Perovskite high-temperature thermoelectric ceramic material and preparation method thereof

Abstract

The application discloses a high-temperature thermoelectric ceramic material of perovskite type, which is a thermoelectric ceramic material Sr 1‑x Sm x Ti 1‑y Ta y O3, wherein x=0.05-0.12 and y=0.01-0.03. The application effectively improves the Seebeck coefficient (about 1300K, increased from 278.66 muV / K of single Sm-doped to 663.61 muV / K) and reduces the thermal conductivity (about 1300K, increased from 278.66 muV / K of single Sm-doped to 663.61 muV / K) of the perovskite ceramic material by co-doping Sm and Ta in strontium titanate, while not reducing the conductivity of the material, thereby improving the thermoelectric figure of merit of the ceramic to 1.3, which is 3 times of that of the single Sm-doped strontium titanate ceramic material.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric material preparation technology, specifically to a perovskite-type high-temperature thermoelectric ceramic material and its preparation method. Background Technology

[0002] Thermoelectric materials are functional materials capable of directly converting heat energy and electrical energy into each other. They exhibit the thermoelectric effect: when one end of a thermoelectric material is heated, the electrons at that heated end, having a higher temperature, move to the cooler end. This movement generates an electric current, causing charge to accumulate at both ends of the material, creating a potential difference. Based on the thermoelectric effect, we can fabricate thermoelectric cooling and thermoelectric power generation devices.

[0003] The performance of thermoelectric materials is evaluated using the dimensionless thermoelectric figure of merit ZT. For thermoelectric materials, whether used for power generation or refrigeration, a higher zT value is desirable. The calculation formula is as follows:

[0004]

[0005] Where K is the thermal conductivity, σ is the electrical conductivity, S is the thermoelectric potential, and r is the absolute temperature. The formula shows that a good thermoelectric material should have a large Seebeck coefficient and electrical conductivity, while its thermal conductivity should be relatively low. In practical applications, materials with a thermoelectric figure of merit (ZT) close to 1 achieve commercially viable efficiency and are thus likely to be widely used.

[0006] Currently discovered thermoelectric materials mainly include metal alloy thermoelectric materials, oxide thermoelectric materials, and composite thermoelectric materials. Alloy materials have high thermoelectric conversion efficiency and perform well at low and room temperature conditions, but they are prone to oxidation and performance instability at high temperatures. Oxide thermoelectric materials, on the other hand, exhibit stable performance across various ambient temperatures, have simple preparation processes, and long service lives. Perovskite oxide thermoelectric materials are a type of oxide thermoelectric material. Although strontium titanate thermoelectric materials possess a high Seebeck coefficient, they also have high thermal conductivity, a large band gap, and low electrical conductivity. This significantly impacts their thermoelectric figure of merit, preventing them from being considered high-quality thermoelectric materials. Therefore, elemental doping is necessary to improve their thermoelectric performance and operating temperature. Research on strontium titanate doping modification is of great significance for the development of environmentally friendly thermoelectric materials. Existing techniques (“Improvements in the thermoelectric efficiency of SrTiO3 through donor doping” Hamed Bakhshi et al., *Ceramics International*) involve co-doping SrTiO3 with samarium and niobium. However, after doping Sm onto Nb, the Seebeck coefficient of the ceramic material significantly decreases, and the highest thermoelectric figure of merit at 850 K is only 0.4. Other techniques (“Synthesis and thermoelectric performance of Ta-doped SrTiO3”) also involve... 0.9 La 0.1 TiO3ceramics” HC Wang et al., used lanthanum and tantalum co-doped strontium titanate, and adjusted the tantalum doping amount on the basis of lanthanum. They found that as the tantalum doping amount increased, the Seebeck coefficient also decreased, and the final thermoelectric figure of merit also decreased. The thermoelectric figure of merit of the finally prepared strontium titanate-based ceramic materials were not ideal, and it was extremely difficult to break through 1.0. Summary of the Invention

[0007] To address the aforementioned problems, the present invention aims to provide a perovskite-type high-temperature thermoelectric ceramic material. This material effectively improves the Seebeck coefficient of strontium titanate-based ceramics at high temperatures while significantly reducing thermal conductivity without increasing electrical conductivity, thereby effectively improving the thermoelectric figure of merit of the material.

