JPH1135371A - Piezoelectric porcelain and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a piezoelectric porcelain having a high electromechanical coupling factor, undergoing easy control of the temp. coefft. of resonance frequency and less liable to vary resonance frequency after a thermal shock. SOLUTION: The piezoelectric porcelain comprises grains of two or more perovskite type compds. different from each other in piezoelectric characteristics. Each of the perovskite type compds. has >=45% electromechanical coupling factor Kps and at least one of the compds. has <=0.5% variation ΔFrs of resonance frequency when it receives a thermal shock at 25-280 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezoelectric ceramic and a method of manufacturing the same, for example, a ceramic filter, a ceramic resonator, an ultrasonic transducer, a piezoelectric buzzer, a piezoelectric ignition unit, an ultrasonic motor, a piezoelectric fan, a piezoelectric actuator, and the like. Acceleration sensor, knocking sensor, A
The present invention relates to a piezoelectric ceramic suitable for a piezoelectric sensor such as an E sensor and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, products using piezoelectric ceramic compositions include, for example, ceramic filters, ceramic resonators, ultrasonic transducers, piezoelectric buzzers, piezoelectric speakers, ultrasonic motors, piezoelectric fans, and piezoelectric actuators.

Conventionally, as a material of the piezoelectric sounding body elements such as a buzzer or a _speaker, ceramic composition mainly composed of PbZrO 3 -PbTiO ₃ are utilized, this Nb ₂
Metal oxides such as O ₅ and MnO ₂ , Pb (Nb _2/3 Sn
_1/3 ) Addition or substitution of a composite perovskite oxide such as O ₃ improves the piezoelectric properties.

For example, Pb (Nb _2/3 Sn _1/3 ) O ₃ -PbZrO ₃ -P described in JP-B-54-36756.
A bTiO ₃ -based piezoelectric ceramic composition is disclosed.

On the other hand, in a ceramic filter, a ceramic resonator, or the like, in order to maximize its characteristics, it is generally better that the piezoelectric ceramic has a large electromechanical coupling coefficient Kp. On the other hand, in recent years, electronic components have been used not only for indoor-use equipment but also for communication devices mounted on vehicles that undergo drastic environmental changes, and are required to have reliability against temperature changes.

Accordingly, in recent years, the electromechanical coupling coefficient Kp is high, and the temperature coefficient of the resonance frequency (FrT
A material having a small C) is desired.

In recent years, surface mounting on circuit boards has progressed, and when soldering the above electronic components onto the board, the electronic components are exposed to a high temperature of about 230 ° C. for a short time. For this reason, the piezoelectric material used for the above electronic components has a temperature of 230 ° C.
It is necessary to be able to withstand a certain degree of thermal shock (thermal shock).

Then, for example, Pb (Nb _2/3
Sn _1/3 ) O ₃ —PbZrO ₃ —PbTiO ₃ -based piezoelectric ceramics include, for example, Pb (Nb _2/3 Sn _1/3 ) O ₃ powder,
After preparing PbZrO ₃ powder and PbTiO ₃ powder, mixing these in a predetermined amount, and calcining to prepare a solid solution powder,
Thereafter, a solid solution powder was formed and calcined at 1200 to 1300 ° C. for 2 to 4 hours to obtain a solid solution powder.

[0009]

However, in the piezoelectric ceramic described above, it was difficult to control the piezoelectric characteristics, for example, the electromechanical coupling coefficient Kp and the temperature coefficient FrTC of the resonance frequency. That is, the piezoelectric ceramic generally has the above-mentioned Pb (Nb
_{Since 2/3} Sn _1/3 ) O ₃ —PbZrO ₃ —PbTiO ₃ based piezoelectric ceramics are calcined to produce solid solution powders and the solid solution powders are used to produce piezoelectric ceramics, they are almost uniform. Is a single crystal phase piezoelectric ceramic having various characteristics, and the characteristics of the crystal phase become the characteristics of the piezoelectric ceramic as it is, but the crystal phase is easily affected by firing conditions and the like, and the crystal phase may change for some reason. In fact, unless piezoelectric ceramics were manufactured, the actual characteristics could not be known, and it was difficult to control the piezoelectric characteristics.

