A method for preparing a barrier layer for GeTe-based thermoelectric devices

Abstract

The application belongs to the technical field of thermoelectric materials and devices, and specifically provides a preparation method of a barrier layer for a GeTe-based thermoelectric device, to solve the problems of high preparation cost, poor barrier effect, and poor interface combination of the existing barrier layer; in the application, firstly, a GeTe ingot is prepared by a high-temperature melting method, to effectively improve the purity and uniformity of the material and reduce impurities and defects; then, a layered structure is constructed by using a layered paving process, and an SPS sintering process is combined to activate the surface of the Nb foil through a Te transition layer, so as to promote the mutual diffusion and reaction of the GeTe matrix and the Nb barrier layer, promote the good combination of the thermoelectric matrix and the barrier layer, and improve the interlayer combination tightness; finally, the Nb barrier layer that is tightly combined with the thermoelectric matrix is prepared, and the interface contact resistance is low, so that the service stability of the thermoelectric device is effectively improved; and the application also has the advantages of simple and controllable preparation process, which is beneficial to reducing the preparation cost.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric materials and devices, and relates to GeTe-based thermoelectric devices. Specifically, it provides a method for preparing a barrier layer for GeTe-based thermoelectric devices. Background Technology

[0002] GeTe-based thermoelectric materials, as one of the preferred materials for thermoelectric conversion in the mid-temperature range (500K~773K), possess excellent thermoelectric properties and have broad application prospects in fields such as industrial waste heat recovery and new energy power generation. The service stability and thermoelectric conversion efficiency of GeTe-based thermoelectric devices depend on the interfacial properties between the thermoelectric matrix and the electrodes. Among these, Ge element is prone to diffusion reaction with electrode materials, forming brittle intermetallic compounds, which leads to increased interfacial contact resistance, interlayer delamination, and ultimately device failure. Therefore, the diffusion of Ge element becomes a key issue leading to device performance degradation.

[0003] To address the aforementioned issues, a barrier layer is typically placed between the thermoelectric substrate and the electrodes in GeTe-based thermoelectric devices to prevent the diffusion of Ge. Currently, barrier layer materials are mostly Mo, Ti, and Fe-Ni-Co alloys, which suffer from poor compatibility with GeTe-based materials, weak interfacial bonding, and limited barrier effect. Niobium (Nb), as a transition metal, possesses advantages such as a high melting point, good chemical stability, and low reactivity with Ge and Te, theoretically making it an ideal material for barrier layers in GeTe-based thermoelectric devices. Studies have shown that Nb, as a barrier layer, can effectively suppress the interfacial diffusion of active elements. Even after long-term high-temperature aging, the thickness of the interfacial diffusion layer increases slowly, maintaining excellent barrier performance and low interfacial contact resistivity. This characteristic has been verified in other thermoelectric systems. However, there are currently no publicly available reports on using Nb as a barrier layer in GeTe-based thermoelectric devices, nor is a mature fabrication process developed, preventing the full utilization of Nb's advantages and limiting the industrial application of GeTe-based thermoelectric devices. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a barrier layer for GeTe-based thermoelectric devices, in order to solve the problems of high cost, poor barrier effect, and loose interface bonding of existing barrier layers.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for fabricating a barrier layer for GeTe-based thermoelectric devices includes the following steps:

[0007] Step 1. GeTe ingots are prepared by high-temperature melting and then GeTe powder is obtained by grinding.

[0008] Step 2. Select Nb foil and Te powder, and lay GeTe powder, Te powder and Nb foil in layers in the mold in the order of GeTe-Te-Nb, so that the GeTe powder layer, Te powder layer and Nb foil form a stacked structure;

[0009] Step 3. Place the mold in the SPS equipment and sinter it under vacuum. The sintering temperature is 520℃~550℃, the sintering pressure is 50MPa~60MPa, and the holding time is 5min~10min. After sintering, cool it to room temperature to prepare an Nb barrier layer on the GeTe thermoelectric substrate.

[0010] Furthermore, the method for preparing the barrier layer for GeTe-based thermoelectric devices further includes:

[0011] Step 4. After completing step 3, perform annealing under inert gas protection at a temperature of 500℃~550℃ for 48h~72h. After annealing, cool to room temperature.

[0012] Furthermore, in step 1, the high-temperature melting method specifically involves: weighing Ge and Te elemental raw materials in a 1:1 molar ratio, placing them into a quartz tube, and sealing it after vacuuming; placing the sealed quartz tube in a pit furnace and melting it at 900~1100℃ for 20~24 hours, then cooling it to room temperature with the furnace to obtain a GeTe ingot; even further, the purity of the Ge and Te elemental raw materials is ≥99.999%, and the vacuum degree in the quartz tube is not higher than 10. -3 Pa.

