JP2003020275A - Piezoelectric ceramic and composition therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a piezoelectric ceramic which can be burned at a low temperature in a short time without deteriorating its piezoelectric characteristics, and to obtain a composition therefore. SOLUTION: In the piezoelectric ceramic composed of a sintered compact essentially consisting of Sr2 NaNb5 O15 , the average grain size of the crystals of the sintered compact is <=10 μm, and further, the ceramic consists of a sintered compact obtained by incorporating Ti or Ti and Ba in 0.1 to 3.0% by weight expressed in terms of TiO2 and BaCO3 into a composition of Sr2-x Cax NaNb5-y Tay O15 (0.01<=x<=0.5, and 0.01<=y<=2.0).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel piezoelectric ceramic used in actuators, vibrators, pressure sensors, filters, transformers, etc. and its composition.

[0002]

As a piezoelectric ceramic composition, a multi-component material containing PbZrO ₃ -PbTiO ₃ called PZT is the mainstream. As a lead-free system, JP-A-55-1
Na described in JP-A-04970 and JP-A-57-95869
_1-x Li _x Nb0 _3, perovskite compounds such as NaNbO ₃ -BaNiO ₃ -KNbO ₃ described in JP-A-9-1 165262, FC Report 15 (1997) No.6 ( Institute
(Na published by Japan Fine Ceramics Association)
_0.5 Bi _0.5 ) _0.95 Ca _0.05 Bi ₄ Ti ₄ O ₁₅ + MnCO ₃
(0.1 wt%) bismuth layer compound or tungsten bronze type compound as Ferroelectrics 160 (199
4) Sr _1.8 Ca _0.2 NaNb ₅ O ₁₅ described above is known.

Further, JP-A-10-297969 and JP-A-11-
No. 240759 and Japanese Patent Laid-Open No. 11-278932 disclose the general formula S
r ₂ NaNb ₅ O _{15 with} respect to Ti, Bi or Ca, T
A piezoelectric ceramic composition containing a, etc. is shown.

[0004]

PZT, which is a typical typical piezoelectric ceramic composition at the present time, contains lead (lead oxide). As environmental issues and legal regulations have been highlighted, it has become necessary to consider disposal of this material, and the emergence of a material that does not contain lead and has practical piezoelectric properties is strongly desired. . Therefore, from the viewpoint of reducing the lead-free materials or the environmental load as described above, P
Materials having a relatively low lead content, such as bBi ₄ Ti ₄ O ₁₅ series, have been developed, but their applications are limited due to piezoelectric characteristics.

In consideration of actuators, piezoelectric transformers, etc., which are actual applications, the piezoelectric ceramic composition is often made of a green sheet made of ceramics. However, since conventional lead-free materials have high sintering temperatures, it is difficult to use Ag / Pd paste with a high Ag content used in PZT for internal electrodes. Therefore, the cost may increase in a structure having a large number of layers. Also, if the piezoelectric ceramic composition can be fired at a low temperature, the amount of electric power at the time of manufacturing can be reduced, so that the cost can be reduced. Further, the above-mentioned publication does not refer to a specific composition and particle size.

An object of the present invention is to provide a piezoelectric ceramic and a composition thereof which can be fired at a low temperature in a short time without impairing the piezoelectric characteristics.

[0007]

The present invention is directed to Sr ₂ NaN.
A piezoelectric ceramic made of a sintered body containing b ₅ O ₁₅ as a main component is characterized in that the average grain size of crystals of the sintered body is 10 μm or less.

The present invention is also directed to Sr _2-x Ca _x NaNb ₅ O
_{15 (0.01 ≦ x ≦ 0.5)} , Sr 2 NaNb 5 -y Ta y O 15 (0.01
≦ y ≦ 2.0) and _{Sr 2-x Ca x NaNb 5} -y Ta y O 15 (0.
01 ≦ x ≦ 0.5, 0.01 ≦ y ≦ 2.0) Sintered body containing 0.1 to 3.0% by weight of one or more of Ti and Ba in terms of TiO ₂ and BaCO ₃ in any composition. It is in a piezoelectric ceramic.

Further, Sr _2-x Ca _x NaNb _5-y Ta _y O ₁₅
Is 0 ≦ x ≦ 0.5 and 0 ≦ y ≦ 2.0, and one or more kinds of Ti and Ba are converted into TiO ₂ and BaCO ₃ by weight, and 0.1 to
The composition is a composition having an average grain size of 10 μm or less of crystals made of a sintered body containing 3.0%.

