CN112239355A

CN112239355A - A kind of holmium-doped copper ferrite multiferroic ceramic and preparation method thereof

Info

Publication number: CN112239355A
Application number: CN202011111967.9A
Authority: CN
Inventors: 代海洋; 龚高尚; 王曼曼; 尚翠; 谢罗刚; 李涛; 陈靖; 李子炯
Original assignee: Zhengzhou University of Light Industry
Current assignee: Zhengzhou University of Light Industry
Priority date: 2020-10-16
Filing date: 2020-10-16
Publication date: 2021-01-19

Abstract

The invention discloses holmium-doped copper ferrite multiferroic ceramic and a preparation method thereof_1‑xHo_xFeO₂Expressed in the formula, x is more than 0 and less than or equal to 0.08, and the catalyst is prepared by taking copper nitrate trihydrate, ferric nitrate nonahydrate, holmium nitrate pentahydrate, citric acid monohydrate and ethylene glycol as raw materials and adopting a sol-gel self-propagating combustion method. The ceramic material has single-phase structure, giant dielectric property at room temperature and low-temperature magnetism, and Ho is changed³⁺The doping amount can adjust the giant dielectric property and magnetism of the material; the preparation process is simple and has noNeeds to be presintered, has low sintering phase forming temperature, short sintering time, low cost, environmental protection and no harm, and has wide application prospect in the fields of high dielectric capacitors, information storage, spinning electronic devices, magnetoelectric sensors and the like.

Description

Holmium-doped copper ferrite multiferroic ceramic and preparation method thereof

Technical Field

The invention belongs to the technical field of inorganic nonmetallic materials, and particularly relates to holmium-doped copper ferrite multiferroic ceramic and a preparation method thereof.

Background

The multiferroic material is a novel multifunctional material, and various effects (ferroelectricity, ferromagnetism and ferroelasticity) of the multiferroic material are mutually coupled and mutually regulated, so that abundant physical phenomena are obtained, the application space of the multiferroic material is greatly expanded, the material guarantee is provided for the miniaturization of electronic information devices, and the multiferroic material has wide application prospects in the fields of spintronics, information storage, sensors and the like.

CuFeO of quasi-two-dimensional triangular magnet at normal temperature₂Has the advantages of

And (4) space group. Magnetic Fe³⁺Ionic and non-magnetic Cu⁺When any two adjacent spins are antiferromagnetically arranged (with the lowest energy), the direction of the third spin cannot form antiferromagnetic arrangement with the first two spins at the same time, and the system is in a mishandling state. CuFeO₂Magnetic structure with singularity: the magnetic ground state is along [110 ]]A quartic lattice antiferromagnetic structure with collinear directions; CuFeO₂At 14K (T)_N1) And 11K (T)_N2) The two antiferromagnetic phase changes experienced at temperature are both accompanied by structural phase changes (fromR3m to C_2/mSpace group), showing that it has a good spin-lattice coupling effect. CuFeO₂Belongs to a class II multiferroic substance, and becomes a candidate material with great application potential in a multifunctional magnetoelectronics device due to the huge magnetoelectric effect of the multiferroic substance.

However, CuFeO₂The magnetic transformation temperature is low, the ferroelectricity and the magnetism are weak, and the electric control magnetism phenomenon is not obvious. Research shows that the microstructure of the material can be regulated and controlled by ion substitution so as to influence the physical properties of the material. The structure and the physical property of samples of different doping systems are obviously different, and the doping concentration has larger influence on the structure and the physical property of the samples.

The preparation of ferromagnetic nanomaterials is generally carried out by wet-chemical methods such as sol-gel method, codeposition method, hydrothermal method and the like. The traditional sol-gel method generally adopts organic metal alkoxide as a raw material, obtains a solid precursor through hydrolysis, polymerization, drying and other processes, and finally obtains the nano material through proper heat treatment. Because the metal alkoxide is used as a raw material, the method has higher cost, and the metal alkoxide is often toxic. Protection is sometimes required during operation and organic environments may be used. The codeposition method is the method which is firstly adopted for synthesizing the metal oxide nano particles by liquid phase chemical reaction, has lower cost, but has the following problems: the precipitate is usually jelly, and is difficult to wash and filter; the precipitant is easy to be mixed as impurity; various components may be segregated during the precipitation process, and a part of the precipitate may be dissolved during the water washing. This method is only applicable to metals that are capable of undergoing precipitation reactions. The hydrothermal method is a method for preparing nano particles by synthesizing substances through hydrothermal reaction and then separating and carrying out heat treatment, and the prepared nano particles have the advantages of high purity, good dispersity, good crystal form, controllable size, complete crystal grain development, complex operation, high requirement on equipment and higher cost.

The sol-gel self-spreading combustion method is a new material synthesis method combining sol-gel method with self-spreading high-temp. synthesis method, and is characterized by that it utilizes the strong redox exothermic reaction of nitrate and some organic fuels (such as citric acid, urea and glycine, etc.) when they are heated, and combusts them to produce lots of gases,can maintain the reaction process and cause self-propagating combustion to synthesize oxide powder. At present, the method for preparing Ho by adopting a sol-gel self-propagating combustion method is not seen³⁺Doped CuFeO₂The related reports of multiferroic ceramic materials.

