Cu composite n-type ZnO thermoelectric ceramic and preparation method thereof

Abstract

The application discloses a Cu composite n-type ZnO thermoelectric ceramic and a preparation method thereof. Pure ZnO powder with regular morphology and uniform particle size is prepared by a hydrothermal synthesis method, copper acetate monohydrate is used as a copper source, and Cu nanoparticles are uniformly compounded on the surface of the ZnO powder through solution reduction, and the obtained composite powder is compacted and formed, and then is sintered at high temperature under the protection of an argon atmosphere. The application realizes uniform dispersion of Cu phases in the ZnO matrix, constructs a ZnO / Cu heterojunction interface, on the one hand, improves the carrier concentration and the electrical conductivity, and on the other hand, strengthens the interface phonon scattering and reduces the lattice thermal conductivity, and thus a stable ZnO-based composite ceramic with a significantly improved thermoelectric figure of merit is prepared. The ZT value of the optimal sample reaches 0.53 at 800K, which is more than 12 times higher than that of pure ZnO. In addition, the process is simple in preparation, low in cost and flexible in operation process, and can be used for practical production and application in the field of medium and high temperature thermoelectricity in the future.

Description

Technical Field

[0001] This invention relates to a Cu composite n-type ZnO thermoelectric ceramic and its preparation method, belonging to the field of new energy materials. Background Technology

[0002] Thermoelectric conversion technology can convert waste heat into usable electrical energy. Compared with traditional power generation methods, this technology utilizes temperature differences to generate electricity and significantly improves energy efficiency through waste heat recovery, which is of positive significance for alleviating environmental pollution. Thermoelectric materials have advantages such as small size and light weight, and can be used to prepare portable energy sources such as wearable electronic devices. In addition, thermoelectric conversion technology is not easily affected by environmental interference, is noiseless, and has a simple structure, making it of significant application value in fields such as communications, refrigeration, printing, and automotive waste heat recovery.

[0003] Research on p-type thermoelectric materials began earlier and is relatively mature. Researchers have conducted extensive studies on various p-type thermoelectric materials, including Bi₂Te₃, SnTe, PbS, SnSe, GeTe, Mg₃Sb₂, PbTe, and Sb₂Te₃. Among them, Bi₂Te₃ is considered the most promising room-temperature thermoelectric material, achieving a ZT value of 1.38 at 380 K. Due to its excellent thermoelectric conversion efficiency, Bi₂Te₃-based thermoelectric materials have gradually achieved commercialization. Although p-type thermoelectric materials exhibit high conversion efficiency, thermoelectric devices typically require p-type and n-type thermoelectric materials to be connected in series to form a π-type structure to achieve continuous and efficient conversion of thermal energy into electrical energy. Both are indispensable. Currently, p-type thermoelectric materials have made breakthrough progress; therefore, research on n-type thermoelectric materials is particularly important.

[0004] Among numerous thermoelectric material systems, oxide-based thermoelectric materials have gradually become a research focus in the field of medium- and high-temperature thermoelectrics due to their advantages such as good high-temperature stability, oxidation resistance, non-toxicity, abundant raw materials, and low preparation costs. ZnO, as a typical direct bandgap n-type semiconductor oxide, has characteristics such as stable crystal structure, good mechanical properties, and high temperature resistance, and is considered one of the most promising oxide thermoelectric materials. However, intrinsic ZnO has inherent problems such as low carrier concentration, low electrical conductivity, and excessively high lattice thermal conductivity, resulting in poor thermoelectric performance and making it difficult to directly apply in practical applications.

[0005] To improve the thermoelectric properties of ZnO, current research both domestically and internationally mainly focuses on modification methods such as elemental doping, microstructure control, and second-phase composite. Donor doping is a common method to improve the electrical conductivity of ZnO, achieved by introducing Al... 3+ Ga 3+ In 3+ Zn in plasma-substituted lattice 2+Doping can effectively increase carrier concentration and improve electrical conductivity. However, single doping strategies often lead to enhanced carrier scattering, while having limited effect on suppressing lattice thermal conductivity, making it difficult to achieve synergistic optimization of electrical and thermal properties.

