Nd / Zr-doped high-performance BaHfS3-based thermoelectric block material and preparation method thereof

Abstract

The invention is suitable for the technical field of thermoelectric materials, and provides an Nd / Zr-doped high-performance BaHfS3-based thermoelectric block material and a preparation method thereof, and the preparation method comprises the following steps: weighing and mixing BaCO3, HfO2, ZrO2 or Nd2O3 raw material powder according to a target stoichiometric ratio, then placing in a muffle furnace, carrying out heat preservation for 1.8-2.2 hours at 1150-1250 DEG C, and carrying out solid-phase sintering to obtain an oxide precursor BaHf (1-x) MxO3, 0 < = x < 1; the preparation method comprises the following steps: by taking BaHf (1-x) MxO3 as a raw material and carbon disulfide as a sulfur source, carrying out anion replacement on BaHf (1-x) MxO3 under the conditions that the temperature is 950-1050 DEG C and the temperature is kept for 2-12 hours, and converting oxide into sulfide, so as to obtain BaHf (1-x) And after the BaHf < 1-x > MxS3 powder is subjected to cold press molding, rapid sintering is carried out, the sintering condition is 1550-1650 DEG C, heat preservation is carried out for 5 minutes, and a target block material is obtained. The BaHfS3-based block material with a high thermoelectric figure of merit is obtained through an innovative material component design and an adaptive preparation process, BaHfS3 is introduced into the thermoelectric field, the BaHfS3-based block material has initiative in the thermoelectric application aspect of Hf-based sulfide perovskite, and the application potential of BaHfS3 in the thermoelectric conversion field is disclosed.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric materials technology, and particularly relates to a high-performance BaHfS3-based thermoelectric bulk material doped with Nd / Zr and its preparation method. Background Technology

[0002] Thermoelectric conversion technology is a solid-state energy technology that enables the direct conversion between thermal and electrical energy. It can be applied in fields such as industrial waste heat recovery and power supply for aerospace probes. However, current mainstream thermoelectric material systems, such as Bi₂Te₃, PbTe, GeTe, AgSbTe₂, and SiGe, typically contain expensive, scarce, and toxic elements like Te / Ag / Ge / Pb, severely limiting their large-scale application. Therefore, developing novel thermoelectric materials based on environmentally friendly elements with abundant reserves is an urgent need in this field.

[0003] Existing technologies provide preparation techniques for Zr-based systems such as BaZrS3 (patent number ZL202210442365.4) and SrZrS3 (patent number ZL202411441957.X), providing a basic method for thermoelectric research on sulfide perovskites. However, BaZrS3 and SrZrS3 have poor thermal stability (significant volatilization and performance deterioration occur when the application temperature is >350℃), which is not conducive to practical applications. Due to the high Hf-O bond energy, strong chemical inertness, and high activation energy of the HfO2 precursor, and the extreme stability of the intermediate HfS2, the phase purity and synthesis efficiency of the final product are directly affected, resulting in poor intrinsic BaHfS3 performance. Currently, there are no dedicated BaHfS3 preparation process parameters that can overcome the unique chemical inertness and the formation of impurity phases, nor are there effective material design (such as elemental doping) and electroacoustic transport control schemes to regulate and improve its thermoelectric properties. Furthermore, existing related technologies lack universality; directly applying them while ignoring the inherent characteristics of BaHfS3 will lead to low sulfidation conversion rates and the formation of difficult-to-remove impurity phases (such as HfO2 and HfS2). This constitutes an inherent technical obstacle in the preparation of high-performance BaHfS3. Therefore, a novel, original technical solution encompassing material preparation and performance regulation is urgently needed for bulk BaHfS3 thermoelectric materials.

