JPH0714836B2 - Pyroelectric porcelain composition - Google Patents

Description

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

(Prior Art) A pyroelectric body causes a temperature change by absorbing infrared radiant energy emitted from an object to be detected, and the spontaneous polarization changes due to the temperature change. It is used as a material for infrared sensors that utilize the effect.

In this type of pyroelectric infrared sensor, the impedance of the pyroelectric element itself having electrodes formed on the pyroelectric body is too high to be practical. Therefore, as shown in FIG. Impedance conversion type in which impedance is converted into an appropriate impedance by the field effect transistor 2 and current mode detection type in which generated current is directly input to the operational amplifier 3 having high input impedance to be amplified as shown in FIG. Is being developed.

In the case of the impedance conversion type which is currently popular, a material evaluation index (F _V ) for output voltage sensitivity and a material evaluation index (F _D , for a specific detection rate (D) including noise,
Hereinafter referred to as S / N ratio evaluation index. ) Is its pyroelectric coefficient λ, specific heat Cp, density d, relative permittivity ε _r , dielectric loss tangent
Let tan δ be given by the following equations.

F _V = λ / Cp · d · ε _r (1) Therefore, it can be said that the larger the values of F _V and F _D , the better the pyroelectric material. Therefore, as the pyroelectric material, (1)
From Equations (2) and (2), the change in spontaneous polarization with respect to the temperature change of the pyroelectric material is large, that is, the pyroelectric coefficient (λ) of the pyroelectric material is large, the relative dielectric constant is small, and the dielectric loss tangent is small. Is required. However, as the relative permittivity of the pyroelectric body becomes smaller, the pyroelectric element becomes more susceptible to the stray capacitance of the external circuit, which increases the noise of the sensor, and if the relative permittivity is too large, the figure of merit decreases. , From the viewpoint of noise reduction and pyroelectric performance, the relative permittivity is 200-400
The range is appropriate. In addition, from the viewpoint of noise reduction, in order to reduce the wall thickness of the pyroelectric element and maximize the electrostatic capacitance, appropriate strength is required.

On the other hand, in the case of the current mode detection type, which has recently become practical due to the development of an operational amplifier with high input impedance, since the generated charges are directly converted, its detection sensitivity does not depend on the relative permittivity of the pyroelectric body, Since it depends only on the pyroelectric current generated with respect to the temperature change of the pyroelectric body, and therefore only on the pyroelectric coefficient, the evaluation method for the impedance conversion type cannot be applied, and it is required to have a pyroelectric coefficient as large as possible.

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

Conventionally, pyroelectric materials have been LiTaO ₃ , LiNbO ₃ , glycine sulfate (TGS), SrxBa _1- xNb ₂ O ₆ (SBN), lead germanate porcelain, lead titanate porcelain and lead zirconate titanate porcelain. Porcelain and the like are known.

(Problems to be solved by the invention) However, most of the known pyroelectric materials other than the lead titanate-based porcelain and the lead zirconate titanate-based porcelain have a small dielectric constant of 30 to 50 and are pyroelectric. Although preferable from the viewpoint of evaluation index, when the electrode area of the pyroelectric element is small, there is a drawback that the element capacitance becomes smaller than the stray capacitance of the external circuit and the noise of the sensor increases. Also, LiTaO ₃ and
LiNbO ₃ is relatively expensive, and lead germanate-based porcelain has a low Curie temperature, so that it has a drawback that the performance of the pyroelectric element is inferior in temperature stability.

On the other hand, lead titanate-based porcelain shows a moderate relative dielectric constant of around 200, but its polarization temperature is high at around 200 ° C, making it difficult to select electrode materials. Therefore, it was difficult to put it into practical use.

Therefore, at present, an intrinsic or modified lead zirconate titanate porcelain, for example, Pb (Sn _1/2 Sb _1/2 ) O ₃ -PbTiO _3-
Main component consisting of PbZrO _{3 with} MnO ₂ , CoO, Cr ₂ as secondary components
Those containing O ₃ are widely used. This type of lead zirconate titanate porcelain can be polarized under appropriate conditions, is inexpensive and has good workability, and exhibits relatively good pyroelectric performance. As a material, more excellent pyroelectric characteristics are demanded, and when applied as a material for a current mode detection type pyroelectric infrared sensor, the pyroelectric coefficient is not sufficient at present. is there.

