JPH01230467A - Pyroelectric porcelain composition - Google Patents

Abstract

PURPOSE:To obtain a pyroelectric porcelain composition expressed by the specific formula, consisting of a complex oxide containing Pb, Bi, Sn, Sb, Ti and Zr as main components and having large pyroelectric coefficient, proper dielectric constant and material evaluation index to output voltage sensitivity. CONSTITUTION:The aimed pyroelectric porcelain composition containing a compound having composition expressed by the formula as a main component and 0.3-2.5atom.% of one or more kind of Mg, Cr and Mn as subsidiary components. The pyroelectric porcelain composition is basically a composition replacing a part of Pb in Sn.Sb-modified titanatate zirconate lead salt with Bi and provides pyroelectric body having 200-400 proper dielectric constant and excellent material evaluation index and suitable as impedance exchange type pyroelectric sensor by setting Bi replacing amount of pyroelectrics and/or of x, y and z of B site in the main component within the composition range.

Description

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

(Prior art) A pyroelectric substance causes a temperature change by absorbing infrared radiation energy emitted from a sensing object, and a change in spontaneous polarization occurs due to the temperature change. It is used as a material for infrared sensors that utilize this effect.

In this type of pyroelectric infrared sensor, the impedance of the pyroelectric element itself, which is formed by forming electrodes on a pyroelectric material, is too high to be practical. There is an impedance conversion type that converts the impedance into an appropriate impedance using a field effect transistor 2, and a current mote detection type that amplifies the generated current by directly inputting it to an operational amplifier 3 with a high input impedance, as shown in Figure 2. type has been developed.

In the case of the currently popular impedance conversion type, the material evaluation index (Fv) for output voltage sensitivity and the material evaluation index (FD,
Hereinafter, it will be referred to as an S/N ratio evaluation index. ) are given by the following equations, where λ is the pyroelectric coefficient, Cp is the specific heat, d is the density, ε7 is the relative permittivity, and tanδ is the dielectric loss tangent.

FV-λ/cp-c+・ε, ・・・・・・
・(1) FD-λ/Cp-d-F1-Kogo T Fu ・・
(2) Therefore, it can be said that the larger the values of FV and Fo, the better the pyroelectric material. Therefore, as a pyroelectric material, from equations (1) and (2), the change in spontaneous polarization with respect to temperature change of the pyroelectric material is large, that is, the pyroelectric coefficient (λ) of the pyroelectric material is large; It is also required that the dielectric constant be small and the dielectric loss tangent be small. However, the specific MN ratio of the pyroelectric material is small (I see, it is easily affected by the stray capacitance of the pyroelectric element or external circuit, so the noise of the sensor increases, and the larger the relative permittivity, the smaller the figure of merit. Therefore, from the perspective of noise reduction and pyroelectric performance, the relative permittivity is appropriate within the range of 200 to 400. Also, from the perspective of noise reduction, the thickness of the pyroelectric element is made thinner to reduce the capacitance.
In order to make it as large as possible, a moderate amount of strength is required.

On the other hand, in the case of the current mote detection type, which has recently become practical due to the development of operational amplifiers with high input innovation, the generated charge is directly converted, so the detection sensitivity is dependent on the dielectric constant of the pyroelectric material. The pyroelectric current generated varies by ζ1 due to the temperature change of the pyroelectric body. Therefore, it depends only on the pyroelectric coefficient, so the evaluation method for impedance conversion type cannot be applied, and the pyroelectric coefficient is as large as possible. This is required.

In addition, in any of the above types, from the viewpoint of practical use, it is desirable that the pyroelectric material has a temperature at which its pyroelectricity disappears, that is, a Curie temperature of at least 150'C or higher.

Conventionally, pyroelectric materials include LiTaO3 and LiNbO.
3. Glycysulfate: / (TGS), 5rxBa, -x
Nb.

06 (SBN), lead germanate-based porcelain, lead titanate-based porcelain, lead zirconate titanate-based porcelain, and the like.

(Invention or problem to be solved) However, most of the known pyroelectric materials other than lead titanate-based porcelain and lead zirconate titanate-based porcelain have a small dielectric constant of 30 to 50. Although this is preferable from the point of view of the pyroelectric evaluation index, it has the drawback that if the electrode area of the pyroelectric element -4= is small, the element capacitance becomes smaller than the free capacitance of the external circuit, and the noise of the sensor increases. Also, LiTaO3 and LiNbO3
is relatively expensive, and because lead germanate-based porcelain has a low Curie temperature, it has the disadvantage that the temperature stability of the pyroelectric element performance is poor.

