JP7439954B2 - Electric calorific effect element - Google Patents

Description

The present disclosure relates to electrocaloric effect elements.

In recent years, new solid-state cooling elements and cooling systems that utilize the electrocaloric effect have been attracting attention as cooling elements, and research and development thereof has been actively conducted. Compared to existing cooling systems that use refrigerants, which are greenhouse gases, this system has the advantage of high efficiency and low power consumption because it does not require a refrigerant, and it also has the advantage of being quiet because it does not use a compressor. In order to obtain an excellent electrocaloric effect, it is necessary to be a ferroelectric material that exhibits a first-order phase transition in the desired temperature range and to which it is possible to apply a large electric field, and PbSc _0.5 Ta _0.5 O ₃ (hereinafter, ceramics containing Pb, Sc, and Ta are also referred to as "PST") is known as the most promising material. For example, Non-Patent Documents 1 to 3 report that PbSc _0.5 Ta _0.5 O ₃ exhibits a large electrocaloric effect.

Nature volume 575, pages468-472(2019) Ferroelectrics, 184, 239 (1996) J. Am. Ceram. Soc, 78 [71] 1947-52 (1995)

The above PST shows an electrocaloric effect, but in order to obtain a larger electrocaloric effect:
(1) It has a high withstand voltage and can apply a large electric field,
(2) Sc and Ta, which are cations at the B site of PST, are required to exhibit a high degree of order. That is, since the adiabatic temperature change ΔT, which is one of the performance indicators of the electrocaloric effect, depends on the strength of the applied electric field, it is not necessary to apply a sufficient electric field unless the ceramic itself or the element has a high withstand voltage. Therefore, large adiabatic temperature changes cannot be obtained. In addition, the electrocaloric effect is influenced by the degree of order of the B site of PST, and the higher the degree of order of the B site, the better the ferroelectric properties can be obtained, and the larger the electric caloric effect (adiabatic temperature change) can be obtained. can.

Furthermore, when the above-mentioned PST is used in a solid cooling element, it should exhibit a large electrical calorific value effect at a temperature appropriate for its use (e.g., refrigerator, freezer, etc.) (e.g., 4°C or less for a refrigerator, -18°C or less for a freezer). is required.

However, although the conventional PST exhibits a large electrocaloric effect at temperatures above 20° C., the electrocaloric effect decreases significantly at low temperatures, and there is a problem in its use as a solid cooling element at low temperatures.

Therefore, the present disclosure provides an electrocaloric effect element having a laminate in which electrode layers whose main component is Pt and PST ceramic layers are alternately laminated, wherein the PST ceramic layer has a high withstand voltage and degree of order, and can be used at low temperatures. An object of the present invention is to provide an electrocaloric effect element that exhibits a large electrocaloric effect.

As a result of intensive studies, the present inventors found that the ceramic layer has a perovskite structure and contains Na in addition to Pb, Sc, and Ta:
(Pb _1-x Na _x ) _m (Sc _0.5-x/2-y Ta _0.5+x/2+y ) O ₃
[In the formula,
x satisfies 0.01≦x≦0.08,
y satisfies -0.03≦y≦0.03,
m satisfies 0.97≦m≦1.03. ]
The present inventors have discovered that by using the ceramic represented by the above, it is possible to obtain an electrocaloric effect element that has a high withstand voltage and high degree of order in the PST ceramic layer and exhibits a large electrocaloric effect at low temperatures, and has completed the present invention. .

The present disclosure includes the following aspects.
[1] An electrocaloric effect element having a laminate in which an electrode layer whose main component is Pt and a ceramic layer are stacked, the ceramic layer having a perovskite structure and having the formula:
(Pb _1-x Na _x ) _m (Sc _0.5-x/2-y Ta _0.5+x/2+y ) O ₃
[In the formula,
x satisfies 0.01≦x≦0.08,
y satisfies -0.03≦y≦0.03,
m satisfies 0.97≦m≦1.03. ]
An electrocaloric effect element whose main component is ceramic represented by
[2] The electrocaloric effect element according to [1] above, wherein y is 0 and m is 1.
[3] The electrocaloric effect element according to [1] or [2] above, wherein the thickness of the ceramic layer in the laminate is 50 μm or less.
[4] The electrocaloric effect element according to any one of [1] to [3] above, wherein the thickness of the ceramic layer in the laminate is 10 μm or more and 50 μm or less.
[5] An electronic component comprising the electrocaloric effect element according to any one of [1] to [4] above.

