JPH05139824A - Piezoelectric ceramic composition - Google Patents

Abstract

PURPOSE:To provide a piezoelectric ceramic composition capable of obtaining a product having qualities being good in sintering property, high in heat resistance and stabilized in mechanical quality coefficient. CONSTITUTION:The objective ceramic composition obtained by adding Mn and Cr to a lead titanate based material in which a part of Pb of PbTiO3 is replaced with La and having a composition expressed by the general formula Pb1-3y/2LayTiO3+z.{(1-x)MnO2+(x/2).Cr2O3} [0<x<1 and 0<z<=5wt.%].

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic composition used for a high frequency ceramic filter, a ceramic oscillator, a ceramic discriminator, a surface acoustic wave device, and the like. The present invention relates to a piezoelectric ceramic composition having a stable mechanical quality factor (Qmt) and good group delay characteristics.

[0002]

2. Description of the Related Art Conventionally, as a material of a piezoelectric ceramic element used for a ceramic filter, for example, lead titanate (PbTiO ₃ ) based material has been known. This PbTiO ₃ system is excellent as a resonator material for high frequencies at high temperatures because of its small relative permittivity, high mechanical quality factor, and high Curie point. This is because it is desired to reduce the mechanical quality factor (Qmt) without lowering the electromechanical coupling factor in order to improve the resolution of the filter. In addition, in recent years, electronic parts have been made into chips, and in addition to conventional resin mold elements with leads and elements enclosed in metal cases, small surface mountable ceramic filters, ceramic oscillators, ceramic discriminators, ceramics, etc. Piezoelectric elements such as traps have been developed. In addition to the conventional resin mold element with leads and the element enclosed in the metal case, the temperature rise of the piezoelectric ceramics was suppressed to about 200 ° C. at the time of soldering mounting. Ceramics are also exposed to high temperatures of about 300 ° C. P as a piezoelectric ceramic that meets the demands of electronic components whose characteristics do not change at high temperatures
bTiO ₃ based porcelain is used. However, PbT
The iO ₃ -based porcelain could not be upsized because it had poor sinterability and poor polarizability. Therefore, in order to solve these drawbacks, there is a lead titanate-based piezoelectric ceramic composition in which Pb is partially replaced with La and Mn is added.

[0003]

However, when a part of Pb of the above-mentioned conventional PbTiO ₃ system is replaced with La, Mn is replaced by Mn.
The piezo-electric porcelain composition to which is added has a mechanical quality factor (Qm
There is a problem in that t) is large and the group delay characteristic when the filter is used deteriorates. Therefore, if the amount of Mn added is reduced in an attempt to improve it, Qmt may change abruptly, and this control is difficult and there is a problem that it is difficult to produce a product of stable and required quality.

The present invention has been made in view of the above problems of the prior art, and has good sinterability and high heat resistance temperature,
An object of the present invention is to provide a piezoelectric porcelain composition capable of obtaining a product having a stable mechanical quality factor.

[0005]

The piezoelectric porcelain composition according to the present invention has a general formula of Pb, which is obtained by adding Mn and Cr to a lead titanate system in which a part of Pb of PbTiO ₃ is replaced with La.
_{1-3y / 2 La y TiO 3 +} Z · {(1-x) MnO 2 +
(X / 2) .Cr ₂ O ₃ } (where 0
<X <1, 0 <z ≦ 5 wt%).

In the present invention, the reason why the composition of the piezoelectric ceramic composition is limited to the above range is as follows. Unless a part of Pb is replaced with La, the sinterability is poor and the strength is low.
The polarizability is also bad, so the size cannot be increased. MnO as an accessory component
Including ₂ and Cr ₂ O ₃ improves the heat resistance and aging without deteriorating the piezoelectric characteristics, and improves the Qmt.
This is to avoid sudden changes in the temperature and stabilize it. M
If nO ₂ and Cr ₂ O ₃ are not added, heat resistance and aging cannot be improved, and if MnO ₂ or Cr ₂ O ₃ exceeds 5 wt%, heat resistance and sinterability are deteriorated and strength is increased. become weak. Especially when MnO ₂ exceeds 5 wt%, Qm
If t becomes too large at 2000 or more and the group delay characteristic is deteriorated, and if MnO ₂ is not added or is out of the range, Q
The mt becomes too small as 700 or less, the separation performance deteriorates, and it becomes unsuitable as a filter. Moreover, the ratio of the added amounts of MnO ₂ and Cr ₂ O ₃ is defined by a function of x, and the x
Is 0 <x <1 because when Cr ₂ O ₃ is not added,
A composition having a rapidly changing Qmt is formed. Further, if x exceeds 1, MnO ₂ will not be added, and the piezoelectric characteristics will deteriorate and the separation performance when used as a filter will deteriorate. Therefore, 0 <x <1 is set.

