KR102515781B1 - Electret - Google Patents

Abstract

The electret 1 includes a composite oxide having an ABO ₃ type perovskite structure including two different metal elements (A and B). The composite oxide is in a polarized state, at least a part of one of the metal elements (A and B) is substituted with a dopant element having a lower valence than the one of the metal elements (A and B), and Oxides have band gap energies greater than 4 eV.

Description

electret {ELECTRET}

The present disclosure relates to electrets.

As an energy harvesting technology that converts energy existing in the environment into electric power, practical use of a vibrating power generation element using an electret or the like is being considered. As a constituent material of the electret, for example, an organic polymer material such as fluororesin is generally used. Organic polymer materials have advantages such as freedom of shape in thin film formation and excellent controllability of film thickness, but because they are organic materials, there are concerns about thermal stability of surface potential and performance degradation over time in a high temperature environment.

On the other hand, forming an electret using an inorganic compound material having excellent stability at high temperatures has been studied. For example, JP 6465377 B2 proposes an electret material using a sintered body having a crystal structure of hexagonal hydroxyapatite and having a lower hydroxide ion content than that of hydroxyapatite having a stoichiometric composition. This sintered body is obtained by sintering and dehydrating a molding made of hydroxyapatite powder at a high temperature of more than 1250°C and less than 1500°C, and it is thought that a high surface potential is developed after polarization treatment due to hydroxide ion defects.

In the electret material of 6465377 B2, when hydroxyapatite is dehydrated at high temperature, a part of hydroxyapatite becomes oxyhydroxyapatite and crystal defects occur. In that case, although it is possible to adjust the amount of dehydration to some extent depending on processing conditions and the like, it is difficult to accurately control the amount of dehydration. It was also difficult to quantitatively evaluate the amount of defects in the device geometry. Therefore, it is difficult to control the amount of defects generated in the apatite structure, and it is not always easy to obtain an electret having a desired surface potential.

In view of the above problems, an object of the present disclosure is to provide an electret that has excellent thermal stability, is capable of controlling the amount of crystal defects, and has stable characteristics in a use environment.

An electret according to aspects of the present disclosure comprises a composite oxide having an ABO ₃ type perovskite structure comprising two different metal elements (A and B), the composite oxide being in a polarized state, and At least a part of one of the metal elements (A and B) is substituted with a dopant element having a lower valence than the one of the metal elements (A and B), and the composite oxide has a bandgap energy of 4 eV or more. ) has

The electret having the above configuration uses an ABO ₃ type composite oxide, and oxygen defects are introduced by substituting a part of at least one of the metal elements with a dopant element having a low valence. Therefore, by controlling the amount of replacement by the dopant element, it is possible to control the amount of defects presumed to contribute to the expression of surface potential. In addition, the composite oxide, which is an inorganic dielectric material, is thermally stable and has a high band gap energy of 4 eV or more, so that the dielectric breakdown voltage during the polarization process can be increased. Therefore, a high surface potential can be obtained by applying a high voltage under heating conditions, and the electret has stable characteristics in a high-temperature environment and long-term use.

As described above, according to the above aspect, it is possible to provide an electret that has excellent thermal stability, can control the amount of crystal defects, and has stable characteristics in a use environment.

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawing:
1 is a schematic diagram for explaining a schematic configuration of an electret and a polarization method in a first embodiment;
2 is a schematic diagram for explaining a specific example of an electret polarization method according to an embodiment;
Fig. 3 is a diagram showing the relationship between the amount of Ca replacement and the surface potential in Examples;
Fig. 4 is a diagram showing the relationship between the amount of Ca replacement and the surface potential in the examples.

(First Embodiment)

The electret according to the first embodiment will also be described with reference to FIG. 1 . As shown in FIG. 1 , the electret 1 of this embodiment includes a composite oxide having an ABO ₃ type perovskite structure including two different metal elements (A and B), and the composite oxide is in a polarized state. In the composite oxide, at least one of the metal elements (A and B) is partially substituted with a dopant element having a lower valence than that of the metal elements (A and B), and the bandgap energy is 4 eV or more. Preferably, a sintered body in which complex oxides are formed in a predetermined shape is used.