According to the present invention, it is possible to provide an electrocaloric effect element in which the PST ceramic layer has a high withstand voltage and high degree of order, and exhibits a large electrocaloric effect at low temperatures.

FIG. 1 is a schematic cross-sectional view of an electrocaloric effect element according to one embodiment of the present disclosure. FIG. 2 is a diagram for explaining the measurement sequence of the electrocaloric effect. FIG. 3 is a diagram showing the measurement results of the electrocaloric effect of samples Nos. 1, 2, and 5 in the example.

Hereinafter, the electrocaloric effect element of the present disclosure will be described in detail with reference to the drawings. However, the shape, arrangement, etc. of the electrocaloric effect element and each component of this embodiment are not limited to the illustrated example.

The electrocaloric effect element of the present disclosure has a laminate in which Pt electrode layers and ceramic layers are alternately stacked.

As shown in FIG. 1, in an electrocaloric effect element 1 according to an embodiment of the present disclosure, Pt electrode layers 2a and 2b (hereinafter also collectively referred to as "Pt electrode layer 2") and a ceramic layer 4 are arranged alternately. It has a laminated body 6 and external electrodes 8a and 8b (hereinafter collectively referred to as "external electrodes 8") connected to the Pt electrode layer 2. The Pt electrode layers 2a and 2b are electrically connected to external electrodes 8a and 8b arranged on the end faces of the laminate 6, respectively. When a voltage is applied from the external electrodes 8a and 8b, an electric field is formed between the Pt electrode layers 2a and 2b. This electric field causes the ceramic layer 4 to generate heat due to the electrocaloric effect. Furthermore, when the voltage is removed, the electric field disappears, and as a result, the ceramic layer 4 absorbs heat due to the electrocaloric effect.

The Pt electrode layer 2 is a so-called internal electrode. In addition to the function of applying an electric field to the ceramic layer 4, the Pt electrode layer 2 may also have the function of transporting heat between the ceramic layer 4 and the outside.

The above-mentioned Pt electrode layer means an electrode layer whose main component is Pt. Here, the "main component" in the electrode layer means that the electrode layer consists of 80% by mass or more of Pt, for example, 95% by mass or more of the electrode layer, more preferably 98% by mass or more, and even more preferably means that 99% or more, even more preferably 99.5% by mass or more, particularly preferably 99.9% by mass or more is Pt. However, from the viewpoint of improving chemical durability and/or cost, the effect of the present invention is that the Pt electrode layer is an alloy or mixture of Pt and other elements (for example, Ag, Pd, Rh, Au, etc.). Good too. Similar effects can be obtained even if the Pt electrode layer is made of an alloy or a mixture of these. It may also contain other elements that may be mixed in as impurities, particularly unavoidable elements (eg, Fe, Al ₂ O ₃ , etc.). In this case as well, similar effects can be obtained.

The thickness of the Pt electrode layer 2 is preferably 0.2 μm or more and 10 μm or less, more preferably 1.0 μm or more and 5.0 μm or less, for example 2.0 μm or more and 5.0 μm or less, or 2.0 μm or more and 4.0 μm or less. obtain. By setting the thickness of the Pt electrode layer to 0.5 μm or more, the resistance of the Pt electrode layer can be reduced and the heat transport efficiency can be increased. Further, by setting the thickness of the Pt electrode layer to 10 μm or less, the thickness (and thus the volume) of the ceramic layer can be increased, and the amount of heat that can be handled by the electric calorie effect of the entire device can be increased. Furthermore, the element can be made smaller.

In one embodiment, the ceramic layer 4 is a layer whose main component is a ceramic containing Pb, Na, Sc, and Ta. The above ceramic has a perovskite structure and contains Pb, Na, Sc, and Ta, and when the content ratio of Na is "x", the content ratio of Pb is "1-x", and the content ratio of Sc is is "0.5-x/2-y", the content ratio of Ta is "0.5+x/2-y", the range of x is 0.01≦x≦0.08, and the range of y is The range is -0.03≦y≦0.03, and when the ratio of the sum of Pb and Na to the sum of Sc and Ta is “m”, the range of m is 0.97≦m≦1.03. It is. Note that all the above ratios are molar ratios. In the ceramic constituting the ceramic layer 4, by having a composition within the above range, high withstand voltage (for example, 15 MV/m or more), high order degree of B site (for example, 75% or more), and large An electrocaloric effect (for example, ΔTa of 1K or more) can be obtained. Furthermore, even when no annealing treatment is performed or when the annealing treatment time is shortened (for example, annealing treatment for 100 to 500 hours), it is possible to obtain a high degree of order, further improving productivity. . Furthermore, even if the thickness of the element is reduced, a high degree of order can be obtained, and the degree of freedom in element design is improved.

