JP2002284574A - Manufacturing method of piezoelectric ceramic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an excellent piezoelectricity for a lead-free piezoelectric ceramic. SOLUTION: In manufacturing a piezoelectric ceramic comprising a bismuth layer-structured compound containing MII (MII=Sr, Ba, or Ca), Bi, Ti, and O and MIIBi4 Ti4 O15 -type crystals, the calcined powder of the above, which shows both diffraction lines attributable to Bi4 Ti3 O12 -type crystals and MIIBi4 Ti4 O15 -type crystals in its X-ray diffraction chart and has the ratio of diffraction line intensities of 0.05<=B/(A+B)<=0.82 (A and B = the highest diffraction line intensities of the former and the latter, respectively), is formed and sintered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing piezoelectric ceramics which can be widely applied to fields such as resonators and pressure sensors.

[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 these lead-based piezoelectric materials are manufactured 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.

Examples of the piezoelectric material containing no lead include, for example, BaTi having a perovskite structure belonging to a tetragonal system.
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 having a high Curie point, for example, a bismuth layer compound is known. However, a bismuth layered compound containing no lead has a problem that Q _{max, which} is important when applied to a resonator, is small.
Q _max is tan θ when the maximum value of the phase angle is θ _max
max . 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. Oscillation is more stable as _Qmax is larger, and oscillation at a lower voltage is possible.

[0008] The present inventors have proposed in Patent No. 3032761 discloses, containing no lead, and, as a Q _max is greater bismuth layer compound, the piezoelectric ceramic obtained by adding lanthanoid the SrBi ₄ Ti ₄ O ₁₅ based composition are doing.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to realize excellent piezoelectric characteristics in a lead-free piezoelectric ceramic.

[0010]

The above object is achieved by the following (1).
This is achieved by the present invention according to (5). (1) Piezoelectric ceramics containing M ^II (M ^II is an element selected from Sr, Ba and Ca), a bismuth layered compound containing Bi, Ti and O, and containing M ^II Bi ₄ Ti ₄ O ₁₅ type crystal Wherein the piezoelectric ceramic is produced by molding and sintering a calcined powder, and in the X-ray diffraction chart of the calcined powder,
Diffraction line derived from i ₄ Ti ₃ O ₁₂ type crystal and M ^II Bi ₄ Ti ₄
And diffraction lines originating from the O ₁₅ type crystal, and Bi ₄ Ti ₃ O
The maximum intensity of the diffraction line derived from the type ₁₂ crystal is represented by A, and M ^II
The highest intensity of the diffraction line derived from Bi ₄ Ti ₄ O ₁₅ type crystal is B
A method for producing a piezoelectric ceramic in which 0.05 ≦ B / (A + B) ≦ 0.82. (2) The method for producing a piezoelectric ceramic according to the above (1), wherein the calcined powder is a mixture of plural kinds of calcined powders having different B / (A + B). (3) When the atomic ratio in M ^II expressed in _{Sr x Ba y Ca z, x} + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 0.9, piezoelectric ceramics produced is 0 ≦ z ≦ 1 The method for producing a piezoelectric ceramic according to the above (1) or (2). (4) A piezoelectric ceramic containing a lanthanoid oxide and having an atomic ratio Ln / (Ln + M ^II ) of 0 <Ln / (Ln + M ^II ) <0.5 when the lanthanoid is represented by Ln. ) ~
(3) The method for producing a piezoelectric ceramic according to any of (3). (5) The method for producing a piezoelectric ceramic according to any one of the above (1) to (4), wherein a piezoelectric ceramic containing a Mn oxide is produced.

[0011]

[Function and Effect] A piezoelectric ceramic is usually produced by calcining a starting material to obtain a calcined powder, molding the calcined powder, and sintering. In the present invention, M ^II Bi ₄ Ti ₄ O
_In producing a piezoelectric ceramic having a _15- system composition, the piezoelectric properties, particularly _Qmax, are improved by controlling the proportion of crystals contained in the calcined powder.

[0012]

Piezoelectric ceramics produced by the piezoelectric ceramic the present invention DETAILED DESCRIPTION OF THE INVENTION, M ^II (M
^II is an element selected from Sr, Ba and Ca), B
It is a bismuth layered compound containing i, Ti and O, and is a composite oxide containing M ^II Bi ₄ Ti ₄ O ₁₅ type crystal.

