Ceramics with excellent piezoelectric property and their...

Details Ceramics with excellent piezoelectric property and their... Ceramics with excellent piezoelectric property and their...

1999-12-28

2002-09-17

Derrington, James (Department: 1731)

Plastic and nonmetallic article shaping or treating: processes

Outside of mold sintering or vitrifying of shaped inorganic...

Of electrical article or electrical component

C264S646000, C264S658000, C264S674000, C264S681000, C501S134000

Reexamination Certificate

active

06451244

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to piezoelectric ceramics which can be used as materials for solid displacement elements such as ceramic actuators, and to a method for producing them, and more particularly to Pb(Ni
⅓
Nb
⅔
)O
3
—PbTiO
3
—PbZrO
3
solid solution piezoelectric ceramics demonstrating far better displacement properties than piezoelectric ceramics produced by conventional manufacturing methods, as well as to a method for producing such solid solution ceramics. The piezoelectric ceramics of the present invention are useful as solid displacement elements, and can be applied to solid displacement elements such as actuators to produce solid displacement elements with displacement several times greater than that of conventional solid displacement elements, yielding the promise of lower drive voltage, greater compactness, and thus greater expansion in fields involving the application of solid displacement elements.
2. Description of the Related Art
With the advent of more compact and more intelligent electronic devices recently, the importance of ceramic actuators in the form of solid displacement elements has continued to increase. PbTiO
3
—PbZrO
3
solid solutions (hereinafter referred to as PZT) comprising the perovskite compounds PbTiO
3
(hereinafter referred to as PT) and PbZrO
3
(hereinafter referred to as PZ) are mainly used at present as ceramic actuator materials. So-called PNN—PT—PZ solid solutions, which are Pb(Ni
⅓
Nb
⅔
)O
3
—PbTiO
3
—PbZrO
3
solid solutions (hereinafter sometimes referred to as PNN—PT—PZ) obtained by mixing the complex perovskite compound Pb(Ni
⅓
Nb
⅔
)O
3
(hereinafter sometimes referred to as PNN) to the above solid solutions, have also been attracting more attention recently as materials for the next generation of ceramic actuators, because they can be sintered at lower temperatures than PZT solid solutions and because they show relatively high strain (~0.12%) around a composition consisting of 50 mol % PNN-35 mol % PT-15 mol % PZ.
Although the use of ceramic actuators has been studied in a variety of industrial fields recently, the displacement afforded by conventional piezoelectric ceramics has been unsatisfactory in terms of the displacement properties required in ceramic actuator applications, making the development of novel ceramic actuator materials and the further improvement of the displacement properties of conventional materials increasingly important issues. As a result of extensive research on methods for producing PNN—PT—PZ solid solutions, the inventors have perfected the present invention upon discovering piezoelectric ceramics with far better strain properties, as well as a method for producing such piezoelectric ceramics.
PNN, which is a primary component of PNN—PT—PZ solid solutions, is known to be extremely difficult to obtain in the form of a perovskite single phase in conventional methods for producing ceramics. It is also difficult to obtain high purity ceramics by conventional ceramic manufacturing methods when attempting to produce PNN—PT—PZ solution solutions with a high proportion of PNN.
However, the use of the novel method for producing piezoelectric ceramics developed by the inventors allows high purity PNN—PT—PZ solid solution piezoelectric ceramics to be readily produced, so that ceramics with far better strain properties than conventional PNN—PT—PZ piezoelectric ceramics can be developed.
SUMMARY OF THE INVENTION