In another aspect, the ceramic layer 4 has a perovskite structure and has the formula:
(Pb _1-x Na _x ) _m (Sc _0.5-x/2-y Ta _0.5+x/2+y ) O ₃
[In the formula,
x satisfies 0.01≦x≦0.08,
y satisfies -0.03≦y≦0.03,
m satisfies 0.97≦m≦1.03. ]
The main component is ceramics represented by By setting x, y, and m within the above ranges, high withstand voltage (e.g., 15 MV/m or more), high degree of B site order (e.g., 75% or more), and large electrocaloric effect at low temperatures (e.g., , ΔTa) of 1K or more can be obtained.

Although the present disclosure is not bound by any theory, the mechanism by which the above effects are obtained is thought to be as follows.
Conventional techniques related to PST veneer samples include firing at a high temperature of 1500°C or higher (for example, Non-Patent Document 3), since PST is a difficult-to-sinter material, or using a hot press method that allows firing under pressure. However, in the case of a multilayer device like the one disclosed in the present disclosure, it is difficult to co-sinter Pt at temperatures above 1450°C, and the device structure will be destroyed, so it is difficult to co-sinter Pt under pressure. Firing is also difficult. Therefore, in the case of a multilayer element, sintering is performed at a slightly lower temperature than ideal. Furthermore, it is presumed that the Pt electrode layers sandwiching the ceramic layer impede the diffusion of oxygen, Pb, etc., thereby reducing the diffusion coefficient of cations constituting the B site, making it difficult to obtain a high degree of order. Furthermore, for the same reason, inherent defects tend to remain, and variations in withstand voltage tend to increase. In the ceramics used in the present disclosure, by substituting a part of Pb with Na and further setting the ratio of Pb, Na, Sc, and Ta within the composition range of the present disclosure, both the A site and the B site of the perovskite are appropriately depleted. It is surmised that homogenization was achieved and element diffusion was promoted, making it easier for the B site order to occur. In addition, it is thought that due to the promoted diffusion of elements, sintering progresses more easily than in conventional PST, and the withstand voltage also improves.

In a preferred embodiment, y is 0 and m is 1. That is, the formula represented by (Pb _1-x Na _x ) _m (Sc _0.5-x/2-y Ta _0.5+x/2+y )O ₃ is (Pb _1-x Na _x )(Sc _{0. 5-x/2} Ta _0.5+x/2 ) O ₃ .

The ceramic layer 4 may contain one type of ceramic as a main component, or may contain two or more types of ceramics as a main component.

Here, the "main component" in the ceramic layer means that the ceramic layer essentially consists of the target ceramic, for example, 90% by mass or more, more preferably 95% or more, even more preferably 95% or more by mass of the ceramic layer. This means that 98% by mass or more, even more preferably 99% by mass or more, particularly preferably 99.5% by mass or more is the subject ceramic. Other components may include a crystalline phase having a structure different from the perovskite structure called a pyrochlore structure, other elements mixed as impurities, and particularly unavoidable elements (for example, Zr, C, etc.).

The composition of the ceramic layer 4 can be determined by high-frequency inductively coupled plasma emission spectroscopy, fluorescent X-ray analysis, or the like. Further, the structure of the ceramic layer 4 can be determined by powder X-ray diffraction.

The thickness of the ceramic layer 4 is preferably 5 μm or more and 100 μm or less, more preferably 5 μm or more and 50 μm or less, even more preferably 10 μm or more and 50 μm or less, even more preferably 20 μm or more and 50 μm or less, and particularly preferably 20 μm or more and 40 μm or less. . By increasing the thickness of the ceramic layer, the amount of heat that the element can handle can be increased. By making the thickness of the ceramic layer thinner, the withstand voltage can be improved and a higher ΔT can be obtained.

