Ag-Pd alloy nanoparticles and method for producing the same

Abstract

This invention provides Ag-Pd alloy nanoparticles with improved migration resistance and a method for producing the same. [Solution] One aspect of the present invention relates to Ag-Pd alloy nanoparticles comprising an Ag-Pd solid solution phase and a Pd-rich phase in which Ag and Pd are solidly dissolved on the particle surface, wherein the Pd content relative to the number of Ag atoms on the particle surface is 30 atomic percent or more, and to a method for producing the same.

Description

Technical Field

[0001] One aspect of the present invention relates to Ag-Pd alloy nanoparticles and a method for producing the same.

Background Art

[0002] Metal nanoparticles, which may have properties different from those of bulk materials, are being used and studied in various applications such as catalysts, ink materials, and electronic component members.

[0003] For example, in the field of electronics mounting, metal nanoparticles are being studied as lead-free bonding materials that can be bonded at low temperatures.

[0004] Common silver (Ag) nanoparticles as metal nanoparticles are known to be elements that are prone to ion migration. Ion migration refers to a phenomenon in which, when a voltage is applied in a state where a printed circuit board is installed under high-humidity environmental conditions, ionized Ag moves between electrodes, causing a short circuit.

[0005] As a method for suppressing such a phenomenon, adding palladium (Pd) to Ag particles can be mentioned.

[0006] For example, Patent Document 1 discloses conductive ink containing nanoparticles of an Ag-Pd alloy, and discloses that, in the Ag-Pd alloy, the content of Pd is more than 5% by weight and less than 40% by weight.

[0007] Patent Document 2 discloses core-shell particles composed of Ag core particles mainly containing silver and a Pd shell mainly containing palladium that coats at least a part of the surface of the Ag core particles, and discloses that polyvinylpyrrolidone is selectively attached to the surface of the Pd shell.

[0008] Patent Document 3 discloses a conductive paste comprising (A) conductive particles and (B) a binder resin, wherein (A) the conductive particles comprises surface-treated metal particles, the surface-treated metal particles comprises metal particles and a surface treatment layer disposed on at least a portion of the surface of the metal particles, and the surface treatment layer comprises a palladium compound. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2006-257403 [Patent Document 2] Japanese Patent Publication No. 2019-178404 [Patent Document 3] Japanese Patent Publication No. 2024-31862 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] However, conventional technology has not clarified the specific structure of Ag-Pd alloy particles. Furthermore, while it is necessary to add a large amount of Pd to obtain sufficient migration resistance, this also increases the amount of Pd on the particle surface, leading to problems such as a decrease in electrical conductivity.

[0011] Therefore, one aspect of the present invention aims to provide Ag-Pd alloy nanoparticles with improved migration resistance and a method for producing the same. [Means for solving the problem]

[0012] Ion migration in wiring made of Ag is a phenomenon of Ag ions moving on the wiring surface. Therefore, Pd, which suppresses ion migration, does not need to be uniformly present throughout the wiring, i.e., throughout the entire Ag-Pd alloy nanoparticle, but only needs to be abundant on the surface of the Ag-Pd alloy nanoparticle. In other words, if two types of particles have the same Pd content as a whole, and one particle has Pd uniformly distributed throughout, while the other particle has a layer of abundant Pd formed on its surface, the latter will have higher migration resistance.

[0013] Therefore, the present inventors investigated various means to solve the above problem and found that in a method for producing silver nanoparticles by reducing silver ions in a reaction solution, by coexisting palladium ions with silver ions in the reaction solution and carrying out the reduction reaction using a microwave synthesis apparatus, a Pd layer is formed on the surface of Ag particles after the formation of Ag particles due to the difference in reduction rates between Ag and Pd, and thus it is possible to produce Ag-Pd alloy nanoparticles in which a large amount of Pd is present on the particle surface, thus completing one aspect of the present invention.