[0013] Furthermore, in step 2, the purity of the Nb foil is ≥99.6%, and the purity of the Te powder is ≥99.99%, with a particle size of 1μm~10μm.

[0014] Furthermore, in step 2, the thickness of the GeTe powder layer is 3mm~5mm, the thickness of the Te powder layer is 10μm~300μm, and the thickness of the Nb foil is 100μm~200μm.

[0015] Furthermore, in step 3, the cooling rate is 20℃ / min~30℃ / min.

[0016] Furthermore, in step 3, the thickness of the Nb barrier layer is 100μm~200μm, and the density is ≥95%; even further, the density is ≥98%.

[0017] Based on the above technical solution, the beneficial effects of the present invention are as follows:

[0018] This invention provides a method for preparing a barrier layer for GeTe-based thermoelectric devices. On one hand, it proposes an Nb barrier layer for GeTe-based thermoelectric devices, with a preferred thickness of 100μm~200μm. This thickness range ensures effective element diffusion barrier while avoiding excessive thickness that could increase interfacial resistance. On the other hand, it proposes a method for preparing the Nb barrier layer. First, a high-temperature melting method is used to prepare GeTe ingots, which effectively improves the purity and uniformity of the GeTe material, reduces impurities and defects, and lays the foundation for subsequent layered sintering and interlayer bonding. Then, a layered structure is constructed using a layered planarization process to ensure that each powder layer is flat and uniform, with no accumulation or gaps between adjacent powder layers. Simultaneously, a Te transition layer is introduced, combined with SPS sintering technology, and the process parameters such as sintering temperature and sintering pressure are controlled. The rigorous design ensures that the Te transition layer is molten and extruded during sintering. Due to the low chemical reaction temperature between Te and Nb, Te can activate the Nb surface during this process, promoting the diffusion and reaction between the GeTe matrix and the Nb barrier layer, significantly improving the interlayer bonding tightness, thus solving the problem of poor interfacial bonding between the GeTe matrix and the Nb barrier layer. Finally, an Nb barrier layer with a density ≥98% is prepared and forms a tight bond with the GeTe thermoelectric matrix. In addition, the SPS sintering process has the advantages of rapid heating, short sintering time, and low energy consumption, which can realize the integrated sintering of the GeTe thermoelectric matrix and the Nb barrier layer, further ensuring the tight interlayer bonding, while avoiding excessive element diffusion caused by long-term sintering under high temperature conditions, thus ensuring the barrier performance of the barrier layer.

[0019] In summary, this invention provides a method for preparing a barrier layer for GeTe-based thermoelectric devices. A tightly bonded Nb barrier layer is successfully prepared on a GeTe thermoelectric substrate. This Nb barrier layer exhibits low reactivity with Ge and Te elements, does not form brittle intermetallic compounds, and thus effectively blocks the diffusion of Ge and Te elements. Simultaneously, the Nb barrier layer is tightly bonded to the GeTe thermoelectric substrate, resulting in low interfacial contact resistance, which significantly improves the service stability of GeTe-based thermoelectric devices. Furthermore, this invention has the advantages of simple and controllable preparation process, which helps reduce production costs and is suitable for industrial-scale mass production. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of the barrier layer preparation method for GeTe-based thermoelectric devices in Embodiment 1 of the present invention.

[0021] Figure 2 This is a physical image of the GeTe-Nb-GeTe bulk sample in Embodiment 1 of the present invention.

[0022] Figure 3 This is an EDS image of the GeTe-Nb-GeTe bulk sample in Example 1 of the present invention.

[0023] Figure 4 This is a cross-sectional SEM image of the GeTe-Nb-GeTe bulk sample in Embodiment 1 of the present invention.

[0024] Figure 5 This is a line scan result at point 1 of the online data of the GeTe-Nb-GeTe bulk sample in Embodiment 1 of the present invention.

[0025] Figure 6 This is a line scan result at point 2 of the online data of the GeTe-Nb-GeTe bulk sample in Embodiment 1 of the present invention.

[0026] Figure 7 This is a line scan result at point 3 of the online data of the GeTe-Nb-GeTe bulk sample in Embodiment 1 of the present invention.

[0027] Figure 8 The figure shows the interface resistance test results of the GeTe-Nb-GeTe bulk sample in Embodiment 1 of the present invention.

[0028] Figure 9 The figure shows the interface resistance test results of the GeTe-Nb-GeTe bulk sample in Embodiment 2 of the present invention.