Further, when a thermal shock of about 230 ° C. is received, the resonance frequency changes, and there is a problem that the use as an electronic component element is greatly restricted.

[0011]

Means for Solving the Problems The present inventors have conducted intensive studies in view of the above problems, and as a result, instead of the conventional piezoelectric ceramic composed of a single kind of perovskite-type crystal phase having substantially uniform characteristics, Control of the resonance frequency temperature coefficient FrTC, electromechanical coupling coefficient Kp, thermal shock resistance, etc. by combining two or more kinds of perovskite-type crystal phases with little change in resonance frequency due to thermal shock and different piezoelectric characteristics. Have been found to be easy, and have led to the present invention. In addition, the inventors have found that a composite of two or more kinds of perovskite-type crystal phases having different piezoelectric characteristics can be achieved by firing with a microwave, and the present invention has been accomplished.

That is, the piezoelectric ceramic of the present invention is a piezoelectric ceramic comprising two or more kinds of perovskite type crystal particles having different piezoelectric characteristics, wherein the two or more kinds of perovskite type crystal particles have an electromechanical coupling coefficient Kps of 45%. It has the above characteristics, and at least one kind of perovskite crystal particles has a characteristic that the rate of change ΔFrs of the resonance frequency when subjected to a thermal shock at 25 to 280 ° C. is 0.5% or less.

Here, two or more kinds of perovskite type crystal particles having different piezoelectric characteristics are composed of Pb, Zr,
A perovskite-type crystal particle containing Ti, Nb, Cr, Sr, La, Y, and Co;
It is desirable to include perovskite-type crystal particles containing Zr, Ti, Nb, Sb and Cr.

Further, two or more kinds of perovskite-type crystal grains having different piezoelectric characteristics have a temperature coefficient of resonance frequency FrTCs
Preferably contains positive crystal grains and negative crystal grains.

Furthermore, the temperature coefficient of resonance frequency FrTC is -150 to 150 ppm / ° C., and the electromechanical coupling coefficient Kp is 55% or more. It is desirable to have a characteristic of 7% or less.

Such a piezoelectric ceramic is a mixed powder composed of two or more kinds of perovskite oxide powders having an electromechanical coupling coefficient Kps of 45% or more.
At least one of the perovskite-type oxide powders is a perovskite-type oxide powder having a characteristic that the rate of change in resonance frequency ΔFrs is 0.5% or less when subjected to a thermal shock at 25 to 280 ° C. A molded body is produced using the powder, and the molded body is baked by microwaves.
It is manufactured by compounding two or more kinds of perovskite type crystal phases having different piezoelectric characteristics.

[0017]

In the piezoelectric ceramic of the present invention, two or more kinds of perovskite-type crystal phases having different piezoelectric properties are compounded. For example, a perovskite-type crystal having a high electromechanical coupling coefficient Kps and having thermal shock resistance is provided. By having two or more types of perovskite-type crystal phases having different temperature coefficients FrTCs of the resonance frequency and adjusting the ratio thereof, the crystal phase has a high electromechanical coupling coefficient Kp and thermal shock resistance. The temperature coefficient FrTC of the resonance frequency of the piezoelectric ceramic can be controlled within the range of the temperature coefficient of resonance frequency FrTCs of the perovskite-type crystal phase.

Further, since one of the perovskite-type crystal phases has thermal shock resistance, the thermal shock resistance of the entire piezoelectric ceramic can be improved. For example, it has thermal shock resistance and a negative temperature coefficient FrT
By combining a perovskite-type crystal phase having Cs with a perovskite-type crystal phase having a high electromechanical coupling coefficient Kps and a positive temperature coefficient FrTCs,
A piezoelectric ceramic having a high electromechanical coupling coefficient Kp and thermal shock resistance and having a temperature coefficient of resonance frequency FrTC near 0 is obtained.

