A holmium-doped copper ferrite multiferroic ceramic and a method of making the same

Abstract

This invention discloses a holmium-doped copper ferrite multiferroic ceramic and its preparation method. The holmium-doped copper ferrite multiferroic ceramic is made from Cu... 1‑x Ho x FeO2 represents a ceramic material prepared using a sol-gel self-propagating combustion method, where 0 < x ≤ 0.08, with copper nitrate trihydrate, ferric nitrate nonahydrate, holmium nitrate pentahydrate, citric acid monohydrate, and ethylene glycol as raw materials. This ceramic material possesses a single-phase structure, room-temperature giant dielectric properties, and low-temperature magnetism. Furthermore, by changing Ho... 3+ The amount of doping can adjust the giant dielectric properties and magnetism of the material; its preparation process is simple, requiring no pre-firing, with low sintering temperature, short sintering time, low cost, and is environmentally friendly and harmless, and has broad application prospects in fields such as high dielectric capacitors, information storage, spintronic devices, and magnetoelectric sensors.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic materials technology, specifically relating to a holmium-doped copper ferrite multiferroic ceramic and its preparation method. Background Technology

[0002] Multiferroic materials are a new type of multifunctional material. Their various effects (ferroelectricity, ferromagnetism, and ferroelasticity) are coupled and mutually regulated to obtain a wealth of physical phenomena, which greatly expands the application space of multiferroic materials. They provide material support for the miniaturization of electronic information devices and make multiferroic materials have broad application prospects in spintronics, information storage, sensors and other fields.

[0003] At room temperature, the quasi-two-dimensional trigonometric magnet CuFeO2 has Space group. Magnetic Fe 3+ Ionic and nonmagnetic Cu + The ions form a triangular layered structure. When any two nearest-neighbor spins are antiferromagnetically aligned (at the lowest energy), the direction of the third spin cannot simultaneously form an antiferromagnetic alignment with the first two spins. At this time, the system is in a disordered state. CuFeO2 has a unique magnetic structure: the ground state is a collinear fourth-order lattice antiferromagnetic structure along the

[110] direction; CuFeO2 at 14K (T N1 ) and 11K(T N2 Both antiferromagnetic phase transitions at the specified temperature were accompanied by structural phase transitions (from R3m to C). 2 / m The space group indicates that it has a good spin-lattice coupling effect. CuFeO2 belongs to the type II multiferroic material, and its huge magnetoelectric effect makes it a candidate material with great application potential in multifunctional magnetoelectronic devices.

[0004] However, CuFeO2 has a low magnetic transition temperature, weak ferroelectricity and magnetism, and its electromagnetism is not obvious. Studies have shown that the microstructure of the material can be controlled by ion substitution, thereby affecting its physical properties. Samples with different doping systems exhibit significant differences in structure and physical properties, and the doping concentration has a substantial impact on the sample's structure and physical properties.

[0005] Common wet chemical methods for preparing ferromagnetic nanomaterials include the sol-gel method, co-deposition method, and hydrothermal method. The traditional sol-gel method typically uses organometallic alkoxides as raw materials, obtaining a solid precursor through hydrolysis, polymerization, and drying, followed by appropriate heat treatment to obtain the nanomaterials. Due to the use of metal alkoxides as raw materials, this method is costly, and metal alkoxides are often toxic. Protective measures are sometimes required during operation, and an organic environment may be involved. The co-deposition method was the earliest method used for synthesizing metal oxide nanoparticles through liquid-phase chemical reactions. This method is relatively low-cost, but it has the following problems: the precipitate is usually a gel-like substance, making washing and filtration difficult; the precipitant is easily mixed in as an impurity; various components may segregate during precipitation, and some precipitate may dissolve during washing. This method is only suitable for metals capable of precipitation reactions. The hydrothermal method utilizes hydrothermal reactions to synthesize substances, followed by separation and heat treatment to prepare nanoparticles. The prepared nanoparticles have high purity, good dispersibility, good crystal morphology, controllable size, and complete crystal development, but the operation is complex, requires sophisticated equipment, and is relatively expensive.

[0006] The sol-gel self-propagating combustion method is a novel material synthesis method that combines the sol-gel method with a self-propagating high-temperature synthesis method. It utilizes the strong exothermic redox reaction between nitrates and some organic fuels (such as citric acid, urea, and glycine) upon heating, which generates a large amount of gas that sustains the reaction and induces self-propagating combustion, synthesizing oxide powders. Currently, no methods have been found to prepare Ho using the sol-gel self-propagating combustion method. 3+ Reports on CuFeO2-doped multiferroic ceramic materials. Summary of the Invention

[0007] The purpose of this invention is to solve the above-mentioned problems and provide a holmium-doped copper ferrite multiferroic ceramic and its preparation method. The CuFeO2 multiferroic ceramic is prepared using a sol-gel self-propagating method, and the method utilizes Ho... 3+ The ion undergoes Cu-site substitution, resulting in a product with the chemical formula Cu. 1-x Ho x Holmium-doped copper ferrite polyferric ceramics of FeO2 exhibit both significant magnetic properties and giant dielectric properties.

[0008] To achieve the above objectives, the inventive concept of this invention is as follows: CuFeO2 is an oxide with an AMO2-type copper-iron ore structure, possessing a quasi-two-dimensional hexagonal lattice structure at room temperature, and exhibiting... The space group consists of alternating layers of hexagonal close-packed Cu and FeO2 layers composed of octahedral FeO6, forming a layered structure. + The two O atoms in the FeO2 layer 2- Ion linear bonding. The magnetic properties of the CFO system primarily originate from Fe. 3+Because of its spin-displaced magnetic structure, researchers have focused primarily on Fe-site doping, with relatively little research on Cu-site doping. However, Fe-site doping reduces the Fe ion content, thus weakening the magnetism of CuFeO2. As a strongly correlated electron system, Cu sites in CuFeO2 do not generate magnetism, but Cu-site doping, without changing the Fe ion concentration, still perturbs the crystal and magnetic structures of CuFeO2, affecting the valence states of Fe and Cu ions, introducing new magnetic interactions, altering the electronic structure, modulating grain size and grain / grain boundary resistance, and ultimately affecting the physical properties of the system. Based on this concept, this invention utilizes magnetic Ho... 3+ Ions undergo Cu substitution at the site and by changing Ho 3+ The amount of doping causes lattice structure distortion, resistivity, and affects Fe. 3+ -Fe 3+ Ho 3+ -Fe 3+ Interactions between them, introduction of cation vacancies and Fe 2+ Effects on Fe 3+ Spin alignment, thereby modulating the magnetic and dielectric properties of ceramic materials.

[0009] This invention provides a holmium-doped copper ferrite multiferroic ceramic, which is composed of Cu... 1-x Ho x FeO2 represents the formula, where 0 < x ≤ 0.08.