Disclosure of Invention

The invention aims to solve the problems and provides holmium-doped copper ferrite multiferroic ceramic and a preparation method thereof₂Multiferroic ceramics by Ho³⁺Ion carries out Cu site substitution, and the prepared chemical formula is Cu_1-xHo_xFeO₂The holmium-doped copper ferrite multiferroic ceramic has remarkable magnetic performance and simultaneously shows giant dielectricity.

In order to achieve the purpose, the invention idea is as follows: CuFeO₂Is a film with AMO₂The oxide of the delafossite structure belongs to a quasi two-dimensional hexagonal lattice structure at normal temperature and has

Space group, hexagonal close packed Cu layer and common octahedral FeO₆FeO of structure₂The layers being alternately stacked in a layered structure, Cu⁺Ions with FeO₂Two of the layers O^2-The ions are linearly connected. The magnetic property of the CFO system is mainly derived from Fe³⁺Because of the spin-induced magnetic structure, researchers are more devoted to the Fe-doping research, and relatively less research is conducted on the Cu-doping. However, Fe site doping can reduce the content of Fe ions and further weaken CuFeO₂The magnetic properties of (1). As a strongly associated electron system, CuFeO₂Although the Cu site in the alloy can not generate magnetism, the Cu site doping can also be applied to CuFeO on the premise of not changing the Fe ion concentration of the system₂The crystal structure and the magnetic structure of the material generate disturbance, the ionic valence states of Fe and Cu in a sample are influenced, new magnetic interaction is introduced, the electronic structure of a system is changed, the grain size, the grain boundary resistance and the like are modulated, and the physical performance of the system is further influenced. Based on the conception, the invention adopts the magnetic Ho³⁺Ion Cu site substitution and by changing Ho³⁺The amount of the dopant causes distortion and inhibition of the lattice structureDegree of influence on Fe³⁺-Fe³⁺、Ho³⁺-Fe³⁺Interaction between them, introduction of cation vacancies and Fe²⁺Influencing Fe³⁺Spin arrangement, thereby regulating and controlling the magnetic and dielectric properties of the ceramic material.

The invention provides holmium-doped copper ferrite multiferroic ceramic which is represented by the general formula Cu_1-xHo_xFeO₂Wherein x is more than 0 and less than or equal to 0.08.

The holmium-doped copper ferrite multiferroic ceramic, Ho³⁺Since a hetero phase may occur when the doping amount of (b) is too large, 0.03. ltoreq. x.ltoreq.0.08 is preferable, and 0.08 is more preferable in the general formula. When x is 0.08, the dielectric constant can reach 17998 and the residual magnetization can reach 7.2emu/g under the test frequency of 1 MHz.

The preparation method of the holmium-doped copper ferrite multiferroic ceramic comprises the following steps:

(1) the materials are prepared from copper nitrate trihydrate, ferric nitrate nonahydrate, holmium nitrate pentahydrate, organic fuel and glycol as raw materials according to a general formula of Cu_1-xHo_xFeO₂Weighing and proportioning according to a chemical formula determined by a set value of x, wherein the molar ratio of metal ions to the organic fuel is 1: 1-2; the molar ratio of the metal ions to the ethylene glycol is 1: 1.8 to 2.3

(2) Dissolving, namely fully dissolving the organic fuel, the copper nitrate trihydrate, the ferric nitrate nonahydrate and the holmium nitrate pentahydrate in the deionized water in turn under the stirring condition to obtain a mixed solution;

(3) adjusting the pH value, and adding ammonia water under the stirring condition to adjust the pH value of the mixed solution to 5.5-7.5;

(4) preparing a precursor liquid, adding ethylene glycol into the mixed solution, and continuously stirring at 75-85 ℃ until the solution is fully reacted to obtain the precursor liquid;

(5) preparing xerogel, heating the precursor liquid to 110-130 ℃ and continuously stirring until xerogel is formed;

(6) preparing precursor powder, grinding the xerogel into powder, placing the powder in an inert gas atmosphere, heating to the temperature of 230-250 ℃, igniting the xerogel powder, and carrying out self-propagating combustion to obtain loose precursor powder.

(7) Sintering, fully grinding the obtained precursor powder to prepare a blank, sintering the blank in an inert gas atmosphere at the sintering temperature of 750-820 ℃ for 1.5-3 h to obtain the precursor powder with the chemical formula of Cu_1-xHo_xFeO₂The holmium-doped copper ferrite multiferroic ceramic.

In the preparation method of the holmium-doped copper ferrite multiferroic ceramic, the organic fuel has the function of carrying out a strong oxidation-reduction exothermic reaction with nitrate during heating so as to maintain the reaction process and cause self-propagating combustion, so that the organic fuel can be selected from conventional organic fuels in the field such as citric acid, aminoacetic acid, oxalic acid or polyacrylic acid and the like, and is further preferably citric acid which is a ternary weak acid, is subjected to multistage ionization in an aqueous solution, and then is mixed with Ho³⁺、Fe³⁺、Cu⁺A complexation reaction occurs. The nitrate/citric acid ratio affects the stability and self-combustion of the gel.

