Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from solid or gel state
Reexamination Certificate
2001-12-14
2004-08-31
Norton, Nadine G. (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from solid or gel state
Reexamination Certificate
active
06783588
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the BaTiO
3
—PbTiO
3
series single crystal that can be utilized as a piezoelectric element, for example, and also, relates to the method of manufacturing the same. Further, the invention relates to a piezoelectric type actuator formed by the BaTiO
3
—PbTiO
3
series single crystal, and the liquid discharge head that uses such piezoelectric type actuator as well.
2. Related Background Art
The BaTiO
3
series single crystal is a nonlinear optical crystal utilized for optical communications, information processing, or the like, and having a great marketability, which is not only used as a phase conjugate wave generating medium for a high resolution image processing, a real-time hologram, or a laser resonator, but also, used as a highly capable piezoelectric material if the crystallization thereof can be implemented at lower costs.
Now, obviously, the composition of the BaTiO
3
makes it difficult to obtain single crystal directly from the BaTiO
3
solution when BaTiO
3
series single crystal is manufactured. Therefore, only the flux growth that uses solution (flux) having fluoride and chloride as main component or the method, in which the BaTiO
3
series single crystal of low-temperature component is picked up directly by making the composition of the solution TiO
2
rich (the so-called top seeded solution growth (TSSG method)), is applicable to the growth thereof. With the flux growth, the obtainable size is only 1 mm
3
or less approximately. Also, for the TSSG method, not only an expensive noble metal crucible, such as a platinum crucible, is needed, but the growing speed is slow to make the manufacturing costs extremely high.
Conventionally, it has been attempted to provide a method for manufacturing larger BaTiO
3
series single crystal more effectively and easily with the improvement of the aspects that present the problems as described above.
For example, there are experiments carried out in manufacturing BaTiO
3
series single crystal efficiently by sintering method. In the specifications of Japanese Patent Application Laid-Open Nos. 4-300296, 5-155696 and 5-155697, a method for manufacturing BaTiO
3
series single crystal is disclosed, in which the BaTiO
3
series single crystal serving as the seed crystal is coupled with the BaTiO
3
polycrystal, and heated to mono-crystalize such polycrystal by means of solid-phase reaction. In the specification of Japanese Patent Application Laid-Open No. 9-263496, a method for manufacturing BaTiO
3
series single crystal is disclosed, in which a temperature gradient is given to the BaTiO
3
micro-crystal granular aggregate, the mol ratio of Ti/Ba of which is 1.0 or more and 1.1 or less, for the execution of single crystallization thereof. With these methods, however, the mono-crystalline growth rate greatly varies to make it impossible to grow any bulky single crystal with good reproducibility. Also, the rearrangement density is high, and the crystallinity of the BaTiO
3
series single crystal thus obtained is inferior to the one obtained by the conventional TSSG method and the flux method. There are also the examples of solid-phase methods other than the sintering method. In the specification of Japanese Patent Application Laid-Open No. 59-3091, there is the disclosure of a method for manufacturing the oxide single crystal, in which a crystal oxide, such as PbTiO
3
, BaTiO
3
, SrTiO
3
, CaTiO
3
, is quenched and solidified after molten to make it amorphous, and then, re-crystallized under a temperature gradient. This method makes the manufacturing apparatus and process complicated, because there is a need for a process to melt the crystal oxide. Also, the single crystal thus obtained has inferior crystallization properties, and only the crystal that has a high ratio of pore content is obtainable eventually.
Also, improvement studies have been made on the TSSG method and the flux method. In the specification of Japanese Patent Application Laid-Open No. 6-321698, there is disclosed, as the flux method, a method for manufacturing BaTiO
3
using a mixed substance of BaF
2
, NaF, Li
2
MoO
4
, or the like as flux. In this method, the solubility of BaTiO
3
is enhanced for the purpose of obtaining bulky BaTiO
3
series single crystal with a long-time crystal growth. However, this method is not fully satisfactory in terms of the time required for manufacturing and costs. In the specification of Japanese Patent Application Laid-Open No. 9-59096, there is disclosed BaTiO
3
series single crystal having the doping of fine quantities of Mg and Fe. This material aims at obtaining a high photo-refractivity in the near infrared range, but Mg, Fe, or some other element, which may exert unfavorable influence on the piezoelectric property, is contained in that material. As a result, it is not preferable to use this as a piezoelectric material. Also, for the utilization at the industrial level, it is not satisfactory in terms of the time required for manufacture and costs.
As described above, the TSSG or flux method for manufacturing BaTiO
3
series single crystal makes it extremely difficult to improve problems related to manufacturing efficiency, such as the time required for manufacturing and costs, among some others. Here, although the sintering method is anticipated to enhance the manufacturing efficiency, the variation of growing speed of BaTiO
3
series single crystal makes it impossible to obtain any satisfactory result, and also, the crystallinity of the BaTiO
3
series single crystal thus obtained is inferior to the one obtainable by means of TSSG or flux method. In other words, it has been difficult to implement the manufacture of BaTiO
3
series single crystal having excellent crystallinity and property in a shorter period of time at lower costs.
SUMMARY OF THE INVENTION
For the formation of BaTiO
3
series single crystal by sintering method, the inventors hereof have attempted to make the enhancement of the reproducibility of single crystal growth compatible with the enhancement of crystallinity and other substances by adding other component to BaTiO
3
itself. With this in view, the inventors hereof have studied assiduously, with the result that a system, in which PbTiO
3
is added to BaTiO
3
, is found to enable a crystallization growth to occur with an extremely fine reproducibility, satisfied only with a predetermined condition Therefore, the studies have been made further in detail on the BaTiO
3
—PbTiO
3
system to design the present invention completely.
The inventors hereof have measured the crystallinity of the BaTiO
3
—PbTiO
3
series single crystal obtained in accordance with the present invention. As a result, it is found that the BaTiO
3
—PbTiO
3
of the present invention is extremely fine in the crystallinity thereof. It is also confirmed by the X-ray diffraction and electron beam diffraction that the crystal orientation of the single crystal is completely coincident. Also, by the observation of etch pit, which will be described later, it is confirmed that the rearrangement density of the crystal is low, and that from this observation, the excellent crystal has a small amount of lattice defect. The ratio of pore content is also extremely small.
Following this, the other properties of the BaTiO
3
—PbTiO
3
series single crystal, such as permittivity, piezoelectric property, and pyroelectric property, among some others, are examined. As a result, it is found that the piezoelectric property is excellent in particular, which is far superior to the property of PZT (Pb (Ti, Zr) O
3
) polycrystal currently used as standards, or that of BaTiO
3
series single crystal manufactured by means of the TSSG method, not to mention that of BaTiO
3
polycrystal.
From the viewpoint of the BaTiO
3
—PbTiO
3
series single crystal as a piezoelectric material, it has such advantages as the wide range of temperatures at which it can be used, and the lower amount of lead content that it has attained, as well as the excellent piezoelectric property that it can pr
Aoto Hiroshi
Fukui Tetsuro
Ikesue Akio
Unno Akira
Anderson Matthew
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Norton Nadine G.
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