The electret 1 is a charging material that retains positive or negative charges on its surface and provides an electrostatic field to its surroundings. A polarization treatment described later is performed on the composite oxide as an inorganic dielectric material to develop a surface potential. The electret 1 is used, for example, as an integrated circuit-embedded power generation element in various devices that convert mechanical energy and electrical energy to each other, for example, a small-sized electrostatic vibration generator that uses environmental vibration as a power source.

The composite oxide constituting the electret 1 has a perovskite type crystal structure represented by the composition formula (ABO ₃ ) as a basic structure, and typically has a cubic unit cell. The metal element (A) is located at each vertex of the cubic crystal, the metal element (B) is located at the central position of the cubic crystal, and the oxygen atom (O) is coordinated to each of the metal elements (A and B) in a regular octahedron.

The dopant element is substituted for both the metal element (A) or the metal element (B) or the metal elements (A and B) in the composition formula (ABO ₃ ). The combination of the metal elements (A and B) is not particularly limited as long as it is a composite oxide having a bandgap energy of 4 eV or more, and the dopant element is a metal element having a valence lower than that of the metal element (A or B) to be substituted as long as it is a metal element. do. By substituting with a dopant element of a lower valence, crystal defects due to oxygen vacancies are generated in the perovskite structure in order to maintain electrical neutrality, which contributes to the improvement of the surface potential.

At this time, since there is a correlation between the amount of replacement by the dopant element and the amount of defects, it is possible to control the amount of defects affecting the surface potential by controlling the amount of introduction of the dopant element. In addition, since the dielectric breakdown voltage of the composite oxide is increased by using an inorganic dielectric material having a relatively large bandgap energy of 4 eV or more, the electret 1 can develop a desired high potential by applying a high voltage during the polarization process. It is more preferable to use an inorganic dielectric material having a bandgap energy of 4.5 eV or more, more preferably 5.5 eV or more.

In the perovskite structure, the combination of the metal element (A) occupying the A site and the metal element (B) occupying the B site is not particularly limited as long as the combination satisfies the composition formula (ABO ₃ ). In that case, for example, in addition to the combination of the trivalent metal element (A) and the trivalent metal element (B), a combination of monovalent and pentavalent and a combination of divalent and tetravalent may be used.

As a specific example, in the ABO ₃ type perovskite structure, the A site can be occupied by a rare earth element (R) (metal element A) selected from La, Y, Pr, Sm and Nd, and the B site can be occupied by Al (metal element B) can occupy. Rare earth aluminate in which these components are combined has a large bandgap energy of 4 eV or more and a relatively small relative permittivity (for example, 100 or less), so a high surface potential can be realized. In addition, rare earth aluminates can be produced using relatively inexpensive materials, which is advantageous in terms of manufacturing cost.

In this case, the dopant element to be substituted for the metal elements A and B may be a metal element having a lower valence than the trivalent metal elements A and B. For example, when the metal element (A) is a trivalent rare earth element (R), a divalent alkaline earth metal element (including Mg) is preferably used, and Ca or Sr can be suitably used. When the metal element (B) is trivalent Al, at least one element selected from divalent alkaline earth metal elements (including Mg) and Zn, such as Zn or Mg, is preferably used.

Specifically, lanthanum aluminate (LaAlO ₃ ) is exemplified as a representative rare earth aluminate, and a structure in which La is partially substituted with an alkaline earth metal element (eg, Ca) can be used. In that case, it can be represented by the composition formula ((La, Ca)AlO _3-δ ), where δ represents the amount of oxygen defects. The amount of oxygen defects varies depending on the amount of replacement by the dopant element, the atmosphere, and the like. When the substitution rate by the dopant element is x (atomic %), if the oxygen defect is due to substitution, the composition formula is La _(1-x) Ca _x AlO _3-x/2 .