[0008] Another objective of this invention is to provide a method for preparing the above-mentioned perovskite-type high-temperature thermoelectric ceramic material.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A perovskite-type high-temperature thermoelectric ceramic material, characterized in that it is a thermoelectric ceramic material Sr formed by co-doping with samarium and tantalum metals as a matrix, using strontium titanate as the matrix.1-x Sm x Ti 1-y Ta y O3, where x = 0.05~0.12 and y = 0.01~0.03.

[0011] Preferably, the Sr of the thermoelectric ceramic material 0.92 Sm 0.08 Ti 1-y Ta y O3, y = 0.01~0.03.

[0012] More preferably, the Sr of the thermoelectric ceramic material 0.92 Sm 0.08 Ti 1-y Ta y In O3, y = 0.02, meaning the thermoelectric ceramic material is Sr. 0.92 Sm 0.08 Ti 0.98 Ta 0.02 O3.

[0013] A method for preparing a perovskite high-temperature thermoelectric ceramic material is characterized by: firstly ball milling zirconium balls, raw materials and ethanol, then drying to obtain a mixture, pre-sintering the mixture to obtain a pre-synthesized powder, then ball milling a second time, and finally plasma sintering to form a ceramic.

[0014] Furthermore, the first ball milling involves mixing zirconium balls, raw materials, and ethanol in a mass ratio of 1:1:1, ball milling at 400-600 rpm for 10-14 hours, and drying the mixture at 70-90°C after ball milling.

[0015] Furthermore, the raw materials are selected according to the elements Sr, Sm, Ti, and Ta in the chemical formula Sr 1-x Sm x Ti 1-y Ta y The molar ratio of the corresponding elements in O3 is 0.88~0.95:0.05~0.12:0.97~0.99:0.01~0.03. The corresponding masses of strontium carbonate (SrCO3), samarium oxide (Sm2O3), titanium dioxide (TiO2), and tantalum oxide (Ta2O5) are calculated.

[0016] Furthermore, the pre-calcination involves keeping the dried mixture at 1150~1250℃ for 3~5 hours, and then naturally cooling it to room temperature to obtain a pre-synthesized powder.

[0017] Furthermore, the secondary ball milling involves mixing the pre-synthesized powder with an equal amount of zirconium balls and ethanol, ball milling at 400-600 rpm for 10-14 hours, drying, and then grinding to obtain the secondary ball-milled powder.

[0018] Furthermore, the plasma sintering involves heating the ground powder to 1110-1150°C within 8-12 minutes. o C, hold at temperature for 4~6 minutes, sinter at a pressure of 45~55 MPa, and sinter into ceramic material.

[0019] In this invention, strontium titanate is co-doped with samarium and tantalum to induce vacancies. By adjusting the oxygen vacancy concentration, the Seebeck coefficient is increased, reducing the material's thermal conductivity without decreasing its electrical conductivity, thus achieving a high thermoelectric figure of merit. Due to the differences in atomic radii of the doping elements, the crystal structure undergoes varying degrees of change, and the lattice vibrations are also altered, affecting the lattice waves and reducing their scattering while increasing thermal conductivity.

[0020] Most specifically, a method for preparing a perovskite high-temperature thermoelectric ceramic material is characterized by comprising the following steps:

[0021] (1) Using strontium carbonate (SrCO3), samarium oxide (Sm2O3), titanium dioxide (TiO2) and tantalum oxide (Ta2O5) as raw materials with the molar ratio of Sr, Sm, Ti and Ta being 0.88~0.95:0.05~0.12:0.97~0.99:0.01~0.03, zirconium balls, raw materials and ethanol are mixed in a mass ratio of 1:1:1 and placed in a ball mill. The mixture is ball-milled at 400~600 rpm for 10~14 h. The discharged material is then dried at 70~90℃ to obtain a mixture.

