2002 Fiscal Year Final Research Report Summary
Development and Characterization of Langasite-type crystals for surface acoustic wave device
| Project/Area Number |
13650346
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Electronic materials/Electric materials
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| Research Institution | NARA INSTITUTE OF SCIENCE AND TECHNOLOGY |
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Principal Investigator |
SHINOSAKI Tadashi Nara Institute of Science and Technology, Graduate School of Materials Science, Professor, 物質創成科学研究科, 教授 (80026153)
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| Co-Investigator(Kenkyū-buntansha) |
TAKEDA Hiroaki Nara Institute of Science and Technology, Graduate School of Materials Science, Assistant Professor, 物質創成科学研究科, 助手 (00324971)
NISHIDA Takashi Nara Institute of Science and Technology, Graduate School of Materials Science, Assistant Professor, 物質創成科学研究科, 助手 (80314540)
OKAMURA Soichiro Nara Institute of Science and Technology, Graduate School of Materials Science, Associate Professor, 物質創成科学研究科, 助教授 (60224060)
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| Project Period (FY) |
2001 – 2002
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| Keywords | Piezoelectric material / Crystal growth / Czochralski technique / Surface acoustic wave device / Crystal structure |
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| Research Abstract |
In this study, we paid attention to Langasite (La_3Ga_5Sio_<14>: LGS) -type crystals. The LGS crystal is a leading material suitable for piezoelectric applications, because the crystal has intermediate properties between those properties of quartz and lithium tantalate (LiTaO_3) in electricity. However, a large amount of expensive gallium oxide as the raw material is necessary for mass-production. The aims of this study are to develop new LGS-type crystals consisting of lower gallium oxides.
In the first year, we have developed Al substituted LGS crystals (La_3Ga_<5-x>Al_xSiO_<14> (0<x<1): LGAS) crystals. The single crystals, with a 20-25 mm diameter and a 100-150 mm length, were grown by a conventional Czochralski technique. The chemical composition data disclosed that the effective segregation coefficient k_<eff> of Al in LGS was 1.03 to 1.07 and that the Al solubility limit was x<1.0. A single-crystal x-ray structure analysis reveals that Al atoms are distributed in all cation sites
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except for the decahedral one occupied by La, by rather favoring the smallest tetrahedral one. The piezoelectric modulus l d_<11> l increased; 1.3% and d_<14> decreased; 7.7% with the increasing Al content, x, up to 1.0. The Al-content obtaining the maximum electromechanical coupling factors (k_<12>, k_<25>, and k_<26>) was x=0.6.
In the second year, new piezoelectric Ba_3TaGa_3Si_2O_<14> (BTGS) crystal was synthesized by the Czochralski technique using raw materials with stoichiometric compositions. An analysis of growing process showed that the BTGS crystal congruently melts. The crystal structure of BTGS has been refined using single-crystal X-ray diffraction data. The distribution pf each cation was found to be ordered in each site. The maximum electromechanical factors k^2 in Y-cut BTGS wafer was about 0.43% at X-axis propagation. This value was larger than those of LGS.
For both LGAS and BTGS crystals enables the use of a lower amount of expensive gallium oxide as the raw material. Therefore, we can say that these two crystals are the preferable piezoelectric materials with the Langasite-type structure for both bulk- and surface-acoustic wave devices. Less
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Research Products
(10 results)