[0006] Second-phase composites are considered an effective way to further overcome the bottleneck of ZnO's thermoelectric properties. By introducing highly conductive metals, carbon materials, or oxides as the second phase, heterogeneous interfaces can be constructed in the ZnO matrix, which can both regulate carrier transport behavior and enhance phonon scattering while reducing thermal conductivity.

[0007] In 2022, Chen et al. studied the effect of graphene composites on the thermoelectric properties of ZnO, finding that graphene could refine ZnO grains and form conductive pathways, which improved the ZT value to some extent, but the problem of uneven dispersion of the second phase under solid-state processing was still difficult to avoid; in 2024, Tran et al. and Hashir et al. prepared ZnO / W using solid-state reaction methods. 18 O 49 While ZnO / CoFe2O4 composite thermoelectric materials optimize electroacoustic transport properties through interfacial effects, existing preparation processes still struggle to achieve uniform dispersion of the second phase and precise interfacial control, leading to issues such as particle agglomeration and poor interfacial bonding, thus limiting the improvement in thermoelectric performance. Although these methods are simple to operate, they fail to achieve uniform distribution of the Cu phase within the ZnO matrix, easily resulting in Cu particle agglomeration, poor interfacial bonding, and low density. Furthermore, traditional processes struggle to precisely control the interfacial structure and phase composition, preventing the full realization of Cu's conductivity-enhancing and phonon scattering effects, further limiting the improvement in thermoelectric performance and falling far short of the requirements for industrial applications. Summary of the Invention

[0008] To address the problem of poor thermoelectric conversion efficiency of existing ZnO, this invention provides a zinc oxide-based composite material with high electrical conductivity and low thermal conductivity, and its preparation method.

[0009] On one hand, the present invention provides a Cu composite n-type ZnO thermoelectric ceramic, which is mainly composed of ZnO and a composite phase. In the Cu composite n-type ZnO thermoelectric ceramic ZnO / xCu, the Cu composite phase exists in the form of elemental Cu nanoparticles, where x is 0, 0.02, 0.04, 0.05, the Cu source is copper acetate monohydrate, the reducing agent is L-ascorbic acid, and the molar ratio of the reducing agent to copper acetate monohydrate is 3:1.

[0010] On the other hand, the present invention also provides a method for preparing the above-mentioned Cu composite n-type ZnO thermoelectric ceramic, which uses a hydrothermal method to prepare ZnO powder with uniform particle size, and then uses hot stirring to mix Cu... 2+The ZnO / Cu composite material is obtained by reducing it to Cu and combining it with ZnO, followed by centrifugation, drying, molding and sintering.

[0011] In the preparation method of this invention, the zinc source used is zinc acetate dihydrate, sodium hydroxide is used as a mineralizing agent, citric acid is used as a morphology regulator, the reaction temperature is 140℃, and the holding time is 4h. The resulting ZnO powder has uniform particle size and pure phase.

[0012] In the preparation method of this invention, copper acetate monohydrate is used as the copper source, L-ascorbic acid is used as the reducing agent, and the Cu preparation is completed under water bath conditions at 70°C. 2+ The reduction and homogeneous compounding.

[0013] Specifically, in the preparation method of this invention, ZnO precursor powder with regular morphology and uniform particle size is mixed with copper source solution, and L-ascorbic acid is added for reduction reaction under the conditions of heating and stirring in a water bath at 70°C for 30 min. After the reaction is completed and naturally cooled to room temperature, it is washed three times by centrifugation with deionized water and anhydrous ethanol, and then vacuum dried at 60°C for 12 h to obtain ZnO / xCu composite powder.

[0014] In the preparation method of this invention, ZnO / xCu powder is pressed into shape by an electric tablet press. The pressing pressure is 120MPa and the holding time is 3min, resulting in a blank with a smooth surface and no cracks.

