JP2001072466A - Piezoelectric ceramic composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a piezoelectric ceramic composition by designing itself to contain Li, Nb and Ba as metallic elements and the respective molar ratios for their oxides to fall within a specified range to raise its Curie temperature, increase its mechanical quality factor and frequency constant and diminish the absolute value of its temperature coefficient of resonance frequency. SOLUTION: This piezoelectric ceramic composition is represented by the compositional formula xLiNbO3.yNaNbO3.zBaNb2O6 in terms of the respective molar ratios for Li, Nb and Ba oxides (where x+y+z=1); wherein a point (x, y, z) falls within the area enclosed by a polygon with points A to E as apexes in a triangular coordinate diagram, and the respective coordinates of the points A to E are shown as follows in the order of x, y and z: A: (0.050, 0.250, 0.770), B: (0.300, 0.250, 0.450), C: (0.300, 0.450, 0.250), D: (0.150, 0.600, 0.250), and E: (0.050, 0.600, 0.350).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric porcelain composition, and more particularly to a piezoelectric porcelain composition which can be used for applications such as a piezoelectric resonator and an oscillator.

[0002]

Of the Prior Art Materials piezoelectric resonator and oscillator conventionally, as a main component PT ceramics and _{Pb (Zr 1-x Ti x} ) O 3 as a main component a PbTiO ₃ PZ
T-based ceramics have been used. These lead-based ceramics have a high Curie temperature and can withstand reflow soldering.

Some of these ceramics contain various minor additives so that the mechanical quality factor is improved, and some of Pb are replaced with Ba, Sr and C.
a substituted by a divalent element such as a, or P
b (Sb _1/2 Nb _1/2 ) O ₃ or Pb (Mg _1/3 N
b _2/3 ) A solid solution of a third component such as O ₃ has been used.

However, PT-based ceramics and PZT-based ceramics contain lead at a ratio of about 60% by weight, and lead components which are harmful to ecosystems are scattered in a manufacturing process such as firing, which adversely affects the environment. Is worried. In particular, in the case of industrial production, there has been a problem that the lead component volatilizes and diffuses in a large amount into the atmosphere.

Furthermore, used lead-based waste is exposed to acid rain and the like, and there is a risk that lead components are eluted. From the viewpoint of ecological viewpoint and pollution prevention, lead-free and excellent piezoelectric characteristics are obtained. Therefore, the development of lead-free ceramic materials has begun. For example, Japanese Unexamined Patent Application Publication No.
No. 69 discloses a composition formula (Ba _1-x Sr _x ) ₂ NaNb
A piezoelectric ceramic composition represented by ₅ O ₁₅ is disclosed.

[0006]

However, the composition disclosed in Japanese Patent Application Laid-Open No. Hei 10-297969 has a Curie temperature,
A composition that simultaneously satisfies the mechanical quality factor, the frequency constant, and the temperature coefficient of the resonance frequency cannot be obtained, and there has been a problem that it has not been possible to cope with recent improvements in the precision of electronic devices such as ceramic filters and oscillators.

Accordingly, the present invention has a high Curie temperature,
It has excellent characteristics that the mechanical quality coefficient and the frequency constant are large, and the absolute value of the temperature coefficient of the resonance frequency is small,
An object of the present invention is to provide a lead-free piezoelectric ceramic composition that can be used for applications such as a piezoelectric resonator and an oscillator.

[0008]

The piezoelectric ceramic composition of the present invention SUMMARY OF] contains a Li, Nb, Na and Ba as the metal element, xLiNbO ₃ · yNaNbO ₃ the composition formula by molar ratio of the oxides of the metal elements・ ZBaNb ₂ O
₆ (x + y + z = 1), the point represented by x, y, and z exists in a range surrounded by the following point ABCDCA. It is a porcelain composition.

Xyz A 0.050 0.250 0.700 B 0.300 0.250 0.450 C 0.300 0.450 0.250 D 0.150 0.600 0.250 E 0.050 0.600 0.350 The point (z, y, z) is, as shown in FIG.
-Curing temperature of 250 ° C. or higher and frequency constant of 25 by being present in a composition range surrounded by -DEA.
Above 00 Hz · m, the absolute value of the temperature coefficient of the resonance frequency can be 150 ppm / ° C. or less, and the mechanical quality constant can be 200 or more.

