Ceramics with excellent electrostrictive property

Details Ceramics with excellent electrostrictive property Ceramics with excellent electrostrictive property

2000-02-18

2001-09-11

Brunsman, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

Titanate, zirconate, stannate, niobate, or tantalate or...

C252S06290R

Reexamination Certificate

active

06288002

ABSTRACT:

TECHNICAL FIELD
The present invention relates to electrostrictive ceramics, which have recently received attention as ceramic actuator materials, and in further detail, to electrostrictive ceramic materials comprising Pb(Ni
⅓
Nb
⅔
)O
3
—PbTiO
3
solid solution having markedly excellent electrostrictive property than that of conventional electrostrictive ceramics, and a method of producing these solid solution ceramics.
The electrostrictive ceramics of the present invention are useful as materials for solid displacement elements and practical use of electrostrictive ceramic actuators will probably be promoted and their application fields will be expanded by using this materials for the solid displacement elements, typically actuators.
BACKGROUND ART
The importance of ceramic actuators as solid displacement elements has increased in recent years with the development of miniaturized, intelligent electronic equipment. Today piezoelectric ceramics and electrostrictive ceramics are known as ceramic actuator materials, and with respect to the piezoelectric ceramics, they have already been used in many fields. On the other hand, although electrostrictive ceramics do have preferable actuator properties than piezoelectric ceramics, it is difficult to synthesize pure compounds by conventional ceramic synthesis methods and the amount of displacement of electrostrictive ceramics that are obtained by conventional method is approximately half compared with that of piezoelectric ceramics. Therefore, practical use of electrostrictive ceramics for displacement elements has been delayed. Since electrostrictive ceramic actuators have advantages in that their hysteresis and change over time in strain are less than that of piezoelectric ceramic actuators, their use is expected in fields where high accuracy and precise control of the amount of displacement are required (reference: “From Piezoelectric/Electrostrictive Actuator, Fundamentals to their Actual Use”: Kenji Uchino, Morihoku Shuppan, 1994).
Today a solid solution of the composite perovskite-type compound Pb(Mg
⅓
Nb
⅔
)O
3
(referred to as PMN below) and the primitive perovskite-type compound PbTiO
3
(referred to below as PT), that is a so-called PMN-PT solid solution, is being developed as an electrostrictive ceramics for practical use. This compound shows an extremely high relative dielectric constant at room temperature in the region of a composition of approximately 0.9 PMN-0.1 PT, and generates relatively large electric-field induced strain (~1 &mgr;m/mm). However, this amount of strain is about half compared with that of (Pb, La)(Zr, Ti)O
3
solid solution (PLZT), which, of the piezoelectric ceramics, is known to generate particularly large electric-field induced strain, and is not sufficient for an actuator material. Furthermore, the composition of a PMN-PT solid solution with which extreme strain is. obtained has a high ratio of Nb
2
O
5
, which is expensive, and it is difficult to obtain single-phase perovskite by ordinary ceramic synthesis methods. Thus, there is a problem with the current electrostrictive ceramics in that in addition to the fact that the amount of displacement that is obtained is small, the degree of freedom of material design is very limited.
Therefore, the inventors performed intense studies of electrostrictive materials showing large displacement in light of the above-mentioned prior art and as a result, they completed the present invention upon discovering that Pb(Ni
⅓
Nb
⅔
)O
3
—PbTiO
3
solid solution, which is known to show the same very high relative dielectric constant as PMN-PT solid solution, has an excellent electrostrictive property and is useful as electrostrictive material. This solid solution is known to have a very high relative dielectric constant near room temperature when 30 molar % primitive perovskite-type compound PbTiO
3
is made into a solid solution with the composite perovskite-type compound Pb(Ni
⅓
Nb
⅔
)O
3
(referred to below as PNN). However, it is difficult to obtain single-phase particles of perovskite in a PMN-PT solid solution by conventional ceramic synthesis methods and therefore, there has been very little research of its properties. Nevertheless, as a result of showing that particles of high purity can be easily obtained by the synthesis methods developed by the present inventors in recent years, they have discovered that this material has excellent electrostrictive properties and is useful as electrostrictive ceramic.
SUMMARY OF INVENTION
The present invention provides novel ceramic materials with excellent electrostrictive property.
The present invention relates to electrostrictive material ceramics comprising solid-solution ceramics where the primitive perovskite-type compound PbTiO
3
is contained in the region of 30 molar % to the composite perovskite-type compound Pb(Ni
⅓
Nb
⅔
)O
3
, and to a method of producing said solid-solution ceramics.
When the materials developed by the present invention are used in solid displacement elements, typically ceramic actuators, electrostrictive ceramic actuators which show displacement that is several times compared with that of Pb(Mg
⅓
Nb
⅔
)O
3
—PbTiO
3
solid solutions, which are now being tested for practical use as electrostrictive ceramic actuators, are newly provided at a low cost. Moreover, since the electrostrictive ceramics have theoretically little hysteresis and change over time in their strain, and the problems with the amount of strain that is generated can be solved by this invention, their use can be expected in fields where piezoelectric ceramic actuators have already been used, and therefore, the industrial value of the present invention is very great.
DISCLOSURE OF INVENTION
The object of the present invention is to provide a novel electrostrictive material having excellent electrostrictive properties that are much better than those of conventional electrostrictive ceramics.
Moreover, the object of the present invention is to provide a method of producing a Pb(Ni
⅓
Nb
⅔
)O
3
—PbTiO
3
solid solution that is useful as the above-mentioned electrostrictive material by a relatively simple synthesis process.
The present invention, which solves the above-mentioned subjects, comprises the following technological means:
(1) An electrostrictive ceramic having excellent electrostrictive property, comprising a solid-solution ceramic which can be obtained by combining a 26 to 34 molar % of primitive perovskite-type compound PbTiO
3
with a composite perovskite-type compound Pb(Ni
⅓
Nb
⅔
)O
3
.
(2) A method of producing the Pb(Ni
⅓
Nb
⅔
)O
3
—PbTiO
3
solid solution ceramic defined in (1), which comprises mixing tin oxide (PbO), nickel oxide (NiO), niobium oxide (Nb
2
O
5
), and titanium oxide (TiO
2
), forming the mixture, heat treating the formed body in air, and next, dissolving unreacted product, separating particles of product, forming the particles, and then sintering the product in a PbO atmosphere to obtain the sintered body.
(3) The above-mentioned method of producing a solid solution ceramic in (2), where heat treatment of the formed body is performed in air at 850 to 1,000° C.
(4) The above-mentioned method of producing a solid solution ceramic in (2), where after the particles of product are formed, they are sintered in a PbO atmosphere at 1,100 to 1,300° C. to obtain the sintered body.
The present invention will now be explained in further detail:
The present invention, which solves the above-mentioned subjects, relates to a novel electrostrictive material Pb(Ni
⅓
Nb
⅔
)O
3
—PbTiO
3
solid solution having much better electrostrictive properties than conventional electrostrictive ceramics. By using this compound as an actuator material, the problems of conventional electrostrictive ceramic actuators will be solved and actual use of electrostrictive ceramic actuators will be promoted.
By means of the present invention, a solid solution ceramic comprising a solid solution of 26 t

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