JP2001220226A - Piezoelectric ceramic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic free from lead, having the high Curie point, and further having excellent piezoelectric characteristics. SOLUTION: This piezoelectric ceramic is a bismuth layered compound containing MII, Bi, Ti, Ln and O (MII is at least one kind of elements selected from Sr, Ba and Ca; and Ln is at least one element selected from lanthanides), and contains MIIBi4Ti4O15 type crystal. Further, the molar ratio Ln/(Sr+Ln) satisfies the inequality: 0<Ln/(Sn+Ln)<0.5, and the molar ratio 4Bi/Ti satisfies the formula: 4.000<4Bi/Ti<=4.030.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic widely applicable 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 an external stress and an inverse piezoelectric effect in which distortion is generated by applying an electric field. Piezoelectric materials are sensors 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
Ferroelectrics having a perovskite structure such as iO ₃ ) are generally used. By adding various sub-components to these, various requirements are met.

However, PZT and PT piezoelectric materials are
Many practical compositions have a Curie point of about 300 to 350 ° C. On the other hand, the processing temperature in the current soldering process is usually 230 to 250 ° C., and therefore, a piezoelectric material having a Curie point of about 300 to 350 ° C. is likely to cause characteristic deterioration in the soldering process. In addition, when a lead-free solder (lead-free solder) is put into practical use, the processing temperature in the soldering process is further increased. Therefore, it is extremely important to increase 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.
% By mass), which is not preferable from an ecological point of view and pollution control. Specifically, when producing these lead-based piezoelectric materials as ceramics or single crystals, heat treatment such as firing and melting is inevitable, and when considered at the industrial level, lead oxide, a volatile component, is contained in air. The amount of volatilization and diffusion to the water becomes extremely large. Although lead oxide released during the manufacturing stage can be recovered, most of the lead oxide contained in piezoelectric materials put on the market as industrial products cannot be recovered at present, and these are widely used in the environment. If released to the public, it will inevitably cause pollution.

As a piezoelectric material containing no lead, for example, BaTi having a perovskite structure belonging to a tetragonal system is used.
O ₃ is well known and has a Curie point of 120
It is not practical because of low temperature. Also, JP-A-9-10
No. 0156 discloses a (1-x) having a perovskite structure.
Although a (Bi _1/2 Na _1/2 ) TiO ₃ -xNaNbO ₃ solid solution is described, the publication does not describe a solid solution having a Curie point exceeding 370 ° C.

As a piezoelectric substance whose Curie point can be raised to 500 ° C. or higher, for example, a bismuth layer compound is known.
However, a 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 a reactance and R is a resistance, it is the maximum value of Q (= | X | / R) between the resonance frequency and the antiresonance frequency. The larger the Qmax is, the more stable the oscillation becomes, and the oscillation at a low voltage becomes possible.

The 16th Ferroelectric Application Conference (May 26, 1999-2)
On pages 97-98 of the proceedings of 9), there is a report on improving the Qmax of a bismuth layered compound containing no lead. This report, as the bismuth layer compound containing no lead _{(Sr 1- x Me x) Bi} 4 Ti 4 O 15
Is described. Me = Ba, Ca, La, Sm, G
d, Ba and Ca are in the range of x ≦ 0.1, and Sm
And Gd are added in a range of x ≦ 0.4, and La is added in a range of x ≦ 0.5. In the proceedings of the above lecture, Qmax in the thickness longitudinal fundamental vibration was measured.
that Qmax is improved by the addition of
It is shown that the addition of a lowers 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 has excellent piezoelectric characteristics.

[0010]

The above object is achieved by the following (1).
This is achieved by the present invention according to (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
Bismuth layered compound containing i, Ti, Ln and O, containing M ^II Bi ₄ Ti ₄ O ₁₅ type crystal, molar ratio Ln
A piezoelectric ceramic wherein // (Sr + Ln) is 0 <Ln / (Sr + Ln) <0.5 and the molar ratio 4Bi / Ti is 4.000 <4Bi / Ti ≦ 4.030. (2) The piezoelectric ceramic according to the above (1), containing a Mn oxide. (3) The content of Mn oxide is 0.6 in terms of MnO.
The piezoelectric ceramic according to the above (2), which is less than 2% by mass. (4) The piezoelectric ceramic according to any one of the above (1) to (3), containing a Co oxide. (5) The piezoelectric ceramic according to (4), wherein the content of the Co oxide is less than 0.7% by mass in terms of CoO.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 , M ^II , Bi, Ti,
A bismuth layered compound containing Ln and O;
^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 relative 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. In addition, Qmax is rather lowered. In order to increase the improvement rate of Qmax, it is preferable that 4.010 <4Bi / Ti. In order to further suppress the decrease in insulation resistance, it is preferable that 4Bi / Ti ≦ 4.028.

