JPH08268756A - Production of ferroelectric ceramics - Google Patents

Abstract

PURPOSE: To easily produce PZT having high mechanical strength. CONSTITUTION: Powders of PbO, TiO2 and ZrO2 as starting materials are prepd. so as to give a compsn. deficient in Pb in anticipation of the deposition of ZrO2 . The powders are mixed and this powdery mixture is calcined under conditions not causing scattering due to the sublimation of PbO. The resultant calcined product is fired at 900-1,200 deg.C under conditions not causing scattering due to the sublimation of PbO and fine ZrO2 is dispersed and deposited in Pb(Zrx Ti1-x )O3 (0.4<=x<=0.6) during the firing to obtain the objective ferroelectric ceramics contg. ZrO2 of <=1μm average particle diameter dispersed and deposited in the Pb(Zrx Ti1-x )O3 matrix.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ferroelectric ceramic which can be used in an actuator or the like which is subjected to a high mechanical load.

[0002]

As a piezoelectric material used for a piezoelectric element, P
Ceramics made of ZT-based oxide are known. This PZT (Pb (Zr _x Ti _1-x ) O ₃ ; 0 ≦ x ≦ 1)
Has a characteristic of exhibiting a high electromechanical conversion efficiency particularly in the composition around x = 0.53, and is widely used as a sensor, an actuator and the like.

PZT has good electrical characteristics such as a dielectric constant and a piezoelectric constant, but its mechanical strength is weak, which causes a problem when it is used as an actuator. As a method of improving this mechanical strength, a method of refining the crystal grain size,
Method of compounding with other high strength ceramics material
No. 109263, etc.), but all of them have a demerit that electrical characteristics are deteriorated.

As a conventional technique that does not deteriorate the electrical characteristics
Fine PZT powder₂O ₃Mix powder and fire
Method (Japanese Patent Application Laid-Open No. 4-1284887) and PZT table
Al on the surface₂O₃Method of permeating sol (Japanese Patent Laid-Open No. 5-90)
54). The method of PZT powder is Al₂O₃
The powder is mixed in an amount of 0.5 to 20% by weight and baked at 1100 ° C.
Method. This method requires fine powder of nm order.
Therefore, there is a problem that the cost is high.

In addition, the method (1) uses Al from the surface of PZT.
_This is a method of forming a surface-strengthening layer by permeating ₂ O ₃ sol. This method has a problem that the manufacturing process is complicated because a step of infiltrating the Al ₂ O ₃ sol is added.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a manufacturing method capable of easily manufacturing PZT having high mechanical strength.

[0007]

[Means for Solving the Problems] PZT is composed of PbO, Ti
The powders of O ₂ and ZrO ₂ are mixed, and the mixed powder is heated and fired in an electric furnace to manufacture. The reaction during heating / baking is presumed to be as follows. (I) Part of PbO reacts with TiO ₂ to form PbTiO ₃
And (ii) then a part of PbO reacts with ZrO ₂ to produce PbZrO ₃ , (iii) PbTiO ₃ and Pb
ZrO ₃ reacts to produce Pb (Zr _x Ti _1-x ) O ₃ .

In these reactions, when the partial pressure of PbO in the atmosphere is low, PbO is sublimated and P
b Insufficient state, so for example, reaction formula (1) shown below
As described above, there is a problem that ZrO ₂ is deposited, the composition is shifted, and the electrical characteristics are deteriorated. _{PbO + 0.530ZrO 2 + 0.470TiO 2 →} 0.950Pb (Zr 0. 505 Ti 0.495) O 3 + 0.05ZrO 2 + 0.05PbO ↑ ── (1) Thus, as normally no sublimation of PbO, Pb into the furnace
It has been devised to arrange ZrO ₃ or the like and increase the partial pressure of PbO in the atmosphere to perform firing.

The present inventors have made sure that PbO does not sublime.
Ingenuity and mechanical strength without deteriorating electrical characteristics
From the matrix in a self-generated manner to improve
rO ₂To precipitate ZrO in the matrix₂Finely
It came to the invention of the idea of dispersion
is there. That is, the production of the ferroelectric ceramics of the present invention
The method is ZrO₂The amount of Pb was deficient in consideration of the precipitation amount of
PbO, TiO₂And ZrO ₂
And the step of preparing the raw material powder of
Calcining the mixed powder under the condition that there is no separation due to sublimation of O
The calcination process and the condition that there is no separation due to sublimation of PbO
Simultaneously with baking the baked product at a temperature of 900 to 1200 ° C.
And fine ZrO₂To Pb (Zr_xTi_1-x) O
₃Main firing process to disperse and precipitate in (0.4 ≦ x ≦ 0.6)
It is characterized by consisting of

