High-entropy flexible functional ceramic nanofiber material and preparation method thereof

Abstract

The invention discloses a method for preparing a flexible functional ceramic nanofiber material through entropy design, which comprises the following steps: weighing a plurality of metal salt powder in a set proportion to obtain raw material powder, the metal salt powder comprises first metal salt powder and second metal salt powder, the first metal salt powder is used for forming an Aurivillius type compound matrix, and the second metal salt powder is used for forming an Aurivillius type compound matrix; the second metal salt powder comprises at least four metal elements, and the radius of metal ions in the second metal salt powder is matched with the radius of metal ions in the first metal salt powder, so that the second metal salt powder is used for replacing metal in the Aurivillius type compound matrix; mixing and stirring the raw material powder and an organic solvent to obtain sol; mixing and stirring a spinning aid and the sol to obtain a precursor spinning solution; performing electrostatic spinning on the precursor spinning solution under set conditions to form an initial fiber material; the initial fiber material is heated to a set temperature and then subjected to heat preservation, and the high-entropy flexible functional ceramic nanofiber material is obtained. The invention further discloses the high-entropy flexible functional ceramic nanofiber material.

Description

Technical Field

[0001] The present invention belongs to the field of fiber material applications, and specifically relates to a high-entropy flexible functional ceramic nanofiber material and a preparation method thereof. Background Art

[0002] Flexible ceramic nanofiber materials are mainly used in flexible electronics, high-temperature machinery, biomedicine and other application fields. However, the current preparation process of flexible ceramic nanofiber materials is relatively complicated, and there is a lack of research on the performance optimization and regulation of flexible ceramic nanofiber materials, resulting in the problem of brittleness and easy breakage of ceramic materials.

[0003] Therefore, developing and designing a new type of ceramic nanofiber material and a preparation method thereof to reduce the brittleness of the ceramic nanofiber material and improve its flexibility is an urgent problem to be solved in this field. Summary of the Invention

[0004] The present invention aims to solve one of the technical problems in the related art to a certain extent, and to this end provides a method for preparing a high-entropy flexible functional ceramic nanofiber material, comprising:

[0005] Weighing a plurality of metal salt powders in a set ratio to obtain a raw material powder, the metal salt powders comprising a first metal salt powder and a second metal salt powder, the first metal salt powder being used to form an Olivierius-type compound matrix, the second metal salt powder comprising at least four metal elements, the metal ion radius in the second metal salt powder matching the metal ion radius in the first metal salt powder, so as to be used to replace the metal in the Olivierius-type compound matrix;

[0006] Mixing the raw material powder with an organic solvent to obtain a sol;

[0007] mixing the spinning aid with the sol to obtain a precursor spinning solution;

[0008] Electrospinning the precursor solution under set conditions to form an initial fiber material;

[0009] The initial fiber material is heated to a set temperature and then kept warm to obtain the high-entropy flexible functional ceramic nanofiber material.

[0010] Furthermore, the Olivierius-type compound matrix includes a layered structure and a perovskite structure arranged in layers, the first metal salt powder comprises a first metal element, the first metal element has a first metal ion site in the layered unit, corresponding to a first ionic radius, the first metal element has a second metal ion site in the perovskite structure unit, corresponding to a second ionic radius, and the second ionic radius is greater than the first ionic radius.

[0011] The radius of metal ions in the second metal salt powder is between the first ionic radius and the second ionic radius.

[0012] Furthermore, the first metal salt powder includes a bismuth salt, the second metal salt powder includes a lanthanide metal salt, and the raw material powder further includes at least one of a titanium salt, an iron salt, an organic titanate, and an organic ferrite.

[0013] Furthermore, in the second metal salt powder, the lanthanide metal salt includes a plurality of lanthanide metal elements, and the molar ratios of the lanthanide metal atoms corresponding to the plurality of lanthanide metal elements are consistent;

[0014] The ratio of the molar amount of the corresponding metal atoms of the metal element in the bismuth salt to the molar amount of the corresponding metal atoms of the metal element in the lanthanide metal salt satisfies the following formula:

[0015] A:B=(1-x):x

[0016] Among them, 0 <x≤0.75,

[0017] A represents the molar amount of bismuth atoms in the bismuth salt;

[0018] B represents the molar amount of all lanthanide metal atoms in the lanthanide metal salt.

[0019] Furthermore, the spinning aid includes polyethylene oxide and / or polyvinyl pyrrolidone.

[0020] Furthermore, in the step of mixing the spinning aid with the sol to obtain a precursor spinning solution,

[0021] A spinning aid prepared by mixing polyethylene oxide and acetic acid solution is mixed with the sol and stirred. The mass fraction of polyethylene oxide in the acetic acid solution is between 1wt% and 3wt%, and the weight ratio of the spinning aid to the sol is between 0.5 and 1.5.

