JPH0818873B2 - Piezoelectric composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a piezoelectric ceramic composition, and more particularly to a piezoelectric ceramic composition that can be fired at a low temperature.

Prior art As a piezoelectric ceramic composition, Pb (Sn _1/3 Nb _2/3 ) _x Ti _y Zr _z O
₃ type composition (described in Japanese Examined Patent Publication No. 45-37508 and Japanese Patent Publication No. 46-42548), Pb (Sn _a Sb _1-a ) _x Ti _y Zr _z O ₃ type composition (Japanese Examined Patent Publication No. 5
4-32516, Japanese Patent Publication No. 54-36757), Pb (Zn _1/3
Nb _2/3 ) _A (Sn _1/3 Nb _2/3 ) _B Ti _C Zr _D O ₃ composition (Japanese Patent Publication No. 52
-17239, Japanese Patent Publication No. 51-7318), etc. These compositions are piezoelectric materials having characteristics such as excellent piezoelectricity, small crystal grain size, and high mechanical strength, and are excellent piezoelectric ceramic materials applicable to high frequencies. Further, in these compositions, by selecting the composition ratio of the components, it is possible to obtain piezoelectric ceramics having various characteristics according to the application. These piezoelectric ceramic compositions are used in ceramic filters, piezoelectric buzzers, piezoelectric ignition plugs, ultrasonic vibrators, and the like.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, the firing temperature of these piezoelectric ceramic compositions during production is usually as high as 1200 to 1300 ° C. Even if a fine powder is used as the raw material, the firing temperature must be as high as 1100 ° C or higher. For this reason, the vaporization of lead oxide is significant during firing, which causes fluctuations and variations in composition. To prevent such evaporation,
A firing container made of a material with low reactivity with lead oxide, a firing container mainly containing magnesia or alumina, or sealed,
For controlling the lead oxide atmosphere, lead oxide powder, lead zirconate powder, etc. are filled in a firing container and fired, but still it is not possible to sufficiently prevent composition deviation and composition variation due to evaporation of lead oxide.

Means for Solving the Problems The piezoelectric ceramic composition of the present invention is composed of Pb (Zn _1/3 Nb _2/3 ) _A (Sn
_1/3 Nb _2/3 ) _B Ti _C Zr _D O ₃ (However 0.01 ≦ A ≦ 0.50, 0.01 ≦ B
≤0.25, 0≤C≤0.75, 0≤D≤0.875, A + B + C +
D = 1) to the basic composition with MgO as an accessory ingredient
It is characterized in that it contains 0.02 to 2% by weight.

In addition, MnO ₂ as a _second accessory component is added to the above composition in an amount of 0.05 to
It is characterized in that it is added by 5% by weight.

Action A small amount of MgO or a small amount of M as an accessory component to the basic composition
By adding gO and MnO ₂ , the firing temperature of the composition can be significantly lowered. As a result, the amount of lead oxide evaporated during firing is reduced, compositional variations and variations in the piezoelectric ceramic can be reduced, and the energy required for firing can be reduced. At the same time, addition of MgO improves the dielectric constant and electromechanical coupling coefficient, and addition of MgO and MnO ₂ improves the dielectric constant, electromechanical coupling coefficient and mechanical Q.

Examples Examples of the present invention will be shown below.

Using Pb ₃ O ₄ , ZnO, SnO ₂ , Nb ₂ O ₅ , TiO ₂ , and ZrO ₂ as raw materials, Pb (Zn _1/3 Nb _2/3 ) _0.09 (Sn _1/3 Nb _2/3 ) _0.09 Ti
_A basic composition of _0.42 Zr _0.40 O ₃ was obtained. Next, as an accessory ingredient
Use MgO and MnO ₂ and weigh them in the composition ratio shown in Table 1 to the basic composition, and mix with a ball mill.
It was calcined at 50 ° C for 2 hours. Then, finely pulverized with a medium stirring mill, and the obtained powder (average particle diameter of about 0.2 μm) has a diameter of 13 m.
A disc-shaped molded body with a thickness of 1 mm and a thickness of 1 mm was prepared and
It was fired at the temperature shown in the table for 2 hours.