Meanwhile, glycol is added in the sol preparation process, the glycol plays the role of a dispersing agent and a stabilizing agent, citric acid complex salt is obtained by adjusting the pH value, and then the glycol is added to prevent the gel from agglomerating and improve the stability of the gel. Specifically, the alcoholic hydroxyl group and the carboxyl group of the citric acid form a hydrogen bond, and further esterification occurs at a certain temperature, which contributes to the formation of a stable sol-gel network. The formation of gel network can prevent the segregation of a small amount of metal salt, ensure the uniformity of gel components and improve the agglomeration of products. Therefore, the dosage proportion of the metal ions, the citric acid and the glycol is within the reasonable range provided by the invention, and the corresponding effect can be better played.

In the preparation method of holmium-doped copper ferrite multiferroic ceramic, the deionized water is mainly used for fully dissolving organic fuel, copper nitrate trihydrate, ferric nitrate nonahydrate and holmium nitrate pentahydrate, the water content influences the multistage ionization of citric acid, the rate of sol formation, the self-combustion of gel and the like, and the high water content is beneficial to the multistage ionization of the citric acid, but can reduce the collision between metal ions and ionized citrate ionsResulting in a reduced rate of sol formation, even no sol formation at all, and no spontaneous combustion, preferably in a molar ratio [ H [ ]₂O]/[Fe³⁺]＝28～36，

In the preparation method of holmium-doped copper ferrite multiferroic ceramic, the pH value of the system can influence the multistage ionization of citric acid, and further influences the distribution of components in the sol. When the pH value of the reaction system is lower, the multi-stage ionization of the citric acid is inhibited, part of metal ions in the sol system is complexed with citrate, and part of metal ions still exist in the form of nitrate, so that the components of the sol are unevenly distributed; when the pH value is higher, the system is alkalescent, the ionization of the citric acid is more complete, but the alkaline condition can lead metal ions to form precipitates which can not be fully complexed, and the uniformity of gel components is also influenced, thereby further influencing the self-combustion characteristic of the xerogel. In the invention, the pH value is controlled to be 5.5-7.5, and within the range, the full complexation of the citrate and the metal ions and the complete combustion of the subsequent xerogel can be realized.

In the preparation method of holmium-doped copper ferrite multiferroic ceramic, in the step (4), the stirring time is ensured to ensure that the solution can fully react, and generally the stirring time is more than 6 hours, preferably 6-9 hours.

In the preparation method of the holmium-doped copper ferrite multiferroic ceramic, in the step (6), the heating rate is only required to be a conventional rate, but the heating rate is not too fast, and the too fast material is easy to be not compact, preferably 2-5 ℃/min.

In the preparation method of the holmium-doped copper ferrite multiferroic ceramic, in the combination of the sol-gel method and the self-propagating conventional method, the precursor powder is prepared in air generally, and the inventor finds that CuFeO can be treated by repeated experiments₂The material can generate impurity phase when heated and self-propagating burnt in the air, and no impurity phase is generated in the protective gas. The inert gas atmosphere is generally a nitrogen or argon atmosphere. In addition, the heating temperature also has influence on the structure of the product, and the inventor finds that a temperature lower than 230 ℃ or higher than 250 ℃ generates a heterogeneous phase in the sample through repeated experiments, so that the precursor powder is prepared between 230 ℃ and 250 ℃ in the invention.

In the preparation method of the holmium-doped copper ferrite multiferroic ceramic, a sol-gel method is combined with a self-propagating high-temperature synthesis method, and the method combines the advantages of two technologies of sol-gel and self-propagating combustion. The sol-gel method has low synthesis temperature, can uniformly mix all the components in the solution on molecular and atomic scales, and has fine powder granularity, uniform distribution and no obvious agglomeration; the self-propagating combustion mode has simple process, short synthesis time and high product purity, and is beneficial to improving the material structure and forming a complete crystal form; the crystal prepared by self-propagating combustion and calcination has regular shape, complete crystal structure and good dispersibility.

The holmium-doped copper ferrite multiferroic ceramic and the preparation method thereof provided by the invention have the following beneficial effects:

(1) cu provided by the invention_1-xHo_xFeO₂The multiferroic ceramic material has single-phase structure, low-temperature magnetism and room-temperature giant dielectricity, and is prepared by changing Ho³⁺The doping amount of the Fe-based alloy causes the distortion of the lattice structure, the measure resistance and influences the Fe³⁺-Fe³⁺、Ho³⁺-Fe³⁺Interaction between them, introduction of cation vacancies and Fe²⁺Influencing Fe³⁺Spin-aligned to control the magnetic and dielectric properties of the material, the Cu_1-xHo_xFeO₂The multiferroic ceramic material is a multifunctional ceramic material with wide application prospect.