In addition to the above, Mg, Mn, Li, La
And one or more of Bi and MgCO ₃ and MnC, respectively.
It is preferable to contain 0.01 to 3.0% by weight in terms of O ₃ , Li ₂ CO ₃ , La ₂ O ₃ and Bi ₂ O ₃ .

Further, the present invention is characterized in that, in the piezoelectric ceramic composition containing Sr ₂ NaNb ₅ O ₁₅ as a main component, the powder particle size after calcination is 1 μm or less, preferably 0.5 to 1.0 μm. .

Further, Sr_2-xCa_xNaNb_FiveO₁₅(0.01≤x
≤0.5), Sr₂NaNb_5-yTa_yO_{1 Five}(0.01 ≦ y ≦ 2.0)
And Sr_2-xCa_xNaNb_5-yTa_yO₁₅(0.01≤x≤0.
5, 0.01 ≤ y ≤ 2.0) either composition of Ti and Ba
TiO for one or more₂And BaCO ₃Converted to and weighted to 0.
It is characterized by containing 1 to 3.0% and consisting of powder after temporary sintering.
In the piezoelectric ceramic composition.

Further, Sr _2-x Ca _x NaNb _5-y Ta _y O
_In a composition of ₁₅ (0 ≦ x ≦ 0.5, 0 ≦ y ≦ 2.0), at least one of Ti and Ba is converted into TiO ₂ and BaCO ₃ , and the weight of the composition is 0.1.
The piezoelectric ceramic composition is characterized by comprising 1 to 3.0% of powder after calcination and having a particle size of 1 μm or less, preferably 0.5 to 1.0 μm.

The above-mentioned piezoelectric ceramic composition is composed of Mg, Mn, L
One or more of i, La and Bi are MgC
O ₃ , MnCO ₃ , Li ₂ CO ₃ , La ₂ O ₃ and Bi ₂ O ₃
It is preferable that the content is 0.01 to 3.0% in terms of weight.

As described above, the present invention resides in a piezoelectric ceramic composition mainly composed of a composite compound composed of a plurality of lead-free tungsten bronze type compounds. Further, it is preferable that the particle size of the raw material powder pulverized after the preliminary sintering before the main sintering which is the basis of the piezoelectric ceramic composition is 0.5 to 1.0 μm.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION (Example 1) Sr _2-x Ca _x NaN
The b _5-y Ta _y O ₁₅ composite compound will be described. First, as a starting material, SrCO ₃ , CaCO ₃ , Na ₂ CO ₃ , and Nb _{2 are used.}
Predetermined amounts of O ₅ and Ta ₂ O ₅ were weighed so that 0.01 ≦ x ≦ 0.5 and 0.01 ≦ y ≦ 2.0. In addition, instead of SrCO ₃ , Sr
O may be used. Next, as additives, Ti or both Ti and Ba were converted into TiO ₂ and BaCO ₃ and weighed in the range of 0.1 wt% to 3.0 wt% with respect to the weight of the composite oxide. Next, these starting materials were wet mixed with zirconia balls having a diameter of 1 to 10 mm for 24 to 48 hours, dried, and then calcined at 1000 to 1100 ° C for 2 to 12 hours.

Then, the mixture is pulverized by a pot mill or a ball mill for about 2 hours to obtain a powder having a particle size of 1.0 μm or less and mixed, and a binder such as PVA or PVB is added and pressure-molded. Firing was performed for a time to obtain a bulk sintered body. The structure of this bulk sintered body was analyzed by X-ray diffraction, and it was confirmed that it was a tungsten bronze type compound. The relative density of all the obtained samples was 94 to 96%, and the average crystal grain size was 1.0 to 12.6 μm or less.

Next, the sintered body was processed into a size of 3 mm × 3 mm × 10 mm and subjected to polarization treatment by applying a voltage of 1 to 5 kV / mm for 30 minutes in silicon oil at room temperature to 200 ° C. After that, the piezoelectric constant d33 of the obtained sample was measured by the resonance anti-resonance method using an impedance analyzer.

