Compositions – Piezoelectric
Reexamination Certificate
1999-03-16
2001-10-16
Kopec, Mark (Department: 1751)
Compositions
Piezoelectric
C310S311000
Reexamination Certificate
active
06303048
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to piezoelectric optical materials and more particularly to Langasite-type crystals and the method for manufacturing these crystals.
Recent development of digital communications devices and demands for them are remarkable. The system for the recent mobile communications, including portable telephones and personal handy phones, has been rapidly expanding. In such a digitalized communications field, an improvement of performance in filters and oscillators incorporated in communications devices is very important.
Piezoelectric crystals are excellent electronic components and their properties are preferably used in the filters and oscillators of the communications devices. For example, the quartz is used in SAW (i.e., surface acoustic wave) filters of the portable telephones, and LiTaO
3
is used in TV or VTR (or VCR) filters.
The quartz is robust against temperature change, however its band width is narrow. On the contrary, the LiTaO
3
is weak against temperature change but its band width is wide.
Therefore, the recent research and development is directed to new materials which possess the excellent properties of both the quartz and the LiTaO
3
. Namely, the newly developed materials will be small in the frequency change when the temperature changes, stable in the oscillation, wide in the band width, and small in the insertion loss.
Among the conventionally developed crystals, &agr;-AlPO
4
is not suitable for the industrialized manufacturing due to generation of twin crystals and Li
2
B
4
O
7
is deliquescent and low in the growth speed.
SUMMARY OF THE INVENTION
An object of the present invention is to provide excellent Langasite-type crystals having no coloring problems and free from inclusions and cracks. Furthermore, the present invention relates to the method for manufacturing the Langasite-type crystals.
In order to accomplish the above and other related objects, the present invention provides a method for manufacturing a Langasite-type crystal according to the Czochralski process. In this manufacturing method, a melt containing lanthanum oxide, tantalum oxide, and gallium oxide is prepared by mixing the powders of these oxides so as to have a stoichiometric composition ratio of an intended lanthanum/tantalum/gallium oxide to be manufactured. A crystal is pulled up from the melt stored in a crucible in an atmosphere of the mixture of argon and oxygen gases.
Preferably, the concentration of the oxygen is in a range from 0.1 vol % to 1.5 vol % with respect to the concentration of the argon.
Preferably, the lanthanum oxide, the tantalum oxide, and the gallium oxide are mixed to satisfy the following relationship:
33.14≦X≦33.41, 5.24≦Y≦5.73, 61.02≦Z≦61.45, and X+Y+Z=100
where X, Y and Z represent the molecular percentages (mol %) of the lanthanum oxide, tantalum oxide, and gallium oxide in the melt, respectively.
Another aspect of the present invention provides a Langasite-type crystal manufactured from a melt containing lanthanum oxide, tantalum oxide, and gallium oxide which are mixed to have a mixing ratio of X:Y:Z defined by the following relationship:
33.14≦X≦33.41, 5.24≦Y≦5.73, 61.02≦Z≦61.45, and X+Y+Z=100
where X, Y and Z represent the molecular percentages (mol %) of the lanthanum oxide, the tantalum oxide, and the gallium oxide in the melt, respectively.
REFERENCES:
Fukuda et al “Growth of New Langasite Single Crystals . . . ” Proc. IEEE Int. Symp. Appl. Ferroelectric 11th (1998) pp. 315-319.*
Hyoung Jung et al “Crystal Growth & Piezoelectric Properties of Langasite . . . ” Mater. Lett. (1999) 41(5), 241-246 (Abstract Only).*
Bohm et al “(Zochrelski Growth and Characterization of Piezoelectric Single Crystals . . . ”Journal of Crystal Growth, 204(Jul. 1999) pp. 128-136.*
B.V. Mill et al., “Modified rare-earth gallates with a Ca3Ga2Ge4O14structure”,Sov. Phys. Dokl., 27(6), pp. 434-437 (Jun. 1982).
H. Kawanaka et al., “Growth and characterization of La3Ta0.5Ga5.5O14single crystals”,Journal of Crystal Growth, 183, pp. 274-277 (Jan. 1998).
Fukuda Tsuguo
Kawanaka Hiroyuki
Anderson Kill & Olick P.C.
Kopec Mark
Victor Company of Japan Ltd.
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