JP2000281443A - Piezoelectric ceramic composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To a lead-free piezoelectric ceramic composition excellent in piezoelectric characteristics by including a tungsten bronze-type compound oxide comprising Na, Ba, Nb and a specific content of Bi as metal elements. SOLUTION: This composition comprises a compound oxide containing Na, Ba, Nb and 3-6 wt.% (in terms of metal and based on the total weight of the composition) Bi as a principal ingredient. In the molar ratio composition formula xNaNbO3-yBaNb2O6-zBiNb3O9 [wherein, (x)+(y)+(z)=1], the composition preferably exists in the region surrounded by a quadrangle having apexes located at the points A (0.382, 0.560, 0.058), B (0.422, 0.520, 0.058), C (0.422, 0.505, 0.073) and D(0.382, 0.545, 0.073). The composition has a crystalline structure where almost all Bi are dissolved in crystal grains of ceramics to form a solid solution, and has the high Curie temperature of >=250 deg.C and low resonance frequency change with temperature of <=50 ppm/ deg.C. No danger of the vaporization/diffusion into the air and elution of lead doesn't exist.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic composition which can be used for a piezoelectric element, in particular, a piezoelectric resonator and an oscillator.

[0002]

2. Description of the Related Art Conventionally, as a material for a piezoelectric resonator and an oscillator, a PT-based ceramic containing PbTiO ₃ as a main component and a P _- based ceramic containing Pb (Zr _1-x Ti _x ) O ₃ as a main component have been used.
ZT ceramics have been widely used. Further, in order to improve their piezoelectric characteristics and suppress the temperature change of the resonance frequency, various additives are added, and a part of Pb is replaced with a divalent element such as Ba, Sr and / or Ca. Or Pb (Sb _1/2 Nb _1/2 ) O ₃
And a solid solution of a third component such as Pb (Mg _1/3 Nb _2/3 ) O ₃ has been used.

[0003] With the recent miniaturization and high precision of electronic equipment, materials for piezoelectric resonators and oscillators having a small change in resonance frequency with temperature have been desired, and PTs suitable for these applications have been desired.
And PZT-based ceramics have been used.

[0004]

However, the above P
T and PZT-based ceramics contain lead as a main component at a ratio of about 60% of their own weight, and there is a concern that harmful lead components are diffused in a manufacturing process such as firing to adversely affect the environment. Considering production at the industrial level, the volatilization and diffusion of lead components into the atmosphere is extremely large.

Further, recently, there has been a concern that the lead component may be eluted when the used lead-based waste is exposed to acid rain or the like. From the viewpoint of ecological viewpoint and pollution prevention, lead-free or lead-free waste is considered. There is a demand for a material having excellent piezoelectric properties even when the content is reduced.

The present invention has been made in view of the above problems, and has as its object to provide a piezoelectric ceramic composition which does not contain lead and can be used for applications such as piezoelectric resonators and oscillators.

[0007]

According to the present invention, Na, Ba,
A piezoelectric ceramic composition mainly containing a tungsten bronze-type composite oxide containing Bi and Nb metal elements, wherein Bi is contained in a proportion of 3 to 6% by weight in terms of metal in the total weight. Is a piezoelectric ceramic composition.

The piezoelectric ceramic composition of the present invention has a composition formula based on a molar ratio of xNaNbO ₃ —yBaNb ₂ O ₆ —
When represented by zBiNb ₃ O ₉ (where x + y + z = 1), (x, y, z) is point A (0.382, 0.56).
0, 0.058), point B (0.422, 0.520,
0.058), point C (0.422, 0.505, 0.0
73), point D (0.382, 0.545, 0.073)
Is preferably in a region surrounded by a square having a vertex as a vertex.

Further, the piezoelectric ceramic composition of the present invention contains at least one kind of the first transition metal in the porcelain in terms of oxide.
It is preferable to add it in the range of not more than weight%. Here, the first transition metal refers to 21Sc or more in the periodic table of the elements.
Metal element up to 30 Zn, and in the above configuration, the first transition metal is, in particular, V, Cr, Mn, Fe, Co
And / or Ni.

[0010]

The piezoelectric ceramic composition of the present invention comprises Na, Ba, Bi.
A piezoelectric ceramic composition mainly containing a tungsten bronze type composite oxide containing a metal element of Nb and Nb, wherein Bi is contained in a total amount of 3 to 6% by weight in terms of metal.