On the other hand, lead titanate-based porcelain exhibits a moderate dielectric constant of around 200, but its polarization temperature is high at around 200°C, making it difficult to choose the electrode material, and it is difficult to select an electrode material that is strong enough to be made thinner. Therefore, it was difficult to put it into practical use.

Therefore, at present, pure or modified lead zirconate titanate-based porcelain, such as P b (S n +ztSb
+z, )03-PbTiOa-PbZrO3 as a main component, with subcomponents M n O2, Coo, Cr2O
It is widely used, such as those containing 3.

This type of lead titanate/ruconate porcelain can be polarized under moderate conditions, is inexpensive, has good workability, and exhibits relatively good pyroelectric performance or impedance conversion type infrared porcelain. As a sensor material, better pyroelectric properties are required, and when applied as a material for a current mode detection type pyroelectric infrared sensor, it does not fully satisfy the pyroelectric coefficient. is the current situation.

Therefore, the present invention possesses the advantages of a three-component lead zirconate titanate-based pyroelectric element that is inexpensive and easy to process, has a large pyroelectric coefficient, has an appropriate relative dielectric constant, and has material evaluation for output voltage sensitivity. The object of the present invention is to obtain a pyroelectric ceramic composition that has an index (Fv) and an S/N ratio evaluation index and can be used as a pyroelectric material for infrared sensors of not only impedance conversion type but also current mode detection type.

(Means for Solving the Problems) The present invention provides, as a means for solving the above-mentioned problems, - Formula % Formula %) (However, α, β, x, y and 2 are the mole fractions of each component, and 001 ≦α≦0.09.0.25≦β≦0.75.0
．． O1≦X≦020.005≦y≦097.002≦2
≦0.94, x+y+z−1°00. ) is the main component, with Mg as a subcomponent.
, Cr, and Mn in an amount of 0.3 to 25 at. %.

(Function) The pyroelectric ceramic composition according to the present invention basically replaces a part of I) b in tin/antimony modified lead zirconate titanate with 31, and also contains Mg and Cr as subcomponents.
The reason why the composition range is limited will be explained below.

B1 has the effect of improving pyroelectric performance and lowering the sintering temperature; if α is less than 0.01, no improvement in pyroelectric performance can be obtained by Bi substitution; If it exceeds this range, Bi, O, etc. will precipitate and the sinterability will drop sharply, so it was set in the above range.

Further, the reason why β is set to 0.25 to 0.75 is because if β is out of this range, a dense sintered body cannot be obtained. X
If it is less than 0.001, sintering will be difficult, and if it exceeds 0.20, it will be difficult to sinter, and at the same time the Curie point will drop significantly, making it impractical. When y is less than 0.05, antiferroelectricity is exhibited and performance as a pyroelectric material cannot be obtained, and when y exceeds 097, sintering becomes difficult, so y was set in the above range. If Z is less than 002, the sinterability is poor, and if it exceeds 094, antiferroelectricity is exhibited and the performance as a pyroelectric material cannot be obtained, so the above range was set. The composition range of the main components is shown in FIG.

In addition to the main components of the composition, Mg, Cr and M are added as subcomponents.
Among these elements, Mg has the effect of suppressing grain growth, increases mechanical strength after sintering, and improves polishing. If it is less than 0.3 atom%, the effect will not be obtained, and if it exceeds 2.5 atom%, the effect will be lost and the dielectric loss will increase significantly. , the range was set to 03 to 25 at%.

Further, Cr has the effect of preventing loss of polarization even after repeated thermal aging, but if the content is outside the range of 0.3 to 25 at %, no significant effect will be observed, so the above range was set. Furthermore, Mn reduces dielectric loss and
If the content is outside the range of 0.3 to 2.5 atom %, the effect of addition is lost, so the above range is set. In addition, the Mg, Cr and M
When two or more types of n are added together, the total amount is 0 for the above reason.
It is necessary that it be between 3 and 25%.

