JP2841911B2 - PZT ceramic composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a dielectric material, a piezoelectric material,
The present invention relates to a PZT ceramic composition used for an electronic material such as a pyroelectric material and an insulating material.

[0002]

2. Description of the Related Art Generally, ceramics have hardness, elasticity,
It has excellent heat resistance and is used as a mechanical part or an electronic material part. However, at present, ceramics slurry is formed into a predetermined shape based on normal ceramic manufacturing methods such as doctor blade method, press method, extrusion method, slurry casting method, etc. The above-mentioned excellent properties cannot be sufficiently obtained from an engineering viewpoint. This is because ceramics have pores and minute defects in the sintered body to some extent, and when an external force acts, stress concentrates on the pores and the like, causing breakage. In recent years, in the field of structural ceramics, the mechanism by which high strength and high toughness characteristics can be obtained has been clarified, and the aforementioned ceramic firing methods such as the HIP method and the control of the fine structure of ceramics have been specially devised. The disadvantages of ceramics are being overcome.

[0003] However, in the field of ceramics for electronic materials, the use of high-frequency and high-power areas, such as piezoelectric materials, has been expanding, but high strength and high toughness, which are important for applications in these areas, have been developed. There are few material studies that focus on them. With respect to dielectric materials, with the recent trend toward smaller and thinner electronic components, there has been a demand for an improvement in mechanical strength. However, at present, such measures have not been taken. Typical piezoelectric materials, barium titanate (BaTi0 ₃₎ and lead titanate (P
bTi0 ₃₎ PT based ceramics was mainly composed of, and lead titanate and lead zirconate and (PbZr0 ₃₎ as a main component,
This by mixing various additives (PbTi0 ₃ -Pb
Zr0 ₃₎ based ferroelectric ceramics so-called PZT-based ceramics such as polycrystalline are known. Nowadays, in ultrasonic detectors, ultrasonic delay lines, devices for surface acoustic waves, etc., as the operating frequency increases, the relative dielectric constant and dielectric loss in the high-frequency region are small, and the piezoelectric properties of the electromechanical coupling coefficient are large. There is a strong demand for the development of ceramics. The PZT-based material is divided into a tetragonal phase and a trigonal phase with a component of Zr: Ti = 55: 45 as a boundary, and the piezoelectric effect near this phase transition point is large. PZT-based materials are excellent piezoelectric materials because there is no transition temperature in the range of −50 to 250 ° C. Zr: Ti = 52: 48
Has a relative dielectric constant of 399 and an electromechanical coupling coefficient of 0.529. According to the conventional sintering method, the PZT-based material is sintered at a firing temperature of about 1200 ° C.

[0004]

However, even in PZT-based materials which are rich in useful and functional characteristics and widely used as piezoelectric ceramics, the improvement in mechanical strength is not affected by the piezoelectric output coefficient g. _In addition to the study of increasing the number of pores to increase the number of pores and increasing the number of pores, research has been conducted to reduce the number of pores by a hot press method so that the strength does not decrease. When the porosity to 50% or more in order to increase the piezoelectric output coefficient g _33,
Flexural strength is significantly reduced. Therefore, using the liquid phase sintering method of ceramics, in which a component that forms a liquid phase at low temperature is added to a ceramic material and sintered, ceramics for electronic materials are also coated with ceramic particles with the liquid phase component during firing. It is conceivable to improve the strength of the ceramic sintered body by eliminating defects on the ceramic surface. This method does not require any special ingenuity in the sintering technology itself,
Unless an additive serving as a liquid phase component is selected, there is a problem in that the functional properties of ceramics, that is, dielectric properties, piezoelectric properties, pyroelectricity, and insulation properties are impaired.

An object of the present invention is to provide a PZT-based ceramic composition capable of increasing the mechanical strength of the PZT-based material without impairing functional properties such as the piezoelectric properties of the PZT-based material, and a method for producing the same. It is in.

[0006]

The present inventors have formed a liquid phase at the same temperature as the sintering temperature of PZT ceramics,
The present invention has been achieved by selecting, as an additive, a compound having the same functional properties as PZT ceramics. The PZT-based ceramic composition of the present invention has a chemical formula P
b _1.01 (Zr _0.53 Ti _0.47 ) O ₃ + 0.5mo 1% Nb ₂ O
0.5% by weight to 100% by weight of the PZT-based material represented by ₅
More than 5% by weight of bismuth sodium titanate is added.

Hereinafter, the present invention will be described in detail. PZT of the present invention
The system material is Zr: Ti = 53: 47 and has the chemical formula Pb
_1.01 (Zr _0.53 Ti _0.47 ) O ₃ + 0.5mo 1% Nb ₂ O ₅
It is represented by The composition of this Zr / Ti is MPB (Morphotr
It is considered that the tetragonal phase and the rhombohedral phase coexist. This PZT material mixes PbO, ZrO ₂ , TiO ₂ and Nb ₂ O ₅ ,
After calcining the mixture, it is ground and made in powder form. The reason for making Pb excessive by 1% is to consider evaporation during firing. The addition of 0.5 mol% of Nb ₂ O ₅ is for facilitating polarization and stabilizing electrical characteristics.

