Bismuth niobate-based pyrochlore phase high-entropy ceramics and their single-phase preparation methods

Abstract

This invention relates to the field of multifunctional high-entropy ceramics technology, specifically disclosing a bismuth niobate-based pyrochlore phase high-entropy ceramic and its single-phase preparation method. The chemical formula of this material is (Nb... 0.36 Bi 1.64 (Fe) 0.2 Co 0.2 Ni 0.2 Mn 0.2 Cr 0.2 )NbO 7‑δ Its crystal structure belongs to the defective A2B2O7 type single-phase pyrochlore phase structure. Its internal structure exhibits positional disorder, meaning that some B-site niobium ions occupy A-site bismuth ion positions, and five equimolar magnetic transition metal ions occupy B-site niobium ion positions, along with a certain proportion of oxygen vacancy defects. The single-phase high-entropy ceramic material provided by this invention exhibits ferromagnetism at room temperature, along with room-temperature magnetoelectric multiferroic properties and broad-spectrum light absorption characteristics in the visible-near-infrared 300nm-2000nm region. Moreover, it maintains a stable pyrochlore cubic crystal phase structure even after calcination at 1000℃ for 5 hours, demonstrating excellent high-temperature resistance.

Description

Technical Field

[0001] This invention belongs to the field of multifunctional high-entropy ceramics technology, specifically relating to bismuth niobate-based pyrochlore phase high-entropy ceramics and their single-phase preparation method. Background Technology

[0002] A2B2O7 type oxides are generally classified into two main categories: fluorite structure and pyrochlore structure. Due to the high tolerance of their crystal structure, they can accommodate the coexistence of multiple types of components, thus possessing multiple functions such as electrical, magnetic, optical and catalytic properties in a single phase. Therefore, they can be regarded as an important candidate material system for the discovery of high-entropy ceramics. At present, the high-entropy research of this type of material mainly focuses on the RE2Zr2O7 (RE is a rare earth element) system. By using the high-entropy design of rare earth elements at the A site, low thermal conductivity can be achieved for application in thermal barrier environment coatings, and relaxed ferroelectric behavior can be induced to achieve ultra-high dielectric energy storage density. For related research progress, please refer to the review Recent Progress and Current Challenges of High-entropy A2B2O7-type Oxides[J], Journal of Xinyang Normal University (Natural Science Edition), 2023, 36(4):679-683.

[0003] Niobium-bismuth-based A2B2O 7-δ Bi-type oxides have gradually attracted attention in recent years. Their structure is a cubic defect pyrochlore phase structure, and their general chemical formula is Bi. 2-M Nb 2+M The O6O′ structure has three main characteristics: bismuth atoms in approximately the stoichiometric ratio M are occupied by niobium atoms, resulting in a disordered arrangement; a large number of unoccupied oxygen vacancies exist; and vacancy defects exist at both oxygen and bismuth atom positions. This unique structure readily accommodates many disordered arrangements, exhibiting flexibility in atomic arrangement, yet its crystal structure remains stable, making it well-suited for high-entropy design with multiple components. Bismuth niobate in the pyrochlore phase possesses excellent dielectric and optical properties, attributed to the 6s electron pair of bismuth atoms and the hybridization of 2p empty orbitals with oxygen atom orbitals, but also influenced by complex and varied defects. Introducing magnetism could enable the material to possess multiple functions including magneto-optical-electric properties, placing it within the category of advanced functional materials with significant application potential. However, research has found that single or dual magnetic atom doping cannot excite the material's magnetism, let alone achieve near-room-temperature magnetism, as reported in the literature regarding Bi... 1.647 (Fe 1-y Co y ) 1.157 Nb 1.118The magnetic transition temperature of O7 (0≤y≤0.5) single-phase ceramics is only 7-9K, and it is non-magnetic near room temperature (J.Mater.Chem.C,2019,7,1263).