Accordingly, the temperature coefficient of resonance frequency, FrTC, which is difficult to obtain with the conventional piezoelectric ceramic, is -150.
１５０150 ppm / ° C., a rate of change of resonance frequency ΔFr after a thermal shock (thermal shock) of 25 to 250 ° C. of 0.5% or less, and an electromechanical coupling coefficient Kp of 55% or more can be easily obtained. Can be.

In such a piezoelectric ceramic, a compact is produced from two or more kinds of composite perovskite-type oxide powders having different piezoelectric characteristics, and the compact is subjected to microwave treatment at a low temperature of, for example, 1000 to 1200 ° C. It is easily obtained by baking in time.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The piezoelectric ceramic of the present invention contains two or more kinds of perovskite type crystal particles having different piezoelectric characteristics, and may further contain metal particles and oxide particles. The average crystal grain size of the perovskite-type crystal grains is from 0.3 to 1 μm, especially from 0.5 to 1 μm from the viewpoint of high strength.
Desirably, the particles are 0.8 μm. Further, it is desirable that other metal particles and oxide particles do not exist, but when present, the average particle is desirably 1 μm or less from the viewpoint of high strength.

The two or more kinds of perovskite-type crystal grains having different piezoelectric characteristics have a property of having an electromechanical coupling coefficient Kps of 45% or more, and at least one kind of perovskite-type crystal grains has a thermal conductivity of 25 to 280 ° C. It is necessary that the rate of change ΔFrs of the resonance frequency upon receiving a shock has a characteristic of 0.5% or less. This is because, by controlling the content of perovskite-type crystal particles having thermal shock resistance, the piezoelectric ceramic can also have thermal shock resistance, and is highly useful in the above-mentioned application fields.

The two or more kinds of perovskite type crystal particles are
Temperature coefficient of resonance frequency FrTCs is -70 to 400 pp
m / ° C. is desirable.

The perovskite-type crystal particles having an electromechanical coupling coefficient Kps of 45% or more are defined as a perovskite-type crystal particle having an electromechanical coupling coefficient Kps of 45% or more when the piezoelectric ceramic is constituted by the perovskite-type crystal particles. It means that it has characteristics. The same applies to thermal shock resistance and temperature coefficient of resonance frequency FrTCs.

Two or more kinds of perovskite type crystal particles having different piezoelectric characteristics are composed of Pb, Zr, Ti, N
b, Cr, Sr, La, Y, and Co containing perovskite-type crystal particles, and Pb, Zr, T
It is desirable to include perovskite-type crystal particles containing i, Nb, Sb and Cr. In particular, it is desirable that these two types of perovskite-type crystal particles are used.

This is because Pb, Zr, T
The perovskite-type crystal particles containing i, Nb, Cr, Sr, La, Y, and Co have a large temperature coefficient of resonance frequency, FrTCs, in the negative direction when a porcelain is formed from these particles. Coefficient Kps is high,
This is because the rate of change ΔFrs in the resonance frequency has a small characteristic even when a thermal shock is applied, and the temperature coefficient FrTCs of the resonance frequency of the perovskite-type crystal particles changes depending on the composition.

Further, the perovskite-type crystal grains containing Pb, Zr, Ti, Nb, Sb and Cr are weak to thermal shock when porcelain is formed from these grains, but the temperature coefficient of resonance frequency FrTCs is positive. This is because the electromechanical coupling coefficient Kps is higher.
By compounding these perovskite-type crystal particles, they have a high electromechanical coupling coefficient Kp, a high thermal shock resistance, and a temperature coefficient of resonance frequency FrTC of 0.
This is because excellent characteristics in the vicinity can be obtained.

Examples of two or more kinds of perovskite type crystal particles having different piezoelectric characteristics include, for example, perovskite having thermal shock resistance, high electromechanical coupling coefficient Kps, and temperature coefficient of negative resonance frequency FrTCs FrTCs. Having high electromechanical coupling coefficient Kps
Further, there is a combination of perovskite-type crystal grains having a temperature coefficient FrTCs of a positive resonance frequency. In this case, it is resistant to thermal shock and has a high electromechanical coupling coefficient K.
A piezoelectric ceramic having p and having a temperature coefficient of resonance frequency FrTC close to 0 can be obtained.

