1990 Fiscal Year Final Research Report Summary
Ferroelectric Domain Inversion Caused by Heat Treatment of Piezoelectric Crystals and Its Application.
| Project/Area Number |
01460154
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
電子機器工学
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| Research Institution | Tohoku University |
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Principal Investigator |
NAKAMURA Kiyoshi Tohoku University, Faculty of Eng., Professor, 工学部 (00005365)
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| Co-Investigator(Kenkyū-buntansha) |
YAMADA Ken Tohoku University, Faculty of Eng., Research Associate, 工学部, 助手 (80134021)
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| Project Period (FY) |
1989 – 1990
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| Keywords | Ferroelectrics / Domain Reversal / Piezoelectricity / Lithium Niobate / Lithium Tantalate / Proton Exchange / Domain / Heat Treatment |
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| Research Abstract |
We found that ferroelectric domain inversion took place when bare LiNbO_3 plates underwent heat treatment above 1060^0 C, or when LiTaO_3 plates underwent proton exchange followed by heat treatment. The purpose of this research is to clarify the phenomena and develop piezoelectric devices utilizing antipolarity domains. The results can be summarized as follows :
1. The dependence of the inversion layer thickness on heat treatment conditions was investigated. As the heat treatment time was increased, the inversion layer became thick and the domain boundary finally stopped at the median plane. Water vapor in the atmosphere exhibited a notable effect in promoting domain inversion. 2. The dependence of the thickness of inversion layers formed by heat treatment of proton-exchanged LiTaO_3 on conditions of proton exchange and heat treatment was examined. Inversion layers thickened with increasing proton exchange time and heat treatment time, while remaining almost constant at longer times tha
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n 1h. It was shown that the use of masks for preventing proton exchange permitted selective domain formation. 3. A method proposed for estimating the inversion laver thickness by measuring piezoelectric responses clarified that the antipolarity domain nucleated at the initial stage of heat treatment. This fact denies the possibility that the domain inversion is caused by pyroelectric fields. 4. A model that the domain inversion is caused by the electric field of space charges induced by Li_2O outdiffusion or proton exchange was proposed and shown to explain most of the domain inversion phenomena. This was supported by an experimental result that when a multi-domain LiTaO_3 was proton-exchanged and heat-treated, single-domain layers with a polarization directed outward were formed on both surfaces. 5. Various high-performance pizoelectric devices utilizing reversed domains have been proposed and developed. They include bending vibrators and hysteresis-free actuators with no bonding layer, resonators operating in even order modes, SAW reflectors, and transducers. Less
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