Preparation method of high dielectric high curie temperature garnet ferrite without rare earth

Abstract

The application relates to a preparation method of a high-dielectric high-Curie-temperature garnet ferrite without rare earth, which comprises the following steps: pre-treating raw materials to make the raw materials with different particle sizes basically reach the same particle size state, and then obtaining mixed materials with uniform components through mechanical stirring and one-time granulation, so that ideal pre-sintering effect can be realized. Meanwhile, three kinds of second grinding materials with different pre-sintering temperatures and particle sizes are uniformly mixed to control the sintering activity of the powder, and the sintering process is matched, so that the microstructure of the sintered body can be finally improved, the porosity of the ferrite material is reduced, and the ferromagnetic resonance line width is reduced. Through the combined substitution of bismuth, zirconium and calcium elements and the adjustment of the preparation process, the particle size of the powder is adjusted, the sintering stage is controlled to the end of continuous grain growth, the microstructure of the garnet ferrite material is improved, and finally the ferrite material with high dielectric constant, high saturation magnetization, low ferromagnetic resonance line width and high Curie temperature is prepared.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a high dielectric high Curie temperature garnet ferrite without rare earth elements, and particularly relates to improving the performance of a high dielectric garnet ferrite by controlling the particle size of the powder and the sintering process. BACKGROUND

[0002] With the rapid development of microwave technology in recent years, the system has put forward higher requirements for the miniaturization, lightweight and high performance of components. As an important component of communication systems such as 5G and radar, the development direction of microwave ferrite circulator has turned to miniaturization, lightweight, low loss and large bandwidth. Compared with other types of ferrites, polycrystalline garnet ferrite has the remarkable advantages of adjustable saturation magnetization, dielectric constant and low loss, and has become the first choice material for X-band and below ferrite circulators. The key to the miniaturization and integration of circulator isolators is to use a microwave ferrite material with high dielectric constant, suitable 4πM s and T c , low ΔH. At present, the research on high dielectric low loss YIG mainly focuses on the substitution of Y 3+ and Fe 3+ .

[0003] The patent US20200027632A1《Magnetic materials with high Curie temperatures and dielectric constants》 discloses a CaBiInV substituted garnet ferrite. The chemical formula is Bi 1.4 Y 0.66 Ca 0.94 In 0.4 V 0.47 Fe 4.13 O 12 The material has the following properties: 4πM s =1263Gs, ΔH=68Oe, ε'=27.57, T c =221.87℃. The Curie temperature and dielectric constant of the material are relatively high, but the substitution amount of Fe 3+ in the formula is too large, a large amount of rare earth elements are used, the saturation magnetization is low, and the cost is high.

[0004] The patent CN 111285673 A《A high dielectric constant microwave ferrite material, a preparation method and a microwave communication device》 discloses a Bi 1.25 Ca 0.25+2x Y 1.5-2x Zr 0.25 Al x Mn y Fe4.75-x-y 0.05≤x≤0.3, 0.05≤y≤0.15 ferrite. The preparation method comprises preparing raw materials according to the stoichiometric ratio of Bi 1.25 Ca 0.25+2x Y 1.5- 2x Zr 0.25 Al x Mn y Fe 4.75-x-y , 0.05≤x≤0.3, 0.05≤y≤0.15, and using the raw materials to prepare the microwave ferrite material, so that the microwave ferrite material has a dielectric constant of about 28, a 4πM s of 1850-1950Gs, and a ΔH of 45-50Oe, but the Curie temperature is relatively low, generally about 200℃, the substitution amount of Bi 3+ is 1.25 at most, the dielectric constant cannot be further improved, and too many element substitution types are not conducive to cost reduction and efficiency improvement.

[0005] A high-stability garnet microwave ferrite magnetic sheet and a preparation method thereof are disclosed in Chinese Patent Publication No. 111187064A, the chemical formula of which is Y (3-f-2d-a )Gd f Ca (2d+a) Bi e Fe (5-a-b-c-d-σ) Sn a In b Mn c V d O 12 , wherein 0≤a≤0.7, 0≤b≤0.7, 0≤c≤0.6, 0≤d≤1.5, 0≤e≤0.6, 0≤f≤0.8, and 0≤σ≤0.4, a garnet material with a 4πM s of 900-1400Gs, a ΔH≤20Oe, an ε' of 14, and a T c of 180-220℃ is prepared. The garnet ferrite material prepared by the patent has a medium saturation magnetization and a very low line width, and the corresponding microwave ferrite device can only be applied to the S-band, and the low dielectric constant is not conducive to miniaturization and light weight.