An object of the present invention is to provide piezoelectric ceramic materials having far better strain properties than that of conventional piezoelectric ceramics, as well as a novel method for producing such piezoelectric ceramics. The present invention is a solid solution piezoelectric ceramic primarily comprising the complex perovskite compound Pb(Ni
⅓
Nb
⅔
)O
3
, the simple perovskite compound PbTiO
3
, and PbZrO
3
, wherein the aforementioned ceramic primarily comprises compositions within a triangle in which the compositional vertices are (X=52, Y=34, Z=14), (X=49,Y=37, Z=14), and (X=49, Y=34, Z=17), where Pb(Ni
⅓
Nb
⅔
)O
3
is X mol %, PbTiO
3
is Y mol %, and PbZrO
3
is Z mol % (X+Y+Z=100) among the triangular coordinates of the phase diagram in which the vertices are Pb(Ni
⅓
Nb
⅔
) O
3
, PbTiO
3
, and PbZrO
3
, as well as a method for producing such a solid solution ceramic.
The present invention provides high purity piezoelectric ceramics with a high proportion of PNN. When the piezoelectric ceramics developed in the present invention are used as ceramic actuator materials, the resulting ceramic actuators show far greater displacement than conventional ceramic actuators, with the promise of far more compact ceramic actuators and lower drive voltage, making the invention extremely valuable for industrial purposes.
The present invention, which solves the aforementioned drawbacks, comprises the following technical means.
(1) A method for producing Pb(Ni
⅓
Nb
⅔
)O
3
—PbTiO
3
—PbZrO
3
solid solution piezoelectric ceramics with high purity of PNN, which comprises preparing lead oxide (PbO), nickel oxide (NiO), niobium oxide (Nb
2
O
5
), titanium oxide (TiO
2
), and zirconium oxide (ZrO
2
) as starting materials by measuring out the lead oxide (PbO) in excess of that in the perovskite composition, mixing, forming the materials, heat treating the materials in air, then dissolving unreacted materials in the heat treated materirals to separate particles thereof, molding the resulting particles, and then sintering the molded product to produce a sinter.
(2) The method for producing solid solution piezoelectric ceramics with high purity of PNN according to the above (1), wherein said ceramics primarily comprising compositions within a triangle in which the compositional vertices are (X=52, Y=34, Z=14), (X=49, Y=37, Z=14), and (X=49, Y=34, Z=17), where Pb(Ni
⅓
Nb
⅔
)O
3
is X mol %, PbTiO
3
is Y mol %, and PbZrO
3
is Z mol % (X+Y+Z=100) among the triangular coordinates in the phase diagram in which the vertices are Pb(Ni
⅓
Nb
⅔
)O
3
, PbTiO
3
, and PbZrO
3
.
(3) The method according to the above (1), wherein the lead oxide (PbO) is added to the starting materials in excess of that in the perovskite composition of PNN—PT—PZ, and the materials are heat treated for 1 to 2 hours in air at 950 to 1000° C.
The present invention is described in further detail below.
The present invention for solving the aforementioned drawbacks relates to Pb(Ni
⅓
Nb
⅔
)O
3
—PbTiO
3
—PbZrO
3
solid solution piezoelectric ceramics demonstrating far better displacement properties than piezoelectric ceramics produced by conventional manufacturing methods, as well as to a method for producing such solid solution ceramics. The high-performance piezoelectric ceramics produced by this method can be used to manufacture ceramic actuators demonstrating displacement several times greater than that of conventional ceramic actuators, resulting in ceramic actuators that have extremely high displacement, that are more compact, and that require a lower drive voltage.
In the method of the present invention, lead oxide (PbO), nickel oxide (NiO), niobium oxide ((Nb
2
O
5
), titanium oxide (TiO
2
), and zirconium oxide (ZrO
2
) are used as starting materials. These materials are mixed in a predetermined ratio, such as 5 PbO+0.5 NiO+0.5 Nb
2
O
5
+1.05 TiO
2
+0.45 ZrO
2
, formed into a suitable form such as a tablet or square rod on the like, and suitably heat treated for 1 to 2 hours in air 950 to 1000° C. As preferable examples of methods for mixing the materials, wet milling or dry milling is included, as preferable examples of forming methods, mold pressing or wet pressing is included, and as preferable examples of heat treatment, heat treatment in air is included, but

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