A multi-element rare earth doped modified bismuth ferrite-based ceramic and its preparation method

Abstract

This invention relates to the field of dielectric materials technology, specifically to a multi-element rare earth-doped modified bismuth ferrite-based ceramic and its preparation method. The method employs a standard solid-state reaction sintering process, which includes drying the raw materials, weighing them according to the correct stoichiometric ratio, batching, ball milling, drying, sieving, and pressing to obtain a BiFeO3-based ceramic green body. Finally, it is sintered at a high temperature of 900℃ to form a ceramic. This ceramic exhibits good ferroelectricity and magnetism, and possesses excellent magnetoelectric coupling. Furthermore, the preparation method is simple to implement and can be mass-produced.

Description

Technical Field

[0001] This invention relates to the field of dielectric materials technology, specifically to a multi-element rare-earth-doped modified bismuth ferrite-based ceramic and its preparation method. Background Technology

[0002] Miniaturization and integration of electronic components have become a major trend in development. Against this backdrop, the optimization of data storage and retrieval components has come into focus for researchers. Magnetoelectric coupling materials, due to their unique magnetoelectric coexistence characteristics, can achieve rapid electrical writing and magnetic reading, significantly reducing losses compared to traditional data storage devices and meeting the ever-increasing demands for information storage density and manipulation speed.

[0003] BiFeO3, as one of the most well-known single-phase room-temperature multiferroic materials, has broad application prospects in the memory field due to its unique physical properties. However, BiFeO3 also suffers from several problems, such as high leakage current, high coercivity field, and weak magnetic properties caused by its spin-cycloidal structure. Crucially, the magnetoelectric coupling effect of BiFeO3 is also relatively weak.

[0004] To address the aforementioned issues, researchers have proposed targeted modification schemes involving A- and B-site ion substitution. Taking A-site ion substitution as an example, the main substitutions are Group II elements (Sr, Ba, Ca, etc.) and rare earth elements (Sm, Nd, Dy, La, Ce, Ho, Yb, etc.). The fundamental principle behind enhancing magnetic and electrical properties is to suppress leakage current and alter the phase structure. Therefore, finding suitable substitution elements and amounts for BiFeO3 to form stable ceramic materials is particularly important.

[0005] During the research, it was discovered that BiFeO3 undergoes a phase structure change after ion substitution at the A-site. The magnetic properties of BiFeO3 are constrained by the cycloidal spin structure of the R3c phase, and it does not exhibit external magnetism. In June 2012, the *Journal of Magnetism and Magnetic Materials* published an article entitled "Magnetic, ferroelectric and magnetic properties of Ba-doped BiFeO3," which described the preparation of BiFeO3 using a standard double-sintering ceramic method. 1−x Ba xStudies on multiferroic ceramics in the FeO3 system have found that Ba substitution can distort some of the R3c phase into a monoclinic or tetragonal structure, enhancing magnetic properties and magnetoelectric coupling. However, this also results in lower remanent polarization and higher leakage current. In July 2022, the *Journal of the American Ceramic Society* published a paper titled "Giant electric field–controlled magnetism in Bi..." 0.86 Sm 0.14 The article "FeO3 multiferroicceramics with Pna21 symmetry" describes the preparation of Bi using a standard solid-state sintering method. 0.86 Sm 0.14 This study investigated the transformation mechanism between the R3c and Pna21 phases in FeO3 ceramics after Sm doping, and examined the interconversion characteristics between the Pna21 phase and the R3c phase under external conditions, demonstrating the unique advantages of the Pna21 phase in magnetoelectric coupling. On November 23, 2018, *Advanced Functional Materials* published a paper titled "Symmetry Modulation and Enhanced Multiferroic Characteristics in Bi 1-x Nd x The article "FeO3 Ceramics" also describes the preparation of Bi using the standard solid-state sintering method. 1-x Nd x This study investigated the changes in ferroelectric and magnetic properties of BiFeO3 ceramics after Nd doping. Nd doping effectively enhanced the magnetoelectric properties of the ceramics. However, this system exhibits high remanent polarization (>25 μC / cm). 2 ) only exists x The narrow doping range of 0.10 to 0.13 limits its large-scale application to some extent.

[0006] Based on the conclusions of the above studies, how to expand the range of high remanent polarization values ​​in BiFeO3 ceramics modified by elemental doping at the A site, and how to enhance the magnetoelectric coupling performance of BiFeO3 ceramic materials by changing the phase structure, have become urgent problems to be solved.

