JP2006182643A - Piezoelectric ceramic composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic composition which is free from lead and can be used for applications such as piezoelectric resonators or oscillators. <P>SOLUTION: The piezoelectric ceramic composition contains, as a main component, a tungsten bronze-type multiple oxide containing metal elements of Na, Ba, Bi and Nb, and the amount of Bi based on total weight is 3-6 wt.% expressed in terms of metal. When the molar compositional formula is expressed by xNaNbO<SB>3</SB>-yBaNb<SB>2</SB>O<SB>6</SB>-zBiNb<SB>3</SB>O<SB>9</SB>(wherein, x+y+z=1), x, y and z exist within an area surrounded by a polygon having, as apexes, following 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). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a piezoelectric ceramic composition that can be used for applications such as piezoelectric elements, particularly piezoelectric resonators and oscillators.

Conventionally, PT ceramics mainly composed of PbTiO ₃ and PZT ceramics mainly composed of Pb (Zr _1-x Ti _x ) O ₃ have been widely used as materials for piezoelectric resonators and oscillators. In addition, in order to improve the piezoelectric characteristics and to suppress the temperature change of the resonance frequency to be small, a part of Pb is added, and a part of Pb is replaced with a divalent element such as Ba, Sr and / or Ca. Or a solid solution of a third component such as Pb (Sb _1/2 Nb _1/2 ) O ₃ or Pb (Mg _1/3 Nb _2/3 ) O 3 has been used.

  As electronic devices have become smaller and more accurate in recent years, piezoelectric resonators and oscillator materials that have a small temperature change in the resonance frequency have been desired, and PT and PZT ceramics suitable for these applications have been used. It was.

  The present invention has been invented in view of the above problems, and an object of the present invention is to provide a piezoelectric ceramic composition that can be used for applications such as a piezoelectric resonator and an oscillator having a small change in resonance frequency and a high Curie temperature. And

The present invention relates to a piezoelectric ceramic composition mainly composed of a tungsten bronze type composite oxide containing metal elements of Na, Ba, Bi and Nb, wherein Bi in the total weight is 3 to 6% by weight in terms of metal. When the composition formula by molar ratio is represented by xNaNbO ₃ -yBaNb ₂ O ₆ -zBiNb ₃ O ₉ (where x + y + z = 1), x, y and z A piezoelectric ceramic composition characterized by being in a region surrounded by a polygon.

  Accordingly, it is possible to provide a piezoelectric ceramic composition having a low Curie temperature as high as 250 ° C. and a small absolute value of the temperature change of the resonance frequency of 50 ppm / ° C. or less (hereinafter, the temperature change of the resonance frequency is indicated by an absolute value).

  In particular, it is preferable that at least one of the first transition metals is added to the porcelain in a range of 2% by weight or less in terms of oxide. The first transition metal mentioned here is a metal element from 21Sc to 30Zn in the periodic table of elements, and in the above configuration, the first transition metal is V, Cr, Mn, Fe, Co and / or in particular. Or it is preferable that it is Ni.

  As a result, the electromechanical coupling coefficient and the mechanical quality factor are improved, and the use of a piezoelectric resonator, an oscillator, or the like having a very low Curie temperature of 250 ° C. or less and a temperature change of the resonance frequency of 10 ppm / ° C. or less. It becomes a suitable piezoelectric ceramic composition.

As described above, in the piezoelectric ceramic composition of the present invention, Bi is 3 in terms of metal in the total amount of porcelain mainly composed of a tungsten bronze type complex oxide containing metal elements of Na, Ba, Bi and Nb. When contained in a ratio of ˜6% by weight and expressed by xNaNbO ₃ —yBaNb ₂ O ₆ —zBiNb ₃ O ₉ (where x + y + z = 1), (x, y, z) in the above general formula represents the following points: A (0.382, 0.560, 0.058), point B (0.422, 0.520, 0.058), point C (0.422, 0.505, 0.073), point D ( 0.382, 0.545, 0.073) in a region surrounded by a quadrangle, and a tungsten bronze type complex oxide containing a metal element of Na, Ba, Bi and Nb in particular is a main component. In the total amount of porcelain , Bi is contained at a rate of 3 to 6% by weight in terms of metal, and at least one of the first transition metals is contained at a rate of 2% by weight or less in the total amount of porcelain, so that the temperature change of the resonance frequency is small. Thus, it is possible to provide a piezoelectric ceramic composition that can be used for applications such as a piezoelectric resonator and an oscillator having a high Curie temperature.