[0004] The current method for preparing BaHfS3 is mainly a solid-state method, which involves mixing BaS and HfS2 and then melting them at 1100℃ for 48 hours. The product contains 20 mol% of HfO2 impurity phase (Journal of the American Chemical Society, 2019, 141(13), 5343-5349). Alternatively, BaS, Zr, and S powders can be mixed with BaCl2 as raw materials and then melted. This method requires strict control of the element ratio, otherwise ZrS3 and HfS3 impurity phases that are difficult to remove will be generated (ChemPhysChem, 2024, 25(23), e202400340). In addition, this high-temperature melting method has problems such as complicated preparation process and high energy consumption, impurity phase in the product, and easy volatilization of low melting point elements, which is not conducive to the exploration and optimization of the thermoelectric properties of BaHfS3. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing Nd / Zr-doped high-performance BaHfS3-based thermoelectric bulk materials, aiming to solve the problems mentioned in the background art.

[0006] The present invention is implemented as follows: a method for preparing a high-performance BaHfS3-based thermoelectric bulk material doped with Nd / Zr includes the following steps: (1) Solid-state doping: Weigh the raw material powders of BaCO3, HfO2, ZrO2 or Nd2O3 according to the target stoichiometric ratio, mix them, and then place them in a muffle furnace for solid-state sintering at 1150-1250℃ for 1.8-2.2 hours to obtain the oxide precursor BaHf 1-x M x O3, where M is Nd or Zr, 0 ≤ x < 1; (2) Gas-phase sulfidation: Using carbon disulfide as the sulfur source, BaHf is subjected to sulfidation at 950-1050℃ for 2-12 hours. 1- x M x O3 undergoes anion substitution, converting the oxide into a sulfide to obtain BaHf. 1-x M x S3 powder; (3) Rapid sintering: BaHf 1-x M x S3 powder is cold-pressed and then rapidly sintered at 1550-1650℃ for 5 minutes to obtain the target block material.

[0007] Another objective of this invention is to provide a high-performance BaHfS3-based thermoelectric bulk material doped with Nd / Zr, which is prepared using the above-described preparation method.

[0008] Another objective of this invention is to provide an application of Nd / Zr-doped high-performance BaHfS3-based thermoelectric bulk material in the field of thermoelectric conversion.

[0009] This invention synthesizes a BaHfO3-based precursor through solid-phase doping, obtains BaHfS3-based powder through gas-phase sulfidation, and then uses a rapid sintering method to obtain a high-density bulk material, thus preparing a high-phase-purity, high-density BaHfS3 bulk material. This method is low-cost and has a short production cycle. The material possesses excellent thermoelectric performance potential and is rich in constituent elements, containing no toxic elements such as Pb / Te / Ge / Ag, making it environmentally friendly. Specifically: Regarding the preparation method, this invention has developed a relatively inexpensive, efficient, and mass production process. The cost of raw materials (BaCO3, HfO2, and doped oxides) is significantly lower than that of solid-state reactions (BaS, HfS2), and the preparation cycle is significantly shortened (total preparation process ≤ 20 hours, while traditional methods require tens of hours). This overcomes the drawbacks of traditional methods, such as long preparation processes, harsh preparation conditions, and high raw material costs, as well as the problems of easily generating impurities and component segregation. It can achieve mass production of BaHfS3 bulk materials with a density close to 100% and high phase purity. Based on this preparation technology, it is possible to achieve component doping with different elements and contents to regulate related properties such as photothermal and electrical properties, expand its multifunctional applications, and obtain a maximum ZT value of 0.47 through component regulation strategy. The Zr-doped BaHfS3 bulk material prepared in this invention exhibits the following performance breakthroughs: a maximum Seebeck coefficient of -318.53 μV / K at 773 K, and a maximum electrical conductivity of 22.55 × 10⁻⁶ at 373 K. 3 The lowest lattice thermal conductivity is 0.88 W / mK at 723K, and the maximum ZT value at 723K is 0.47. These thermoelectric performance parameters are significantly better than those of BaZrS3 (patent number ZL202210442365.4) and SrZrS3 (patent number ZL202411441957.X) reported in the prior art. In addition, this bulk material has good thermal stability in the temperature range of 300~773K, which is also significantly better than the sulfide perovskite materials disclosed in the prior art. Compared with existing technologies, the embodiments of this invention have significant advantages in thermoelectric performance, environmental friendliness, and industrial benefits, which can greatly promote the commercial application of sulfide perovskites. At the same time, based on the preparation method provided by the embodiments of this invention, the design of Ba(Hf,Zr)S3-based solid solutions can be further explored, and the trace doping composition can be optimized to synergistically regulate electron transport and phonon scattering, thereby achieving a breakthrough in ZT value. This provides a new and referable solution for the development of other perovskite thermoelectric materials that are difficult to sulfide. Attached Figure Description