[0007] In view of the above-mentioned defects, the inventors of this invention have finally obtained this invention after a long period of research and practice. Summary of the Invention

[0008] The purpose of this invention is to solve the problems of how to expand the range of high remanent polarization values ​​in BiFeO3 ceramics modified by elemental doping at the A site, and how to enhance the magnetoelectric coupling performance of BiFeO3 ceramic materials by changing the phase structure. This invention provides a multi-element rare earth doped modified bismuth ferrite-based ceramic and its preparation method.

[0009] To achieve the above objectives, this invention discloses a multi-element rare earth-doped modified bismuth ferrite-based ceramic, wherein the bismuth ferrite-based ceramic is an A-site multi-element rare earth element-doped bismuth ferrite-based ceramic, and the composition of the bismuth ferrite ceramic is Bi. 1-x (La 1 / 4Nd 1 / 4 Sm 1 / 4 Gd 1 / 4 ) x FeO3, where 0.06≤ x ≤0.14.

[0010] The x The values ​​are 0.06, 0.08, 0.10, 0.12, and 0.14.

[0011] This invention also discloses a method for preparing the above-mentioned multi-element rare earth doped modified bismuth ferrite-based ceramics, comprising the following steps:

[0012] S1, first dry the raw materials Bi2O3, Fe2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3, then mix them according to the stoichiometric ratio Bi 1-x (La 1 / 4 Nd 1 / 4 Sm 1 / 4 Gd 1 / 4 ) x FeO3 is weighed out from the raw materials;

[0013] S2, add deionized water to the raw materials weighed in step S1 and ball mill until the raw materials are mixed evenly;

[0014] S3, dry the raw material after ball milling in step S2 to remove moisture;

[0015] S4. Grind and sieve the dried raw material from step S3.

[0016] S5, Place the sieved powder from step S4 into a mold and press it into a green body;

[0017] S6. The green body obtained in step S5 is heated to 900-920 ℃ and held at that temperature to obtain ceramic sheets.

[0018] In step S1 x =0.06, 0.08, 0.10, 0.12, 0.14.

[0019] In step S1, the drying temperature is 80 ℃ and the drying time is 48 h.

[0020] In step S2, the ball milling process involves clockwise ball milling for 12 hours, followed by a 0.5-hour stop, and then counterclockwise ball milling for 12 hours at a speed of 200 r / min.

[0021] In step S3, the drying temperature is 80 ℃ and the drying time is 48 h.

[0022] In step S4, the raw material is sieved through a mesh size of 120.

[0023] In step S5, the mold is pressed at a pressure of 158 MPa for 2 minutes.

[0024] In step S6, the green body is buried with a powder of the same composition, and the heating rate is 5. o The temperature is C / min, and the holding time is 3h.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] The bismuth ferrite-based ceramic material obtained in this invention introduces multiple rare earth elements at the A-site. With increasing rare earth element doping, the phase composition gradually transforms from R3c phase to a coexistence of R3c and Pna21 phases. Part of the rhombohedral polar R3c phase is transformed into the orthorhombic polar Pna21 phase. The Pna21 phase exhibits weak ferromagnetism, while the R3c phase exhibits G-type antiferromagnetism and macroscopically does not show magnetism. Therefore, with increasing Pna21 phase content, the magnetic properties of the ceramic material gradually increase. By selecting an appropriate system, optimal ferroelectric and magnetic properties can be obtained. Simultaneously, R... 3+ Bi replaced position A 3+ This method can effectively suppress the volatilization of bismuth, control the formation of oxygen vacancies, and effectively reduce leakage current. It overcomes the shortcomings of existing intrinsic BiFeO3 ceramics, such as large leakage current, low ferromagnetic and ferroelectric properties, and poor magnetoelectric coupling effect.

[0027] The preparation process of the bismuth ferrite-based ceramic material obtained in this invention is an improvement on the existing single rare earth element doping process. It incorporates the idea of ​​increasing local polarization through multi-element doping, changing the single-element doping to multi-element doping. The preparation method employs the traditional standard solid-state reaction method, while eliminating the binder commonly added in current preparation processes and the subsequent debinding step, thus simplifying the process flow and reducing costs.

