JPH11100265A - Piezoelectric ceramic composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain practical piezoelectric characteristic and excellent strength by controlling a value obtained by dividing the difference of the lattice constant of single compounds such as plural kinds of bismuth layer compounds constituting a multiple compound by the average value of the lattice constant of the single compounds to equal to or below a specific value. SOLUTION: The multiple compound is constituted of plural kinds of the bismuth layer compounds as the single compounds and is controlled to be smaller in the value obtained by dividing the difference of the lattice constant of the single compounds by average value of the lattice constant of the single compounds than 0.029. As the multiple compound, (SrBi4 Ti4 O15 )x (BaBi4 Ti4 O15 )1-x , (SrBi2 Ta2 O9 )x (SrBi2 Nb2 O9 )1-x or the like are exemplified. A bulk sintered compact is obtained by blening and mixing SrO, Ba2 O3 and TiO2 each having several μm particle diameter so as to have the composition of SrBi4 Ti4 O15 and BaCO3 , Bi2 O3 and TiO2 so as to have the composition of BaBi4 Ti4 O15 , calcining, further pulverizing and mixing, adding a coupling agent to press mold and firing the molding at 900-1,000 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an actuator,
The present invention relates to a piezoelectric ceramic composition used for a vibrator, a pressure sensor, a filter, a transformer, and the like.

[0002]

2. Description of the Related Art As a piezoelectric ceramic composition, the multi-component material containing a PbZrO ₃ -PbTiO ₃ called PZT is the mainstream. A system containing no lead is disclosed in JP-A-60-21.
937 JP, Na _1-x described in JP-A-60-52098
Li _x NbO _3, as the NaNbO ₃ -BaNiO ₃ -KNbO _3, or bismuth layer compound described in JP-A-9-165262, FC Report 15 (1997) No.6
(Na _0.5 Bi _0.5 ) _0.95 Ca _0.05 Bi ₄ Ti ₄ O ₁₅ + described in (issued by Japan Fine Ceramics Association)
MnCO ₃ (0.1 wt%) is known.

[0003]

SUMMARY OF THE INVENTION PZT, which is a typical piezoelectric ceramic composition at present, contains lead (lead oxide). As environmental issues are becoming more important, disposal of this material has become a problem, and the emergence of a lead-free material having practical piezoelectric properties has been strongly desired.

[0004] In view of the above, from the viewpoint of reducing lead-free materials or the environmental burden as much as possible, PbBi
Materials with a relatively low lead content, such as ₄ Ti ₄ O _15, have been developed, but their use is limited for reasons of piezoelectric properties or strength.

[0005] In view of the above situation, a first object of the present invention is to provide a piezoelectric ceramic composition containing no lead and having practical piezoelectric characteristics.

[0006] A second object of the present invention is to contain no lead,
An object of the present invention is to provide a piezoelectric ceramic composition having excellent material strength.

[0007]

The first means for achieving the first object is to provide a piezoelectric ceramic composition comprising a plurality of bismuth layered compounds not containing lead, wherein The value obtained by dividing the difference in the lattice constant of the simple compound (bismuth layered compound) by the average value of the lattice constant of the simple compound is set to be smaller than 0.029.

A second means for achieving the first object is to provide a piezoelectric ceramic composition in a composite compound composed of a plurality of types of bismuth layered compounds containing no lead, and a simple compound (bismuth layered compound) serving as a base of the composite compound. Compound) in a combination of a ferroelectric substance and a non-ferroelectric substance.

The first means for achieving the second object is the first means.
In the first and second means for achieving the object of the invention, SrBi ₂ Ta ₂ O ₉ and SrBi ₂ Nb ₂
O ₉ is used.

A second means for achieving the second object is a second means.
In a first means for achieving the object of (1), SrBi ₂ Ta ₂
The content of O ₉ is 10 mol% or more and 40 mol% or less.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The first invention is described as SrBi ₄ Ti ₄ O ₁₅
The description will be based on a BaBi ₄ Ti ₄ O ₁₅ composite compound. First, as starting materials, SrO, Bi ₂ O ₃ ,
TiO ₂ was weighed to give a SrBi ₄ Ti ₄ O ₁₅ composition. Similarly, BaCO ₃ , Bi ₂ O ₃ , and TiO ₂ were also weighed in predetermined amounts. Since SrO reacts exothermically with water,
SrCO ₃ may be used instead of rO. Next, these starting materials were wet-mixed with zirconia balls having a diameter of 1 to 5 mm for 24 to 48 hours, dried, and then calcined at 700 to 750 ° C. for about 2 hours.

Next, pulverization and mixing are performed by a pot mill or a ball mill for about 2 hours, and a binder such as PVA or PVB is put in, pressed and formed, and baked at 900 to 1000 ° C. for about 2 hours to obtain a bulk sintered body. I got

When the structure of this bulk sintered body was analyzed by X-ray diffraction, it was found to be a bismuth layered compound. Next, the sintered body is processed into a size of 3 mm x 3 mm x 10 mm,
A voltage of 3 to 5 kV / mm was applied for 1 hour in silicon oil at 100 to 200 ° C. to cause polarization. Then, the piezoelectric constant d33 of the obtained sample was measured by a resonance anti-resonance method using an impedance analyzer.