The substitution ratio of the dopant element substituting the metal element (A) can be appropriately set within a range of, for example, 20 atomic % or less. Similarly, the substitution rate of the dopant element substituting the metal element (B) is preferably in the range of, for example, 20 atomic %. When the substitution ratio exceeds 0, an effect of improving the surface potential can be obtained compared to the case where no dopant element is introduced. Preferably, when the substitution ratio is 0.05 atomic % or more, the surface potential is greatly improved. However, when the substitution ratio increases, the effect of introducing the dopant element tends to decrease. Although the reason for this is not entirely clear, it is speculated that the increase in relative permittivity acts to lower the surface potential. Therefore, it is preferable to set the substitution ratio appropriately so that desired properties can be obtained within a range where the substitution ratio does not exceed 20 atomic %. The substitution ratio is preferably in the range of 0.05 atomic % to 18.8 atomic %, more preferably in the range of 0.05 atomic % to 2.5 atomic %.

The electret 1 can be obtained, for example, by subjecting a complex oxide having such a perovskite structure to polarization treatment to make it into a sintered body having a predetermined shape (hereinafter referred to as a complex oxide sintered body). The composite oxide sintered body to be the electret 1 may have an arbitrary external shape (for example, a rectangular flat plate shape or a disk shape). Here, the vertical direction in the drawing is referred to as the thickness direction (X) of the electret 1, and the surface in the thickness direction (X) is hereinafter described as an upper surface or a lower surface.

The polarization treatment method is not particularly limited, but, for example, as shown in FIG. 1 , electrodes 21 and 22 are formed on the upper surface 11 and the lower surface 12 of the electret 1, respectively; Apply voltage. Regarding the polarization treatment conditions, it is preferable to apply a direct current voltage so that the electric field intensity becomes 4 kV/mm or more at 100°C or higher, for example. In order to realize efficient power generation for devices such as vibration power generation, a surface potential of 400 V or more is required, and a desired surface potential can be realized by polarization treatment with an electric field strength of 4 kV/mm or more. In addition, by performing the polarization treatment at a temperature higher than room temperature, stable electret performance can be realized even in applications where the usage environment is high temperature.

[Example]

(Example 1)

The electret 1 having the configuration shown in FIG. 1 was manufactured by the following method. As the inorganic dielectric material constituting the electret 1, an LAO-based composite oxide having a composition in which a part of La of lanthanum aluminate (LaAlO ₃ ) having a perovskite structure is substituted with a dopant element was used. In Example 1, a composite oxide sinter obtained by using Ca as a dopant element and preparing a raw material to have a composition of (La _0.9995 , Ca _0.0005 )AlO _3-δ was subjected to polarization treatment to become the electret 1.

Lanthanum aluminate (LaAlO ₃ ), a typical composition of LAO-based inorganic dielectric materials, has a band gap energy of 5.6 eV, and a composition in which a portion of Al is substituted with Ca as a dopant element has almost the same band gap energy.

<Manufacture of powder>

First, as a raw material for the LAO-based composite oxide sintered body, the following nitrate reagent was prepared and weighed so that the Ca substitution amount was 0.05 atomic%. 20 ml of ultrapure water was added to the beaker containing each reagent to obtain a solution in which each reagent was dissolved.

6.03 g of La(NO ₃ ) ₃ 6H ₂ O manufactured by FUJIFILM Wako Pure Chemical Corporation

5.25 g of Al(NO ₃ ) ₃ 9H ₂ O manufactured by FUJIFILM Wako Pure Chemical Corporation

1.65 mg of Ca(NO ₃ ) ₂ 4H ₂ O manufactured by FUJIFILM Wako Pure Chemical Corporation

The obtained solution of each reagent was transferred to a plastic beaker and stirred and mixed using a stirrer. Stirring was performed by placing a stirrer in a plastic beaker and rotating the stirrer at 500 rpm. To the beaker containing this mixed solution, an aqueous NaOH solution having a molar concentration of 12 M was added little by little using a dropper while measuring with a pH meter to adjust the pH to 10.5. Thereafter, the precipitate was recovered by filtration under reduced pressure and washed with about 100 ml of ethanol and ultrapure water. The following reagents were used for NaOH and ethanol for NaOH aqueous solution.

· NaOH special grade (granular) manufactured by Kanto Chemical Co., Inc.

Ethanol (99.5) manufactured by Kanto Chemical Co., Inc.

Then, the filter paper on which the washed sample was placed was placed in a dryer at 120° C., and dried for 12 hours or longer. The dried samples were placed in an agate mortar and pulverized, and also classified (<100 μm).