[0028] The ceramic materials prepared by the existing invention have uniform composition, fine grains and excellent performance. The preparation method is mature and reliable, the process is short and simple to operate, and it is convenient for large-scale production. Attached Figure Description

[0029] Figure 1 XRD images of bismuth ferrite-based ceramics with good magnetoelectric properties prepared in Examples 1-8;

[0030] Figure 2 SEM images of bismuth ferrite-based ceramics with good magnetoelectric properties prepared in Examples 1-8;

[0031] Figure 3 Hysteresis curves of bismuth ferrite-based ceramics with good magnetoelectric properties prepared in Examples 1-6;

[0032] Figure 4 Hysteresis curves of bismuth ferrite-based ceramics with good magnetoelectric properties obtained in Examples 1-8;

[0033] Figure 5 The bismuth ferrite-based ceramics with good magnetoelectric properties prepared in Examples 1-6 are described in section a. ME -H curve. Detailed Implementation

[0034] The above-mentioned and other technical features and advantages of the present invention will be described in more detail below with reference to the accompanying drawings. Example

[0035] This embodiment provides a multi-element rare earth doped modified bismuth ferrite-based ceramic, the chemical composition of which is: Bi 0.9 6La 0.01 Nd 0.01 Sm 0.01 Gd 0.01 FeO3.

[0036] The specific preparation steps for this ceramic material are as follows:

[0037] Ingredients: Place the raw materials Bi2O3, Fe2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 (where the purity of Bi2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 is not less than 99.99%, and the purity of Fe2O3 is not less than 99.9%) into a drying oven and dry at 80°C. o Dry at C for 48 h to remove any moisture that may be present in the raw material, and then weigh it according to the correct chemical weighing ratio.

[0038] Ball milling: Place the weighed raw material into a nylon container, add the milling media (zirconia balls) and deionized water, and load it into a planetary ball mill. Mill clockwise for 12 hours, stop for 0.5 hours, then mill counter-clockwise for 12 hours. The ball mill speed is 200 r / min. Then, mill for 24 hours at 200 r / min.

[0039] Drying: Pour the ball-milled raw material into a crystallizing dish, place it in a drying oven, and dry at 80°C. o Dry at C for 48 h to remove moisture;

[0040] Sieving: Grind the dried raw materials using an agate mortar and pestle, and then pass them through a 120-mesh sieve to obtain powder with uniform particle size;

[0041] Pressing: Weigh about 0.5 g of the sieved powder, place it in a mold, and press it into a ceramic green body under 158 MPa;

[0042] Sintering: The obtained ceramic green body is sintered in a muffle furnace at 5°C. o The temperature was increased to 900℃ at a heating rate of C / min, held for 3 hours, and then the cooling rate was controlled at 5. o Cool down to 300°C / min o After C, the ceramic sheet is cooled in the furnace to obtain ceramic pieces.

[0043] Sample preparation: The obtained ceramic pieces are crushed and silvered to obtain the sample to be tested.

[0044] The performance results of the sample are as follows:

[0045]

[0046] Where Pr is the remanent polarization, Mr is the remanent magnetization, and M is the remanent magnetization. max Hc is the maximum magnetization, Hc is the coercive field, and a is the maximum magnetization. ME is the magnetoelectric coupling coefficient.

[0047] Example 2

[0048] This embodiment provides a multi-element rare earth doped modified bismuth ferrite-based ceramic, the chemical composition of which is: Bi 0.9 4La 0.015 Nd 0.015 Sm 0.015 Gd 0.015 FeO3.

[0049] The specific preparation steps for this ceramic material are as follows:

[0050] Ingredients: Place the raw materials Bi2O3, Fe2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 (where the purity of Bi2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 is not less than 99.99%, and the purity of Fe2O3 is not less than 99.9%) into a drying oven and dry at 80°C. o Dry at C for 48 h to remove any moisture that may be present in the raw material, and then weigh it according to the correct chemical weighing ratio.

[0051] Ball milling: Place the weighed raw material into a nylon container, add the milling media (zirconia balls) and deionized water, and load it into a planetary ball mill. Mill clockwise for 12 hours, stop for 0.5 hours, then mill counter-clockwise for 12 hours. The ball mill speed is 200 r / min. Then, mill for 24 hours at 200 r / min.

[0052] Drying: Pour the ball-milled raw material into a crystallizing dish, place it in a drying oven, and dry at 80°C. o Dry at C for 48 h to remove moisture;

[0053] Sieving: Grind the dried raw materials using an agate mortar and pestle, and then pass them through a 120-mesh sieve to obtain powder with uniform particle size;

[0054] Pressing: Weigh about 0.5 g of the sieved powder, place it in a mold, and press it into a ceramic green body under 158 MPa;

[0055] Sintering: The obtained ceramic green body is sintered in a muffle furnace at 5°C. o The temperature was increased to 900℃ at a heating rate of C / min, held for 3 hours, and then the cooling rate was controlled at 5. o Cool down to 300°C / min o After C, the ceramic sheet is cooled in the furnace to obtain ceramic pieces.

[0056] Sample preparation: The obtained ceramic pieces are crushed and silvered to obtain the sample to be tested.