[0022] (2) The mixture prepared in step (1) is kept at 1150~1250℃ for 3~5 h, and then naturally cooled to room temperature to obtain the pre-synthesized powder;

[0023] (3) Mix the pre-synthesized powder, zirconium balls and ethanol in a mass ratio of 1:1:1, ball mill at 400-600 rpm for 10-14 h, then dry the discharged material at 70-90℃ and grind it to obtain secondary ball milled powder.

[0024] (4) The secondary ball-milled powder is loaded into a graphite mold with a diameter of 15 mm and placed in a spark plasma sintering furnace. The temperature is raised to 1110-1150 °C within 8-12 minutes. o C, hold at temperature for 4~6 min, sinter at pressure of 45~55 MPa, and sinter into ceramic material.

[0025] The present invention has the following technical effects:

[0026] This invention reduces the sintering temperature during the preparation process by co-doping specific amounts of Sm and Ta into strontium titanate, and effectively improves the Seebeck coefficient of the perovskite ceramic material (from 278.66 μV / K with single Sm doping to 663.61 μV / K at around 1300 K) and reduces its thermal conductivity (from 278.66 μV / K with single Sm doping to 663.61 μV / K at 1300 K), without reducing the electrical conductivity of the material. This improves the thermoelectric figure of merit of the ceramic to 1.3, which is three times that of strontium titanate ceramic material with single Sm doping. Attached Figure Description

[0027] Figure 1 Sr prepared at 1130℃ 0.92 Sm 0.08 Ti 1-y Ta y SEM images of cross sections of O3 samples; (a) y=0, (b) y=0.01, (c) y=0.02, (d) y=0.03.

[0028] Figure 2 Sr prepared in Example 1 0.92 Sm 0.08 Ti 1-y Ta y XRD pattern of O3.

[0029] Figure 3 Sr prepared in Example 1 0.92 Sm 0.08 Ti 1-y Ta y The resistivity of O3 as a function of temperature.

[0030] Figure 4 Sr prepared in Example 1 0.92 Sm 0.08 Ti 1-y Ta y The Seebeck coefficient of O3 varies with temperature.

[0031] Figure 5 Sr prepared in Example 1 0.92 Sm 0.08 Ti 1-y Ta y The thermal diffusivity of O3 varies with temperature.

[0032] Figure 6 Sr prepared in Example 1 0.92 Sm 0.08 Ti 1-y Ta y The thermal conductivity of O3 varies with temperature.

[0033] Figure 7 Sr prepared in Example 1 0.92 Sm 0.08 Ti 1-y Ta y The power factor of O3 varies with temperature.

[0034] Figure 8 Sr prepared in Example 1 0.92 Sm 0.08 Ti 1-y Ta y The thermoelectric figure of merit of O3 varies with temperature.

[0035] Figure 9 Sr prepared in Example 1 0.92 Sm 0.08 Ti 1-y Ta y Variation in the bandgap width of O3. Detailed Implementation

[0036] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0037] Comparative Example 1:

[0038] (1) Sr doped with Sm alone 1-x Sm x Preparation of TiO3:

[0039] The preparation steps are the same as in Example 1 above, except that the raw materials do not contain Ta2O5, and the doping amount of Sm2O3 is adjusted to x=0.05, 0.08, 0.10, and 0.12 respectively. During the sintering process, the ceramic structure that cannot be effectively sintered at 1110~1150℃ is not ideal, and the sintering temperature needs to be further increased to above 1400℃.

[0040] Sr with different Sm doping levels prepared 1-x Sm x The Seebeck coefficient of TiO3 varies between -100 and -250 μV / K, and decreases with increasing doping concentration. The thermoelectric properties of Sm-doped strontium titanate increase continuously with temperature up to 800 K, with Sr... 0.9 Sm 0.1 TiO3 has the highest thermoelectric figure of merit, reaching only 0.22 at 800K.

[0041] (2) SrTi doped with Ta alone 1-y Tay Preparation of O3:

[0042] The preparation steps are the same as in Example 1 above, except that the raw materials do not contain Sm2O3 and the doping amount of Ta2O5 is adjusted to y=0.01, 0.03 and 0.05 respectively. During the sintering process, ceramics with good structure cannot be effectively sintered at 1110~1150℃, and the sintering temperature needs to be further increased to above 1400℃.

