JPH01261876A - Pyroelectric porcelain composition - Google Patents

Abstract

PURPOSE:To obtain dense composition wherein mechanical strength is large, pyroelectricity evaluation index is large, and Curie temperature is comparatively high, by using compound with a specified composition as main component, and containing Mn as subcomponent. CONSTITUTION:Main component is compound shown by the following general expression; (Pb1-xCax) [(Ni1/3Nb2/3)yTi1-y]O3 (where 0.25<=x<=0.35, 0.01<=y<=0.06). Subcomponent is porcelain composition containing Mn of 0.3-2.5atom%. After Pb3O4, CaCO3, NiO, NbO3, TiO2 and MnO2, as original material, are weighted and wet-mixed, these are dried and calcinated. After the calcinated material is grinded, and granulated by mixing organic binder, they are dried, ordered, press-molded, baked, and a porcelain circular plate is obtained. The relative permittivity of the porcelain composition is adequately 200-360, and the S/N ratio estimation index (FD) is improved. Further the Curie temperature also is high, and the anti-deflection strength also is increased by a factor of 1.6.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to pyroelectric porcelain compositions.

(Prior art) Pyroelectric materials are used as pyroelectric infrared sensors because when they absorb infrared radiation energy and cause a temperature change, a charge is generated on the surface due to a change in spontaneous polarization. As electric material, LiTaos, LiNbO
5. Glycine sulfate (TGS), S rxBat-xNb
*o* (S B N), lead titanate-based porcelain, lead zirconate titanate-based porcelain, lead germanate-based porcelain, etc. are known.

Typically, pyroelectric infrared sensors using these materials are
Since the impedance of a pyroelectric element itself, which is made by forming electrodes on a pyroelectric material, is too high for practical use, it is generally put into practical use that uses a field effect transistor to convert the impedance to an appropriate impedance before outputting it. . The quality of this infrared sensor is determined by the material evaluation index (Fv) for output voltage sensitivity and the material evaluation index (F, hereinafter referred to as S/N ratio evaluation index) for specific detection rate (D) including noise. These evaluation indices are: λ for the pyroelectric coefficient, Cp for the specific heat, d1 for the density, and ε1 for the relative dielectric constant.
, and the dielectric loss tangent is given by the following equations.

Fv=λ/Cp-d・ε, ・・・・・・(1
)F0=λ/Cp-d-,/""T;ηITF'...
...(2) Therefore, as a sensor, Fv and F
Since the larger the value of o, the better the pyroelectric material, from equations (1) and (2), the change in spontaneous polarization with respect to temperature change of the pyroelectric material, that is, the pyroelectricity of the pyroelectric material coefficient(
λ) is required to be large, the relative dielectric constant is small, and the dielectric voltage junction is required to be small. However, the smaller the dielectric constant, the more susceptible the sensor is to the stray capacitance of external circuits (
As a result, the noise of the sensor becomes large, so that the dielectric constant is required to be relatively large, and is practically desired to be 200 or more.

Further, from the viewpoint of temperature stability of the sensor, it is desirable that the pyroelectric substance 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 dielectric constant of 30 to 50, so they are preferable from the viewpoint 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 (
LiTag, LiNbO5, and lead germanate-based porcelain have a relative dielectric constant of about 60 or less, making it difficult to use glycine sulfate or S.
In addition to the disadvantage of increased noise like BN,
The former two are relatively expensive, and the latter has a low Curie temperature, so the temperature stability of the pyroelectric element performance is poor. Furthermore, lead titanate-based porcelain has a Curie temperature of 4
Although it is as high as 70°C, it has the disadvantage that it has a small dielectric constant of 200 or less and is difficult to sinter. For this reason, lead zirconate titanate-based porcelain is now widely used.

(Problem to be solved by the invention) However, lead zirconate titanate-based porcelain, for example,
Pb (Sn+ztSblzt)03-PbT 10,
-PbZrO, as a main component, and MnO as a subcomponent.
,,Coo, Cr, O, etc. are added.
Although it shows relatively good pyroelectric performance in practical use, its Curie temperature is low at 200°C or less, and its bending strength is low, so it tends to crack or chip when forming electrodes or polarizing. was there.