[0057] The performance results of the sample are as follows:

[0058]

[0059] Where Pr is the remanent polarization, Mr is the remanent magnetization, and M is the remanent magnetization. max Hc is the maximum magnetization, Hc is the coercive field, and a is the maximum magnetization. ME is the magnetoelectric coupling coefficient.

[0060] Example 3

[0061] This embodiment provides a multi-element rare earth doped modified bismuth ferrite-based ceramic, the chemical composition of which is: Bi 0.9 8La 0.02 Nd 0.02 Sm 0.02 Gd 0.02 FeO3.

[0062] The specific preparation steps for this ceramic material are as follows:

[0063] Ingredients: Place the raw materials Bi2O3, Fe2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 (where the purity of Bi2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 is not less than 99.99%, and the purity of Fe2O3 is not less than 99.9%) into a drying oven and dry at 80°C. o Dry at C for 48 h to remove any moisture that may be present in the raw material, and then weigh it according to the correct chemical weighing ratio.

[0064] Ball milling: Place the weighed raw material into a nylon container, add the milling media (zirconia balls) and deionized water, and load it into a planetary ball mill. Mill clockwise for 12 hours, stop for 0.5 hours, then mill counter-clockwise for 12 hours. The ball mill speed is 200 r / min. Then, mill for 24 hours at 200 r / min.

[0065] Drying: Pour the ball-milled raw material into a crystallizing dish, place it in a drying oven, and dry at 80°C. o Dry at C for 48 h to remove moisture;

[0066] Sieving: Grind the dried raw materials using an agate mortar and pestle, and then pass them through a 120-mesh sieve to obtain powder with uniform particle size;

[0067] Pressing: Weigh about 0.5 g of the sieved powder, place it in a mold, and press it into a ceramic green body under 158 MPa;

[0068] Sintering: The obtained ceramic green body is sintered in a muffle furnace at 5°C. o The temperature was increased to 900℃ at a heating rate of C / min, held for 3 hours, and then the cooling rate was controlled at 5. o Cool down to 300°C / min o After C, the ceramic sheet is cooled in the furnace to obtain ceramic pieces.

[0069] Sample preparation: The obtained ceramic pieces are crushed and silvered to obtain the sample to be tested.

[0070] The performance results of the sample are as follows:

[0071]

[0072] Where Pr is the remanent polarization, Mr is the remanent magnetization, and M is the remanent magnetization. max Hc is the maximum magnetization, Hc is the coercive field, and a is the maximum magnetization. ME is the magnetoelectric coupling coefficient.

[0073] Example 4

[0074] This embodiment provides a multi-element rare earth doped modified bismuth ferrite-based ceramic, the chemical composition of which is: Bi 0.9 0La0.025 Nd 0.025 Sm 0.025 Gd 0.025 FeO3.

[0075] The specific preparation steps for this ceramic material are as follows:

[0076] Ingredients: Place the raw materials Bi2O3, Fe2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 (where the purity of Bi2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 is not less than 99.99%, and the purity of Fe2O3 is not less than 99.9%) into a drying oven and dry at 80°C. o Dry at C for 48 h to remove any moisture that may be present in the raw material, and then weigh it according to the correct chemical weighing ratio.

[0077] Ball milling: Place the weighed raw material into a nylon container, add the milling media (zirconia balls) and deionized water, and load it into a planetary ball mill. Mill clockwise for 12 hours, stop for 0.5 hours, then mill counter-clockwise for 12 hours. The ball mill speed is 200 r / min. Then, mill for 24 hours at 200 r / min.

[0078] Drying: Pour the ball-milled raw material into a crystallizing dish, place it in a drying oven, and dry at 80°C. o Dry at C for 48 h to remove moisture;

[0079] Sieving: Grind the dried raw materials using an agate mortar and pestle, and then pass them through a 120-mesh sieve to obtain powder with uniform particle size;

[0080] Pressing: Weigh about 0.5 g of the sieved powder, place it in a mold, and press it into a ceramic green body under 158 MPa;

[0081] Sintering: The obtained ceramic green body is sintered in a muffle furnace at 5°C. o The temperature was increased to 900℃ at a heating rate of C / min, held for 3 hours, and then the cooling rate was controlled at 5. o Cool down to 300°C / min o After C, the ceramic sheet is cooled in the furnace to obtain ceramic pieces.

[0082] Sample preparation: The obtained ceramic pieces are crushed and silvered to obtain the sample to be tested.

[0083] The performance results of the sample are as follows:

[0084]

[0085] Where Pr is the remanent polarization, Mr is the remanent magnetization, and M is the remanent magnetization. max Hc is the maximum magnetization, Hc is the coercive field, and a is the maximum magnetization.ME is the magnetoelectric coupling coefficient.