[0043] Prepared SrTi with different Ta doping 1-y Ta y The Seebeck coefficient of O3 varies between -100 and -250 μV / K, and decreases with increasing Ta doping concentration. The thermoelectric figure of merit gradually decreases with increasing Ta doping concentration.

[0044] Example 1

[0045] A perovskite high-temperature thermoelectric ceramic material Sr 1-x Sm x Ti 1-y Ta y The method for preparing O3 includes the following steps:

[0046] (1) Strontium carbonate (SrCO3), samarium oxide (Sm2O3), titanium dioxide (TiO2) and tantalum oxide (Ta2O5) were used as raw materials with a molar ratio of Sr, Sm, Ti and Ta of 0.92:0.08:0.98:0.02. Zirconium balls, raw materials and ethanol were mixed in a mass ratio of 1:1:1 and placed in a ball mill. The mixture was ball-milled at 500 rpm for 12 h. The discharged material was then dried at 80 °C to obtain a mixture.

[0047] (2) The mixture prepared in step (1) was kept at 1200 °C for 4 h and then naturally cooled to room temperature to obtain the pre-synthesized powder;

[0048] (3) The pre-synthesized powder, zirconium balls and ethanol were mixed in a mass ratio of 1:1:1 and ball-milled at 500 rpm for 12 h. The discharged material was then dried at 80 °C and ground to obtain secondary ball-milled powder.

[0049] (4) The secondary ball-milled powder is loaded into a graphite mold with a diameter of 15 mm, placed in a spark plasma sintering furnace, and heated to 1130 °C in 10 min. o C, hold at temperature for 5 min, sinter at a pressure of 50 MPa, and sinter into ceramic material Sr. 0.92 Sm 0.08 Ti 0.99 Ta 0.01 O3 (denoted as Sm08Ta01-STO).

[0050] Following the steps above, by changing the Ta₂O₅ content in the raw materials and adjusting the Ta doping amount, Sr₂ was prepared respectively. 0.92 Sm 0.08 TiO3 (denoted as SmO8-STO), Sr 0.92 Sm 0.08 Ti 0.98 Ta 0.02 O3 (denoted as Sm08Ta02-STO) and Sr 0.92 Sm 0.08 Ti 0.97 Ta 0.03 O3 (denoted as Sm08Ta03-STO).

[0051] The Sr prepared in this embodiment 1-x Sm x Ti 1-y Ta y Electron micrograph of the O3 cross section is shown below. Figure 1 As shown, observations reveal that the grain size tends to increase with increasing tantalum content. Due to the fast speed of spark plasma sintering, the grain size is 100-200 nm, and the fracture surface after Ta doping is mainly intergranular fracture.

[0052] Figure 2 Sr with different Ta doping concentrations 0.92 Sm 0.08 Ti 1-y Ta y The X-ray diffraction pattern of the O3 sample was obtained. Based on the diffraction peaks in the pattern, a comparison was made between the samarium and tantalum-doped strontium titanate powder samples and the standard powder diffraction card (PDF#35-0734) for strontium titanate. The position, shape, and width of the diffraction peaks in the sample are basically consistent with those of the strontium titanate material. This indicates that the crystal structure of the samarium and tantalum-doped strontium titanate powder samples remains a perovskite structure, without any change in crystal structure. Slight shifts in the position of the diffraction peaks for different concentrations of powder indicate that different doping concentrations cause varying degrees of lattice distortion in the strontium titanate crystal. Variations in peak width suggest that the grain size changes with the doping of samarium and tantalum.

[0053] Figure 3 Sr with different Ta doping concentrations 0.92 Sm 0.08 Ti 1-y Ta y The resistivity curve of the O3 sample versus temperature shows that in the lower temperature range (0~800℃), at the same temperature, the resistivity of the sample increases with the increase of Ta doping amount. However, in the higher temperature range (above 1000℃), the co-doping of Ta and Sm has almost no effect on the resistivity of the sample.