[0010] The above-mentioned holmium-doped copper ferrite multiferroic ceramics, Ho 3+ Excessive doping can lead to impurity phases. Therefore, in the general formula, 0.03 ≤ x ≤ 0.08 is preferred, and x = 0.08 is even more preferred. When x = 0.08, at a test frequency of 1 MHz, the dielectric constant can reach 17998 and the remanent magnetization can reach 7.2 emu / g.

[0011] The method for preparing holmium-doped copper ferrite multiferroic ceramics provided by this invention includes the following steps:

[0012] (1) Ingredients: Copper nitrate trihydrate, ferric nitrate nonahydrate, holmium nitrate pentahydrate, organic fuel, and ethylene glycol are used as raw materials, according to the general formula Cu 1-x Ho x The chemical formula for determining the set value of x in FeO2 is used for weighing and mixing, wherein the molar ratio of metal ions to organic fuel is 1:1–2; and the molar ratio of metal ions to ethylene glycol is 1:1.8–2.3.

[0013] (2) Dissolving: Under stirring conditions, organic fuel, copper nitrate trihydrate, ferric nitrate nonahydrate and holmium nitrate pentahydrate are dissolved in deionized water in sequence to obtain a mixed solution;

[0014] (3) Adjust the pH value by adding ammonia water under stirring to adjust the pH value of the mixed solution to 5.5-7.5;

[0015] (4) To prepare the precursor fluid, ethylene glycol is added to the mixed solution and stirred continuously at 75-85°C until the solution reacts fully to obtain the precursor fluid.

[0016] (5) To prepare a dry gel, heat the precursor fluid to 110-130°C and stir continuously until a dry gel is formed.

[0017] (6) Prepare precursor powder: grind the dry gel into powder, place it in an inert gas atmosphere and heat it to 230-250℃ to ignite the dry gel powder and cause self-propagating combustion to obtain loose precursor powder.

[0018] (7) Sintering: The obtained precursor powder is thoroughly ground to form a green body, which is then sintered in an inert gas atmosphere at a temperature of 750–820℃ for 1.5–3 hours to obtain Cu. 1-x Ho x Holmium-doped copper ferrite polyferric ceramics of FeO2.

[0019] In the above-mentioned method for preparing holmium-doped copper ferrite multiferroic ceramics, the role of the organic fuel is to undergo a strong redox exothermic reaction with the nitrate during heating, thereby maintaining the reaction process and inducing self-propagating combustion. Therefore, the organic fuel can be selected from, but is not limited to, conventional organic fuels in the art such as citric acid, glycine, oxalic acid, or polyacrylic acid. Citric acid is more preferably preferred, as it is a tribasic weak acid that undergoes multi-stage ionization in aqueous solution before reacting with Ho. 3+ Fe 3+ Cu + A complexation reaction occurs. The ratio of nitrate to citric acid affects the stability of the gel and its self-ignition properties.

[0020] Simultaneously, ethylene glycol is added during the sol preparation process. Ethylene glycol acts as a dispersant and stabilizer. First, the pH value is adjusted to obtain the citrate complex salt, and then ethylene glycol is added to prevent gel aggregation and improve its stability. Specifically, the hydroxyl groups of the alcohol and the carboxyl groups of citric acid form hydrogen bonds, which further undergo esterification at a certain temperature, contributing to the formation of a stable sol-gel network. The formation of the gel network can prevent the segregation of small amounts of metal salts, ensure the uniformity of the gel components, and improve the product's agglomeration resistance. Therefore, the appropriate ratio of metal ions to citric acid and ethylene glycol within the reasonable range given in this invention is crucial for maximizing their respective effects.

[0021] In the above-mentioned method for preparing holmium-doped copper ferrite multiferroic ceramics, the amount of deionized water used is mainly sufficient to fully dissolve the organic fuel, copper nitrate trihydrate, ferric nitrate nonahydrate, and holmium nitrate pentahydrate. The water content affects the multi-stage ionization of citric acid, the sol formation rate, and the self-ignition of the gel. Although a large amount of water is beneficial to the multi-stage ionization of citric acid, it will reduce the probability of collision between metal ions and ionized citrate ions, thus leading to a decrease in the sol formation rate, or even no sol formation at all, and thus no ability to initiate self-ignition. The preferred molar ratio is [H2O] / [Fe 3+ ] = 28~36,

[0022] In the above-mentioned method for preparing holmium-doped copper ferrite multiferroic ceramics, the pH value of the system affects the multi-stage ionization of citric acid, thereby influencing the component distribution in the sol. When the pH value of the reaction system is low, the multi-stage ionization of citric acid is inhibited, and some metal ions in the sol system are complexed with citrate ions, while others remain in the form of nitrates, resulting in uneven distribution of sol components. When the pH value is high, the system is weakly alkaline, and the ionization of citric acid is more complete. However, alkaline conditions cause metal ions to precipitate and cannot be fully complexed, which also affects the uniformity of the gel components and thus the self-combustion characteristics of the dry gel. In this invention, the pH value is controlled between 5.5 and 7.5. Within this range, sufficient complexation of citrate ions and metal ions and subsequent complete combustion of the dry gel can be achieved.

[0023] In the above method for preparing holmium-doped copper ferrite multiferroic ceramics, in step (4), the stirring time is to ensure that the solution can react fully. Generally, the stirring time exceeds 6 hours, preferably 6 to 9 hours.

[0024] In the above method for preparing holmium-doped copper ferrite multiferroic ceramics, in step (6), the heating rate can be a conventional rate, but the heating rate should not be too fast, as the material is prone to being non-dense if the heating rate is too fast. Preferably, the heating rate is 2-5℃ / min.

[0025] In the aforementioned method for preparing holmium-doped copper ferrite multiferroic ceramics, the precursor powder preparation in the conventional sol-gel method combined with self-propagating combustion is generally carried out in air. Through repeated experiments, the inventors discovered that CuFeO2 material exhibits impurity phases upon self-propagating combustion in air, while no impurity phases are generated in a protective gas atmosphere. Nitrogen or argon atmospheres are typically used as the inert gas atmosphere. Furthermore, the heating temperature also affects the product structure. Through repeated experiments, the inventors found that temperatures below 230℃ or above 250℃ will generate impurity phases in the sample. Therefore, in this invention, the precursor powder is prepared between 230℃ and 250℃.

[0026] The above-mentioned method for preparing holmium-doped copper ferrite multiferroic ceramics employs a sol-gel method combined with self-propagating high-temperature synthesis. This method combines the advantages of both sol-gel and self-propagating combustion techniques. The sol-gel method has a low synthesis temperature, allowing the constituent elements to mix uniformly at the molecular and atomic scale in the solution, resulting in finer and more uniformly distributed powder particles without significant agglomeration. The self-propagating combustion method is simple, has a short synthesis time, produces high-purity products, and helps improve the material structure, forming a complete crystal form. The crystals prepared by self-propagating combustion followed by calcination have regular shapes, complete crystal structures, and good dispersibility.