[0006] In summary, the material has the following problems: first, the dielectric constant of the garnet ferrite is improved by Bi 3+ and other high-polarization ions, and too much Bi 3+ is introduced to obtain a high dielectric constant, which will lead to a large ΔH of the material and increase the loss; second, in order to reduce the problem of large ΔH caused by Bi 3+ ion substitution, the substitution amount of Fe 3+ ions is relatively large, and the Curie temperature (T cThe garnet ferrite has a low Curie temperature (<200℃) and a low saturation magnetization, and cannot be applied to the X-band, in order to improve the Curie temperature, a lanthanide element is usually added to the dodecahedron site, so that the cost is increased. SUMMARY

[0007] The present application aims at the problems in the background art, and provides a preparation method of a rare-earth-free high-dielectric high-Curie-temperature garnet ferrite. 3+ 4+ 2+ The garnet ferrite has a high dielectric constant, a high Curie temperature and a low line width.

[0008] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows:

[0009] A preparation method of a rare-earth-free high-dielectric high-Curie-temperature garnet ferrite, comprising the following steps:

[0010] Step 1, raw material pretreatment:

[0011] Analytically pure Bi2O3, CaCO3, Y2O3, ZrO2 and Fe2O3 are used as raw materials, and the above-mentioned raw materials, zirconia balls and deionized water are ball milled in a planetary ball mill, the mass ratio of zirconia balls, raw materials and deionized water is 4:1:1.5, and the particle size of each raw material is controlled by controlling the ball milling speed and time;

[0012] Step 2, batching:

[0013] According to the stoichiometric ratio of the chemical formula Bi a Ca b Y c Zr d Fe 5-d-δ O 12 , the Bi2O3, CaCO3, Y2O3, ZrO2 and Fe2O3 raw materials treated in step 1 are weighed; wherein 1.4≤a≤1.5, 0<b≤0.4, 1.0<c≤1.6, 0<d≤0.4, 0<δ≤0.2, and δ is the iron deficiency;

[0014] Step 3, mechanical stirring:

[0015] Anhydrous ethanol is added to the raw materials weighed in step 2 according to the mass ratio of anhydrous ethanol:raw materials=1:1.5, and the anhydrous ethanol is completely volatilized by water bath heating and stirring, so that a mixed material with uniform mixing is obtained;

[0016] Step 4, primary granulation:

[0017] ​​The mixture obtained in step 3 is granulated by adding 4wt% polyvinyl alcohol (PVA) by mass percentage;

[0018] Step 5, pre-burning:

[0019] The powder after granulation in step 4 is evenly divided into three parts, and the three parts of powder are heat treated at different pre-burning temperatures for 1-5h, ground and sieved to obtain three pre-burning powders; wherein the pre-burning temperatures of the three powders are set in the temperature range of 800-900℃ with a step of 30℃, and the starting temperature is set according to the substitution amount of Bi;

[0020] Step 6, secondary ball milling:

[0021] The three pre-burning powders obtained in step 5 are respectively subjected to secondary ball milling in a planetary ball mill, the mass ratio of ball:powder:water is 4:1:1.5, the ball milling time is 2-4h, and the dried and 80-mesh sieved three secondary milling powders with uniform particle size and particle distribution are obtained;

[0022] Step 7, secondary granulation:

[0023] The three secondary milling powders obtained in step 6 are mixed uniformly, 12wt% polyvinyl alcohol (PVA) is added by weight percentage, and granulation is performed, sieving is performed, and 80-200-mesh granulated materials are taken;

[0024] Step 8, molding:

[0025] The granulated material obtained in step 7 is placed in a mold for compression molding, and the compression pressure is 150-200MPa;

[0026] Step 9, sintering:

[0027] The green body obtained by compression molding in step 8 is placed in an air atmosphere sintering furnace and sintered by a multi-step sintering method to obtain the garnet ferrite; wherein the process of the multi-step sintering method is: the sintering temperature of the first process is 400-500℃, and the holding time is 1-3h; the sintering temperature of the second process is 800-900℃, and the holding time is 1-5h; the sintering temperature of the third process is 900-1000℃, and the holding time is 1-5h; the sintering temperature of the fourth process is 930-1050℃, and the holding time is 5-15h.