Thus, the Curie temperature is as high as 250 ° C. or more, and the absolute value of the temperature change of the resonance frequency is 100 ppm.
/ ° C. or less (hereinafter, the temperature change of the resonance frequency is indicated by an absolute value), and a piezoelectric ceramic composition as small as possible can be provided.

Further, the composition formula based on the molar ratio of the piezoelectric ceramic composition is expressed as xNaNbO ₃ -yBaNb ₂ O ₆ -zBi.
When represented by Nb ₃ O ₉ (where x + y + z = 1),
(X, y, z) in the composition formula is the point A (0.382, 0.560, 0.05) on the three-component composition diagram.
8), point B (0.422, 0.520, 0.058),
Point C (0.422, 0.505, 0.073), Point D
This is a region surrounded by a rectangle having (0.382, 0.545, 0.073) as a vertex.

Thus, the Curie temperature is 2 as described above.
It is as high as 50 ° C. or more, and the temperature change of the resonance frequency is 50 pp.
The piezoelectric ceramic composition is as small as m / ° C. or less.

Further, by including at least one kind of the first transition metal in the above-described piezoelectric ceramic composition in a range of 2% by weight or less in terms of oxide in the total amount, the electromechanical coupling coefficient and the mechanical quality are improved. The coefficient is improved, the Curie temperature is 250 ° C or higher, and the temperature change of the resonance frequency is 10 pp.
A piezoelectric ceramic composition suitable for applications such as a piezoelectric resonator and an oscillator having a very small m / ° C or less is obtained.

Moreover, the above-described piezoelectric ceramic composition is a lead-free piezoelectric ceramic composition that causes serious environmental problems, and is very easy to handle.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The piezoelectric ceramic composition of the present invention will be described with reference to the drawings as necessary.

The piezoelectric ceramic composition of the present invention comprises Na, Ba,
The piezoelectric ceramic composition is mainly composed of a tungsten bronze-type composite oxide containing Bi and Nb metal elements.

Bi is contained at a ratio of 3 to 6% by weight in terms of metal in the total amount, and Bi has a crystal structure in which most of the solid solution is dissolved in the crystal grains of the porcelain.

By specifying the amount of Bi, the Curie temperature is high (250 ° C. or higher), the temperature change of the resonance frequency is small, and it can be suppressed to 100 ppm / ° C. or lower.

The reason why the amount of Bi contained in the whole porcelain is 3 to 6% by weight as described above is that, for example, if the amount of Bi is less than 3% by weight, Bi dissolved in crystal grains is insufficient, and as a result, In addition, the temperature change of the resonance frequency becomes large, resulting in a piezoelectric ceramic composition that is not practically used.

On the other hand, if it exceeds 6% by weight, the amount of Bi dissolved in the crystal grains becomes excessive, and as a result, the Curie temperature is remarkably lowered to become lower than 200 ° C.

The Bi contained in the porcelain is desirably dissolved in crystal grains of the porcelain in order to suppress the temperature change of the resonance frequency.

The tungsten bronze type composition partially substituted with Bi is represented by the general formula: xNaNbO ₃ -yBa
Nb ₂ O ₆ -z BiNb ₃ O ₉ (where x + y + z =
When expressed by 1), this equation (x, y, z) is expressed by each point A (0.382, 0.56) on the three-component composition diagram of FIG.
0, 0.058), point B (0.422, 0.520,
0.058), point C (0.422, 0.505, 0.0
73), point D (0.382, 0.545, 0.073)
Is desirably an area surrounded by rectangles A, B, C, and D having a vertex as a vertex. Thereby, in particular, the temperature change of the resonance frequency can be suppressed to 50 ppm / ° C. or less, and a very stable piezoelectric ceramic composition can be obtained.

Further, in the piezoelectric ceramic composition of the present invention, the first transition metal (21.
It is preferable that at least one kind of metal elements from Sc to 30 Zn) is contained in a proportion of 2% by weight or less in terms of oxide in the total amount of the porcelain. At least one of the first transition metals in the porcelain
By including a specific amount of the seed, the piezoelectric characteristics of the porcelain, in particular, the temperature change of the resonance frequency can be reduced to 10 ppm / ° C. or less, and the electromechanical coupling coefficient and the mechanical quality coefficient can be greatly improved. it can. Incidentally, the first transition metal has a great effect of improving the electromechanical coupling coefficient and the mechanical quality coefficient, and therefore, V, Cr, M
Preferably it is n, Fe, Co and / or Ni. And, in this piezoelectric ceramic composition containing a specific amount of the first transition metal, when the content of the first transition metal increases, a part of those metal elements may also exist in the grain boundary part. There is.

