments with the kinetic model may have significant potential towards the development of shape-controlled growth with defined conditions.更多还原