[0028] Further, in step 1, by controlling the ball milling speed and time, the particle size of the raw materials of different particle sizes is uniformly controlled at D50=0.6-0.9μm.

[0029] Further, in step 5, when the substitution amount of Bi a=1.4, the starting temperature of the pre-burning temperature of the three powders is set to 830℃, i.e. the pre-burning temperatures of the three powders are 830℃, 860℃ and 890℃ respectively.

[0030] Further, in step 5, the starting temperature of the pre-sintering temperature of the three powders decreases with the increase of the Bi substitution amount.

[0031] Further, due to the different pre-sintering temperatures of the three powders, the hardness of the obtained pre-sintered material is different, and the mixing and second grinding are difficult to control the particle size distribution, therefore, in step 6, the three powders are respectively subjected to second grinding, and by controlling the second grinding speed (200-300 r / min) and time (2-4 h), the particle size and particle size distribution of the obtained second ground material are controlled. Preferably, the particle size D50 of the second ground material powder with the highest pre-sintering temperature is 2-3 μm, and D90 is 6-7 μm; the particle size D50 of the second ground material powder with the second highest pre-sintering temperature is 1.5-2 μm, and D90 is 6-7 μm; and the particle size D50 of the second ground material powder with the lowest pre-sintering temperature is 1.0-1.5 μm, and D90 is 5-6 μm.

[0032] Further, in step 9, a multi-step sintering method is used to control the sintering process to the end of continuous grain growth, to regulate the microstructure of the sintered body. The first process is a degassing stage, the second process is a pre-sintering temperature near 1-5 h, to make the remaining raw materials fully react, the third process is to heat to a temperature 30-50 ℃ lower than the final sintering temperature for 1-5 h, to make the grains begin to grow, and the fourth process is to heat to the optimal sintering temperature.

[0033] The application provides a preparation method of a rare-earth-free high-dielectric high-curie-temperature garnet ferrite, which realizes ideal pre-sintering effect and obtains a wide optimal sintering interval by pre-treating raw materials and primary granulation to make raw materials of different particle sizes basically reach the same particle size state and uniformity of composition.

[0034] The particle size of the two-milling powder and the activity of the powder have a significant influence on the microstructure and performance of the sintered body, and it is well known that any system has a tendency to develop towards a state of minimum energy, so the reduction of the surface energy of the system is the driving force for powder sintering, and the size depends on the radius of the powder particles, the finer the particle size, the larger the surface area, and the larger the contact area between the particles, so that the solid phase diffusion rate can be improved, and the sintering activity of the powder can be increased. Moreover, from the perspective of close packing, different sizes of particle groups can obtain close packing, so that the particles can be easily combined, and the overall density can be increased. The powder with a low pre-sintering temperature has a high activity, but the particle size distribution is wide, and during the sintering process, large grains can swallow small grains, resulting in uneven structure and difficult to control the microstructure; and the two-milling powder with a high pre-sintering temperature has a narrow particle size distribution and uniform packing, so that the microstructure can be well controlled, but the activity of the powder is poor, which can affect the growth of the crystal grains during the later sintering, resulting in discontinuous growth of the crystal grains and pores at the grain boundaries. In order to improve the uniformity of the continuous growth of the crystal grains, the two-milling powders with different pre-sintering temperatures are obtained by two-milling, and the three two-milling powders with different particle size distributions are mixed, granulated, pressed and sintered, so that the sintering activity of the powder is controlled to improve the completion degree of the solid phase reaction.

[0035] Compared with the prior art, the beneficial effects of the present application are:

[0036] 1. The present application adjusts the saturation magnetization and the ferromagnetic resonance line width of the ferrite material by substituting Zr 4+ , and the dielectric constant of the garnet ferrite material is improved by the mutual coordination of Bi 3+ , Ca 2+ , and the substitution amount of Bi 3+ is greater than or equal to 1.4, the dielectric constant ε' is greater than or equal to 30, which belongs to high dielectric material, and there is no lanthanide rare earth element, the formula is simple, and the cost is low.