(2) According to the preparation method of the holmium-doped copper ferrite multiferroic ceramic, the holmium-doped copper ferrite multiferroic ceramic is synthesized by using a sol-gel self-propagating method, compared with the traditional chemical preparation method of ceramic materials, the preparation method has the advantages of no need of pre-sintering, low sintering phase temperature and short sintering time, and achieves a good energy-saving effect; and the preparation process is simple, the cost is low, the paint is non-toxic and environment-friendly, and the paint has good application prospect and is worth of being popularized and applied in the field.

Drawings

FIG. 1 is a schematic representation of examples 1-3 for the preparation of Cu_1-xHo_xFeO₂Ceramic sample and CuFeO prepared in comparative example 1₂XRD pattern of ceramic sample;

FIG. 2 is Cu prepared in example 1 and comparative example 2_1-xHo_xFeO₂XRD pattern of ceramic sample;

FIG. 3 is Cu prepared in examples 4 to 5 and comparative examples 3 to 4_1-xHo_xFeO₂XRD pattern of ceramic sample;

FIG. 4 shows Cu preparation of examples 1-3 at a temperature of 20K_1-xHo_xFeO₂Ceramic sample and CuFeO prepared in comparative example 1₂Hysteresis loops of the ceramic samples;

FIG. 5 is a schematic representation of Cu preparation in examples 1-3_1-xHo_xFeO₂Ceramic sample and CuFeO prepared in comparative example 1₂Room temperature dielectric frequency curve of ceramic samples.

FIG. 6 shows the Cu1-xHoxFeO2 ceramic samples prepared in examples 1-3 and CuFeO prepared in comparative example 1₂Dielectric constant spectrum of ceramic sample.

Detailed Description

The technical solutions of the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings, and it is to be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, belong to the present invention.

Example 1

This example uses citric acid-nitrate sol-gel self-propagating combustion method to prepare Cu with chemical formula_0.97Ho_0.03FeO₂The holmium-doped copper ferrite multiferroic ceramic (namely x is 0.03) specifically comprises the following steps:

(1) mixing copper nitrate trihydrate (Cu (NO)₃)₂·3H₂O), ferric nitrate nonahydrate (Fe (NO)₃)₃·9H₂O), holmium nitrate pentahydrate (Ho (NO)₃)₃·5H₂O), citric acid monohydrate (C)₆H₈O₇·H₂O) as raw material, Cu according to the chemical formula_0.97Ho_0.03FeO₂The molar ratio of the metal ions to the citric acid is 1: 1.5, the molar ratio of the metal ions to the ethylene glycol is 1: 2;

(2) dissolving, pouring deionized water into a beaker by using a measuring cylinder, wherein the deionized water is used in such an amount that the molar ratio of metal ions [ H ]₂O]/[Fe³⁺]Completely dissolving citric acid monohydrate, copper nitrate trihydrate, iron nitrate nonahydrate and holmium nitrate pentahydrate in sequence into deionized water at room temperature under the stirring condition, namely, immediately stirring by using a glass rod until all the reagents are dissolved to obtain a mixed solution;

(3) adjusting the pH value, and adding ammonia water under the stirring condition to adjust the pH value of the mixed solution to be 6;

(4) preparing a precursor liquid, adding ethylene glycol into the mixed solution, and continuously stirring for 6 hours at 80 ℃ by using a magnetic stirrer until the solution is fully reacted to obtain the precursor liquid;

(5) preparing xerogel, pouring the precursor liquid into an evaporating dish, heating at 120 ℃ and continuously stirring until xerogel is formed;

(6) preparing precursor powder, grinding the dry gel into powder, putting the powder into a crucible, then putting the crucible into a tubular furnace filled with argon, heating to 240 ℃, igniting the dry gel powder, and carrying out self-propagating combustion to obtain loose precursor powder.

(7) Sintering, fully grinding the obtained precursor powder, then preparing a ceramic blank sheet, filling the ceramic blank sheet into a crucible, sintering in an argon atmosphere at the sintering temperature of 800 ℃ for 2 hours to obtain the chemical formula Cu_0.97Ho_0.03FeO₂The holmium-doped copper ferrite multiferroic ceramic is shown.

Example 2

This example uses citric acid-nitrate sol-gel self-propagating combustion method to prepare Cu with chemical formula_0.95Ho_0.05FeO₂The holmium-doped copper ferrite multiferroic ceramic (namely x is 0.05) specifically comprises the following steps:

(1) mixing copper nitrate trihydrate (Cu (NO)₃)₂·3H₂O), ferric nitrate nonahydrate (Fe (NO)₃)₃·9H₂O), holmium nitrate pentahydrate (Ho (NO)₃)₃·5H₂O), citric acid monohydrate (C)₆H₈O₇·H₂O) as raw materialAccording to the chemical formula Cu_0.97Ho_0.03FeO₂The molar ratio of the metal ions to the citric acid is 1: 1.5, the molar ratio of the metal ions to the ethylene glycol is 1: 2;

(7) Sintering, fully grinding the obtained precursor powder, then preparing a ceramic blank sheet, filling the ceramic blank sheet into a crucible, sintering in an argon atmosphere at the sintering temperature of 800 ℃ for 2 hours to obtain the chemical formula Cu_0.95Ho_0.05FeO₂The holmium-doped copper ferrite multiferroic ceramic is shown.