Further, the piezoelectric ceramic composition of the present invention comprises
b ₃ O ₉ that preferably contains 1 to 25 mol% in the total amount. This improves the mechanical quality factor,
The slope of the temperature coefficient changes from negative to positive, and its absolute value can be reduced.

Further, it is preferable that at least one kind of the first transition metal is contained in an amount of 0.01 to 5% by weight based on the total amount of oxides. This makes it possible to improve the mechanical quality factor and the temperature coefficient of the resonance frequency of the piezoelectric ceramic.

Therefore, the piezoelectric ceramic composition of the present invention can be suitably used as a resonator or an oscillator due to these piezoelectric characteristics.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The piezoelectric ceramic composition of the present invention has a composition formula based on a molar ratio represented by xLiNbO ₃ .yNaNbO _3.
When represented by zBaNb ₂ O ₆ (where x + y + z = 1), as shown in FIG. 1, the point (x, y, z) is the point A (0.0
50, 0.250, 0.700), B (0.300,
0.250, 0.450), C (0.300, 0.45
0, 0.250), D (0.150, 0.600, 0.
250), E (0.050, 0.600, 0.350)
Are located in a region surrounded by a polygon having a vertex as a vertex.

X, y and z are points A, B, C,
The reason for setting the range surrounded by a polygon having D and E as vertices is that when x, y and z are within this range, the Curie temperature is 250 ° C. or more, the mechanical quality factor is 200 or more,
This is because the frequency constant can be 2500 Hz · m or more, and the absolute value of the temperature coefficient of the resonance frequency can be 150 ppm / ° C. or less.

Further, the piezoelectric ceramic composition of the present invention comprises BiN
b ₃ O ₉ that preferably contains 1 to 25 mol% in the total amount. That is, (1−α) (xLiNbO ₃ .yNaNbO
₃ · zBaNb ₂ O ₆ ) · αBiNb ₃ O ₉ (where x
+ Y + z = 1), when α is expressed in a molar ratio, it is preferable that α be in the range of 1 mol to 25 mol%.
Thereby, the frequency constant can be 2900 Hz · m or more, and the mechanical quality factor can be 500 or more.

On the other hand, BiNb ₃ O ₉ contains 25 mol% of the total amount.
If the Curie temperature exceeds 230 ° C., the Curie temperature tends to decrease, and it will not be able to withstand the reflow soldering temperature of 230 ° C. If it is less than 1 mol%, the effect of addition will not be sufficient.
1 to 25 mol% is preferred.

In order to obtain excellent piezoelectric properties, the main crystal is a tungsten bronze type composite oxide,
It is preferable that the metal elements i, Na, Ba, Bi, and Nb are dissolved in the main crystal with each other.

Further, at least one of the first transition metals (elements from Sc having an atomic number of 21 to Zn having an atomic number of 29) is contained in the above-described piezoelectric ceramic composition in an amount of from 0.01 to 0.01 in terms of oxide in the total amount. It is preferable to contain 5% by weight. With this piezoelectric ceramic composition, a piezoelectric ceramic having a mechanical quality factor of 1000 or more and an absolute value of the temperature coefficient of the resonance frequency of 20 ppm / ° C. or less can be obtained.

Here, the addition amount of the first transition metal is 0.01
If it is less than 5% by weight, the effect is small, and if it exceeds 5% by weight, the sinterability of the porcelain deteriorates, and the mechanical quality factor tends to decrease. Therefore, 0.01 to 5% by weight is preferable.

In addition, the first transition metal has a great effect of improving the mechanical quality factor, so that V, Cr, M
It is particularly preferable to select from at least one of n, Fe, Co and Ni.

Further, the first transition metal is preferably dissolved in the crystal grains of the main crystal phase of the tungsten bronze type composite oxide of the porcelain, because the temperature coefficient of the resonance frequency is remarkably improved. . However, when the content of the first transition metal increases, a part of those metal elements may be present in a large amount in the second phase or in the grain boundary part, but the composition is within the scope of the present invention. If so, you can do nothing.

The piezoelectric ceramic comprising the piezoelectric ceramic composition of the present invention can be produced, for example, as follows. As starting materials, Li ₂ CO ₃ , Na ₂ CO ₃ , BaCO
₃ , each powder of Nb ₂ O ₅ and, if desired, Bi ₂ O ₃ or an oxide of a first transition metal is mixed at a predetermined ratio,
After calcining at 950 ° C. for 3 to 5 hours, a powder having a desired material composition is produced by pulverization.

