JP3032761B1 - Piezoelectric ceramics - Google Patents

Abstract

Abstract: free of lead, high Curie point, excellent piezoelectric characteristics, in particular, has a large mechanical quality factor (Q _m), and capable of oscillation at a stable oscillation and low voltage Provide piezoelectric ceramics. SOLUTION: This is a bismuth layered compound containing Sr, Bi, Ti and Ln (lanthanoid).
Including ₄ Ti ₄ O ₁₅ type crystal, atomic ratio Ln / (Sr + Ln)
Is 0 <Ln / (Sr + Ln) <0.5, and contains a Mn oxide.

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 high-temperature 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. For example, an actuator for position adjustment, which requires a large displacement amount in a DC manner, has a large piezoelectric constant (d ₃₃ ) instead of a small mechanical quality factor (Q _m ). In applications where alternating current is used, such as an ultrasonic wave generating element used for a piezoelectric element, an element having a large mechanical quality factor (Q _m ) instead of a small piezoelectric constant (d ₃₃ ) is used.

However, PZT and PT piezoelectric materials are
Many practical compositions have a Curie point of about 200 to 400 ° C. At higher temperatures, they become paraelectric and lose their piezoelectricity. Is not applicable. Further, since these lead-based piezoelectric materials contain a large amount (approximately 60 to 70% by weight) of lead oxide (PbO), which is extremely volatile even at a low temperature, it is also preferable from an ecological point of view and pollution prevention. Absent. 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 on an industrial level, lead oxide, a volatile component, is contained in the atmosphere. The amount of volatilization and diffusion to the water becomes extremely large. In addition, lead oxide released during the manufacturing stage can be recovered, but 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
It is inevitable that it causes 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.
(Bi _1/2 Na _1/2 ) TiO ₃ -xNaNbO ₃ solid solution is described, but there is no description of a solid solution having a Curie point exceeding 370 ° C. It is impossible to apply to an element for ultra-high temperature.

A piezoelectric body whose Curie point can be raised to 500 ° C. or higher
For example, a bismuth layer compound is known.
However, bismuth layered compounds that do not contain lead at all
Q that is important when applied to zonators_mAnd Qmax
There is a problem of being small. Q _mWill be smaller
Is considered to be because the coercive electric field is large and sufficient polarization cannot be performed.
It is. Qmax refers to the case where the maximum value of the phase angle is θmax.
tan θmax. That is, X is reactance and R is
Distance, the resonance frequency and the anti-resonance frequency
It is the maximum value of Q (= | X | / R) between the two. Qmax
The larger the value, the more stable the oscillation
It works. Japanese Patent Application Laid-Open No. 6-305817 discloses bismuth.
Pb as a layered compound_xBi_3-xTi_1-xNb_{1 + x}O
₉(0.3 ≦ x ≦ 0.75) is described. This group
In Curing, the Curie temperature is 500 ° C or higher.
According to their experiments, a sufficiently large Q_mAnd Qmax are obtained
There is also the problem of containing lead. In addition,
JP-A-54-32957 discloses (Pb_1-XSr_X) Bi_Four
Ti_FourO₁₅(However, bismuth represented by 0 <X <1)
In a sintered body having a layered structure, Mn, Fe, Co, N
Ferroelectric piezoelectric containing at least one of i and Cr
Although a porcelain material is described, this composition also contains lead.
You.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lead-free, high Curie point, excellent piezoelectric properties, especially a large mechanical quality factor (Q _m ), and stable oscillation. And a piezoelectric ceramic capable of oscillating at a low voltage.

[0008]

The above object is achieved by the following (1).
This is achieved by the present invention of (3). (1) Sr, Bi, Ti and Ln (lanthanoid)
Bismuth layer compound containing SrBi ₄ Ti ₄
A piezoelectric ceramic containing an O ₁₅ type crystal, an atomic ratio Ln / (Sr + Ln) of 0 <Ln / (Sr + Ln) <0.5, and containing a Mn oxide. (2) The content of Mn oxide is 0.6 in terms of MnO.
The piezoelectric ceramic according to the above (1), which is less than 2% by weight. (3) The content of Mn oxide is 0.4 in terms of MnO.
The piezoelectric ceramic according to the above (1), which is not more than 3% by weight.

Japanese Patent Publication No. 54-32957 discloses a ferroelectric material having a bismuth layered structure represented by (Pb ₁ -x Sr _x ) Bi ₄ Ti ₄ O ₁₅ and containing Mn. Piezoceramic materials are described. However, this porcelain material differs from the present invention in that it contains Pb and does not contain lanthanoids.