[0004] It is evident that the successful preparation of single-phase samples using magnetic transition metal elements for high-entropy design at niobium sites in pyrochlore-phase bismuth niobate has significant scientific research value. Furthermore, leveraging the high-entropy effect, it is highly likely that near-room-temperature magnetism can be achieved in this material system, thereby expanding the material's order parameter number, increasing magnetic order, and ultimately obtaining a novel single-phase high-entropy ceramic material integrating magneto-optical-electric properties. However, related research is currently scarce. High-entropy ceramics are typically prepared using solid-state methods, but the complex structure of pyrochlore-phase bismuth niobate makes phase formation difficult using traditional solid-state methods, easily leading to the formation of Bi5Nb3O. 15 Impurities such as BiNbO4 or other impurities make single-phase preparation difficult. Therefore, successfully preparing single-phase bismuth niobate-based pyrochlore phase high-entropy ceramics is a huge challenge. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art by providing a bismuth niobate-based pyrochlore phase high-entropy ceramic with multiple magnetoelectric and optical properties and its single-phase preparation method. This material can achieve the disordered coexistence of various magnetic atoms in the bismuth niobate-based pyrochlore phase structure, inducing complex magnetic interactions or room temperature ferromagnetic states, thereby generating new functions such as room temperature magnetism and room temperature magnetoelectric effect.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The first objective of this invention is to provide a bismuth niobate-based pyrochlore phase high-entropy ceramic, wherein the chemical formula of the bismuth niobate-based pyrochlore phase high-entropy ceramic is as follows:

[0008] (Nb 0.36 Bi 1.64 (Fe) 0.2 Co 0.2 Ni 0.2 Mn 0.2 Cr 0.2 )NbO 7-δ .

[0009] Furthermore, the crystal structure of the bismuth niobate-based pyrochlore phase high-entropy ceramic is a defect A2B2O7 type single-phase pyrochlore phase structure, in which some niobium ions occupy bismuth ion positions, and five equimolar magnetic transition metal ions occupy niobium ion positions and there is a certain proportion of oxygen vacancy defects.

[0010] Furthermore, the bismuth niobate-based pyrochlore phase high-entropy ceramic exhibits ferromagnetism and magnetoelectric multiferroism at room temperature.

[0011] Furthermore, the bismuth niobate-based pyrochlore phase high-entropy ceramic exhibits excellent broadband light absorption characteristics in the visible-near infrared 300nm-2000nm region.

[0012] A second objective of this invention is to provide a single-phase preparation method for the above-mentioned bismuth niobate-based pyrochlore phase high-entropy ceramics, comprising the following steps:

[0013] S1. Weigh a certain amount of the amorphous compound containing water of crystallization Nb2O5·3H2O and dissolve it in deionized water. Then, add citric acid in an equal molar ratio to complex it. After heating and stirring in a water bath at a certain temperature, a transparent solution A is obtained.

[0014] S2. Weigh out the bismuth source compound, iron source compound, cobalt source compound, nickel source compound, manganese source compound and chromium source compound that are soluble in acid according to the stoichiometric ratio shown in the chemical formula, and dissolve the above components in diluted acid solution respectively. After stirring at room temperature, a clear solution B is formed.

[0015] S3. Add solution A to solution B dropwise and stir continuously to form a mixed and clear solution C. Add citric acid and ethylenediaminetetraacetic acid to solution C as complexing agents and combustion aids, and then add ammonia water dropwise to adjust the pH value to neutral, finally forming a transparent solution D.

[0016] S4. Transfer solution D to an evaporation crucible. After heating, solution D passes through a sol and gel and spontaneously combusts. Collect the remaining powder to obtain primary powder. Then, grind the collected powder and place it in a muffle furnace for high-temperature pre-firing and high-temperature sintering to obtain the single-phase high-entropy ceramic block.

[0017] Furthermore, in step S2, the bismuth source compound is bismuth nitrate pentahydrate, the iron source compound is ferric nitrate nonahydrate, the cobalt source compound is cobalt nitrate hexahydrate, the nickel source compound is nickel acetate, the manganese source compound is manganese oxalate, and the chromium source compound is chromium nitrate nonahydrate.

[0018] Furthermore, in step S3, the molar ratio of the total metal ions, complexing agent, and combustion improver is 1:1:1, wherein the complexing agent is citric acid and the combustion improver is ethylenediaminetetraacetic acid.

[0019] Furthermore, in step S4, the high-temperature preheating temperature is between 500 and 800°C, and the holding time is 2 hours.

[0020] Furthermore, the high-temperature sintering temperature is 900–1000℃, and the sintering time is 5–7 hours.

