JP2001181035A - Piezoelectric ceramic composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain piezoelectric ceramics excellent in piezoelectric characteristics and mechanical strength and sinterable at relatively low temperatures. SOLUTION: This piezoelectric ceramic composition is represented by PbA[(Zn1/3Nb2/3)xTiyZrz]BO3 in which 0.96<=A/B<1 or 0.96<=A/B<=1. In the case of 0.96<=A/B<=1, the piezoelectric ceramic composition is obtained by adding a prescribed amount of at least one kind of oxide selected from Ta2O5, Sb2O3 and Nb2O5 thereto.

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 used for a piezoelectric vibrator such as a piezoelectric sounding body or a piezoelectric actuator, particularly, Pb (Zn ₁ / 3.Nb _2/3 ) O _3.
The present invention relates to a piezoelectric ceramic composition containing -PbTiO ₃ -PbZrO ₃ as a main component.

[0002]

2. Description of the Related Art Conventionally, Pb (Z
A ternary piezoelectric ceramic composed of (n ₁ / 3.Nb _2/3 ) O ₃ —PbTiO ₃ —PbZrO ₃ is known (Japanese Patent Publication No. 44-44).
17344) Further, a piezoelectric ceramic whose dielectric constant is improved by substituting a part of lead atoms of the ternary piezoelectric ceramic with calcium, strontium or barium is known (JP-B-45-399977). Japanese Patent Application Laid-Open No. 61-129888 discloses a piezoelectric ceramic in which a part of lead atoms of a similar ternary piezoelectric ceramic is replaced with Ba and Sr for the purpose of improving the relative dielectric constant and the electromechanical coupling coefficient. And JP-A-3-2563.
79 shows Pb, Ba and S in the piezoelectric ceramic.
A piezoelectric ceramic in which the amount of r is limited to a specific range to solve the problem of variation in characteristics between products and improve the piezoelectric constant has been disclosed.

[0003]

SUMMARY OF THE INVENTION Piezoelectric ceramics
It is widely used for piezoelectric filters, piezoelectric transformers, ultrasonic transducers, piezoelectric sounding bodies, piezoelectric actuators, piezoelectric buzzers, and the like. In particular, in recent years, piezoelectric vibrators such as piezoelectric sounding bodies and piezoelectric actuators have been reduced in size and thickness. In particular, the use of piezoelectric actuators as microactuators for personal computer hard disk drive heads, for example, has attracted attention, and with the increase in recording density, the development of ultra-compact piezoelectric actuators that control minute displacements on the order of sub-microns has been actively pursued. It has been done. Particularly when the piezoelectric material is used as an actuator for displacement control, it is desirable that the piezoelectric material has excellent piezoelectricity, that is, a material having a large piezoelectric constant d. In general, the piezoelectric constant d, the electromechanical coupling coefficient k and the relative permittivity ε
Has a relationship of d∝k√ε, and in order to increase the piezoelectric constant d, the electromechanical coupling coefficient k and the relative permittivity ε must be increased. Also, miniaturization of the piezoelectric element,
As the thickness becomes thinner, the mechanical strength of the element decreases, and the possibility of breakage increases during processing in manufacturing and driving of the element. As a result, a reduction in manufacturing yield and a reduction in product reliability occur. Therefore, a piezoelectric ceramic composition having good mechanical strength is required. Also, the development of multilayer piezoelectric elements has been actively carried out. Conventional Pb
(Zn ₁ / 3.Zb _2/3 ) O ₃ —PbTiO ₃ —PbZrO ₃
The firing temperature of the ternary piezoelectric ceramics is 120
The temperature is as high as about 0 ° C. For this reason, when manufacturing a laminated piezoelectric element with this piezoelectric ceramic composition, expensive noble metals such as platinum and palladium that can withstand the firing temperature must be used as the internal electrodes, and the manufacturing cost is reduced. There was a problem of high. If the firing temperature can be lowered, a cheaper silver-palladium alloy can be used as the internal electrode. When a silver-palladium alloy is used as the internal electrode, the cost of palladium is high, and when the content of palladium is large, palladium causes an oxidation-reduction reaction during firing, causing cracks and the like in the laminated piezoelectric element. In order to cause peeling, the proportion of palladium is required to be 30% or less. In order to reduce the proportion of palladium to 30% or less, the sintering temperature should be 1150 ° C. or less, preferably 1120 ° C. according to the Ag-Pd phase diagram.
It is necessary to be below ° C. For this reason, the conventional Pb (Zn
In the case of manufacturing the stacked piezoelectric device in _{1/3 · Nb 2/3) O 3 -PbTiO} 3 -PbZrO 3 based piezoelectric ceramic compositions of the calcined powder or pulverized, or the HIP treatment Such a complicated operation is required. In order to further reduce the production cost, in order to reduce the proportion of palladium to 20% or less, the sintering temperature should be 1050 ° C. or less, preferably 100 ° C.
The temperature must be 0 ° C. or lower. As the firing temperature decreases, the energy consumption of the electric furnace used for firing also decreases. Accordingly, it is an object of the present invention to provide a piezoelectric ceramic composition having excellent piezoelectric properties and having sufficient mechanical strength even when processed into an ultra-small and thin element. It is a further object of the present invention to provide a piezoelectric ceramic composition that can be fired at a relatively low temperature.