[0015] In the preparation method of this invention, the pressed and shaped blank is placed in a sealed quartz tube under an argon atmosphere for sintering, heated to 1000°C at a heating rate of 10°C / min and held for 1 hour. After the holding period, the blank is naturally cooled to room temperature in the furnace to obtain a dense Cu composite n-type ZnO thermoelectric ceramic.

[0016] In this invention, Cu nanoparticles are composited into a ZnO matrix using a simple process. Due to the difference in electron concentration between the metal and the semiconductor, electrons flow towards ZnO, increasing the carrier concentration of the matrix. Simultaneously, Cu... 3d Orbit and O 2p The hybridization effect of the orbitals narrows the band gap of the composite material, facilitating electron transitions from the valence band to the conduction band and increasing electrical conductivity. Simultaneously, the introduction of the second phase creates heterogeneous interfaces within the composite material. These interfaces scatter phonons, significantly reducing the material's lattice thermal conductivity. The zinc oxide-based composite material of this invention exhibits a conductivity of 470.77 S cm⁻¹ at 800 K. -1 The Seebeck coefficient is -250 μV K. -1 The power factor is 2940.99 μW K. -2 m -1 The thermoelectric figure of merit ZT is 0.53.

[0017] Based on the above technical solutions, this invention solves the technical problems of extremely low carrier concentration, overall low conductivity, and difficulty in improving the power factor of intrinsic ZnO. Intrinsic ZnO itself has insufficient carrier quantity and weak conductivity. Even if modified through recombination, if the structure and interface are not properly controlled, it is still impossible to effectively improve the carrier transport efficiency, resulting in a long-term low power factor and poor thermoelectric conversion capability.

[0018] Based on the above technical solutions, this invention solves the technical problems of excessively high lattice thermal conductivity of ZnO matrix, insufficient phonon scattering mechanism, and inability to effectively reduce thermal conductivity. ZnO is composed of light elements, and its lattice phonons have a long mean free path and fast propagation speed, resulting in extremely high intrinsic thermal conductivity, which is the most critical factor restricting the improvement of ZT. Existing composite methods often cannot form enough effective scattering centers, making it difficult to achieve full-scale scattering of broadband phonons, and the reduction in thermal conductivity is limited.

[0019] Based on the above technical solutions, this invention solves the technical problems of Cu particle agglomeration, uneven distribution, and poor interfacial bonding strength in the preparation of ZnO / Cu composite materials using traditional processes. Physical mixing methods such as solid-phase mixing and ball milling can only achieve macroscopic mixing and cannot achieve uniform dispersion of Cu at the nanoscale. Agglomerated Cu particles not only fail to provide continuous conductivity but also cause internal stress concentration and uneven microstructure, resulting in large fluctuations and poor repeatability of material properties.

[0020] Based on the above technical solutions, this invention solves the technical problems of poor bonding at the ZnO / Cu heterostructure interface, excessive interface defects, and obstructed carrier transport. Traditional methods often result in mechanical bonding between ZnO and Cu, leading to unreasonable interface barriers and high defect density. This reduces carrier mobility and prevents the formation of a stable and effective phonon scattering interface, resulting in a failure to simultaneously improve electrical and thermal performance.

[0021] Based on the above technical solutions, this invention solves the technical problems of lack of systematic optimization of Cu composite ratio and the inability to achieve optimal synergy between electrical conductivity and thermal conductivity. Too little Cu addition results in insufficient improvement in conductivity; too much addition reduces carrier mobility, and excessive interface increases, which in turn deteriorates transport performance. Existing technologies generally lack precise control of the optimal ratio, making it difficult to achieve the best match between power factor and thermal conductivity.

[0022] Based on the above technical solutions, this invention solves the technical problem of Cu's easy oxidation during high-temperature sintering. When sintered directly in air, Cu is easily oxidized to insulating impurities such as CuO or Cu₂O, losing its conductivity-enhancing effect. This invention uses argon atmosphere sintering, which not only solves the Cu oxidation problem, but also increases the oxygen vacancy concentration in zinc oxide under low-oxygen conditions, thereby increasing the carrier concentration and ultimately improving conductivity.