[0021] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows:

[0022] (1) The bismuth niobate-based pyrochlore phase high-entropy ceramic provided by the present invention has a high-entropy structure designed by using magnetic elements to make high-entropy components at the B site in the defective A2B2O7 type bismuth niobate system. The resulting high-entropy ceramic material still has the characteristics of a single-phase pyrochlore phase structure.

[0023] (2) The bismuth niobate-based pyrochlore phase high-entropy ceramic provided by this invention has a structure with positional disorder, that is, some B-site niobium ions occupy A-site bismuth ion positions, and five kinds of equimolar magnetic transition metal ions occupy B-site niobium ion positions and a certain proportion of oxygen vacancy defects. Usually, the regular pyrochlore phase structure is a regular arrangement of two sets of bismuth-oxygen tetrahedra and niobium-oxygen octahedra. However, the positional disorder, the presence of multiple types of vacancy defects and disordered iron / cobalt / nickel / manganese / chromium-oxygen octahedra will lead to structural distortion and local stacking disorder. Superexchange interactions will exist between neighboring magnetic atoms, which may induce local short-range magnetic ordering and form a spin glass state or ferromagnetic state. At the same time, the 3d orbitals of multiple types of transition metals have unfilled electrons, which can easily hybridize with the 2p orbitals of oxygen atoms, affecting the band structure and thus changing the optical properties.

[0024] (3) The bismuth niobate-based pyrochlore phase high-entropy ceramic provided by the present invention exhibits ferromagnetism at room temperature, and also possesses room temperature magnetoelectric multiferroic properties and good broadband light absorption characteristics in the visible-near infrared 300nm-2000nm region. In addition, it was found that the ceramic material has a very stable structure. Even after calcination at 1000℃ for 5h, it can still maintain a stable pyrochlore cubic crystal phase structure, and has excellent high temperature resistance.

[0025] (4) This invention successfully prepared a novel single-phase high-entropy ceramic material by means of an improved sol-gel combustion method. The preparation method is simple to operate, energy-saving and efficient, and easy to promote. At the same time, it can solve the dissolution problem of niobium-based oxides and the problem that traditional solid-phase methods are difficult to form phases.

[0026] (5) The bismuth niobate-based pyrochlore phase high-entropy ceramic provided by the present invention can maintain its dielectric properties and photocatalytic properties, and adds room temperature ferromagnetism and magnetic dielectric coupling, thereby realizing the multifunctionality of the material with both magneto-optical and photoelectric properties. It has good application prospects in the fields of magneto-electric sensors, high-density memory devices, and optoelectronic devices. Attached Figure Description

[0027] Figure 1 The images show the XRD patterns of the sample powders in the examples and comparative examples, as well as the comparison images with the PDF cards of the pyrochlore phase standard.

[0028] Figure 2 The images show the cross-sectional SEM images and corresponding SEM-EDX spectra of the ceramic samples in the examples and comparative examples.

[0029] Figure 3Images of the ceramic sample from Example 1 sintering at different temperatures;

[0030] Figure 4 The figures show a comparison of the ZFC-FC magnetization curves and room temperature hysteresis loops of the samples in the examples and comparative examples.

[0031] Figure 5 The hysteresis loop diagram at room temperature is shown for the ceramic sample in Example 1.

[0032] Figure 6 Comparison of room temperature UV-Vis-NIR diffuse reflectance spectra of sample powders in the examples and comparative examples;

[0033] Figure 7 The graph shows the magnetic dielectric curve and the relationship between the magnetic dielectric effect and temperature for the ceramic sample in Example 1.

[0034] Figure 8 The ON-OFF transient photocurrent density-time curve is measured when the electrode is made from the sample powder in Example 1. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the specific embodiments and accompanying drawings are described in further detail below. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0036] Example 1

[0037] This embodiment provides a bismuth niobate-based pyrochlore phase high-entropy ceramic.

[0038] (Nb 0.36 Bi 1.64 (Fe) 0.2 Co 0.2 Ni 0.2 Mn 0.2 Cr 0.2 )NbO 7-δ Preparation of powders and bulk materials.