[0029] Figure 10 This is a physical image of the SPS sintered ingot in Comparative Example 1 of this invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0031] Example 1: This example provides a method for preparing a barrier layer for GeTe-based thermoelectric devices. A niobium (Nb) barrier layer with a thickness of 100 μm and a density of 98% is prepared, and the surface is free of cracks, pores, and impurities. The niobium barrier layer is applied in GeTe-based thermoelectric devices and is disposed between the thermoelectric substrate and the electrode to solve the problem of Ge element diffusion. It should be noted that, in order to more intuitively present the barrier effect of the niobium barrier layer, this example places the niobium barrier layer between two thermoelectric substrates, and verifies the feasibility of the niobium barrier layer by EDS interface surface scanning and interface contact resistivity testing.

[0032] like Figure 1 The diagram shows a flow chart of the barrier layer fabrication method for GeTe-based thermoelectric devices, which specifically includes the following steps:

[0033] Step 1. Preparation of GeTe powder;

[0034] Select elemental Ge and elemental Te with a purity ≥ 99.999%, weigh them in a 1:1 molar ratio, and place them into a clean quartz tube. Use a vacuum system to evacuate the quartz tube to a vacuum level not exceeding 10. -3 Pa, then the quartz tube was sealed with an oxyhydrogen flame sealing machine; the sealed quartz tube was placed in a pit furnace and kept at 900℃ for 20 hours, and then cooled to room temperature with the furnace to obtain a GeTe bulk ingot; the GeTe bulk ingot was placed in an agate mortar and ground for 10 minutes to obtain uniform GeTe powder.

[0035] Step 2. Lay the tiles in layers;

[0036] Nb foil with a purity of 99.6% and a thickness of 100 μm and Te powder with a purity of 99.99% and a particle size of 5 μm were selected. In an argon glove box, GeTe powder, Nb foil and Te powder were layered in a graphite mold (circular with a diameter of 10 mm) in the order of GeTe-Te-Nb-Te-GeTe. The thickness of the GeTe powder layer was 3 mm and the thickness of the Te powder layer was 50 μm. During the layering process, it was ensured that each layer of powder was flat and uniform, so that there was no accumulation or gaps between the powder layers.

[0037] Step 3. SPS sintering and shaping;

[0038] The graphite mold was placed in an SPS device and sintered under vacuum at a temperature of 550℃, a pressure of 50MPa, and a holding time of 10min. After sintering, the temperature was lowered to room temperature at a rate of 25℃ / min to obtain a GeTe-Nb-GeTe bulk sample.

[0039] Based on the above steps, this embodiment successfully prepared a niobium (Nb) barrier layer with a thickness of 100 μm and a density of 98%, with no cracks, pores, or impurities on the surface. More importantly, a Te powder layer was set as a Te transition layer during the preparation process. Through strict design of process parameters such as sintering temperature and sintering pressure during SPS sintering, the Te transition layer was converted into a molten state and extruded. Due to the low reaction temperature between Te and Nb, the Nb surface was activated by Te, which promoted the mutual diffusion and reaction between the GeTe thermoelectric matrix and the Nb barrier layer during subsequent heat preservation, significantly improving the interlayer bonding tightness, thereby solving the problem of poor interfacial bonding between the GeTe matrix and the Nb barrier layer. Furthermore, the preparation process is simple and cost-controllable.

[0040] The beneficial effects of the present invention will be described in detail below with reference to testing. The bulk sample prepared in the above steps was cut along a direction perpendicular to the layered structure. The cut surface was ground and polished to remove the surface oxide layer and impurities. The elemental distribution of the cross section of the bulk sample was analyzed by EDS (energy dispersive spectroscopy) to observe the distribution of Ge, Nb, and Te, in order to observe whether Ge diffuses into the Nb barrier layer. At the same time, the interfacial contact resistivity between the Nb barrier layer and the adjacent GeTe thermoelectric substrate was tested at room temperature using the four-probe method. If the EDS detection shows that Ge is only distributed in the GeTe thermoelectric substrate and there is no obvious diffusion peak in the Nb barrier layer, and the interfacial contact resistivity is ≤20μΩ·cm, then the analysis is successful. 2 This indicates that the Nb barrier layer has a good blocking effect and is feasible.

[0041] like Figure 2 The image shown is a physical picture of the GeTe-Nb-GeTe bulk sample in this embodiment. As can be seen from the figure, there is no obvious interface delamination or fracture marks on the bulk sample, indicating that the Nb barrier layer and the GeTe thermoelectric matrix are well bonded.

[0042] like Figure 3 The figure shows the EDS image of the GeTe-Nb-GeTe bulk sample in this embodiment. As can be seen from the figure, the Ge and Te elements are only distributed in the GeTe thermoelectric matrix, and there is no obvious diffusion peak in the Nb barrier layer. The element distribution boundary is clear.

[0043] like Figure 4 The image shown is a cross-sectional SEM image of the GeTe-Nb-GeTe bulk sample in this embodiment. Three line scan positions are selected and labeled as line data 1, line data 2, and line data 3. The results for the three line scan positions are shown in the image below. Figure 5 , Figure 6 , Figure 7 As shown, this further demonstrates that the Nb barrier layer bonds well with the GeTe thermoelectric matrix, and that the Nb barrier layer has a significant barrier effect.