[0023] Based on the above technical solutions, this invention solves the technical problems of complex preparation process conditions, poor consistency of finished product performance, and difficulty in large-scale production. Traditional process routes are long, parameters are inaccurate, and repeatability is poor, making it impossible to stably prepare high-performance ZnO / Cu thermoelectric ceramics in batches. This makes it difficult to transform laboratory results into industrial products, limiting their practical application in fields such as waste heat recovery and high-temperature devices.

[0024] The present invention achieves the following technical effects:

[0025] The ZnO / Cu composite thermoelectric ceramic prepared by this invention has the characteristics of low raw material cost, simple process, no toxic and harmful additives, and excellent comprehensive thermoelectric performance. Moreover, the preparation process has good repeatability and is easy to scale up, which has strong practical value and application prospects.

[0026] This invention uses a hydrothermal method to synthesize ZnO matrix powder, which can effectively control the morphology and particle size of the powder, avoiding problems such as large particles, uneven distribution, and severe agglomeration that are common in traditional solid-phase methods, and providing a high-quality precursor for the subsequent uniform composite of Cu phase.

[0027] Unlike the traditional method of modifying ZnO by element doping, this invention introduces a second phase of metallic Cu into the ZnO matrix to construct a composite system. The high conductivity of the Cu phase is used to improve the carrier concentration and conductivity, while the ZnO / Cu heterostructure enhances phonon scattering, thereby achieving synergistic optimization of electrical and thermal properties.

[0028] The Cu phase selected in this invention is a low-cost metal material that is readily available in industry. Compared with expensive nano-reinforced phases such as Ag and Au, it has a lower cost, does not require complex surface modification treatment, has higher process stability, and is more suitable for large-scale production.

[0029] This invention involves sintering under an argon atmosphere, which not only suppresses the oxidation of the Cu phase at high temperatures but also introduces an appropriate amount of oxygen vacancies into the ZnO matrix, further increasing the carrier concentration and conductivity, and ultimately significantly improving the power factor and ZT value of the material. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of the composite thermoelectric material of the present invention.

[0031] Figure 2 These are scanning electron microscope (SEM) images of the fracture morphology of embodiments (b, c, d, which are embodiments 1, 2, and 3) and comparative example (a) of the present invention.

[0032] Figure 3 These are the UV-Vis coefficient spectra of the embodiments and comparative examples of the present invention.

[0033] Figure 4 These are bandgap diagrams of embodiments and comparative examples of the present invention.

[0034] Figure 5 These are the σ-T curves, Seebeck-T curves, and PF-T curves of the embodiments and comparative examples of the present invention.

[0035] Figure 6 These are Hall effect diagrams of embodiments and comparative examples of the present invention.

[0036] Figure 7 K is the embodiment and comparative example of the present invention. tot -T curve, K E -T curve, K l -T curve graph.

[0037] Figure 8 These are ZT value curves for embodiments and comparative examples of the present invention. Detailed Implementation

[0038] To illustrate the technical solution, implementation process, and technical effects of the present invention in detail, the present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments described herein are merely preferred embodiments of the present invention and are used only as examples to illustrate the present invention, and are not intended to limit the scope of protection of the present invention.

[0039] In this invention, thermoelectric performance testing employs industry-standard characterization methods: electrical conductivity and Seebeck coefficient are simultaneously tested under vacuum using a commercial thermoelectric performance testing system (NAMICRO-Ⅲ), with a test temperature range of 300K-800K. The power factor is calculated based on the test data. The thermal diffusivity is tested using a laser scintillation thermal conductivity meter (Netzsch LFA467), and the specific heat capacity is calibrated using a standard reference sample via a comparative method. Combined with the sample density measured by the Archimedes method, the specific heat capacity is calculated using the formula K. tot =ρ C p The total thermal conductivity is calculated using D, where ρ is the sample density and C is the total thermal conductivity. p ρ is the specific heat capacity, D is the thermal diffusivity, and all tests ensure the accuracy and reliability of the data.