[0004]

According to the present invention, a basic composition formula P
In the oxide composition represented by b [(Zn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ , when the atomic ratio of Pb is set to a certain range smaller than 1, or the atomic ratio of Pb Is 1 or less, and when a certain amount of at least one oxide selected from Ta ₂ O ₅ , Sb ₂ O ₃ and Nb ₂ O ₅ is added,
It is based on the finding that firing at relatively low temperatures is possible and its piezoelectric properties and mechanical strength are also improved. That is, the present invention for achieving the above object, the following basic _{formula: Pb A [(Zn 1/3 Nb} 2/3) x Ti y Zr z] B O 3 ( where, A, B, x, y and z are the following conditions: 0.96 ≦ A / B <1 x + y + z = 1 0.05 ≦ x ≦ 0.40 0.1 ≦ y ≦ 0.5 0.2 ≦ z ≦ 0.6 Is a piezoelectric ceramic composition comprising an oxide composition represented by the following formula: Furthermore, the present invention has the following basic _{formula: Pb A [(Zn 1/3 Nb} 2/3) x Ti y Zr z] B O 3 ( where, A, B, x, y and z are the following conditions: 0.96 ≦ A / B ≦ 1 x + y + z = 1 0.05 ≦ x ≦ 0.40 0.1 ≦ y ≦ 0.5 0.2 ≦ z ≦ 0.6) More than 0.2% by weight of at least one oxide selected from the group consisting of Ta ₂ O ₅ , Sb ₂ O ₃ and Nb ₂ O ₅ is added to the oxide composition.
A piezoelectric ceramic composition characterized by being added in a range of not more than% by weight.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The oxide composition Pb _A [(Zn _1/3 N)
b _2/3 ) _x Ti _y Zr _z ] _B O ₃
0.96 ≦ A / B <1 and x + y + z = 1 (provided that
0.05 ≦ x ≦ 0.40; 0.1 ≦ y ≦ 0.5; and 0.2 ≦ z ≦ 0.6). A piezoelectric ceramic composition having a modulus and an electromechanical coupling coefficient can be obtained. When the composition ratio A / B is smaller than 0.96, the dielectric constant and the electromechanical coupling coefficient decrease. (Zn _1/3 Nb
_The dielectric constant increases as the composition ratio x of _2/3 ) increases, but is not suitable for mass production because the Nb raw material is expensive. When x is smaller than 0.05, both the dielectric constant and the electromechanical coupling coefficient are low, and the necessary piezoelectric characteristics cannot be obtained. The composition ratio y of Ti and the composition ratio z of Zr greatly affect the dielectric constant and the electromechanical coupling coefficient, and are particularly preferably near the morphotropic phase boundary. From these points, in the present invention, the composition ratios x, y, and z are 0.05 ≦ x ≦ 0.40, 0.1
≦ y ≦ 0.5 and 0.2 ≦ z ≦ 0.6 (where x
+ Y + z = 1).

