JPH04357164A - Production of piezoelectric porcelain - Google Patents

Abstract

PURPOSE:To provide a method for production of a piezoelectric porcelain, capable of readily producing a PbLaTiO3-based piezo-electric porcelain sufficiently avoidable e.g. spurious generation in the vicinity of triplen vibration and scattering of P/V value at ordinary pressure. CONSTITUTION:A molding containing Pb, Ti and La respectively in an amount of 43-48mol%, 47-50mol% and 2-15mol% on oxide base based on the whole quantity is sintered at 1150-1250 deg.C and ordinary pressure of >=80% oxygen partial pressure.

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 piezoelectric ceramics used in high frequency resonators and the like, and more particularly to a method for manufacturing piezoelectric ceramics useful for third harmonic vibration.

0002

[Prior Art] Conventionally, PbT has been used as a piezoelectric ceramic composition.
Starting with iO3, Pb(Ni1/3 Nb2/
3) Products in which O3, etc. are dissolved in solid solution, and products in which a third component is added to these systems are known. Used for parts.

Incidentally, in recent years, there has been a demand for miniaturization of electronic components as described above, but when piezoelectric ceramic elements are applied to electronic components, miniaturization is difficult due to the nature of piezoelectric ceramics. There is a limit. Therefore, attempts have been made to further reduce the size and improve the performance of high frequency electronic components by applying third harmonic vibration.

[0004] As described above, PbLaTiO3 type piezoelectric ceramics to which triple harmonic vibration can be applied are mainly used, and various additives are being investigated in order to improve each characteristic.

[0005] Such PbLaTiO3 piezoelectric ceramics have conventionally been obtained by molding a mixed powder mainly composed of Pb, La2 O3, and TiO2 and then firing it in the atmosphere at a temperature of 1200 to 1350°C.

[0006]

[Problems to be Solved by the Invention] However, although PbLaTiO3-based piezoelectric ceramics can be easily manufactured using such conventional manufacturing methods, even if sintering has progressed sufficiently, the theoretical density ratio is 95. %, further densification is not possible, and there is a problem in that it is not possible to sufficiently eliminate the occurrence of spurious waves near the third harmonic vibration, P/V variations, etc.

[0007] On the other hand, as a result of numerous studies, the inventors of the present invention have developed a piezoelectric ceramic that sufficiently eliminates the occurrence of spurious waves near the 3rd harmonic vibration, P/V variations, ripples within the 3rd harmonic vibration, etc. developed and applied for it first (patent application Hei 1-192)
No. 062).

[0008] This contains Pb in a proportion of 43 to 48 mol% in terms of oxide, Ti in a proportion of 47 to 50 mol% in terms of oxide, and La in a proportion of 2 to 15 mol% in terms of oxide, and has a theoretical density. Since it is a dense piezoelectric ceramic with a ratio of 96% or more, it can sufficiently eliminate the occurrence of spurious waves near the third harmonic vibration and variations in P/V. However, in order to increase the density of the sintered body, In addition, it is necessary to perform hot isostatic sintering at high pressures of 200 to 1,500 atmospheres, the so-called HIP process, which poses handling difficulties when using high-pressure gas, and requires extensive equipment and large buildings. etc. are required, and P
There was a problem in that it was difficult to manufacture bLaTiO3-based piezoelectric ceramics.

[0009]

[Means for Solving the Problems] The present inventors have conducted intensive research on various factors in order to easily obtain piezoelectric ceramics that can sufficiently eliminate spurious generation and P/V variations. However, as shown in Figure 1,
There is a correlation between P/V value and oxygen concentration, and the higher the oxygen concentration, the higher the P
/V value also becomes high, and as shown in Figure 2,
It was discovered that there is a correlation between oxygen concentration and porosity, which is the cause of spurious emissions.

That is, in the present invention, Pb is contained in an amount of 43 to 48 mol % in terms of oxide, and Ti is contained in an amount of 47 to 48 mol % in terms of oxide, based on the total amount.
A piezoelectric ceramic characterized in that a molded body containing 50 mol% and La in a ratio of 2 to 15 mol% in terms of oxide is fired at a firing temperature of 1150 to 1250°C under normal pressure with an oxygen partial pressure of 80% or more. It is in the manufacturing method.

The present invention will be explained in more detail below.

The feature of the present invention is that Pb in terms of oxide
In order to increase the density of the sintered body whose basic components are 43 to 48 mol% of Ti, 47 to 50 mol% of Ti, and 2 to 15 mol% of La, the firing temperature is 1150 mol% under normal pressure with an oxygen partial pressure of 80% or more. The point is that it is fired at ~1250°C. Here, in order to increase the density of the sintered body or from the point of view of the properties as a piezoelectric ceramic, 44 to 46 mol% of Pb and T were added in terms of oxide.
It is most desirable that i be 49 to 51 mol% and La be 4 to 10 mol%. Further, in order to achieve densification, it is desirable to use a powder synthesized by liquid phase synthesis with excellent sinterability, such as a coprecipitation method, an alkoxide method, or a sol-gel method, as a raw material.

In the present invention, the basic components are specified within the above-mentioned ranges because when Pb is less than 42 mol% in terms of oxide, the mechanical quality factor decreases, and when it exceeds 48 mol%, polarization becomes difficult. Even if it is less than 47 mol% in terms of oxide, polarization becomes difficult. In addition, Ti is 50% in terms of oxide.
When the amount exceeds mol%, the Curie point decreases and P/V
value decreases.

Furthermore, when the amount of La in terms of oxide is less than 2 mol %, the temperature coefficient of the frequency of the third harmonic vibration increases, and when it exceeds 15 mol %, the Curie point decreases and P/V decreases. .