The order degree of the B site of the ceramic layer 4 may be preferably 75% or more, more preferably 76% or more, and still more preferably 77% or more. By increasing the degree of order of the B site, a larger electric heat amount effect can be obtained. The order degree of the B site of the ceramic layer is preferably as high as possible, but the upper limit thereof may be, for example, 99% or less, 90% or less, or 85% or less. By lowering the degree of order of the B site, the annealing time during manufacturing can be shortened and productivity is improved.

The degree of order of the B site of the ceramic layer 4 is calculated by measuring the 111 and 200 diffraction intensities of the perovskite structure by powder X-ray diffraction, and using the measured values and the structure in which the B site is completely ordered. It can be determined from the value using the following formula.

［式中、Ｓ^２ _１１１は、オーダー度を表し、
Ｉ_１１１及びＩ_２００は、それぞれ、１１１と２００回折の強度を表し、
observedは、測定値を表し、
calculatedは、計算値を表す。］

[In the formula, S ² ₁₁₁ represents the degree of order,
I ₁₁₁ and I ₂₀₀ represent the intensities of 111 and 200 diffraction, respectively;
observed represents a measured value,
calculated represents a calculated value. ]

The withstand voltage of the ceramic layer 4 may be preferably 15 MV/m or more, more preferably 20 MV/m or more, even more preferably 25 MV/m or more. By increasing the withstand voltage of the ceramic layer, a larger electric field can be applied and a larger ΔT can be obtained.

Materials constituting the pair of external electrodes 8a, 8b include, but are not limited to, Ag, Cu, Pt, Ni, Al, Pd, Au, or alloys thereof (for example, Ag-Pd, etc.). The electrode may be made of metal and glass or may be made of metal and resin. Among the metals, Ag is preferred.

In the electrocaloric effect element 1, the Pt electrode layers 2 and the ceramic layers 4 are alternately laminated, but in the electrocaloric effect element of the present disclosure, the number of laminated Pt electrode layers and ceramic layers is not particularly limited. Further, all of the internal electrodes do not need to be connected to external electrodes, and internal electrodes that are not connected to external electrodes may be included as necessary for heat transfer or stress relaxation due to piezoelectricity or electrostriction. For example, the lower limit of the number of laminated ceramic layers may be 1 or more, preferably 5 or more, for example 10 or more, or 20 or more. Further, the upper limit of the number of laminated ceramic layers may be several hundred or less, preferably 300 or less, more preferably 100 or less, for example 50 or less.

In the electrocaloric effect element 1, the internal electrode and the ceramic layer are in contact with each other on substantially the entire surface, but the electrocaloric effect element of the present disclosure is not limited to such a structure, and can apply an electric field to the ceramic layer. There are no particular limitations as long as it is a structure. Further, although the electrocaloric effect element 1 has a rectangular parallelepiped block shape, the shape of the electrocaloric effect element of the present disclosure is not limited to this, and may be, for example, cylindrical or sheet-like, and may also have unevenness or through holes. etc. may be included. Furthermore, internal electrodes may be exposed on the surface for heat transport and heat exchange with the outside.

The electrocaloric effect element of this embodiment described above is manufactured, for example, as follows.
High-purity lead oxide (Pb ₃ O ₄ ), tantalum oxide (Ta ₂ O ₅ ), scandium oxide (Sc ₂ O ₃ ), and sodium carbonate (Na ₂ CO ₃ ) are used as raw materials, and the desired composition ratio is achieved after firing. Weigh as follows. The above raw materials are pulverized and mixed with partially stabilized zirconia (PSZ) balls, pure water, a dispersant, etc. in a ball mill. Thereafter, the pulverized and mixed slurry is dried, sized, and then calcined, for example, at 800° C. to 900° C. in the atmosphere. The obtained calcined powder is mixed with PSZ balls, ethanol, toluene, a dispersant, etc., and pulverized. Next, a binder solution dissolved in the obtained pulverized powder is added and mixed to create a slurry for sheet molding. The prepared slurry is formed into a sheet shape on a support, and a Pt electrode paste is printed on it. After laminating a printed sheet and an unprinted sheet into a desired structure, they are pressed together under a pressure of 100 MPa to 200 MPa and cut to create a green chip. The green chips are heat-treated at 500°C to 600°C in the atmosphere to remove the binder. Next, the binder-removed chip is fired at 1300° C. to 1500° C. using, for example, a sealed sheath made of alumina together with PbZrO ₃ powder to create a Pb atmosphere. After firing, if necessary, the chip and the PbZrO ₃ powder can be heat-treated again at about 1000° C. for a predetermined time to adjust the structure. Thereafter, the end face of the chip is polished with sandpaper, an external electrode paste is applied, and a baking process is performed at a predetermined temperature to obtain an electrocaloric effect element as shown in FIG.