[0022] Furthermore, in the step of forming an initial fiber material by electrospinning the precursor spinning solution under set conditions,

[0023] The precursor spinning solution is pushed through an injector to form droplets, and a set voltage is applied to stretch the droplets to form a fiber structure. The initial fiber material formed by the fiber structure is collected in a receiving device, wherein the injection speed of the precursor spinning solution is between 0.1mL / min and 0.5mL / min, the set voltage is between 5kV and 50kV, the working temperature is between 15°C and 35°C, the receiving distance between the injector and the receiving device is between 5cm and 30cm, the relative humidity is within the range of 35±10%, the receiving device used includes any one of non-woven fabric, aluminum foil and copper mesh, and the rotation speed of the receiving device is between 100r / min and 160r / min.

[0024] Furthermore, in the step of heating the initial fiber material to a set temperature and then keeping the temperature to obtain the high entropy flexible functional ceramic nanofiber material,

[0025] The set temperature is between 600° C. and 700° C., the holding time is between 50 min and 70 min, and the heating rate is between 3° C. / s and 7° C. / s.

[0026] As a second aspect of the present application, a high-entropy flexible functional ceramic nanofiber material is provided, which is prepared using the above-mentioned preparation method.

[0027] Furthermore, the high-entropy flexible functional ceramic nanofiber material includes a composite structure of amorphous and nanocrystals, the proportion of the amorphous is between 6% and 94%, and the size of the nanocrystals is not greater than 5 nm.

[0028] The present invention utilizes a novel component design, introducing metal elements with specific ionic radii to replace specific active sites in the Olivieris compound, thereby controlling the degree of compound distortion. Furthermore, the introduction of multiple different elements increases the system's configurational entropy. Through this high-entropy component design, combined with electrospinning technology, the fibers of the present invention have a higher amorphous content and smaller grain size, overcoming the brittleness of traditional ceramic materials and exhibiting excellent flexibility, capable of withstanding large bending deformations without breaking. Furthermore, their dielectric constant and temperature stability surpass those of traditional polymer-based flexible dielectric materials, enabling them to be used as dielectric capacitors in flexible wearable applications. This entropy-driven approach is expected to promote the development of flexible functional ceramics, with applications extending beyond traditional simple oxides such as amorphous silicon dioxide and aluminum oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0030] Figure 1 This is a flow chart of an embodiment of the method for preparing high-entropy flexible functional ceramic nanofiber materials provided in this application;

[0031] Figure 2 is a schematic diagram of the matrix structure of the Olivieris-type compound provided in this application;

[0032] Figure 3 is the X-ray diffraction pattern (XRD) of the fiber materials prepared in the examples and comparative examples of the present application;

[0033] Figure 4 2 are transmission electron microscope photos of fiber samples with different entropy values ​​prepared in the examples and comparative examples of the present application;

[0034] Figure 5 is an element distribution diagram of a cross section of a nanofiber prepared in an embodiment of the present application;

[0035] Figure 6 This is a graph showing in-situ bending test data of the nanofibers prepared in the examples of the present application;

[0036] Figure 7 1 is a graph showing the relationship between the dielectric constant and loss tangent of the nanofibers prepared in the examples of the present application and the temperature;

[0037] Figure 8 3 is a graph showing the relationship between the capacitance change of the nanofibers prepared in the examples of the present application and the change of pressure. DETAILED DESCRIPTION

[0038] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described in the embodiments are intended to explain the present invention and are not to be construed as limiting the present invention.

[0039] References in this specification to "one embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with the embodiment itself can be included in at least one embodiment disclosed herein. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

[0040] The inventors of this application have found that polymer-based dielectric capacitors (such as BOPP, PEI, PDMS, etc.) have good mechanical flexibility and have great application potential in the field of flexible energy storage. However, the poor thermomechanical stability and low dielectric constant (<10) of polymer-based materials limit their further application in complex environments. In contrast, ceramic-based dielectric materials are known for their excellent temperature stability and high dielectric constant, and are expected to become substitutes for polymer-based dielectrics. However, ceramic materials usually exhibit inherent brittleness at room temperature. This is because their bonding mode, which is mainly ionic or covalent, directly limits their plastic deformation capacity. When subjected to external force, ceramics lack an energy dissipation mechanism, and stress concentration at defects will cause cracks to expand rapidly according to Griffith theory, ultimately leading to macroscopic brittle fracture.

[0041] Currently, the research on flexible ceramic thin film dielectric capacitors mainly focuses on depositing ceramic films on flexible substrates (such as mica sheets, metal foils, etc.), and giving ceramic thin film dielectric capacitors a certain flexibility by "borrowing" the bendable properties of the substrate. However, this type of material has significant limitations in practical applications: the mechanical mismatch and stress / strain concentration at the interface between the "hard" ceramic film and the "flexible" substrate will affect the growth quality of the dielectric film, reduce the density and uniformity of the ceramic film, and thus lead to a significant decrease in energy storage performance. For example, Lee et al. spin-coated La-PbZrO3 film on stainless steel foil to prepare a ceramic thin film capacitor with a certain degree of flexibility, but its energy storage density was only 15.2 J / cm 3 , which is much lower than that of similar capacitors deposited on hard LNO / Ni substrates under the same conditions (energy storage density of about 85 J / cm 3 ), the energy storage density loss is as high as 82%. Therefore, the realization of flexible preparation of self-supporting ceramic dielectric materials that do not rely on substrates is the key to the development of advanced flexible electronics.