[0040] The specific embodiments of the present invention are as follows:

[0041] Example 1

[0042] A method for preparing Cu composite n-type ZnO thermoelectric ceramics, combined with Figure 1 The preparation process is described in detail below:

[0043] Step 1: Using 0.015 mol zinc acetate dihydrate and 0.075 mol sodium hydroxide as raw materials, add 40 ml of deionized water and stir on a magnetic stirrer for 30 min to obtain a milky white solution.

[0044] Step 2: Add 0.015 mol of citric acid to the solution and stir for 1 hour. Transfer the resulting solution to a high-pressure reactor lined with polytetrafluoroethylene and place it in a forced-air drying oven for hydrothermal reaction, setting the parameters to 140 degrees Celsius and heating for 4 hours.

[0045] Step 3: After natural cooling, wash the product twice each with deionized water and anhydrous ethanol, and then dry it in a drying oven for 12 hours.

[0046] Step 4: Add copper acetate monohydrate with a molar ratio of 0.02 to 40 ml of deionized water and stir for 30 min at a temperature of 70 °C. Then add the prepared zinc oxide and stir for 1 h.

[0047] Step 5: Continue to add the reducing agent L-ascorbic acid, with a molar ratio of 3:1 to copper acetate monohydrate, and heat and stir for 30 minutes.

[0048] Step 6: Wash the solution by centrifugation with deionized water and anhydrous ethanol, and place the precipitate into a vacuum drying oven. Set the vacuum drying oven to 60 degrees Celsius and dry for 14 hours to obtain ZnO / Cu composite powder.

[0049] Step 7: Weigh 0.6g of powder and pour it into the mold. Hold the pressure at 120MPa for 3 minutes to obtain the molded sample.

[0050] Step 8: Place the block in an argon atmosphere and sinter it in a muffle furnace. Heat it to 1000 degrees Celsius at a heating rate of 10℃ / min and hold it for 60 minutes. After holding, allow it to cool naturally to room temperature to obtain the ZnO / Cu thermoelectric composite material.

[0051] Step nine involves characterizing the sample in this embodiment using SEM, and testing its electrical conductivity, Seebeck coefficient, and thermal conductivity, as well as calculating the ZT value. The results show that adding Cu nanoparticles to zinc oxide narrows the band gap of the composite material, facilitating electron transitions from the valence band to the conduction band, thereby increasing carrier concentration and ultimately improving electrical conductivity. At 800 K, the electrical conductivity is 239 S cm⁻¹. -1 Furthermore, the addition of Cu nanoparticles increases the number of interfacial scattering centers in the matrix, leading to a decrease in lattice thermal conductivity. Since the contribution of lattice thermal conductivity to the total thermal conductivity is far greater than that of electronic thermal conductivity, the total thermal conductivity is significantly reduced, reaching 5.18 W / m² at 800 K. -1 K -1In summary, the ZT value of the ZnO / 0.02Cu composite thermoelectric material is 0.35 at 800K.

[0052] Example 2

[0053] The operation steps are the same as in Example 1, except that the molar ratio of copper acetate monohydrate in step four is changed to 0.04.

[0054] The samples in this embodiment were characterized by SEM, and their electrical conductivity, Seebeck coefficient, and thermal conductivity were measured. The ZT value was also calculated. The results show that adding Cu nanoparticles to zinc oxide narrows the band gap of the composite material, facilitating electron transitions from the valence band to the conduction band, thereby increasing carrier concentration and ultimately improving electrical conductivity. At 800 K, the electrical conductivity was 470 Scm. -1 Furthermore, the addition of Cu nanoparticles increases the number of interfacial scattering centers in the matrix, leading to a decrease in lattice thermal conductivity. Since the contribution of lattice thermal conductivity to the total thermal conductivity is far greater than that of electronic thermal conductivity, the total thermal conductivity is significantly reduced, reaching 4.45 W / m² at 800 K. -1 K -1 In summary, the ZT value of the ZnO / 0.04Cu composite thermoelectric material is 0.53 at 800K.