Since the electrocaloric effect element of the present invention exhibits an excellent electrocaloric effect, it can be used as a heat management element, particularly a cooling element (including cooling/heat pump elements for air conditioners such as air conditioners, refrigerators, and freezers).

The present disclosure also provides an electronic component comprising the electrocaloric effect element of the present disclosure, and an electronic device comprising the electrocaloric effect element or electronic component of the present disclosure.

Examples of electronic components include, but are not limited to, electronic components used in air conditioners, refrigerators, or freezers; central processing units (CPUs), hard disks (HDDs), power management ICs (PMICs), and power amplifiers (PAs). , integrated circuits (ICs) such as transceiver ICs and voltage regulators (VRs), light emitting elements such as light emitting diodes (LEDs), incandescent light bulbs, and semiconductor lasers, components that can be heat sources such as field effect transistors (FETs), and other components. Parts include, for example, parts commonly used in electronic devices such as lithium ion batteries, circuit boards, heat sinks, and casings.

Examples of electronic devices include, but are not limited to, small electronic devices such as air conditioners, refrigerators, or freezers; mobile phones, smartphones, personal computers (PCs), tablet terminals, hard disk drives, and data servers.

<Production of electrocaloric effect element>
High purity lead oxide (Pb ₃ O ₄ ), tantalum oxide (Ta ₂ O ₅ ), scandium oxide (Sc ₂ O ₃ ), and sodium carbonate (Na ₂ CO ₃ ) were prepared as raw materials. These raw materials were weighed so as to have a predetermined composition ratio as shown in Tables 1 to 7 after firing, and heated in a ball mill for 16 hours with partially stabilized zirconia (PSZ) balls having a diameter of 2 mm, pure water, and a dispersant. Grinding and mixing were performed. Thereafter, the pulverized and mixed slurry was dried on a hot plate, sized, and then calcined in the atmosphere at 850° C. for 2 hours.

The obtained calcined powder was mixed with PSZ balls having a diameter of 5 mm, ethanol, toluene, and a dispersant for 16 hours, and then pulverized. Next, a dissolved binder solution was added to the obtained pulverized powder and mixed for 4 hours to prepare a slurry for sheet molding. The prepared slurry was formed into a sheet shape with a thickness corresponding to the thickness of the predetermined ceramic layer on a PET film using a doctor blade method, and after cutting into strips, a platinum internal electrode paste was screen printed. Note that the sheet thickness of the laminated element to be produced was controlled by changing the gap of the doctor blade used during sheet forming.

A predetermined number of printed sheets and non-printed sheets were laminated, then pressed together with a pressure of 150 MPa and cut to create a green chip. The green chips were heat-treated at 550° C. for 24 hours in the air to remove the binder. Next, the green chip was sealed in an alumina sealed sheath together with PbZrO ₃ powder for creating a Pb atmosphere, and fired at 1350 to 1400° C. for 4 hours. For sample No. 2 only, after firing, the chip and PbZrO ₃ powder were placed in a sealed sheath again, and heat treatment (annealing treatment) was performed at a temperature of 1000° C. for 1000 hours.

Thereafter, the end face of the chip was polished with sandpaper, an Ag external electrode paste was applied, and a baking process was performed at a temperature of 750° C. to obtain an electrocaloric effect element as shown in FIG. 1.

The size of the obtained element was approximately L10.2 mm x W7.2 mm x T0.88 for an element in which the thickness of the ceramic layer was 40 μm. The number of ceramic layers sandwiched between the internal electrode layers was 19, the electrode area was 49 mm ² /layer, and the total electrode area was 49 mm ² ×19 layers. The thickness of the ceramic layer of the element obtained above was confirmed using a scanning electron microscope after polishing the cross section of the element.

<Evaluation>
(composition)
The ceramic composition of the obtained element was confirmed using high frequency inductively coupled plasma emission spectroscopy and fluorescent X-ray analysis.