[0042] Over the past few decades, researchers have been working to improve the deformability of ceramic materials. A common approach is to reduce the material size to one-dimensional nanowires / nanofibers or two-dimensional ultrathin films. For example, alumina-based ceramic nanofibers with a diameter of approximately 300 nm can achieve a tensile fracture deformation of 4.84%. Amorphous SiO2 nanowires with a diameter of 5.3 nm can achieve a tensile fracture deformation of up to 18%. Crystalline La0.7Ca0.3MnO3 films with a thickness of 8 nm exhibit a tensile deformation of 8.2%, but when the thickness exceeds 20 nm, the maximum deformation value drops below 2% due to periodic crack formation. Single-crystalline ferroelectric BaTiO3 films with a thickness of 120 nm can achieve a tensile strain of 10.05% through the unique dynamic evolution of ferroelectric nanodomains. Despite these advances, the practical application of these materials remains challenging due to limitations in their small size, application difficulties, and complex preparation processes.

[0043] To solve the above problems, as the first aspect of this application, a method for preparing a high entropy flexible functional ceramic nanofiber material is disclosed, such as Figure 1 As shown, specifically including:

[0044] S100, weighing a plurality of metal salt powders in a set ratio to obtain a raw material powder, the metal salt powders including a first metal salt powder and a second metal salt powder, the first metal salt powder being used to form an Olivierius-type compound matrix, the second metal salt powder including at least four metal elements, the metal ion radius in the second metal salt powder matching the metal ion radius in the first metal salt powder, so as to be used to replace the metal in the Olivierius-type compound matrix;

[0045] S110, mixing the raw material powder with the organic solvent to obtain a sol;

[0046] S120, mixing the spinning aid and the sol to obtain a precursor spinning solution;

[0047] S130, forming an initial fiber material by electrospinning the precursor spinning solution under set conditions;

[0048] S140, heating the initial fiber material to a set temperature and then keeping the temperature to obtain a high-entropy flexible functional ceramic nanofiber material.

[0049] In step S100, the present application does not specifically limit the source of the metal salt powder, which can be obtained by purchasing or self-production.

[0050] The present application does not impose any special restrictions on the material of the second metal salt powder. It only needs to satisfy the requirement that the metal ion radius in the second metal salt powder matches the metal ion radius in the first metal salt powder. As an optional implementation method, the Olivierius-type compound matrix includes a layered structure and a perovskite structure arranged in layers. The first metal salt powder has a first metal element, and the first metal element has a first metal ion site in the layered unit, corresponding to a first ionic radius. The first metal element has a second metal ion site in the perovskite structure unit, corresponding to a second ionic radius. The second ionic radius is larger than the first ionic radius, and the metal ion radius in the second metal salt powder is between the first ionic radius and the second ionic radius.

[0051] For ease of understanding, the following is an explanation of the composition design of this application. Aurivillius-type compounds are a type of layered bismuth-based oxides, the general formula of which can be expressed as Bi2O2(A n-1 B n O 3n+1 ), composed of perovskite type [A n-1 B n O 3n+1] 2- layer and [Bi2O2] 2+ The layers are arranged alternately, such as Figure 2 The figure shows an Olivierius compound Bi4Ti3O 12 In this structure, [Bi2O2] 2+ The Bi atoms in the layer are in a stable configuration with five adjacent O atoms (hereinafter referred to as Bi 3+ -V), and the Bi atom in the perovskite structure is located at the center of the regular octahedron and is also -3valent (hereinafter referred to as Bi 3+ -XII). The inventors have conducted in-depth research and found that Bi 3+ The ionic radius of -V is 0.96A, while Bi 3+ -XII has an ionic radius of 1.36A. If the metal ionic radius of the second metal salt powder used for substitution is selected in Bi 3+ -V and Bi 3+ -XII Bi ion radius is between 0.96A and 1.36A, which means that Bi 3+ The radius of Bi ions at -XII sites is larger than that of substituted metal ions, which is beneficial for the introduced metal ions to preferentially replace Bi 3+ -V site Bi ions, which can achieve metal substitution at specific sites, on the other hand, the ionic radius of the introduced element is similar to that of Bi 3+ The difference between the ionic radius of -V causes a certain degree of structural distortion, and in Bi 3+ Partial substitution at the -XII site increases the degree of structural deformation. As a result, the substituted metal ions are evenly distributed in the perovskite structure. The disordered distribution of the substituted elements at this site leads to large lattice distortion within the material, which in turn generates local stress fields. These local stress fields can effectively hinder the diffusion of charge carriers, thereby reducing dielectric loss and improving the temperature stability of the dielectric constant.