[0054] Figure 4 For Sr 0.92 Sm 0.08 Ti 1-y Ta y The Seebeck coefficient curve of the O3 sample versus temperature shows that the Seebeck coefficient is negative, indicating that the Sm and Ta co-doped Sr titanate ceramic is an n-type semiconductor. The Seebeck coefficient of the Sm08-STO sample increases with increasing sintering temperature, reaching a minimum of 110.11 μV / K at 300 K and a maximum of 278.66 μV / K at 1000 °C. Further doping with Ta significantly alters the Seebeck coefficient. Overall, with further Ta doping at the same temperature, the Seebeck coefficient shows a significant increasing trend compared to the undoped form, with the highest value being Sr. 0.92 Sm 0.08 Ti 0.97 Ta 0.03 The O3 sample reached 663.61 μV / K at 1000℃, while the Sr 0.92 Sm 0.08 The Seebeck coefficient was 2.38 times that of the TiO3 sample, while with single Ta doping, the Seebeck coefficient decreased with increasing Ta doping amount at the same temperature. This shows that samarium and tantalum doping significantly improve the thermoelectric properties of strontium titanate, and its optimal application temperature is in the high-temperature region.

[0055] Figure 5 and Figure 6 They are Sr 0.92 Sm 0.08 Ti 1-y Ta y The curves showing the thermal diffusivity and thermal conductivity of the O3 sample as a function of temperature, with thermal conductivity calculated based on the thermal diffusivity, show that both decrease with increasing temperature. Good thermoelectric materials require low thermal conductivity. It can be seen that the increase in samarium and tantalum content leads to an increase in thermal conductivity, but the overall trend indicates that strontium titanate materials are suitable for high-temperature environments.

[0056] Figure 7 and Figure 8 It is Sr 0.92 Sm 0.08 Ti 1-y Ta yThe power factor and thermoelectric figure of merit (PGM) of the O3 sample change with temperature. These two values ​​are characteristic quantities describing the overall thermoelectric performance of the material, calculated by combining the previously measured Seebeck coefficient, electrical conductivity, and thermal conductivity. Higher values ​​for both are better. As shown in the figure, both the power factor and PGM increase with increasing temperature, indicating improved thermoelectric performance of the samarium and tantalum co-doped strontium titanate ceramic material, with the best performance at 1000°C. The PGM of Sm08Ta03-STO reaches 1.3.

[0057] Sr was prepared by plasma sintering. 0.92 Sm 0.08 Ti 1-y Ta y In the O3 samples, it can be observed that when the sintering temperature is from 1110℃ to 1150℃, the microstructure of the samples shows that at the sintering temperature of 1150℃, most of the grain boundaries are blurred. This is because the co-doping of samarium and tantalum elements reduces the sintering temperature of the strontium titanate material.

[0058] Because strontium titanate has a wide bandgap, it can be classified as a wide bandgap insulator, exhibiting extremely poor electrical conductivity. For example... Figure 9 As shown, the introduction of samarium and tantalum elements also reduced Sr 0.92 Sm 0.08 Ti 1-y Ta y The band gap of the O3 sample improves upon the shortcomings of previous samples, which had a large band gap and thus low conductivity.

[0059] Example 2

[0060] A method for preparing a perovskite high-temperature thermoelectric ceramic material includes the following steps:

[0061] (1) SrCO3, Sm2O3, TiO2 and Ta2O5 were prepared as raw materials with a molar ratio of Sr, Sm, Ti and Ta of 0.88:0.12:0.98:0.02. Zirconium balls, raw materials and ethanol were mixed in a mass ratio of 1:1:1 and placed in a ball mill. The mixture was ball-milled at 400 rpm for 14 h. The discharged material was then dried at 70 °C to obtain a mixture.

[0062] (2) The mixture prepared in step (1) is kept at 1150℃ for 5 h and then naturally cooled to room temperature to obtain a pre-synthesized powder;

[0063] (3) The pre-synthesized powder, zirconium balls and ethanol are mixed in a mass ratio of 1:1:1, ball-milled at 600 rpm for 10 h, and then the discharged material is dried at 90 °C and ground to obtain secondary ball-milled powder.

[0064] (4) The secondary ball-milled powder is loaded into a graphite mold with a diameter of 15 mm, placed in a spark plasma sintering furnace, and heated to 1110 °C within 8 min. o C, hold at temperature for 6 minutes, sinter at a pressure of 55 MPa, and sinter into a ceramic material.