[0027] The holmium-doped copper ferrite multiferroic ceramic and its preparation method provided by this invention have the following beneficial effects:

[0028] (1) Cu provided by the present invention 1-x Ho x FeO2 multiferroic ceramic materials possess a single-phase structure, low-temperature magnetism, and room-temperature giant dielectric properties. These properties can be achieved by modifying Ho... 3+ The amount of doping causes lattice structure distortion, resistivity, and affects Fe. 3+ -Fe 3+ Ho 3+ -Fe 3+ Interactions between them, introduction of cation vacancies and Fe 2+ Effects on Fe 3+ Spin arrangement allows for the tuning of the material's magnetic and dielectric properties; this Cu 1-x Ho x FeO2 multiferroic ceramic materials are a class of multifunctional ceramic materials with broad application prospects.

[0029] (2) The method for preparing holmium-doped copper ferrite multiferroic ceramics provided by the present invention utilizes the sol-gel self-propagating method to synthesize holmium-doped copper ferrite multiferroic ceramics. Compared with the traditional chemical preparation method of ceramic materials, it does not require pre-firing, has a low sintering phase formation temperature, and a short sintering time, achieving a good energy-saving effect. Moreover, the preparation process is simple, low-cost, non-toxic and environmentally friendly, and has good application prospects, making it worthy of promotion and application in this field. Attached Figure Description

[0030] Figure 1 Cu prepared in Examples 1-3 1-x Ho x XRD patterns of FeO2 ceramic samples and CuFeO2 ceramic samples prepared in Comparative Example 1;

[0031] Figure 2 Cu prepared in Example 1 and Comparative Example 2 1-x Ho x XRD patterns of FeO2 ceramic samples;

[0032] Figure 3 The Cu prepared in Examples 4-5 and Comparative Examples 3-4 1-x Ho x XRD patterns of FeO2 ceramic samples;

[0033] Figure 4 Cu was prepared in Examples 1-3 at 20K temperature. 1-x Ho x Magnetic hysteresis loops of FeO2 ceramic samples and CuFeO2 ceramic samples prepared in Comparative Example 1.

[0034] Figure 5 Cu prepared in Examples 1-3 1-x Ho x Room temperature dielectric frequency curves of FeO2 ceramic samples and CuFeO2 ceramic samples prepared in Comparative Example 1.

[0035] Figure 6 The dielectric constant spectrum of Cu1-xHoxFeO2 ceramic samples prepared in Examples 1-3 and CuFeO2 ceramic samples prepared in Comparative Example 1 are shown. Detailed Implementation

[0036] The technical solutions of various embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are part of the present invention.

[0037] Example 1

[0038] This embodiment utilizes the citric acid-nitrate sol-gel self-propagating combustion method to prepare a mixture of Cu... 0.97 Ho 0.03 The holmium-doped copper ferrite multiferroic ceramic represented by FeO2 (i.e., x = 0.03) specifically includes the following steps:

[0039] (1) Ingredients: Copper nitrate trihydrate (Cu(NO3)2·3H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), holmium nitrate pentahydrate (Ho(NO3)3·5H2O), and citric acid monohydrate (C6H8O7·H2O) are used as raw materials, according to the chemical formula Cu 0.97 Ho 0.03 The stoichiometric ratio of FeO2 was used for weighing and mixing, wherein the molar ratio of metal ions to citric acid was 1:1.5, and the molar ratio of metal ions to ethylene glycol was 1:2.

[0040] (2) Dissolve the deionized water by measuring it with a graduated cylinder and pouring it into a beaker. The amount of deionized water used should be such that the molar ratio of metal ions is [H2O] / [Fe] = 0. 3+=30, under room temperature and stirring conditions, citric acid monohydrate, copper nitrate trihydrate, ferric nitrate nonahydrate, and holmium nitrate pentahydrate are dissolved in deionized water in sequence until completely dissolved, i.e., each reagent is added and immediately stirred with a glass rod until completely dissolved to obtain a mixed solution;

[0041] (3) Adjust the pH value by adding ammonia water under stirring to adjust the pH value of the mixed solution to 6;

[0042] (4) To prepare the precursor fluid, ethylene glycol was added to the mixed solution and stirred continuously at 80°C with a magnetic stirrer for 6 hours until the solution was fully reacted to obtain the precursor fluid.

[0043] (5) To prepare a dry gel, pour the precursor fluid into an evaporating dish, heat at 120°C and stir continuously until a dry gel is formed.

[0044] (6) To prepare precursor powder, the dry gel is ground into powder and placed in a crucible. Then, the crucible is placed in a tube furnace with argon gas and heated to 240°C. The dry gel powder is ignited and self-propagating combustion occurs to obtain loose precursor powder.

[0045] (7) Sintering: The obtained precursor powder is thoroughly ground, then made into ceramic blanks and placed in a crucible. Sintering is carried out in an argon atmosphere at 800℃ for 2 hours to obtain a product composed of Cu... 0.97 Ho 0.03 FeO2 represents holmium-doped copper ferrite multiferroic ceramics.

[0046] Example 2

[0047] This embodiment utilizes the citric acid-nitrate sol-gel self-propagating combustion method to prepare a mixture of Cu... 0.95 Ho 0.05 The holmium-doped copper ferrite multiferroic ceramic represented by FeO2 (i.e., x = 0.05) specifically includes the following steps:

[0048] (1) Ingredients: Copper nitrate trihydrate (Cu(NO3)2·3H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), holmium nitrate pentahydrate (Ho(NO3)3·5H2O), and citric acid monohydrate (C6H8O7·H2O) are used as raw materials, according to the chemical formula Cu 0.97 Ho 0.03 The stoichiometric ratio of FeO2 was used for weighing and mixing, wherein the molar ratio of metal ions to citric acid was 1:1.5, and the molar ratio of metal ions to ethylene glycol was 1:2.

[0049] (2) Dissolve the deionized water by measuring it with a graduated cylinder and pouring it into a beaker. The amount of deionized water used should be such that the molar ratio of metal ions is [H2O] / [Fe] = 0. 3+=30, under room temperature and stirring conditions, citric acid monohydrate, copper nitrate trihydrate, ferric nitrate nonahydrate, and holmium nitrate pentahydrate are dissolved in deionized water in sequence until completely dissolved, i.e., each reagent is added and immediately stirred with a glass rod until completely dissolved to obtain a mixed solution;

[0050] (3) Adjust the pH value by adding ammonia water under stirring to adjust the pH value of the mixed solution to 6;

[0051] (4) To prepare the precursor fluid, ethylene glycol was added to the mixed solution and stirred continuously at 80°C with a magnetic stirrer for 6 hours until the solution was fully reacted to obtain the precursor fluid.

[0052] (5) To prepare a dry gel, pour the precursor fluid into an evaporating dish, heat at 120°C and stir continuously until a dry gel is formed.

[0053] (6) To prepare precursor powder, the dry gel is ground into powder and placed in a crucible. Then, the crucible is placed in a tube furnace with argon gas and heated to 240°C. The dry gel powder is ignited and self-propagating combustion occurs to obtain loose precursor powder.

