1993 Fiscal Year Final Research Report Summary
Material strength study on cracking of oxide bulk single crystals for optelectronic use
| Project/Area Number |
04650089
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
材料力学
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
MIYAZAKI Noriyuki Kyushu University, Department of Chemical Engineering, Associate Professor, 工学部, 助教授 (10166150)
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| Co-Investigator(Kenkyū-buntansha) |
IKEDA Toru Kyushu University, Department of Chemical Engineering, Research Associate, 工学部, 助手 (40243894)
MUNAKATA Tsuyoshi Kyushu University, Department of Chemical Engineering, Professor, 工学部, 教授 (00037714)
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| Project Period (FY) |
1992 – 1993
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| Keywords | Oxide Single Crystal / Czochralski Growth / Thermal Stress / Finite Element Method / Thermal Expansion Coefficient / Elastic constants / Anisotropy / Cracking |
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| Research Abstract |
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.
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