Method for simply preparing yttrium iron garnet-doped magneto-optical ceramic

Abstract

The invention relates to the technical field of ferrite magnetic materials, in particular to a simple method for preparing yttrium iron garnet-doped magneto-optical ceramic, the chemical formula of the ceramic is BixCeyY3-x-yFe5O12, x is more than or equal to 1.0 and less than or equal to 1.2, y is more than or equal to 0.1 and less than or equal to 0.8, and the yttrium iron garnet-doped magneto-optical ceramic belongs to bismuth ion and rare earth ion co-doped yttrium iron garnet type ferrite. By doping high-concentration Bi < 3 + >, the sintering temperature of the yttrium iron garnet is reduced to 1200-1000 DEG C, so that the energy consumption in the preparation process of the yttrium iron garnet material is reduced, the density and hardness of the yttrium iron garnet ceramic chip are increased, and the ceramic is prepared by proportioning, ball milling, centrifugal drying, pre-sintering, granulating and sieving, dry pressing, high-temperature sintering and grinding and polishing. According to the preparation method, the quality of the final ceramic is improved, the obtained ceramic keeps good dielectric constant stability within the microwave frequency band of 300MHZ-600MHZ, the change along with frequency is small, the dielectric constant value is always above 20, and the requirement of a microwave device on high dielectric property is met.

Description

Technical Field

[0001] The invention relates to the technical field of ferrite magnetic materials, in particular to a method for simply preparing doped yttrium iron garnet magneto-optical ceramics. Background Art

[0002] Microwave ferrite materials have high magnetic permeability and high electrical resistivity, making them widely used in microwave and radio frequency fields, including wireless communications, radar, electronic warfare and satellite systems. As wireless technology develops, there is a continuous demand for improved performance, smaller size, lower cost and lower energy consumption of microwave ferrite components.

[0003] In addition to its strong Faraday effect and high Verdet constant, yttrium iron garnet ferrite also has excellent properties such as low infrared absorption and low damping. It has high research value and research prospects in the field of non-reciprocity and is often used to prepare isolators, circulators, resonators, phase shifters, magneto-optical switches and filters. In addition, the magnetic properties of yttrium iron garnet, such as low magnetic damping and high magnetic permeability, are used to manufacture magnetic sensors, magnetic storage elements and magnetic filters. Currently, the most commonly used method for preparing yttrium iron garnet crystals is the oxide solid phase method, and the main process is high-speed ball milling and high-temperature sintering. Compared with other preparation methods, it has low equipment requirements, simple preparation process, large output, low cost, and particles are not easy to agglomerate, which can be mass-produced in industry.

[0004] However, the traditional oxide solid phase method has a complicated procedure, a long cycle, a high sintering temperature, and usually requires sintering at a temperature above 1300°C for several hours, and impurities are easily introduced during the preparation process, the sample loss rate is large, and the energy consumption is large. For example, CN118221429 A discloses a preparation method for a high-dielectric, low-loss garnet ferrite substituted with high bismuth, which requires secondary ball milling and multi-step sintering, and the pressure required for embryo formation is relatively high, which is 150-200MPa. CN201910592145.8 discloses a preparation method for a high-power rare earth yttrium iron garnet composite ferrite material, which also requires secondary ball milling, the drying time of the material is too long, and the sintering reaction temperature is too high, thereby increasing energy consumption and making it difficult to meet the requirements of energy saving and environmental protection. Therefore, it is necessary to improve the traditional oxide solid phase method. Summary of the invention

[0005] In view of the problems in the prior art that the sintering reaction temperature is too high, the energy consumption is large, and the preparation process is complicated, the present invention provides a method for simply preparing doped yttrium iron garnet magneto-optical ceramics.

[0006] The present invention is achieved through the following technical solutions: A doped yttrium iron garnet magneto-optical ceramic, the chemical formula of which is Bi x Ce y Y 3-x-y Fe5O 12,1.0≤x≤1.2,0.1≤y≤0.8,it belongs to yttrium iron garnet ferrite co-doped with bismuth ions and rare earth ions.