On the other hand, bismuth sodium titanate
(Bi, Na)_1/2Ti0_ThreeHas a low relative permittivity
-Ceramics with high temperature and large electromechanical coupling coefficient
It is a box. This bismuth sodium titanate
General formula (Bi_1/2Na_1/2)_1-x(Sr _aPb_bCa_c)_xTiO_Threeso
Those represented are preferred. In particular, x = 0, a = b = c =
0 (Bi_1/2Na_1/2) TiO_Three, X = 0.12, a = b
= 0.5, c = 0 (Bi_1/2Na_1/2)_0.88(Sr_1/2Pb
_1/2)_0.12TiO_ThreeOr x = 0.12, a = 0, b = c =
0.5 (Bi_1/2Na_1/2)_0.88(Pb_1/2Ca_1/2)_0.12T
iO_ThreeIs preferred for the purpose of the present invention. Also, JP
As disclosed in Japanese Patent Laid-Open No. 1-242464, (Bi
_1/2Na_1/2) TiO_ThreeSrTi0 as a modifying component_Three,
PbTi0_ThreeOr CaTi0_ThreeAny one or more of
What added the above may be used. With these additions
Bismuth sodium titanate with a large coercive electric field
Can be easily polarized and at a relatively low temperature of 1000-1100 ° C
It can be easily densified. This bismuth sodium
Mutitanate sinter has a dielectric constant of 250 or less, Curie
The temperature is about 300 ° C and the electro-mechanical coupling coefficient is large.
Yes, it can also be used for special piezoelectric ceramics for high frequencies
Things.

The bismuth sodium titanate described above sinters at substantially the same or slightly lower temperature as the PZT-based material,
It is the same piezoelectric material as the ZT-based material. This bismuth sodium titanate is 0.5% to 100% by weight of the PZT-based material.
% By weight and less than 5% by weight. If the amount is less than 0.5% by weight, the effect of the present invention is not exhibited, and if the amount is more than 5% by weight, the functional characteristics of PZT such as the electromechanical coupling coefficient deteriorate.

[0010]

By adding the above-mentioned predetermined amount of bismuth sodium titanate to the PZT material, the bismuth sodium titanate forms a liquid phase when the PZT material is calcined, and forms a bismuth sodium titanate phase at the grain boundaries. The formation of the liquid phase allows the PZT particles to move flexibly and the pores to move easily, so that the densification becomes faster and the number of defects is reduced as compared with the conventional sintered body. As a result, when external force is applied and stress is concentrated, the probability of breakage can be reduced, and mechanical strength can be improved. Bismuth sodium titanate does not react with PZT particles in a liquid phase state and does not directly control the piezoelectric properties of PZT. However, if it remains at the grain boundary of PZT particles, bismuth sodium titanate itself becomes a piezoelectric substance. Therefore, a decrease in the piezoelectric characteristics of the PZT-based material is suppressed. When the coercive electric field is increased by the addition of bismuth sodium titanate to cause a problem, as described above, SrTiO ₃ ,
PbTi0 ₃ or CaTi0 ₃ of any one or two or more may be added as the modifying component.

[0011]

As described above, according to the present invention, a liquid phase is formed around the sintering temperature of this ceramic on a PZT-based material which is a typical piezoelectric material, and the same functional characteristics as this ceramic are obtained. A bismuth sodium titanate, also known as a piezoelectric material,
By adding as a component, the mechanical strength of this ceramic can be improved without impairing the functional characteristics and piezoelectric characteristics of PZT. According to the present invention, the mechanical strength of a sintered body of PZT is significantly enhanced compared to the mechanical strength of PZT ceramics manufactured by a conventional method, and the use of electronic ceramics can be expanded to high frequency and high power regions like piezoelectric materials. become. PZT as a dielectric material
With respect to system materials, improvement in mechanical strength has been demanded in recent years as electronic components have become smaller and thinner. However, the use of the composition of the present invention can achieve the object.

