XJIPC OpenIR  > 材料物理与化学研究室
深紫外光功能应用为导向的硼酸盐结构设计
卞强
学位类型博士
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
学位专业微电子学与固体电子学
关键词硼酸盐 双折射值 结构预测
摘要

搜寻可用的深紫外光区功能晶体材料是激光和通信领域的热点问题,因而引起了人们广泛的研究兴趣。目前能够应用于深紫外区的光功能晶体性能还不够好,无法满足日益增长的应用需求,因此人们投入了大量的人力物力,以期发现新的晶体材料。当前以实验合成为主的新材料研发模式,依赖于大量的“重复法”实验,新材料主要靠随机发现产生,这种方式不仅浪费资源,也延长了材料开发周期。因此先在理论上确定材料的结构-性能关系,然后再利用可靠的晶体结构预测方法设计出具有特定功能的新材料,最后进行实验合成,这种以理论指导实验的方式是材料开发领域长久的期望。根据能量最低原理,物质的能量越低越稳定,因而理论上晶体结构预测的本质就是在给定的化学组分下,确定物质势能面上的全局能量最小值点。近年来,随着计算机运算能力的提高、材料模拟计算方法的完善和材料结构-性能关系的进一步研究,理论上设计具有特殊功能的材料已经成为可能。在本文中,我们首次引入了晶体结构预测CALYPSO算法,并结合第一性原理方法,设计出了具有特定双折射值的全局能量优化的深紫外光功能晶体材料,主要设计思路如下:(1)研究硼酸盐晶体的结构-双折射性能关系。硼酸盐一般具有短的紫外截止边,它们是紫外光学晶体的备选材料。通过研究硼酸盐的结构-双折射性质之间关系,在晶体生长之前,准确的根据结构评估其双折射值,将能有效的评估晶体的实际应用价值,使新晶体开发具有明确的导向性。在本文中,首先选取了五种不同构型的硼酸盐晶体材料,它们分别具有孤立的B-O基团和网状的B-O基团。利用第一性原理方法计算出这五种不同硼酸盐构型的晶体的双折射值,并且同时调研了一千多种人工晶体和天然矿物晶体的实验双折射值,对比以上所有晶体的双折射值和其对应的结构类型,总结发现硼酸盐的双折射变化具有明显的规律性特征。对于大多数硼酸盐,其双折射与结构类型具有如下定性的关系:平面状B-O基团的平行或类平行分布(?n ≈ 0.07-0.13) > 平面状B-O基团的近平面分布或链状B-O基团的共平面分布(?n ≈ 0.04-0.08) > 平面状B-O基团的混乱取向分布或网状B-O基团的混乱取向分布(?n < 0.05)。这个规律结合第一性原理计算结果,可以评估硼酸盐是否具有合适的双折射值。同时,也可以利用这个规律设计具有合适双折射值的新型硼酸盐材料。(2)设计具有0.07-0.1双折射值的硼酸盐晶体材料。众所周知,双折射值在0.07-0.1范围内的非中心对称硼酸盐晶体在深紫外相位匹配方面具有非常大的优势,因此设计双折射值在这个范围内的硼酸盐晶体具有重要的实用价值。从上面论述的硼酸盐双折射变化规律可以发现,设计具有0.07-0.1双折射值的硼酸盐晶体,可供选择的最好的基础结构基因主要集中在平面状的B-O基团,同时含Be硼酸盐一般具有较短的深紫外截止边,因此我们选择了包含BO3基团的NaBeBO3进行研究。由能量最低原理可知,目前理论设计上使用的替代方法和高通量筛选方法都不能有效的探索未知化学组分下具有能量稳定性的物质结构。为了解决这个问题,我们首次将全局优化的CALYPSO结构预测方法引入到硼酸盐结构预测当中,对化学组分为NaBeBO3的常压下结构进行预测。第一次得到了NaBeBO3的热动力学稳定结构,并找到了其全局能量最小点附近所有的极小值点结构。同时预测结果显示,四个最低能量的NaBeBO3结构均具有0.07-0.1范围的双折射值,并且具有170 nm左右的深紫外截止边,它们都是深紫外双折射晶体的备选材料。其中空间群为P-6的NaBeBO3结构具有1倍KDP的非线性光学效应,并且最短相位匹配波长为195 nm左右,它是优良的深紫外非线性光学材料。总的来说,以深紫外光功能为导向的光学材料设计才刚刚开始,这种设计方式为实验指明了确切的方向,并且缩短了材料的开发周期。将来还会有更多的具有优良深紫外光学性能的材料通过这种方式被开发出来。