[0037] 2. The traditional process is to directly mill raw materials with different particle sizes and then pre-sinter, which is difficult to unify the particle sizes of various raw materials. The present application can basically achieve the same particle size state of raw materials with different particle sizes through raw material pretreatment, and then obtain a mixture with uniform composition through mechanical stirring and primary granulation, so that an ideal pre-sintering effect can be achieved. Meanwhile, the three two-milling powders with different pre-sintering temperatures and particle sizes are uniformly mixed to control the sintering activity of the powder, and are matched with the sintering process, so that the microstructure of the sintered body can be finally improved, the porosity of the ferrite material is reduced, and the ferromagnetic resonance line width is reduced.

[0038] In summary, the garnet ferrite material prepared by the method of the present application is substituted by bismuth, zirconium and calcium elements, and the particle size of the powder is adjusted, the sintering stage is controlled to the end of the continuous growth of the crystal grains, the microstructure of the garnet ferrite material is improved, and finally a garnet ferrite material with a high dielectric constant ε' ≥ 30 and a high saturation magnetization 4πMs 1750-1950Gs, low ferromagnetic resonance linewidth ΔH≤30Oe, high Curie temperature T c Ferrite material with Curie temperature ≥245℃. This material not only effectively reduces the size of microwave ferrite devices, but also reduces the insertion loss of the device, increases the bandwidth of the device, and is low in cost. BRIEF DESCRIPTION OF DRAWINGS

[0039] Fig. 1 Scanning electron micrograph of the garnet ferrite material obtained in Example 1;

[0040] Fig. 2 Scanning electron micrograph of the garnet ferrite material obtained in Example 2;

[0041] Fig. 3 Scanning electron micrograph of the garnet ferrite material obtained in Example 3. DETAILED DESCRIPTION

[0042] The present application provides a preparation method of a high dielectric constant and high Curie temperature garnet ferrite which is only substituted by bismuth, zirconium and calcium elements, focusing on different high Bi 3+ The improvement of the preparation process of the garnet ferrite material of the formula mainly lies in the improvement of the pre-sintering temperature, the grinding time and the sintering temperature. The present application will be described in more detail through specific examples, but the protection scope of the present application is not limited to these examples.

[0043] Example 1

[0044] A preparation method of a rare earth-free high dielectric high Curie temperature garnet ferrite, specifically comprising the following steps:

[0045] Step 1, raw material pretreatment:

[0046] Take analytical pure Bi2O3, CaCO3, Y2O3, ZrO2 and Fe2O3 as raw materials, and ball mill the above-mentioned raw materials with zirconia balls and deionized water in a planetary ball mill. The mass ratio of zirconia balls, raw materials and deionized water is 4:1:1.5. The particle size of each raw material is controlled to be D50=0.6-0.9μm by controlling the ball milling speed and time;

[0047] Step 2, batching:

[0048] According to the chemical formula Bi a Ca b Y c Zr d Fe 5-d-δ O 12The raw materials of Bi2O3, CaCO3, Y2O3, ZrO2 and Fe2O3 treated in step 1 are weighed according to the stoichiometric ratio, wherein a = 1.4, b = 0.4, c = 1.2, d = 0.4, 0 < δ ≤ 0.2, and δ is the amount of iron deficiency;

[0049] Step 3, mechanical stirring:

[0050] According to the mass ratio of anhydrous ethanol: raw materials = 1:1.5, anhydrous ethanol is added to the raw materials weighed in step 2, and stirring is performed by water bath heating until the anhydrous ethanol is completely volatilized, to obtain a uniformly mixed mixture;

[0051] Step 4, primary granulation:

[0052] Polyvinyl alcohol (PVA) with a mass percentage of 4wt% is added to the mixture obtained in step 3 for spray granulation;

[0053] Step 5, pre-burning:

[0054] The powder after granulation in step 4 is evenly divided into three parts, and the three parts of powder are heat treated at different pre-burning temperatures for 1-5h, ground and sieved to obtain three pre-burning materials; wherein the pre-burning temperatures of the three parts of powder are 830℃, 860℃ and 890℃;

[0055] Step 6, secondary ball milling:

[0056] The three pre-burning materials obtained in step 5 are respectively subjected to secondary ball milling in a planetary ball mill, with a mass ratio of ball: material: water of 4:1:1.5, ball milling for 2-4h, drying, and sieving through an 80 mesh sieve to obtain three secondary milling materials with uniform particle size and particle distribution;

[0057] Step 7, secondary granulation:

[0058] After the three secondary milling materials obtained in step 6 are uniformly mixed, 12wt% of polyvinyl alcohol (PVA) is added for granulation, sieving, and taking the granulated material between 80-200 meshes;