<Production of molded body/sintered body>

The powder obtained by classification was placed in an alumina boat and calcined. As a calcination condition, the temperature was raised to 1000 °C at a temperature ramping rate of 2.5 °C/min, held at 1000 °C for 6 hours, and then lowered to room temperature at a temperature lowering rate of 2.5 °C/min.

The calcined sample was placed in an agate mortar, pulverized, and further classified (<100 μm) to obtain molded powder. About 0.65 g of the molding powder was put into a pellet forming unit having a diameter of φ13 mm, and pressed at a pressure of 250 MPa for 3 minutes to form disk-shaped pellets.

The obtained molded pellets were fired at a temperature higher than the sintering temperature to obtain sintered pellets made of an LAO-based composite oxide sintered body. As a sintering condition, the temperature was raised to 1650°C at a temperature rising rate of 2.5°C/min, maintained at 1650°C for 2 hours, and lowered to room temperature at a temperature decreasing rate of 2.5°C/min. The diameter of the obtained sintered pellets was about Φ11 mm. The thickness was adjusted to 1 mm by polishing.

Further, the obtained LAO-based composite oxide sintered body was subjected to elemental analysis using ICP radiation spectroscopy, and it was confirmed whether a sintered body having a desired composition ((La _0.9995 , Ca _0.0005 )AlO _3-δ ) could be obtained. Specifically, a solution obtained by dissolving the sintered body ground in a mortar in a solvent was used as an analysis sample, and constituent elements of the sintered body were determined from emission lines generated by ICP (Induction Coupled Plasma). As a result, as shown below, almost the same analysis result (0.051 atomic %) was obtained with respect to 0.05 atomic %, which is the substitution ratio of Ca (input Ca substitution amount) at the time of raw material production.

(Input Ca replacement amount 0.05 atomic%)

ICP analysis result 0.051 atomic %

The analysis of the LAO-based complex oxide sintered body is not limited to ICP radiation spectroscopy, and any method such as XPS (X-ray photoelectron spectroscopy) method and XRF (X-ray fluorescence analysis) method can be employed. By introducing the dopant element in this way, the amount of substitution can be easily controlled, and quantitative evaluation can be easily performed.

<Polarization treatment>

The sintered pellets obtained as described above were subjected to polarization treatment using the polarization treatment apparatus shown in FIG. 2 . In FIG. 2, in the sintered pellet 10, a pair of gold electrodes 21 and 22 were printed in advance on the upper and lower surfaces 11 and 12 in the thickness direction X (gold electrodes on the lower surface 12). (22) is not shown). The sintered pellet 10 was sandwiched between two alumina rods 3 around which a platinum wire 31 was wound so that a voltage could be applied between the pair of gold electrodes 21 and 22 . The two alumina rods 3 were longer than the diameter of the sintered pellets 10, and at both ends in the longitudinal direction (direction perpendicular to the thickness direction X), yarns 4 made of fluorine resin (polytetrafluoroethylene) ) was fixed by tying them together. Next, this was wound around a device for polarization, and the whole was coated with silicone oil 5 to prevent dielectric breakdown in air.

This polarizing device was placed in a box furnace and left standing until the temperature inside the furnace stabilized at 200°C. Next, polarization was performed by applying a DC electric field of 8.0 kV/mm between the pair of gold electrodes 21 of the sintered pellet 10 in a state stabilized at 200°C. After a predetermined period of time had elapsed, the sintered pellets 10 were allowed to cool until the temperature reached 40° C. or lower while the direct current electric field was continuously applied.

<Production of the electret>

After the polarization treatment, the gold electrodes 21 and 22 on both surfaces of the sintered pellet 10 were removed using a polishing sheet. Subsequently, the sintered pellets (10) were ultrasonically cleaned using ethanol and pure water for 10 minutes each, and left in a dryer at 100°C for 3 hours or more to obtain an electret (1).

<Surface potential measurement>

The surface potential of the electret 1 (Example 1) obtained as described above was measured. For the measurement, a surface potential was measured without contact using a surface potential meter (MODEL341-B: manufactured by Trek Japan Co., Ltd.), and the value after 5400 seconds had elapsed was read. The results are shown in Table 1.