Therefore, the temperature coefficient FrTC and the electromechanical coupling coefficient Kp of the resonance frequency of the piezoelectric ceramic can be controlled by variously changing the combination of the perovskite crystal grains having different piezoelectric characteristics. By using perovskite-type crystal particles having high thermal shock resistance as one type, a piezoelectric ceramic having high thermal shock resistance can be obtained. That is, in the piezoelectric ceramic of the present invention, the temperature coefficient FrTC of the resonance frequency is −
150 to 150 ppm / ° C, electromechanical coupling coefficient Kp is 5
The rate of change ΔFr of the resonance frequency after receiving a thermal shock of 5% or more and 25 to 280 ° C. can be 0.7% or less.

The piezoelectric ceramic of the present invention may contain, as unavoidable impurities, one or more elements which can become ions having +1, 2, 3, 4, and pentavalent charges, and at least 5% by weight or less. It is desirable not to contain such inevitable impurities, but it is inevitable to be mixed in the raw material, and it is desirable that the amount is small.

The method for manufacturing a piezoelectric ceramic according to the present invention includes, for example,
It is produced by the following method. First, for example, PbO, ZrO ₂ , TiO ₂ , Nb ₂ O ₅ , C
r ₂ O ₃ , SrCO ₃ , La ₂ O ₃ , Y ₂ O ₃ , Co ₃
A predetermined amount of each raw material powder of O ₄ is weighed, and 10
Wet-mix for ~ 24 hours to make a mixed powder.

Further, separately, PbO, ZrO ₂ , Ti
A predetermined amount of each raw material powder of O ₂ , Nb ₂ O ₅ , Sb ₂ O ₅ , and Cr ₂ O ₃ is weighed and wet-mixed with a ball mill or the like for 10 to 24 hours to prepare a mixed powder.

Then, after drying these mixed powders,
Each is calcined at 800 to 1300 ° C. for 1 to 3 hours and pulverized by a ball mill or the like. Thereafter, an organic binder is mixed with the pulverized material, and the mixture is granulated by a spray drier or the like, to thereby produce granules of two kinds of composite perovskite compounds having different piezoelectric characteristics.

Then, these granules are mixed at an appropriate ratio, and for example, the mixed powder is formed at a predetermined pressure to produce a formed body, which is then subjected to 1000 to 1200 in air.
It is obtained by firing in a microwave at 5 ° C. for 5 to 30 minutes. The density of the obtained piezoelectric ceramic of the present invention is 7.0 g /
cm ³ or more.

When a molded body made of granules of two or more composite perovskite type compounds having different piezoelectric properties is fired by microwaves, the perovskite crystal particles are fired at a low temperature for a short time. Almost no grain growth,
In addition, since perovskite-type crystal particles having different piezoelectric characteristics do not form a solid solution with each other, the added perovskite-type crystal particles almost exist as they are.

The piezoelectric ceramic obtained by such a method is composed of two or more kinds of perovskite-type crystal grains having different piezoelectric properties as described above. May be present. In some cases, a constituent element compound of the perovskite-type crystal particles and a pyrochlore phase are present.

[0037]

EXAMPLES PbO, ZrO ₂ , Ti
O ₂ , Nb ₂ O ₅ , Sb ₂ O ₅ , Cr ₂ O ₃ , SrCO
₃ , La ₂ O ₃ , Y ₂ O ₃ , and Co ₃ O ₄ were wet-mixed in a ball mill using ZrO ₂ balls, dried, calcined at 900 ° C. for 3 hours, and then Cr ₂ O ₃
Is added by external addition at 2% by weight, and the mixture is pulverized again by a ball mill. Thereafter, an organic binder was mixed with the pulverized material, dried and granulated by a spray drier, and (Pb _0.96 Sr
_0.03 La _0.01 ) (Nb _1/2 Cr _1/2 ) _0.232 (Nb _1/2 Y
_1/2 ) _0.232 (Nb _2/3 Co _1/3 ) _0.416 Nb _0.12 ]
_0.06 first and spray material consisting of _{[Zr 0.505 Ti 0. 495] 0.94} O 3, Pb (Nb 1/2 Sb 1/2) (Zr 0. 52 Ti
_0.48) to produce a O ₃ + 0.2 wt% second spray material consisting of Cr ₂ O _3.

