JPH0672047B2 - Pyroelectric porcelain composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pyroelectric porcelain composition.

(Prior Art) A pyroelectric material is used as a pyroelectric infrared sensor because it absorbs infrared radiant energy to cause a temperature change, which causes a change in spontaneous polarization. Examples of electrical materials include LiTaO ₃ , LiNbO ₃ , glycine sulfate (TGS), SrxBa _1-x Nb ₂ O ₆ (SBN), lead titanate porcelain, lead zirconate titanate porcelain, lead germanate porcelain, etc. It has been known.

Usually, pyroelectric infrared sensors using these materials,
Since the impedance of the pyroelectric element itself, which has electrodes formed on the pyroelectric body, is too high to be practical, a field-effect transistor that converts the impedance to an appropriate impedance for output is generally used. . The quality of the infrared sensor is determined by the material evaluation index (F _v ) for the output voltage sensitivity and the material evaluation index (F _D , hereinafter, S / N ratio evaluation index) for the specific detection rate (D) including noise. These evaluation indices are as follows: pyroelectric coefficient of pyroelectric material is λ, specific heat is Cp, density is d, relative permittivity is ε _r , and dielectric loss tangent is t.
Let an δ be given by the following equations.

Therefore, the larger the values of F _v and F _D are, the better the sensor is. Therefore, as the pyroelectric material, from the expressions (1) and (2), the change of spontaneous polarization with respect to the temperature change of the pyroelectric material is shown. That is, it is required that the pyroelectric coefficient (λ) of the pyroelectric body is large, the relative dielectric constant is small, and the dielectric loss tangent is small. However, the smaller the relative permittivity, the more susceptible the sensor is to the stray capacitance of the external circuit and the greater the noise of the sensor, so the relative permittivity is required to be large to some extent, and it is practically 200-600. Is desired.

From the viewpoint of the temperature qualitativeness of the sensor, it is desirable that the pyroelectric body has a temperature at which its pyroelectricity disappears, that is, a Curie temperature of at least 150 ° C or higher.

However, among the known pyroelectric materials, glycine sulfate and SBN have a small relative dielectric constant of 30 to 50, which is preferable in terms of material evaluation index, but when the electrode area of the pyroelectric element is small, the element capacitance is Smaller than the stray capacitance of the external circuit,
There is a drawback that the noise of the sensor becomes large, and LiTaO ₃ , LiNbO ₃ and lead germanate based porcelain have the drawback that the relative dielectric constant is about 60 or less and the noise becomes large like glycine sulfate and SBN. The former two are relatively expensive, and the latter one has a drawback that the temperature stability of the performance of the pyroelectric element is poor because the Curie temperature is low. Further, the lead titanate-based porcelain has a high Curie temperature of 470 ° C., but has a small relative permittivity of 200 or less and has a drawback that it is difficult to sinter. Therefore, at present, lead zirconate titanate-based porcelain is widely used.

(Problems to be Solved by the Invention) However, lead zirconate titanate porcelain, for example,
Pb (Sn _1/2 Sb _1/2 ) O ₃ -PbTiO ₃ -PbZrO ₃
Those containing MnO ₂ , CoO, Cr ₂ O ₃ etc. added as sub-components show relatively good pyroelectric performance in practical use, but the Curie temperature is as low as 200 ° C or less and the bending strength is small. Therefore, there is a problem that cracks and chips are likely to occur when forming electrodes or during polarization.

Therefore, an object of the present invention is to obtain a pyroelectric porcelain composition which is dense and has a large mechanical strength, a high pyroelectric evaluation index, and a relatively high Curie temperature.

(Means for Solving the Problem) The present invention provides, as a means for solving the above problems, a compound represented by the general formula: (Pb _1-x Ca _x ) [(Cu _1/2 W _1/2 ) _y Ti _1-y ] O ₃ (where x and y are the molar fractions of Ca and (Cu _1/2 W _1/2 )) 0.25 ≦ x ≦ 0.32, 0.02 ≦
y ≦ 0.04. The present invention provides a pyroelectric porcelain composition comprising a compound having a composition represented by the formula (4) as a main component and containing Mn in an amount of 0.3 to 2.5 atom% as a subcomponent.

(Function) The reason why the pyroelectric porcelain composition according to the present invention is limited to the range of the component composition will be described together with the function of those components.