Therefore, the present invention possesses the advantages that the three-component lead zirconate titanate-based pyroelectric element is inexpensive and has good workability, has a large pyroelectric coefficient, and is evaluated as a material for an appropriate relative dielectric constant and output voltage sensitivity. An object is to obtain a pyroelectric porcelain composition which has an index (F _V ) and an S / N ratio evaluation index and can be applied as a pyroelectric material for not only an impedance conversion type but also a current mode detection type infrared sensor. .

(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-α Bi _α ) [(Sn _1-β Sb _β ) _x Ti _y Zr _z ] O
₃ (where α, β, x, y and z are the mole fractions of the respective components, 0.01 ≦ α ≦ 0.09, 0.25 ≦ β ≦ 0.75, 0.01 ≦ x ≦ 0.2
0, 0.05 ≦ y ≦ 0.97, 0.02 ≦ z ≦ 0.94, x + y + z = 1.0
It is 0. ) Is contained as a main component, and at least one element selected from the group consisting of Mg, Cr, and Mn is contained in the main component in an amount of 0.3 to 2.5 atom%.

(Operation) The pyroelectric porcelain composition according to the present invention basically comprises a part of Pb in tin / antimony-modified lead zirconate titanate.
Along with substituting Bi, at least one element selected from the group consisting of Mg, Cr and Mn as a sub-component, respectively.
The content of 3 to 2.5 atomic% is added, and the reason for limiting the composition range will be described.

Bi has the effect of lowering the sintering temperature as well as improving the pyroelectric performance. When α is less than 0.01, the pyroelectric performance cannot be improved by Bi substitution, and when α exceeds 0.09, Bi ₂ O ₃ Is precipitated and the sinterability is drastically reduced, so the above range was set.

Further, β is set to 0.25 to 0.75 because if β is out of this range, a dense sintered body cannot be obtained. When x is less than 0.01, it becomes difficult to sinter, and when it exceeds 0.20, it becomes difficult to sinter, and at the same time, the Curie point is remarkably lowered and it becomes unpractical. When y is less than 0.05,
It exhibits antiferroelectricity, and the performance as a pyroelectric material cannot be obtained.
When y exceeds 0.97, it becomes difficult to sinter, so y was set to the above range. When z is less than 0.02, the sinterability is poor, and when it exceeds 0.94, antiferroelectricity is exhibited and the performance as a pyroelectric material cannot be obtained. The composition range of the main component is shown in FIG.

In the main component of the composition, at least one element selected from the group consisting of Mg, Cr and Mn as an accessory component is contained in the form of an oxide, but among these elements, Mg has the effect of suppressing grain growth. However, if it is less than 0.3 atom%, the effect cannot be obtained, and if it exceeds 2.5 atom%, the effect is lost and the dielectric loss is reduced. The range is set to 0.3 to 2.5 atom% because it causes the problem of becoming significantly large. Further, Cr has an effect of preventing polarization from being lost even if heat aging is repeated, but when the content thereof is out of the range of 0.3 to 2.5 atom%, a remarkable effect cannot be recognized, so the above range is made. Further, Mn has the effect of reducing the dielectric loss and increasing the S / N ratio evaluation index, but if the content thereof is outside the range of 0.3 to 2.5 at%, the addition effect is lost, so the above range was made. When two or more kinds of Mg, Cr and Mn are added together, the amount of each element needs to be 0.3 to 2.5 atom% for the above reason. When three elements are added together, as shown in the examples, Mg is 1.0 to 2.5 atomic% and Cr is
It is preferable to add 0.5 to 0.95 atomic% and 0.5 to 1.2 atomic% of Mn.

(Example) as raw _{materials, Pb 3 O 4, SnO 2} , Sb 2 O 3, TiO 2, ZrO 2, Bi 2 O
₃ , PbCrO ₄ , MnO ₂ and MgO were weighed so as to have the composition shown in Table 1, each mixed raw material was wet mixed for about 16 hours, dried, and calcined at 900 ° C. for 3 hours. The calcined raw material was wet pulverized with an organic binder of 2 to 5% by weight for 10 to 20 hours, dried, and sized through a 60-mesh sieve. The obtained powder was molded into a disk having a diameter of 12 mm and a thickness of 1 mm at a pressure of 750 to 1000 kg / cm ² and fired at 1100-1150 ° C. for 2 hours to obtain a pyroelectric porcelain.