[0044] like Figure 8 The figure shows the interface resistance test results of the GeTe-Nb-GeTe bulk sample in this embodiment. As can be seen from the figure, the interface contact resistivity test result is 2.925 μΩ·cm. 2 Much less than 20 μΩ·cm 2 This indicates that the Nb blocking layer obtained in this embodiment was successfully prepared and has excellent blocking effect.

[0045] Example 2 also provides a method for preparing a barrier layer for GeTe-based thermoelectric devices, obtaining a niobium (Nb) barrier layer with a thickness of 200 μm (in step 2, the Nb foil has a thickness of 200 μm), a density of 99%, and a surface free of cracks, pores, and impurities; the difference between this example and Example 1 is that it also includes:

[0046] Step 4. Annealing treatment;

[0047] The GeTe-Nb-GeTe bulk sample obtained in step 3 was annealed under inert gas protection at a temperature of 500℃ for 48 hours and then cooled to room temperature.

[0048] After annealing, the interfacial contact resistivity test results between the Nb barrier layer and the GeTe thermoelectric substrate are as follows: Figure 9 As shown, specifically 0.86 μΩ·cm 2 Therefore, annealing can further promote the interfacial bonding between the Nb barrier layer and the GeTe thermoelectric substrate, thereby improving the interfacial stability and long-term service performance of GeTe-based thermoelectric devices.

[0049] Furthermore, to more intuitively demonstrate the beneficial effects of the present invention, a comparative example is also provided, the only difference from Example 1 being that: in step 2, GeTe powder and Nb foil are layered and laid in a graphite mold in the order of GeTe-Nb-GeTe; the sample after SPS sintering is as follows. Figure 10 As shown in the figure, without the Te transition layer, the Nb barrier layer and the GeTe thermoelectric matrix cannot be bonded together at all.

[0050] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A method for preparing a barrier layer for GeTe-based thermoelectric devices, characterized in that, Includes the following steps: Step 1. GeTe ingots are prepared by high-temperature melting and then GeTe powder is obtained by grinding. Step 2. Select Nb foil and Te powder, and lay GeTe powder, Te powder and Nb foil in layers in the mold in the order of GeTe-Te-Nb, so that the GeTe powder layer, Te powder layer and Nb foil form a stacked structure; Step 3. Place the mold in the SPS equipment and sinter it under vacuum. The sintering temperature is 520℃~550℃, the sintering pressure is 50MPa~60MPa, and the holding time is 5min~10min. After sintering, cool it to room temperature to prepare an Nb barrier layer on the GeTe thermoelectric substrate.

2. The method for preparing a barrier layer for a GeTe-based thermoelectric device according to claim 1, characterized in that, Also includes: Step 4. After completing step 3, perform annealing under inert gas protection at a temperature of 500℃~550℃ for 48h~72h. After annealing, cool to room temperature.

3. The method for preparing a barrier layer for a GeTe-based thermoelectric device according to claim 1, characterized in that, In step 1, the high-temperature melting method specifically refers to: Ge and Te elemental raw materials are weighed in a 1:1 molar ratio, placed in a quartz tube, and sealed after vacuuming. The sealed quartz tube is then placed in a pit furnace and melted at 900~1100℃ for 20~24 hours. The furnace is then cooled to room temperature to obtain GeTe ingots.

4. The method for preparing a barrier layer for a GeTe-based thermoelectric device according to claim 3, characterized in that, The purity of Ge and Te elemental raw materials is ≥99.999%.

5. The method for preparing a barrier layer for a GeTe-based thermoelectric device according to claim 3, characterized in that, The vacuum level in the quartz tube is no higher than 10. -3 Pa.

6. The method for preparing a barrier layer for a GeTe-based thermoelectric device according to claim 1, characterized in that, In step 2, the purity of Nb foil is ≥99.6%, and the purity of Te powder is ≥99.99%, with a particle size of 1μm~10μm.

7. The method for preparing a barrier layer for a GeTe-based thermoelectric device according to claim 1, characterized in that, In step 2, the thickness of the GeTe powder layer is 3mm~5mm, the thickness of the Te powder layer is 10μm~300μm, and the thickness of the Nb foil is 100μm~200μm.

8. The method for preparing a barrier layer for a GeTe-based thermoelectric device according to claim 1, characterized in that, In step 3, the cooling rate is 20℃ / min to 30℃ / min.

9. The method for preparing a barrier layer for a GeTe-based thermoelectric device according to claim 1, characterized in that, In step 3, the thickness of the Nb barrier layer is 100μm~200μm, and the density is ≥95%.

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