JP3367929B2 - Piezoelectric ceramics - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic which can be widely applied to fields such as a resonator and a pressure sensor.

[0002]

2. Description of the Related Art A piezoelectric material is a material having a piezoelectric effect in which electric polarization is changed by receiving a stress from the outside and an inverse piezoelectric effect in which strain is generated by applying an electric field. Piezoelectric is a sensor for measuring pressure and deformation,
It is applied to resonators and actuators.

Most of the piezoelectric materials currently in practical use are tetragonal or rhombohedral PZT (PbZrO _3).
-PbTiO ₃ solid solution) or tetragonal PT (PbT
Ferroelectric materials having a perovskite structure such as iO ₃ ) are generally used. By adding various subcomponents to these, various required characteristics can be met.

However, PZT-based and PT-based piezoelectric materials are
Most practical compositions have a Curie point of about 300 to 350 ° C. On the other hand, since the current processing temperature in the soldering process is usually 230 to 250 ° C., the piezoelectric material having a Curie point of about 300 to 350 ° C. is likely to cause characteristic deterioration in the soldering process. Moreover, when a solder containing no lead (lead-free solder) is put into practical use, the processing temperature in the soldering process becomes higher. Therefore, it is extremely important to raise the Curie point of the piezoelectric material.

Further, these lead-based piezoelectric materials contain a large amount (60 to 70) of lead oxide (PbO), which is extremely volatile even at low temperatures.
It is not preferable from the ecological point of view and from the standpoint of pollution prevention. Specifically, when manufacturing these lead-based piezoelectric materials as ceramics or single crystals, heat treatment such as firing and melting is inevitable, and when considered at an industrial level, lead oxide, which is a volatile component, in the atmosphere. The amount of volatilization and diffusion is extremely large. Also, lead oxide released in the manufacturing stage can be recovered, but most lead oxide contained in piezoelectric materials marketed as industrial products is currently unrecoverable, and these are widely used in the environment. If released to, it is unavoidable to cause pollution.

As a piezoelectric material containing no lead, for example, BaTi having a perovskite structure belonging to the tetragonal system is used.
O ₃ is well known, but it has a Curie point of 120.
Since it is as low as ℃, it is not practical. In addition, JP-A-9-10
Japanese Patent No. 0156 discloses that the perovskite structure is (1-x).
Although a (Bi _1/2 Na _1/2 ) TiO ₃ —xNaNbO ₃ solid solution is described, the publication does not describe a Curie point of more than 370 ° C.

Bismuth layered compounds, for example, are known as piezoelectric materials having a Curie point of 500 ° C. or higher.
However, the bismuth layered compound containing no lead has a problem that Qmax, which is important when applied to a resonator, is small. Qmax is tan θmax when the maximum value of the phase angle is θmax. That is, when X is the reactance and R is the resistance, it is the maximum value of Q (= | X | / R) between the resonance frequency and the anti-resonance frequency. The larger Qmax is, the more stable the oscillation becomes, and the lower voltage the oscillation becomes possible.

The 16th Ferroelectric Application Conference (1999.5.26-2)
The reports of the proceedings of 9), pages 97 to 98, describe a report for improving the Qmax of a bismuth layered compound containing no lead at all. In this report, as a bismuth layer compound containing no lead, (Sr _{1- x} Me _x ) Bi ₄ Ti ₄ O ₁₅
Is listed. Me = Ba, Ca, La, Sm, G
d and Ba and Ca in the range of x ≦ 0.1, Sm
And Gd are added in the range of x ≦ 0.4, and La is added in the range of x ≦ 0.5. In the above-mentioned lecture proceedings, Qmax in the thickness longitudinal fundamental vibration is measured.
Improvement of Qmax by addition of a and Ba or C
It has been shown that the addition of a reduces Qmax.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a piezoelectric ceramic which does not contain lead, has a high Curie point and excellent piezoelectric characteristics.