FIG. 1 is a graph showing the relationship between the Ca content and the piezoelectric constant of Sr _2-x Ca _x NaNb ₅ O ₁₅ . In addition,
As an additive, 0.1 wt% of Ti is converted to TiO ₂ with respect to the weight of the composite oxide, and the firing temperature is 1200 to 1250 ° C.
In addition, the conventional piezoelectric constant is the d33 characteristic of a material that does not contain Ti when fired at 1300 to 1400 ° C. Ti as shown in Fig. 1
The piezoelectric constant d33 of the sample added with was higher than that of the conventional sample in the range of 0.01 ≦ x ≦ 0.5. The maximum reached 130%. When the composition ratio x exceeds 0.5, the piezoelectric constant is lower than that of the conventional one when fired at 1200 to 1250 ° C. This tendency was the same for Ba. Further, the same tendency was exhibited when both Ti and Ba were converted into TiO ₂ and BaCO ₃ and added by 0.1 to 3.0% by weight with respect to the weight of the composite oxide.

FIG. 2 is a diagram showing the relationship between the amount of Ta and the piezoelectric constant d33 for Sr ₂ NaNb _5-y Ta _y O ₁₅ . In addition, 0.1% by weight of the additive is added to the composite oxide by converting Ti into TiO ₂ , and the firing temperature is 1200 to 1250 ° C. The conventional piezoelectric constant is the characteristic when fired at 1300 to 1400 ° C. As shown in FIG. 2, the composition ratio of the sample added with Ti is
In the range of 0.01 ≦ y ≦ 2.0, the piezoelectric constant was improved compared to the conventional one. The maximum reached 115%. When the composition ratio y exceeds 2.0, the piezoelectric constant is lower than that of the conventional one when fired at 1200 to 1250 ° C. This tendency was the same for Ba. Also, the same tendency was exhibited when both Ti and Ba were converted into TiO ₂ and BaCO ₃ and added by 0.1 to 3.0% by weight to the composite oxide.

FIG. 3 is a combination of the above two types S
r _2-x Ca _x NaNb the _5-y Ta y O ₁₅ in Ti by weight with respect to the entire composite oxide in terms of TiO _2, 12 by the addition of 0.1%
When the piezoelectric constant d33 of the sample fired at 00 to 1250 ° C was measured, it was found that the composition ratio of ○ in the range surrounded by A, B, C and D in FIG. There was a tendency for the piezoelectric characteristics to improve, and for the composition ratio marked with X to decrease. Composition ratio 0.01 ≦ x in the range surrounded by A, B, C and D in FIG.
In the case of ≦ 0.5 and 0.01 ≦ y ≦ 2.0, as in the case of Ba, even if both Ti and Ba are converted to TiO ₂ and BaCO ₃ and added to the weight of the composite oxide in an amount of 0.1 wt% or more and 3.0 wt% or less. This tendency was shown.

Example 2 Sr _1.8 Ca _0.2 NaNb ₅ O
_It will be explained based on ₁₅ . As before, SrC was used as the starting material.
O ₃ , CaCO ₃ , Na ₂ CO ₃ , Nb ₂ O ₅ and Sr _1.8 C
It was weighed so as to a _0.2 NaNb ₅ O _{1 5} composition. Then T
A predetermined amount of i or both Ti and Ba was converted to TiO ₂ or BaCO _{3 and} was weighed so as to be 0.1 wt% or more and 3.0 wt% or less with respect to the weight of the composite oxide. In addition, Mg, M as additives
One or more of n, Li, La, and Bi are M
gCO ₃ , MnCO ₃ , Li ₂ CO ₃ , La ₂ O ₃ , Bi ₂ O
Converted to ₃ , 0.01 wt% or more based on the weight of the piezoelectric ceramic composition
A predetermined amount was weighed so as to be 3.0 wt% or less. Subsequent processes such as powder mixing, pressure molding, degreasing, and sintering were the same as those described above, and a sample similar to that of Example 1 was prepared. The polarization conditions are also the same. The obtained bulk sintered body is X
The structure was analyzed by line diffraction and it was confirmed to be a tungsten bronze compound. The relative density of all the obtained samples is
It was 94 to 96%.

Table 1 shows Sr _1.8 Ca _0.2 NaNb ₅ O
1 w in the form of each additive to ₁₅ (composition ratio x = 0.2, y = 0, Ti converted to TiO ₂ and added 0.1 wt% to the weight of the composite oxide)
The values of the electromechanical coupling coefficient k33 and the piezoelectric constant d33 when t% is added are shown. The sample of No. 6 is the value of the conventional Sr _1.8 Ca _0.2 NaNb ₅ O ₁₅ which was calcined at 1300 ° C. without adding any additive. As shown in No.1 to No.5, the sample with the additive has a piezoelectric constant d33 improved by 1.4 to 1.6 times as compared with the conventional No.6, and the value exceeding 100 pC / N can be obtained. It was Regarding the firing temperature, it was confirmed that the piezoelectric characteristics did not deteriorate even when firing at a temperature of about 1180 to 1230 ° C.