The composition of PbO, TiO ₂ and Zr should be adjusted so that the amount of Pb is deficient in consideration of the precipitation amount of ZrO _2.
To prepare a raw material powder of O ₂ means that the composition of the ferroelectric ceramic to be produced reacts with ZrO ₂ precipitated
b (Zr _x Ti _1-x ) O ₃ (0.4 ≦ x ≦ 0.6) P to be reacted with the precipitated ZrO ₂ so as to form a mixture with
It means to prepare a raw material powder in a state where bO is deficient. In other words, the number of moles of TiO _{2 in} the raw material powder and Z
The raw material powder is prepared so that the number of moles of PbO is smaller than the total number of moles of TiO ₂ and ZrO _{2 to which} the number of moles of rO ₂ is added.

Specifically, for example, P of x = 0.525
When it is desired to obtain ZT, the starting composition shown in reaction formula (2) may be used. _{0.950PbO + 0.550ZrO 2 + 0.450TiO 2 →} 0.950P b (Zr 0.525 Ti 0.475) O 3 + 0.05ZrO 2 ── Scheme (2) That is, in molar _{ratio, PbO: TiO 2: ZrO 2} =
The composition should be 0.950: 0.550: 0.450.

In the calcination step, the prepared raw material powders are mixed,
PbO ₃ , PbZr and PbZr
This is a step of using O ₃ or Pb (Zr _x Ti _1-x ) O ₃ . Usually, the calcination step is performed by heating at 750 to 850 ° C. for 2 to 6 hours. In the calcination step, all ZrO ₂ of the raw material powder and a part of PbO were calcinated to obtain PbZrO ₃ , or a commercially available product which was already PbZrO ₃ was used, and then obtained. PbZrO ₃ and the remaining T
It is also possible to mix iO ₂ and the balance PbO and calcine.

The calcined product obtained by calcining is preferably pulverized and mixed again. This makes the composition distribution more uniform. The crushed powder is press-molded into a green compact having a predetermined shape. In the main firing process, the calcined product is 900
It is a step of heating at ~ 1200 ° C for 1 to 8 hours. All PbO component _{Pb (Zr x Ti 1-x} ) O 3 becomes in this process, a part of the ZrO ₂ is uniformly precipitated in the matrix of _{Pb (Zr x Ti 1-x} ) O 3. This precipitated ZrO
₂ is preferably precipitated as fine crystals of 1 μm or less.

Firing at a temperature lower than 900 ° C. or for less than 1 hour is not preferable because the reaction does not proceed sufficiently and the electrical characteristics deteriorate. Baking at a temperature higher than 1200 ° C. or for 8 hours or more is not preferable because the grain growth proceeds and the mechanical strength decreases.

[0015]

The reason why the ferroelectric ceramics manufacturing method of the present invention can manufacture the ferroelectric ceramics having the electrical characteristics equal to or higher than those of the conventional PZT and excellent in mechanical strength is presumed as follows. PbO, TiO ₂ and Z
At the stage where the mixed powder mixed with rO ₂ was calcined, a part of Z
rO ₂ reacts with PbO to form PbZrO ₃ , and when the composition becomes uniform in the firing step, excess Zr is precipitated from PbZrO ₃ as ZrO ₂ (tetragonal crystal).
Therefore, it has a precise structure.

The precipitated ZrO ₂ imparts compressive stress to PZT due to volume expansion accompanying a tetragonal (high temperature) -monoclinic phase (low temperature) phase transition (during cooling to 500 ° C.). While receiving compressive stress, PZT is cubic (high temperature) -tetragonal (low temperature)
Phase transition (during cooling to 350 ° C.) to form a domain structure that relieves stress. In this way, it is estimated that the internal stress field is complicatedly affected to produce a PZT having electrical characteristics equal to or higher than that of the conventional PZT and excellent in mechanical strength.

[0017]

According to the method for producing a ferroelectric ceramic of the present invention, there is an advantage that a ferroelectric ceramic having electric characteristics equal to or higher than that of the conventional PZT and excellent in mechanical strength can be easily produced at low cost.

[0018]

【Example】

(1) Preparation of Sample A method for producing PZT having a composition of x = 0.525 in which 5 mol% of ZrO ₂ is dispersed and deposited will be shown below as an example. P
Each powder of bO, ZrO ₂ and TiO ₂ (particle size 1 to 5 μ
m) in a total amount of 250 g in a molar ratio of Pb: Zr: Ti =
Weighed to be 0.950: 0.550: 0.450.