其他摘要

Searching for viable deep-ultraviolet (DUV) functional crystal materials in laser industry and optical communication has been the subject of considerable interest. Present DUV functional optical crystal materials suffer some drawbacks, which seriously hinder their commercial availability, thus can not meet the growing application demands. As a result, research on deep-ultraviolet functional optical crystal materials is a topic of general interest in the new field of functional material at present. Current development method of optical materials is mainly experimental synthesis, which relies on large amount of repeat experiments. In the experiment, the discovery of novel optical material is stochastic. Such development method not only wastes the experimental resource, but also prolongs the cycle of development for optical materials. Thus, the theoretical prediction of crystal structures with special optical properties independent of previous experimental knowledge is greatly necessary. According to the principle of minimum energy, for a closed system with fixed entropy, the total energy is minimized at equilibrium. Thus, the structure prediction method is to explore the free energy surfaces and uncover the global minimum. In recent years, as the progress of calculative power and the improvement of basic materials theory, the global minimum structure prediction of materials is possible now. By using global optimization method, we for the first time realize the design of the global optimization structures of deep-ultraviolet optical materials with fixed birefringence values. This design is as follows: (1) The investigation of the relationship between crystal structure and birefringence properties. Before the growth of crystals, accurate predictions of birefringence values are very important. These will efficiently evaluate industrial usability for crystals, and provide clear guidance for further experimental exploration. Here, to uncover the relationship, five borates with isolated BO3 groups or network B?O structure are chosen. Their birefringence values calculated by first principle are compared with the structure type. In the same way, more than one thousands artificial or natural crystals' experimental birefringence values are compared with their structure type. A change law of birefringence for borates is uncovered: for most of borates, the birefringence can be divided by the different arrangement of B?O groups that follow the trend of (parallel arrangement of planar B-O groups, ?n ≈ 0.07-0.13) > (coplanar arrangement of planar B-O groups and one-dimensional chain B-O groups, ?n ≈ 0.04-0.08) > (disorder arrangement of planar B-O groups and network B-O groups). This change law combines with the results calculated by first principle is sufficient to identify the birefringence values of borates for evaluating their birefringence values. Simultaneously, it can be used in the design of novel borates featuring given birefringence values. (2) The design of borate crystal materials possessing the birefringence values ranging from 0.07 to 0.01. Non-centrosymmetric borates whose birefringence values belong to this range (0.07-0.1) have great advantages in achieving DUV phase matching condiction. They may be excellent candidates for DUV nonlinear optical materials. Thus, it is the subject of considerable interest to investigate this kind of borate (that is the target borate). In consideration of the change law of birefringence, the planar B-O groups are basic units of the target borate. On the other hand, beryllium borates exhibit short DUV cutoff edge. Thus the chemical formula of the target borate is chosen to be NaBeBO3 with the planar BO3 units. Current theoretical substitution method and high-throughput computational materials design have some shortcomings, they cannot find the most stable structure of unknown chemical compositions. To search out the most stable structure, we for the first time introduced CALYPSO global optimization method to predict the stable phase of NaBeBO3 at ambient pressure, and established the thermodynamically stable structures for NaBeBO3. We discovered all the structures near the global minimum. In doing so, the four lowest energy NaBeBO3 structures are observed to exhibit 0.07-0.1 birefringence values. They are excellent candidates of DUV birefringent materials. Among them, the NaBeBO3 with space group P-6 features a second harmonic generation coefficient close to that of KH2PO4. Its shortest phase matching edge is 195 nm. These results demonstrate that it is promising candidate of DUV nonlinear optical material. In summary, we provide the first design of functional materials oriented by deep-ultraviolet functional optical applications. This design method provides clear guidance for experimental exploration, and it shorts the cycle of materials development. We believe that more functional optical materials will be discovered in the same way.

文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4957
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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GB/T 7714
卞强. 深紫外光功能应用为导向的硼酸盐结构设计[D]. 北京. 中国科学院大学,2017.
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