[0007] A method for simply preparing doped yttrium iron garnet magneto-optical ceramics comprises the following steps: Step 1, ingredients: weigh different masses of yttrium oxide, iron oxide, bismuth oxide and cerium oxide raw materials according to molar ratio; Step 2, ball milling: mixing the raw materials and performing wet ball milling; Step 3, centrifugation and drying: centrifuging the ball-milled mixed slurry at high speed and drying; Step 4, pre-burning: pre-burning the dried mixed raw material and cooling it with the furnace to obtain a pre-burned raw material; Step 5, granulation and sieving: grinding the pre-burned raw material, adding polyvinyl alcohol solution to granulate, and then sieving to obtain powder with uniform particle size; Step 6, dry pressing: pressing the granulated and sieved powder into a blank; Step 7, high temperature sintering: sintering the green embryo, and then cooling it in the furnace to obtain a sintered doped yttrium iron garnet magneto-optical ceramic sheet; Step 8, grinding and polishing: grinding and polishing the sintered doped yttrium iron garnet magneto-optical ceramic sheet to obtain doped yttrium iron garnet magneto-optical ceramic.

[0008] Preferably, in step 1, the ratio of each raw material is 12.2~24.9 parts of Y2O3, 43.3~46.3 parts of Fe2O3, 25.9~31.5 parts of Bi2O3, and 1.9~15.3 parts of CeO2; the average particle size of Y2O3, Fe2O3, Bi2O3 and CeO2 is 0.45μm.

[0009] Preferably, in step 2, during wet ball milling, the medium is anhydrous ethanol, the mass ratio of raw materials, ball milling beads and anhydrous ethanol is 1:10:1.5, the rotation speed is 200-300 r / min, the ball milling procedure is alternating forward and reverse, and the time is 6-7 h.

[0010] Preferably, in step 3, during high-speed centrifugation, the speed is 10000 r / min and the time is 5 to 10 min; During drying, the temperature is 60~70℃ and the time is 6~8h.

[0011] Preferably, in step 4, the specific steps of pre-sintering are as follows: first, heating to 450-550°C at a heating rate of 3-5°C / min, and sintering at this temperature for 2 hours, then heating to 900°C at a heating rate of 3-5°C / min, and sintering at this temperature for 4-6 hours.

[0012] Preferably, in step 5, the concentration of the polyvinyl alcohol solution added during the granulation process is 10 wt %, and the amount added is 5% of the mass of the powder; and a nylon sieve with a specification of 150 mesh is used for sieving.

[0013] Preferably, in step 6, during dry pressing, the pressure is 4-6 MPa and the holding time is 0.5-1 min.

[0014] Preferably, in step 7, before sintering, powders of the same composition are placed on the bottom of the green embryo; The specific steps of sintering are: first increase the temperature to 500-600°C at a heating rate of 3-5°C / min, then increase the temperature to 1000-1200°C at a heating rate of 3-5°C / min, and sinter at this temperature for 3-4 hours.

[0015] A simple method for preparing doped yttrium iron garnet magneto-optical ceramics for use in wireless microwave and radio frequency fields.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The invention discloses a doped yttrium iron garnet magneto-optical ceramic containing high concentration of Bi 3+ The doping reduces the sintering temperature of yttrium iron garnet to 1200~1000℃, thereby reducing the energy consumption in the process of preparing yttrium iron garnet materials, improving experimental safety, and increasing the density and hardness of yttrium iron garnet ceramic sheets, thereby improving the feasibility of ceramic sheet device preparation.