[0065] The Sr prepared in this embodiment 0.88 Sm 0.12 Ti 0.98 Ta 0.02 O3 achieves a thermoelectric figure of merit of 1.0 at 1000°C.

[0066] Example 3

[0067] A method for preparing a perovskite high-temperature thermoelectric ceramic material includes the following steps:

[0068] (1) SrCO3, Sm2O3, TiO2 and Ta2O5 were prepared as raw materials with the molar ratio of Sr, Sm, Ti and Ta being 0.95:0.05:0.98:0.02. Zirconium balls, raw materials and ethanol were mixed in a mass ratio of 1:1:1 and placed in a ball mill. The mixture was ball-milled at 600 rpm for 10 h. The discharged material was then dried at 90°C to obtain a mixture.

[0069] (2) The mixture prepared in step (1) is kept at 1250℃ for 3 h and then naturally cooled to room temperature to obtain the pre-synthesized powder;

[0070] (3) The pre-synthesized powder, zirconium balls and ethanol are mixed in a mass ratio of 1:1:1, ball-milled at 400 rpm for 14 h, and then the discharged material is dried at 70 °C and ground to obtain secondary ball-milled powder.

[0071] (4) The secondary ball-milled powder is loaded into a graphite mold with a diameter of 15 mm, placed in a spark plasma sintering furnace, and heated to 1150 °C within 12 min. o C, hold at temperature for 4 min, sinter at a pressure of 45 MPa, and sinter into ceramic material.

[0072] The Sr prepared in this embodiment 0.95 Sm 0.05 Ti 0.98 Ta 0.02 O3 achieves a thermoelectric figure of merit of 1.1 at 1000°C.

Claims

1. A perovskite-type high-temperature thermoelectric ceramic material, characterized in that: Sr is a thermoelectric ceramic material formed by co-doping strontium titanate and samarium and tantalum. 1-x Sm x Ti 1-y Ta y O3, where x=0.05~0.12 and y=0.01~0.03, is obtained by ball milling zirconium balls, raw materials and ethanol once, then drying to obtain a mixture, pre-sintering the mixture to obtain a pre-synthesized powder, then ball milling a second time, and finally plasma sintering.

2. A method for preparing the perovskite-type high-temperature thermoelectric ceramic material as described in claim 1, characterized in that: The process involves ball milling zirconium balls, raw materials, and ethanol once, then drying the mixture to obtain a pre-synthesized powder. This powder is then ball-milled a second time and finally plasma-sintered into ceramic.

3. The method for preparing a perovskite-type high-temperature thermoelectric ceramic material as described in claim 2, characterized in that: The first ball milling involves mixing zirconium balls, raw materials, and ethanol in a mass ratio of 1:1:1, ball milling at 400-600 rpm for 10-14 hours, and drying the mixture at 70-90°C after ball milling.

4. A method for preparing a perovskite-type high-temperature thermoelectric ceramic material as described in claim 2 or 3, characterized in that: The raw material is composed of strontium carbonate, samarium oxide, titanium dioxide and tantalum oxide in a molar ratio of Sr, Sm, Ti and Ta of 0.88~0.95:0.05~0.12:0.97~0.99:0.01~0.

03.

5. The method for preparing a perovskite-type high-temperature thermoelectric ceramic material as described in claim 4, characterized in that: The pre-sintering process involves holding the dried mixture at 1150~1250℃ for 3~5 hours, and then naturally cooling it to room temperature to obtain a pre-synthesized powder.

6. The method for preparing a perovskite-type high-temperature thermoelectric ceramic material as described in claim 5, characterized in that: The secondary ball milling involves mixing the pre-synthesized powder with an equal amount of zirconium balls and ethanol, ball milling at 400-600 rpm for 10-14 hours, drying, and then grinding to obtain the secondary ball-milled powder.

7. The method for preparing a perovskite-type high-temperature thermoelectric ceramic material as described in claim 6, characterized in that: The plasma sintering process involves heating the ground powder to 1110-1150°C within 8-12 minutes. o C, hold at temperature for 4~6 minutes, sinter at a pressure of 45~55MPa, and sinter into ceramic material.

Images