[0086] Example 5

[0087] This embodiment provides a multi-element rare earth doped modified bismuth ferrite-based ceramic, the chemical composition of which is: Bi 0.8 8La 0.03 Nd 0.03 Sm 0.03 Gd 0.03 FeO3.

[0088] The specific preparation steps for this ceramic material are as follows:

[0089] Ingredients: Place the raw materials Bi2O3, Fe2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 (where the purity of Bi2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 is not less than 99.99%, and the purity of Fe2O3 is not less than 99.9%) into a drying oven and dry at 80°C. o Dry at C for 48 h to remove any moisture that may be present in the raw material, and then weigh it according to the correct chemical weighing ratio.

[0090] Ball milling: Place the weighed raw material into a nylon container, add the milling media (zirconia balls) and deionized water, and load it into a planetary ball mill. Mill clockwise for 12 hours, stop for 0.5 hours, then mill counter-clockwise for 12 hours. The ball mill speed is 200 r / min. Then, mill for 24 hours at 200 r / min.

[0091] Drying: Pour the ball-milled raw material into a crystallizing dish, place it in a drying oven, and dry at 80°C. o Dry at C for 48 h to remove moisture;

[0092] Sieving: Grind the dried raw materials using an agate mortar and pestle, and then pass them through a 120-mesh sieve to obtain powder with uniform particle size;

[0093] Pressing: Weigh about 0.5 g of the sieved powder, place it in a mold, and press it into a ceramic green body under 158 MPa;

[0094] Sintering: The obtained ceramic green body is sintered in a muffle furnace at 5°C. o The temperature was increased to 900℃ at a heating rate of C / min, held for 3 hours, and then the cooling rate was controlled at 5. o Cool down to 300°C / min o After C, the ceramic sheet is cooled in the furnace to obtain ceramic pieces.

[0095] Sample preparation: The obtained ceramic pieces are crushed and silvered to obtain the sample to be tested.

[0096] The performance results of the sample are as follows:

[0097]

[0098] Where Pr is the remanent polarization, Mr is the remanent magnetization, and M is the remanent magnetization. max Hc is the maximum magnetization, Hc is the coercive field, and a is the maximum magnetization. ME is the magnetoelectric coupling coefficient.

[0099] Example 6

[0100] This embodiment provides a multi-element rare earth doped modified bismuth ferrite-based ceramic, the chemical composition of which is: Bi 0.8 6La 0.035 Nd 0.035 Sm 0.035 Gd 0.035 FeO3.

[0101] The specific preparation steps for this ceramic material are as follows:

[0102] Ingredients: Place the raw materials Bi2O3, Fe2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 (where the purity of Bi2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 is not less than 99.99%, and the purity of Fe2O3 is not less than 99.9%) into a drying oven and dry at 80°C. o Dry at C for 48 h to remove any moisture that may be present in the raw material, and then weigh it according to the correct chemical weighing ratio.

[0103] Ball milling: Place the weighed raw material into a nylon container, add the milling media (zirconia balls) and deionized water, and load it into a planetary ball mill. Mill clockwise for 12 hours, stop for 0.5 hours, then mill counter-clockwise for 12 hours. The ball mill speed is 200 r / min. Then, mill for 24 hours at 200 r / min.

[0104] Drying: Pour the ball-milled raw material into a crystallizing dish, place it in a drying oven, and dry at 80°C. o Dry at C for 48 h to remove moisture;

[0105] Sieving: Grind the dried raw materials using an agate mortar and pestle, and then pass them through a 120-mesh sieve to obtain powder with uniform particle size;

[0106] Pressing: Weigh about 0.5 g of the sieved powder, place it in a mold, and press it into a ceramic green body under 158 MPa;

[0107] Sintering: The obtained ceramic green body is sintered in a muffle furnace at 5°C. o The temperature was increased to 900℃ at a heating rate of C / min, held for 3 hours, and then the cooling rate was controlled at 5.o Cool down to 300°C / min o After C, the ceramic sheet is cooled in the furnace to obtain ceramic pieces.

[0108] Sample preparation: The obtained ceramic pieces are crushed and silvered to obtain the sample to be tested.

[0109] The performance results of the sample are as follows:

[0110]

[0111] Where Pr is the remanent polarization, Mr is the remanent magnetization, and M is the remanent magnetization. max Hc is the maximum magnetization, Hc is the coercive field, and a is the maximum magnetization. ME is the magnetoelectric coupling coefficient.