[Crystal structure and degree of order]
(Crystal structure)
Powder X-ray diffraction measurements were performed to evaluate the crystal structure and degree of order (S ₁₁₁ ) of the obtained device. One element was randomly selected from each lot, ground in a mortar, and then an X-ray diffraction profile was obtained. From the obtained X-ray diffraction profile, it was confirmed whether the crystal structure of the ceramic was a perovskite structure, and the presence or absence and abundance ratio of impurity phases (mainly pyrochlore phase) were estimated from the intensity ratio. When the abundance ratio of perovskite structure was 0.9 or more, it was determined that the main component had a perovskite structure, and when it was less than 0.9, it was determined that there was a different phase.

(order degree)
The degree of ordering at site B was estimated using the formula below.

In the above formula, I ₁₁₁ and I ₂₀₀ are the 111 and 200 diffraction intensities of the perovskite structure, respectively, and the order degree of the B site was determined from the measured value and the calculated value from the structure in which the B site is completely ordered. A product with an order degree of 75% or more was considered to be a good product and was judged as Go. The results are shown in Tables 1-7.

[Withstand voltage and electric heating effect]
An ultra-fine K thermocouple with a diameter of 50 μm is attached to the center of the element surface using Kapton tape to constantly monitor the temperature, a voltage application wire is glued to both ends of the external electrode with Ag paste, and a voltage is applied using a high voltage generator. did.

(Electric heat effect)
The electrocaloric effect was evaluated by applying voltage to the sample in the sequence shown in the upper graph of FIG. That is, first, a voltage was applied to the sample, the voltage was maintained as it was, then the applied voltage was removed and the voltage was maintained as it was, and this operation was repeated to measure changes in the electrocaloric effect. When voltage is applied in this sequence, in the step of applying voltage, the sample temperature rises at the same time as the voltage is applied, and in the step of maintaining the applied state, the heat is gradually diffused and the sample temperature remains the same as before voltage application. In the process of lowering the sample temperature to the same temperature and removing the applied voltage, the sample temperature decreases simultaneously with the removal, and in the process of maintaining the non-applied state, the sample temperature gradually increases to the original temperature. This is because the ferroelectric domains are aligned or disordered by voltage application or removal, and the change in entropy produces such heat absorption and heat absorption effects (electrocaloric effect). The adiabatic temperature change ΔT is determined from the temperature change when the above voltage is applied and removed. Specifically, in this example, after applying a voltage of 15 MV/m, the temperature was measured by holding the applied voltage for 50 seconds, and then after removing the voltage, the temperature was measured by holding the voltage in a non-applied state for 50 seconds. did. This sequence was repeated three times. During the sequence of voltage application and voltage removal, the temperature of the element was constantly measured, and the adiabatic temperature change ΔT was determined from the temperature change. ΔT). This measurement was carried out in a temperature range of -90°C to 160°C. As a representative, the results of sample numbers 1, 2, and 5 are shown in FIG. In addition, the adiabatic temperature change ΔT at -5° C. and 0° C. was determined to be Go if it was 1.5 K or more and 1 K or more, respectively. The results are shown in Table 1 and Tables 3 to 7.

(Withstand voltage)
The withstand voltage was measured by changing only the thickness of the ceramic element without changing the number of laminated layers. The withstand voltage was determined by applying a voltage to the element in the same manner as in the measurement of the electrocaloric effect described above, and examining whether or not dielectric breakdown occurred at that time. Specifically, the applied voltage was increased in steps of 5 MV/m from 10 MV/m, and the electric field strength one level before the voltage at which dielectric breakdown occurred was defined as the withstand voltage. The results are shown in Table 2.

The above evaluation results are shown below. In addition, the samples marked with "*" in the table are comparative examples, and the other samples are examples.

(Relationship between order degree and annealing treatment)
As shown in Table 1, among samples No. 1 and No. 2 having the composition of PbSc _0.5 Ta _0.5 O ₃ , which are conventional PST ceramics, the order degree of Sample No. 1 without annealing treatment is On the other hand, in sample number 2, which was annealed for 1000 hours, the degree of order improved to 0.82. From these results, it was confirmed that the degree of order of PST ceramics strongly depends on the heat treatment time, and that a long heat treatment of 1000 hours is required to obtain a high degree of order. Although not shown above, there is a problem in that the degree of order varies between production lots in the conventional multilayer element having Pt internal electrodes using PST ceramics.

On the other hand, sample numbers 3 to 6, which fall within the scope of the present invention, have order degrees exceeding 0.75 even without annealing. That is, samples within the scope of the present invention can obtain a high degree of order even without long-term heat treatment. This means extremely high productivity. Although not shown above, an even higher degree of order, for example, a degree of order exceeding 0.80, can be obtained by performing a relatively short annealing process of 300 hours.