The piezoelectric ceramic of the present invention contains a lanthanoid oxide to further improve Qmax. Lanthanoids are 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 preferred, and La is most preferred. The molar ratio Ln / (Ln + M ^II ) in the piezoelectric ceramic of the present invention is 0 <Ln / (Ln + M ^II ) <0.5, preferably 0.03 ≦ Ln / (Ln + M ^II ) ≦ 0.3. . If Ln / (Ln + M ^II ) is too large, Qmax
On the contrary, it becomes lower. The improvement in Qmax due to the addition of the Ln oxide is considered to be due to the improvement in sinterability. In addition, CaBi ₄ Ti ₄ O ₁₅ -based ceramics containing no Ln oxide are difficult to polarize, but the addition of the Ln oxide improves this.

Further, Qmax can be improved by adding a Mn oxide. In particular, by combined addition of the Mn oxide and Ln oxide, can significantly improve the Q _max. However, if the content of the Mn oxide is too large, the insulation resistance becomes low and the polarization treatment becomes difficult. Therefore, the content of the Mn oxide is preferably less than 0.62 mass% in terms of MnO, more preferably. Is 0.60% by mass or less, more preferably 0.43% by mass.
The following is assumed. On the other hand, in order to sufficiently exhibit the effect of the addition of the Mn oxide, the Mn oxide is preferably contained at 0.02% by mass or more in terms of MnO.
When the content is 3% by mass or more, the effect of improving Qmax becomes particularly high.

[0015] Qmax can also be improved by containing a Co oxide. In order to sufficiently exhibit the effect of improving Qmax, the content in terms of CoO should be set to 0.
It is preferably at least 1% by mass. However, when the content of the 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 to M ^II is too high, the piezoelectric ceramic is likely to be melted during firing.

The piezoelectric ceramic of the present invention contains M ^II Bi ₄ Ti ₄ O ₁₅ type crystal, which is a bismuth layered compound, and is preferably constituted substantially by this crystal. , For example, may contain a different phase.
In this piezoelectric ceramic, Ln is M ^II Bi ₄ T
Although it is considered that the M ^II site of the i ₄ O ₁₅ type crystal is mainly substituted, some of the M ^II site may be substituted for another site, and some 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
i / Ti (= b) should be within the above range,
In the case where a Mn oxide or a Co oxide is contained, MnO or CoO may be added thereto,
It may deviate 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 according to the valence of the metal element, oxygen vacancy, and the like.

The piezoelectric ceramic of the present invention may contain Pb oxide, Cr oxide, Fe oxide, etc. as impurities or trace additives, but the content of these oxides is PbO, Cr Each oxide is preferably 0.5% by mass or less in terms of oxides having a stoichiometric composition such as ₂ O ₃ and Fe ₂ O ₃ .
More preferably, the content is 5% by mass or less. If the content of these oxides is too large, the effect of the present invention may be impaired. It is most preferable that Pb is not contained in the piezoelectric ceramic of the present invention, but there is substantially no problem if the content is about the above.

The crystal grains of the piezoelectric ceramic of the present invention have a spindle shape or a needle shape. 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 ceramic of the present invention can be at least 380 ° C. or higher.
It is easy to raise the temperature to not less than ° C.

The piezoelectric ceramic of the present invention is suitable for a resonator, a high temperature sensor and the like.

The mode of use of the piezoelectric ceramic of the present invention is not particularly limited, and any mode such as thickness longitudinal vibration and thickness shear vibration can be used. A relatively high Qmax can be obtained in the thickness longitudinal fundamental vibration. However, the spurious vibration increases, and as a result, the stability of oscillation is slightly lowered. In contrast, in the third harmonic mode of thickness longitudinal vibration,
Qmax decreases, but spurious vibrations decrease. On the other hand, in the thickness-shear fundamental vibration, a spurious vibration is small and a sufficiently large Qmax is obtained.

According to the study by the present inventors, it has been found that when 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, further result of repeated experiments by the molar ratio in M ^II and x / 6 + 0.2 ≦ y ≦ 0.8, i.e., at least B as M ^II
Ba + C in M ^II using a and / or Ca
It has been found that the temperature characteristic of the resonance frequency can be made considerably flat by setting the ratio of a within the predetermined range.

[0025] In the above has been described piezoelectric ceramics containing M ^II Bi ₄ Ti ₄ O ₁₅ type crystal, 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
^I _0.5 Ti ₄ O ₁₅ type crystal (M ^I is Na, at least one alkali metal element K, etc.), also in the piezoelectric ceramic containing _{^{M II 2 Bi 4 Ti 5 O}} 18 type crystal, metal elements contained By deviating the ratio from the stoichiometric composition, Qma
It is possible to improve x.

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

First, as a starting material, an oxide or
Compounds may vary in the oxide by firing, for example, carbonates, hydroxides, oxalates, nitrates, specifically M ^II
CO ₃ , Bi ₂ O ₃ , TiO ₂ , La ₂ O ₃ , MnO ₂ , Mn
Powders such as CO ₃ are prepared and wet-mixed with a ball mill or the like.