[0054] (7) Sintering: The obtained precursor powder is thoroughly ground, then made into ceramic blanks and placed in a crucible. Sintering is carried out in an argon atmosphere at 800℃ for 2 hours to obtain a product composed of Cu... 0.95 Ho 0.05 FeO2 represents holmium-doped copper ferrite multiferroic ceramics.

[0055] Example 3

[0056] This embodiment utilizes the citric acid-nitrate sol-gel self-propagating combustion method to prepare a mixture of Cu... 0.92 Ho 0.08 The holmium-doped copper ferrite multiferroic ceramic represented by FeO2 (i.e., x = 0.08) specifically includes the following steps:

[0057] (1) Ingredients: Copper nitrate trihydrate (Cu(NO3)2·3H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), holmium nitrate pentahydrate (Ho(NO3)3·5H2O), and citric acid monohydrate (C6H8O7·H2O) are used as raw materials, according to the chemical formula Cu 0.92 Ho 0.08 The stoichiometric ratio of FeO2 was used for weighing and mixing, wherein the molar ratio of metal ions to citric acid was 1:1.5, and the molar ratio of metal ions to ethylene glycol was 1:2.

[0058] (2) Dissolve the deionized water by measuring it with a graduated cylinder and pouring it into a beaker. The amount of deionized water used should be such that the molar ratio of metal ions is [H2O] / [Fe] = 0. 3+=30, under room temperature and stirring conditions, citric acid monohydrate, copper nitrate trihydrate, ferric nitrate nonahydrate, and holmium nitrate pentahydrate are dissolved in deionized water in sequence until completely dissolved, i.e., each reagent is added and immediately stirred with a glass rod until completely dissolved to obtain a mixed solution;

[0059] (3) Adjust the pH value by adding ammonia water under stirring to adjust the pH value of the mixed solution to 6;

[0060] (4) To prepare the precursor fluid, ethylene glycol was added to the mixed solution and stirred continuously at 80°C with a magnetic stirrer for 6 hours until the solution was fully reacted to obtain the precursor fluid.

[0061] (5) To prepare a dry gel, pour the precursor fluid into an evaporating dish, heat at 120°C and stir continuously until a dry gel is formed.

[0062] (6) To prepare precursor powder, the dry gel is ground into powder and placed in a crucible. Then, the crucible is placed in a tube furnace with argon gas and heated to 240°C. The dry gel powder is ignited and self-propagating combustion occurs to obtain loose precursor powder.

[0063] (7) Sintering: The obtained precursor powder is thoroughly ground, then made into ceramic blanks and placed in a crucible. Sintering is carried out in an argon atmosphere at 800℃ for 2 hours to obtain a product composed of Cu... 0.92 Ho 0.08 FeO2 represents holmium-doped copper ferrite multiferroic ceramics.

[0064] Example 4

[0065] This embodiment utilizes the citric acid-nitrate sol-gel self-propagating combustion method to prepare Cu at 230°C. 0.95 Ho 0.05 The process involves preparing bulk ceramics by sintering holmium-doped copper ferrite precursor powder, represented by FeO2 (i.e., x = 0.05), specifically including the following steps:

[0066] (1) Ingredients: Copper nitrate trihydrate (Cu(NO3)2·3H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), holmium nitrate pentahydrate (Ho(NO3)3·5H2O), and citric acid monohydrate (C6H8O7·H2O) are used as raw materials, according to the chemical formula Cu 0.97 Ho 0.03 The stoichiometric ratio of FeO2 was used for weighing and mixing, wherein the molar ratio of metal ions to citric acid was 1:1.5, and the molar ratio of metal ions to ethylene glycol was 1:2.

[0067] (2) Dissolve the deionized water by measuring it with a graduated cylinder and pouring it into a beaker. The amount of deionized water used should be such that the molar ratio of metal ions is [H2O] / [Fe] = 0. 3+=30, under room temperature and stirring conditions, citric acid monohydrate, copper nitrate trihydrate, ferric nitrate nonahydrate, and holmium nitrate pentahydrate are dissolved in deionized water in sequence until completely dissolved, i.e., each reagent is added and immediately stirred with a glass rod until completely dissolved to obtain a mixed solution;

[0068] (3) Adjust the pH value by adding ammonia water under stirring to adjust the pH value of the mixed solution to 6;

[0069] (4) To prepare the precursor fluid, ethylene glycol was added to the mixed solution and stirred continuously at 80°C with a magnetic stirrer for 6 hours until the solution was fully reacted to obtain the precursor fluid.

[0070] (5) To prepare a dry gel, pour the precursor fluid into an evaporating dish, heat at 120°C and stir continuously until a dry gel is formed.

[0071] (6) To prepare precursor powder, the dry gel is ground into powder and placed in a crucible. Then, the crucible is placed in a tube furnace with argon gas and heated to 230°C. The dry gel powder is ignited and self-propagating combustion occurs to obtain loose precursor powder.

[0072] (7) Sintering: The obtained precursor powder is thoroughly ground, then made into ceramic blanks and placed in a crucible. Sintering is carried out in an argon atmosphere at 800℃ for 2 hours to obtain a product composed of Cu... 0.95 Ho 0.05 FeO2 represents holmium-doped copper ferrite multiferroic ceramics.

[0073] Example 5

[0074] This embodiment utilizes the citric acid-nitrate sol-gel self-propagating combustion method to prepare Cu at 250°C. 0.95 Ho 0.05 The process involves preparing bulk ceramics by sintering holmium-doped copper ferrite precursor powder, represented by FeO2 (i.e., x = 0.05), specifically including the following steps:

[0075] (1) Ingredients: Copper nitrate trihydrate (Cu(NO3)2·3H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), holmium nitrate pentahydrate (Ho(NO3)3·5H2O), and citric acid monohydrate (C6H8O7·H2O) are used as raw materials, according to the chemical formula Cu 0.97 Ho 0.03 The stoichiometric ratio of FeO2 was used for weighing and mixing, wherein the molar ratio of metal ions to citric acid was 1:1.5, and the molar ratio of metal ions to ethylene glycol was 1:2.

[0076] (2) Dissolve the deionized water by measuring it with a graduated cylinder and pouring it into a beaker. The amount of deionized water used should be such that the molar ratio of metal ions is [H2O] / [Fe] = 0. 3+=30, under room temperature and stirring conditions, citric acid monohydrate, copper nitrate trihydrate, ferric nitrate nonahydrate, and holmium nitrate pentahydrate are dissolved in deionized water in sequence until completely dissolved, i.e., each reagent is added and immediately stirred with a glass rod until completely dissolved to obtain a mixed solution;

[0077] (3) Adjust the pH value by adding ammonia water under stirring to adjust the pH value of the mixed solution to 6;

[0078] (4) To prepare the precursor fluid, ethylene glycol was added to the mixed solution and stirred continuously at 80°C with a magnetic stirrer for 6 hours until the solution was fully reacted to obtain the precursor fluid.

