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含碱金属线性/非线性光学材料结构性能关系研究及新结构预测
侯典伟
学位类型硕士
导师杨志华
2017-05-31
学位授予单位中国科学院大学
学位授予地点北京
学位专业物理电子学
关键词非线性光学 碱金属 共轭体系 键级 倍频
摘要

为实现线性/非线性光学材料的有效设计,探索微观基元对宏观性能的影响机制,并以此进行新材料预测,是当今材料基因组计划的一项重要研究议题。碱金属/碱土金属与其它元素成键时无d-d、f-f电子跃迁,从而易于获得大带隙(或高激光损伤阈值)线性/非线性光学材料。鉴于此,本论文以系列碱金属化合物为研究体系,通过第一性原理方法探究π共轭体系、反常P-O-P连接等特殊基元的微观结构、电子结构特征,阐明其对晶体倍频效应、折射率等宏观光学性质的影响规律。并在此基础上,通过理论方法设计预测性能优异的碱金属非线性光学材料。1. 研究碱金属化合物中微观共轭体系的影响机制:使用第一性原理方法研究两例碱金属有机无机杂化材料ASr[C4H2O6B(OH)2]·4H2O (A=K, Rb),通过计算发现其发色团为[C4H2O6B(OH)2]3-。为阐明共轭体系对宏观倍频效应的影响机制,对该发色团进行修饰,引入共轭体系C=C-C=O,得到两例模拟结构。该模拟结构倍频效应为初始结构倍频效应的三倍左右,经过计算表明倍频效应增大的主要原因是电荷离域能力的增强。对比修饰前后发色团的超极化率及超极化率密度可进一步证明共轭体系是其倍频效应增大的原因之一。因此引入共轭体系是获得大倍频效应化合物的一种有效途径。2. 研究碱金属化合物中反常P-O-P连接对结构、性能影响的微观机理:在硼磷酸盐化合物中P-O-P连接极少出现,该连接违反Pauling第四规则:以低配位阳离子为中心的多面体表现出彼此之间尽可能不连接的趋势。到目前为止,仅有六例P-O-P连接硼磷酸盐被报道。对于这种特殊的连接方式,并没有给出定量解释。本文选取四例碱金属P-O-P连接硼磷酸盐作为研究对象。首先构建两个同构团簇结构,一个团簇结构含P-O-P连接,另一个团簇结构不含该连接方式。Wiberg键级值表明B-O-P连接中P-O键的强度大于P-O-P连接中P-O键的强度。同时计算了四例碱金属硼磷酸盐中包含P-O-P连接片段结构的键级,发现其键级值与团簇结构键级值非常相近,通过该过程定量解释了硼磷酸盐中P-O-P连接的特殊性。同时计算了以上四例化合物的电子结构以及光学性质。3. 研究红外非线性光学材料中GaS4对光学性能的影响机制以及新结构预测:通过前期调研发现,微观基元GaS4四面体是众多红外非线性光学材料的结构基元以及倍频效应的主要贡献来源。选定碱金属镓硫三元体系,使用对称性限制条件下的人工蜂群算法,结合密度泛函理论方法,对一定摩尔比的1-6倍胞势能面进行搜索,发现一种全局能量最低的碱金属硫属化合物,通过形成焓及声子谱计算表征其热力学及动力学稳定性。理论计算表明该化合物拥有较大的带隙,适中的双折射率以及较强的倍频效应。

其他摘要

In order to effectively design linear or nonlinear optical materials, it is an important research topic of materials genome initiative to explore the relationship between microscopic units and macroscopic performances and then predict new materials. Alkali metal or alkaline earth metals are liable to obtain large band gap (or high laser damage threshold) optical materials due to the absence of d-d, f-f electron transitions. This dissertation takes a series of alkali metal compounds as the research system. The microstructure and electronic structure of special units such as π-conjugated system and abnormal P-O-P linkage in borophosphates were explored by the first-principles method, and the influence of the macroscopic optical properties such as second harmonic generation (SHG) effect and refractive index was elucidated. Based on the understanding of microscopic units, theory method was applied to design and predict new alkali metal materials with excellent performances.1. To study the mechanism of microscopic conjugated system in alkali metal compounds: ASr[C4H2O6B(OH)2]·4H2O (A=K, Rb) were studied with first-principle method and the results demonstrate that the chromophore is [C4H2O6B(OH)2]3-. In order to elucidate the effect of the conjugated system to SHG, the chromophore was modified and the conjugated system C=C-C=O was introduced to the chromophore to obtain two virtual structures. SHG strength of virtual structures is about three times of that of initial structures, and the calculation shows that the main reason for the increase of the SHG value comes from the enhancement of the charge transfer. Hyperpolarizability and hyperpolarizability density of the chromophore and modified chromophore further prove that the conjugated system is one of the sources for the increase of the SHG value. Therefore, introduction of conjugated system is an effective way to obtain larger SHG value compounds.2. The microscopic mechanism of the abnormal P-O-P linkage on the structure-properties of alkali metal compounds: P-O-P linkage rarely appears in borophosphates. This kind of linkage avoids Pauling’s fourth rule: polyhedron around cations with small coordination number does not tend to share elements with each other. So far, there are only six compounds having been reported. There is no quantitative explanation for this particular linkage. In this dissertation, four alkali metal P-O-P linkage borophosphates were chosen for research. To elucidate the difference of P-O bond between B-O-P and P-O-P linkage, two isomer clusters were built. One isomer is in the absence of P-O-P linkage and the other with the existence of it. The Wiberg bond order values indicates that the intensity of the P-O bond in B-O-P linkage is stronger than that in P-O-P linkage. At the same time, bond order of four fragments of alkali metal borophosphates with P-O-P linkage was calculated. It is found that the Wiberg bond order value is extremely similar to that of cluster structures. This process quantitatively explains the special of the P-O-P linkage. Electronic structure and optical properties of the above four compounds were also calculated.3. Study on the influence mechanism of GaS4 on infrared nonlinear optical materials and new structure prediction: through the preliminary investigation, it is found that microscopic unit GaS4 tetrahedron is the building units and the main contributor to the SHG effect of most of the infrared nonlinear optical materials. The alkali metal chalcogenide system was selected and the artificial bee colony algorithm, combined with DFT method, was used to search for 1 to 6-fold potential surface of a certain molar ratio. One alkali metal chalcogenide with the lowest global energy is found and the enthalpy of formation and phonon spectrum demonstrate the stability of the compound. Theoretical calculation demonstrates this compound has a large band gap, moderate birefringence and excellent SHG effect.

文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4954
专题材料物理与化学研究室
作者单位中国科学院新疆理化技术研究所
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侯典伟. 含碱金属线性/非线性光学材料结构性能关系研究及新结构预测[D]. 北京. 中国科学院大学,2017.
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