[0010]

[Means for Solving the Problems] The above-mentioned object is as follows (1)
It is achieved by the present invention of (5). (1) When at least one element selected from Sr, Ba and Ca is represented by M ^II and at least one element selected from lanthanoids is represented by Ln, M ^II , B
A bismuth layered compound containing i, Ti, Ln and O, which contains M ^II Bi ₄ Ti ₄ O ₁₅ type crystals and has a molar ratio Ln.
Piezoelectric ceramics in which / ( M ^II + Ln) is 0 <Ln / ( M ^II + Ln) <0.5 and the molar ratio 4Bi / Ti is 4.000 <4Bi / Ti ≦ 4.030. (2) The piezoelectric ceramic of (1) above, which contains Mn oxide. (3) The content of Mn oxide is 0.6 in terms of MnO.
The piezoelectric ceramic of (2) above, which is less than 2% by mass. (4) The piezoelectric ceramic according to any one of (1) to (3) above, which contains a Co oxide. (5) The piezoelectric ceramic according to (4) above, wherein the content of Co oxide is less than 0.7% by mass in terms of CoO.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION When at least one element selected from Sr, Ba and Ca is represented by M ^II and at least one element selected from lanthanoids is represented by Ln, the piezoelectric ceramic of the present invention is , M ^II , Bi, Ti,
A bismuth layered compound containing Ln and O, M
^II A composite oxide containing Bi ₄ Ti ₄ O ₁₅ type crystals.

In the piezoelectric ceramic of the present invention, the molar ratio of 4Bi / Ti is 4.000 <4Bi / Ti ≦ 4.030. Thus, the stoichiometric composition of M ^II Bi ₄ T
By making Bi rich with respect to i ₄ O ₁₅ , Qmax is improved. However, when 4Bi / Ti exceeds 4.03, the insulation resistance becomes low and the polarization treatment becomes difficult. Also, Qmax is rather low. In order to increase the improvement rate of Qmax, it is preferable that 4.010 <4Bi / Ti. Further, in order to further suppress the decrease in insulation resistance, it is preferable to satisfy 4Bi / Ti ≦ 4.028.

The piezoelectric ceramic of the present invention contains a lanthanoid oxide in order to further improve Qmax. Lanthanoids include La, Ce, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y
b and Lu, of which La, Nd,
At least one of Sm, Gd, Dy, Ho, Er and Yb is preferable, and La is most preferable. The molar ratio Ln / (Ln + M ^II ) in the piezoelectric ceramic of the present invention is 0 <Ln / (Ln + M ^II ) <0.5, and preferably 0.03 ≦ Ln / (Ln + M ^II ) ≦ 0.3. . If Ln / (Ln + M ^II ) is too large, Qmax
On the contrary, it becomes low. It is considered that the improvement of Qmax due to the addition of the Ln oxide is due to the improvement of sinterability. Also, CaBi ₄ Ti ₄ O ₁₅ based ceramics containing no Ln oxide is difficult to polarize, but this is improved by the addition of Ln oxide.

Further, Qmax can be improved also by containing Mn oxide. In particular, by adding Mn oxide and Ln oxide together, Q _max can be remarkably improved. However, when the content of Mn oxide is too large, the insulation resistance becomes low and the polarization treatment becomes difficult. Therefore, the content of Mn oxide is preferably less than 0.62 mass% in terms of MnO, more preferably Is 0.60 mass% or less, more preferably 0.43 mass%
Below. On the other hand, in order to fully exert the effect of the addition of Mn oxide, the Mn oxide is preferably contained in an amount of 0.02 mass% or more in terms of MnO.
When it is contained in an amount of 3% by mass or more, the effect of improving Qmax becomes particularly high.