[0014]

[Table 1]

As shown in Table 1, the piezoelectric constant d33 is SrB
₁₅ pC / i ₄ Ti ₄ O ₁₅ alone (sample a-1)
N, 1 in the case of BaBi ₄ Ti ₄ O ₁₅ alone (sample a-2)
It was 2 pC / N. On the other hand, (SrBi ₄ Ti ₄ O ₁₅ ) _x (BaBi ₄ Ti ₄ O ₁₅ ) _{1-x ′} x prepared by the above procedure.
In the case of = 0.4 (sample a-3), d33 is 40 pC / N
, Which is about three times that of a single unit.

When various bismuth layered compounds were prepared by the same procedure, sample a-4 in Table 1 showed that d33 was about 10%.
As small as pC / N, practical piezoelectric characteristics were not shown.
Further, even if the sample a-5 did not become a sintered body or became a small mass, the electric resistance was small and the sample could not be polarized. On the other hand, for samples a-6 to a-8, sample a-6
D33 comparable to -3 was shown.

The lattice dimensions of the bismuth layered compound are defined by lattice constants in the a-axis and c-axis directions. Focusing on the lattice constant of the a-axis where a relatively large difference occurs between the single compounds, a value (Δa / a _ave ) obtained by dividing the difference of the lattice constant of the a-axis of the single compound by the average value of the lattice constants of the a-axis. It is shown in Table 1.

Looking at d33 based on Δa / a _ave , Δa
In a material system where / a _ave is relatively large at 0.029,
It was found that a practical piezoelectric material could not be obtained, and a large d33 could be obtained with a material system having a material less than 0.029.

[0019]

[Table 2]

Next, the second invention will be described with reference to Table 2.
The materials shown in Table 2 were also manufactured by the above-described procedure. Both are X
It was confirmed by a line diffraction that the compound was a bismuth layered compound. F in the table indicates a ferroelectric, and NF indicates a non-ferroelectric. From the comparison of the test materials b-1 to b-4, it was found that a relatively large d33 was obtained by the combination of the ferroelectric and the non-ferroelectric. In addition, Sr in Table 2
D33 of _{Bi 2 Ta 2 O 9 -SrBi 2} Nb 2 O 9 is 80p
It was found that C / N was particularly large and practical characteristics were obtained.

As described above, piezoelectric elements are used for actuators, vibrators, pressure sensors, filters,
In a wide range of fields, such as transformers, in recent years, devices that can be used at high temperatures have been strongly desired.

Generally, when a piezoelectric element is used at a high temperature, depolarization is caused by thermal energy. Therefore, normally, about 1/2 of the Curie temperature (expressed in Celsius) is set as the upper limit of use. In the case of SrBi ₂ Ta ₂ O ₉ -SrBi ₂ Nb ₂ O ₉ , since the Curie temperature is 370 ° C., it can be used even at a high temperature of around 180 ° C. where the use of the piezoelectric element was not easy due to depolarization.

Also, SrBi ₂ Ta ₂ O ₉ -SrBi ₂ Nb
_{Since the} 2O ₉ composite compound has a large piezoelectric constant d33,
In terms of performance, it can also be used as an actuator. Generally, a piezoelectric material for an actuator also needs to have high strength. From this viewpoint, SrBi ₂ Ta ₂ O ₉ −
When the resistance strength of the SrBi ₂ Nb ₂ O ₉ material was measured, it was 60
８０80 Mpa, which is 1.5 to 2 times that of normal PZT. In general, bismuth layered compounds often have a high strength, which is considered to be due to a structure in which micro columnar crystals are entangled with each other.

FIG. 1 shows SrBi ₂ Ta ₂ O ₉ -SrBi ₂ Nb
FIG. 3 is a view showing the relationship between the mole fraction of SrBi ₂ Ta ₂ O ₉ of ₂ O ₉ material and d33. The mole fraction of SrBi ₂ Ta ₂ O ₉ is 3
10 mol% or more and 40 mol% with the peak around 0 mol%
In the following, it was found that d33 increased.

[0025]

According to the present invention, a piezoelectric ceramic composition containing no lead, having practical piezoelectric characteristics, and excellent material strength can be created. Therefore, according to the present invention, it is possible to obtain a piezoelectric element which has no environmental problems and can be used in a wide range of applications.

[Brief description of the drawings]

FIG. 1 shows SrBi ₂ Ta ₂ O ₉ -SrBi ₂ Nb ₂ O ₉
FIG. 3 is a characteristic diagram showing a relationship between a mole fraction of SrBi ₂ Ta ₂ O ₉ and a piezoelectric constant of the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Osamu Shiono 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Motoyuki Miyata 7, Omikamachi, Hitachi City, Ibaraki Prefecture No. 1-1, Hitachi Research Laboratory, Hitachi, Ltd.

Claims (4)

[Claims] 1. In a composite compound composed of a plurality of types of bismuth layered compounds not containing lead, the difference between the lattice constants of the simple compounds (bismuth layered compounds) that form the basis of the composite compound is calculated as the average value of the lattice constants of the single compounds. The value divided by
A piezoelectric ceramic composition having a size smaller than 029. 2. A composite compound comprising a plurality of types of bismuth layered compounds not containing lead, wherein a simple compound (bismuth layered compound) serving as a base of the composite compound is a combination of a ferroelectric substance and a non-ferroelectric substance. A piezoelectric ceramic composition characterized by the following. 3. The method according to claim 1, wherein the single compounds are SrBi ₂ Ta ₂ O ₉ and SrBi ₂ Nb.
A piezoelectric ceramic composition using ₂ O ₉ . 4. The voltage ceramic composition according to claim 3, wherein the content of SrBi ₂ Ta ₂ O ₉ is 10 mol% or more and 40 mol% or less.