[0013] When the atomic ratio in M ^II expressed in _{Sr x Ba y Ca z, x} + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 0.9, is preferably 0 ≦ z ≦ 1. If the ratio y of Ba to M ^II is too high, the piezoelectric ceramic is likely to be melted during firing. If the proportion of Ca in M ^II is too high, the coercive electric field becomes high and polarization becomes difficult. Considering this point, it is preferable that z <1, and it is more preferable that z ≦ 0.8. However, when a lanthanoid oxide described later is contained, no problem occurs with respect to polarization even if the ratio of Ca to M ^II is high, for example, z = 1.

[0014] In the piezoelectric ceramics made according to the present invention, in order to further improve the Q _max, it is preferable to incorporate a lanthanoid oxide. Lanthanoids include La, Ce, Pr, Nd, Pm, Sm, Eu, G
d, Tb, Dy, Ho, Er, Tm, Yb and Lu, of which La, Nd, Sm, Gd, D
At least one of y, Ho, Er and Yb is preferred, and La is most preferred. When a lanthanoid (Ln) is contained, the atomic ratio Ln / (Ln + M ^II ) is 0 <Ln / (Ln + M ^II ) <0.5, preferably 0.03 ≦ Ln / (Ln + M ^II ) ≦ 0.3 It is. If Ln / (Ln + M ^II ) is too large, Q _max
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.

[0015] Further, Q _max can be improved by containing a Mn oxide. In particular, by combined addition of the Mn oxide and Ln oxide, can significantly improve the Q _max. However, when the content of the Mn oxide is too large, the specific resistance becomes low and the polarization treatment becomes difficult. Therefore, the content of the Mn oxide is preferably less than 0.62% by mass in terms of MnO, more preferably. Is 0.
It is 60% by mass or less, more preferably 0.43% by mass or less. On the other hand, in order to sufficiently exhibit the effect of the addition of the Mn oxide, the Mn oxide is converted to MnO at 0.1.
It is preferably contained in an amount of not less than 02% by mass, and when it is contained in an amount of not less than 0.03% by mass, the Q _max improving effect is particularly high.

Further, Q _max can be improved by containing a Co oxide. In order to sufficiently exhibit the Q _max improving effect, the content in terms of CoO should be set to 0.1.
It is preferably at least 1% by mass. However, when the content of the Co oxide is too large, the specific 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 piezoelectric ceramic made according to the present invention includes the M ^II Bi ₄ Ti ₄ O ₁₅ type crystal bismuth layered compound, it is preferably composed of a substantially crystals, perfectly homogeneous However, for example, it may include a different phase. In this piezoelectric ceramic, Ln
Is considered to mainly substitute for the M ^II site of the M ^II Bi ₄ Ti ₄ O ₁₅ type crystal, but some may substitute for other sites, and some may be substituted for crystal grain boundaries. May be present.

The overall composition of the piezoelectric ceramic made according to the present invention, as a ≧ 0, generally ^{_{(M II 1-a Ln a}} )
Bi ₄ Ti ₄ O ₁₅ may be used, and Mn oxide or Co
In the case where an oxide is contained, MnO or CoO may be added to this, but it may be deviated from these. For example, the ratio of M ^II + Ln to Ti, T
The ratio of Bi to i may deviate from the stoichiometric composition by about ± 5%. For example, it is possible to make Q _max higher by making the ratio of Bi to Ti higher. Further, the amount of oxygen can also change according to the valence of the metal element, oxygen vacancy, and the like.

The piezoelectric ceramics manufactured according to the present invention may contain Pb oxides, Cr oxides, Fe oxides and the like as impurities or trace additives. Is PbO, Cr ₂ O ₃ , F
It is preferable that each of the oxides is 0.5% by mass or less in terms of oxides having a stoichiometric composition such as e ₂ O _3, and the total of these oxides is 0.5% by mass or less. preferable. If the content of these oxides is too large, the piezoelectric properties may be impaired. It is most preferable that Pb is not contained in the piezoelectric ceramics, but there is substantially no problem if the content is about the above.

The crystal grains of the piezoelectric ceramic produced according to 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, more preferably 3 to 5 μm in the major axis direction.