Example 3

This example uses citric acid-nitrate sol-gel self-propagating combustion method to prepare Cu with chemical formula_0.92Ho_0.08FeO₂The holmium-doped copper ferrite multiferroic ceramic (namely x is 0.08) specifically comprises the following steps:

(1) mixing copper nitrate trihydrate (Cu (NO)₃)₂·3H₂O), nine waterFerric nitrate (Fe (NO)₃)₃·9H₂O), holmium nitrate pentahydrate (Ho (NO)₃)₃·5H₂O), citric acid monohydrate (C)₆H₈O₇·H₂O) as raw material, Cu according to the chemical formula_0.92Ho_0.08FeO₂The molar ratio of the metal ions to the citric acid is 1: 1.5, the molar ratio of the metal ions to the ethylene glycol is 1: 2;

(7) Sintering, fully grinding the obtained precursor powder, then preparing a ceramic blank sheet, filling the ceramic blank sheet into a crucible, sintering in an argon atmosphere at the sintering temperature of 800 ℃ for 2 hours to obtain the chemical formula Cu_0.92Ho_0.08FeO₂The holmium-doped copper ferrite multiferroic ceramic is shown.

Example 4

This example prepared Cu of the formula at 230 ℃ by a citric acid-nitrate sol-gel self-propagating combustion method_0.95Ho_0.05FeO₂The holmium-doped copper ferrite precursor powder (namely x is 0.05) is sintered to prepare the bulk ceramic, and the method specifically comprises the following steps:

(6) preparing precursor powder, grinding the dry gel into powder, putting the powder into a crucible, then putting the crucible into a tubular furnace filled with argon gas, respectively heating the crucible to 230 ℃ to ignite the dry gel powder, and carrying out self-propagating combustion to obtain loose precursor powder.

Example 5

This example prepared Cu of the formula at 250 ℃ by a citric acid-nitrate sol-gel self-propagating combustion method_0.95Ho_0.05FeO₂The holmium-doped copper ferrite precursor powder (namely x is 0.05) is sintered to prepare the bulk ceramic, and the method specifically comprises the following steps:

(6) preparing precursor powder, grinding the dry gel into powder, putting the powder into a crucible, then putting the crucible into a tubular furnace filled with argon gas, respectively heating the crucible to 250 ℃ to ignite the dry gel powder, and carrying out self-propagating combustion to obtain loose precursor powder.

Example 6

This example uses citric acid-nitrate sol-gel self-propagating combustion method to prepare Cu with chemical formula_0.97Ho_0.03FeO₂The holmium-doped copper ferrite precursor powder (namely x is 0.03) is sintered to prepare the bulk ceramic, and the method specifically comprises the following steps:

(1) mixing copper nitrate trihydrate (Cu (NO)₃)₂·3H₂O), ferric nitrate nonahydrate (Fe (NO)₃)₃·9H₂O), holmium nitrate pentahydrate (Ho (NO)₃)₃·5H₂O), citric acid monohydrate (C)₆H₈O₇·H₂O) as raw material, Cu according to the chemical formula_0.97Ho_0.03FeO₂The molar ratio of the metal ions to the citric acid is 1: 1, the molar ratio of the metal ions to the ethylene glycol is 1: 2.3;

(3) adjusting the pH value, and adding ammonia water under the stirring condition to adjust the pH value of the mixed solution to 7.5;

(4) preparing a precursor liquid, adding ethylene glycol into the mixed solution, and continuously stirring for 6 hours at 75 ℃ by using a magnetic stirrer until the solution is fully reacted to obtain the precursor liquid;

(5) preparing xerogel, pouring the precursor liquid into an evaporating dish, heating at 130 ℃ and continuously stirring until xerogel is formed;

(6) preparing precursor powder, grinding the dry gel into powder, putting the powder into a crucible, then putting the crucible into a tubular furnace filled with argon gas, respectively heating the crucible to 240 ℃, igniting the dry gel powder, and carrying out self-propagating combustion to obtain loose precursor powder.

(7) Sintering, fully grinding the obtained precursor powder, then preparing a ceramic blank sheet, filling the ceramic blank sheet into a crucible, sintering in an argon atmosphere at the sintering temperature of 820 ℃ for 2 hours to obtain the chemical formula Cu_0.97Ho_0.03FeO₂The holmium-doped copper ferrite multiferroic ceramic is shown.