[0010] Figure 1 A flowchart illustrating a method for preparing a high-performance BaHfS3-based thermoelectric bulk material doped with Nd / Zr according to an embodiment of the present invention; Figure 2 The images show the XRD patterns of the BaHfS3 matrix bulk materials prepared in Examples 1, 2, and 3 of this invention. Figure 3 The image shows the SEM morphology of the BaHfS3 bulk material prepared in Example 1 of this invention. Figure 4 This is an elemental distribution mapping diagram of the BaHfS3 bulk material prepared in Example 1 of the present invention; Figure 5 The energy spectrum and atomic ratio of the BaHfS3 bulk material prepared in Example 1 of this invention; Figure 6 The variable-temperature thermoelectric properties of the BaHfS3 bulk materials prepared in Examples 1, 2, and 4 of this invention are shown, where a is the Seebeck coefficient, b is the electrical conductivity, c is the power factor, d is the thermal conductivity, e is the lattice thermal conductivity, and f is the ZT value. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0012] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0013] Example 1: BaHfS3 bulk thermoelectric material, its preparation process is as follows: Figure 1 As shown, the specific steps include: Step S1, Precursor Design and Synthesis: According to the stoichiometric ratio of the chemical formula BaHfO3, accurately weigh BaCO3 and HfO2 powders and mix them evenly. Place the powder mixture in a corundum crucible and heat it to 1200℃ at 10℃ / min in a muffle furnace under air atmosphere. After holding at this temperature for 2 hours, allow it to cool naturally to room temperature to obtain BaHfO3 oxide precursor powder. Step S2, gas phase sulfidation: Take 10 g of the above precursor powder, place it in a quartz boat and put it into a tube furnace. After vacuuming, carbon disulfide is introduced for sulfidation. The temperature is kept at 1000℃ for 12 hours and then naturally cooled to room temperature to obtain BaHfS3 powder. Step S3, rapid sintering: The sulfurized powder is loaded into a graphite mold with an inner diameter of 12.7 mm, pre-pressed, and then placed in a rapid sintering chamber. After vacuuming, the temperature is raised to 1600℃ and held for 5 minutes. After cooling, a dense cylindrical BaHfS3 block is obtained.

[0014] Example 2, BaHf 0.95 Nd 0.05 The preparation process of S3 bulk thermoelectric material is as follows: Figure 1 As shown, the specific steps include: Step S1, Precursor Design and Synthesis: According to the chemical formula BaHf 1-x Nd x To obtain BaCO3 (x=0.05) powder, accurately weigh BaCO3, HfO2, and Nd2O3 powders, mix them thoroughly, place the powder mixture in a corundum crucible, and heat it to 1200℃ at 10℃ / min in a muffle furnace under air atmosphere. After holding at this temperature for 2 hours, allow it to cool naturally to room temperature to obtain BaHfO2 powder. 0.95 Nd 0.05 O3 oxide precursor powder; Step S2, Gas-phase sulfidation: Take 10 g of the above precursor powder, place it in a quartz boat and put it into a tube furnace. After evacuation, carbon disulfide is introduced for sulfidation. The furnace is held at 1000℃ for 12 hours and then naturally cooled to room temperature to obtain BaHf. 1-x Nd x S3 powder; Step S3, Rapid Sintering: The sulfidation powder is loaded into a graphite mold with an inner diameter of 12.7 mm, pre-pressed, and then placed in a rapid sintering chamber. After vacuuming, the temperature is raised to 1600℃ and held for 5 minutes. After cooling, a dense cylindrical BaHf is obtained. 0.95 Nd 0.05 S3 block.