The Curie point of the piezoelectric ceramic having the above composition can be at least 380 ° C. or higher.
It is easy to raise the temperature to not less than ° C.

The piezoelectric ceramic manufactured according to the present invention is suitable for a resonator, a high temperature sensor and the like. The mode of use is not particularly limited, and any mode such as, for example, thickness longitudinal vibration and thickness shear vibration can be used.

Manufacturing Method Next, the manufacturing method 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 to obtain a calcined body. In addition, usually, it forms temporarily before calcination and grinds after calcination. The pulverization of the calcined body is preferably performed by a wet method using a ball mill or the like.

In the present invention, at least Bi ₄ Ti ₃ O ₁₂ type crystal and M ^II B
A calcined powder containing i ₄ Ti ₄ O ₁₅ type crystals is produced. In the present invention, in the X-ray diffraction chart of the calcined powder, Bi ₄ Ti ₃
The maximum intensity of the diffraction line derived from the O ₁₂ type crystal is represented by A,
^When the maximum intensity of the diffraction line derived from the ^II Bi ₄ Ti ₄ O ₁₅ type crystal is represented by B, it is 0.05 ≦ B / (A + B) ≦ 0.82, and preferably 0.05 ≦ B / (A + B). ) ≦ 0.67. If B / (A + B) is too small or too large,
Q _max decreases.

In the present invention, the intensity of the diffraction line is Cu-K
Measure with alpha rays. Among the diffraction lines derived from the Bi ₄ Ti ₃ O ₁₂ type crystal, the one showing the highest intensity is the (171) plane diffraction line appearing near 2θ = 30.1 °. On the other hand, M ^II Bi
Among the diffraction lines derived from the ₄ Ti ₄ O ₁₅ type crystal, the one showing the highest intensity is the diffraction line of the (119) plane or the (0014) plane which appears around 2θ = 30.5 °. The X-ray diffraction chart of the calcined powder sometimes has a peak derived from the M ^II TiO ₃ type crystal.

Means for obtaining a calcined powder having B / (A + B) within the above range is not particularly limited.
In particular, B / (A + B) can be controlled by controlling the calcination temperature. The appropriate calcination temperature may be determined experimentally, but is preferably 720 to 980 ° C, particularly 750 to 980 ° C.
It is preferable to select from the range of 900 ° C. The calcination time is not particularly limited, but is usually preferably 1 to 3 hours. The calcination may be performed in air, or may be performed in an atmosphere having a lower or higher oxygen partial pressure than in air, or in a pure oxygen atmosphere.

The calcined powder having B / (A + B) within the above range may be a mixture of a plurality of calcined powders having different B / (A + B). That is, the calcined powder is B / (A
A mixture obtained by independently producing a calcined body having a relatively small + B) and a calcined body having a relatively large B / (A + B), and pulverizing and mixing them.
Even in such a mixture, B / (A + B) can be set to a value within the above-mentioned limited range, and in that case, the effect of the present invention is realized.

The calcined powders of a plurality of types need only have B / (A + B) within the range defined by the present invention when they are mixed, and B / (A + B) when used alone is particularly preferable. Not limited. For example, a mixture of a calcined powder in which B / (A + B) is 0 and a calcined powder in which B / (A + B) is 1 may be used.

The average particle size of the calcined powder is not particularly limited.
In consideration of the ease of subsequent molding, the thickness is preferably about 1 to 5 μm.

Next, after adding a small amount of water (about 4 to 8% by mass) to the calcined powder, press molding is performed under a pressure of about 100 to 400 MPa to obtain a molded body. At this time, a binder such as polyvinyl alcohol may be added.

Next, the compact is sintered 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 sintering may be performed in air, or may be performed in an atmosphere having a lower or higher oxygen partial pressure than in air, or in a pure oxygen atmosphere.

After sintering, a polarization process 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.

[0035]

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

As starting materials, CaCO ₃ , Bi ₂ O ₃ ,
Each powder of TiO ₂ , La ₂ O ₃ , and MnCO ₃ was mixed with (Ca _0.9 La _0.1 ) Bi ₄ Ti ₄ O ₁₅ + MnO (0.31
% By mass) and wet-mixed in pure water by a ball mill using zirconia balls for 10 hours.