[0055] Example 3

[0056] The operation steps are the same as in Example 1, except that the molar ratio of copper acetate monohydrate in step four is changed to 0.05.

[0057] The samples in this embodiment were characterized by SEM, and their electrical conductivity, Seebeck coefficient, and thermal conductivity were measured. The ZT value was also calculated. The results show that adding Cu nanoparticles to zinc oxide narrows the band gap of the composite material, facilitating electron transitions from the valence band to the conduction band, thereby increasing the carrier concentration and ultimately improving the electrical conductivity. At 800 K, the electrical conductivity was 434 Scm. -1 Furthermore, the addition of Cu nanoparticles increases the number of interfacial scattering centers in the matrix, leading to a decrease in lattice thermal conductivity. Since the contribution of lattice thermal conductivity to the total thermal conductivity is far greater than that of electronic thermal conductivity, the total thermal conductivity is significantly reduced, reaching 5.06 W / m² at 800 K. -1 K -1 In summary, the ZT value of the ZnO / 0.05Cu composite thermoelectric material is 0.42 at 800K.

[0058] Comparative Example 1

[0059] The operation steps are basically the same as in Example 1, except that steps four to six are omitted to obtain ZnO thermoelectric material.

[0060] The samples in this embodiment were characterized by SEM, and their electrical conductivity, Seebeck coefficient, and thermal conductivity were measured. The ZT value was also calculated. The results show that the electrical conductivity at 800 K is 42 S / m. -1 The total thermal conductivity is 9.37 W / m. -1 K -1 The ZT value is 0.04.

[0061] This invention significantly improves the electrical conductivity of zinc oxide-based thermoelectric materials through a composite strategy, while effectively reducing their thermal conductivity, thereby increasing their ZT value.

[0062] Figure 2 The fracture morphology of the embodiments of the present invention (b, c, d are embodiments 1, 2, and 3) and the comparative example (a) are shown in the scanning electron microscope (SEM) images, illustrating that the composite does not significantly change the morphology of the sample.

[0063] Figure 3 The UV-Vis coefficient spectra of embodiments and comparative examples of the present invention are shown. It is noted that the intrinsic absorption edge of the composite sample exhibits a red shift, and the red shift effect becomes more pronounced with increasing Cu content, which may lead to a decrease in the band gap width of the sample.

[0064] Figure 4 The bandgap diagrams of embodiments and comparative examples of the present invention are shown, illustrating that: when the bandgap width of the sample is reduced, electrons can more easily transition from the valence band to the conduction band, thereby improving conductivity.

[0065] Figure 5 The σ-T curves, Seebeck-T curves, and PF-T curves of embodiments and comparative examples of the present invention are shown. It is illustrated that the conductivity of the composite sample is higher than that of pure ZnO. Although the absolute value of the Seebeck coefficient is reduced, the contribution of the increase in conductivity to the power factor is greater than the contribution of the decrease in the absolute value of the Seebeck coefficient, resulting in a higher power factor for the composite sample than that for pure ZnO.

[0066] Figure 6 Hall effect diagrams of embodiments and comparative examples of the present invention are shown. It is explained that the increase in conductivity of the composite sample is due to the combined effect of carrier concentration and carrier mobility. Although the carrier concentration and carrier mobility of the optimal sample Example 2 are not at their maximum values, the combined effect of the two results in the highest conductivity of the sample.

[0067] Figure 7 K is shown in the embodiments of the present invention and comparative examples. tot -T curve, K E -T curve, K l -T curve diagram, indicating that the thermal conductivity of the examples decreased compared to the comparative examples, especially the lattice thermal conductivity K. lThis indicates that the scattering of phonons at the two-phase interface significantly reduces thermal conductivity.