[0024]

[Table 1]

The amount of addition and the piezoelectric constant of these additives
Examination of the relationship between d33, as shown in FIG. 4 Sr _1.8 C
a _0.2 NaNb ₅ O ₁₅ (composition ratio x = 0.2, y = 0) with Mg
It was confirmed that when CO ₃ is added, the piezoelectric constant d33 is improved as compared with the conventional sample manufactured at 1300 to 1400 ° C. in the addition amount range of 0.01 to 3.0 wt%. The firing temperature of this sample is 1180-1230 ℃. This tendency also had the same effect when two or more kinds of additives shown in Table 1 were added. Furthermore, the composite compound of the base material to which the additive is added is the Sr _2-x Ca _x NaNb _5-y Ta _y in Example 1 described above.
The same tendency was shown in the range of O ₁₅ of 0.01 ≦ x ≦ 0.5 and 0.01 ≦ y ≦ 2.0.

(Embodiment 3) Since the piezoelectric constant d33 is closely related to the density of the sintered body, the characteristics change depending on the size of the crystal grains of the sintered body. Also, the size of the crystal grains changes depending on the firing conditions. Therefore, we investigated the piezoelectric constant and average particle size. Table 2 is a summary of the material composition of each of the prepared samples, and Table 3 is the result.

In Table 2, sample Nos. A-1 to a-8 and sample N
ob-1 to b-8 have different composition ratios, sample No. c-1 to c-
Sample No.d-1 is a sample with fixed composition ratio and additive.
~ D-8 is a combination of these. The firing temperature was 1200 to 1250 ° C, and the relative density of all the obtained samples was 94 to 96%. In addition, all these samples have Ti
0.1 wt% was added to the weight of the composite oxide in terms of iO ₂ . Regarding ○ and × marks in Table 3, ○ marks are those which are improved or do not change than the piezoelectric constants of the samples prepared at the firing temperature of 1300 to 1400 ° C of the conventional method, and X marks are decreased or cannot be sintered at low temperature. Each one is shown.

As shown in Table 3, those having an average particle size of 10 μm or less in each material composition were obtained in which the piezoelectric constant was not improved or changed as compared with the sample prepared at 1300 to 1400 ° C. in the conventional method. It was also found that the same effects can be obtained for sample Nos. A-, b-, c-, and d- due to the difference in composition ratio and the difference in additives. Furthermore, the same was true for these combinations. In Tables 2 and 3, although the same material composition is used, the size of the crystal grains is different because the size of the crystal grains can be controlled by the sintering temperature and the holding time during sintering. .

From the above, if the average particle size of the sintered body is 10 μm or less, it can be fired at a low temperature of 1200 to 1250 ° C. without deteriorating the piezoelectric characteristics.

[0030]

[Table 2]

[0031]

[Table 3]

(Example 4) One of the low temperature sintering methods for ceramics is the miniaturization of the raw material powder. As shown in Example 3, the crystal grains of the sintered body and the piezoelectric constant are closely related.
In addition, since the sintering process involves grain growth, it is fully conceivable that the grain size of the raw material powder depends on the piezoelectric constant. Therefore,
The relationship between the grain size in the calcined powder and the crystal grain in the sintered body was investigated.
As a result, it was already described that the crystal grain size can be controlled by the sintering temperature and the holding time. However, even if the firing temperature and the holding time are the same, the smaller the size of the starting raw material powder, the smaller It turned out to be small. A detailed examination showed that the initial raw material powder size was 0.5 to 1.0 μ.
It was found that the average grain size of the crystals of the sintered body was 10 μm or less when the sintering temperature was 1200 to 1250 ° C. and the holding time was 2 to 24 hours.

Even if the grain size of the raw material powder is 0.5 to 1.0 μm, if the sintering temperature is 1200 to 1250 ° C. and the holding time exceeds 2 to 24 hours, the average grain size of the crystals of the sintered body is 10 μm. However, in this case, the productivity decreases because the time required for producing the sintered body increases and the amount of electric power supplied to the electric furnace increases.

When the grain size of the raw material powder is less than 0.5 μm, the average grain size of the crystal of the sintered body is 10
It can be suppressed to less than μm, but the powder tends to be clogged in the jig during the production of the compact, the production of the green sheet becomes a little difficult due to the large amount of binder, and it takes time to make the raw material powder finer. Deficiency occurs.