An organic binder is mixed with the powder, molded into a desired shape by a mold press, an isostatic press, or the like, and then subjected to an oxygen-containing atmosphere such as air at a temperature of from 1020 to 1280 ° C.
And baking for 2 to 5 hours to obtain a porcelain. The same effect can be obtained when the oxide of the first transition metal to be added is mixed with the calcined powder during the above-described production process, not only at the time of blending.

The raw material powder to be used is not limited to carbonates and oxides, and may be any compound such as acetate or organic metal as long as it becomes an oxide by a heat treatment process such as firing. Absent.

Further, in the piezoelectric ceramic according to the present invention, K, Mg, Ca, S
Even if unavoidable impurities such as i or Ta may be mixed, there is no problem as long as the characteristics are not affected.

[0026]

EXAMPLES Example 1 Li ₂ CO ₃ , Na ₂ CO ₃ , BaCO 3
_3, using a _{Bi 2 O 3, Nb 2 O} 5 powder, weighed as x in the above composition formula, y, and z, and the amount alpha (mol%) of BinB ₃ O ₉ becomes a value shown in Table 1 did. This mixture was wet-mixed in a ball mill using ZrO ₂ balls for 12 hours. Next, after drying this mixture, it was calcined at 950 ° C. for 3 hours in the air, and the obtained 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 16 mm in diameter at a pressure of 1.5 t / cm ² ,
It was press-formed into a cylindrical shape having a thickness of 1.5 mm.
These molded products are treated at a temperature of from 1020 to 1280 ° C for 2 to 5
Fired for hours. The obtained porcelain was polished to a thickness of 0.5 mm to obtain a piezoelectric plate.

A silver electrode was formed on this piezoelectric plate, and a polarization treatment was performed by applying a DC electric field of 4 kV / mm in silicon oil at 200 ° C. Then, the resonance / anti-resonance frequency, resonance resistance, and capacitance of the thickness longitudinal mode are measured using an impedance analyzer, and the mechanical quality factor (Qm), the relative dielectric constant (ε ₃₃ T / ε ₀ ), and the frequency constant ( N) was determined. Further, the dielectric constant (ε ₃₃ T /
The Curie temperature of the porcelain was measured from the temperature dependence of ε ₀ ).

Further, assuming that the resonance frequency is fr, -20 to 20
Measured in a temperature range of 80 ° C., f at −20 to 80 ° C.
r (△ fr), the resonance frequency at 20 ° C. is fr
Using (20), the equation: frTC = △ fr / ｛fr (2
0) × 100 ° × 10 ⁶ (ppm / ° C.), the temperature coefficient frTC of the resonance frequency was determined, and these results are shown in Table 1.

[0030]

[Table 1]

Sample No. of the present invention 2, 3, 5, 6, 8-
10 and 12 show that the mechanical quality factor is 200 or more, the frequency constant is 2503 Hz · m or more, the absolute value of the temperature coefficient of the resonance frequency is 150 ppm / ° C. or less, and the Curie temperature is 426 ° C. or more.

Sample No. 2 comprising a piezoelectric ceramic using the piezoelectric ceramic composition of the present invention containing BiNb ₃ O ₉ in an amount of 1 to 25 mol% based on the total amount. 13 to 27 have a mechanical quality factor of 5
Since the temperature coefficient of the resonance frequency changes from negative to positive as the number of BiNb ₃ O ₉ increases, the absolute value of the temperature coefficient decreases to 100 ppm / ° C. or less.

On the other hand, the sample Nos. 1, 4,
In Nos. 7 and 11, the mechanical quality factor was 133 or less, and the absolute value of the temperature coefficient of the resonance frequency was 169 ppm / ° C. or more.

Example 2 Li ₂ CO ₃ , Na ₂ CO ₃ , BaCO ₃ as starting materials
₃ , Bi ₂ O ₃ , Nb ₂ O ₅ , MnO ₂ powder,
The samples were weighed so that x, y, z representing the molar ratio and α representing the amount of BiNb ₃ O ₉ described above were the values shown in Table 2, and were produced in the same manner as in Example 1. The evaluation method is also the same as in Example 1.
Is the same as The results are shown in Table 2.

