JPH06305817A - Ferrodielectric piezoelectric porcelain composition - Google Patents

Abstract

PURPOSE:To obtain a ferrodielectric piezoelectric porcelain composition capable of being used at high temperature and not requiring a correction circuit. CONSTITUTION:The characteristic of this bismuth lamellar ferrodielectric piezoelectric porcelain composition is to have the general formula: PbxBi3-xTi1-xNb1+xO9 wherein (x) is 0.3-0.75. The amount of Cr2O3 added for enlarging an electromechanical coupling factor in the thick vertical direction is controlled to <=0.5%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric piezoelectric ceramic composition for sensors, and more particularly to a ferroelectric piezoelectric ceramic composition having a high Curie point.

[0002]

2. Description of the Related Art Nowadays, various electronic devices are used in automobiles as electronics are remarkably used in various fields. Above all, the engine, which is the heart of an automobile, is being controlled electronically, starting with the fuel supply system. In order to control this engine, it is necessary to detect the state of the engine, and various sensors have been adopted for that purpose, and a cylinder pressure sensor that uses a piezoelectric body to detect the pressure in the cylinder of the engine is It is used.

This cylinder internal pressure sensor is used in a high temperature environment because it is installed in the cylinder of the engine. Therefore, it is required to be usable at high temperature, that is, to have a high Curie point, to have little change in electrical characteristics even at high temperature, and to have small capacitance temperature characteristic (CTC).

Conventionally, lead zirconate titanate (Pb (Zr, Ti) O has been used as a piezoelectric material used for an in-cylinder pressure sensor.
₃ = PZT) or lead titanate (PbTiO ₃ = PT)
Is used. However, since these piezoelectric materials have a large temperature coefficient of capacitance, when they are used as sensors, it is necessary to correct them using a correction circuit.

On the other hand, a bismuth layered ferroelectric substance is known as a piezoelectric material having a high Curie point as described in JP-B-54-18395 or JP-B-54-18394. Among the bismuth layered ferroelectrics, the main component (Pb _0.99 Sr _0.01 ) Bi ₂ Nb ₂ O ₉ is 0.1
Some have added 5 wt% MnCO ₃ , and their Curie point is as high as 590 ° C. However, -40 ℃ ~ +180 ℃
Temperature coefficient of capacitance (CTC) at about 1420ppm
Since it is as large as / ° C, it is difficult to use it as a sensor without a correction circuit.

[0006]

DISCLOSURE OF THE INVENTION In the present application, there is provided a ferroelectric piezoelectric ceramic composition which can be used at a high temperature which cannot be solved by the conventional piezoelectric ceramic materials and which does not require a correction circuit. This is the subject of the invention.

[0007]

In order to solve the above-mentioned problems of the invention, in the present application, the "general formula Pb _x Bi _3-x Ti
_A ferroelectric piezoelectric ceramic composition represented by _1-x Nb _{1 + x} O ₉ , wherein x is in a range of 0.3 ≦ x ≦ 0.75. An invention is provided that is configured as "a thing."

[0008]

The piezoelectric ceramic material according to the present invention having the above structure has a Curie point of 5 compared with the conventional piezoelectric ceramic material.
While it is about 90, it is about 600 to 900 ° C. Further, while the temperature coefficient of capacitance of the conventional piezoelectric ceramic material is 1420 ppm / ° C., the temperature coefficient of capacitance of the piezoelectric ceramic material according to the present invention is 496-12.
It is as small as 68ppm / ℃. The dielectric loss tan δ is 1.3% in the conventional piezoelectric ceramic material, while it is 1.0% or less in the piezoelectric ceramic material according to the present invention.

The CTC was obtained by dividing the difference between the electrostatic capacity at 180 ° C and the electrostatic capacity at -40 ° C by the electrostatic capacity at 25 ° C and the temperature difference 220 between 180 ° C and -40 ° C. CTC (-40 ℃ to + 180 ℃) = {[C180 ℃ -C-40 ℃] /
[C25 ° C. (180 − (− 40)]} where C180 ° C .: electrostatic capacity at 180 ° C. C-40 ° C .: electrostatic capacity at −40 ° C. C25 ° C .: electrostatic capacity at 25 ° C.

[0010]

EXAMPLES Examples of the present invention will be described. FIG. 1 shows a manufacturing process diagram of the piezoelectric ceramic material according to the present invention. The piezoelectric ceramic materials according to the present invention are all Pb, Bi, Ti, N
b, Cr oxides, ie PbO, Bi ₂ O ₃ , Ti
O ₂ , Nb ₂ O ₅ , and Cr ₂ O ₃ are used as starting materials, and are manufactured through the following steps.

(1) Weighing / mixing / drying All raw materials are oxides (PbO, Bi ₂ O ₃ , TiO ₂ , N
b ₂ O ₅ , Cr ₂ O ₃ ), each raw material is weighed so as to have a predetermined composition, and wet-mixed for a predetermined time with a ball mill,
dry.