[0010] Also, "Trend Survey Report on Piezoelectric Ceramic Materials" issued by the Electronic Materials Industry Association in March 1979
Table 5 on page 18 also lists SrBi ₄ Ti ₄ O ₁₅ materials that can include Mn as an additional element. But,
The addition of lanthanoids is not described.

[0011] In the piezoelectric ceramic of the present invention, by containing both the Mn and lanthanoids, with very large Q _m can be obtained, a very large Qmax is obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION
This is a composite oxide containing r, Bi, Ti and Ln (lanthanoid), and further contains a Mn oxide.

In the piezoelectric ceramic of the present invention, the atomic ratio Ln / (Sr + Ln) is 0 <Ln / (Sr + Ln) <0.5. If Ln is not included, it is impossible to increase the Q _m and Qmax. On the other hand, Ln / (Sr + Ln)
Is Q _m and Qmax too large becomes low. L
A preferred range of n / (Sr + Ln) is 0.03 ≦ Ln / (Sr + Ln) ≦ 0.3.

As Ln, La, Ce, Er, Nd,
At least one of Sm, Eu, Gd, Dy and Ho is preferred.

[0015] Mn oxide, by combined addition with Ln oxide, significantly improves the Q _max improves the Q _m. As described above, the oscillation is more stable as Q _max is larger. Therefore, the piezoelectric ceramic of the present invention has better oscillation stability. If the content of the Mn oxide is too large, the insulation resistance becomes low and the polarization treatment becomes difficult.
The content of the n-oxide is preferably 0.6 in terms of MnO.
It is less than 2% by weight, more preferably 0.60% by weight or less, further preferably 0.43% by weight or less. On the other hand, Ln
In order to sufficiently exhibit the effect of the composite addition with the oxide, the Mn oxide is preferably contained in an amount of 0.02% by weight or more in terms of MnO. In particular, the effect of improving Qmax is enhanced.

The piezoelectric ceramic of the present invention contains SrBi ₄ Ti ₄ O ₁₅ type crystal, which is a bismuth layered compound, and is preferably substantially composed of this crystal. Heterophases may be included.
In this piezoelectric ceramic, Ln is SrBi ₄ T
It is considered that the Sr site of the i ₄ O ₁₅ type crystal is mainly substituted, but a part may be substituted for another site, or a part may be present at a crystal grain boundary. .

The overall composition of the piezoelectric ceramic of the present invention is:
Generally _{(Sr 1-x Ln x)} Bi 4 may be the Ti ₄ O ₁₅ which MnO is added in, but they may from now biased. For example, the ratio of Sr + Ln to Ti or the ratio of Bi 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 Ba, Ca, Pb, etc. as impurities or trace additives, but the total content of these is Ba.
In terms of oxides such as O, CaO, PbO, etc.
It is preferably at most 5% by weight. If the content of these elements is too large, the effects 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 450 ° C.
It is easy to raise the temperature to not less than ° C. In addition, the Q _m, 4.5M
At least around 2000 in the vicinity of Hz and 300
It is also easy to set it to 0 or more.

The piezoelectric ceramic of 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.

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

First, as a starting material, an oxide or
Compounds that can be converted to oxides by firing, for example, carbonates, hydroxides, oxalates, nitrates and the like, specifically Sr
Powders such as CO ₃ , Bi ₂ O ₃ , TiO ₂ , La ₂ O ₃ and MnO ₂ are prepared, and these are wet-mixed by a ball mill or the like.

Then, at about 800 to 1000 ° C., 1 to 3
Calcination is performed for about an hour, the obtained calcination product is converted into a slurry, and wet crushed using a ball mill or the like.

After the wet pulverization, the powder of the calcined product is dried, and a small amount of water (about 4 to 8% by weight) is added to the dried product, and 1 to 4 t / c
Press molding is performed under a pressure of about m ² to obtain a molded body. At this time, a binder such as polyvinyl alcohol may be added.

Next, the formed body is fired to obtain a piezoelectric ceramic. The firing temperature is preferably 1200 to 1350
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.

[0027]

Example 1 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 _{(Sr 1-x Ln x)} Bi 4 Ti 4 O 15 (x is a value shown in Table 1)
+ MnO (content is as shown in Table 1) and wet-mixed in pure water for 10 hours by a ball mill using zirconia balls.

Next, the mixture was sufficiently dried, press-molded, and calcined at 800 to 900 ° C. for 2 hours. The obtained calcined product was pulverized by a ball mill, dried, and granulated by adding a binder (polyvinyl alcohol). The obtained granulated powder is 2,000 to 3,000 using a uniaxial press molding machine.
A load of kgf / cm ² was applied to form a thin plate having a plane size of 20 mm × 20 mm and a thickness of about 1.5 mm. After subjecting the obtained molded body to a heat treatment to volatilize the binder, 1200 to 135
Baking at 0 ° C. for 2 to 4 hours. The obtained sintered body is polished to a thickness of about 0.5 mm.
After cutting to 6mm, flat dimensions of 5mm x 5 on both sides
mm silver electrodes were formed. Next, an electric field of 5 to 15 MV / m was applied in a silicone oil bath at 200 to 250 ° C for 1 to 10 MV / m.
The sample was subjected to a polarization treatment by applying a voltage for minutes, thereby obtaining a sample for characteristic measurement.