After mixing the above powders with a household mixer,
It was put in a MgO container and calcined at 800 ° C. for 5 hours. This calcined powder was put in a polyethylene pot together with ZrO ₂ balls, ethanol was added, and ball milling was performed for 24 hours. After removing the ZrO ₂ balls, ethanol was evaporated in a hot water bath and further dried in a thermostat at 80 ° C. for 20 hours.

After crushing the calcined powder with a household mixer,
0.25 wt% of polyvinyl alcohol was added to obtain a granulated powder. 2g of granulated powder is weighed and the diameter of the cavity is φ
A pressure of 1 ton was applied to an 18 mm die for press molding. This molded body was degreased at 600 ° C. for 4 hours and then Al ₂
In an O ₃ container, the calcined powder of the same composition was used as the filling powder, and 115
Firing was performed at 0 ° C. for 1, 2, 4, and 8 hours (hereinafter, referred to as Samples C1, C2, C3, and C4 in order).

As a comparative material, the molar ratio Pb: Zr: Ti =
A mixed powder that was weighed to be 1.00: 0.525: 0.475 was used as a starting composition, and a sample (Sample A) produced by the same process and a calcinated powder of this composition were mixed with 5 mol% of ZrO ₂ powder. After further adding and mixing, a sample (Sample B) was fired in the same process. 2) Preparation and evaluation of test sample Each sample prepared as described above was ground (surface finish # 600) to a diameter of 12 mm and a thickness of 0.5 mm, and then subjected to chemical analysis, lattice constant measurement by X-ray diffraction, Precipitation Z by chemical analysis and calibration of X-ray diffraction intensity from ZrO ₂
It was subjected to quantitative analysis of rO ₂ , measurement of average particle diameter by SEM observation (intercept method), and density measurement.

As a representative of the electrical properties, the dielectric constant and its temperature dependence, and the amount of piezoelectric displacement under a periodic electric field were measured. The dielectric constant was measured by the impedance analyzer after forming the gold electrode by the sputtering method after the above grinding process.
The measurement of kHz was performed. The temperature dependence was measured by raising the temperature at 100 ° C./h in a high temperature furnace. The amount of displacement is 2 kV / mm in silicon oil at 110 ° C after electrode formation.
Polarization for 10 minutes under an electric field of 10 minutes, and after leaving for 1 day or longer, 0.1Hz, -0.4 using a laser displacement meter.
The displacement amount under an electric field of up to 1.2 kV / mm is 20 MPa.
Was measured under the stress of.

The mechanical properties were evaluated by carrying out a biaxial bending test on the above-ground sample. 3) Evaluation results In Table 1, chemical analysis, lattice constant measurement by X-ray diffraction, chemical analysis and quantitative analysis of precipitated ZrO ₂ by calibration of X-ray diffraction intensity from ZrO ₂ , measurement of average particle diameter by SEM observation (intercept method) ), And each result of a density measurement are shown. Compared with the sample A, since the analyzed values of Ti of other samples are almost the same and the lattice constants are almost the same, it is understood that Pb (Zr _0.525 Ti _0.475 ) O ₃ is obtained as the composition of PZT.

On the other hand, Zr by chemical analysis and X-ray diffraction
Considering the calibration results of the diffraction line intensity from O ₂ together, it can be seen that in Samples B and C1 to C4, about 5 mol% of ZrO ₂ was precipitated and the desired sample was obtained. In fact, in these samples, fine ZrO ₂ having a particle size of 1 μm or less was confirmed by SEM observation. Also, the average particle size slightly increased with the sintering time, but there was no great difference like the density.

Table 2 shows the measurement results of the dielectric constant of each sample. The dielectric constant at room temperature and the phase transition temperature is small only in Sample B, which can be understood as a result of the combination of ZrO ₂ .
The decrease was not seen in the samples C1 to C4. on the other hand,
Samples C1 to C4 have a phase transition temperature lowered by several degrees Celsius. P
According to the ZT experimental results, it is known that the phase transition temperature decreases under compressive stress. Therefore, it is estimated that the difference in electrical properties is due to compressive stress.