Next, it is calcined. In addition, usually, it preliminarily forms before calcination. The calcination temperature is preferably 700 to 1000
° C, more preferably 750-850 ° C. If the calcining temperature is too low, the chemical reaction does not end sufficiently and the calcining becomes insufficient. On the other hand, when the calcination temperature is too high, the tentative compact starts to sinter, so that subsequent pulverization becomes difficult. The calcination time is not particularly limited, but is usually preferably 1 to 3 hours.

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

After the wet pulverization, the calcined powder is dried, and a small amount of water (about 4 to 8% by mass) is added to the dried substance.
Press molding is performed under 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 compact is fired to obtain a piezoelectric ceramic. The firing temperature is preferably 1100 to 1250 ° C.
And the firing time is preferably about 1 to 5 hours. The baking may be performed in the air, or may be performed in an atmosphere having a lower or higher oxygen partial pressure than in the air, or in a pure oxygen atmosphere.

After firing, a polarization treatment is performed. The conditions for the polarization treatment may be appropriately determined according to the composition of the piezoelectric ceramics. Usually, 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]

EXAMPLE A piezoelectric ceramic sample shown in Table 1 was produced by the following procedure.

As starting materials, SrCO ₃ , Bi ₂ O ₃ ,
Each powder _{TiO 2, La 2 O 3,} MnCO 3, final composition was blended so that _{Sr 0.9 La 0.1 Bi b Ti 4} O 15 + MnO (0.5 wt%), zirconia balls in pure water The mixture was wet-mixed by a ball mill for 16 hours. Table 1 shows b indicating the Bi content in the final composition.

Next, the mixture was sufficiently dried and preliminarily molded, and then calcined in the air for 2 hours. Calcination temperature is 80
It was selected from the range of 0-1000 ° C. The obtained calcined product was roughly pulverized in a mortar, and further pulverized by a grinder.
Next, the resultant was finely pulverized by a ball mill for 16 hours and dried. Next, after adding 10% by mass of a 10% polyvinyl alcohol solution as a binder and granulating, the mixture was press-molded at a pressure of 300 MPa to obtain a plane size of 20 mm × 20 mm and a thickness of 1 mm.
A 3 mm compact was obtained. After vacuum-packing this compact,
It was formed by a hydrostatic press at a pressure of 400 MPa.

The obtained molded body was fired. Firing is Bi
In a sealed container made of MgO in order to prevent evaporation. The firing temperature was selected from the range of 1120 to 1235 ° C, and the firing time was 4 hours.

From the obtained sintered body, a plane size of 15 mm × 1
A plate having a thickness of 5 mm and a thickness of 0.55 mm was cut out and lap-polished to obtain a thin plate having a thickness of 440 μm. Cu electrodes were formed on the upper and lower surfaces of the thin plate by vapor deposition to obtain a sample for measuring piezoelectric characteristics and a sample for measuring specific resistance.

In a silicone oil bath at 250 ° C., 1.5 × E _C (MV /
m) The above electric field was applied for 1 minute to perform polarization processing. Note that E _C is the coercive electric field of each sintered body at 250 ° C.

Next, the Cu electrode was removed by etching using an FeCl ₂ solution, and then the chip was cut out to 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 the chip by a vapor deposition method. The dimensions of the Ag electrode were 1.5 mm in diameter and 1 μm in thickness.

For each sample, the impedance characteristic was measured in the third harmonic mode of thickness longitudinal vibration using an impedance analyzer HP4194A manufactured by Hewlett-Packard Company, and Qmax was determined. Table 1 shows the results.

Further, regarding the sample for measuring the specific resistance,
A voltage of 100 V was applied at 250 ° C., and the specific resistance was measured. Table 1 shows the results.

[0042]

[Table 1]

From Table 1, it can be seen that by making Bi-rich within the range defined 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 sample of the present invention shown in Table 1 was analyzed by the powder X-ray diffraction method, it was found that M ^II B
It was confirmed that the i ₄ Ti ₄ O ₁₅ type crystal was almost a single phase.

The sample in the above embodiment is Mn
Is added, but even when Mn is not added,
Further, even when Co was added instead of part or all of Mn, improvement of Qmax was observed 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 (72) Inventor Junji Terauchi 1-1-13 Nihonbashi, Chuo-ku, Tokyo FDT term in TDK Corporation (reference) 4G030 AA08 AA09 AA10 AA11 AA13 AA16 AA25 AA28 AA43 BA10 CA01 4G031 AA04 AA05 AA06 AA09 AA11 AA19 AA22 AA35 BA10 CA01

Claims (5)

[Claims] 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 / (Sr + Ln) of 0 <Ln / (Sr + Ln) <0.5 Wherein the molar ratio 4Bi / Ti is 4.00 <4Bi / Ti ≦ 4.030. 2. The piezoelectric ceramic according to claim 1, comprising a Mn oxide. 3. The piezoelectric ceramic according to claim 2, wherein the content of the 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 method according to claim 1, wherein the content of the Co oxide is 0.1% in terms of CoO.
The piezoelectric ceramic according to claim 4, which is less than 7% by mass.