[0079] (5) To prepare a dry gel, pour the precursor fluid into an evaporating dish, heat at 120°C and stir continuously until a dry gel is formed.

[0080] (6) Prepare precursor powder: grind the dry gel into powder and put it into a crucible. Then place the crucible in a tube furnace with argon gas and heat it to 250°C to ignite the dry gel powder and cause self-propagating combustion to obtain loose precursor powder.

[0081] (7) Sintering: The obtained precursor powder is thoroughly ground, then made into ceramic blanks and placed in a crucible. Sintering is carried out in an argon atmosphere at 800℃ for 2 hours to obtain a product composed of Cu... 0.95 Ho 0.05 FeO2 represents holmium-doped copper ferrite multiferroic ceramics.

[0082] Example 6

[0083] This embodiment utilizes the citric acid-nitrate sol-gel self-propagating combustion method to prepare Cu... 0.97 Ho 0.03 The process involves preparing bulk ceramics by sintering holmium-doped copper ferrite precursor powder, represented by FeO2 (i.e., x = 0.03), specifically including the following steps:

[0084] (1) Ingredients: Copper nitrate trihydrate (Cu(NO3)2·3H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), holmium nitrate pentahydrate (Ho(NO3)3·5H2O), and citric acid monohydrate (C6H8O7·H2O) are used as raw materials, according to the chemical formula Cu 0.97 Ho 0.03 The FeO2 was weighed and mixed according to its stoichiometric ratio, wherein the molar ratio of metal ions to citric acid was 1:1, and the molar ratio of metal ions to ethylene glycol was 1:2.3.

[0085] (2) Dissolve the deionized water by measuring it with a graduated cylinder and pouring it into a beaker. The amount of deionized water used should be such that the molar ratio of metal ions is [H2O] / [Fe] = 0. 3+=30, under room temperature and stirring conditions, citric acid monohydrate, copper nitrate trihydrate, ferric nitrate nonahydrate, and holmium nitrate pentahydrate are dissolved in deionized water in sequence until completely dissolved, i.e., each reagent is added and immediately stirred with a glass rod until completely dissolved to obtain a mixed solution;

[0086] (3) Adjust the pH value by adding ammonia water under stirring to adjust the pH value of the mixed solution to 7.5;

[0087] (4) To prepare the precursor fluid, ethylene glycol was added to the mixed solution and stirred continuously at 75°C with a magnetic stirrer for 6 hours until the solution was fully reacted to obtain the precursor fluid.

[0088] (5) To prepare a dry gel, pour the precursor fluid into an evaporating dish, heat it at 130°C and stir continuously until a dry gel is formed.

[0089] (6) Prepare precursor powder: grind the dry gel into powder and put it into a crucible. Then place the crucible in a tube furnace with argon gas and heat it to 240°C to ignite the dry gel powder and cause self-propagating combustion to obtain loose precursor powder.

[0090] (7) Sintering: The obtained precursor powder is thoroughly ground, then made into ceramic blanks and placed in a crucible. Sintering is carried out in an argon atmosphere at a temperature of 820℃ for 2 hours to obtain a product composed of Cu... 0.97 Ho 0.03 FeO2 represents holmium-doped copper ferrite multiferroic ceramics.

[0091] Example 7

[0092] This embodiment utilizes the citric acid-nitrate sol-gel self-propagating combustion method to prepare Cu... 0.97 Ho 0.03 The process involves preparing bulk ceramics by sintering holmium-doped copper ferrite precursor powder, represented by FeO2 (i.e., x = 0.03), specifically including the following steps:

[0093] (1) Ingredients: Copper nitrate trihydrate (Cu(NO3)2·3H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), holmium nitrate pentahydrate (Ho(NO3)3·5H2O), and citric acid monohydrate (C6H8O7·H2O) are used as raw materials, according to the chemical formula Cu 0.97 Ho 0.03 The stoichiometric ratio of FeO2 was used for weighing and mixing, wherein the molar ratio of metal ions to citric acid was 1:2, and the molar ratio of metal ions to ethylene glycol was 1:1.8.

[0094] (2) Dissolve the deionized water by measuring it with a graduated cylinder and pouring it into a beaker. The amount of deionized water used should be such that the molar ratio of metal ions is [H2O] / [Fe] = 0. 3+=30, under room temperature and stirring conditions, citric acid monohydrate, copper nitrate trihydrate, ferric nitrate nonahydrate, and holmium nitrate pentahydrate are dissolved in deionized water in sequence until completely dissolved, i.e., each reagent is added and immediately stirred with a glass rod until completely dissolved to obtain a mixed solution;

[0095] (3) Adjust the pH value by adding ammonia water under stirring to adjust the pH value of the mixed solution to 5.5;

[0096] (4) To prepare the precursor fluid, ethylene glycol was added to the mixed solution and stirred continuously at 80°C with a magnetic stirrer for 6 hours until the solution was fully reacted to obtain the precursor fluid.

[0097] (5) To prepare a dry gel, pour the precursor fluid into an evaporating dish, heat at 110°C and stir continuously until a dry gel is formed.

[0098] (6) Prepare precursor powder: grind the dry gel into powder and put it into a crucible. Then place the crucible in a tube furnace with argon gas and heat it to 240°C to ignite the dry gel powder and cause self-propagating combustion to obtain loose precursor powder.

[0099] (7) Sintering: The obtained precursor powder is thoroughly ground, then made into ceramic blanks and placed in a crucible. Sintering is carried out in an argon atmosphere at 800℃ for 1.5 hours to obtain a product composed of Cu... 0.97 Ho 0.03 FeO2 represents holmium-doped copper ferrite multiferroic ceramics.

[0100] Example 8

[0101] This embodiment utilizes the citric acid-nitrate sol-gel self-propagating combustion method to prepare Cu... 0.97 Ho 0.03 The process involves preparing bulk ceramics by sintering holmium-doped copper ferrite precursor powder, represented by FeO2 (i.e., x = 0.03), specifically including the following steps:

[0102] (1) Ingredients: Copper nitrate trihydrate (Cu(NO3)2·3H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), holmium nitrate pentahydrate (Ho(NO3)3·5H2O), and citric acid monohydrate (C6H8O7·H2O) are used as raw materials, according to the chemical formula Cu 0.97 Ho 0.03 The stoichiometric ratio of FeO2 was used for weighing and mixing, wherein the molar ratio of metal ions to citric acid was 1:1.5, and the molar ratio of metal ions to ethylene glycol was 1:2.1.

[0103] (2) Dissolve the deionized water by measuring it with a graduated cylinder and pouring it into a beaker. The amount of deionized water used should be such that the molar ratio of metal ions is [H2O] / [Fe] = 0. 3+=30, under room temperature and stirring conditions, citric acid monohydrate, copper nitrate trihydrate, ferric nitrate nonahydrate, and holmium nitrate pentahydrate are dissolved in deionized water in sequence until completely dissolved, i.e., each reagent is added and immediately stirred with a glass rod until completely dissolved to obtain a mixed solution;

[0104] (3) Adjust the pH value by adding ammonia water under stirring to adjust the pH value of the mixed solution to 6;

[0105] (4) To prepare the precursor fluid, ethylene glycol was added to the mixed solution and stirred continuously at 85°C with a magnetic stirrer for 6 hours until the solution was fully reacted to obtain the precursor fluid.