[0015] Example 3, BaHf 0.75 Zr 0.25 The preparation process of S3 bulk thermoelectric material is as follows: Figure 1 As shown, the specific steps include: Step S1, Precursor Design and Synthesis: According to the chemical formula BaHf 1-x Zr x Based on the stoichiometric ratio of O3 (x=0.25), accurately weigh BaCO3, HfO2, and ZrO2 powders, mix them thoroughly, place the powder mixture in a corundum crucible, and heat it to 1200℃ in a muffle furnace under air atmosphere at a rate of 10℃ / min. After holding at this temperature for 2 hours, allow it to cool naturally to room temperature to obtain BaHfO2. 0.75 Zr 0.25 O3 oxide precursor powder; Step S2, Gas-phase sulfidation: Take 10 g of the above precursor powder, place it in a quartz boat and put it into a tube furnace. After evacuation, carbon disulfide is introduced for sulfidation. The furnace is held at 1000℃ for 12 hours and then naturally cooled to room temperature to obtain BaHf. 0.75 Zr 0.25 O3 powder; Step S3, Rapid Sintering: The sulfidation powder is loaded into a graphite mold with an inner diameter of 12.7 mm, pre-pressed, and then placed in a rapid sintering chamber. After vacuuming, the temperature is raised to 1600℃ and held for 5 minutes. After cooling, a dense cylindrical BaHf is obtained. 0.75 Zr 0.25 S3 block.

[0016] Example 4, BaHf 0.25 Zr 0.75 S3 bulk thermoelectric material, its preparation process is as follows: Figure 1 As shown, the specific steps include: Step S1, Precursor Design and Synthesis: According to the chemical formula BaHf 1-x Zr x Based on the stoichiometric ratio of O3 (x=0.75), accurately weigh BaCO3, HfO2, and ZrO2 powders, mix them thoroughly, place the powder mixture in a corundum crucible, and heat it to 1200℃ in a muffle furnace under air atmosphere at a rate of 10℃ / min. After holding at this temperature for 2 hours, allow it to cool naturally to room temperature to obtain BaHfO2. 0.25 Zr 0.75 O3 oxide precursor powder.

[0017] Step S2, Gas-phase sulfidation: Take 10 g of the above precursor powder, place it in a quartz boat, and put it into a tube furnace. After evacuation, carbon disulfide is introduced for sulfidation. The furnace is held at 1000℃ for 12 hours and then naturally cooled to room temperature to obtain BaHf. 0.25 Zr 0.75 O3 powder; Step S3, Rapid Sintering: The sulfidation powder is loaded into a graphite mold with an inner diameter of 12.7 mm, pre-pressed, and then placed in a rapid sintering chamber. After vacuuming, the temperature is raised to 1600℃ and held for 5 minutes. After cooling, a dense cylindrical BaHf is obtained. 0.25 Zr 0.75 S3 block.