After forming Ag electrodes on both surfaces of the porcelain disk by vapor deposition, the electrodes were immersed in insulating oil at 80 ° C. and a DC voltage of 3.0 to 4.0 kv / mm was applied for 30 minutes to prepare a sample.

For each sample, the relative permittivity (ε _r ), tan δ, pyroelectric coefficient (λ), volume specific heat (C _V ), Curie temperature, and bending strength were measured, and the material evaluation index (F _V for output voltage sensitivity) was measured. ) And S / N ratio evaluation index (F _D ) were obtained, and the results are shown in Table 2. In addition, in Tables 1 and 2, the samples marked with * are outside the scope of the present invention.

(Comparative Example) Tables 3 and 4 show the pyroelectric characteristics of samples made of pyroelectric materials having the respective compositions shown in Tables 3 and 4.

As is clear from the results shown in Tables 2 to 4, in the pyroelectric porcelain composition according to the present invention, the substitution amount of Bi and / or the ratio of x, y, z of B site in the main component is set. By setting it appropriately within the range of its composition, the relative dielectric constant is about 230 to 1
At 490, the pyroelectric coefficient reaches 6 × 10 ⁻⁸ C · cm / K and shows an excellent evaluation index (F _V and F _D ).

For example, comparing the characteristics of Sample 4 of Tables 1 and 2 made of the pyroelectric porcelain composition of the present invention with the characteristics of Sample 1 of Table 4 having the same x, y, z ratio, It can be seen that the pyroelectric porcelain composition of the invention is improved in both pyroelectric coefficient and evaluation index (F _V , F _D ) by Bi substitution.

Further, the pyroelectric porcelain composition according to the present invention contains a part of Pb as Bi.
Sintering temperature is 50 ~ 100 compared to those not replaced by
It was confirmed that the temperature was low.

(Effect) As described above, according to the present invention, the substitution amount of Bi in the pyroelectric material and / or the x, y, z of the B site in the main component is
By appropriately setting the ratio in the composition range, the relative permittivity is 200 to 400, and it is suitable for the impedance conversion type pyroelectric wire sensor having an excellent material evaluation index (F _V , F _D ). While a pyroelectric body is obtained, a pyroelectric body having a large pyroelectric coefficient and suitable for a current mode detection type infrared sensor can be obtained. Therefore, when the pyroelectric porcelain composition according to the present invention is applied to an impedance conversion type infrared sensor, it is possible to obtain a low noise and voltage sensitivity which does not deteriorate, and a current mode type in which the detection sensitivity depends only on the pyroelectric coefficient. When applied to the infrared sensor of, high sensitivity can be obtained. Also, the sintering temperature is
Since the temperature is low by 50 to 100 ° C, excellent effects such as improvement in productivity can be obtained.

[Brief description of drawings]

1 is an equivalent circuit diagram of an impedance conversion type pyroelectric infrared sensor, FIG. 2 is an equivalent circuit diagram of a current mode type pyroelectric infrared sensor, and FIG. 3 is a pyroelectric porcelain composition according to the present invention. FIG. 3 is a ternary diagram showing the composition range of the main components of FIG. 1-pyroelectric element, 2-field effect transistor, 3-operational amplifier, Rg, Rs, Rf-resistor, Cf-capacitor.

Claims (2)

[Claims] 1. A general formula: (Pb _1-α Bi _α ) [(Sn _1-β Sb _β ) _x Ti _y Zr _z ] O ₃ (where α, β, x, y and z are moles of each component). 0.01 ≤ α ≤ 0.09, 0.25 ≤ β ≤ 0.75, 0.01 ≤ x ≤ 0.2
0, 0.05 ≦ y ≦ 0.97, 0.02 ≦ z ≦ 0.94, x + y + z = 1.0
It is 0. ) A pyroelectric porcelain containing a compound having a composition shown in (4) as a main component, and containing at least one element selected from the group consisting of Mg, Cr and Mn as an auxiliary component in an amount of 0.3 to 2.5 at%, respectively. Composition. 2. As an accessory component, Mg is 1.0 to 2.5 atomic%, and Cr is 0.1.
The pyroelectric porcelain composition according to claim 1, containing 5 to 0.95 atom% and Mn in an amount of 0.5 to 1.2 atom%.