[0106] (5) To prepare a dry gel, pour the precursor fluid into an evaporating dish, heat at 120°C and stir continuously until a dry gel is formed.

[0107] (6) Prepare precursor powder: grind the dry gel into powder and put it into a crucible. Then place the crucible in a tube furnace with argon gas and heat it to 240°C to ignite the dry gel powder and cause self-propagating combustion to obtain loose precursor powder.

[0108] (7) Sintering: The obtained precursor powder is thoroughly ground, then made into ceramic blanks and placed in a crucible. Sintering is carried out in an argon atmosphere at a temperature of 750℃ for 3 hours to obtain a product composed of Cu... 0.97 Ho 0.03 FeO2 represents holmium-doped copper ferrite multiferroic ceramics.

[0109] Comparative Example 1

[0110] Compared with Example 1, this comparative example is identical in all steps and parameters except for the value of x.

[0111] This comparative example utilizes the citric acid-nitrate sol-gel self-propagating combustion method to prepare undoped CuFeO2 multiferroic ceramics (i.e., x = 0.00), specifically including the following steps:

[0112] (1) Ingredients: Copper nitrate trihydrate (Cu(NO3)2·3H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), and citric acid monohydrate (C6H8O7·H2O) are used as raw materials and weighed according to the stoichiometric ratio of the chemical formula CuFeO2. The molar ratio of metal ions to citric acid is 1:1.5, and the molar ratio of metal ions to ethylene glycol is 1:2.

[0113] (2) Dissolve the deionized water by measuring it with a graduated cylinder and pouring it into a beaker. The amount of deionized water used should be such that the molar ratio of metal ions is [H2O] / [Fe] = 0. 3+=30, under room temperature and stirring conditions, citric acid monohydrate, copper nitrate trihydrate, and ferric nitrate nonahydrate are dissolved in deionized water in sequence until completely dissolved, i.e., each reagent is added and immediately stirred with a glass rod until completely dissolved to obtain a mixed solution;

[0114] (3) Adjust the pH value by adding ammonia water under stirring to adjust the pH value of the mixed solution to 6;

[0115] (4) To prepare the precursor fluid, ethylene glycol was added to the mixed solution and stirred continuously at 80°C with a magnetic stirrer for 6 hours until the solution was fully reacted to obtain the precursor fluid.

[0116] (5) To prepare a dry gel, pour the precursor fluid into an evaporating dish, heat at 120°C and stir continuously until a dry gel is formed.

[0117] (6) To prepare precursor powder, the dry gel is ground into powder and placed in a crucible. Then, the crucible is placed in a tube furnace with argon gas and heated to 240°C. The dry gel powder is ignited and self-propagating combustion occurs to obtain loose precursor powder.

[0118] (7) Sintering: The obtained precursor powder is thoroughly ground, then ceramic blanks are made and placed in a crucible. Sintering is carried out in an argon atmosphere at a temperature of 800°C for 2 hours to obtain holmium-doped copper ferrite multiferroic ceramic represented by the chemical formula CuFeO2.

[0119] Comparative Example 2

[0120] Compared with Example 1, this comparative example is identical in all steps and parameters except for the gas atmosphere in step (6).

[0121] This comparative example utilizes the citric acid-nitrate sol-gel self-propagating combustion method to prepare Cu in an air atmosphere. 0.97 Ho 0.03 The process involves preparing bulk ceramics by sintering holmium-doped copper ferrite precursor powder, represented by FeO2 (i.e., x = 0.03), specifically including the following steps:

[0122] (1) Ingredients: Copper nitrate trihydrate (Cu(NO3)2·3H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), holmium nitrate pentahydrate (Ho(NO3)3·5H2O), and citric acid monohydrate (C6H8O7·H2O) are used as raw materials, according to the chemical formula Cu 0.97 Ho 0.03 The stoichiometric ratio of FeO2 was used for weighing and mixing, wherein the molar ratio of metal ions to citric acid was 1:1.5, and the molar ratio of metal ions to ethylene glycol was 1:2.

[0123] (2) Dissolve the deionized water by measuring it with a graduated cylinder and pouring it into a beaker. The amount of deionized water used should be such that the molar ratio of metal ions is [H2O] / [Fe] = 0. 3+ =30, under room temperature and stirring conditions, citric acid monohydrate, copper nitrate trihydrate, ferric nitrate nonahydrate, and holmium nitrate pentahydrate are dissolved in deionized water in sequence until completely dissolved, i.e., each reagent is added and immediately stirred with a glass rod until completely dissolved to obtain a mixed solution;

[0124] (3) Adjust the pH value by adding ammonia water under stirring to adjust the pH value of the mixed solution to 6;

[0125] (4) To prepare the precursor fluid, ethylene glycol was added to the mixed solution and stirred continuously at 80°C with a magnetic stirrer for 6 hours until the solution was fully reacted to obtain the precursor fluid.

[0126] (5) To prepare a dry gel, pour the precursor fluid into an evaporating dish, heat at 120°C and stir continuously until a dry gel is formed.

[0127] (6) To prepare the precursor powder, the dry gel was ground into powder and placed in a crucible. The crucible was then placed in an air-filled tube furnace and heated to 240°C. The dry gel powder was ignited, resulting in self-propagating combustion, yielding a loose Cu-based precursor powder. 0.97 Ho 0.03 FeO2 represents holmium-doped copper ferrite precursor powder.

[0128] (7) Sintering: The obtained precursor powder is thoroughly ground, then made into ceramic blanks and placed in a crucible. Sintering is carried out in an argon atmosphere at 800℃ for 2 hours to obtain a product composed of Cu... 0.97 Ho 0.03 FeO2 represents holmium-doped copper ferrite multiferroic ceramics.

[0129] Comparative Example 3

[0130] Compared with Examples 4-5, this comparative example is identical in all steps and parameters except for the heating temperature in step (6).

[0131] This comparative example utilizes the citric acid-nitrate sol-gel self-propagating combustion method to prepare Cu at 220℃. 0.95 Ho 0.05 The process involves preparing bulk ceramics by sintering holmium-doped copper ferrite precursor powder, represented by FeO2 (i.e., x = 0.05), specifically including the following steps:

[0132] (1) Ingredients: Copper nitrate trihydrate (Cu(NO3)2·3H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), holmium nitrate pentahydrate (Ho(NO3)3·5H2O), and citric acid monohydrate (C6H8O7·H2O) are used as raw materials, according to the chemical formula Cu0.97 Ho 0.03 The stoichiometric ratio of FeO2 was used for weighing and mixing, wherein the molar ratio of metal ions to citric acid was 1:1.5, and the molar ratio of metal ions to ethylene glycol was 1:2.