The piezoelectric ceramic composition of the present invention can be produced, for example, as follows.

As starting materials, Na ₂ CO ₃ , BaCO 3
₃ , each powder of Bi ₂ O ₃ , Nb ₂ O ₅ and the oxide of the first transition metal is mixed at a predetermined ratio, and 900 to 1100 ° C.
After calcining for 3 to 5 hours, a powder having a desired material composition is produced by crushing. An organic binder is mixed with the powder, molded into a desired shape by a die press, an isostatic press, or the like, and then fired at 1150 to 1280 ° C. for 2 to 5 hours to obtain a porcelain. The same effect can be obtained by mixing the oxide of the first transition metal with the calcined powder during the above production process, not only at the time of preparation, but also at the time of calcining.

The raw material powder may be not only a carbonate or an oxide but also a compound such as an acetate or an organic metal as long as it becomes an oxide by a heat treatment process such as firing.

Further, in the piezoelectric ceramic composition of the present invention, K, Mg, Ca, S
Inevitable impurities such as i and Ta may be mixed.

[0029]

EXAMPLES As starting materials, Na ₂ CO ₃ , BaCO ₃ ,
Bi ₂ O ₃ , Nb ₂ O ₅ , V ₂ O ₅ , Cr ₂ O ₃ , Mn
Using O ₂ , Fe ₂ O ₃ , Co ₃ O ₄ and NiO, the porcelain composition was weighed so as to have the values shown in Tables 1 and 2, for example. This mixture was wet-mixed in a ball mill using ZrO ₂ balls for 12 hours. Next, after drying this mixture, it was calcined in the air at 900 to 1100 ° C. for 3 hours, and the calcined product was again finely pulverized by the ball mill. Thereafter, a binder such as polyvinyl alcohol (PVA) was mixed with the pulverized product and granulated. The obtained powder was used for 1.
It was press-formed at a pressure of 5 t / cm ² into a disk having a size of 16 mm in diameter and 1.5 mm in thickness. These compacts were fired at 1150 ° C. to 1280 ° C. for 2 to 5 hours.
The obtained porcelain was polished to a thickness of 0.5 mm.
As a result of measuring the X-ray diffraction pattern of the porcelain produced by the above method, the sample of the present invention was a tungsten bronze-type composite oxide, and Bi contained in the porcelain was dissolved in crystal particles. It was confirmed that. In addition, it was confirmed that most of the metal element as the first transition metal was dissolved in the crystal grains, but as the content increased, a part thereof also existed in the grain boundaries.

A silver electrode was formed on the porcelain obtained by the above method,
Polarization was performed by applying a DC electric field of 4 kV / mm in a silicone oil at 00 ° C. However, sample number 15 is 15
Polarization treatment was performed in silicone oil at 0 ° C. Then, the resonance-anti-resonance frequency of a thickness extensional direction were measured resonance resistance, using an impedance analyzer capacitance, the electromechanical coupling coefficient (k _t), mechanical quality factor (Q _m) and the relative dielectric constant (epsilon ₃₃ ^T / ε ₀ ).

[0031] examined the temperature variation in the thickness longitudinal resonance frequency (f _r) in the range of -20 to 80 ° C.. Temperature coefficient of f _r (f _r -TC) the _{formula: f r -TC = △ f r} / (f r
[20 ° C.] × 100) × 10 ⁶ (ppm / ° C.). However, △ f _r - amount of change fr in the range of _{20~80 ℃, f r [20 ℃} ] is the value of f _r at 20 ° C.. Further, the relative permittivity (ε ₃₃ ^T / ε ₀ ) was plotted as a function of temperature to determine the Curie temperature (T _C ) of the porcelain.

The results are shown in Tables 1 and 2.