(Example) As raw materials, Pb, 0. ,SnO2,Sb,03,T
iO2, ZrO2, B12O3, PbCrO4, MnO
7 and MgO were weighed so as to have the composition shown in Table 1, and each mixed raw material was wet mixed for about 16 hours, dried, and calcined at 900°C for 3 hours.

This calcined raw material was mixed with 2 to 5% by weight of organic hindrance to
After wet milling for ~20 hours, it was dried and sized through a 60 mesh sieve. The obtained powder is 750-10
00kg/cm2 pressure, diameter 12mm, thickness 1mm
It was molded into a disc and fired at 1100 to 1150°C for 2 hours to obtain pyroelectric porcelain.

After forming Ag electrodes on both sides of the porcelain disk by a vapor deposition method, it was immersed in insulating oil at 80°C. Qkv
A DC voltage of /mm was applied for 30 minutes to prepare a sample.

For each sample, the relative permittivity (εr), tanδ, pyroelectric coefficient (λ), volumetric specific heat (Cv), Curie temperature, and bending strength were measured, and the material evaluation index (Fv) for output voltage sensitivity and S /N ratio evaluation index (FD) was determined. The results are shown in Table 2. Note that in Tables 1 and 2, samples marked with * are outside the scope of the present invention.

Tables 1 and 2 (Comparative Examples) Tables 3 and 4 show the pyroelectric properties of samples made of pyroelectric materials having the respective compositions shown in Tables 3 and 4.

Table 3 Table 4 As is clear from the results shown in Tables 2 to 4, the pyroelectric porcelain composition according to the present invention has the following characteristics:
Alternatively, by appropriately setting the ratio of X, y, and z of the B site in the main component within the range of its composition, a dielectric constant of about 230 to 1490 and a pyroelectric coefficient of 6 x 10
-8C-cm/K, showing excellent evaluation indices (Fv and Fl).

For example, if we compare the properties of Sample 4 in Tables 1 and 2, which is made of the pyroelectric porcelain composition of the present invention, with the properties of Sample 1 in Table 4, which has the same ratio of x, y, and 2. It can be seen that the pyroelectric coefficient and evaluation index (FV, FD) of the pyroelectric ceramic composition of the present invention are improved by the B1 substitution.

Furthermore, the pyroelectric ceramic composition according to the present invention has a sintering temperature of 50
It was confirmed that the temperature was ~100°C lower.

(Effects) As explained above, according to the present invention, the Bi
The amount of substitution and/or x of the B site in the main component,
By appropriately setting the ratio of y and z within the composition range, an impedance conversion type pyroelectric wire sensor has a moderate dielectric constant of 200 to 400 and excellent material evaluation index (Fv, Fr1). On the other hand, it is possible to obtain a pyroelectric material suitable for use in current mote detection type infrared sensors with a large pyroelectric coefficient. Therefore, when the pyroelectric ceramic composition according to the present invention is applied to an impedance conversion type infrared rays 1-, it is possible to obtain a device with low noise and no drop in voltage sensitivity, and the detection sensitivity is reduced only by the pyroelectric coefficient. When applied to dependent current mode type infrared sensors, high sensitivity can be obtained. In addition, since the sintering temperature is 50 to 100°C lower than that of the conventional method, excellent effects such as improved productivity can be obtained.

[Brief explanation of the drawing]

Fig. 1 is an equivalent circuit diagram of an impedance conversion type pyroelectric infrared sensor, Fig. 2 is an equivalent circuit diagram of a current mote type pyroelectric infrared sensor, and Fig. 3 is a pyroelectric porcelain composition according to the present invention. It is a ternary diagram showing the composition range of the main components of an object. 1 - Pyroelectric element, 2 - Field effect transnoster, 3 - Operational amplifier, Rg, Rs, Rf - Resistor, Cf - Contents. Patent distributor Murata Manufacturing Co., Ltd.

Claims (1)

[Claims] (1) General formula: (Pb_1_−_αBi_α) [(Sn_1_−_βS
b_β)_xTi_yZr_z]O_3 (however, α, β
, x, y and z are the mole fractions of each component, 0.01≦α
≦0.09, 0.25≦β≦0.75, 0.01≦x≦
0.20, 0.05≦y≦0.97, 0.02≦z≦0
．． 94, x+y+z=1.00. ) is the main component, with Mg and C as subcomponents.
A pyroelectric ceramic composition containing 0.3 to 2.5 at.% of at least one element selected from the group consisting of r and Mn.