[0035]

According to the present invention, it is possible to provide a piezoelectric ceramic which does not contain lead and can be fired at a low temperature without impairing the piezoelectric characteristics and a composition thereof. Therefore, according to the present invention, it is environmentally friendly and can be used for the piezoelectric element for a wide range of applications described above.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between a composition ratio x of Sr _2-x Ca _x NaNb ₅ O _{15 and} a ratio of a sample manufactured by a conventional method to a piezoelectric constant.

FIG. 2 is a characteristic diagram showing the relationship between the composition ratio y of Sr ₂ NaNb _5-y Ta _y O _{15 and} the ratio of the sample prepared by the conventional method to the piezoelectric constant.

FIG. 3 is an Sr showing the scope of claim 1 of the present invention._2-x
Ca_xNaNb_5-yTa_yO ₁₅Composition diagram.

FIG. 4 MgCO ₃ addition amount and Sr _1.8 Ca without additive
FIG. 6 is a characteristic diagram showing the relationship between _0.2 NaNb ₅ O ₁₅ (composition ratio x = 0.2, y = 0) and the ratio of the sample manufactured by the conventional method to the piezoelectric constant.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Mitsuo Hayashibara             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. F-term (reference) 4G030 AA02 AA03 AA07 AA09 AA13                       AA20 AA25 AA43 BA10 CA05                       GA08 GA11

Claims (8)

[Claims] 1. A piezoelectric ceramic comprising a sintered body containing Sr ₂ NaNb ₅ O ₁₅ as a main component, and the average grain size of crystals of the sintered body is 10 μm or less. 2. Sr _2-x Ca _x NaNb ₅ O ₁₅ (0.01 ≦ x ≦ 0.
5), Sr ₂ NaNb _5-y Ta _y O ₁₅ (0.01 ≦ y ≦ 2.0) and Sr _2-x Ca _x NaNb _5-y Ta _y O ₁₅ (0.01 ≦ x ≦ 0.5, 0.
01≤y≤2.0) 0.1 to 3.0 by weight of one or more of Ti and Ba in terms of TiO ₂ and BaCO ₃ in any composition.
A piezoelectric ceramic characterized by comprising a sintered body containing 100%. 3. Sr _2-x Ca _x NaNb _5-y Ta _y O ₁₅ (0 ≦ x
≦ 0.5, 0 ≦ y ≦ 2.0) and 0.1 to 3.0% by weight in terms of TiO ₂ and BaCO _{3 of} at least one of Ti and Ba.
A piezoelectric ceramic comprising the sintered body contained therein, wherein the average grain size of the crystal of the sintered body is 10 μm or less. 4. The method according to claim 1, wherein Mg,
One or more of Mn, Li, La and Bi are each M
gCO ₃ , MnCO ₃ , Li ₂ CO ₃ , La ₂ O ₃ and Bi ₂
A piezoelectric ceramic containing 0.01 to 3.0% by weight in terms of O ₃ . 5. A piezoelectric ceramic composition comprising a powder obtained by pre-sintering a composition mainly composed of Sr ₂ NaNb ₅ O ₁₅ and having a particle size of 1 μm or less. 6. Sr _2-x Ca _x NaNb ₅ O ₁₅ (0.01 ≦ x ≦ 0.
5), Sr ₂ NaNb _5-y Ta _y O ₁₅ (0.01 ≦ y ≦ 2.0) and Sr _2-x Ca _x NaNb _5-y Ta _y O ₁₅ (0.01 ≦ x ≦ 0.5, 0.
01≤y≤2.0) 0.1 to 3.0 by weight of one or more of Ti and Ba in terms of TiO ₂ and BaCO ₃ in any composition.
%, And is composed of powder after provisional sintering, which is a piezoelectric ceramic composition. 7. Sr _2-x Ca _x NaNb _5-y Ta _y O ₁₅ (0 ≦ x
≦ 0.5, 0 ≦ y ≦ 2.0) and 0.1 to 3.0% by weight in terms of TiO ₂ and BaCO _{3 of} at least one of Ti and Ba.
Containing and consisting of powder after calcination, the particle size of the powder is 1μ
A piezoelectric ceramic composition characterized in that it is m or less. 8. The method according to claim 5, wherein Mg,
One or more of Mn, Li, La and Bi are each M
gCO ₃ , MnCO ₃ , Li ₂ CO ₃ , La ₂ O ₃ and Bi ₂
A piezoelectric ceramic composition containing 0.01 to 3.0% by weight in terms of O ₃ .