[0014] In other words, the gist of one aspect of the present invention is as follows: (1) Ag-Pd alloy nanoparticles comprising an Ag-Pd solid solution phase in which Ag and Pd are solidly dissolved on the particle surface and a Pd-rich phase, wherein the Pd content relative to the number of Ag atoms on the particle surface is 30 atomic percent or more. (2) Ag-Pd alloy nanoparticles as described in (1), wherein the molar ratio of Pd in ​​the Pd-rich phase and the Ag-Pd solid solution phase (Pd-rich phase / Ag-Pd solid solution phase) is in the range of 1.1 to 3.0. (3) Ag-Pd alloy nanoparticles according to (1) or (2), wherein the Pd-rich phase occupies a range of 20% to 80% of the total surface area of ​​the particles. (4) Ag-Pd alloy nanoparticles as described in any one of (1) to (3), wherein the average particle size is in the range of 5 nm to 20 nm. (5) A method for producing Ag-Pd alloy nanoparticles according to any one of (1) to (4), wherein a reaction solution containing silver ions and palladium ions is irradiated with microwaves to produce Ag-Pd alloy nanoparticles.

Advantages of the Invention

[0015] According to one aspect of the present invention, Ag-Pd alloy nanoparticles with improved migration resistance and a method for producing the same are provided.

Brief Description of the Drawings

[0016] [Figure 1] It is a diagram showing the relationship between the voltage application time and the leakage current due to the difference in the Pd content in Ag-Pd alloy nanoparticles. [Figure 2] It is a diagram showing the TEM-EDX photograph and the results of elemental analysis of the particles of Example 1. [Figure 3] It is a schematic diagram of Ag-Pd alloy nanoparticles having various configurations based on the experiments in the examples.

Modes for Carrying Out the Invention

[0017] Hereinafter, preferred embodiments of one aspect of the present invention will be described in detail. In this specification, the features of one aspect of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of one aspect of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. Note that the Ag-Pd alloy nanoparticles and the method for producing the same according to one aspect of the present invention are not limited to the following embodiments, and can be implemented in various forms with modifications and improvements that can be made by those skilled in the art without departing from the gist of one aspect of the present invention.

[0018] The Ag-Pd alloy nanoparticles of one aspect of the present invention are nanoparticles composed of an alloy containing silver (Ag) and palladium (Pd). In one embodiment, they are nanoparticles of an alloy composed only of Ag and Pd. Their composition is not uniform throughout the particles and includes an Ag-Pd solid solution phase and a Pd-rich phase on the particle surface.

[0019] The average particle size of the primary particles of the Ag-Pd alloy nanoparticles of one aspect of the present invention is not limited, but usually ranges from 1 nm to 30 nm, in one embodiment from 2 nm to 25 nm, in one embodiment from 5 nm to 20 nm, and in one embodiment from 10 nm to 18 nm. Here, the average particle size is a value calculated as the average from the equivalent diameters of the projected areas of randomly selected 100 or more Ag-Pd alloy nanoparticles in the TEM image of the Ag-Pd alloy nanoparticles.

[0020] By the average particle size of the Ag-Pd alloy nanoparticles being within the above range, the melting characteristics of the Ag-Pd alloy nanoparticles, that is, low-temperature fusibility, can be ensured.

[0021] The overall Pd content of the Ag-Pd alloy nanoparticles of one aspect of the present invention is usually in the range of 15 atomic % to 55 atomic % with respect to the total number of Ag atoms in the Ag-Pd alloy nanoparticles, in one embodiment in the range of 16 atomic % to 50 atomic %, in one embodiment in the range of 17 atomic % to 40 atomic %, in one embodiment in the range of 18 atomic % to 30 atomic %, in one embodiment in the range of 20 atomic % to 28 atomic %, and in one embodiment in the range of 22 atomic % to 25 atomic %.

[0022] The overall Pd content of the Ag-Pd alloy nanoparticles can be measured by ICP, TEM-EDX, or EPMA. By the overall Pd content of the Ag-Pd alloy nanoparticles being within the above range, while suppressing the decrease in electrical conductivity due to Pd, the migration resistance can be improved.

[0023] In one embodiment of the present invention, the particle surface is typically a range of several nanometers from the outermost surface of the particle, for example, between 1 nm and 5 nm, and in one embodiment, a range of between 2 nm and 4 nm. Therefore, the particle surface is the outermost layer of the particle with a thickness of several nanometers, for example, between 1 nm and 5 nm, and in one embodiment, a range of between 2 nm and 4 nm. In one embodiment of the present invention, the particle surface is the range in which Ag and Pd of EDX are observed when measured under TEM-EDX conditions of an acceleration voltage of 200 kV and an observation magnification of 2,000,000 times.