[0068] Figure 8 The ZT value curves of the embodiments and comparative examples of the present invention are shown. It is noted that the ZT values ​​of the embodiments are higher than those of the comparative examples, with the highest being that of Embodiment 2, indicating that the thermoelectric conversion efficiency of this embodiment is optimal.

[0069] For those skilled in the art, the present invention is obviously not limited to the specific details of the above exemplary embodiments. Without departing from the core concept and essential characteristics of the present invention, those skilled in the art can make reasonable adjustments, optimizations, and improvements to the technical solutions of the present invention to adapt to different application scenarios and process conditions. Therefore, the above embodiments are merely illustrative examples of the present invention and do not constitute any limitation on the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims. All modifications, variations, and equivalent solutions falling within the scope of the claims and their equivalents should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing Cu composite n-type ZnO thermoelectric ceramics, characterized in that, The specific steps are as follows: Preparation steps of ZnO powder: Pure ZnO powder with regular morphology and uniform particle size is synthesized by hydrothermal method; Preparation steps of ZnO / xCu composite powder: Cu nanoparticles are uniformly composited onto the surface of ZnO powder by solution reduction, and the composite powder is obtained after cooling and drying; where x is 0, 0.02, 0.04, 0.05; The steps for compound powder compression molding are as follows: ZnO / xCu powder is compressed into shape using an electric tablet press; Preparation steps of Cu composite ZnO-based thermoelectric ceramics: Sintering is carried out under argon atmosphere protection to obtain dense and highly stable Cu composite ZnO-based thermoelectric ceramics.

2. The preparation method of Cu composite n-type ZnO thermoelectric ceramic according to claim 1, characterized in that: In the preparation of ZnO powder, the zinc source used is zinc acetate dihydrate, sodium hydroxide is used as the mineralizing agent, citric acid is used as the morphology control agent, the reaction temperature is 140℃, and the holding time is 4h.

3. The preparation method of Cu composite n-type ZnO thermoelectric ceramic according to claim 1, characterized in that: In the preparation of ZnO / xCu composite powder, copper acetate monohydrate was used as the copper source and L-ascorbic acid as the reducing agent, and Cu was prepared under 70℃ water bath conditions. 2+ The reduction and homogeneous compounding.

4. The preparation method of Cu composite n-type ZnO thermoelectric ceramic according to claim 3, characterized in that: In the preparation steps of ZnO / xCu composite powder, ZnO precursor powder with regular morphology and uniform particle size is mixed with copper acetate monohydrate solution. Under the conditions of heating and stirring in a water bath at 70℃, L-ascorbic acid is added to carry out a reduction reaction for 30 min. After the reaction is completed and naturally cooled to room temperature, the powder is washed three times by centrifugation with deionized water and anhydrous ethanol, and then vacuum dried at 60℃ for 12 h to obtain ZnO / xCu composite powder.

5. The method for preparing Cu composite n-type ZnO thermoelectric ceramics according to claim 1, characterized in that: In the composite powder pressing process, the electric tablet press is operated at a pressure of 120 MPa and a holding time of 3 minutes to obtain a flat, crack-free blank.

6. The method for preparing Cu composite n-type ZnO thermoelectric ceramics according to claim 1, characterized in that: In the preparation steps of Cu composite ZnO-based thermoelectric ceramics, the pressure-formed green body is placed in a sealed quartz tube under an argon atmosphere for sintering. The temperature is raised to 1000℃ at a heating rate of 10℃ / min and held for 1 hour. After the holding period, the green body is naturally cooled to room temperature in the furnace to obtain dense Cu composite n-type ZnO thermoelectric ceramics.

7. A Cu composite n-type ZnO thermoelectric ceramic, characterized in that: The material is prepared by the preparation method described in any one of claims 1-6, and has a chemical composition of ZnO / xCu, where x is the molar ratio of Cu to the composite material, and x = 0, 0.02, 0.04, or 0.

05. Cu is uniformly distributed in the form of nanoparticles at the ZnO grain boundaries, forming a stable heterogeneous interface with ZnO, without the formation of impurity phases, and is an n-type semiconductor.

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