Example/Comparative Example Ca replacement amount (atomic %) surface potential (V) Example 1 0.05 438 Comparative Example 1 - 20 Comparative Example 2 - 4

(Comparative Examples 1 and 2)

For comparison, as a LaAlO ₃ sintered body in which La is not substituted, a commercially available LaAlO ₃ (100) single crystal substrate (manufactured by Crystal Base Co., Ltd.) was used, in the same manner as in Example 1. Polarization treatment was performed to obtain the electret of Comparative Example 1. In addition, a sintered body of barium titanate (BaTiO ₃ ), which is a complex oxide having a perovskite structure and a band gap energy of 3.5 eV, was prepared, and a polarization treatment was performed in the same manner as in Example 1 to obtain the electret of Comparative Example 2. got it

Here, in the BaTiO ₃ sintered body of Comparative Example 2, the following reagents were used as raw materials for molding.

Barium titanate nanopowder (purity 99%, manufactured by FUJIFILM Wako Pure Chemical Corporation)

This raw material for molding was put into a pellet forming unit having a diameter of 13 mm in the same manner as in Example 1, and pressed at a pressure of 250 MPa for 3 minutes, and the resulting molded pellets were sintered to obtain sintered pellets. The sintering conditions were a temperature increase rate and a temperature decrease rate of 2.5°C/min, and sintering was performed at 1255°C for 0.5 hour.

The surface potential of the electrets of Comparative Examples 1 and 2 was measured in the same manner as in Example 1, and the results are also shown in Table 1. As is clear from Table 1, in Example 1 in which a part of La in LaAlO ₃ was replaced with Ca, the surface potential was 438 V, and a high surface potential of 400 V or more was obtained by applying a DC potential of 8.0 kV/mm. On the other hand, in Comparative Example 1 made of a single crystal of LaAlO ₃ and not substituted with a dopant element, the surface potential was significantly lowered to 20V. Further, in Comparative Example 2 using BaTiO ₃ having a band gap energy of less than 4 eV, the surface potential was further lowered to 4 V.

(Examples 2 to 5)

In the composition of La _(1-x) Ca _x AlO _3-δ , in the same manner as in Example 1, the substitution ratio (x) of La by the dopant element (Ca) was changed, and 1 atomic% to 20 atomic% ( A raw material was prepared to have a composition within a range of input Ca replacement amount), and an electret 1 made of a LAO-based composite oxide sintered body was manufactured.

Example 2 1 atomic %

Example 3 5 atomic %

Example 4 10 atomic %

Example 5 20 atomic %

Molding pellets were prepared using a raw material prepared so that the substitution ratio (x) of La by the dopant element (Ca) was in the range of 1 atomic % to 20 atomic %, and polarization treatment was applied to the sintered pellets obtained by sintering the molding pellets. This was done to obtain an electret (1). As shown in Examples 2 to 5 in Table 2, the obtained LAO-based composite oxide sintered body was subjected to elemental analysis using ICP radiation spectroscopy, and the composition was confirmed. As a result, the actual substitution ratio was in the range of 0.16 atomic% to 0.93 atomic%, which is 1/5 or less of the Ca substitution ratio (input Ca substitution amount) at the time of raw material production.

The surface potential of the obtained electret (1) of Examples 2 to 5 was measured in the same manner as in Example 1, and the results are also shown in Table 2. The reason why the electrets 1 of Examples 2 to 5 were not sufficiently combined with Ca when the raw material was prepared by the same manufacturing method (liquid phase method) as in Example 1 is not completely clear, but the relationship between the input Ca substitution amount and the actual substitution amount By knowing the relationship in advance, the electret 1 having a desired substitution ratio can be obtained.

Example Ca replacement amount (atomic %) surface potential (V) Example 2 0.16 3688 Example 3 0.3 2155 Example 4 0.5 1400 Example 5 0.93 3433

As is clear from Table 2, in Examples 2 to 5, the surface potential is higher than that in Example 1, and the surface potential is 1400 V (Example 4) to 3688 V (Example 2), which is higher than 1000 V. is obtained This is presumed to be because, for LaAlO ₃ having a perovskite structure, substitution with a lower valence dopant element causes oxygen vacancies depending on the amount of substitution, which contributes to the development of a high surface potential. Fig. 3 shows the relationship between the amount of Ca substitution and the surface potential based on Comparative Example 1 and Examples 1 to 5, and a high surface potential develops when the amount of Ca substitution is 0.05 atomic% or more. When the Ca substitution amount is increased to 0.16 atomic % or more, the surface potential also increases greatly.