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

(Means for Solving the Problems) The present invention provides a general formula: % formula %) y≦hook06 as a means for solving the above-mentioned problems. ) is the main component, and Mn is 0.3 to 2.5 at% as a subcomponent.
The object of the present invention is to provide a pyroelectric ceramic composition characterized by containing:

(Function) The reason why the pyroelectric ceramic composition according to the present invention is limited to the range of the above-mentioned component composition will be explained together with the function of those components.

X in the general formula, that is, (p b+ -xc a
x) If the mole fraction of Ca at the site is less than 0.25, polarization will be difficult and the relative permittivity will be less than 200, resulting in large sensor noise; if X exceeds 0.35, the relative permittivity will be exceeds 400 and the pyroelectric evaluation index decreases,
Moreover, since the Curie temperature drops below 190°C and the usable temperature range narrows, X is 0.25 to 0.35.
And so.

Also, y1, that is, [(NLz3Nbtzs)yT I
+-y] When the molar fraction of (NLzsNbtz3) at the site is less than 0°01, tanδ increases rapidly and S/
If the N ratio evaluation index deteriorates and exceeds 0.06, the sinterability deteriorates and the tan δ increases, so it was set in the above range.

Mn has the effect of suppressing dielectric loss (tanδ), but
If the content is less than 0.3 at%, a sufficient effect cannot be obtained, and if it exceeds 2.5 at%, the effect disappears, so it is set at 0.3 to 2.5 at%.

Examples of the present invention will be described below.

(Example) Raw materials: pb, o, , Ca COs, Nip, Nb
O3, Tie, and MnO, respectively, the first
Weigh out the composition shown in the table, and add approximately 16% of each mixed raw material.
After wet mixing for an hour, it was dried and calcined at 850°C for 3 hours. This calcined product was pulverized and granulated by wet mixing with 2 to 5% by weight of an organic binder for 10 to 20 hours, then dried and sized using a 60 mesh sieve. The obtained powder was dry-pressed into a disc with a diameter of 12 mm and a thickness of 1.3 mm at a pressure of 750 to 1000 kg/cm'', and was fired at 1100 to 1200°C for 2 hours to obtain a porcelain disc. .

Ag electrodes were baked on both sides of the porcelain disk at a temperature of 150°C.
'C1 applied voltage 4. The sample was subjected to polarization treatment at Okv/mm for 30 minutes.

For each sample, relative dielectric constant (εr), dielectric voltage junction (tanδ
), pyroelectric coefficient (λ), volumetric specific heat (Cv), Curie temperature, and bending strength were measured, and the material evaluation index (FV) and S/N ratio evaluation index (F, ) for output voltage sensitivity were determined. . The results are shown in Table 1. In Table 1, samples marked with * have compositions outside the scope of the present invention.

(Comparative example) Table 2 shows the properties of conventionally known pyroelectric materials having the following compositions.

As is clear from the results in Tables 1 and 2, the pyroelectric ceramic composition according to the present invention has a moderate dielectric constant of 200 to 360, which is higher than that of the conventional PZT system. The S/N ratio evaluation index (F,) is improved by 10 to 30% compared to the previous model. Also,
The Curie temperature is as high as about 200°C or more, and the bending strength is about 1.6 times higher than that of conventional PZT-based materials.

(Effects) As is clear from the above description, according to the present invention, a highly sensitive pyroelectric element having a high pyroelectric coefficient, a Curie point of 200° C. or higher, and good temperature stability can be obtained. Furthermore, when the pyroelectric ceramic composition of the present invention is applied to a pyroelectric infrared sensor, it has a moderate dielectric constant of 200 to 360, so it is not affected by external stray capacitance even if the electrode area is reduced. A pyroelectric element with low noise, high sensitivity, and good response can be obtained. Further, since it is dense and has high mechanical strength, excellent effects such as improved yield can be obtained.

Patent applicant: Murata Manufacturing Co., Ltd. Representative patent attorney: Haka Aoyama, 1 person

Claims (1)

[Claims] (1) General formula: (Pb_1_−_xCa_x) [(Ni_1_/_3N
b_2_/_3)_yTi_1_-_y]O_3 (However, x and y are 0.25≦x≦0.35, 0.01≦y≦0
．． It is 06. ) A pyroelectric porcelain composition characterized in that it contains a compound having the composition shown in the following formula as a main component and 0.3 to 2.5 at % of Mn as a subcomponent.