[0112] Example 7

[0113] This embodiment provides a multi-element rare earth doped modified bismuth ferrite-based ceramic, the chemical composition of which is: Bi 0.8 4La 0.04 Nd 0.04 Sm 0.04 Gd 0.04 FeO3.

[0114] The specific preparation steps for this ceramic material are as follows:

[0115] Ingredients: Place the raw materials Bi2O3, Fe2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 (where the purity of Bi2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 is not less than 99.99%, and the purity of Fe2O3 is not less than 99.9%) into a drying oven and dry at 80°C. o Dry at C for 48 h to remove any moisture that may be present in the raw material, and then weigh it according to the correct chemical weighing ratio.

[0116] Ball milling: Place the weighed raw material into a nylon container, add the milling media (zirconia balls) and deionized water, and load it into a planetary ball mill. Mill clockwise for 12 hours, stop for 0.5 hours, then mill counter-clockwise for 12 hours. The ball mill speed is 200 r / min. Then, mill for 24 hours at 200 r / min.

[0117] Drying: Pour the ball-milled raw material into a crystallizing dish, place it in a drying oven, and dry at 80°C. o Dry at C for 48 h to remove moisture;

[0118] Sieving: Grind the dried raw materials using an agate mortar and pestle, and then pass them through a 120-mesh sieve to obtain powder with uniform particle size;

[0119] Pressing: Weigh about 0.5 g of the sieved powder, place it in a mold, and press it into a ceramic green body under 158 MPa;

[0120] Sintering: The obtained ceramic green body is sintered in a muffle furnace at 5°C. o The temperature was increased to 900℃ at a heating rate of C / min, held for 3 hours, and then the cooling rate was controlled at 5. o Cool down to 300°C / min o After C, the ceramic sheet is cooled in the furnace to obtain ceramic pieces.

[0121] Sample preparation: The obtained ceramic pieces are crushed and silvered to obtain the sample to be tested.

[0122] The performance results of the sample are as follows:

[0123]

[0124] Where Pr is the remanent polarization, Mr is the remanent magnetization, and M is the remanent magnetization. max Hc is the maximum magnetization, Hc is the coercive field, and a is the maximum magnetization. ME is the magnetoelectric coupling coefficient.

[0125] Example 8

[0126] This embodiment provides a multi-element rare earth doped modified bismuth ferrite-based ceramic, the chemical composition of which is: Bi 0.8 2La 0.045 Nd 0.045 Sm 0.045 Gd 0.045 FeO3.

[0127] The specific preparation steps for this ceramic material are as follows:

[0128] Ingredients: Place the raw materials Bi2O3, Fe2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 (where the purity of Bi2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3 is not less than 99.99%, and the purity of Fe2O3 is not less than 99.9%) into a drying oven and dry at 80°C. o Dry at C for 48 h to remove any moisture that may be present in the raw material, and then weigh it according to the correct chemical weighing ratio.

[0129] Ball milling: Place the weighed raw material into a nylon container, add the milling media (zirconia balls) and deionized water, and load it into a planetary ball mill. Mill clockwise for 12 hours, stop for 0.5 hours, then mill counter-clockwise for 12 hours. The ball mill speed is 200 r / min. Then, mill for 24 hours at 200 r / min.

[0130] Drying: Pour the ball-milled raw material into a crystallizing dish, place it in a drying oven, and dry at 80°C. o Dry at C for 48 h to remove moisture;

[0131] Sieving: Grind the dried raw materials using an agate mortar and pestle, and then pass them through a 120-mesh sieve to obtain powder with uniform particle size;

[0132] Pressing: Weigh about 0.5 g of the sieved powder, place it in a mold, and press it into a ceramic green body under 158 MPa;

[0133] Sintering: The obtained ceramic green body is sintered in a muffle furnace at 5°C. o The temperature was increased to 900℃ at a heating rate of C / min, held for 3 hours, and then the cooling rate was controlled at 5. o Cool down to 300°C / min o After C, the ceramic sheet is cooled in the furnace to obtain ceramic pieces.

[0134] Sample preparation: The obtained ceramic pieces are crushed and silvered to obtain the sample to be tested.

[0135] The performance results of the sample are as follows:

[0136]

[0137] Where Pr is the remanent polarization, Mr is the remanent magnetization, and M is the remanent magnetization. max Hc is the maximum magnetization, Hc is the coercive field, and a is the maximum magnetization. ME is the magnetoelectric coupling coefficient.