[0133] (2) Dissolve the deionized water by measuring it with a graduated cylinder and pouring it into a beaker. The amount of deionized water used should be such that the molar ratio of metal ions is [H2O] / [Fe] = 0. 3+ =30, under room temperature and stirring conditions, citric acid monohydrate, copper nitrate trihydrate, ferric nitrate nonahydrate, and holmium nitrate pentahydrate are dissolved in deionized water in sequence until completely dissolved, i.e., each reagent is added and immediately stirred with a glass rod until completely dissolved to obtain a mixed solution;

[0134] (3) Adjust the pH value by adding ammonia water under stirring to adjust the pH value of the mixed solution to 6;

[0135] (4) To prepare the precursor fluid, ethylene glycol was added to the mixed solution and stirred continuously at 80°C with a magnetic stirrer for 6 hours until the solution was fully reacted to obtain the precursor fluid.

[0136] (5) To prepare a dry gel, pour the precursor fluid into an evaporating dish, heat at 120°C and stir continuously until a dry gel is formed.

[0137] (6) To prepare precursor powder, the dry gel is ground into powder and placed in a crucible. Then, the crucible is placed in a tube furnace with argon gas and heated to 220°C to ignite the dry gel powder and cause self-propagating combustion, thus obtaining a loose precursor powder.

[0138] (7) Sintering: The obtained precursor powder is thoroughly ground, then made into ceramic blanks and placed in a crucible. Sintering is carried out in an argon atmosphere at 800℃ for 2 hours to obtain a product composed of Cu... 0.95 Ho 0.05 FeO2 represents holmium-doped copper ferrite multiferroic ceramics.

[0139] Comparative Example 4

[0140] Compared with Examples 4-5, this comparative example is identical in all steps and parameters except for the heating temperature in step (6).

[0141] This comparative example utilizes the citric acid-nitrate sol-gel self-propagating combustion method to prepare Cu at 260℃. 0.95 Ho 0.05 The process involves preparing bulk ceramics by sintering holmium-doped copper ferrite precursor powder, represented by FeO2 (i.e., x = 0.05), specifically including the following steps:

[0142] (1) Ingredients: Copper nitrate trihydrate (Cu(NO3)2·3H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), holmium nitrate pentahydrate (Ho(NO3)3·5H2O), and citric acid monohydrate (C6H8O7·H2O) are used as raw materials, according to the chemical formula Cu 0.97 Ho 0.03 The stoichiometric ratio of FeO2 was used for weighing and mixing, wherein the molar ratio of metal ions to citric acid was 1:1.5, and the molar ratio of metal ions to ethylene glycol was 1:2.

[0143] (2) Dissolve the deionized water by measuring it with a graduated cylinder and pouring it into a beaker. The amount of deionized water used should be such that the molar ratio of metal ions is [H2O] / [Fe] = 0. 3+ =30, under room temperature and stirring conditions, citric acid monohydrate, copper nitrate trihydrate, ferric nitrate nonahydrate, and holmium nitrate pentahydrate are dissolved in deionized water in sequence until completely dissolved, i.e., each reagent is added and immediately stirred with a glass rod until completely dissolved to obtain a mixed solution;

[0144] (3) Adjust the pH value by adding ammonia water under stirring to adjust the pH value of the mixed solution to 6;

[0145] (4) To prepare the precursor fluid, ethylene glycol was added to the mixed solution and stirred continuously at 80°C with a magnetic stirrer for 6 hours until the solution was fully reacted to obtain the precursor fluid.

[0146] (5) To prepare a dry gel, pour the precursor fluid into an evaporating dish, heat at 120°C and stir continuously until a dry gel is formed.

[0147] (6) Prepare precursor powder: grind the dry gel into powder and put it into a crucible. Then place the crucible in a tube furnace with argon gas and heat it to 260°C to ignite the dry gel powder and cause self-propagating combustion to obtain loose precursor powder.

[0148] (7) Sintering: The obtained precursor powder is thoroughly ground, then made into ceramic blanks and placed in a crucible. Sintering is carried out in an argon atmosphere at 800℃ for 2 hours to obtain a product composed of Cu... 0.95 Ho 0.05 FeO2 represents holmium-doped copper ferrite multiferroic ceramics.

[0149] Cu prepared in Examples 1-8 1-x Ho x The structure and properties of the FeO2 ceramic samples and the CuFeO2 ceramic samples prepared in Comparative Examples 1-4 are analyzed as follows.

[0150] (I) Structural Analysis

[0151] To investigate the phase structure of the holmium-doped copper ferrite multiferroic ceramics prepared by the method of this invention, X-ray diffraction (XRD) was used to analyze the Cu prepared in Examples 1-3. 1-x Ho x Phase analysis was performed on the FeO2 ceramic sample and the CuFeO2 ceramic sample prepared in Comparative Example 1. The results are shown in the figure. Figure 1 As shown. From Figure 1 As can be seen from the examples 1-3, Cu was prepared... 1-x Ho x Both the FeO2 ceramic sample and the CuFeO2 ceramic sample prepared in Comparative Example 1 exhibit a hexagonal lattice copper-iron ore structure, with no diffraction peaks indicating a second phase, suggesting that all samples are single-phase structures. With increasing holmium doping concentration x, the main diffraction peaks shift towards smaller angles, indicating that Ho... 3+ Able to completely replace Cu 2+ It enters the CuFeO2 lattice and causes structural distortion.

[0152] To investigate the effects of air and inert gas atmosphere on the product structure during precursor powder preparation, phase analysis was performed on the precursor powders prepared in Example 1 and Comparative Example 2. Figure 2 As shown, comparative analysis of Example 1 and Comparative Example 2 revealed that the precursor powder prepared under an air atmosphere mainly consisted of CuFe2O4 and CuO phases, while the precursor powder prepared under an argon atmosphere was a single-phase CuFeO2. This indicates that the precursor powder prepared under an argon atmosphere... 0.97 Ho 0.03 FeO2 precursor powder can yield a pure phase structure, while Cu prepared under an air atmosphere 0.97 Ho 0.03 The FeO2 precursor powder mainly produces CuFe2O4 and CuO. Therefore, the precursor powder is prepared under an argon atmosphere in this invention.

[0153] To investigate the effect of different heating temperatures on the product structure, phase analysis was performed on the precursor powders prepared in Examples 4-5 and Comparative Examples 3-4, such as... Figure 3 As shown, comparative analysis of Examples 4-5 and Comparative Examples 3-4 reveals that Cu prepared at 220℃... 0.95 Ho 0.05 The FeO2 precursor powder sample contained a significant amount of Fe2O3 and CuO impurities. Cu was prepared at 230℃ and 250℃. 0.95 Ho 0.05 The FeO2 precursor powder sample site showed a single-phase structure, while Cu was prepared at 260℃. 0.95 Ho 0.05The FeO2 precursor powder sample contained CuFe2O4 and CuO impurity phases; this indicates that a single-phase CuFeO2 structure sample can be obtained at 230℃-250℃, while impurity phases will be generated in the sample below 230℃ or above 250℃. Therefore, the precursor powder was prepared in this invention between 230℃ and 250℃.