(2) Pre-baking After drying, pre-baking is performed at a temperature of 780 ° C. to 850 ° C. for 2 hours.

(3) Coarse crushing / crushing / drying The calcined product is roughly crushed, wet-crushed in a ball mill for a predetermined time, and dried.

(4) Granulation and molding After drying, an organic binder is added to granulate, and 196 to 392.
It is pressure-molded at a pressure of MPa into a disk having a diameter of 16.5 mm and a thickness of 1 mm.

(5) Firing The formed disc is fired at 1030 ° C to 1100 ° C for 2 hours.

(6) Plane polishing / electrode formation / polarization The obtained sintered body was plane-polished to a thickness of 0.6 mm, and then A
A g electrode is provided on both sides, and a DC electric field of 5 ° C is applied in oil at 250 ° C.
MV / m is applied for 15 minutes to polarize.

The resonance frequency f _r , the anti-resonance frequency f _a , the electrostatic capacitance C _d , and the dielectric loss tan δ of the piezoelectric element manufactured in the above steps were measured with an impedance analyzer model HP4194A manufactured by Yokogawa Hewlett-Packard Co., and the thickness was measured. The longitudinal electromechanical coupling coefficient k _t and the relative dielectric constant ε _d were calculated.

Table 1 shows various characteristics when the value of x of the bismuth layered ferroelectric substance represented by Pb _x Bi _3-x Ti _1-x Nb _{1 + x} O ₉ is changed. For comparison, Table 1 also shows examples of various characteristics of the conventional piezoelectric composition.

[Table 1]

Based on the data shown in this table, the Curie point T _c is 600 ° C. or higher, which is equal to or higher than that of the conventional example, the capacitance temperature coefficient CTC is 1300 ppm / ° C. or lower, and the dielectric loss tan δ is 1.3%. The following samples were judged to be good, and the other samples were judged to be bad. As a result, samples 2, 3,
4,5,6,7,8,9,10,11 were judged to be good, and samples 12,13,14 were judged to be bad. However, Sample 1 having a small thickness electro-mechanical coupling coefficient k _t of 3% cannot be used as an in-cylinder pressure sensor, and was therefore determined to be defective. From this table, 0.3≤x≤0.
It can be said that the range of 75 achieves the object of the present invention.

Next, the characteristics when Cr ₂ O ₃ is added in an amount of 0.05 to 1.0 wt% to each of the samples with x = 0.3, 0.5, 0.75 are shown in Table 3, Table 4, and Table 4. It shows in Table 5. The purpose of adding Cr ₂ O ₃ is to increase the thickness longitudinal electromechanical coupling coefficient K _t without lowering the Curie T _c point.

Table 2 shows Pb _0.3 with x = _0.3.
When + Cr ₂ O ₃ is added to Bi _2.7 Ti _0.7 Nb _1.3 O ₉ , Pb _0.5 Bi _{2.5 when} x = 0.5 is shown in Table 3.
Table 4 in the case of adding Cr ₂ O ₃ to Ti _0.5 Nb _1.5 O ₉
Is Pb _0.75 Bi _2.25 Ti with x = 0.75.
_This is the characteristic when Cr ₂ O ₃ is added to _0.25 Nb _1.75 O ₉ .

[Table 2]

[0022]

[Table 3]

[0023]

[Table 4]

As shown in these tables, the samples 21, 22, 28, 29, _{3 in} which Cr ₂ O ₃ exceeds 0.5 wt%.
In Nos. 5 and 36, the firing density ρ _s decreased, the insulation resistance value decreased, and the polarization treatment could not be performed. Therefore, in order to use it as a piezoelectric material, the amount of Cr ₂ O ₃ added must be 0.5 wt% or less.

[0025]

As is apparent from the above description,
The ferroelectric piezoelectric ceramic composition according to claim 1 of the present invention has a high Curie point, and is therefore useful when used in a high temperature environment such as an in-cylinder pressure sensor. Moreover, since the temperature coefficient of capacitance is small, not only a correction circuit is not required when used, but also the dielectric loss tan δ.
Is also small. Further, the ferroelectric piezoelectric ceramic composition according to claim 2 has a large thickness longitudinal electromechanical coupling coefficient K _t , and is therefore more useful.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of a piezoelectric ceramic material according to the present invention.

Claims (2)

[Claims] 1. The general formula is Pb _x Bi _3-x Ti _1-x Nb _{1 + x} O.
_A ferroelectric piezoelectric ceramic composition represented by ₉ , wherein x is in the range of 0.3 ≦ x ≦ 0.75. 2. A ferroelectric piezoelectric ceramic composition according to claim 1, further comprising 0.5 wt% or less of Cr ₂ O ₃ .