[0039] (1) Niobium pentoxide containing water of crystallization was prepared using conventional methods. The chemical formula Nb₂O₅·3H₂O and the amorphous phase were determined by thermogravimetric analysis and X-ray diffraction. A certain amount of the dried and stored amorphous Nb₂O₅·3H₂O containing water of crystallization was weighed and dissolved in deionized water. To achieve the dissolution of niobium pentoxide containing water of crystallization and to stably disperse niobium ions in water, citric acid was added in an equimolar ratio for complexation. At the same time, the solution was heated in a water bath on a heating platform to maintain the temperature of the aqueous solution at about 80°C. The solution was continuously stirred with a magnetic stirrer. After about 10 minutes, the solution was completely dissolved, forming a clear, colorless, and transparent solution A.

[0040] (2) Based on the above-mentioned amounts and stoichiometric ratios of niobium source, weigh out the acid-soluble bismuth source compound, iron source compound, cobalt source compound, nickel source compound, manganese source compound, and chromium source compound in sequence, and dissolve them in another beaker containing diluted concentrated nitric acid solution. In the embodiments, the preferred compounds are: bismuth source compound is bismuth nitrate pentahydrate, iron source compound is ferric nitrate nonahydrate, cobalt source compound is cobalt nitrate hexahydrate, nickel source compound is nickel acetate, manganese source compound is manganese oxalate, and chromium source compound is chromium nitrate nonahydrate. Under room temperature conditions, by magnetic stirring, a transparent solution B is finally obtained, which is dark red.

[0041] (3) Then, solution A is added dropwise to solution B using a dropper, and a clear mixed solution C is formed by continuous stirring. The solution is dark brown. Next, a complexing agent and a combustion accelerant are added to solution C in a molar ratio of total metal ions: complexing agent: combustion accelerant = 1:1:1. In this embodiment, the complexing agent and combustion accelerant are citric acid and ethylenediaminetetraacetic acid, respectively. The pH of the mixture is neutralized by adding an alkaline solution to approximately 7. In this embodiment, ammonia is preferred as the alkaline solution. The above process requires continuous stirring until a clear solution D is formed, ultimately yielding the precursor solution.

[0042] (4) The precursor solution is transferred to an evaporation crucible. After heating, solution D undergoes sol-gel transformation and spontaneous combustion. The remaining powder is collected to obtain the primary powder. The heating is performed on a resistance wire furnace. The collected powder is then ground and placed in a muffle furnace for high-temperature pre-calcination. The pre-calcination temperature is between 500-800°C, preferably 750°C in this embodiment, and the pre-calcination holding time is 2 hours. This step is to remove residual organic carbon from the powder. Too low a temperature will not allow the organic carbon to volatilize, while too high a temperature will easily cause the grains in the powder to fuse and grow, which is detrimental to the volatilization of organic carbon. The remaining powder after pre-calcination is the single-phase powder of the material described in this invention.

[0043] (5) The synthesized single-phase powder is pressed into sheets using a mold and then placed in a high-temperature muffle furnace for long-term high-temperature sintering. The high-temperature sintering temperature is 900-1000℃, preferably 950℃ in the embodiment, and the sintering time is 5 hours. After the high-temperature sintering is completed, the obtained ceramic block is the high-entropy ceramic of the present invention.

[0044] Comparative Example 1

[0045] This comparative example provides (Nb) 0.36 Bi 1.64 (Fe) 1 / 3 Co 1 / 3 Ni 1 / 3 )NbO 7-δ Preparation of ceramic powders and bulk materials.

[0046] (1) Weigh a certain amount of the amorphous compound containing water of crystallization Nb2O5·3H2O and dissolve it in deionized water. Then, add citric acid in an equal molar ratio to complex it. After heating and stirring in a water bath at a certain temperature, a transparent solution A' is formed.

[0047] (2) Weigh out bismuth nitrate pentahydrate, ferric nitrate nonahydrate, cobalt nitrate hexahydrate and nickel acetate according to the stoichiometric ratio, dissolve them in dilute nitric acid solution, and stir at room temperature to form a clear solution B';

[0048] (3) Add solution A' to solution B' and stir continuously to form a mixed and clear solution C'; then add citric acid and ethylenediaminetetraacetic acid in equal molar ratios of metal ions to solution C', and then add ammonia water to neutralize the pH value, finally forming a transparent solution D';

[0049] (4) Transfer the solution D' to an evaporation crucible. After heating, the solution D' passes through a sol and gel and spontaneously combusts. Collect the remaining powder to obtain the primary powder. Then, grind the collected powder and place it in a muffle furnace for high-temperature pre-firing at 750℃ / 2h to obtain pure material powder. Finally, press the powder into sheets and sinter it at 950℃ / 5h to obtain the ceramic block material described in Comparative Example 1.