[0138] The bismuth ferrite-based ceramic sheets in Examples 1-8 were subjected to XRD, SEM, hysteresis loop, magnetic hysteresis loop, and magnetoelectric coupling to obtain the following graphs. The spectral analysis is shown below:

[0139] Figure 1 The multi-element rare earth-doped modified bismuth ferrite-based ceramics prepared in Examples 1-8: x XRD patterns with α values ​​ranging from 0.06 to 0.18 show that the main structure of the ceramic is a rhombohedral R3c phase, and the composition... x The concentration of the impurity phase Bi₂Fe₄O₉ (Pbam space group) exists in the range of 0.04–0.08, exhibiting weak ferromagnetism and having little effect on ferroelectricity and magnetism. (Composition) x The Pna21 phase begins to appear at a value of 0.10, and continues to appear as... x As the concentration increases, the characteristic peaks of the Pna21 phase become more prominent.

[0140] Figure 2The images shown are SEM images of the multi-element rare earth doped modified bismuth ferrite ceramic sheets prepared in Examples 1-8. Among them, (a) is a SEM image of the multi-element rare earth doped modified bismuth ferrite ceramic prepared in Example 1, (b) is a SEM image of the multi-element rare earth doped modified bismuth ferrite ceramic prepared in Example 2, (c) is a SEM image of the multi-element rare earth doped modified bismuth ferrite ceramic prepared in Example 3, (d) is a SEM image of the multi-element rare earth doped modified bismuth ferrite ceramic prepared in Example 4, (e) is a SEM image of the multi-element rare earth doped modified bismuth ferrite ceramic prepared in Example 5, (f) is a SEM image of the multi-element rare earth doped modified bismuth ferrite ceramic prepared in Example 6, (g) is a SEM image of the multi-element rare earth doped modified bismuth ferrite ceramic prepared in Example 7, and (h) is a SEM image of the multi-element rare earth doped modified bismuth ferrite ceramic prepared in Example 8. In (a)-(c), some impurity phases Bi2Fe4O9 and a very small amount of Bi2O3 can be observed, but they have little impact on the ceramic properties. However, in (g)-(h), more voids are observed, indicating that the ceramic has a relatively high porosity and is not dense enough. At the same time, it can be seen from the figure that as the amount of rare earth element doping increases, the average grain size of the ceramic gradually decreases. The reduction in grain size helps to improve the ferroelectric properties of the ceramic.

[0141] Figure 3 Images show the hysteresis loops (DHMs) of the multi-element rare-earth-doped modified bismuth ferrite ceramic sheets prepared in Examples 1-6. (a) is the DHM image of the multi-element rare-earth-doped modified bismuth ferrite ceramic prepared in Example 1; (b) is the DHM image of the multi-element rare-earth-doped modified bismuth ferrite ceramic prepared in Example 2; (c) is the DHM image of the multi-element rare-earth-doped modified bismuth ferrite ceramic prepared in Example 3; (d) is the DHM image of the multi-element rare-earth-doped modified bismuth ferrite ceramic prepared in Example 4; (e) is the DHM image of the multi-element rare-earth-doped modified bismuth ferrite ceramic prepared in Example 5; and (f) is the DHM image of the multi-element rare-earth-doped modified bismuth ferrite ceramic prepared in Example 6. In Examples 7 and 8, due to the non-dense ceramics and large leakage current, no corresponding hysteresis loops were measured. As can be seen from the figures, with the increase of rare-earth element doping, the remanent polarization value of the ceramic shows a trend of first increasing and then decreasing, particularly in (c). x The ceramic exhibits the highest remanent polarization value, reaching 33.14 μC / cm², when the polarization ratio is 0.10. 2 Subsequently, due to the disruption of Bi-O bond hybridization caused by rare earth element doping, the polarization value gradually decreased. Meanwhile, it can be observed in the figure that... x When the polarization value is between 0.06 and 0.14, the remanent polarization value reaches 25 μC / cm. 2 The system achieves high remanent polarization over a wide range of substitutions.