Also, Qmax can be improved by containing a Co oxide. In order to fully exert the effect of improving Qmax, the content in terms of CoO is set to 0.
It is preferably 1% by mass or more. However, if the content of Co oxide is too large, the insulation resistance increases and polarization becomes difficult. Therefore, the content in terms of CoO is preferably less than 0.7% by mass, more preferably 0.5% by mass or less. The Mn oxide and the Co oxide are
Each may be added alone or in combination.

[0016] M molar ratio in ^II Sr _x Ba _y Ca _z (provided that, x + y + z = 1 ) when expressed in, 0 ≦ x ≦ 1, 0 ≦ y ≦ 0.9 that is a 0 ≦ z ≦ 1 Is preferred. If the ratio y of Ba in M ^II is too high, the piezoelectric ceramics are likely to melt during firing.

The piezoelectric ceramics of the present invention include an M ^II Bi ₄ Ti ₄ O ₁₅ type crystal that is a bismuth layered compound, and it is preferable that the piezoelectric ceramics be substantially composed of this crystal, but it is not absolutely homogeneous. , For example, may contain a heterogeneous phase.
In this piezoelectric ceramic, Ln is M ^II Bi ₄ T
It is considered that the M ^II site of the i ₄ O ₁₅ type crystal is mainly substituted, but a part of the i ₄ O ₁₅ type crystal may be replaced with another site, or a part thereof may be present at the crystal grain boundary. Good.

The overall composition of the piezoelectric ceramic of the present invention is
Generally, in the ^{_{(M II 1-a Ln a}} ) Bi b Ti 4 O, 4B
As long as i / Ti (= b) is within the above range,
Further, in the case of containing Mn oxide or Co oxide, MnO or CoO may be added thereto,
It may be deviated from these. For example, the ratio of (M ^II + Ln) to Ti may deviate from the stoichiometric composition by about ± 5%. Further, the amount of oxygen can also change depending on the valence of the metal element, oxygen defects, and the like.

The piezoelectric ceramics of the present invention may contain Pb oxide, Cr oxide, Fe oxide and the like as impurities or trace additives, but the content of these oxides is PbO, Cr. It is preferably 0.5% by mass or less of each of the oxides having a stoichiometric composition such as ₂ O ₃ and Fe ₂ O _3, and the total amount of these oxides is not more than 0.
It is more preferably 5% by mass or less. If the content of these oxides is too high, the effects of the present invention may be impaired. It is most preferable that the piezoelectric ceramic of the present invention does not contain Pb, but if the content is in the above range, there is substantially no problem.

The crystal grains of the piezoelectric ceramic of the present invention are spindle-shaped or needle-shaped. The average crystal grain size is not particularly limited, but is preferably 1 to 10 μm in the major axis direction.
m, more preferably 3 to 5 μm.

The Curie point of the piezoelectric ceramics of the present invention can be at least 380 ° C. or higher and 430.
It is also easy to set the temperature above ℃.

The piezoelectric ceramics of the present invention are suitable for resonators, high temperature sensors and the like.

The mode of use of the piezoelectric ceramics of the present invention is not particularly limited, and any mode such as thickness longitudinal vibration or thickness shear vibration can be used. A relatively high Qmax is obtained with the thickness longitudinal fundamental vibration. However, there are more spurious vibrations, and as a result, the stability of oscillation is slightly lower. On the other hand, in the third harmonic mode of thickness longitudinal vibration,
Although Qmax decreases, spurious vibration decreases. On the other hand, in the thickness-shear fundamental vibration, spurious vibrations are small and a sufficiently large Qmax is obtained.

According to the research conducted by the present inventors, it was found that when the thickness shear vibration is used, the temperature characteristic of the resonance frequency becomes relatively steep and the temperature dependence of the oscillation frequency becomes relatively large. . Therefore, as a result of further experiments, by setting the molar ratio in M ^II to x / 6 + 0.2 ≦ y ≦ 0.8, that is, as M ^II , at least B
a + and / or Ca is used, and Ba + C occupied in M ^II
It has been found that the temperature characteristic of the resonance frequency can be made fairly flat by setting the ratio of a within the predetermined range.