Next, the mixture was sufficiently dried and pressed, and then calcined in air at a temperature selected from the range of 600 to 1000 ° C. for 2 hours. The obtained calcined body was pulverized with a ball mill and then dried to obtain a calcined powder. These calcined powders were subjected to X-ray diffraction using Cu-Kα radiation, the above-mentioned diffraction line intensities A and B were measured, and B / (A
+ B). Table 1 shows the results. 1 and 2 show X-ray diffraction charts of some calcined powders.

Next, the calcined powder was granulated by adding a binder (polyvinyl alcohol). The obtained granulated powder was molded into a thin plate having a thickness of about 1.5 mm by applying a load of 294 MPa using a uniaxial press molding machine. After subjecting the obtained molded body to a heat treatment to volatilize the binder, the molded body is exposed to air in air.
Sintered at 00 ° C for 4 hours. The obtained sintered body has a thickness of 500
lap polishing until it reaches μm, and the plane size is 15m
It was cut to a size of mx 15 mm.

Next, after forming Cu electrodes on the upper and lower surfaces of each sintered body by vapor deposition, an electric field of 1.1 × E _C (MV / m) or more is applied for 1 minute in a silicone oil bath at 250 ° C. Then, a polarization treatment was performed to obtain a piezoelectric ceramic sample. Note that E _C is the coercive electric field of each sintered body at 250 ° C.

Next, after removing the Cu electrode, each sample was lapped and polished to obtain a thin plate having a thickness of 435 μm. Ag electrodes were formed on both surfaces of this thin plate by vapor deposition, and an impedance analyzer HP419 manufactured by Hewlett-Packard Company was used.
Using 4A, the impedance characteristic was measured in the third harmonic mode of thickness longitudinal vibration, and _Qmax was determined. Table 1 shows the results.

[0041]

[Table 1]

Table 1 clearly shows the effect of the present invention. That is, a critically large _Qmax is obtained by controlling the calcined powder so that B / (A + B) falls within the range defined by the present invention.

The Curie point of each sample was 800 ° C. or higher. Further, when each sample was analyzed by the powder X-ray diffraction method, it was confirmed that it was a single phase of the CaBi ₄ Ti ₄ O ₁₅ type crystal.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction chart of a calcined powder.

FIG. 2 is an X-ray diffraction chart of a calcined powder.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Junji Terauchi 1-1-13 Nihonbashi, Chuo-ku, Tokyo TDK Corporation F-term (reference) 4G031 AA04 AA05 AA06 AA07 AA09 AA11 AA19 AA35 BA10 CA01

Claims (5)

[Claims] 1. A bismuth layered compound containing M ^II (M ^II is an element selected from Sr, Ba and Ca), Bi, Ti and O, and including M ^II Bi ₄ Ti ₄ O ₁₅ type crystal A method for producing a piezoelectric ceramic, wherein the piezoelectric ceramic is produced by molding and sintering a calcined powder, and in the X-ray diffraction chart of the calcined powder, a Bi ₄ Ti ₃ O ₁₂ type crystal Diffraction line and M ^II B
a diffraction line derived from the i ₄ Ti ₄ O ₁₅ type crystal,
_When the maximum intensity of the diffraction line derived from the ₄ Ti ₃ O ₁₂ type crystal is represented by A, and the maximum intensity of the diffraction line derived from the M ^II Bi ₄ Ti ₄ O ₁₅ type crystal is represented by B, 0.05 ≦ B /(A+B)≦0.82 A method for producing a piezoelectric ceramic. 2. The method for producing a piezoelectric ceramic according to claim 1, wherein the calcined powder is a mixture of a plurality of calcined powders having different B / (A + B). Wherein when the atomic ratio in M ^II expressed in _{Sr x Ba y Ca z, x} + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 0.9, a piezoelectric ceramic is 0 ≦ z ≦ 1 Is produced.
Method of manufacturing piezoelectric ceramics. 4. It contains a lanthanoid oxide, and when the lanthanoid is represented by Ln, the atomic ratio is Ln / (Ln + M ^II ).
There 0 <Ln / (Ln + M II) < method of any of the piezoelectric ceramics of claims 1 to 3, a piezoelectric ceramic is produced is 0.5. 5. The method for producing a piezoelectric ceramic according to claim 1, wherein a piezoelectric ceramic containing a Mn oxide is produced.