[0024] The Ag-Pd solid solution phase is a phase in which Ag and Pd are dissolved. On the particle surface, the Ag-Pd solid solution phase typically occupies a range of 20% to 80% of the total surface area of ​​the particle, in one embodiment a range of 30% to 70% of the total surface area, and in another embodiment a range of 40% to 60% of the total surface area. Here, the sum of the area ratios of the Ag-Pd solid solution phase and the Pd-rich phase equals 100% of the total surface area. One or more Ag-Pd solid solution phases exist on the particle surface, for example, one, two, three, or four or more. In one embodiment, one Ag-Pd solid solution phase exists on the particle surface.

[0025] The Pd-rich phase is a phase in which Ag and Pd are in solid solution, and the Pd content is higher compared to the Ag-Pd solid solution phase. On the particle surface, the Pd-rich phase typically occupies a range of 20% to 80% of the total surface area of ​​the particle, in one embodiment a range of 30% to 70% of the total surface area, and in another embodiment a range of 40% to 60% of the total surface area. Here, the Ag-Pd solid solution phase and the Pd-rich phase together account for 100% of the total surface area. One or more Pd-rich phases exist on the particle surface, for example, one, two, three, or four or more. In one embodiment, one Pd-rich phase exists on the particle surface.

[0026] In one embodiment, one Ag-Pd solid solution phase and one Pd-rich phase are present on the particle surface.

[0027] The molar ratio of Pd in ​​the Pd-rich phase to the Ag-Pd solid solution phase (Pd-rich phase / Ag-Pd solid solution phase) is not limited, but is usually in the range of 1.1 to 3.0, in one embodiment it is in the range of 1.2 to 2.8, in one embodiment it is in the range of 1.5 to 2.5, and in one embodiment it is in the range of 1.8 to 2.2. The molar ratio of Pd in ​​the Pd-rich phase to the Ag-Pd solid solution phase can be measured by the TEM-EDX method described above.

[0028] In one embodiment of the present invention, the Pd content relative to the number of Ag atoms on the particle surface is 30 atomic% or more, and in one embodiment, 35 atomic% or more. The upper limit of the Pd content relative to the number of Ag atoms on the particle surface is not limited. For example, the Pd content relative to the number of Ag atoms on the particle surface is usually 50 atomic% or less, and in one embodiment, 40 atomic% or less. The Pd content relative to the number of Ag atoms on the particle surface can be measured by the TEM-EDX method described above.

[0029] The presence of the Ag-Pd solid solution phase and Pd-rich phase on the particle surface of the Ag-Pd alloy nanoparticles, as described above, allows for a higher proportion of Pd present on the wiring surface during wiring formation. As a result, resistance to migration caused by Ag ion migration can be increased.

[0030] Ag-Pd alloy nanoparticles according to one aspect of the present invention can be used not only as conventional catalysts, electronic component materials, printed circuit boards, and ink materials, but also as a high-temperature-resistant, lead-free bonding material in the field of electronics packaging.

[0031] One aspect of the present invention is a method for producing Ag-Pd alloy nanoparticles. In this method for producing Ag-Pd alloy nanoparticles, a reaction solution containing silver ions and palladium ions is irradiated with microwaves to reduce the silver ions and palladium ions, thereby synthesizing Ag-Pd alloy nanoparticles.

[0032] Here, the raw materials for silver ions are not limited, but examples include inorganic salts of silver such as hydrochloride, sulfate, nitrate, and phosphate, organic salts such as carboxylates and sulfonates, and complex salts. In one aspect of the present invention, it is preferable to use inexpensive silver nitrate as the raw material for silver ions.

[0033] The concentration of silver ions in the reaction solution is not limited, but is usually 40 mmol / L (mM) or higher, and in one embodiment, 50 mM or higher. The upper limit of the concentration of silver ions in the reaction solution is not limited, as long as the silver ion raw materials exist as silver ions in the reaction solution. The concentration of silver ions in the reaction solution is usually 500 mM or lower, and in one embodiment, 400 mM or lower.

[0034] By setting the concentration of silver ions in the reaction solution within the aforementioned range, the variability of the resulting Ag-Pd alloy nanoparticles is reduced; in other words, the particle size distribution of the resulting Ag-Pd alloy nanoparticles becomes narrower.