[0059] Step 8, molding:

[0060] The granulated material obtained in step 7 is placed in a mold for compression molding, with a compression pressure of 150-200MPa;

[0061] Step 9, sintering:

[0062] The green compact of step 8 is placed in an air atmosphere sintering furnace and sintered by a multi-step sintering method to obtain the garnet ferrite; wherein the multi-step sintering method comprises the following steps: the sintering temperature of the first step is 400-500℃, and the holding time is 1-3h; the sintering temperature of the second step is 800-900℃, and the holding time is 1-5h; the sintering temperature of the third step is 900℃, and the holding time is 1-5h; the sintering temperature of the fourth step is 970℃, and the holding time is 5-15h.

[0063] Example 2

[0064] The difference between this example and example 1 is that:

[0065] In step 2, the chemical formula of Bi a Ca b Y c Zr d Fe 5-d-δ O 12 , a=1.45, b=0.4, c=1.15, d=0.4, 0<δ≤0.2, δ is the iron deficiency;

[0066] In step 5, the pre-sintering temperatures of the three powders are 820℃, 850℃ and 880℃ respectively;

[0067] In step 9, the sintering temperature of the third step is 910℃, and the holding time is 1h; the sintering temperature of the fourth step is 950℃, and the holding time is 5-15h.

[0068] The remaining steps are the same as those of example 1.

[0069] Example 3

[0070] The difference between this example and example 1 is that:

[0071] In step 2, the chemical formula of Bi a Ca b Y c Zr d Fe 5-d-δ O 12 , a=1.5, b=0.4, c=1.1, d=0.4, 0<δ≤0.2, δ is the iron deficiency;

[0072] In step 5, the pre-sintering temperatures of the three powders are 810℃, 840℃ and 870℃ respectively;

[0073] In step 9, the sintering temperature of the third step is 910℃, and the holding time is 1h; the sintering temperature of the fourth step is 940℃, and the holding time is 5-15h.

[0074] The remaining steps are the same as those of example 1.

[0075] Comparative Example 1

[0076] Step 1, batching:

[0077] Bi2O3, CaCO3, Y2O3, ZrO2, Fe2O3 raw materials are weighed according to the stoichiometric ratio of the chemical formula Bi a Ca b Y c Zr d Fe 5-d-δ O 12 ; wherein a = 1.4, b = 0.4, c = 1.2, d = 0.4, 0 < δ ≤ 0.2, δ is the amount of iron deficiency;

[0078] Step 2, first ball milling;

[0079] The raw materials weighed in step 1 are loaded into a ball mill tank, and zirconia balls and deionized water are added in a mass ratio of 4:1:1.5. After first ball milling for 5-8 h, the material is discharged. The ball mill tank is made of stainless steel to reduce the wear of Fe into the material during ball milling. The slurry is dried and then sieved through an 80-mesh sieve and loaded into a special corundum crucible;

[0080] Step 3, pre-sintering:

[0081] The first ball-milled material obtained in step 2 is pre-sintered at 860°C for 1-5 h;

[0082] Step 4, second ball milling:

[0083] The pre-sintered material obtained in step 3 is subjected to second ball milling in a planetary ball mill with a mass ratio of 4:1:1.5 (ball:material:water). Ball milling is performed for 6-8 h, followed by drying and sieving through an 80-mesh sieve;

[0084] Step 5, granulation:

[0085] The second ball-milled material obtained in step 4 is granulated and sieved after adding 12 wt% PVA solution;

[0086] Step 6, shaping:

[0087] The granulated fine powder is placed in a mold and pressed at a pressure of 150-200 MPa;

[0088] Step 7, sintering:

[0089] The shaped green body is placed in an air atmosphere sintering furnace and heated to 980°C at a rate of 2°C / min, and then held for 8-12 h before cooling in the furnace.

[0090] Comparative Example 2

[0091] The present comparative example differs from Comparative Example 1 in that in Step 1, a = 1.45, b = 0.4, c = 1.15, d = 0.4. The remaining steps are identical to those of Comparative Example 1.

[0092] Comparative Example 3

[0093] The present comparative example differs from Comparative Example 1 in that in Step 1, a = 1.45, b = 0.4, c = 1.15, d = 0.4. The remaining steps are identical to those of Comparative Example 1.