[0015] Then, P formulated within the above-mentioned composition range
A mixed powder of bO, La2 O3, and TiO2 or a calcined product thereof or a powder obtained by the liquid phase synthesis method described above is molded into a predetermined shape and then heated at 1150 to 100% in an atmosphere with an oxygen partial pressure of 80 to 100% under normal pressure. Fire at 1250°C.

Although high densification can be achieved by this oxygen atmosphere firing method, sufficient effects can be obtained in such piezoelectric ceramics even without complete densification, and the theoretical density ratio is 96% or more, especially 97% or more. It should be around 99%. Oxygen partial pressure 80
% or more under normal pressure, the oxygen partial pressure is 80% or more.
%, it is difficult to obtain dense porcelain, and P/
This is because V decreases.

[0017] The reason for firing at a firing temperature of 1150 to 1250°C is that if the firing temperature is lower than 1150°C, sintering will not progress sufficiently and porcelain with a porosity of less than 4% will not be obtained. This is because if the temperature is higher than 1250°C, an oversintered state will occur, which will cause the generation of coarse voids and melting of the porcelain.

Furthermore, with respect to the basic composition of PbLaTiO3 in the above range, some of Pb, La, and Ti may be replaced with other metals,
For example, La may be replaced with Pr, Ce, Sm or Nd, and other additive components, specifically MnO2
0.1 to 2.0 mol%, or Sr, Ca, Ba
Alkaline earth metal oxides such as Al, Fe, Co, Ni
By adding oxides such as , Si, Mg, Cr, Nb, and W in a proportion of 2.0 mol % or less, piezoelectric ceramics with even better characteristics can be obtained.

[0019]

[Operation] Therefore, according to the present invention, a molded body having the above composition is fired at a firing temperature of 11% in an atmosphere with an oxygen partial pressure of 80% or more.
By firing at normal pressure at 50 to 1250°C, the sintered body becomes denser, and characteristics, especially spurious emissions and P/V variations, can be prevented, and mass productivity and low cost are improved. Excellent piezoelectric ceramics can be obtained in this manner.

The present invention will now be explained with reference to the following examples.

[0021]

[Example] As raw materials, PbO, TiO2, La2
O3, MnCO3, SrCO3, BaCO3,
Various metal oxides other than CaCO3 were weighed as shown in Tables 1 and 2, and wet mixed in a pot mill. After mixing,
It was dehydrated and dried and calcined at 850 to 1100°C for 2 hours. Next, the calcined powder was crushed, mixed with an organic binder, and granulated. Approximately 1000 kg of the granulated powder thus obtained
It was molded into a disc with a diameter of 18 mm and a thickness of 1.5 mm under a pressure of /cm3. This molded disk was fired under normal pressure while changing the oxygen partial pressure and firing temperature.

Next, the obtained porcelain was used for measurement at a distance of 0.5 m.
After polishing to a diameter of m, electrodes were formed by silver vapor deposition and polarization treatment was performed at 80 to 100° C. and a voltage of 7.0 to 5.0 kv/mm for 10 minutes. For each of the 20 samples obtained, the theoretical density ratio was calculated using the Archimedes method, and the electromechanical coupling coefficient (kt3) of the thickness longitudinal third harmonic vibration was calculated using an impedance analyzer.
Similarly, the mechanical quality coefficient (Qm3) was measured and the average value was calculated.

Furthermore, the occurrence of spurious signals was determined from waveform observation. In addition, the non-defective product rate was finally calculated from the evaluation of each characteristic.

The results are shown in Tables 3 and 4. In addition, in the table, P/
V represents RA/R0 (resonance and anti-resonance impedance ratio of third harmonic wave), and sample No. 1, 2, 3, 8, 1
1, 14, 15, 16, 17, 18, 19, and 20 show comparative examples.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

[Table 4]

According to these tables, samples outside the scope of the present invention, that is, when the composition, firing temperature, and oxygen partial pressure are outside the scope of the present invention, all exhibit spurious vibrations near the third harmonic vibration.
Although variations in P/V and ripples within the third harmonic vibration occurred, samples within the scope of the present invention did not have the above-mentioned problems and exhibited excellent characteristics.

[0030]

[Effects of the Invention] As detailed above, according to the present invention,
Based on the total amount, Pb is 43 to 48 mol% in terms of oxide, T
A molded body containing i in a proportion of 47 to 50 mol% in terms of oxide and La in a proportion of 2 to 15 mol% in terms of oxide is fired at a temperature of 1150 to 12% under normal pressure with an oxygen partial pressure of 80% or more.
Since it was fired at 50°C, by increasing the theoretical density ratio of PbLaTiO3-based piezoelectric ceramics, it is possible to eliminate large voids in the ceramics and at the same time prevent disturbances in the vibrations of the piezoelectric ceramics and disturbances in the electric field between the electrodes. A piezoelectric ceramic having excellent properties and a high yield can be easily manufactured under normal pressure.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between oxygen amount and P/V.

FIG. 2 is a graph showing the relationship between oxygen content and porosity.

Claims (1)

[Claims] Claim 1: Based on the total amount, Pb is 43 to 4 in terms of oxide.
8 mol%, Ti 47 to 50 mol% in terms of oxide, and L
A molded body containing a in a proportion of 2 to 15 mol% in terms of oxide was fired at a temperature of 1 at normal pressure with an oxygen partial pressure of 80% or more.
A method for producing piezoelectric ceramics, which comprises firing at a temperature of 150 to 1250°C.