[0035] The solvent used in the reaction solution in one embodiment of the present invention is not limited as long as it is a solvent that absorbs microwaves. Examples of solvents used in the reaction solution in one embodiment of the present invention include low-boiling-point polar solvents having a boiling point of 300°C or less. Examples of low-boiling-point polar solvents are not limited, but include water, alcohols such as ethanol, other organic solvents such as DMF, or mixtures of two or more of these. In one embodiment, the solvent used in the reaction solution is a mixed solvent of water and DMF.

[0036] In one embodiment of the present invention, by using a low-boiling point solvent as the solvent in the reaction solution, the handling of the solvent can be improved and the environmental burden can be reduced.

[0037] A particle protectant may be added to the reaction solution. The particle protectant is a compound that binds to part or all of the surface of Ag-Pd alloy nanoparticles suspended in the solvent, and suppresses aggregation of Ag-Pd alloy nanoparticles. Examples of particle protectants are not limited, but include polyvinylpyrrolidone (PVP), thiols, and polyvinyl alcohol (PVA). The molecular weight of the particle protectant is not limited, but the weight-average molecular weight is usually in the range of 1,000 to 100,000, and in one embodiment, it is in the range of 10,000 to 50,000. In one embodiment, the particle protectant is PVP.

[0038] The amount of particle protective agent is not limited and can be changed according to the desired particle size of the Ag-Pd alloy nanoparticles, and is usually in the range of 1 to 10 times, and in one embodiment, in the range of 1.5 to 2.5 times, relative to the molecular weight of Ag and Pd, which are the raw materials for the Ag-Pd alloy nanoparticles.

[0039] In one embodiment of the present invention, the aggregation of generated Ag-Pd alloy nanoparticles can be suppressed by using a particle protective agent.

[0040] The raw materials for palladium ions are not limited to those mentioned above, but examples include inorganic salts of palladium such as hydrochloride, sulfate, nitrate, and phosphate, organic salts such as carboxylates and sulfonates, and complex salts. In one aspect of the present invention, it is preferable to use inexpensive palladium nitrate as the raw material for palladium ions.

[0041] The concentration ratio of silver ions and palladium ions in the reaction solution will be equivalent to the ratio of Ag and Pd content in the entire Ag-Pd alloy nanoparticle. Therefore, the ratio of silver ion raw materials to palladium ion raw materials can be determined so that the overall Pd content of the Ag-Pd alloy nanoparticle is as described above.

[0042] By introducing silver ions and palladium ions into the reaction system, Ag forms nanoparticle nuclei from the silver ions before palladium ions do. As a result, palladium ions can precipitate and grow as Pd on the nuclei formed by Ag, enabling the synthesis of Ag-Pd alloy nanoparticles having an Ag-Pd solid solution phase and a Pd-rich phase on the particle surface.

[0043] Reducing agents containing silver ions and palladium ions may be added to the reaction solution. A reducing agent is a material that can reduce silver ions and palladium ions to Ag and Pd, which have an oxidation state of 0, through a redox reaction.

[0044] Examples of reducing agents, though not limited to them, include DMF, citric acid or its salts, such as trisodium citrate, disodium citrate, monosodium citrate, oxalic acid or its salts, such as sodium oxalate, ascorbic acid or its salts, such as sodium ascorbate. Since DMF acts as both a solvent and a reducing agent, in one embodiment, DMF is used as both a solvent and a reducing agent.

[0045] In one aspect of the present invention, the order of addition of each material, the addition temperature, the mixing method, the mixing time, etc., are not limited, and the materials are mixed so as to prepare a homogeneous reaction solution. In one aspect of the present invention, the reaction is started after a homogeneous reaction solution has been prepared.

[0046] A manufacturing method according to one aspect of the present invention can be carried out by using a microwave synthesis apparatus.

[0047] In one embodiment of the present invention, a method using a microwave synthesis apparatus involves irradiating a reaction solution with microwaves to allow the reaction to proceed. Therefore, as the solvent contained in the reaction solution, a polar solvent is used that, when irradiated with microwaves, absorbs microwaves and generates heat by converting them into thermal energy.

[0048] In the method using a microwave synthesis apparatus, the material of the container holding the reaction solution is not limited as long as the raw material solution can be uniformly irradiated with microwaves. For example, when microwaves are irradiated onto the raw material solution from outside the reactor through the reactor, a material that transmits microwaves, such as ceramics or glass, can be used. When microwaves are irradiated directly onto the raw material solution from above, a material that reflects microwaves, such as aluminum or stainless steel, can be used.