(Examples 6 to 12)

As an inorganic dielectric material constituting the electret 1, a YAO-based composite oxide having a composition in which a part of Y of yttrium aluminate (YALO ₃ ) is substituted with a dopant element was used. The dopant element was Ca, and in the composition of Y _(1-x) Ca _x AlO _3-δ , the substitution ratio (x) of Y by Ca was changed to prepare the electret 1 made of the YAO-based composite oxide sintered body. It became. At this time, the raw material was prepared to have a composition in the range of 1 atomic % to 20 atomic % (input Ca substitution amount).

Example 6 0.05 atomic %

Example 7 1 atomic %

Example 8 2.5 atomic %

Example 9 3.5 atomic %

Example 10 5 atomic %

Example 11 10 atomic %

Example 12 20 atomic %

Yttrium aluminate (YALO ₃ ), a representative composition of YAO-based inorganic dielectric materials, has a band gap energy of 7.9 eV, and a composition in which a portion of Y is substituted with Ca as a dopant element has almost the same band gap energy.

<Manufacture of powder>

First, as raw materials for the YAO-based composite oxide sintered body, the following oxide and carbonate reagents were prepared and weighed so that the Ca substitution amount was 1 atomic % to 20 atomic %.

8.211 g to 10.161 g of Y ₂ O ₃ manufactured by FUJIFILM Wako Pure Chemical Corporation

4.635 g of Al ₂ O ₃ manufactured by FUJIFILM Wako Pure Chemical Corporation

0.091 g to 1.820 g of CaCO ₃ manufactured by FUJIFILM Wako Pure Chemical Corporation

The weighed reagent was put into an agate mortar, mixed, and further classified (< 100 μm).

<Production of molded body/sintered body>

The powder obtained by classification was placed in an alumina crucible and calcined. As a calcination condition, the temperature was raised to 1100°C at a temperature rising rate of 2.5°C/min and maintained at 1100°C for 10 hours. Further, the temperature was raised to 1350°C at a temperature rising rate of 2.5°C/min, maintained at 1350°C for 10 hours, and then lowered to room temperature at a temperature decreasing rate of 2.5°C/min.

The calcined sample was placed in an agate mortar, pulverized, and further classified (<100 μm) to obtain molded powder. About 0.5 g of the molding powder was put into a pellet forming unit having a diameter of ?10 mm and pressed at a pressure of 20 MPa for 5 minutes to form disk-shaped pellets.

The obtained molded pellets were sintered at a temperature higher than the sintering temperature to obtain sintered pellets made of a YAO-based composite oxide sintered body. As a sintering condition, the temperature was raised to 1600°C at a temperature rising rate of 2.5°C/min, maintained at 1600°C for 2 hours, and then lowered to room temperature at a temperature decreasing rate of 2.5°C/min. The diameter of the obtained sintered pellets was about φ9.5 mm. The thickness was adjusted to 1 mm by polishing.

In addition, as shown in Table 3, elemental analysis was performed on the obtained YAO-based composite oxide sintered body using energy dispersive X-ray analysis (hereinafter appropriately referred to as EDX), and a sintered body having a substantially desired composition was obtained. Confirmed. Specifically, powder obtained by crushing the sintered body in a mortar was used as an analysis sample, and constituent elements of the sintered body were determined from the spectrum of characteristic X-rays generated by electron beam irradiation. As a result, with respect to Examples 6 to 12, almost the same analysis results were obtained with respect to the Ca replacement ratio (input Ca replacement amount) at the time of raw material production.

The analysis of the YAO complex oxide sintered body is not limited to energy dispersive X-ray analysis, and any method such as ICP radiation spectroscopy, XPS (X-ray photoelectron spectroscopy), and XRF (X-ray fluorescence analysis) is employed. can do. By introducing the dopant element in this way, the amount of substitution can be easily controlled, and quantitative evaluation can be easily performed. Note that an error of about ±1% may occur in the composition result by energy dispersive X-ray analysis.