After firing, the porcelain was polished to a thickness of about 0.3 mm, and Cr-Au vapor deposition electrodes were provided on both surfaces of the porcelain. After that, a direct current electric field of 3 kV / mm was applied between both electrodes in silicon oil at 160 ° C. for 30 minutes to perform polarization treatment on this device. This sample (No.1
.About.11), the dielectric constant, the coupling coefficient, and the mechanical Q were measured. The firing temperature is the temperature at which the density becomes maximum. The measurement results are shown in Table 1.

As is clear from the above examples, the composition of the present invention containing a small amount of MgO has a significantly lower firing temperature than those containing no MgO. The amount of MgO added is 0.1-
It was confirmed that in the composition in the range of 0.5% by weight, the firing temperature was remarkably lowered and the dielectric constant and the coupling coefficient were increased. In addition, in the composition in which MnO ₂ is added to the basic composition, Mg
The mechanical Q increased as the firing temperature decreased due to the addition of O 2.

It should be noted that the effect of lowering the firing temperature was the same with the addition of MgO even after calcination. MgO may be any such as carbonates and hydroxides that can obtain Mg components by heating, and are included in the scope of the present invention. In addition, the basic composition of the present invention, CoO, NiO, Cr
Various additives such as ₂ O ₃ and Al ₂ O ₃ may be added and contained.

In the basic composition represented by Pb (Zn _1/3 Nb _2/3 ) _A (Sn _1/3 Nb _2/3 ) _B Ti _C Zr _D O ₃ , 0.01 ≦ A ≦ 0.50, 0.01 ≦
Compositions within the ranges of B ≦ 0.25, 0 ≦ C ≦ 0.75, and 0 ≦ D ≦ 0.875 exhibit relatively large piezoelectricity and are preferable as piezoelectric ceramic materials.

Further, in the composition in which the added amount of MnO ₂ exceeds 5% by weight, the piezoelectric property is remarkably deteriorated.

Any MnO ₂ may be used as long as it can obtain the Mn component by heating, such as carbonate, hydroxide and nitrate, and is included in the scope of the present invention.

When the amount of MgO added is less than 0.02% by weight, the firing temperature does not decrease, and when the composition exceeds 2% by weight, the dielectric property or coupling coefficient (Kp) decreases significantly, that is, the piezoelectricity decreases. Therefore, the addition amount of MgO is industrially preferable to be in the range of 0.02% by weight or more and 2% by weight or less.

Effects of the Invention As described above, a small amount of the basic composition added and contained.
Compared with the conventional composition, MgO significantly lowers the firing temperature, reduces the evaporation of lead oxide during firing, and reduces the variation in the characteristics of piezoelectric ceramics, while significantly reducing the energy required for firing. Since it is possible to use a cheap material for the electric furnace for firing, it is extremely useful industrially. Furthermore, addition of MgO,
Alternatively, the addition of MgO and MnO ₂ can improve the dielectric constant, the electromechanical coupling coefficient and the mechanical Q, and can significantly increase the utility value of the piezoelectric element.

Claims (2)

[Claims] 1. Pb (Zn _1/3 Nb _2/3 ) _A (Sn _1/3 Nb _2/3 ) _B Ti _C Zr
_D O ₃ (However, 0.01 ≦ A ≦ 0.50, 0.01 ≦ B ≦ 0.25, 0 ≦ C ≦
0.75, 0 ≤ D ≤ 0.875, A + B + C + D = 1) 0.02 to 2% by weight of MgO as an accessory component is added to the basic composition, and a piezoelectric ceramic composition. _2. 0.05 to 5% by weight of MnO ₂ as a _second accessory component
The piezoelectric ceramic composition according to claim 1, wherein the piezoelectric ceramic composition is added.