[0033]

[Table 1]

[0034]

[Table 2]

From Table 1, it can be seen that a piezoelectric ceramic composition mainly composed of a tungsten bronze type composite oxide containing metal elements of Na, Ba, Bi and Nb,
The first piezoelectric ceramic composition of the invention in which the i in a proportion of 3-6 wt% in terms of metal, the temperature coefficient (f _r -TC) is 10
0 ppm / ° C or less (sample numbers 2 to 1).
4). According to a preferred embodiment of the present invention, it exhibits a temperature coefficient of 50 ppm / ° C. or less, and more preferably 10 ppm / ° C. or less, and exhibits PT and PZT ceramics used for conventional piezoelectric resonators and oscillators. It can be seen that they have the same level of temperature coefficient. Sample number 2
From 14 to 14, when the content of Bi contained in the porcelain is 3 to 6% by weight, the temperature coefficient is 100 ppm or less, and at the same time, the Curie temperature (T _C ) is as high as 250 ° C. or more. It can be seen that it can withstand heat during reflow.

In the piezoelectric ceramic composition of the present invention, sample No. 2
As shown in to 14 in a range Bi content of 3-6% by weight, it can be seen that the sign of the temperature coefficient (f _r -TC) is turned from negative to positive. Porcelain having a small value of the temperature coefficient in the composition in the vicinity of the change of the sign can be obtained.

The composition formula based on the molar ratio is expressed as xNaNbO.
₃ -yBaNb ₂ O ₆ -zBiNb ₃ O ₉ (however, x +
When represented by y + z = 1), the molar ratio of x, y, z in FIG. 1 is sample number 3 (point A (0.38
2,0.560,0.058)), sample number 5 (point B
(0.422, 0.520, 0.058)), sample number 11 (point C (0.422, 0.505, 0.07
3)), sample number 13 (point, D (0.382, 0.54
5,0.073) in a region surrounded by rectangles A, B, C, and D having vertices, for example, sample numbers 3, 4,
In 5, 6, 8, 10, 11, 12, and 13, it can be seen that the temperature coefficient is reduced to 50 ppm / ° C. or less due to this Bi-containing effect.

Sample numbers 2 to 13 show that the electromechanical coupling coefficient (k _t ) and the Curie temperature (T _C ) tend to decrease as the Bi content increases. On the other hand, it can be seen that the relative dielectric constant (ε ₃₃ ^T / ε ₀ ) tends to increase as the Bi content increases. Moreover, the mechanical quality factor (Q _m) is, Bi content is seen to exhibit a large value in the range of 3.9 to 5.1.

In the first aspect of the present invention, as shown in FIG.
In Sample Nos. 2, 7, 9, and 14 outside the polygonal areas formed by the quadrangular areas A, B, C, and D shown in the component composition diagram, the temperature coefficients can satisfy the practical level, but are higher than 50 ppm / ° C. It gets bigger. In particular, from the viewpoint of obtaining a piezoelectric ceramic having a small temperature change in the resonance frequency, it is desirable to control the composition so as to be set within the regions of the squares A, B, C, and D shown in the three-component composition diagram.

As shown in sample No. 1, the Bi content was 3
In less than wt% (Sample No. 1 2.1% by weight), the temperature coefficient (f _r -TC) becomes remarkably large, is not preferable for practical use. Further, Sample No. 15 Bi content exceeds 6 wt%, the temperature coefficient (f _r -TC) is 100 ppm / ° C.
And the Curie temperature (T _C ) is remarkably lowered. Sample numbers 16 to 39 shown in Table 2
Shows the results when at least one of the first transition metals is contained in the total amount of the porcelain at a ratio of 0.01 to 2% by weight in terms of oxides using the sample number 8 in Table 1. From this result, it can be seen that the electromechanical coupling coefficient (k ₃₃ ) and the mechanical quality coefficient (Q _m ) are improved as a whole. The temperature coefficient (f _r -TC) also it can be seen that improved as compared with no addition.

[0041] From Sample No. 16 to 24, in the range MnO ₂ added amounts of 0.2 to 2.0 wt%, the mechanical and electromechanical coupling coefficient (k ₃₃₎ in MnO ₂ amount is 0.4 wt% It can be seen that the quality factor (Q _m ) shows a peak (Sample No. 20). In sample No. 20, the electromechanical coupling coefficient (k ₃₃ ) was about 30 compared to the case where MnO ₂ was not added.
%, It can be seen that the mechanical quality factor (Q _m) is improved by about 5 times.

