JP2003327471A - Piezoelectric ceramic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic capable of decreasing dielectric constant and increasing mechanical quality factor Qm and free from causing environmental problems due to lead. <P>SOLUTION: The piezoelectric ceramic consists essentially of a ceramic expressed by a general formula (Sr<SB>1-x</SB>Ca<SB>x</SB>)<SB>1-y</SB>Nd<SB>2y/3</SB>Bi<SB>2</SB>Ta<SB>2</SB>O<SB>9</SB>where (x) is in a composition range of 0<x<1 and (y) is in a composition range of 0≤y≤0.3 and contains <0.5 wt.% (not including 0) manganese expressed in terms of MnCO<SB>3</SB>. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] TECHNICAL FIELD The present invention relates to a ceramic resonator.
Data, ceramic filters, temperature sensors, etc.
It relates to piezoelectric ceramics. [0002] 2. Description of the Related Art Conventional piezoelectric ceramics are called PZT.
PbZrO₃-PbTiO₃MPB of solid solution (m
orphotropic phase boundary
y) There are those having a near composition system. A piezoelectric cell of such a composition system
Lamix is inexpensive and has good electrical characteristics.
Used for child parts. [0003] SUMMARY OF THE INVENTION However, this kind of
Because piezoelectric ceramics contain a large amount of lead,
Release of lead into the atmosphere during heat treatment such as firing and melting in the manufacturing process
After they are sold or marketed in the form of electronic components,
Lead is released into the soil even when child components are discarded.
The effect of lead on the environment is a problem, and industrial use is prohibited.
Are being stopped or restricted. In recent years,
Rapid conversion of electrical signals from analog to digital
And the use range of electronic components is expanding to the high frequency range.
There are two. However, piezoelectric ceramics as described above
Has a large relative dielectric constant of 1000 or more and a mechanical quality factor
Since Qm is as small as 2500 or less, it is used in the high frequency band.
Could not be used for electronic components. [0004] The present invention provides a low dielectric constant and mechanical
The quality factor Qm can be increased and lead
To provide piezoelectric ceramics that do not cause environmental problems
The porpose is to do. [0005] SUMMARY OF THE INVENTION The piezoelectric ceramic of the present invention
Is Sr-B, a kind of bismuth layered structure ferroelectric.
By improving the composition of the i-Ta based ceramic,
It is intended to solve the problem. That is, the piezoelectric of the present invention
Ceramics have the general formula (Sr_1-xCa_x) _1-yN
d_{2y / 3}Bi₂Ta₂O₉Where x is 0 <x <
Ceramics in which 1, y is in the composition range of 0 ≦ y ≦ 0.3
With manganese as MnCO₃Converted to
Contains less than 0.5 wt% (excluding 0). [0006] DESCRIPTION OF THE PREFERRED EMBODIMENTS Sr-Bi-Ta ceramics
Part of Sr is replaced with Ca and manganese is added
Thereby, the mechanical quality factor Qm is improved. Furthermore, Sr
And a part of Ca is substituted with Nd,
The strain increases and the electromechanical coupling coefficient of the spreading vibration of the disk
Kp is improved. In addition, Nd acts as a sintering aid,
The mechanical quality factor Qm may be improved. At this time,
Ree temperature Tc is always 350 ° C. or higher,
When passing through, no problem such as depolarization occurs. [0007] Embodiments of the present invention will be described below. Ma
Regarding the manufacturing method of the piezoelectric ceramics according to the present invention
explain. SrCO ₃, CaCO₃, Nd₂O₃, Bi
₂O₃, Ta₂O₅, MnCO₃Raw material powder
And weighed for 7 hours using a ball mill or the like.
Formula mixed. At 800-1000 ° C
Calcination, and this calcined product is wet-processed for 7 hours using a ball mill or the like.
Crushed. After drying this pulverized material, PVA
Add a binder, granulate, mold and bake.
This gave the material according to the invention. [0008] The measurement of the characteristics of the piezoelectric ceramics according to the present invention.
The dry pulverized material is coated with a binder such as PVA from 1 to 3
wt% and granulated.
Press with 100MPa pressure to make a 2.5mm disc.
And the maximum holding temperature is 1100-1350 ° C.
Baking so that the holding time at the maximum holding temperature is 2 hours
A plate-shaped porcelain, and the disc-shaped porcelain having a thickness of 0.2 to 2
mm, and then form silver electrodes on both sides.
In insulating oil, the temperature is 100-250.
° C, an electric field of 5 to 12 kV / mm, and a time of 1 to 30 minutes.
An evaluation sample was obtained by performing a polarization treatment on the subject. This feature
Is measured by using the resonance / anti-resonance method.
Calculate the dynamic electromechanical coupling coefficient Kp and mechanical quality coefficient Qm
did. Furthermore, the temperature change of the relative permittivity is measured and the Curie
The temperature Tc was calculated. FIG. 1 shows (Sr_1-xCa_x)_1-yNd
_{2y / 3}Bi₂Ta₂O₉In the formula, the substitution amount x of Ca,
The circle when the substitution amount y of Nd and the addition amount z of manganese are changed
Electromechanical coupling coefficient Kp for spread vibration of plate, mechanical quality
Several Qm, Curie temperature Tc and firing temperature are summarized in the table.
It is. In addition, * mark of sample No. is outside the scope of the present invention.
It indicates that Piezoelectric ceramic of the present invention
X is 0 <x <1, y is 0 ≦ y ≦ 0.3, and z is 0 <z
The relative dielectric constant became 200 or less within the range of <0.5. Ma
Also, when the substitution amount x of Ca is increased, the Curie temperature Tc is increased.
A tendency to increase was obtained. In addition, manganese is reduced to 0 <z
When added in the range of <0.5, manganese is not added
The mechanical quality factor Qm is larger than
When the addition amount z becomes 0.5 wt%, the insulation resistance is lowered and the
The poles are difficult, so compared to those without manganese added
In all cases, the mechanical quality factor Qm was small. In particular, Ca
Add 0.2wt% of manganese to the replacement amount x 0.8
As a result, the mechanical quality factor Qm exceeds 10,000
Trends that can be significantly improved
did it. Further, when the substitution amount y of Nd is increased,
Temperature Tc decreases, but the electromechanical coupling coefficient Kp
Tended to increase. At this time, the substitution amount y of Nd
Is less than 0.3, the electronic components are
Does not depolarize even at the reflow temperature when soldering to a board etc.
A practical Curie temperature Tc was obtained. Also,
Nd acts as a sintering aid, further increasing the mechanical quality factor Qm.
Can be improved. Thus, the substitution amount x of Ca is 0 <x <1,
The substitution amount y of Nd is 0 ≦ y ≦ 0.3, and the addition amount of manganese z
Is in the range of 0 <z <0.5, and a good mechanical quality factor Qm
Could be obtained. [0011] According to the present invention, the relative dielectric constant is small,
Obtaining piezoelectric ceramics with large mechanical quality factor Qm
Can be. Further, the piezoelectric ceramic of the present invention contains lead.
Do not have lead in the manufacturing process or when electronic components are discarded.
Is not released and may cause environmental problems.
Absent.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a table of characteristics for explaining characteristics of a piezoelectric ceramic of the present invention.

Claims (1)

[Claims] 1. The general formula (Sr_1-xCa_x)_1-yNd_{2y / 3}Bi₂Ta₂
O₉ Where x is 0 <x <1 and y is 0 ≦ y ≦ 0.3
The main component is ceramics in the range, and manganese is
MnCO₃Less than 0.5 wt% (excluding 0)
A piezoelectric ceramic characterized by containing.