| 题名 | 温梯法生长系统的数值模拟及几种高温氧化物晶体的生长 |
| 作者 | 李红军 |
| 学位类别 | 博士 |
| 答辩日期 | 2008 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 徐军 |
| 关键词 | 晶体生长 温梯法 数值模拟 高温氧化物晶体 生长缺陷 |
| 其他题名 | Numerical Simulation & Crystal Growth of High Temperature Oxides in Temperature Gradient Technique System |
| 中文摘要 | 高熔点氧化物晶体，如Al2O3、YAG、YAP及其掺杂晶体等，在激光、闪烁、窗口、衬底等方面有着广泛的应用。各应用领域需求的不断扩展推动着人们对这些晶体的生长工艺进行深入的研究。但由于这些晶体生长温度高，获得大尺寸高质量的晶体极其不易。温梯法技术是生长高熔点大尺寸晶体较好的方法，但不可避免地也存在着一些局限性，造成晶体中产生一定量的缺陷。分析解决这些问题是我们长期以来一直努力的目标。另外，由于晶体生长实验是一项昂贵的实验过程，尤其是类似采用温梯法生长高熔点大尺寸晶体的实验，所以对于这种问题的解决之道，是使用数值模拟的方式先期获得一些基本的资料，再反复推知所需的生长条件以减少实验所花费的时间和经费。因此，在本论文研究过程中主要采取数值模拟与生长实验相结合的方法来探寻问题的答案。 为获取大尺寸高质量的Al2O3、YAG和YAP晶体，我们系统地分析了现有的温梯法工艺，对存在的问题提出了相应的解决途径，最终提出了改造温梯法系统的方案。本论文主要包括以下几方面的研究内容： 第一：温梯法系统的数值模拟 选用以有限元素法（FEM）为基础的套装软件ANSYS和FIDAP进行模拟分析。在模拟研究的初期，我们采用ANSYS的热－电耦合单元对温梯法系统的温场进行了全局模拟，并且建立了三维模型对温场的对称性进行研究，模拟的结果与实验结果比较吻合。之后我们选用FIDAP的准稳态分析方式针对不同生长参数，如发热体的温度梯度、环境温度、籽晶大小、坩埚形状、材料性质等，对晶体生长过程的热流场及固液界面形状的影响做了较为深入的研究。另外，我们还采用了ANSYS的热－应力耦合单元对晶体中的应力情况进行了分析。 第二：温梯法高温氧化物晶体的生长缺陷分析 系统地研究了Al2O3、YAG、YAP晶体中存在的组分过冷、开裂、浓度不均匀、色心等缺陷；根据各晶体中出现的主要缺陷不同，我们有针对性地进行了重点分析：Al2O3晶体中温场不对称引起的开裂及温度梯度设置不当引起的丝状光路是分析和解决的重点；YAG晶体中掺杂离子的分凝效应引起的浓度不均匀及小面生长现象是着重研究的内容；YAP晶体中热膨胀系数各向异性引起的开裂是要避免的主要缺陷。而温梯法系统中弱还原性气氛造成的色心缺陷则是几种晶体中普遍存在的问题；另外，我们利用这种气氛特点进行了新晶体V:YAG和Al2O3:C的生长实验。 第三：温梯法系统的改造 探索了温梯法装置中实现真空系统、温控系统及监测系统自动化的方案；通过对保温层及发热体的构型进行重新设计和改造，将温梯法50炉的生长能力从三英寸提高到四英寸；实现坩埚下降装置的自动化，发展“低速下拉温梯法”技术增加所生长晶体的长度。 |
| 英文摘要 | High temperature oxide crystals, such as Al2O3, YAG, YAP and doped ones, are wildly used as laser host, scintillation crystal, window, substrate, etc. The increasing demand impels people to improve the growth skill of these crystals. However, due to their high melting temperature, it is not easy to obtain large-sized bulk single crystals with high quality. The temperature gradient technique (TGT) is a good method for growing larger high-optical-quality oxide crystals though it also has some limitations which may result in growth defects. To solve these problems is always our long-term goal. The growth experiment of high-temperature oxide using TGT is very expensive. For cost-saving, numerical simulation tool was firstly used to improve growth parameters before the practical growth process. To obtain high-quality Al2O3, YAG and YAP crystals, we analyzed systematically the present growth technics of TGT to find the ways to solve problems. And finally schemes of TGT upgrade were explored. The main contents of this thesis are described as following: Part one: numerical simulation of TGT system The finite element software ANSYS and FIDAP were employed to study the temperature and velocity distribution and the interface shape during crystal growth process using TGT. Firstly, the thermal-electric coupled elements of ANSYS were introduced to simulate the temperature distribution in the whole TGT furnace, and the effect of unsymmetrical configuration on thermal field was specially discussed using 3D model. Then we applied the quasi-static mode of FIDAP to analyze the effect of the different growth parameters, such as thermal gradient, crucible shape, material properties, ect. Otherwise, the thermal stress in crystal was also simulated. Part two: growth defects in high temperature oxide crystal grown by TGT Growth defects, like constitutional supercooling, cracking, homogeneity, color center and so on, were systematically investigated. According to extent and importance of defects in different crystals, some special ones were selected to analyze emphatically. That is cracking resulting from unsymmetrical thermal field and scattering from unsuitable temperature gradient in Al2O3, inhomongeniety from effect of segregation and facet growth phenomena in doped YAG, and cracking from large anisotropy of thermal expansion coefficient in YAP. And in all crystals grown by TGT, color center induced by the reducing atmosphere is a common problem needed to be solved. On the other hand, we applied the special atmosphere to grow some special crystals, such as V:YAG and Al2O3:C, to enhance their performance. Part three: Upgrade of TGT system Automatic schemes for vacuum system, temperature control system and monitor system were explored. By means of redesign and reconstruction of thermal shield and heater, the crystal diameter grown by TGT-50 furnace is extended to 4 inchs from 3 inchs. The crystal length can be increased more than 2 times by modifying the pulling down mechanism, namely, micro-pulling down temperature gradient technique (MPD－TGT). |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15226]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 李红军. 温梯法生长系统的数值模拟及几种高温氧化物晶体的生长[D]. 中国科学院上海光学精密机械研究所. 2008. |
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