[0094] Figs. 1-3 The SEM of the materials obtained in Examples 1-3 shows that the sintering stage of Examples 1-3 is at the end of continuous grain growth, the average grain size is generally 3-5 μm, the grain boundary is clear, the grain is full, and the uniformity is good.

[0095] The properties of the materials obtained in Examples 1-3 and Comparative Examples 1-3 are shown in the following table:

[0096]

Claims

1. A method for preparing rare-earth-free, high-dielectric, high-Curie-temperature garnet ferrite, characterized in that, Includes the following steps: Step 1, Raw material pretreatment: Using Bi2O3, CaCO3, Y2O3, ZrO2, and Fe2O3 as raw materials, the raw materials are ball-milled, and the particle size of each raw material is controlled by controlling the ball milling speed and time. Step 2, Ingredients: According to the chemical formula Bi a Ca b Y c Zr d Fe 5-d-δ O 12 Weigh the raw materials Bi2O3, CaCO3, Y2O3, ZrO2, and Fe2O3 after step 1; wherein, 1.4≤a≤1.5, 0<b≤0.4, 1.0<c≤1.6, 0<d≤0.4, 0<δ≤0.2, and δ is the amount of iron deficiency; Step 3: Mechanical stirring: Add anhydrous ethanol to the raw materials weighed in step 2, and heat and stir in a water bath until the anhydrous ethanol is completely evaporated to obtain a uniformly mixed material. Step 4, primary granulation: Polyvinyl alcohol is added to the mixture obtained in step 3 for granulation; Step 5, Preheating: The granulated powder from step 4 is divided into three equal portions. The three portions are kept at different pre-calcination temperatures for 1 to 5 hours, then ground and sieved to obtain three pre-calcined materials. The pre-calcination temperature of the three portions is set in 30°C increments within the temperature range of 800 to 900°C. Step 6, Secondary ball milling: The three pre-calcined materials obtained in step 5 were subjected to secondary ball milling for 2-4 hours, dried, and sieved to obtain three portions of secondary abrasive materials. Step 7, Secondary granulation: After mixing the three parts of abrasive obtained in step 6 evenly, add polyvinyl alcohol for granulation, sieve, and take granules with a mesh size of 80-200. Step 8: Shaping The granulated material obtained in step 7 is pressed into shape at a pressure of 150-200 MPa. Step 9, Sintering: The green blank formed in step 8 is placed in an air atmosphere sintering furnace and sintered using a multi-step sintering method to obtain the garnet ferrite. The multi-step sintering process is as follows: the sintering temperature of the first step is 400-500℃, and the holding time is 1-3h; the sintering temperature of the second step is 800-900℃, and the holding time is 1-5h; the sintering temperature of the third step is 900-1000℃, and the holding time is 1-5h; the sintering temperature of the fourth step is 930-1050℃, and the holding time is 5-15h.

2. The method for preparing rare-earth-free, high-dielectric, high-Curie-temperature garnet ferrite according to claim 1, characterized in that, Step 1 involves controlling the ball mill speed and time to uniformly control the particle size of raw materials with different particle sizes within the range of D50 = 0.6–0.9 μm.

3. The method for preparing rare-earth-free, high-dielectric, high-Curie-temperature garnet ferrite according to claim 1, characterized in that, In step 5, when the amount of Bi substitution a = 1.4, the starting temperature of the pre-calcination temperature of the three powders is set to 830℃.

4. The method for preparing rare-earth-free, high-dielectric, high-Curie-temperature garnet ferrite according to claim 1, characterized in that, In step 5, the initial temperature of the pre-calcination of the three powders decreases as the amount of Bi substitution increases.

5. The method for preparing rare-earth-free, high-dielectric, high-Curie-temperature garnet ferrite according to claim 1, characterized in that, In step 6, the particle size and particle size distribution of the resulting abrasives are controlled by controlling the rotation speed and time of the secondary ball mill.

6. The method for preparing rare-earth-free, high-dielectric, high-Curie-temperature garnet ferrite according to claim 5, characterized in that, The particle size of the abrasive powder with the highest pre-sintering temperature is D50 = 2-3 μm and D90 = 6-7 μm; the particle size of the abrasive powder with the second highest pre-sintering temperature is D50 = 1.5-2 μm and D90 = 6-7 μm; and the particle size of the abrasive powder with the lowest pre-sintering temperature is D50 = 1.0-1.5 μm and D90 = 5-6 μm.

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