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Material strength study on cracking of oxide bulk single crystals for optelectronic use

光电用氧化物块体单晶的开裂材料强度研究

基本信息

批准号：
04650089
负责人：
MIYAZAKI Noriyuki
金额：
$ 1.34万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1993
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-04650089/
关键词：
Oxide Single Crystal Czochralski Growth Thermal Stress Finite Element Method Thermal Expansion Coefficient Elastic constants Anisotropy Cracking CZ法異片性

项目摘要

Oxide single crystals such as LiNbO_3(LN) and LiTaO_3(LT) are used as optelectronic materials. Such bulk single crystals are manufactured by the Czochralski growth method. Macroscopic cracking sometimes occurs during growth process. Such cracking would be caused by thermal stress in a single crystal. In the present study, a finite element computer program was developed for the thermal stress analysis of trigonal single crystals such as LN and LT.A tensor transformation technique was used to obtain the elastic constant matrix and the thermal expansion coefficient vector corresponding to an arbitrary pulling direction, and they are incorporated into the finite element program. Using this program, we analyzed the thermal stress in LN bulk single crystals, which were grown in a pulling apparatus in Institute for Materials Research, Tohoku University. The temperature boundary conditions of the crystals were obtained from the heat conduction analysis of the global system. Thermal stress analyzes were performed for the pulling directions of both the a-axis and the c-axis. The results show that the maximum thermal stress is lower in the c-axis pulling than in the a-axis pulling, which indicates that the a-axis pulling is easier to crack than the c-axis pulling. It is also found that a lower stress region spreads widely in the bulk single crystal pulled in the a-axis direction. This predicts that the a-axis pulling could provide a bulk single crystal of higher quality than the c-axis pulling, if macroscopic cracking can be prevented. This prediction was verified by observing microscopic defects in a single crystal obtained by the a-axis pulling.In order to study the cracking of LN single crystals quantitatively, thermal shock experiments were carried out using circular disk speciments. The experimental results show that the cracking mainly occurs at the cleavage planes, which indicates that the stresses normal to the cleavage planes would induce the cracking.

氧化物单晶如LiNbO_3（LN）和LiTaO_3（LT）被用作光电子材料。这种块状单晶通过直拉法（Czochralski growth method）制造。在生长过程中有时会出现宏观裂纹。这种裂纹是由单晶中的热应力引起的。采用张量变换技术，建立了LN和LT等三角单晶体热应力分析的有限元计算程序，得到了任意提拉方向对应的弹性常数矩阵和热膨胀系数矢量，并将其纳入有限元计算程序。利用该程序，我们分析了在东北大学材料研究所的提拉装置中生长的LN块体单晶的热应力。通过对整体系统的热传导分析，得到了晶体的温度边界条件。对a轴和c轴的拉伸方向进行了热应力分析。结果表明，c轴拉伸时的最大热应力小于a轴拉伸时的最大热应力，说明a轴拉伸比c轴拉伸更容易开裂。在a轴方向提拉的大块单晶中，应力较低的区域分布较广。这预示，如果可以防止宏观裂纹，则a轴提拉可以提供比c轴提拉更高质量的块状单晶。为了定量研究LN单晶的开裂，采用圆盘试样进行了热冲击实验。试验结果表明，裂纹主要发生在解理面，表明垂直于解理面的应力是诱发裂纹的主要原因。