When the first spray raw material is made of a piezoelectric ceramic alone, the electromechanical coupling coefficient Kps is 57%,
The temperature coefficient of resonance frequency FrTCs is -70 ppm / ° C., and the rate of change ΔFrs of the resonance frequency after thermal shock is 0.
The second spray raw material has an electromechanical coupling coefficient Kps of 65% and a temperature coefficient of resonance frequency FrTCs when a piezoelectric ceramic is produced alone.
The rate of change ΔFrs of the resonance frequency after thermal shock at 400 ppm / ° C. was 1%.

Then, these first and second spray materials were mixed at the ratio shown in Table 1, and the mixed powder was mixed for 1.5 tons.
It was press-formed into a disk having a size of 23 mm in diameter and 2 mm in thickness at a pressure of / cm ² . Furthermore, these molded articles were degreased in air at 820 ° C. for 2 hours, and then subjected to a frequency of 28 GHz.
It baked for 10 minutes at 1050 degreeC in air | atmosphere using the stainless steel microwave heating furnace using the microwave transmitter which made the gyrotron of the maximum output 10KW the transmission source.

The obtained sintered body was polished to a thickness of 0.5 mm.
Was formed. Electrodes are formed by baking Ag paste on both principal surfaces of the disc, and applying a DC voltage of 3 KV / mm in silicon oil at 80 ° C. for 30 minutes to perform polarization treatment. The temperature coefficient of frequency FrTC was evaluated. Moreover, it passes through a tunnel furnace from room temperature (25 ° C.) to 280 ° C. (25 ° C. to 280 ° C.).
The thermal shock after 100 hours had elapsed was measured, and the rate of change was calculated. Further, the average crystal grain size was determined by an intercept method.

The electromechanical coupling coefficient Kp and the temperature coefficient of resonance frequency FrTC were obtained by calculation from the values of the resonance frequency Fr, anti-resonance frequency Fa, electric capacitance C, and resonance resistance R ₀ measured by an impedance analyzer.

The temperature coefficient FrTC of the resonance frequency is
The resonance frequencies of -30 and 85 ° C. were measured, and FrTC =
(Fr (85) -Fr (-30)) / (Fr (-30)
× 115) × 10 ⁶ (where Fr (85), Fr (−3)
0) are resonance frequency values at 85 ° C. and −30 ° C., respectively. ). Table 1 shows the results.

The crystal particles of the sample of the present invention were subjected to elemental analysis by an X-ray microanalyzer (EPMA). As a result, each crystal particle of each added spray-dried raw material was present, and two types of perovskite-type crystal phases were placed in a piezoelectric ceramic. Was confirmed to exist.

[0044]

[Table 1]

As shown in Table 1, in the piezoelectric ceramic of the present invention, two or more types of spray materials having different electromechanical coupling coefficients Kps and resonance temperature coefficients FrTCs are subjected to microwave firing to obtain an electromechanical coupling coefficient Kp and a resonance frequency. It can be understood that the temperature coefficient FrTC can be controlled. That is, it can be seen that the electromechanical coupling coefficient Kp increases as the proportion of the spray material having a higher electromechanical coupling coefficient Kps increases, and the temperature coefficient of resonance frequency FrTC also increases or decreases according to the proportion.

Regarding thermal shock resistance,
It can be seen that the compounding of the spray material having thermal shock resistance reduces the rate of change ΔFr of the resonance frequency after thermal shock to 0.5%. In particular, when the mixing ratio of the first spray material and the second spray material is 55 to 95:45 to 5 by weight, the electromechanical coupling coefficient Kp is 57.4 to 60.6, and the temperature coefficient of the resonance frequency is It can be seen that FrTC is excellent at −47 to 142 ppm / ° C., and the change rate ΔFr of the resonance frequency after thermal shock is as excellent as 0.5%. In particular, when the mixing ratio of the first spray material and the second spray material is 75 to 95:25 to 5 by weight, the electromechanical coupling coefficient Kp is 57.4 to 59.
0, temperature coefficient of resonance frequency FrTC is -47 to 48 pp
m / ° C., rate of change ΔF of resonance frequency after thermal shock
It can be seen that r is as excellent as 0.5%.