The composition ratio A / B of the oxide composition is 0.9.
In the case of 6 ≦ A / B ≦ 1, in order to obtain a piezoelectric ceramic composition that can be fired at a relatively low temperature, has a large dielectric constant and an electromechanical coupling coefficient, and has an excellent bending strength. , Ta ₂ O ₅ , Sb ₂ O ₃ and Nb ₂ O _{5 in} an amount of at least one oxide selected from the group consisting of more than 0.2% by weight and not more than 1.00% by weight based on the oxide composition. Is preferably added.
If the addition amount of these oxides is 0.2% by weight or less, the effect of the addition is not sufficiently exhibited, while if it exceeds 1.0% by weight, firing at a low temperature becomes impossible, Insufficient sintering makes it impossible to obtain satisfactory properties such as dielectric constant and electromechanical coupling coefficient and sufficient mechanical strength as piezoelectric ceramics.

[0007] The piezoelectric ceramic composition of the present invention can be produced by the following method. As a starting material, P
bO, TiO ₂ , ZrO ₂ , ZnO and Nb ₂ O ₅ or compounds which can be converted to these oxides by firing (oxide 1); at least one oxide selected from SrO, BaO and CaO or these oxides by firing A variable compound (oxide 2); and Ta ₂ O ₅ , Sb ₂ O ₃
And Nb ₂ O at least one oxide selected from ₅ or compounds can be converted into these oxides by firing (oxide 3) can be used. A predetermined amount of each oxide is weighed and wet-mixed using a ball mill or the like. When adding the oxide 3, the mixture of the oxide 1 and the oxide 2 may be calcined and then added. It is desirable to use water, alcohol such as ethanol, or a mixture thereof as a slurry medium in wet mixing. After thoroughly mixing the starting materials, the mixture is temporarily calcined at about 800 to 1000 ° C. for about 1 to 3 hours. The obtained calcined product is wet-pulverized using a ball mill or the like. Also in this wet pulverization, it is desirable to use water, alcohol such as ethanol, or a mixture thereof as a mixing medium. The wet pulverization is preferably performed until the calcined product has an average particle size of about 0.5 to 2.0 μm. The powder of the calcined product obtained by the wet pulverization is dried, and a small amount (about 0.5 to 8% by weight) of water or a binder (for example, polyvinyl alcohol) is added to the dried powder and kneaded. About 98-392 MPa of the obtained paste
(Pressure of 1 to 4 ton / cm ² ) and press molding to obtain a molded product. Extrusion molding and other molding methods can be used for molding. Next, the molded product is fired at about 960 to 1200 ° C. for about 2 to 5 hours to obtain a piezoelectric ceramic. The firing can be performed in the air, in an atmosphere having a higher oxygen partial pressure than in the air, or in a pure oxygen atmosphere.

Hereinafter, the present invention will be described more specifically with reference to examples.