<Polarization treatment>

A polarization treatment was performed on the sintered pellets thus obtained to obtain an electret (1). Corona discharge was used for the polarization treatment, one side of the disk-shaped pellet was grounded, and a corona discharge electrode was disposed facing the other side, and a negative voltage was applied to generate corona discharge. The corona discharge conditions were as follows. Even when the temperature dropped, corona discharge continued until the temperature reached room temperature.

Discharge voltage: -5.5 kV

Temperature: 200℃

· Processing time: 1 minute

As a result, the sintered body containing Y, Ca, Al, and O was polarized, the surface facing the corona discharge electrode was negatively charged, and the electret 1 was formed. At this time, a high surface potential corresponding to the conditions of the polarization treatment can be obtained, and by performing the polarization treatment at a temperature higher than room temperature (eg, 200° C.), fluctuations in the surface potential can be easily made even in applications where the use environment is a high temperature. suppressed, and stable electret performance can be realized. The temperature and other conditions of the polarization treatment can be appropriately changed depending on the characteristics required in the assumed use environment.

<Surface potential measurement>

The surface potential of the electret 1 (Examples 6 to 9) obtained as described above was measured. For the measurement, a surface potential was measured without contact using a surface electrometer (MODEL341-B: manufactured by Trek Japan Co., Ltd.), and the value immediately after polarization was read. The results are shown in Table 3.

Example Ca replacement amount (atomic %) surface potential (V) Example 6 0.05 -908 Example 7 One -1155 Example 8 2.5 -931 Example 9 3.5 -160 Example 10 4.8 -306 Example 11 9.7 -279 Example 12 18.8 -331

As is clear from Table 3, the surface potentials in Examples 6 to 12 in which a part of Y of YAlO ₃ was replaced with Ca were -160 V to -1155 V, and high surface potentials were obtained. In particular, in Examples 6 to 8, high surface potentials of about 1000 V were obtained. In addition, a YAO-based composite oxide sintered body in which a portion of Al of YAlO ₃ is substituted with Zn and a Zn substitution amount of 1 atomic % was used, and the surface potential was measured for the electret 1 prepared and polarized in the same manner as above. . As a result, a value (-1230 V) equivalent to the surface potential in the case of Ca substitution was obtained, and it was found that the surface potential did not depend on the type of dopant. From these results, the substitution ratio of the dopant element to the metal elements (A and B) occupying the A site or B site of the perovskite structure is preferably in the range of 0.05 atomic % to 18.8 atomic %, and further It is preferably in the range of 0.05 atomic % to 2.5 atomic %. In addition, by knowing in advance the relationship between the substitution ratio (input substitution amount) of the dopant element at the time of raw material production and the actual substitution amount, the electret 1 having desired composition and characteristics can be produced.

In this way, it is possible to form the electret 1 having excellent thermal stability, control of the amount of crystal defects, and stable characteristics in a use environment.

The present disclosure is not limited to the above embodiments, but various modifications may be applied within the scope of the present disclosure without departing from the spirit of the disclosure.

Claims (7)

An electret (1) comprising a composite oxide having an ABO ₃ type perovskite structure including two different metal elements (A and B),
The complex oxide is in a polarized state,
At least a part of one of the metal elements (A and B) is substituted with a dopant element having a lower valency than the one of the metal elements (A and B);
The composite oxide has a bandgap energy of 4 eV or more,
The metal element (A) occupying the A site of the perovskite structure is a rare earth element (R) selected from the group including La, Y, Pr, Sm and Nd,
The metal element (B) occupying the B site is Al,
The substitution ratio of the dopant element substituting the metal element (A) is 0.05 atomic% to 2.5 atomic%,
An electret wherein a substitution ratio of a dopant element substituting the metal element (B) is 0.05 atomic % to 2.5 atomic %. According to claim 1,
The dopant element substituting the metal element (A) is an alkaline earth metal element,
The electret, wherein the dopant element substituting the metal element (B) is at least one element selected from the group consisting of an alkaline earth metal element and Zn. According to claim 2,
An electret in which the alkaline earth metal element is Ca or Sr. delete delete delete delete

Images