The inventors of the present invention, as a comparative example,
o.14 spray materials are mixed and 900 ℃
After calcining for an hour and pulverizing, it was molded in the same manner as in the above example, degreased in the air at 820 ° C. for 2 hours, and fired in the air at 1260 ° C. for 2 hours to produce a piezoelectric ceramic. Electrodes are formed by baking Ag paste on both main surfaces of the sintered body, applying a DC voltage of 3 KV / mm in silicon oil at 80 ° C. for 30 minutes, and performing polarization treatment. Temperature coefficient of resonance frequency Fr
TC, rate of change ΔFr in resonance frequency after thermal shock
Was evaluated.

As a result, the electromechanical coupling coefficient Kp is 40
%, Temperature coefficient of resonance frequency FrTC is -2000 ppm
/ ° C, change in resonance frequency ΔFr after thermal shock
Was 1%. In addition, as a result of elemental analysis of the crystal particles by an X-ray microanalyzer (EPMA), it was confirmed that the two types of spray raw materials were dissolved to form a substantially uniform single crystal phase. The results are shown in Sample 1 of Table 1.

[0049]

As described in detail above, according to the present invention,
Since two or more kinds of perovskite-type crystal phases having different piezoelectric characteristics are compounded, the control of the piezoelectric characteristics is facilitated. For example, it has thermal shock resistance, a high electromechanical coupling coefficient Kps, and a negative resistance. Temperature coefficient of resonance frequency FrT
By combining perovskite-type crystal particles having Cs with perovskite-type crystal particles having a high electromechanical coupling coefficient Kps and having a temperature coefficient of positive resonance frequency FrTCs, thermal shock resistance and high electromechanical coupling are obtained. Temperature coefficient F of the resonance frequency
A piezoelectric ceramic having rTC close to 0 can be obtained.

Claims (5)

[Claims] 1. A piezoelectric ceramic comprising two or more types of perovskite type crystal particles having different piezoelectric characteristics, wherein said two or more types of perovskite type crystal particles have an electromechanical coupling coefficient Kps.
Has a characteristic of 45% or more, and the rate of change ΔFrs of the resonance frequency when at least one kind of perovskite crystal grains is subjected to a thermal shock at 25 to 280 ° C. is 0.
A piezoelectric ceramic having a characteristic of 5% or less. 2. The method according to claim 1, wherein two or more kinds of perovskite type crystal particles having different piezoelectric characteristics are used as metal elements such as Pb, Zr, Ti, and N.
b, Cr, Sr, La, Y, and Co containing perovskite-type crystal particles, and Pb, Zr, T
The piezoelectric ceramic according to claim 1, further comprising perovskite-type crystal particles containing i, Nb, Sb, and Cr. 3. The method according to claim 1, wherein the two or more kinds of perovskite crystal grains having different piezoelectric characteristics include crystal grains having positive and negative temperature coefficients of resonance frequency FrTCs. Piezoelectric ceramics. 4. The temperature coefficient of resonance frequency FrTC is -150.
The electro-mechanical coupling coefficient Kp is 55% or more, and the rate of change ΔFr of the resonance frequency when subjected to a thermal shock of 25-280 ° C. is 0.7% or less. The piezoelectric ceramic according to any one of claims 1 to 3. 5. A mixed powder comprising two or more perovskite oxide powders having an electromechanical coupling coefficient Kps of 45% or more, wherein at least one of the two or more perovskite oxide powders is used. Is the change rate ΔF of the resonance frequency when a thermal shock of 25 to 280 ° C. is received.
A molded body is produced using a mixed powder that is a perovskite-type oxide powder having a characteristic of rs of 0.5% or less, and the molded body is fired by a microwave to obtain two or more types of perovskite-type powders having different piezoelectric characteristics. A method for producing a piezoelectric ceramic, comprising compounding a crystal phase.