The piezoelectric ceramics containing M ^II Bi ₄ Ti ₄ O ₁₅ type crystals have been described above. For example, M ^II B
i ₂ Nb ₂ O ₉ type crystal, M ^II Bi ₂ Ta ₂ O ₉ type crystal, Bi ₃
TiNbO ₉ type crystal, Bi ₄ Ti ₃ O ₁₂ type crystal, Bi _4.5 M
^In piezoelectric ceramics including ^I _0.5 Ti ₄ O ₁₅ type crystal (M ^I is at least one kind of alkali metal element such as Na and K) and M ^II ₂ Bi ₄ Ti ₅ O ₁₈ type crystal, By biasing the ratio from the stoichiometric composition, the Qma
It is possible to improve x.

Manufacturing Method Next, an example of a method for manufacturing the piezoelectric ceramics of the present invention will be described.

First, as a starting material, an oxide or
Compounds that can be converted into oxides by firing, such as carbonates, hydroxides, oxalates, nitrates, specifically M ^II
CO ₃ , Bi ₂ O ₃ , TiO ₂ , La ₂ O ₃ , MnO ₂ , Mn
Powder such as CO ₃ is prepared, and these are wet mixed by a ball mill or the like.

Then, calcination is performed. It should be noted that, usually, temporary forming is performed before calcination. The calcination temperature is preferably 700 to 1000.
C., more preferably 750 to 850.degree. If the calcination temperature is too low, the chemical reaction will not be completed sufficiently and calcination will be insufficient. On the other hand, if the calcination temperature is too high, the tentative compact will start to sinter, making subsequent pulverization difficult. Although the calcination time is not particularly limited, it is usually preferably 1 to 3 hours.

The obtained calcined product is slurried and wet-milled using a ball mill or the like. The average particle size of the powder obtained by this pulverization is not particularly limited, but considering the ease of subsequent molding, it is preferably about 1 to 5 μm.

After wet pulverization, the powder of the calcined product is dried, and a small amount of water (about 4 to 8% by mass) is added to the dried product, and then 100
Press molding is performed at a pressure of about 400 MPa to obtain a molded body. At this time, a binder such as polyvinyl alcohol may be added.

Next, the molded body is fired to obtain piezoelectric ceramics. The firing temperature is preferably 1100 to 1250 ° C
The firing time is preferably about 1 to 5 hours. The firing may be performed in the air, an atmosphere having a lower oxygen partial pressure than that in the atmosphere, a high atmosphere, or a pure oxygen atmosphere.

After firing, polarization treatment is performed. The conditions of the polarization treatment may be appropriately determined according to the composition of the piezoelectric ceramics, but normally the polarization temperature is 150 to 250 ° C., the polarization time is 1 to 30 minutes, and the polarization electric field is 1.1 times or more of the coercive electric field. do it.

[0033]

EXAMPLES The piezoelectric ceramic samples shown in Table 1 were prepared by the following procedure.

As starting materials, SrCO ₃ , Bi ₂ O ₃ ,
Powders of TiO ₂ , La ₂ O ₃ , and MnCO ₃ were mixed so that the final composition was Sr _0.9 La _0.1 Bi _b Ti ₄ O ₁₅ + MnO (0.5 mass%), and zirconia balls were added in pure water. Wet mixing was performed for 16 hours by the ball mill used. Table 1 shows b representing the content of Bi in the final composition.

Next, the mixture was thoroughly dried, preformed, and then calcined in air for 2 hours. Calcination temperature is 80
It was selected from the range of 0 to 1000 ° C. The obtained calcined product was roughly crushed in a mortar and then further crushed by a raider.
Then, it was pulverized with a ball mill for 16 hours and then dried. Then, 10% by mass of a 10% polyvinyl alcohol solution was added as a binder to granulate, followed by press molding at a pressure of 300 MPa to obtain a plane size of 20 mm × 20 mm and a thickness of 1
A 3 mm compact was obtained. After vacuum-packing this molded body,
It was molded by a hydrostatic press at a pressure of 400 MPa.