[0017] The present invention discloses a method for preparing doped yttrium iron garnet magneto-optical ceramics by batching, ball milling, centrifugal drying, pre-sintering, granulation and screening, dry pressing, high-temperature sintering and grinding and polishing. The high temperature of pre-sintering causes necessary pre-reactions between powders, thereby improving the quality of the final ceramics. At the same time, the crystal form conversion of the material can be promoted, the shrinkage rate during the final sintering can be reduced, and the performance of the powder can be improved. A medium temperature step is introduced, that is, the temperature is kept at 450-550°C for 2h in the pre-sintering procedure, and the temperature is kept at 500-600°C for 2h in the sintering procedure, and then the temperature is raised to the set pre-sintering temperature or sintering temperature. This process allows the sample to be heated evenly, the solid phase reaction is more sufficient, and the abnormal growth of grains is prevented, thereby improving the phase purity of yttrium iron garnet, the uniformity of chemical composition, and the density of ceramic crystals.

[0018] The invention abandons the complicated secondary ball milling process and only undergoes one wet ball milling process, thereby shortening the experimental time; the material after high-speed centrifugal wet ball milling is separated from the anhydrous ethanol and the mixed raw materials to a large extent, thereby reducing the impurities introduced during the ball milling process, greatly reducing the drying time of the sample, and the sample acquisition rate in the preparation process is as high as more than 95%; by adding a suitable binder for granulation and using a nylon sieve with a higher mesh number for sieving, a manual tablet press with simple operation can be used to press and form a yttrium iron garnet blank with a compact structure under a relatively low pressure, thereby sintering to obtain a yttrium iron garnet ceramic sheet with a complete crystal structure, a uniform particle size and a high density. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flow chart of a method for simply preparing doped yttrium iron garnet magneto-optical ceramics according to the present invention; Figure 2 is an impedance diagram of the bismuth-cerium co-doped yttrium iron garnet ferrite obtained in Example 2 of the present invention; Figure 3 is the XRD pattern of the bismuth-cerium co-doped yttrium iron garnet ferrite obtained in Example 3 of the present invention; Figure 4 is a SEM image of the bismuth-cerium co-doped yttrium iron garnet ferrite obtained in Example 3 of the present invention; Figure 5 3 is a VSM curve diagram of the bismuth-cerium co-doped yttrium iron garnet ferrite obtained in Example 3 of the present invention. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0021] The invention discloses a doped yttrium iron garnet magneto-optical ceramic, the chemical formula of which is Bi x Ce y Y 3-x-y Fe5O 12 ,1.0≤x≤1.2,0.1≤y≤0.8,it belongs to yttrium iron garnet ferrite co-doped with bismuth ions and rare earth ions.

[0022] The present invention discloses a method for preparing a simple doped yttrium iron garnet magneto-optical ceramic. Figure 1 , including the following steps: Step 1, ingredients: weigh different masses of yttrium oxide, iron oxide, bismuth oxide and cerium oxide raw materials according to the molar ratio; wherein the ratio of each raw material is 12.2~24.9 parts of Y2O3, 43.3~46.3 parts of Fe2O3, 25.9~31.5 parts of Bi2O3, and 1.9~15.3 parts of CeO2; the average particle size of Y2O3, Fe2O3, Bi2O3 and CeO2 is 0.45μm.

[0023] Step 2, ball milling: the raw materials weighed in step (1) are mixed and added into a planetary ball mill for wet ball milling; wherein, during the wet ball milling, the medium is anhydrous ethanol, the mass ratio of the raw materials, ball milling beads and anhydrous ethanol is 1:10:1.5, the rotation speed is 200-300 r / min, the ball milling procedure is alternating forward and reverse, and the time is 6-7 h.

[0024] Step 3, centrifugation and drying: centrifuge the ball-milled mixed slurry at a speed of 10,000 r / min for 5 to 10 minutes, and dry it at 60 to 70° C. for 6 to 8 hours.

[0025] Step 4, pre-firing: pre-firing the dried mixed raw materials and cooling them with the furnace; wherein the specific steps of pre-firing are as follows: firstly heating to 450~550℃ at a heating rate of 3~5℃ / min, and sintering at this temperature for 2h, then heating to 900℃ at a heating rate of 3~5℃ / min, and sintering at this temperature for 4~6h.