Example 7

(1) mixing copper nitrate trihydrate (Cu (NO)₃)₂·3H₂O), ferric nitrate nonahydrate (Fe (NO)₃)₃·9H₂O), holmium nitrate pentahydrate (Ho (NO)₃)₃·5H₂O), citric acid monohydrate (C)₆H₈O₇·H₂O) as raw material, Cu according to the chemical formula_0.97Ho_0.03FeO₂The molar ratio of the metal ions to the citric acid is 1: 2, the molar ratio of the metal ions to the ethylene glycol is 1: 1.8;

(3) adjusting the pH value, and adding ammonia water under the stirring condition to adjust the pH value of the mixed solution to 5.5;

(5) preparing xerogel, pouring the precursor liquid into an evaporation pan, heating at 110 ℃ and continuously stirring until xerogel is formed;

(7) Sintering, fully grinding the obtained precursor powder, then preparing a ceramic blank sheet, filling the ceramic blank sheet into a crucible, and sintering in an argon atmosphere at the sintering temperature of 800 ℃ for 1.5 hours to obtain the chemical formula Cu_0.97Ho_0.03FeO₂The holmium-doped copper ferrite multiferroic ceramic is shown.

Example 8

(1) mixing copper nitrate trihydrate (Cu (NO)₃)₂·3H₂O), ferric nitrate nonahydrate (Fe (NO)₃)₃·9H₂O), holmium nitrate pentahydrate (Ho (NO)₃)₃·5H₂O), citric acid monohydrate (C)₆H₈O₇·H₂O) as raw material, Cu according to the chemical formula_0.97Ho_0.03FeO₂The molar ratio of the metal ions to the citric acid is 1: 1.5, the molar ratio of the metal ions to the ethylene glycol is 1: 2.1;

(2) dissolving, pouring deionized water into a beaker by using a measuring cylinder, wherein the deionized water is used in such an amount that the molar ratio of metal ions [ H ]₂O]/[Fe³⁺]30, fully dissolving citric acid monohydrate, copper nitrate trihydrate, iron nitrate nonahydrate and holmium nitrate pentahydrate in sequence in deionized water at room temperature under the condition of stirring, namely adding one reagent each time to immediately use the glass rodStirring until all the components are dissolved to obtain a mixed solution;

(4) preparing a precursor liquid, adding ethylene glycol into the mixed solution, and continuously stirring for 6 hours at 85 ℃ by using a magnetic stirrer until the solution is fully reacted to obtain the precursor liquid;

(7) Sintering, fully grinding the obtained precursor powder, then preparing a ceramic blank sheet, filling the ceramic blank sheet into a crucible, sintering in an argon atmosphere at the sintering temperature of 750 ℃ for 3 hours to obtain the chemical formula Cu_0.97Ho_0.03FeO₂The holmium-doped copper ferrite multiferroic ceramic is shown.

Comparative example 1

Compared with the embodiment 1, except the value of x, all the other steps and parameters are the same.

The comparative example utilizes a citric acid-nitrate sol-gel self-propagating combustion method to prepare the undoped CuFeO₂Multiferroic ceramics (i.e. x ═ 0.00), comprising in particular the following steps:

(1) mixing copper nitrate trihydrate (Cu (NO)₃)₂·3H₂O), ferric nitrate nonahydrate (Fe (NO)₃)₃·9H₂O), citric acid monohydrate (C)₆H₈O₇·H₂O) is taken as a raw material and has the chemical formula of CuFeO₂The molar ratio of the metal ions to the citric acid is 1: 1.5, the molar ratio of the metal ions to the ethylene glycol is 1: 2;

(2) dissolving, pouring deionized water into a beaker by using a measuring cylinder, wherein the deionized water is used in such an amount that the molar ratio of metal ions [ H ]₂O]/[Fe³⁺]30, sequentially and fully dissolving citric acid monohydrate, copper nitrate trihydrate and ferric nitrate nonahydrate in deionized water at room temperature under the stirring condition, namely adding one reagent each time, and stirring by using a glass rod until the reagents are completely dissolved to obtain a mixed solution;

(7) Sintering, fully grinding the obtained precursor powder, then preparing a ceramic blank sheet, filling the ceramic blank sheet into a crucible, sintering in an argon atmosphere at the sintering temperature of 800 ℃ for 2 hours to obtain the CuFeO with the chemical formula₂The holmium-doped copper ferrite multiferroic ceramic is shown.

Comparative example 2

In this comparative example, all steps and parameters were the same except that the atmosphere in step (6) was different from those in example 1.

The comparative example utilizes a citric acid-nitrate sol-gel self-propagating combustion method to prepare the chemical formula Cu in an air atmosphere_0.97Ho_0.03FeO₂The holmium-doped copper ferrite precursor powder (namely x is 0.03) is sintered to prepare the bulk ceramic, and the method specifically comprises the following steps:

(6) preparing precursor powder, grinding the xerogel into powder, putting the powder into a crucible, then putting the crucible into a tubular furnace of air, heating to 240 ℃, igniting the xerogel powder, and carrying out self-propagating combustion to obtain loose chemical formula Cu_0.97Ho_0.03FeO₂Holmium-doped copper ferrite precursor powder is shown.

Comparative example 3

In this comparative example, all the steps and parameters were the same as those in examples 4 to 5 except that the heating temperature in step (6) was different from those in examples 4 to 5.