[0049] In the method using a microwave synthesizer, microwaves are generated from a microwave irradiation source (microwave oscillator (magnetron)), and the microwave irradiation source can be either a single-mode system or a multi-mode system.

[0050] In the method using a microwave synthesis apparatus, the output of the microwave irradiation source can be appropriately changed depending on the reaction conditions, such as the type of reaction, and is not limited to this, but is usually in the range of 100 W / L to 10 kW / L, and in one embodiment, in the range of 100 W / L to 5 kW / L, based on the total volume of the reaction solution.

[0051] In the method using a microwave synthesizer, the frequency of microwaves generated from the microwave irradiation source can be changed as appropriate and is not limited, but is usually in the range of 1 GHz to 10 GHz, and in one embodiment, in the range of 2 GHz to 6 GHz. In one aspect of the present invention, 2.45 GHz, which is the frequency of an industrial microwave power supply, is used as the microwave frequency.

[0052] In the method using a microwave synthesis apparatus, the temperature of the reaction solution, which is heated by microwave irradiation, can be appropriately changed depending on the reaction conditions and is not limited. It is sufficient if it is below the boiling point of the solvent.

[0053] In the method using a microwave synthesis apparatus, the microwave irradiation time to the reaction solution can be appropriately changed depending on the reaction conditions and is not limited. The microwave irradiation time to the reaction solution is usually a few seconds, for example, in the range of 2 seconds to 20 minutes, in one embodiment in the range of 10 seconds to 10 minutes, and in another embodiment in the range of 1 minute to 8 minutes. The reaction rate can be improved by increasing the microwave irradiation time to the reaction solution. Alternatively, the reaction solution can be irradiated with microwaves to maintain the desired temperature of the reaction solution.

[0054] By using a microwave synthesis apparatus as the reaction method, the entire reaction field can be quickly heated to the reaction temperature, enabling uniform and rapid heating.

[0055] In one embodiment of the present invention, the reaction solution may be stirred using a stirring mechanism, such as a propeller-type stirrer or a vibrating stirrer. By stirring the reaction solution, the Ag-Pd alloy nanoparticles generated in the reaction solution can be uniformly dispersed, and the reaction solution can be kept uniform.

[0056] One embodiment of the present invention may be carried out in a batch or flow manner. In one embodiment, the present invention is carried out in a batch manner. By carrying out the process in a batch manner, the synthesis reaction itself can be completed, and the yield of the resulting Ag-Pd alloy nanoparticles can be improved. In addition, the concentration of the reaction solution can be increased, making it less likely for the Ag-Pd alloy nanoparticles to clog the piping, which can occur in a flow manner.

[0057] A dispersion containing Ag-Pd alloy nanoparticles obtained according to one aspect of the present invention can be separated and purified (e.g., by salting out or centrifugation) by methods known in the art to obtain the desired Ag-Pd alloy nanoparticles and / or a dispersion containing Ag-Pd alloy nanoparticles. [Examples]

[0058] The following describes several embodiments relating to one aspect of the present invention, but it is not intended that the embodiments of the present invention are limited to those shown in these embodiments.

[0059] 1. Experiment to confirm the required amount of Pd To investigate the necessary amount of Pd to coexist with Ag, experiments were conducted on alloy nanoparticles containing Ag and Pd with varying amounts of added Pd. The sample preparation method is as follows: After sintering Ag-Pd nanoparticles, test specimens simulating the state of a microstructure where Ag and Pd are uniformly dissolved were prepared by casting Ag and Pd.

[0060] The obtained test specimens showed a uniform distribution of Ag and Pd. The obtained test specimens were evaluated using a general water drop test. The gap between the electrodes was set to 2 mm, and a voltage of 3 V was applied to evaluate the time until leakage current occurred. The results are shown in Figure 1. In Figure 1, Ag-25Pd, Ag-30Pd, Ag-40Pd, and Ag-50Pd are Ag-Pd alloy nanoparticles in which the total Pd content of the Ag-Pd alloy nanoparticles is 25 atomic%, 30 atomic%, 40 atomic%, and 50 atomic%, respectively, relative to the total number of Ag atoms in the Ag-Pd alloy nanoparticles.

[0061] Figure 1 shows that in particles with a Pd content of 25 atomic percent or less, leakage current flows when the voltage application time is prolonged, similar to Ag. On the other hand, in particles with a Pd content of 30 atomic percent or more, no leakage current flows even when the voltage application time is prolonged.