[0035]

[Table 2]

Sample No. 1 consisting of a piezoelectric ceramic using the piezoelectric ceramic composition of the present invention. 28 to 47 have a mechanical quality factor of 1
002 or more, the absolute value of the temperature coefficient of the resonance frequency is 20 pp
In all cases, the characteristics were significantly improved at m / ° C or lower. Further, the frequency constant is 2964 Hz · mm or more, and the Curie temperature is 2
The temperature was 53 ° C. or higher, and the piezoelectric ceramic was suitable for applications such as resonators and oscillators.

Example 3 Li ₂ CO ₃ , Na ₂ CO ₃ , BaCO 3
_{3, Bi 2 O 3, Nb} 2 O 5, MnO 2, Cr 2 O 3,
Using Fe ₂ O ₃ , CoO, NiO, V ₂ O ₅ powder,
x = 0.125, y = 0.375, z = 0.500, α
Was set to 7 mol%, and weighed so that the porcelain composition became the value shown in Table 3, and produced by the same manufacturing method as in Example 1. The evaluation method is the same as that of the first embodiment. The results are shown in Table 3.

[0038]

[Table 3]

Sample No. 1 comprising a piezoelectric ceramic using the piezoelectric ceramic composition of the present invention in which one kind of the first transition metal was contained in the ceramic in an amount of 0.5% by weight in terms of oxide. For 44 to 47, the mechanical quality factor is 1105 or more and the frequency constant is 2985 Hz.
M or more, the temperature coefficient of the resonance frequency is -1 to 5 ppm /
° C and a Curie temperature of 375 ° C or more, which were very suitable piezoelectric ceramics for applications such as resonators and oscillators.

Sample No. 2 comprising a piezoelectric ceramic using the piezoelectric ceramic composition of the present invention in which two kinds of the first transition metals were contained in the ceramic in a total of 0.5% by weight in terms of oxide. 48-51
In, further improvement was seen with a mechanical quality factor of 1310 or more. In addition, the frequency constant is 2990 Hz · m or more,
The temperature coefficient of the resonance frequency was 2 to 6 ppm / ° C., and the Curie temperature was 364 ° C. or higher. Thus, the piezoelectric ceramic was very suitable for applications such as resonators and oscillators.

Further, in addition to the two types of first transition metals, V
Sample No. 2 consisting of a porcelain containing ₂ O ₅ in the proportions shown in Table 3. 52 to 55, the frequency constant is improved to 3004 Hz · m or more, the mechanical quality factor is 1300 or more, the temperature coefficient of the resonance frequency is 7 to 10 ppm / ° C., and the Curie temperature is 3
The temperature was 52 ° C. or higher, and the piezoelectric ceramic was very suitable for applications such as resonators and oscillators.

[0042]

According to the piezoelectric ceramic composition of the present invention, at least Li, Nb, Na and Ba are contained, and the composition formula based on the molar ratio of the metal element oxide is within a specific range, so that the composition has a high Curie temperature. Porcelain having a large mechanical quality factor and a frequency constant and a small resonance frequency temperature coefficient.

[Brief description of the drawings]

FIG. 1 is a composition diagram showing a composition range of a piezoelectric ceramic composition of the present invention.

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 4G030 AA02 AA03 AA10 AA19 AA20 AA22 AA25 AA27 AA28 AA29 AA43 BA10

Claims (3)

[Claims] (1) at least Li, Nb, N
a and Ba, and the composition formula based on the molar ratio of the oxide of the metal element is xLiNbO ₃ .yNaNbO ₃ .zBaNb ₂ O
₆ (x + y + z = 1), the point represented by x, y, and z exists in a range surrounded by the following point ABCDCA. Porcelain composition. xyz A 0.050 0.250 0.700 B 0.300 0.250 0.450 C 0.300 0.450 0.250 D 0.150 0.600 0.250 E 0.050 0.600 0.350 2. The piezoelectric ceramic composition according to claim 1, wherein BiNb ₃ O ₉ is contained in an amount of 1 to 25 mol% based on the total amount. 3. The piezoelectric ceramic composition according to claim 1, wherein at least one of the first transition metals is contained in an amount of 0.01 to 5% by weight in terms of oxides.