The obtained molded body was fired. Firing is Bi
Was carried out in a closed container made of MgO. The firing temperature was selected from the range of 1120-1235 ° C, and the firing time was 4 hours.

From the obtained sintered body, a plane size of 15 mm × 1
After cutting out a plate-shaped body having a thickness of 5 mm and a thickness of 0.55 mm, lapping was performed to obtain a thin plate having a thickness of 440 μm. Cu electrodes were formed on the upper and lower surfaces of this thin plate by vapor deposition to obtain a piezoelectric characteristic measurement sample and a specific resistance measurement sample.

A sample for measuring the piezoelectric characteristics was used in a silicone oil bath at 250 ° C. for 1.5 × E _C (MV / MV /
The above electric field was applied for 1 minute to perform polarization treatment. The above E _C is the coercive electric field of each sintered body at 250 ° C.

Then, the Cu electrode was removed by etching with a FeCl ₂ solution, and then cut into chips each having a plane size of 7 mm × 4.5 mm so that the polarization direction was the thickness direction. Ag electrodes for evaluating thickness longitudinal vibration were formed on the upper and lower surfaces of this chip by vapor deposition. The dimensions of this Ag electrode were 1.5 mm in diameter and 1 μm in thickness.

For each sample, impedance characteristics were measured in a third harmonic mode of thickness longitudinal vibration using an impedance analyzer HP4194A manufactured by Hewlett-Packard Co., and Qmax was obtained. The results are shown in Table 1.

Regarding the sample for measuring the specific resistance,
A voltage of 100 V was applied at 250 ° C. and the specific resistance was measured. The results are shown in Table 1.

[0042]

[Table 1]

From Table 1, it can be seen that by making Bi rich within the range limited by the present invention, Qmax is critically improved and a sufficiently high specific resistance can be obtained.

The Curie temperatures of the samples of the present invention shown in Table 1 were all 510 ° C. or higher. When the samples of the present invention shown in Table 1 were analyzed by the powder X-ray diffraction method, M ^II B
It was confirmed that the i ₄ Ti ₄ O ₁₅ type crystal was almost a single phase.

The samples in the above examples are Mn.
However, even if Mn is not added,
Further, even when Co was added in place of some or all of Mn, it was confirmed that Qmax was improved by adding Bi in excess.

[0046]

According to the present invention, a piezoelectric ceramic having a high Curie point and excellent piezoelectric characteristics is realized.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 2001-2468 (JP, A) JP 2000-313662 (JP, A) JP 2000-264727 (JP, A) JP 2000-143340 (JP, A) JP 2000-72542 (JP, A) JP 2001-192267 (JP, A) JP 2001-192266 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C04B 35 / 46-35/50 CA (STN) REGISTRY (STN)

Claims (5)

(57) [Claims] 1. When at least one element selected from Sr, Ba and Ca is represented by M ^II , and at least one element selected from lanthanoids is represented by Ln, M
A bismuth layered compound containing ^II , Bi, Ti, Ln and O, containing M ^II Bi ₄ Ti ₄ O ₁₅ type crystal, and having a molar ratio Ln / ( M ^II + Ln) of 0 <Ln / ( M ^II + Ln) Piezoelectric ceramics having a ratio of <0.5 and a molar ratio of 4Bi / Ti of 4.000 <4Bi / Ti ≦ 4.030. 2. The piezoelectric ceramic according to claim 1, which contains Mn oxide. 3. The piezoelectric ceramic according to claim 2, wherein the content of Mn oxide is less than 0.62% by mass in terms of MnO. 4. The piezoelectric ceramic according to claim 1, which contains a Co oxide. 5. The content of Co oxide in terms of CoO is 0.
The piezoelectric ceramic according to claim 4, which is less than 7% by mass.