[0154] To investigate the product structures under different experimental parameters, the Cu prepared in Examples 6-8 were analyzed. 1-x Ho x Phase analysis of FeO2 ceramic samples was performed, and the results are shown below. Figure 4 As shown. From Figure 4 As can be seen from Examples 6-8, Cu was prepared 1-x Ho x The FeO2 ceramic samples all exhibited a hexagonal lattice copper-iron ore structure, with no diffraction peaks indicating a second phase. This demonstrates that all samples possessed a single-phase structure, indicating that single-phase Cu structures could be prepared under the selected experimental conditions. 0.97 Ho 0.03 FeO2 materials.

[0155] (II) Performance Analysis

[0156] 1. Magnetic properties

[0157] To investigate the magnetic properties of the holmium-doped copper ferrite multiferroic ceramics prepared by the method of this invention, the Cu prepared in Examples 1-3 were analyzed using the Quantum Design PPMS comprehensive physical property testing system. 1-x Ho x Magnetic measurements were performed on the FeO2 ceramic sample and the CuFeO2 ceramic sample prepared in the comparative example. The results are as follows: Figure 5 As shown. From Figure 5 As can be seen, at the test temperature of 20K, all samples are ferromagnetic, Ho 3+ Doping enhances the magnetism of CuFeO2, and the maximum and remanent magnetization of the sample increases with Ho. 3+ The increase is due to the increase in doping concentration. This is because of the high valence state of Ho. 3+ Doping induces lattice structure distortion, alters sample resistivity, and affects Fe. 3+ -Fe 3+ Ho 3+ -Fe 3+ Interactions between them, and the introduction of cation vacancies and Fe 2+ Effects on Fe 3+ Spin alignment significantly enhances the magnetic properties of the sample. Experimental results show that by using an appropriate amount of Ho... 3+ Doping can increase the magnetic transition temperature and ferromagnetism of a sample.

[0158] 2. Dielectric properties

[0159] To investigate the dielectric properties of the zirconium-doped gadolinium manganate multiferroic ceramics prepared by the method of this invention, an Agilent 4294 A precision impedance analyzer was used to analyze the Cu prepared in Examples 1-3. 1-x Ho x The dielectric properties of the FeO2 ceramic sample and the CuFeO2 ceramic sample prepared in the comparative example were measured, and the results are as follows: Figure 6 As shown. From Figure 6 As can be seen, all samples exhibit giant dielectric properties; the dielectric constant of undoped CuFeO2 shows a strong frequency dependence, with a larger dielectric constant at low frequencies and a lower dielectric constant at high frequencies. 3+ The frequency dependence of the dielectric constant of the doped samples is improved, exhibiting excellent frequency stability; at a test frequency of 1 MHz, the dielectric constants of the samples with x = 0.00, 0.03, 0.05, and 0.08 are 10755, 13275, 21666, and 17998, respectively, indicating that Ho 3+ Doping significantly improved the dielectric constant of the sample. The inventors analyzed that the giant dielectric property of undoped CuFeO2 may be related to the presence of mixed valence states of Fe in the material (Fe...). 2+ and Fe 3+ It is related to grain-grain boundary characteristics; high valence state Ho 3+ The reason why doping enhances the dielectric constant of CuFeO2 may be related to Ho. 3+ Doping increases Fe in the sample 2+ The content (charge compensation effect) is related to lattice distortion. Experimental results show that Cu 1-x Ho x FeO2 samples all exhibited giant dielectric properties at room temperature, and Ho 3+ Doping can improve the dielectric constant and frequency stability of a sample.

[0160] In summary, the chemical formula provided by this invention is Cu. 1-x Ho x The prepared holmium-doped copper ferrite multiferroic ceramics exhibit room-temperature giant dielectric properties and good low-temperature ferromagnetism. (The text abruptly ends here, likely due to an incomplete sentence or missing information.) 3+ Doping can effectively control the magnetic and dielectric properties of copper ferrite, and it has broad application prospects in fields such as high dielectric capacitors, information storage, spintronic devices, and magnetoelectric sensors. It is a novel multiferroic material that is expected to be further studied and explored.

[0161] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method for preparing holmium-doped copper ferrite multiferroic ceramics, characterized in that, This holmium-doped copper ferrite multiferroic ceramic is made of the general formula Cu 1-x Ho x FeO2 represents the formula, where 0 < x ≤ 0.08; The method for preparing holmium-doped copper ferrite multiferroic ceramics includes the following steps: (1) Ingredients: Copper nitrate trihydrate, ferric nitrate nonahydrate, holmium nitrate pentahydrate, organic fuel, and ethylene glycol are used as raw materials, according to the general formula Cu 1-x Ho x The chemical formula for determining the set value of x in FeO2 is used for weighing and mixing, wherein the molar ratio of metal ions to organic fuel is 1:1 to 2; and the molar ratio of metal ions to ethylene glycol is 1:1.8 to 2.

3. (2) Dissolving: Under stirring conditions, organic fuel, copper nitrate trihydrate, ferric nitrate nonahydrate and holmium nitrate pentahydrate are dissolved in deionized water in sequence to obtain a mixed solution; (3) Adjust the pH value by adding ammonia water under stirring to adjust the pH value of the mixed solution to 5.5-7.5; (4) To prepare the precursor fluid, ethylene glycol is added to the mixed solution and stirred continuously at 75-85°C until the solution reacts fully to obtain the precursor fluid. (5) To prepare a dry gel, heat the precursor fluid at a temperature of 110-130°C and stir continuously until a dry gel is formed. (6) Prepare precursor powder: grind the dry gel into powder, place it in an inert gas atmosphere and heat it to 230-250°C to ignite the dry gel powder and cause self-propagating combustion to obtain loose precursor powder. (7) Sintering: The obtained precursor powder is thoroughly ground to form a green body, which is then sintered in an inert gas atmosphere at a temperature of 750–820℃ for 1.5–3 hours to obtain Cu. 1-x Ho x Holmium-doped copper ferrite polyferric ceramics of FeO2.

2. The method for preparing holmium-doped copper ferrite multiferroic ceramics according to claim 1, characterized in that, In the general formula, 0.03 ≤ x ≤ 0.

08.

3. The method for preparing holmium-doped copper ferrite multiferroic ceramics according to claim 1 or 2, characterized in that, The organic fuel is one of citric acid, aminoacetic acid, oxalic acid, or polyacrylic acid.

4. The method for preparing holmium-doped copper ferrite multiferroic ceramics according to claim 1 or 2, characterized in that, The inert gas is nitrogen or argon.

5. Holmium-doped copper ferrite multiferroic ceramics prepared by the method according to any one of claims 1 to 4.

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