[0050] Comparative Example 2

[0051] This comparative example provides (Nb) 0.36 Bi 1.64 FeNbO 7-δ Preparation of ceramic powders and bulk materials.

[0052] (1) Weigh a certain amount of the amorphous compound containing water of crystallization Nb2O5·3H2O and dissolve it in deionized water. Then, add citric acid in an equal molar ratio to complex it. After heating and stirring in a water bath at a certain temperature, a transparent solution A is obtained.

[0053] (2) Weigh out bismuth nitrate pentahydrate and ferric nitrate nonahydrate according to the stoichiometric ratio, dissolve them in dilute nitric acid solution, and stir at room temperature to form a clear solution B”;

[0054] (3) Add solution A" dropwise to solution B" and stir continuously to form a mixed and clear solution C". Then add citric acid and ethylenediaminetetraacetic acid in equal molar ratios of metal ions to solution C" and then add ammonia water dropwise to neutralize the pH value, finally forming a transparent solution D".

[0055] (4) Transfer solution D” to an evaporation crucible. After heating, solution D” passes through sol and gel, and spontaneously combusts. Collect the remaining powder to obtain primary powder. Then, grind the collected powder and place it in a muffle furnace for high-temperature pre-firing at 750℃ / 2h to obtain pure material powder. Finally, press into sheets and sinter at 950℃ / 5h to obtain the ceramic block material described in Comparative Example 2.

[0056] The ceramics prepared in Example 1, Comparative Example 1 and Comparative Example 2 were characterized by X-ray diffraction (XRD) and scanning electron microscopy energy-dispersive spectroscopy (SEM-EDS).

[0057] The relevant testing process is as follows: Take 1g of ceramic powder and place it into a sample cell for XRD testing. Compact the sample using a glass slide. Then, place the glass slide with the sample into the XRD measuring instrument, set the relevant parameters, and perform routine XRD measurements to obtain the XRD spectrum. Take the prepared ceramic slide, break it off, and attach it to the sample holder for SEM testing using conductive tape. Then, place it into the SEM instrument to measure the cross-sectional morphology of the ceramic sample. At the same time, collect EDS data at the corresponding positions to obtain the SEM-EDS spectrum and the corresponding ceramic cross-sectional micromorphology image.

[0058] refer to Figure 1 and Figure 2The measured XRD data were completely consistent with the standard PDF#52-1774 corresponding to the pyrochlore phase structure, indicating that no second impurity phase was found in the samples, and confirming that all three samples had a single-phase pyrochlore phase structure. Compared with the low-entropy ceramic samples, the cross-sectional SEM images of the high-entropy ceramic samples showed that the samples had good density, indicating that the high-entropy design is beneficial to reducing porosity and increasing density of ceramic samples. The measured SEM-EDS spectra clearly showed that there were five magnetic elements in the high-entropy ceramic samples in approximately equimolar ratios, confirming that the actual measured stoichiometry was basically consistent with the theoretical stoichiometry. In addition, the above experimental data also indicated that the sample structure was still dominated by a bismuth-oxygen tetrahedral and niobium-oxygen octahedral lattice interwoven framework, suggesting that its structure still has inherent physical properties, such as dielectric properties, photoelectrocatalytic properties, and structural characteristics, such as high-temperature resistance. Based on the approximate range of oxygen vacancies that could be measured experimentally, the estimated δ range was -0.16 to +0.56.

[0059] refer to Figure 3 To verify the high-temperature resistance of the single-phase high-entropy high-temperature ceramic material of this invention, a high-temperature resistance characteristic was characterized. Specifically, the high-entropy ceramic material was first pressed into sheets and calcined at 900℃ to form a dense ceramic block. The block was then placed in an image-based sintering point tester. The temperature range was set to 900-1000℃ and the heating rate to 1℃ / min. The structural changes of the ceramic block during the heating process were observed by taking pictures. The results showed that at around 1000℃, the macroscopic structure of the ceramic remained unchanged, with no melting or expansion observed. Furthermore, the XRD patterns of the tested sample were compared with those of the untested sample, showing no significant changes, indicating that the prepared ceramic material possesses high-temperature resistance.