[0062] 2. Preparation of Ag-Pd alloy nanoparticles Example 1 (1) Silver nitrate and palladium nitrate dissolved in water were mixed in a 1:1 molar ratio in the same amount as the initial charge. (2) PVP (weight-average molecular weight: 40,000) was added as a protective agent at a molecular weight ratio of twice the total molecular weight of silver nitrate and palladium nitrate in (1). (3) DMF was added as a reducing agent to prepare the reaction solution. The amount added was equal to the amount of water. (4) The reaction solution was irradiated with microwaves to carry out the synthesis. The reaction conditions were 90°C for several seconds to 10 minutes. The reaction solution was heated to 90°C in about 10 seconds.

[0063] Figure 2 shows the TEM-EDX image and elemental analysis results of the particles from Example 1. TEM-EDX was measured under conditions of an acceleration voltage of 200 kV and an observation magnification of 2,000,000 times. In the TEM image in Figure 2, white indicates the element Pd. From Figure 2, it was found that in one embodiment of the present invention, not only an Ag-Pd solid solution phase in which Ag and Pd are solidly dissolved exists on the particle surface, but also a Pd-rich phase in which the Pd content is approximately twice that of the Ag-Pd solid solution phase. It is thought that the Pd-rich phase was formed on the particle surface because the reduction rate of Pd is slower than that of Ag. For comparison, alloy particles manufactured by slow heating and temperature increase contained particles with only Ag (0% Pd) and particles with a low Pd content.

[0064] Figure 3 schematically shows the structure of Ag-Pd alloy nanoparticles based on this experiment. Figure 3A is a schematic diagram of a particle in which Ag and Pd are uniformly distributed. Figure 3B is a schematic diagram of a particle according to one embodiment of the present invention, in which one Ag-Pd solid solution phase and one Pd-rich phase exist on the particle surface, in which Ag and Pd are solid-dissolved. Figure 3C is a schematic diagram of a particle in which an Ag-Pd solid solution core phase in which Ag and Pd are solid-dissolved and a Pd-rich shell phase covering the core exist. From the results in Figure 1, in the case of particles in which Ag and Pd are uniformly solid-dissolved as in Figure 3A, it is necessary to add 30 atomic percent or more of Pd. On the other hand, as shown in Figure 3B, when a Pd-rich phase is formed on the particle surface, for example, if the area of ​​the Pd-rich phase is 50% of the total area and the amount of Pd in ​​the Pd-rich phase is twice the amount of Pd in ​​the Ag-Pd solid solution phase (20 atomic%) (40 atomic%), then the amount of Pd on the particle surface can be 20 atomic% × 50% + 40 atomic% × 50% = 30 atomic%. Therefore, by configuring the particle surface as described above, the amount of Pd added can be 20 atomic% relative to the number of Ag atoms. Note that, as shown in Figure 3C, if the structure of the Ag-Pd alloy nanoparticles is a core-shell structure with a Pd shell on an Ag core, the Pd content can be minimized. However, as a trade-off, since there is no Ag on the surface, sintering occurs between Pd and Pd, resulting in a higher sintering temperature and higher electrical resistance.

Claims

1. Ag-Pd alloy nanoparticles, The particle surface contains an Ag-Pd solid solution phase in which Ag and Pd are solidly dissolved, and a Pd-rich phase. The Pd content relative to the number of Ag atoms on the particle surface is 30 atomic percent or more. Ag-Pd alloy nanoparticles.

2. The Ag-Pd alloy nanoparticle according to claim 1, wherein the molar ratio of Pd in ​​the Pd-rich phase and the Ag-Pd solid solution phase (Pd-rich phase / Ag-Pd solid solution phase) is in the range of 1.1 to 3.

0.

3. The Ag-Pd alloy nanoparticle according to claim 2, wherein the Pd-rich phase occupies a range of 20% to 80% of the total surface area of ​​the particles.

4. Ag-Pd alloy nanoparticles according to claim 3, wherein the average particle size is in the range of 5 nm to 20 nm.

5. A method for producing Ag-Pd alloy nanoparticles according to any one of claims 1 to 4, comprising irradiating a reaction solution containing silver ions and palladium ions with microwaves to produce Ag-Pd alloy nanoparticles.

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