【Example】Examples 1 to 4 and Comparative Example 1 PbO, TiO_Two, ZrO_Two, ZnO and Nb_TwoO_Five of
Each compound is prepared by mixing the metal elements in the molar ratio shown in Table 1.
Mixed. A slurry concentration of 40 for this mixture
Add water to ~ 50% and use a ball mill
After wet mixing for 5 hours, it was calcined at 900 ° C. for 2 hours.
The calcined product has a slurry concentration of 40 to 50%.
Water, and wet-pulverize for 15 hours using a ball mill.
Was. After drying the obtained slurry, 6% by weight of water was added.
39.2 MPa (400 kgf / cm^TwoConversion
Value) and uniaxially press-molded at a pressure of 392 MPa (4
ton / cm^TwoCold isostatic pressing at a pressure of
Thus, a 20 mm square prism was produced. This prism is shown in Table 1.
Baking in air at room temperature for 2 hours to obtain piezoelectric ceramics
Was. The obtained piezoelectric ceramics are sliced and laced.
1.2mm ×
A prism of 1.2 mm × 5.0 mm was produced. Of this prism
Silver paste printed on both ends and baked at 700 ° C
Then, polarization treatment is performed in silicone oil at 150 ° C.
Was. The sample thus obtained is left for 24 hours
After that, the sample's k33, εd (1 kHz) and
d33 is an impedance analyzer HP4194A
EMAS-6 using (Hewlett Packard)
Measured according to 100. The results obtained are shown in Table 1.
It is a cage. Also, the piezoelectric ceramics obtained above
Separately slicing, lapping and dicing
2mm x 4mm x 0.6mm (thickness)
A pull was made. The flexural strength of this sample is
Using a load tester, measure according to JIS (R1601).
Specified. The measurement conditions at this time are the distance between fulcrums and the load.
The speed is 2.0 mm / 0.5 mm / min. So
Was. The results obtained are shown in Table 1.Examples 5 to 13 and Comparative Examples 2 to 7 PbO, TiO_Two, ZrO_Two, ZnO and Nb_TwoO_Five of
Each compound was prepared by mixing the metal elements in the molar ratio shown in Table 2.
Mixed and then Ta_TwoO_Five, Sb_TwoO_ThreeAnd Nb_TwoO_Five
Except that the compound selected from the above was added in the amount shown in Table 2.
Obtained a sample in the same manner as in Examples 1 to 4, and
The same measurement as in Examples 1 to 4 was performed for the sample obtained.
Was. The results obtained are shown in Table 2.Examples 14 to 17 Compound PbO is shown in Table 3 where the Pb element is less than 1.
In a molar ratio, and_TwoO_FiveIn Table 3
Except that it was added in the amount shown, the same as in Examples 1-4
Samples obtained and examples for the obtained samples
The same measurement as that of Nos. 1 to 4 was performed. The results obtained are shown in Table 3.
That's right. Also, Ta_TwoO_Five Sb instead of_TwoO_Three
Or Nb_TwoO_Five When Ta is added, _TwoO_Five Equivalent to
The result is obtained.

[0009]

The piezoelectric ceramics of the present invention have extremely excellent piezoelectric properties and flexural strength.
Since it can be fired at a temperature of not more than ℃, inexpensive internal electrodes of Ag / Pd = 80/20 can be used in the production of the laminated piezoelectric element. It is extremely useful as an application material.

[Table 1]

[Table 2]

[Table 3]

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 4G030 AA16 AA17 AA20 AA21 AA32 AA40 AA42 BA10 GA21 GA25 4G031 AA11 AA12 AA14 AA15 AA26 AA32 AA34 BA10 GA06 GA09

Claims (2)

[Claims] 1. A following basic composition _{formula: Pb A [(Zn 1/3 Nb} 2/3) x Ti y Zr z] B O 3 ( where, A, B, x, y and z are the following conditions: 0 96 ≦ A / B <1 x + y + z = 1 0.05 ≦ x ≦ 0.40 0.1 ≦ y ≦ 0.5 0.2 ≦ z ≦ 0.6) Ceramic composition comprising a composition. 2. A following basic composition _{formula: Pb A [(Zn 1/3 Nb} 2/3) x Ti y Zr z] B O 3 ( where, A, B, x, y and z are the following conditions: 0 96 ≦ A / B ≦ 1 x + y + z = 1 0.05 ≦ x ≦ 0.40 0.1 ≦ y ≦ 0.5 0.2 ≦ z ≦ 0.6) More than 0.2% by weight of at least one oxide selected from Ta ₂ O ₅ , Sb ₂ O ₃ and Nb ₂ O ₅ , based on the total composition.
A piezoelectric ceramic composition which is added in an amount of 0% by weight or less.