FIG. 1 shows the measurement result of the displacement amount. It can be seen that the samples C1 to C4 of the examples according to the present invention do not show a decrease in displacement amount as much as the sample B of the comparative example as compared with the sample A of the comparative example, and show substantially the same or higher performance. FIG. 2 shows the measurement results of biaxial bending strength. The samples C1 to C4 of the examples according to the present invention had higher strength than the sample A of the comparative example, and it was recognized that the maximum improvement was about 10%.

FIG. 3 shows the correlation between biaxial bending strength and displacement. The characteristic required for the actuator or the like is in the upper right direction indicated by the arrow, and C1 of the embodiment obtained in the present invention
It can be seen that C4 exceeds A and B of the comparative example.
As described above, it can be seen that a ferroelectric ceramic having electrical characteristics equal to or higher than that of the conventional PZT and excellent in mechanical strength can be easily manufactured at low cost. Table 1 Characteristics of samples used for measurement ──────────────────────────────────── Characteristics A B C1 C2 C3 C4 ──────────────────────────────────── Chemical composition ZrO ₂ (mol ratio) 52.7 57.5 58.5 58.2 58.5 58.2 TiO ₂ (mol ratio) 47.3 47.3 47.4 47.4 47.4 47.4 PbO (mol ratio) 100.0 100.0 100.0 100.0 100.0 100.0 Lattice constant a (Å) 4.044 4.040 4.044 4.044 4.044 4.044 c (Å) 4.144 4.140 4.140 4.144 4.140 4.140 Excess ZrO ₂ (mol%) From chemical analysis ─ 4.8 5.8 5.5 5.8 5.7 From X-ray diffraction ─ 6.5 5.7 5.4 5.9 6.3 Average particle size (μm) 3.3 3.3 3.1 3.5 3.8 4.1 Density (g / cm ³ ) 7.84 7.82 7.86 7.86 7.86 7.82 ─ ─ ───────────────────────────────── Table 2 Measurement results of the dielectric constant of each sample ─────── ───────────────────────────── AB C1 C2 C3 C4 ──────────────────────────────────── Phase transition temperature 349.5 348.7 346.6 347.0 345.0 345.0 Dielectric constant Room temperature 1230 1140 1220 1240 1230 1240 Phase transition temperature 25600 16700 25100 27000 27500 28800 ──────────────────────────────── ─────

[Brief description of drawings]

FIG. 1 is a diagram showing measurement results of displacement amounts of samples of Examples and Comparative Examples.

FIG. 2 is a diagram showing measurement results of biaxial bending strength of samples of Examples and Comparative Examples.

FIG. 3 is a diagram showing a correlation between biaxial bending strength and displacement of each sample of Examples and Comparative Examples.

[Explanation of symbols]

A ... Sample of Comparative Example B ... Sample of Comparative Example C1 ... Sample of Example C2 ... Sample of Example C3 ... Sample of Example C4 ... Sample of Example

Claims (4)

[Claims] 1. A composition comprising PbO, TiO ₂ and Zr so as to have a composition in which the amount of Pb is deficient in anticipation of a precipitation amount of ZrO _2.
Preparing a raw material powder of O _2, the raw material powder were mixed, in the absence discrete by sublimation of PbO, the mixed powder and calcining step of calcining, in the absence discrete by sublimation of PbO, calcined 9 products
At the same time as firing at a temperature of 00 to 1200 ° C., a fine Z
rO ₂ is replaced with Pb (Zr _x Ti _1-x ) O ₃ (0.4 ≦ x ≦
0.6) A main calcination step of dispersing and precipitating in a ceramic material, and a method for producing a ferroelectric ceramics. 2. Pb (Zr _x Ti _1-x ) O ₃ (0.4 ≦ x
≦ 0.6) The average particle size of ZrO ₂ dispersed and precipitated is 1 μm
The method for producing a ferroelectric ceramic according to claim 1, wherein: 3. The calcining step comprises ZrO _{2 as a} raw material powder and a part of P
bO was calcined to PbZrO ₂ and then P
2. The method for producing a ferroelectric ceramic according to claim 1, wherein the step is a step of mixing bZrO ₃ with the remaining TiO ₂ and the remaining PbO and calcining. 4. In the calcination step, the raw material powders are mixed and heated to obtain Pb.
_1-a (Zr _1-b Ti _b ) O ₃ (where a and b are positive numbers less than 1 each for c), and the main firing step is to obtain Pb _1-a (Zr _1-b Ti _b ) O ₃ to aZrO
_The method for producing a ferroelectric ceramic according to claim 1, which is a step of dispersing and precipitating ₂ in a Pb _1-a (Zr _1-b Ti _ba ) O ₃ matrix.