[0052] The present application does not impose any special restrictions on the components of the first metal salt powder and the second metal salt powder. They only need to meet the above-mentioned corresponding characteristics. The first metal salt powder only needs to be a bismuth source. For example, it can be at least one of bismuth acetate, bismuth aluminate, bismuth molybdate, bismuth stannate, bismuth citrate and bismuth ferrite. Preferably, the first metal salt powder includes a bismuth salt, preferably bismuth acetate. The acetate anion can acidify and adjust the pH of the solution in the solution, and the acidic environment is more conducive to the uniform dispersion of bismuth cations. The second metal salt powder includes a lanthanide metal salt. In some embodiments, the lanthanide metal salt powder forms La in the solution. 3+ 、Pr 3+ 、Nd 3+ and Sm 3+Cations, they all have a trivalent state, and the ionic radii are 1.16A, 1.126A, 1.109A and 1.079A respectively, all satisfying the Bi 3+ -V and Bi 3+ -V Bi ion radius is between 0.96A and 1.36A, which can 3+ -V is replaced by Bi, and with the increase of La, Pr, Nd, and Sm content, Bi 3+ -V will also undergo partial substitution, and the degree of structural deformation will be further enhanced.

[0053] As an optional embodiment, in order to form a stable Olivierius-type compound, the raw material powder also includes at least one of a titanium salt, an iron salt, an organic titanate, and an organic ferrite. The organic titanate includes one or more of isopropyl titanate, tetrabutyl titanate, isobutyl titanate, tetraethyl titanate, and polybutyl titanate. The bismuth titanate system and the bismuth ferrite system are both important multiferroic materials with significant ferroelectric and piezoelectric properties, and are the main materials for flexible ceramic films. In addition, the present application does not make any special restrictions on the substituted metals. Both Bi and Ti can be substituted. If Bi is substituted, the dielectric properties will be greatly affected, while if Ti is substituted, the piezoelectric properties will be greatly affected. It can be adjusted according to specific actual needs.

[0054] In some embodiments, the specific types of bismuth salts, lanthanum salts, neodymium salts, praseodymium salts, samarium salts, and titanium salts are not particularly limited, as long as they provide corresponding metal ions. As some specific examples, organic salts containing various metal ions can be used, such as bismuth acetate, lanthanum acetate, neodymium acetate, praseodymium acetate, samarium acetate, tetrabutyl titanate, etc.

[0055] The present application does not make any special restrictions on the ratio of lanthanide metal salts to bismuth salts, as long as it meets the high configurational entropy. Since the high entropy material is formed by five or more materials of equal or approximately equal amounts, preferably, the lanthanide metal salt of the present application includes a plurality of lanthanide metal elements, at least four lanthanide metal elements that can satisfy the structure of high configurational entropy with Bi metal, and the molar ratio of the multiple lanthanide metal atoms corresponding to the multiple lanthanide metal elements is consistent. Under this ratio, the highest configurational entropy can be obtained. The high entropy effect, hysteresis diffusion effect and cocktail effect brought about by the increase in entropy can effectively improve the organizational uniformity of the high entropy flexible functional ceramic nanofiber material, the amorphous forming ability is higher, it is easier to form an amorphous structure, and the lattice distortion caused by substitution is larger, the degree of structural deformation is enhanced, and the grain size is smaller, not higher than the nanometer range. Macroscopically, the high entropy flexible functional ceramic nanofiber material has higher strength while improving the plastic deformation ability, reducing the possibility of brittle fracture. And as the entropy increases, the maximum withstand voltage field strength of the material increases. This is because as entropy increases, the internal disorder of the material increases, resulting in higher local stress and breakdown field strength. This fully demonstrates the influence of the local stress field effect and cocktail effect in high-entropy materials on material properties.

[0056] In addition, the equiatomic molar ratio enables Bi in high-entropy flexible functional ceramic nanofiber materials to be replaced by other lower-cost compounds without a significant decrease in performance, which is conducive to the large-scale production of high-entropy flexible functional ceramic nanofiber materials.

[0057] As an optional embodiment, the ratio of the corresponding metal atomic molar amount of the metal element in the bismuth salt to the corresponding metal atomic molar amount of the metal element in the lanthanide metal salt satisfies the following formula:

[0058] A:B=(1-x):x

[0059] Among them, 0 <x≤0.75,

[0060] A represents the molar amount of bismuth atoms in the bismuth salt;

[0061] B represents the molar amount of all lanthanide metal atoms in the lanthanide metal salt.

[0062] Specifically, if bismuth titanate-based high-entropy flexible nanofiber material is selected, the corresponding chemical formula must satisfy:

[0063] Bi 4-4x (LaPrNdSm) x TiO 12, where \(0 < x\leqslant0.75\), and the value of \(x\) is not particularly limited. For example, \(x\) can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, etc. The calculation formula for configurational entropy is as follows:

[0064]

[0065] where \(R\) represents the ideal gas constant, and \(x_i\) and \(x_j\) respectively represent the molar ratios of elements at the cation and anion positions. Thus, the configurational entropy can be between \(0R\) and \(1.6R\).