It can be seen that as the amount of added MnO ₂ increases, the Curie temperature (T _C ) decreases and the relative dielectric constant (ε ₃₃ ^T / ε ₀ ) increases. It can be seen that the Curie temperature (T _C ) decreases to 251 ° C. when the amount of added MnO _{2 is} increased to 2% by weight.

Incidentally, the addition of MnO ₂ added of 2.0 wt% or more (Sample No. 24), when compared with Sample No. 8 was not added, the temperature coefficient (f _r -TC) is -10 ppm /
° C to +42 ppm / ° C. Therefore, the addition of the first transition metal is desirably less than 2% by weight.

[0044] Within the scope MnO ₂ added amounts of 0.4 to 0.8 wt%, the sign of the temperature coefficient (f _r -TC) is seen to changes from negative to positive.

[0045] Sample No. 25-29, instead of _{MnO 2, Cr 2 O 3,} Fe 2 O 3, CoO, NiO, V 2
It can be seen that the electromechanical coupling coefficient (k ₃₃ ) and the mechanical quality coefficient (Q _m ) are similarly improved even when O ₅ is added in an amount of 0.4% by weight.

In sample numbers 30 to 39, MnO ₂ , Cr
_In the case where an oxide selected from ₂ O ₃ , Fe ₂ O ₃ , CoO, NiO, and V ₂ O ₅ was added in combination, the total addition amount was 0.4% by weight. In this case, it can be seen that the effect of improving the electromechanical coupling coefficient (k ₃₃ ) and the mechanical quality coefficient (Q _m ) is great. In sample numbers 30 to 33, the mechanical quality factor (Q _m ) exceeds 600. In addition, it can be seen that the effect of improving the electromechanical coupling coefficient (k ₃₃ ) is larger when the additive ratios shown in Sample Nos. 35 to 39 are used than when the oxide is added alone.

In the piezoelectric ceramic composition of the present invention, at least one of the first transition metals is contained in the total amount of the porcelain in order to improve the piezoelectric properties of the porcelain as described above.
It is preferable that the content is not more than the weight%.

[0048]

As described above, according to the present invention, N
In a total amount of porcelain mainly containing a tungsten bronze-type composite oxide containing metal elements a, Ba, Bi, and Nb, Bi is contained at a ratio of 3 to 6% by weight in terms of metal, and a general formula: xNaNbO _{3 -yBaNb 2} O ₆ -z
When represented by BiNb ₃ O ₉ (where x + y + z = 1), (x, y, z) in the above general formula is represented by the following points A:
(0.382, 0.560, 0.058), point B (0.
422, 0.520, 0.058), point C (0.42
2,0.505,0.073), point D (0.382,
0.545, 0.073) in the region surrounded by a square having at the apex at least one kind of the first transition metal contained in the whole amount of the porcelain at a ratio of 2% by weight or less. It is possible to provide a piezoelectric ceramic composition which can be used for applications such as a piezoelectric resonator and an oscillator having a small frequency temperature change and a high Curie temperature. Further, since the piezoelectric ceramic composition of the present invention does not contain any lead, volatilization and diffusion of lead components into the air, which has been a concern when using PT and PZT ceramics, This solves the concern of elution of lead components from waste. Therefore, a great effect can be expected from an ecological point of view and pollution control.

[Brief description of the drawings]

FIG. 1 is a three-component composition diagram of a piezoelectric ceramic composition of the present invention.

[Explanation of symbols]

 A, B, C, D ... Preferred areas according to claim 2

Claims (3)

[Claims] 1. A piezoelectric ceramic composition containing a tungsten bronze-type composite oxide containing metal elements of Na, Ba, Bi and Nb as a main component, wherein Bi is 3 to 6% by weight in terms of metal in the total weight. %. A piezoelectric porcelain composition comprising: 2. The composition formula based on the molar ratio is represented by xNaNbO ₃
−yBaNb ₂ O ₆ −zBiNb ₃ O ₉ (however, x + y
2. The piezoelectric ceramic composition according to claim 1, wherein, when expressed by + z = 1), x, y, and z are in a region surrounded by a polygon having the following points as vertices. xyz A (0.382, 0.560, 0.058) B (0.422, 0.520, 0.058) C (0.422, 0.505, 0.073) D (0.382) , 0.545, 0.073) 3. The piezoelectric ceramic composition according to claim 1, wherein at least one of the first transition metals is added in a proportion of 2% by weight or less in terms of oxide.