The comparative example utilizes a citric acid-nitrate sol-gel self-propagating combustion method to prepare a chemical formula Cu at 220 DEG C_0.95Ho_0.05FeO₂The holmium-doped copper ferrite precursor powder (namely x is 0.05) is sintered to prepare the bulk ceramic, and the method specifically comprises the following steps:

(6) preparing precursor powder, grinding the dry gel into powder, putting the powder into a crucible, then putting the crucible into a tubular furnace filled with argon gas, respectively heating the crucible to 220 ℃ to ignite the dry gel powder, and carrying out self-propagating combustion to obtain loose precursor powder.

Comparative example 4

The comparative example uses citric acid-nitrate sol-gel self-propagating combustion method to prepare the chemical formula Cu at 260 DEG C_0.95Ho_0.05FeO₂The holmium-doped copper ferrite precursor powder (namely x is 0.05) is sintered to prepare the bulk ceramic, and the method specifically comprises the following steps:

(6) preparing precursor powder, grinding the dry gel into powder, putting the powder into a crucible, then putting the crucible into a tubular furnace filled with argon gas, respectively heating the crucible to 260 ℃ to ignite the dry gel powder, and carrying out self-propagating combustion to obtain loose precursor powder.

Preparation of Cu for examples 1 to 8_1-xHo_xFeO₂Ceramic samples and CuFeO prepared in comparative examples 1-4₂The structure and properties of the ceramic samples were analyzed as follows.

(I) structural analysis

To investigate the phase structure of the holmium-doped copper ferrite multiferroic ceramics prepared by the method of the present invention, Cu was prepared for examples 1 to 3 using an X-ray diffractometer (XRD)_1-xHo_xFeO₂Ceramic sample and CuFeO prepared in comparative example 1₂The ceramic samples were subjected to phase analysis and the results are shown in FIG. 1. As can be seen from FIG. 1, examples 1-3 produce Cu_1-xHo_xFeO₂Ceramic sample and CuFeO prepared in comparative example 1₂The ceramic samples are all hexagonal lattice delafossite structures, no diffraction peak of the second phase appears, and all the samples are single-phase structures. With the increase of the holmium doping amount x, the main diffraction peak moves to a small angle direction, which shows that Ho³⁺Can completely replace Cu²⁺Into CuFeO₂And cause structural distortion.

In order to investigate the influence of air and inert gas atmosphere on the structure of the product when preparing the precursor powder, the precursor powders prepared in example 1 and comparative example 2 were subjected to phase analysis, as shown in FIG. 2, and it was found by comparative analysis of example 1 and comparative example 2 that the sample of the precursor powder prepared in the air atmosphere was mainly CuFe₂O₄And CuO phase, whereas the sample of precursor powder prepared under argon atmosphere was single phase CuFeO₂. This illustrates the preparation of Cu under an argon atmosphere_0.97Ho_0.03FeO₂Precursor bodyThe powder can obtain a pure-phase structure, and Cu is prepared in an air atmosphere_0.97Ho_0.03FeO₂The precursor powder mainly produces CuFe₂O₄And CuO. Therefore, the precursor powder is prepared in the argon atmosphere in the invention.

In order to investigate the influence of the difference in heating temperature on the structure of the product, phase analysis was performed on the precursor powders prepared in examples 4 to 5 and comparative examples 3 to 4, as shown in FIG. 3, and it was found by comparative analysis of examples 4 to 5 and comparative examples 3 to 4 that Cu was prepared at 220 deg.C_0.95Ho_0.05FeO₂The sample of the precursor powder contained a large amount of Fe₂O₃CuO mixed phase, preparing Cu at 230 ℃ and 250 DEG C_0.95Ho_0.05FeO₂Sample-site single-phase structure of precursor powder, and preparation of Cu at 260 ℃_0.95Ho_0.05FeO₂The sample of the precursor powder contained CuFe₂O₄And a CuO hybrid phase; this indicates that single-phase CuFeO can be obtained at 230 ℃ -250 DEG C₂Samples of the structure, below 230 ℃ or above 250 ℃, can produce a heterogeneous phase in the sample. Therefore, the precursor powder is prepared at 230-250 ℃ in the invention.

To investigate the product structure under different experimental parameters, Cu prepared in examples 6-8 was used_1-xHo_xFeO₂The ceramic samples were subjected to phase analysis and the results are shown in FIG. 4. As can be seen from FIG. 4, examples 6-8 produce Cu_1-xHo_xFeO₂The ceramic samples and the Cu-Fe alloy are in a hexagonal lattice delafossite structure, no diffraction peak of a second phase appears, and all the samples are in a single-phase structure, so that the Cu with the single-phase structure can be prepared under the selected experimental conditions_0.97Ho_0.03FeO₂A material.

(II) analysis of Properties

1. Magnetic characteristics

In order to study the magnetic properties of the holmium-doped copper ferrite multiferroic ceramic prepared by the method of the invention, a PPMS comprehensive physical property test system of Quantum Design company is adopted to prepare Cu in examples 1-3_1-xHo_xFeO₂Ceramic sample and CuFeO prepared in comparative example₂Ceramic materialThe samples were subjected to magnetic measurements, the results of which are shown in FIG. 5. As can be seen in FIG. 5, all samples were ferromagnetic, Ho, at the 20K test temperature³⁺Doping improves CuFeO₂And the maximum and residual magnetization of the sample follow Ho³⁺The doping concentration increases. This is due to the high valence state of Ho³⁺The doping causes the distortion of the lattice structure, changes the measure resistance of the sample and influences Fe³⁺-Fe³⁺、Ho³⁺-Fe³⁺Interaction between them, and introduction of cation vacancy and Fe²⁺Influencing Fe³⁺Spin alignment, thereby greatly improving the magnetic properties of the sample. The experimental result shows that the proper amount of Ho is passed through³⁺Doping can increase the magnetic transition temperature and ferromagnetism of the sample.