  The piezoelectric ceramic composition of this invention is demonstrated using drawing as needed.

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

  And Bi is contained in the ratio of 3 to 6 weight% in metal conversion in the whole quantity, Bi has the crystal structure where most dissolved in the crystal grain of porcelain.

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

  As described above, the amount of Bi contained in all porcelain is 3 to 6% by weight. For example, when the amount of Bi is less than 3% by weight, Bi dissolved in crystal grains is insufficient, and as a result, the resonance frequency is reduced. As a result, the piezoelectric ceramic composition is not practically used.

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

  The Bi contained in the porcelain is preferably dissolved in the crystal grains of the porcelain because the temperature change of the resonance frequency is kept small.

According to the present invention, a composition of a tungsten bronze type partially substituted with Bi is expressed by the general formula xNaNbO ₃ -yBaNb ₂ O ₆ -zBiNb ₃ O ₉ (where x + y + z = 1). x, y, z) are points A (0.382, 0.560, 0.058), points B (0.422, 0.520, 0.058) on the three-component composition diagram of FIG. It is an area surrounded by rectangles A, B, C, and D having a vertex at a point C (0.422, 0.505, 0.073) and a point D (0.382, 0.545, 0.073) is important. 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 is obtained.

  In particular, in the present invention, it is preferable to contain at least one first transition metal (a metal element from 21Sc to 30Zn in the periodic table of elements) in a proportion of 2% by weight or less in terms of oxide in the total amount of porcelain. .

  By including a specific amount of at least one kind of the first transition metal in the porcelain, the piezoelectric characteristics of the porcelain, in particular, the temperature change of the resonance frequency can be made 10 ppm / ° C. or less, and the electromechanical coupling coefficient and The mechanical quality factor can be greatly improved.

  The first transition metal is preferably V, Cr, Mn, Fe, Co, and / or Ni because the effect of improving the electromechanical coupling coefficient and the mechanical quality factor is great. And in this piezoelectric ceramic composition containing a specific amount of the first transition metal in this way, when the content of the first transition metal increases, a part of those metal elements are also present 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 , Bi ₂ O ₃ , Nb ₂ O ₅ and first transition metal oxide powders were mixed at a predetermined ratio, and temporarily mixed at 900 to 1100 ° C. for 3 to 5 hours. After baking, the powder of a desired material composition is produced by grinding. A porcelain can be obtained by mixing this powder with an organic binder and molding it into a desired shape by a die press, an isostatic press or the like, and then firing at 1150 to 1280 ° C. for 2 to 5 hours. It is to be noted that the same effect can be obtained by mixing the oxide of the first transition metal not only at the time of preparation but also with the calcined powder during the above production process.

  Further, as the raw material powder, not only carbonates and oxides but also compounds such as acetates and organic metals may be used as long as they become oxides by a heat treatment process such as firing.

  Furthermore, in the piezoelectric ceramic composition of the present invention, inevitable impurities such as K, Mg, Ca, Si, and Ta contained in a very small amount in the raw material powder may be mixed.

Porcelain using Na ₂ CO ₃ , BaCO ₃ , Bi ₂ O ₃ , Nb ₂ O ₅ , V ₂ O ₅ , Cr ₂ O ₃ , MnO ₂ , Fe ₂ O ₃ , Co ₃ O ₄ and NiO as starting materials The 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 at 900 to 1100 ° C. for 3 hours in the air, and the calcined product was again finely pulverized by the ball mill. Thereafter, the pulverized material was mixed with a binder such as polyvinyl alcohol (PVA) and granulated.