(Relationship between electric calorie effect and temperature)
As shown in FIG. 3, which shows the relationship between the electrocaloric effect and temperature, for samples Nos. 1 and 2, which are outside the scope of the present invention, the adiabatic temperature change reaches its maximum at around 20 to 30°C, and it reaches 0°C. It is getting smaller in the vicinity. This is because in the conventional sample with the composition of PbSc _0.5 Ta _0.5 O ₃ , the ferroelectric temperature transition is around 0 to 15°C, and a large adiabatic temperature change is realized above that transition temperature. It originates from Since this transition temperature shifts to lower temperatures as the degree of order decreases, sample number 1, which has a low degree of order, exhibits a higher adiabatic temperature change at 0°C. On the other hand, sample number 5, which is within the scope of the present invention, has a smaller maximum adiabatic temperature change than sample numbers 1 and 2, but has a broad peak over a wide temperature range, around -10°C. At low temperatures such as 0°C and -10°C, it was possible to achieve a larger adiabatic temperature change than sample numbers 1 and 2. This is thought to be due to the fact that the ferroelectric transition temperature could be controlled to a low temperature side and that a high degree of order could be achieved without annealing.

(Relationship between withstand voltage and ceramic layer thickness)
As shown in Table 2, all samples numbered 8 to 13 within the scope of the present invention were able to achieve a withstand voltage of 15 MV/m or more. In particular, it was confirmed that a higher withstand voltage was exhibited when the thickness of the ceramic layer was 50 μm or less, particularly 20 μm or more and 50 μm or less. This is because the withstand voltage of the ceramics used in the present invention tends to be lower than that of BaTO ₃ , and defects may easily remain due to defects such as Pb during firing, and these remaining defects may affect the withstand voltage. It is thought that Therefore, it is presumed that as the thickness of the ceramic layer becomes thinner, the absolute number of existing defects decreases accordingly, or that the sintering behavior of the ceramic changes, thereby reducing the number of defects. However, if the thickness of the ceramic layer becomes too thin, structural defects (for example, smoothness of internal electrodes, etc.) become more dominant than defects in the ceramic itself, and it is thought that the withstand voltage decreases a little.

(Ceramic composition range)
As shown in Tables 3 to 7, when comparing the crystal structure, degree of order, and adiabatic temperature change between compositions within and outside the range of the present invention, samples within the range of the present invention do not require annealing treatment. It was also confirmed that it was possible to achieve a degree of B-site order of 75% or more, and it was also possible to realize adiabatic temperature changes of 1.5K and 1K or more at 0°C and -10°C, respectively. In samples outside the scope of the present invention, many different phases appeared, the degree of order was insufficient, and the adiabatic temperature change was particularly small (less than 1 K) at -10°C.

Note that the above effect could not be obtained when, for example, K or La was used instead of Na.

Since the electrocaloric effect element of the present disclosure can exhibit a high electrocaloric effect, it can be used, for example, as a heat management element in air conditioners, refrigerators, freezers, etc., and can also be used in various electronic devices, such as heat countermeasures. It can be used as a cooling device for small electronic devices such as mobile phones, where the problem is becoming more prominent.

1... Electrocaloric effect element 2a, 2b... Pt electrode layer 4... Ceramic layer 6... Laminated body 8a, 8b... External electrode

Claims (5)

An electrocaloric effect element having a laminate in which an electrode layer whose main component is Pt and a ceramic layer are laminated, the ceramic layer having a perovskite structure and having the formula:
(Pb _1-x Na _x ) _m (Sc _0.5-x/2-y Ta _0.5+x/2+y ) O ₃
[In the formula,
x satisfies 0.01≦x≦0.08,
y satisfies -0.03≦y≦0.03,
m satisfies 0.97≦m≦1.03. ]
An electrocaloric effect element whose main component is ceramic represented by The electrocaloric effect element according to claim 1, wherein y is 0 and m is 1. The electrocaloric effect element according to claim 1 or 2, wherein the thickness of the ceramic layer in the laminate is 50 μm or less. The electrocaloric effect element according to any one of claims 1 to 3, wherein the thickness of the ceramic layer in the laminate is 10 μm or more and 50 μm or less. An electronic component comprising the electrocaloric effect element according to any one of claims 1 to 4.

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