2. Dielectric properties

To study the dielectric properties of the zirconium-doped gadolinium manganate multiferroic ceramic prepared by the method of the present invention, a precision impedance analyzer Agilent 4294A model was used to prepare Cu for examples 1-3_1-xHo_xFeO₂Ceramic sample and CuFeO prepared in comparative example₂The ceramic samples were subjected to dielectric property measurement, and the results are shown in FIG. 6. As can be seen in fig. 6, all samples exhibited giant dielectricity; undoped CuFeO₂Has a high frequency dependence, a high dielectric constant at low frequencies and a low dielectric constant at high frequencies, Ho³⁺The frequency dependence of the dielectric constant of the doped sample is improved, and the doped sample has good frequency stability; the dielectric constants of the samples were 10755, 13275, 21666, 17998 at 1MHz test frequency, where x is 0.00, 0.03, 0.05, and 0.08, respectively, indicating Ho³⁺Doping significantly improves the dielectric constant of the sample. Through the analysis of the inventor, the undoped CuFeO₂May have a mixed valence with Fe present in the material (Fe)²⁺And Fe³⁺) Related to grain-boundary characteristics; high valence state of Ho³⁺Doping enhanced CuFeO₂The dielectric constant of (2) may be related to Ho³⁺Doping increases Fe in samples²⁺The content (charge compensation effect) is related to the lattice distortion. The experimental result shows that Cu_1-xHo_xFeO₂The sample has giant dielectric property at room temperature, and Ho³⁺The doping of (2) can improve the dielectric constant and frequency stability of the sample.

In conclusion, the chemical formula provided by the invention is Cu_1-xHo_xFeO₂The prepared holmium-doped copper ferrite multiferroic ceramic has room-temperature giant dielectric property and better low-temperature ferromagnetism, and can be prepared by Ho³⁺The doping can well regulate and control the magnetism and dielectric property of the copper ferrite, has wide application prospect in the fields of high dielectric capacitors, information storage, spin electronic devices, magnetoelectric sensors and the like, and is a novel multiferroic material expected to be further researched and explored.

It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.

Claims

1. A holmium-doped copper ferrite multiferroic ceramic, characterized in that the holmium-doped copper ferrite multiferroic ceramic is represented by the general formula Cu _1- _x Ho _x FeO ₂ , where 0<x≤0.08.

2 . The holmium-doped copper ferrite multiferroic ceramic according to claim 1 , wherein 0.03≦x≦0.08 in the general formula. 3 .

3. the preparation method of the described holmium-doped copper ferrite multiferroic ceramics of claim 1 or 2, is characterized in that, comprises the following steps:

(1) batching, with copper nitrate trihydrate, ferric nitrate nonahydrate, holmium nitrate pentahydrate, organic fuel and ethylene glycol as raw materials, the chemical formula determined by the set value of x in the general formula Cu _1-x Ho _x FeO ₂ Carry out weighing and batching, wherein the molar ratio of metal ions to organic fuel is 1:1-2; the molar ratio of metal ions to ethylene glycol is 1:1.8-2.3;

(2) dissolving, under stirring condition, organic fuel, copper nitrate trihydrate, ferric nitrate nonahydrate and holmium nitrate pentahydrate are fully dissolved in deionized water successively to obtain mixed solution;

(3) Adjust the pH value, add ammonia water under stirring condition to adjust the pH value of the mixed solution to 5.5～7.5;

(4) preparing a precursor liquid, adding ethylene glycol into the mixed solution, and stirring continuously at 75-85° C. until the solution is fully reacted to obtain a precursor liquid;

(5) preparing a dry gel, heating the precursor liquid at a temperature of 110-130° C. and stirring continuously until a dry gel is formed;

(6) preparing the precursor powder, grinding the xerogel into powder, and heating the xerogel powder to 230-250° C. in an inert gas atmosphere to ignite the xerogel powder, causing self-propagating combustion to obtain loose precursor powder;

(7) Sintering, the obtained precursor powder is fully ground to form a green body, and the green body is placed in an inert gas atmosphere for sintering. Holmium-doped copper ferrite multiferroic ceramics of Cu _1-x Ho _x FeO ₂ .

4. the preparation method of holmium-doped copper ferrite multiferroic ceramics according to claim 3, is characterized in that, described organic fuel is a kind of in citric acid, glycine, oxalic acid or polyacrylic acid.

5. The preparation method of holmium-doped copper ferrite multiferroic ceramics according to claim 3 or 4, wherein the inert gas is nitrogen or argon.