If x in the above general formula is less than 0.25, polarization is difficult and the relative permittivity is less than 200, and the noise of the sensor becomes large, and if x exceeds 0.32, the relative permittivity becomes too large and the pyroelectric evaluation index. Since x becomes small and it becomes difficult to sinter at 1100 ° C or lower, x was set to 0.25 to 0.32.

If y is less than 0.02 or exceeds 0.04, it becomes difficult to sinter at low temperature, so the above range is set.

Mn has the effect of suppressing noise when the sensor is made by reducing the dielectric loss (tan δ), but its content is 0.3
If it is less than atomic%, a sufficient effect cannot be obtained, and if it exceeds 2.5 atomic%, the effect disappears, so the content was made 0.3 to 2.5 atomic%.

Examples of the present invention will be described below.

(Example) using a _{Pb 3 O 4, CaCO 3,} CuO, WO 3, TiO 2 and MnO ₂ as raw materials were weighed so as to satisfy the composition respectively shown in Table 1,
Wet mix each mixed material for about 16 hours, then dry and mix.
It was calcined at ℃ for 3 hours. This calcined product was pulverized, wet-mixed with an organic binder of 2 to 5% by weight for 10 to 20 hours, granulated, dried, and sized using a 60-mesh sieve.
The obtained powder at a pressure of 750 to 1000 kg / cm ² , a diameter of 12 mm,
Molded on a 1.3 mm thick disk with a uniaxial press molding machine, and 105-1
A porcelain disc was obtained by firing at 100 ° C. for 2 hours.

Baking Ag electrodes on both sides of the porcelain disk, temperature 150 ℃,
A sample was obtained by polarization for 30 minutes at an applied voltage of 4.0 kv / mm.

Relative permittivity (ε _r ), dielectric loss tangent (tan δ),
Pyroelectric coefficient (λ), volume specific heat (Cv), Curie temperature, flexural strength were measured, and material evaluation index (F _v ) for output voltage sensitivity
I asked. The results are shown in Table 1 together with the sintering temperature. In Table 1, samples marked with * have compositions outside the scope of the present invention.

(Comparative Example) Table 2 shows the characteristics of samples made of pyroelectric materials having the respective compositions shown in Table 2.

As is clear from the results in Tables 1 and 2, the pyroelectric porcelain composition according to the present invention has a reasonably high relative dielectric constant of 200 to 600 and a high evaluation index (F _v ). Also, the Curie temperature
It has a bending strength of 200 ° C or more and reaches about 1600 kg / cm ² , and it can be sintered at a temperature about 150 to 200 ° C lower than that of the conventional lead zirconate titanate porcelain composition.

For example, comparing sample 1 of Table 1 which is a pyroelectric porcelain composition according to the present invention with sample 4 of the conventional lead zirconate titanate porcelain composition shown in Table 2 of the present invention, The thing with the evaluation index improved about 16% compared with the latter. Also,
The sample according to the present invention has a high bending strength of 1400-1600 kg / cm ² , while the bending strength of sample 4 in Table ^{2 is} 630 kg / cm ²
It is about 2.3 times better than. Further, the sintering temperature of each of the porcelain compositions according to the present invention was 1100 ° C. or lower, whereas the sintering temperature of Comparative Sample 4 was 1250 ° C.

(Effect) As is apparent from the above description, according to the present invention, a highly sensitive pyroelectric element having a high pyroelectric coefficient and a Curie point of 200 ° C. or higher and high temperature stability can be obtained. Further, when the pyroelectric porcelain composition of the present invention is applied to a pyroelectric infrared center, since the relative dielectric constant is 200 to 600 and moderate, even if the electrode area is reduced, it is not affected by external stray capacitance, It is possible to obtain a pyroelectric element with low noise, high sensitivity, and good responsiveness. In addition, since it is dense and has high mechanical strength, the yield can be improved, and other excellent effects can be obtained.

Claims (1)

[Claims] 1. A general formula: (Pb _1-x Ca _x ) [(Cu _1/2 W _1/2 ) _y Ti _1-y ] O ₃ (where x and y are Ca and (Cu _1/2 W _1/2 ) mole fraction 0.25 ≦ x ≦ 0.32, 0.02 ≦
y ≦ 0.04. ) A pyroelectric porcelain composition comprising as a main component a compound having a composition represented by the formula (1) and containing 0.3 to 2.5 atom% of Mn as a subcomponent.