[0066] In step S110, when mixing and stirring the raw material powder weighed according to the set ratio with an organic solvent to obtain a mixed sol, this application does not make special limitations on the organic solvent, as long as it can disperse and dissolve the metal salt powder without chemical reaction and is easy to be removed by heating and volatilization. Preferably, the organic solvent is at least one of propionic acid, acetic acid, isopropyl alcohol, and dimethylformamide. At the same time, a stabilizer such as ethanolamine can be added in this step to adjust the pH value of the sol and improve the dispersibility.

[0067] In step S120, the spinning aid is mixed and stirred with the sol to obtain a precursor spinning solution. The present application does not make any special limitation on the spinning aid. In the electrospinning process, the principles for selecting the spinning aid mainly include: improving the rheological properties of the spinning solution to make it have moderate viscosity to form a stable jet; improving the conductivity of the solution to ensure smooth spinning in the electric field; reducing the surface tension to facilitate spinning at a lower electric field strength; having good compatibility with the main polymer to ensure the uniformity of the fiber; and being easy to remove in subsequent processing without affecting the final performance of the fiber. Based on the high entropy component design, the present application comprehensively considers the relationship between the spinning aid and each component. Since the various metal salt powders used in this application have different solubility properties, and the surface tension and conductivity of various metal cations are also different, the spinning solution flows, and it is easy to have uneven structures such as component concentration and segregation in electrospinning, resulting in poor spinning performance. Therefore, as a preferred embodiment, the spinning aid includes polyethylene oxide (PEO) and / or polyvinyl pyrrolidone (PVP), both of which can be dissolved in the above-mentioned organic solvents, thereby forming a uniformly dispersed precursor colloidal spinning solution through a complex adsorption mechanism with the metal salts in the organic solvent, thereby improving the spinnability of the spinning solution and making the fiber forming more stable; adjusting the fiber diameter to achieve precise control of the fiber size; improving the fiber quality and reducing surface defects; enhancing the mechanical properties of the fiber, such as toughness and strength; and in some cases, giving the fiber special properties, such as conductivity. In addition, the complete decomposition temperature of this spinning aid is lower, so that when the subsequent fiber is heated to remove the spinning aid, the decomposition temperature is too high, resulting in a greater driving force for crystallization, avoiding crystallization to form large-sized grains and destroying flexibility.

[0068] In some embodiments, a spinning aid mixed with polyethylene oxide and acetic acid solution is mixed and stirred with the sol, the mass fraction of polyethylene oxide in the acetic acid solution is between 1wt% and 3wt%, and the weight ratio of the spinning aid to the sol is between 0.5 and 1.5. If it exceeds 1.5, it means that the amount of spinning aid is too much, which will cause the viscosity of the spinning solution to be too high, thereby increasing the resistance during the injection process, which is not conducive to the formation of fine fibers. In addition, too much spinning aid may also cause defects or roughness on the fiber surface, affecting the mechanical properties of the fiber and subsequent application effects. Moreover, in some cases, the excess spinning aid may be difficult to completely remove, and the residual spinning aid will have a negative impact on the physical and chemical properties of the fiber, such as conductivity, thermal stability, etc. On the other hand, if the proportion or concentration of the spinning aid is too low, it cannot effectively reduce the surface tension of the spinning solution, thereby affecting the spinnability of the solution, affecting the continuity and uniformity of the fiber, and the fiber may break, have uneven diameter distribution, and other problems, seriously affecting the quality and application performance of the fiber.

[0069] In step S130, specifically, it includes:

[0070] In the step of forming an initial fiber material by electrospinning the precursor spinning solution under set conditions,

[0071] The precursor spinning solution is injected through an injector to form droplets, and a set voltage is applied to stretch the droplets to form a fiber structure. The initial fiber material formed by the fiber structure is collected in a receiving device, wherein the injection speed of the precursor spinning solution is between 0.1mL / min and 0.5mL / min, the set voltage is between 5kV and 50kV, the working temperature is between 15°C and 35°C, the receiving distance between the injector and the receiving device is between 5cm and 30cm, the relative humidity is within the range of 35±10%, the receiving device used includes any one of non-woven fabric, aluminum foil and copper mesh, and the rotation speed of the receiving device is between 100r / min and 160r / min. Since the present application adopts high-entropy designed components, multiple Bi metal sites are replaced by other lanthanide metals, the lattice distortion is large, and the degree of structural deformation is enhanced. Therefore, electrospinning can be prepared in a larger process range and form more amorphous tissue structures, further improving the stability and reliability of the preparation method of high-entropy flexible functional ceramic nanofiber materials, and the prepared fiber surface is smooth and defect-free, the tissue is uniform and the structure is dense.