[0060] The ceramic samples prepared in Example 1, Comparative Example 1 and Comparative Example 2 were characterized by magnetic properties, ferroelectricity, optical absorption spectroscopy, magnetic dielectric properties, and photoelectric effect.

[0061] refer to Figure 4 , Figure 5 and Figure 6 To demonstrate that the single-phase high-entropy ceramic material of this invention possesses excellent magnetic, ferroelectric, and optical properties, magnetic, ferroelectric, and optical absorption spectroscopy measurements were performed on the sample. These measurements are commonly used methods in materials science, and the specific measurement procedures will not be elaborated further. The magnetic measurements mainly involved variable-temperature measurements and hysteresis loop measurements. The experimental results are as follows: Figure 4 As shown. The results indicate that the high-entropy material of this application exhibits good room-temperature ferromagnetism, confirming that high-entropy design of magnetic elements can effectively alter and enhance the magnetism of bismuth niobate-based materials.

[0062] The ferroelectricity measurement was specifically performed using a ceramic sheet with silver electrodes at both ends. Hysteresis loop measurements were then conducted on a ferroelectric measuring instrument. The experimental results are as follows: Figure 5 As shown. The sample exhibits hysteresis loop characteristics under an electric field of 100 kV / cm at room temperature, confirming that the material possesses room-temperature ferroelectricity. The optical absorption spectrum measurement specifically utilizes ultraviolet-visible-near-infrared diffuse reflectance spectroscopy of ceramic powder; the experimental results are as follows. Figure 6 As shown, single-phase high-entropy ceramic materials exhibit good broadband light absorption characteristics in the 300nm-2000nm region.

[0063] Furthermore, to demonstrate that the single-phase high-entropy ceramic material of the present invention, which possesses multiple functions of magnetoelectricity and optics, has coupling characteristics with different order parameters, the material was subjected to magnetoelectric effect measurement and photoelectric effect measurement.

[0064] Magnetic dielectric measurement: First, the dielectric constant as a function of temperature was measured from 50K to 340K under zero magnetic field. Then, the dielectric constant as a function of temperature was measured again under 1 Tesla. The non-overlapping portions of the two curves indicate the presence of a magnetic dielectric effect. Experimental results are as follows: Figure 7 As shown in the figure. The results revealed that after the magnetic structure transition, the magnetic field significantly affected the dielectric constant, and the heating and cooling curves did not coincide after the magnetic transition, indicating magnetothermal hysteresis near room temperature. Furthermore, low temperatures primarily exhibited ferromagnetism, with a magnetic transition occurring around 200K. Above 200K, the magnetism became more complex, with significant interactions between different magnetic structures, making these complex magnetic interactions more likely to induce changes in the dielectric constant. Measurements of the magnetic permittivity showed that the region with a significant magnetic permittivity effect was above 200K, with the magnetic permittivity reaching over 3%, particularly covering the room temperature range.

[0065] Photoelectric effect measurement: The ceramic powder of this application was used to fabricate a photoelectrode of a certain area on an FTO conductive substrate, and then the ON-OFF transient photocurrent Jt curve was measured using the three-electrode method in a neutral sodium sulfate solution. The experimental results are as follows: Figure 8 As shown, the results demonstrate the existence of photoinduced current, i.e., the material exhibits a photoelectric effect.

[0066] The structural and performance characterization experiments described above demonstrate that the high-entropy high-temperature ceramic material prepared by this invention also possesses a pyrochlore phase structure, making it a single-phase material. This fully proves that the preparation method provided by this invention can successfully prepare single-phase high-entropy ceramic materials, demonstrating significant scientific research value. The single-phase high-entropy material of this invention exhibits good room-temperature ferromagnetism, room-temperature ferroelectricity, and a wide visible-near-infrared light absorption range. It also possesses magnetoelectric and photoelectric effects, indicating that it combines magnetoelectric and photoelectric multifunctional characteristics, with coupling effects between order parameters. Furthermore, the experimental data from the comparative samples above show that having a small amount of magnetic element doping does not effectively exhibit room-temperature ferromagnetism and excellent light absorption characteristics. This fully demonstrates that the high-entropy structure design involving magnetic elements in this invention can bring about the uniqueness and superiority of the material's properties.