  The obtained powder was press-molded into a disk having a diameter of 16 mm and a thickness of 1.5 mm at a pressure of 1.5 t / cm 2. These molded bodies were fired in the range of 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 is a tungsten bronze type complex oxide, and Bi contained in the porcelain is dissolved in the crystal particles. It was confirmed that

  In addition, most of the metal element as the first transition metal was dissolved in the crystal grains, but it was confirmed that some of the metal elements were also present at the grain boundaries as the content increased.

A silver electrode was formed on the porcelain obtained by the above method, and polarization treatment was performed by applying a DC electric field of 4 kV / mm in silicon oil at 200 ° C. However, Sample No. 15 was polarized in 150 ° C. silicone oil. Then, the resonance resonance frequency, antiresonance frequency, resonance resistance, and capacitance in the thickness direction are measured using an impedance analyzer, and an electromechanical coupling coefficient (k _t ), a mechanical quality factor (Q _m ), and a relative dielectric constant (ε ₃₃ ^T / ε ₀ ).

Moreover, the temperature change of the resonance frequency (f _r ) in the thickness longitudinal direction was examined in the range of −20 to 80 ° C. The temperature coefficient of fr _(f r -TC) _formula was calculated from _{f r -TC = △ f r /} (f r [20 ℃] × 100) × 10 6 (ppm / ℃). However, △ _{f r} is the amount of change in _{f r} in the range of _{-20~80 ℃, f r [20 ℃} ] is the value of _{f r} at 20 ° C.. Further, the dielectric constant (ε ₃₃ ^T / ε ₀ ) was plotted as a function of temperature, and the Curie temperature (T _C ) of the porcelain was obtained.

These results are shown in Tables 1 and 2.

From Table 1, a piezoelectric ceramic composition mainly composed of a tungsten bronze type composite oxide containing metal elements of Na, Ba, Bi and Nb, wherein Bi in the total weight is 3 to 6% by weight in terms of metal It can be seen that the piezoelectric ceramic composition of the first invention contained at a ratio of 1 to 10 has a temperature coefficient (f _r -TC) of 100 ppm / ° C. or less (sample numbers 2 to 14). According to a preferred example of the present invention, PT and PZT ceramics having a temperature coefficient of 50 ppm / ° C. or less, and more preferably 10 ppm / ° C. or less, which are used for applications such as conventional piezoelectric resonators and oscillators, It can be seen that they have the same level of temperature coefficient.

From Sample No. 2-14, when Bi content in the porcelain of 3-6% by weight, at the same time when the temperature coefficient is 100ppm or less, since the Curie temperature _{(T C)} is as high as 250 ° C. or higher It can be seen that it can withstand the heat during reflow soldering.

In the piezoelectric ceramic composition of the present invention, as shown in sample numbers 2 to 14, the sign of the temperature coefficient (f _r -TC) changes from negative to positive when the Bi content is in the range of 3 to 6% by weight. I understand that. A porcelain having a small temperature coefficient value can be obtained in the vicinity of the composition where the sign changes.

Moreover, when the composition formula by molar ratio is expressed by xNaNbO ₃ -yBaNb ₂ O ₆ -zBiNb ₃ O ₉ (where x + y + z = 1), the molar ratio of x, y, z in FIG. Sample number 3 (point A (0.382, 0.560, 0.058)), sample number 5 (point B (0.422, 0.520, 0.058)), sample number 11 (point C (0 .422, 0.505, 0.073)) and sample number 13 (dot, D (0.382, 0.545, 0.073)) in the area surrounded by rectangles A, B, C, D It can be seen that in a certain sample, for example, sample numbers 3, 4, 5, 6, 8, 10, 11, 12, and 13, the temperature coefficient is reduced to 50 ppm / ° C. or lower due to the effect of containing Bi.