[0072] In step S140, the initial fiber material is heated to a set temperature and then held at that temperature to obtain a high-entropy flexible functional ceramic nanofiber material. Specifically, the step includes setting the temperature between 600°C and 700°C, holding the temperature for 50 to 70 minutes, and heating at a rate between 3°C / s and 7°C / s. The spinning aid component in the composite nanofibers is selectively removed by thermal decomposition, resulting in composite metal oxide nanofibers.

[0073] As the second aspect of the present application, a high-entropy flexible functional ceramic nanofiber material is provided, which is prepared by the preparation method of the present application, and the high-entropy flexible functional ceramic nanofiber material includes a composite structure of amorphous and nanocrystals. The composite structure enables the material to overcome the brittleness problem of traditional ceramic thin film materials, and exhibits excellent flexibility in that the film can withstand large bending deformation without breaking, and the dielectric constant and temperature stability are better than traditional polymer-based flexible dielectric materials. And due to the high-entropy substitution mechanism, the proportion of amorphous is more controllable, the proportion of amorphous is between 6% and 94%, and the size of the nanocrystal is not higher than 5nm. This quasi-amorphous structure gives the one-dimensional nanofiber excellent flexibility, which can be bent into a spring shape in situ without microcracks. The dielectric properties of the high-entropy flexible functional ceramic nanofiber material prepared at the same time do not change with temperature, so that it can be used as a capacitive strain sensor in a wide temperature range.

[0074] The present invention adopts the method of using ferroelectric material Bi4Ti3O 12The four elements La, Pr, Nd and Sm are introduced in equal proportions into the Bi position to control the configuration entropy of the material system, thereby realizing the design of the intrinsic crystal structure of the material (including grain size and amorphous content, etc.). The final Bi4Ti3O 12 The material has a nanocrystalline / amorphous dual-phase structure, which not only overcomes the brittleness of traditional ceramic thin film materials, exhibiting excellent flexibility, allowing it to be folded in half without breaking, but also exhibits a dielectric constant and temperature stability superior to traditional polymer-based flexible dielectric materials. The resulting bismuth titanate-based dielectric high-entropy flexible material can be used in flexible electronic devices, such as dielectric capacitors in flexible wearables.

[0075] The method of achieving flexibility of ceramic dielectric films through entropy regulation in the present invention provides a new solution to the brittleness problem of ceramic materials. The obtained flexible ceramic dielectric film (i.e., bismuth titanate-based dielectric high-entropy flexible nanofiber material) can be used as a dielectric capacitor in the field of flexible wearables. At the same time, this method can be extended to other types of functional ceramic films, and is expected to realize the flexible preparation of various ceramic materials, thereby expanding their application fields.

[0076] In some embodiments, the fibers after electrospinning are collected. In order to test the various properties of the fibers, the fiber materials need to be further processed to form thin films or block materials. Usually, the layer-by-layer stacking method and the freeze-drying method are used to prepare high-entropy flexible material nanofiber blocks. First, layer-by-layer stacking is used to obtain wet three-dimensional fiber aggregates, wherein the impregnation liquid of the layer-by-layer stacking method is a 0.5wt% Al(H2PO4)3 aqueous solution. Further, the moisture in the above-mentioned wet three-dimensional fiber aggregates is removed by freeze-drying to obtain unbonded fiber blocks. Finally, the blocks are calcined at 600°C in a muffle furnace for 1 hour to form a cross-linked structure in the fiber blocks. The flexible high-entropy fiber membrane is further cut into small pieces of the same size. Preferably, the cutting size is a square small piece with a side length of 5mm to 10mm.

[0077] The present invention will be further described below through specific examples and comparative examples.

[0078] Example

[0079] Example 1

[0080] This embodiment provides a method for preparing a high-entropy flexible functional ceramic nanofiber material, comprising:

[0081] Step 1. Weigh a set proportion of multiple metal salt powders to obtain a raw material powder, the metal salt powder including a first metal salt powder and a second metal salt powder, the first metal salt powder being used to form an Olivierius-type compound matrix, the second metal salt powder including at least four metal elements, the metal ion radius in the second metal salt powder matching the metal ion radius in the first metal salt powder, so as to replace the metal in the Olivierius-type compound matrix. Specifically, weigh a set proportion of bismuth acetate, lanthanum acetate, neodymium acetate, praseodymium acetate, samarium acetate, and tetrabutyl titanate, and weigh the corresponding drugs at a molar concentration of 0.02 mol / L, and the ratio satisfies the following relationship:

[0082] Bi 4-4x (LaPrNdSm) x TiO 12 , where x = 0.25;

[0083] The bismuth acetate raw material powder is 5% in excess of the stoichiometric ratio to compensate for the volatilization of the Bi element during the heat treatment process. The amounts of the other components can be calculated according to the stoichiometric ratio to obtain the actual mass of each element required when x = 0.25.