[0018] The BaHfS3 matrix materials prepared in Examples 1, 2, and 3 were analyzed, and the XRD patterns were obtained as follows: Figure 2As shown in the figure, the prepared pure BaHfS3 sample and Nd and Zr doped sample are consistent with the standard spectrum of BaHfS3, have Orthorhombic, Pnma (62) crystal structure, and no obvious impurity phase was detected. This result shows that the preparation process of the present invention can suppress impurity phase and obtain BaHfS3 bulk material with high phase purity. SEM morphology of BaHfS3 bulk material prepared in Example 1 is shown below. Figure 3 As shown in the image, the sample is composed of tightly packed grains with a size of ~10 micrometers, and no pores or cracks were observed, which is consistent with the result that the sample density is close to 100% obtained by the water displacement method test. Example 1: Elemental distribution mapping of BaHfS3 bulk material prepared as shown in the figure. Figure 4 As shown in the image, Ba, Hf, and S elements are uniformly distributed in the 1-10 micrometer scale, with no obvious precipitation or second phase aggregation, which is consistent with the XRD pattern showing no impurities. Example 1: Energy spectrum and atomic composition of BaHfS3 bulk material. Figure 5 As shown, the sample was found to contain Ba, Hf, and S elements. Sulfur vacancies are a common feature of this type of material, and their atomic ratio is basically in line with expectations. The results of the variable-temperature thermoelectric properties of BaHfS3 matrix bulk materials prepared in Examples 1, 2, and 4 are as follows: Figure 6 As shown in the figure, doping with Nd or Zr can improve the electrical conductivity and power factor of the samples. The Zr-doped sample exhibits the highest power factor within the test temperature range, while its thermal conductivity decreases slightly. The relatively low lattice thermal conductivity of the Zr-doped sample is mainly due to the increased point defect scattering intensity. (BaHf) 0.25 Zr 0.75 Sample S3 exhibits high overall thermoelectric performance, with a maximum ZT value of 0.47 at 723 K.

[0019] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-performance BaHfS3-based thermoelectric bulk material doped with Nd / Zr, characterized in that, Includes the following steps: (1) Solid-state doping: Weigh the raw material powders of BaCO3, HfO2, ZrO2 or Nd2O3 according to the target stoichiometric ratio, mix them, and then place them in a muffle furnace for solid-state sintering at 1150-1250℃ for 1.8-2.2 hours to obtain the oxide precursor BaHf 1-x M x O3, where M is Nd or Zr, 0 ≤ x < 1; (2) Gas-phase sulfidation: Using carbon disulfide as the sulfur source, BaHf is subjected to sulfidation at 950-1050℃ for 2-12 hours. 1-x M x O3 undergoes anion substitution, converting the oxide into a sulfide to obtain BaHf. 1-x M x S3 powder; (3) Rapid sintering: BaHf 1-x M x S3 powder is cold-pressed and then rapidly sintered at 1550-1650℃ for 5 minutes to obtain the target block material.

2. The method for preparing Nd / Zr-doped high-performance BaHfS3-based thermoelectric bulk material according to claim 1, characterized in that, The BaHf 1-x M x O3 is BaHfO3, BaHf 1-x Nd x O3, BaHf 1-x Zr x One of O3, when BaHf 1-x M x O3 is BaHf 1-x Nd x When O3, 0 < x ≤ 0.05; when BaHf 1-x M x O3 is BaHf 1-x Zr x When O3 is present, 0 < x ≤ 0.

75.

3. The method for preparing Nd / Zr-doped high-performance BaHfS3-based thermoelectric bulk material according to claim 1, characterized in that, In step (1), the solid-state sintering temperature is 1200℃ and the holding time is 2 hours.

4. The method for preparing Nd / Zr-doped high-performance BaHfS3-based thermoelectric bulk material according to claim 1, characterized in that, In step (2), the temperature is 1000℃ when anion exchange is performed.

5. The method for preparing Nd / Zr-doped high-performance BaHfS3-based thermoelectric bulk material according to claim 1, characterized in that, In step (3), the sintering temperature is 1600℃.

6. A high-performance BaHfS3-based thermoelectric bulk material doped with Nd / Zr, characterized in that, It is prepared using the preparation method described in any one of claims 1-5.

7. The application of the Nd / Zr-doped high-performance BaHfS3-based thermoelectric bulk material as described in claim 6 in the field of thermoelectric conversion.

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