[0142] Figure 4 The figures show the hysteresis loops and remanent magnetization trends of the multi-element rare earth-doped modified bismuth ferrite-based ceramic sheets prepared in Examples 1-8, respectively. Specifically, (a) shows the hysteresis loop of the multi-element rare earth-doped modified bismuth ferrite-based ceramic prepared in Example 1; (b) shows the hysteresis loop of the multi-element rare earth-doped modified bismuth ferrite-based ceramic prepared in Example 2; (c) shows the hysteresis loop of the multi-element rare earth-doped modified bismuth ferrite-based ceramic prepared in Example 3; and (d) shows the hysteresis loop of the multi-element rare earth-doped modified bismuth ferrite-based ceramic prepared in Example 4. The hysteresis loops of the bismuth ferrite-based ceramics are shown in the figures. (e) is the hysteresis loop of the multi-element rare earth doped modified bismuth ferrite-based ceramic prepared in Example 5; (f) is the hysteresis loop of the multi-element rare earth doped modified bismuth ferrite-based ceramic prepared in Example 6; (g) is the hysteresis loop of the multi-element rare earth doped modified bismuth ferrite-based ceramic prepared in Example 7; (h) is the hysteresis loop of the multi-element rare earth doped modified bismuth ferrite-based ceramic prepared in Example 8; and (i) shows the trend of remanent magnetization of the bismuth ferrite-based ceramic sheets in Examples 1-8. It can be seen from the figures that the magnetic properties of the ceramics gradually increase with the increase of rare earth element doping. This is because the R3c structure has a cycloidal spin structure without macroscopic magnetism, while Pna21 destroys the cycloidal spin magnetic order of the matrix ceramic, and the orthorhombic phase structure has weak ferromagnetism. The doping of rare earth elements disrupts the original spin cycloidal structure, releasing macroscopic magnetism.

[0143] Figure 5 The figures show the magnetoelectric coupling curves of the multi-element rare-earth-doped modified bismuth ferrite-based ceramics prepared in Examples 1-6, respectively. As can be seen from the figures, all ceramics showed well-matched linear magnetoelectric coupling coefficients. The magnetoelectric coupling coefficient α... ME exist x The maximum value is obtained when a = 0.10. ME =3.50 mV / cm Oe, in x When a = 0.12, the magnetoelectric coupling coefficient is also quite close, a ME =3.47 mV / cm Oe.

[0144] As described above, the improved magnetoelectric coupling performance in Examples 4 and 5 is significantly enhanced, and Examples 4 and 5 of this invention are preferred embodiments. This invention is merely illustrative and not restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of this invention, all of which will fall within the protection scope of this invention.

Claims

1. A multi-element rare earth-doped modified bismuth ferrite-based ceramic, characterized in that, The bismuth ferrite-based ceramic is an A-site multi-element rare earth element-doped bismuth ferrite-based ceramic, and the composition of the bismuth ferrite-based ceramic is Bi. 1-x (La 1 / 4 Nd 1 / 4 Sm 1 / 4 Gd 1 / 4 ) x FeO3, where 0.04≤ x ≤0.

14.

2. The multi-element rare earth doped modified bismuth ferrite-based ceramic as described in claim 1, characterized in that, The x The values ​​are 0.04, 0.06, 0.08, 0.10, 0.12, or 0.

14.

3. A method for preparing multi-element rare earth doped modified bismuth ferrite-based ceramics as described in claim 1 or 2, characterized in that, Includes the following steps: S1. First, dry the raw materials Bi2O3, Fe2O3, La2O3, Nd2O3, Sm2O3, and Gd2O3, and then weigh the raw materials according to the stoichiometric ratio. S2, add deionized water to the raw materials weighed in step S1 and ball mill until the raw materials are mixed evenly; S3, dry the raw material after ball milling in step S2 to remove moisture; S4. Grind and sieve the dried raw material from step S3. S5, Place the sieved powder from step S4 into a mold and press it into a green body; S6. The green body obtained in step S5 is heated to 900 ℃ and held at that temperature to obtain ceramic sheet.

4. The preparation method of a multi-element rare earth doped modified bismuth ferrite-based ceramic as described in claim 3, characterized in that, In step S1, the drying temperature is 80 ℃ and the drying time is 48 h.

5. The preparation method of a multi-element rare earth doped modified bismuth ferrite-based ceramic as described in claim 3, characterized in that, In step S2, the ball milling process involves clockwise ball milling for 12 hours, followed by a 0.5-hour stop, and then counterclockwise ball milling for 12 hours at a speed of 200 r / min.

6. The preparation method of a multi-element rare earth doped modified bismuth ferrite-based ceramic as described in claim 3, characterized in that, In step S3, the drying temperature is 80 ℃ and the drying time is 48 h.

7. The method for preparing a multi-element rare earth doped modified bismuth ferrite-based ceramic as described in claim 3, characterized in that, In step S4, the raw material is sieved through a mesh size of 120.

8. The method for preparing a multi-element rare earth doped modified bismuth ferrite-based ceramic as described in claim 3, characterized in that, In step S5, the mold pressing pressure is 158 MPa, and the holding time is 2 min.

9. The preparation method of a multi-element rare earth doped modified bismuth ferrite-based ceramic as described in claim 3, characterized in that, In step S6, the green body is buried with powder of the same composition, the heating rate is 5 ℃ / min, and the holding time is 3 h.

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