[0084] Step 2: Mixing the raw material powder with an organic solvent to obtain a sol. Specifically, the raw material powder is mixed with propionic acid solvent and stirred at 60° C. for 10 minutes.

[0085] Step 3, mixing and stirring a spinning aid with the sol to obtain a precursor spinning solution, specifically, a spinning aid mixed with polyethylene oxide and an acetic acid solution is mixed and stirred with the above sol, wherein the mass fraction of polyethylene oxide in the acetic acid solution is between 1 wt% and 3 wt%, and 1 g of each of the spinning aid and the above sol is weighed and stirred at room temperature for 2 hours until uniform, to obtain a precursor spinning solution;

[0086] Step 4: electrospinning the precursor solution to form an initial fiber material under set conditions, specifically comprising: placing the obtained precursor solution in a push injection device at a speed of 0.1 mL min -1 The electrospinning process was carried out at a high speed, and a non-woven fabric was used for receiving. The distance between the injection device and the receiving device was adjusted to 220 mm. A high voltage (14 kV) was applied to stretch the hybrid nanofibers. The electrospinning environment parameters were a temperature of 25 ± 5 °C and a relative humidity of 35 ± 5%. The sliding speed of the injection device was set to 500 mm / min, and the parallel moving distance was ± 70 mm.

[0087] Step 5: Heat the initial fiber material to a set temperature and then keep it warm to obtain a high-entropy flexible functional ceramic nanofiber material. Specifically, the process includes heating the initial fiber material to 600°C at a heating rate of 5°C / min and keeping it warm for 60 minutes to obtain a bismuth titanate-based dielectric high-entropy flexible nanofiber material with an entropy of 0.90R, named BT-0.90R.

[0088] Example 2

[0089] A high-entropy flexible functional ceramic nanofiber material was prepared using the same preparation method as in Example 1, except that x=0.5, and the obtained high-entropy flexible functional ceramic nanofiber material had an entropy of 1.38R, named BT-1.38R.

[0090] Example 3

[0091] A high-entropy flexible functional ceramic nanofiber material was prepared using the same preparation method as in Example 1, except that x=0.75, and the entropy of the obtained high-entropy flexible functional ceramic nanofiber material was 1.6R, named BT-1.6R.

[0092] Comparative Example

[0093] Comparative Example 1

[0094] The nanofiber material was prepared using the same preparation method as in Example 1, except that in step 1, bismuth acetate and tetrabutyl titanate were weighed in a stoichiometric ratio of 0.02 mol / L (corresponding to x=0 in the chemical formula) and mixed in a propionic acid solvent;

[0095] The entropy of the final nanofiber material was 0.0R, named BT-0R.

[0096] Test Case

[0097] The samples prepared in each embodiment and comparative example were subjected to morphology test and mechanical property test, and the results are as follows:

[0098] (1) The samples prepared in each embodiment and comparative example were subjected to X-ray diffraction (XRD) test, and the results are shown in Figure 3 As shown in the figure, the intensity of the visible crystallization peak gradually weakens with increasing entropy value. The BT-1.38R sample has a clear amorphous peak. The XRD analysis of the high entropy flexible functional ceramic nanofiber material (BT-1.60R) shows almost no crystallization peak, indicating its quasi-amorphous structure. The amorphous content of the nanofibers analyzed by XRD patterns is only 6% for BT-0R, while it increases significantly to 94% for BT-1.60R.

[0099] (2) Transmission electron microscopy (TEM) was used to characterize the microstructure of nanofibers with different entropy values, e.g. Figure 4(A) shows low-magnification transmission electron microscopy images of the embodiment and the comparative example. It can be seen that the grain size of the embodiment is significantly smaller than that of the comparative example BT-0R, and the surface of the BT-0R nanofiber is rough, and the transmission electron microscopy image of the cross section shows the presence of micro defects and holes ( Figure 4 (B) and Figure 4 (C) in the figure is prone to rapid crack expansion under the action of external force, leading to brittle fracture.

[0100] Figure 4 As shown in (A), as the entropy value increases, the grain size decreases significantly, and the surface of BT-0.90R, BT-1.38R, and BT-1.60R fibers is smooth. The grain size of BT-1.60R nanofibers is always less than 5nm, and the cross-sectional transmission electron microscopy (TEM) image shows a dense structure with almost no visible micro defects ( Figure 4 (D) and Figure 5 ).

[0101] Figure 4 (B) and Figure 4 (C) in the figure shows high magnification TEM and Fourier transform (FFT) images of BT0R and BT-1.60R nanofibers, respectively. BT-0R fibers exhibit a highly crystalline structure, while BT-1.60R fibers exhibit a quasi-amorphous structure with nanocrystals (<5 nm) embedded in an amorphous matrix. Figure 4 (C)). At the nanoscale, the high entropy fiber elements are still evenly distributed ( Figure 4 (D)). TEM images of BT-0.90R and BT-1.38R nanofibers show that the amorphous content is higher than that of BT-0R, further confirming the entropy-induced formation of amorphous regions.