[0012]

EXAMPLES Next, examples of the present invention will be described together with comparative examples in order to show specific embodiments of the present invention. The embodiments described below do not limit the technical scope of the present invention. Example 1 First, a chemical formula Pb _1.01 (Zr _0.53 Ti _0.47 )
A PZT-based material powder represented by O ₃ +0.5 mol 1% Nb ₂ O ₅ was prepared. As starting materials, metal oxides PbO, ZrO ₂ , TiO _2, and Nb ₂ having a high purity of 99% or more are used.
O ₅ was prepared, after mixing them so as to have a predetermined composition and mixed in a ball mill. This mixture was calcined at 900 ° C. for 2 hours and then pulverized to obtain a PZT-based material powder.
Next, the general formula _{(Bi 1/2 Na 1/2) 1-} x (Sr a Pb b Ca c) x
Of bismuth sodium titanate represented by TiO ₃ , each powder having the following composition was prepared. No. 1: (Bi _1/2 Na _1/2 ) TiO ₃ No. 2: (Bi _1/2 Na _1/2 ) _0.88 (Pb _1/2 Ca _1/2 )
_0.12 TiO ₃ Bi ₂ O ₃ , NaCO ₃ , SrCO ₃ , PbO, and TiO ₂ of reagent grade were prepared as starting materials, and these were blended so as to have a predetermined composition, and then mixed by a ball mill.
The mixture was calcined at 800 ° C. for 1 hour and then pulverized to obtain bismuth sodium titanate powder. When the PZT-based material powder is 100% by weight, 0.5% by weight of bismuth sodium titanate powder is added thereto,
Finish pulverization was performed by a ball mill. To this finished powder,
1. polyvinyl alcohol as a binder for the powder;
Each solution was added so as to have a concentration of 5% by weight and granulated.
1000k to make a disk 25mm in diameter and 1mm thick
Press molding was performed at a pressure of g / cm ² . 1 at 500 ° C
After the binder was removed for 0 hour, it was fired in a magnesia setter to obtain a PZT-based ceramic sintered body. The firing temperature was 1150 ° C, 1175 ° C, and 1200 ° C.
Time.

<Example 2> A sintered body was obtained in the same manner as in Example 1 except that 1.0% by weight of the same bismuth sodium titanate powder as in Example 1 was added to the same PZT-based material powder as in Example 1. Was. Comparative Example 1 The same bismuth sodium titanate powder as in Example 1 was added to the same PZT-based material powder as in Example 1 for 5.0.
A sintered body was obtained in the same manner as in Example 1 except that the addition was performed by weight%. Comparative Example 2 A sintered body was obtained in the same manner as in Example 1, except that bismuth sodium titanate powder was not added to the same PZT-based material powder as in Example 1.

<Measurement and Results> The electromechanical coupling coefficient and the flexural strength of the ceramic sintered bodies produced in the above Examples and Comparative Examples were measured. Table 1 shows the results.

[0015]

[Table 1]

PZT + No. As for No. 1, the electromechanical coupling coefficient was reduced to 0.67 of no addition (Comparative Example 2) from 0.5% by weight (Example 1) to 1.0% by weight (Example 2) of bismuth sodium titanate. 0.6 compared
4 to 0.62, whereas the transverse rupture strength was 893.
It was increased to a maximum 1044kg / cm ² from kg / cm ^2.
The changed ratio was that the electromechanical coupling coefficient was reduced by 7.5%, while the transverse rupture strength was increased by 17%. PZT + No. 2
A similar effect was also observed. This decrease in the electromechanical coupling coefficient is considered to be practically acceptable. When the addition amount of bismuth sodium titanate was 5.0% by weight (Comparative Example 1) and when bismuth sodium titanate was not added (Comparative Example 2), the transverse rupture strength was as low as 893 kg / cm ² . Further, in Comparative Example 1 in which the addition amount is 5.0% by weight, the decrease in the electromechanical coupling coefficient is large, and a problem is likely to occur in practical use.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Mamoru Ueyama 2270 Yokoze, Yokoze-cho, Chichibu-gun, Saitama Mitsubishi Materials Corporation Ceramics Research Laboratory (56) References JP 1-242464 (JP, A) JP Sho A 47-23896 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C04B 35/42-35/49 H01B 3/00-3/14 H01L 41/16-41/18

Claims (4)

(57) [Claims] 1. The chemical formula of Pb _1.01 (Zr _0.53 Ti _0.47 ) O ₃
PZT-based material 10 represented by + 0.5mo1% Nb ₂ O ₅
A PZT-based ceramic composition in which 0.5% by weight or more and less than 5% by weight of bismuth sodium titanate are added to 0% by weight. 2. The PZT ceramic composition according to claim 1, wherein the bismuth sodium titanate is represented by a chemical formula (Bi _1/2 Na _1/2 ) TiO ₃ . 3. The method of claim 1 wherein the bismuth sodium titanate is chemically
The formula (Bi_1/2Na_1/2) _0.88(Sr_1/2Pb_1/2)_0.12TiO_Three
The PZT ceramic composition according to claim 1, which is represented by the following formula:
Stuff. 4. Bismuth sodium titanate is chemically
The formula (Bi_1/2Na_1/2) _0.88(Pb_1/2Ca_1/2)_0.12TiO_Three
The PZT ceramic composition according to claim 1, which is represented by the following formula:
Stuff.