The sample No. 2-13, in accordance with Bi content increases, the electromechanical coupling coefficient _{(k t)} and Curie - temperature _{(T C)} it can be seen that there is a tendency to decrease. On the other hand, it can be seen that the relative permittivity (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 invention, the sample numbers 2, 7, 9, and 14 outside the polygonal area formed by the squares A, B, C, and D shown in the three-component composition diagram shown in FIG. Although it is the temperature coefficient which can satisfy | fill, it will become larger than 50 ppm / degrees C. In particular, it is desirable to control the composition so that it is set within the region of the squares A, B, C, and D shown in the three-component composition diagram from the viewpoint of obtaining a piezoelectric ceramic with a small temperature change of the resonance frequency.

Incidentally, as in Sample No. 1, the Bi content is less than 3 wt% (Sample No. 1 2.1% by weight), the temperature coefficient _(f r -TC) becomes remarkably large, is not preferable for practical use. Sample No. 15 having a Bi content exceeding 6% by weight is not preferable because the temperature coefficient (f _r -TC) is larger than 100 ppm / ° C. and the Curie temperature (T _C ) is significantly reduced.

Sample numbers 16 to 39 shown in Table 2 contain at least one of the first transition metals in the amount of 0.01 to 2% by weight in terms of oxide in the total amount of porcelain using the sample number 8 of Table 1. The result is shown. From this result, it is understood 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.

From sample numbers 16 to 24, when the MnO ₂ addition amount is in the range of 0.2 to 2.0% by weight, the electromechanical coupling coefficient (k ₃₃ ) and the mechanical quality factor (Q _It can be seen that _m ) shows a peak (sample number 20). In Sample No. 20, it can be seen that the electromechanical coupling coefficient (k ₃₃ ) is improved by about 30% and the mechanical quality coefficient (Q _m ) is improved by about 5 times compared to the case where MnO ₂ is not added.

It can be seen that as the amount of MnO ₂ added increases, the Curie temperature (TC) decreases and the relative dielectric constant (ε33T / ε0) increases. It can be seen that the Curie temperature (T _C ) decreases to 251 ° C. when the amount of MnO ₂ added is increased to 2% by weight.

When the addition amount of MnO ₂ is 2.0% by weight or more (sample number 24), the temperature coefficient (f _r -TC) is from −10 ppm / ° C. to +42 ppm / ° C. as compared with sample number 8 not added. Increases to ° C. Therefore, the addition of the first transition metal is desirably less than 2% by weight.

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.

In Sample Nos. 25 to 29, even if Cr ₂ O ₃ , Fe ₂ O ₃ , CoO, NiO, and V ₂ O ₅ are added in an amount of 0.4% by weight instead of MnO _2, the electromechanical coupling coefficient is the same. It can be seen that (k ₃₃ ) and the mechanical quality factor (Q _m ) are improved.

In sample numbers 30 to 39, an oxide selected from MnO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , CoO, NiO, and V ₂ O ₅ was added in combination, and the total addition amount was 0.4 wt%. It was. 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, it can be seen that 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 greater when the ratio of the additives shown in sample numbers 35 to 39 is used than when the oxide is added alone.

  In the piezoelectric ceramic composition according to the present invention, as described above, in order to improve the piezoelectric characteristics of the porcelain, at least one first transition metal may be contained in the total amount of the porcelain in a proportion of 2% by weight or less. preferable.

It is a 3 component composition figure of the piezoelectric ceramic composition of the present invention.

Explanation of symbols

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

Claims (2)

A piezoelectric ceramic composition mainly composed of a tungsten bronze type composite oxide containing metal elements of Na, Ba, Bi and Nb, and containing Bi in a ratio of 3 to 6% by weight in terms of metal. When the composition formula based on the molar ratio is expressed by xNaNbO ₃ -yBaNb ₂ O ₆ -zBiNb ₃ O ₉ (where x + y + z = 1), x, y and z are polygons having the following points as vertices. A piezoelectric ceramic composition characterized by being in an enclosed region.
x y z
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) 2. The piezoelectric ceramic composition according to claim 1, wherein at least one of the first transition metals is added at a ratio of 2% by weight or less in terms of oxide.

Images