[0102] (3) The flexibility of the high entropy BT-1.60R material and the dynamic bending process were further studied using a focused ion beam scanning electron microscope (FIB-SEM) system. Figure 6 ) showed that high-entropy flexible functional ceramic nanofiber materials can gradually bend without breaking, eventually forming a highly curled spring shape, highlighting their excellent flexibility.

[0103] (4) The dielectric constant and dielectric loss of the prepared flexible BT-1.60R high entropy film were tested at different temperatures. The results are shown in Figure 7 Figure 8 , indicating that it has good dielectric constant stability in the temperature range of 20℃ to 200℃, and the dielectric loss remains at a low level.

[0104] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-entropy flexible functional ceramic nanofiber material, characterized in that: include: Weighing a plurality of metal salt powders in a set ratio to obtain a raw material powder, the metal salt powders comprising a first metal salt powder and a second metal salt powder, the first metal salt powder being used to form an Olivierius-type compound matrix, the second metal salt powder comprising at least four metal elements, the metal ion radius in the second metal salt powder matching the metal ion radius in the first metal salt powder, so as to be used to replace the metal in the Olivierius-type compound matrix; Mixing the raw material powder with an organic solvent to obtain a sol; mixing the spinning aid with the sol to obtain a precursor spinning solution; Electrospinning the precursor solution under set conditions to form an initial fiber material; The initial fiber material is heated to a set temperature and then kept warm to obtain the high-entropy flexible functional ceramic nanofiber material.

2. The preparation method according to claim 1, characterized in that The Olivierius-type compound matrix includes a layered structure and a perovskite structure, wherein the first metal salt powder comprises a first metal element, wherein the first metal element has a first metal ion site in the layered unit, corresponding to a first ionic radius, and the first metal element has a second metal ion site in the perovskite structure unit, corresponding to a second ionic radius, wherein the second ionic radius is larger than the first ionic radius. The radius of metal ions in the second metal salt powder is between the first ionic radius and the second ionic radius.

3. The preparation method according to claim 2, characterized in that The first metal salt powder includes a bismuth salt, the second metal salt powder includes a lanthanide metal salt, and the raw material powder further includes at least one of a titanium salt, an iron salt, an organic titanate, and an organic ferrite.

4. The preparation method according to claim 3, characterized in that In the second metal salt powder, the lanthanide metal salt includes a plurality of lanthanide metal elements, and the molar ratio of the lanthanide metal atoms corresponding to the plurality of lanthanide metal elements is consistent; The ratio of the molar amount of the corresponding metal atoms of the metal element in the bismuth salt to the molar amount of the corresponding metal atoms of the metal element in the lanthanide metal salt satisfies the following formula: A:B=(1-x):x Among them, 0 <x≤0.75, A represents the molar amount of bismuth atoms in the bismuth salt; B represents the molar amount of all lanthanide metal atoms in the lanthanide metal salt.

5. The preparation method according to claim 1, characterized in that The spinning aid comprises polyethylene oxide and / or polyvinyl pyrrolidone.

6. The preparation method according to claim 5, characterized in that In the step of mixing the spinning aid with the sol to obtain a precursor spinning solution, A spinning aid prepared by mixing polyethylene oxide and acetic acid solution is mixed with the sol and stirred. The mass fraction of polyethylene oxide in the acetic acid solution is between 1wt% and 3wt%, and the weight ratio of the spinning aid to the sol is between 0.5 and 1.

5.

7. The preparation method according to claim 1, characterized in that In the step of forming an initial fiber material by electrospinning the precursor spinning solution under set conditions, The precursor spinning solution is pushed through an injector to form droplets, and a set voltage is applied to stretch the droplets to form a fiber structure. The initial fiber material formed by the fiber structure is collected in a receiving device, wherein the injection speed of the precursor spinning solution is between 0.1mL / min and 0.5mL / min, the set voltage is between 5kV and 50kV, the working temperature is between 15°C and 35°C, the receiving distance between the injector and the receiving device is between 5cm and 30cm, the relative humidity is within the range of 35±10%, the receiving device used includes any one of non-woven fabric, aluminum foil and copper mesh, and the rotation speed of the receiving device is between 100r / min and 160r / min.

8. The preparation method according to any one of claims 1 to 7, characterized in that In the step of heating the initial fiber material to a set temperature and then keeping the temperature to obtain the high entropy flexible functional ceramic nanofiber material, The set temperature is between 600° C. and 700° C., the holding time is between 50 min and 70 min, and the heating rate is between 3° C. / s and 7° C. / s.

9. A high entropy flexible functional ceramic nanofiber material, characterized in that: The preparation method is described in any one of claims 1 to 8.

10. The high-entropy flexible functional ceramic nanofiber material according to claim 9, characterized in that: The high-entropy flexible functional ceramic nanofiber material includes a composite structure of amorphous and nanocrystals, the proportion of the amorphous is between 6% and 94%, and the size of the nanocrystals is not greater than 5nm.

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