[0067] Where there is no conflict, the above embodiments and features described herein can be combined with each other.

[0068] 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, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A bismuth niobate-based pyrochlore phase high-entropy ceramic, characterized in that, The chemical formula of the bismuth niobate-based pyrochlore phase high-entropy ceramic is (Nb 0.36 Bi 1.64 (Fe) 0.2 Co 0.2 Ni 0.2 Mn 0.2 Cr 0.2 )NbO 7-δ。 2. The bismuth niobate-based pyrochlore phase high-entropy ceramic as described in claim 1, characterized in that, High-entropy design using magnetic transition metal elements at niobium ion sites yields a crystal structure that is still a defective A2B2O7 type single-phase pyrochlore phase structure. In this structure, some niobium ions occupy bismuth ion sites, and five equimolar magnetic transition metal ions occupy niobium ion sites at the B sites.

3. The bismuth niobate-based pyrochlore phase high-entropy ceramic as described in claim 1, characterized in that, The bismuth niobate-based pyrochlore phase high-entropy ceramic exhibits ferromagnetism at room temperature.

4. The bismuth niobate-based pyrochlore phase high-entropy ceramic as described in claim 1, characterized in that, The bismuth niobate-based pyrochlore phase high-entropy ceramic exhibits both ferromagnetism and ferroelectricity at room temperature, i.e., it possesses room-temperature magnetoelectric multiferroic properties.

5. The bismuth niobate-based pyrochlore phase high-entropy ceramic as described in claim 1, characterized in that, The bismuth niobate-based pyrochlore phase high-entropy ceramic exhibits good broadband light absorption characteristics in the visible-near infrared region of 300nm-2000nm.

6. The method for preparing a single-phase bismuth niobate-based pyrochlore-phase high-entropy ceramic according to any one of claims 1-5, characterized in that... Synthesized via a step-by-step dissolution and sol-gel combustion method, specifically including the following steps: S1. Weigh a certain amount of the amorphous compound containing water of crystallization Nb2O5×3H2O and dissolve it in deionized water. Then, add citric acid in an equal molar ratio to complex it. After heating and stirring in a water bath at a certain temperature, a transparent solution A is obtained. S2. Weigh out the bismuth source compound, iron source compound, cobalt source compound, nickel source compound, manganese source compound and chromium source compound that are soluble in acid according to the stoichiometric ratio shown in the chemical formula, and dissolve the above components in diluted acid solution respectively. After stirring at room temperature, a clear solution B is formed. S3. Add solution A to solution B and stir continuously to form a mixed and clear solution C. Add citric acid as a complexing agent and ethylenediaminetetraacetic acid as a combustion aid to solution C, and then add ammonia water to adjust the pH value to neutral, finally forming a transparent solution D. S4. Transfer solution D to an evaporation crucible. After heating, solution D passes through a sol and gel and spontaneously combusts. Collect the remaining powder to obtain primary powder. Then, grind the collected powder and place it in a muffle furnace for high-temperature pre-firing and high-temperature sintering to obtain the single-phase high-entropy ceramic block.

7. The preparation method according to claim 6, characterized in that, In step S2, the bismuth source compound is bismuth nitrate pentahydrate, the iron source compound is ferric nitrate nonahydrate, the cobalt source compound is cobalt nitrate hexahydrate, the nickel source compound is nickel acetate, the manganese source compound is manganese oxalate, and the chromium source compound is chromium nitrate nonahydrate.

8. The preparation method according to claim 6, characterized in that, In step S3, the molar ratio of the total metal ions, complexing agent citric acid, and combustion improver ethylenediaminetetraacetic acid is 1:1:

1.

9. The preparation method according to claim 6, characterized in that, In step S4, the high-temperature preheating temperature is 500~800℃, and the holding time is 2h.

10. The preparation method according to claim 6, characterized in that, In step S4, the high-temperature sintering temperature is 900~1000℃, and the sintering time is 5~7h.

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