The Curie point of each sample was measured using an LCR meter HP4394A manufactured by Hewlett-Packard Company and an electric furnace. In addition, the DE hysteresis was measured using RT-6000HVS manufactured by Radiant Technology Co., and the coercive electric field at 250 ° C. was obtained. Moreover, it was measured by Hewlett Packard impedance analyzer HP4194A, obtains a thickness longitudinal electromechanical coupling coefficient (k _t) and mechanical quality factor (Q _m) by using a resonance-antiresonance method, also, thickness longitudinal vibration Qmax was determined in the fundamental mode. Incidentally, k _t and Q _m is calculated by the following equation, Qmax was the Q = | determined by / R | X.

[0031]

(Equation 1)

[0032]

[Table 1]

From Table 1, in SrBi ₄ Ti ₄ O ₁₅ ,
A part of Sr was substituted with Ln, by further contain an Mn oxide, improves Q _m, also, it can be seen that Qmax is remarkably improved. And even if Ln substitution and Mn addition are performed, the Curie point is hardly reduced.

The resonance frequency of each sample shown in Table 1 was around 4.5 MHz.

FIG. 1 shows (Sr_1-xLa_x) Bi_FourTi_FourO₁₅
+ MnO (0.31% by weight)
3 shows the results of powder X-ray diffraction analysis when the value was changed. same
The figure also shows the results of peak identification. From FIG. 1, La
When SrBi is added _FourTi_FourO₁₅Single phase of type crystal
It turns out that it becomes.

Example 2 A piezoelectric ceramic sample was prepared in the same manner as in Example 1 except that the type of Ln, the amount of Ln added, and the MnO content were as shown in Table 2. These samples, k _t in the same manner as in Example 1, was measured Q _m and Qmax. Table 2 shows the results.

[0037]

[Table 2]

From Table 2, it can be seen that the effects of the present invention are realized even when the MnO content is changed within the range limited by the present invention, or when a lanthanide other than La is used as Ln.

The samples of the present invention shown in Table 2 all had sufficiently high Curie points of 450 ° C. or higher.

The resonance frequency of each sample shown in Table 2 is
It was around 4.5 MHz.

The cross-sectional scanning electron micrographs of the sample substituted with Ln and the sample not substituted with Ln were taken and compared. As a result, pores were reduced by the Ln substitution, and the sintered body was dense. Has been confirmed. In addition, from observation after etching the cross section, it was confirmed that the crystal grains were spindle-shaped or needle-shaped in any of the samples.

[0042]

According to the present invention, a high-density piezoelectric ceramic which does not contain lead, has a high Curie point, a large mechanical quality factor, can stably oscillate and oscillate at a low voltage, is realized. I do.

[Brief description of the drawings]

FIG. 1 is a chart showing a powder X-ray diffraction analysis result when x is changed in a sintered body composed of (Sr _1-x La _x ) Bi ₄ Ti ₄ O ₁₅ + MnO.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Taiji Miyauchi 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDC Corporation (72) Inventor Toshiyuki Suzuki 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDD Inside (72) Inventor Yoshito Asakura 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDC Corporation (56) References JP-A-6-77551 (JP, A) JP-A-6-48826 ( JP, A) JP-A-6-80423 (JP, A) JP-A-6-77552 (JP, A) JP-A-50-34313 (JP, A) International publication 99/530 (WO, A1) Hirose Masakazu, et al. "Piezoelectric properties of Sr Bi4Ti4015-based ceramics", Jpn. J. Appl. Phys. Part 1 (1999), Vol. 38, No. 8, pages 5561-5563 (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/46 CA (STN) REGISTRY (STN)

Claims (3)

(57) [Claims] 1. A bismuth layered compound containing Sr, Bi, Ti and Ln (lanthanoid), wherein SrBi
Including ₄ Ti ₄ O ₁₅ type crystal, atomic ratio Ln / (Sr + Ln)
0 <Ln / (Sr + Ln) <0.5, and a piezoelectric ceramic containing a Mn oxide. 2. The piezoelectric ceramic according to claim 1, wherein the content of the Mn oxide is less than 0.62% by weight in terms of MnO. 3. The piezoelectric ceramic according to claim 1, wherein the content of the Mn oxide is 0.43% by weight or less in terms of MnO.