[0007]

The piezoelectric porcelain composition according to the present invention replaces a part of Pb with La as described above and, at the same time, M as an auxiliary component.
n and Cr are 0 to 5w in the total amount of MnO ₂ and Cr ₂ O _3.
Since t% is added, the mechanical quality factor Qmt is stable without abrupt change due to the interaction between Pb and La and the sub-components MnO ₂ and Cr ₂ O _3.
0 <Qmt <2000 and decreases with the amount of Cr ₂ O ₃ added.

[0008]

EXAMPLES The present invention will now be described in more detail with reference to examples.
As starting materials, PbO, TiO ₂ , La ₂ O ₃ , Cr
₂ O ₃ and MnO ₂ are used, and these powders are mixed with Pb.
Pb _0.85 La _0.1 T, with y = 0.1 of _{1-3y / 2} La _{y
iO 3 +1.5 ((1-x} ) MnO 2 + (x / 2) Cr
₂ O ₃ ) and weighed so as to change x. This raw material powder is wet pulverized, mixed and dried, then about 800
It was calcined at ℃ for 2 hours. Next, 2.5 wt% of vinyl acetate binder is added to and mixed with the calcined powder, and the molding pressure is 1 to
Press molding was carried out at a pressure of n / cm ² to obtain a rectangular plate-shaped molded body having a size of 10 mm × 10 mm × thickness of 1.0 mm. This molded body 12
Firing was performed at 00 to 1250 ° C. for 2 to 4 hours. After wrapping the molded body thus obtained in a thickness of 0.5 mm, silver is vapor-deposited on both sides, and the thickness is 2 to 2 in insulating oil at 80 to 150 ° C.
A polarization process was performed by applying an electric field of 5 KV / mm for 10 to 60 minutes. As shown in FIG. 1, on this molded body, counter electrodes 2 and 3 were formed on the front and back surfaces by etching, and lead electrodes 4 and 5 connected to the counter electrodes, respectively.

By applying a voltage to this electrode, as shown in FIG. 1, the energy trapping vibration of the thickness triple wave is measured, the value of Qmt of the composition is obtained by changing x, and the result is shown in FIG. It was shown to. Moreover, the sinterability was observed by observation. According to the measurement and observation results, the sinterability is good and the Qmt is
Since the value of is gradually decreasing as x increases, it is possible to adjust to a stable desired Qmt value by changing x.

[0010]

According to the piezoelectric porcelain composition of the present invention, a filter having good sinterability, high strength, stable mechanical quality factor, good decomposition performance, and good group delay characteristics can be obtained. be able to.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an electrode formed on a molded body obtained from the piezoelectric porcelain composition according to the present invention.

FIG. 2 shows the relationship x between the addition amounts of Mn and Cr in the above-mentioned embodiment,
It is a figure which shows the relationship with the value of the obtained mechanical quality coefficient.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukio Sakabe 226-10 Tenjin Tenjin, Nagaokakyo, Kyoto Prefecture Murata Manufacturing Co., Ltd.

Claims (1)

[Claims] 1. A lead titanate system obtained by substituting a part of Pb of PbTiO ₃ with La is added with Mn and Cr, and has a general formula of P
_{b 1-3y / 2 La y TiO 3} + z · {(1-x) MnO 2 +
(X / 2) .Cr ₂ O ₃ } (where 0
<X <1,0 <z ≦ 5 wt%), which is a piezoelectric ceramic composition.