[0026] Step 5, granulation and sieving: grind the pre-calcined raw material, add a polyvinyl alcohol solution with a concentration of 10 wt% for granulation, and then sieve through a 150-mesh nylon sieve to obtain a powder with a uniform particle size; specifically, the amount of the added polyvinyl alcohol solution is 5% of the powder mass.

[0027] Step 6, dry pressing: the granulated and sieved powder is pressed into a blank at a pressure of 4-6 MPa and a holding time of 0.5-1 min.

[0028] Step 7, high temperature sintering: sinter the green blank, and then cool it in the furnace to obtain a sintered doped yttrium iron garnet magneto-optical ceramic sheet. Before sintering, a powder with the same composition is placed on the bottom of the green blank.

[0029] The specific steps of sintering are: first increase the temperature to 500-600°C at a heating rate of 3-5°C / min, then increase the temperature to 1000-1200°C at a heating rate of 3-5°C / min, and sinter at this temperature for 3-4 hours.

[0030] Step 8, grinding and polishing: grinding and polishing the sintered doped yttrium iron garnet magneto-optical ceramic sheet to obtain doped yttrium iron garnet magneto-optical ceramic.

[0031] The invention also discloses a method for simply preparing doped yttrium iron garnet magneto-optical ceramics and applying them in the fields of wireless microwave and radio frequency.

[0032] Example 1 Step 1, take 12.2 parts of Y2O3, 43.3 parts of Fe2O3, 30.3 parts of Bi2O3, and 14.2 parts of CeO2 for mixing, and the average particle size is 0.45μm.

[0033] Step 2, put the weighed raw materials into the ball mill, add ball milling beads and anhydrous ethanol according to the mass ratio of raw materials: ball milling beads: anhydrous ethanol = 1:10:1.5. Then fix the ball mill on the planetary ball mill, rotate at 200r / min, and the ball milling program is forward rotation for 30min, stop for 10min, reverse rotation for 30min, stop for 10min, and the total ball milling time is 7h to fully mix the raw materials. The ball milling beads are made of zirconium dioxide (ZrO2), and the ball milling beads with a diameter of 2mm and 3mm are mixed in a ratio of 1:1 as the ball milling medium; anhydrous ethanol is used as a dispersant to improve the ball milling efficiency.

[0034] Step 3: Pour the ball-milled mixed slurry into a centrifuge tube and centrifuge at 10,000 r / min for 10 minutes. Pour off the supernatant containing impurities. Then put the mixed raw material precipitate into an electric hot air drying oven and bake it at 70° C. for 6 hours to remove ethanol.

[0035] Step 4: Place the dried and ground powder in an alumina crucible and pre-sinter it in a muffle furnace to allow the raw materials to fully react and generate the target product. The pre-sintering temperature is 900°C. First, heat it to 480°C at a heating rate of 5°C / min and sinter it for 2 hours. Then heat it to 900°C at a heating rate of 3°C / min and sinter it for 6 hours. After the pre-sintering, the sample is cooled naturally.

[0036] Step 5, grind the pre-burned sample into powder in an agate mortar, add 5% polyvinyl alcohol solution by weight of the powder, wherein the mass fraction of the polyvinyl alcohol (PVA) solution is 10wt%, mix and grind until "sand-like" particles are formed, and then sieve through a 150-mesh nylon sieve to obtain a powder with uniform particle size.

[0037] Step 6, pour the sieved powder into a tablet press mold, and press it into a green embryo at 5 MPa, wherein the pressure holding time is 1 minute.

[0038] Step 7, place the pressed green embryo into an alumina crucible, and pad the bottom of the green embryo with powder of the same composition to prevent the ceramic sheet from sticking to the crucible, and sinter in a muffle furnace at a sintering temperature of 1200°C. First, heat it to 500°C at a heating rate of 5°C / min, and keep it warm for 2 hours, then heat it to 1200°C at a heating rate of 5°C / min, and keep it warm for 4 hours, then cool it to 600°C at a cooling rate of 4°C / min, and keep it warm for 2 hours for debinding. After sintering, the sample is cooled naturally.

[0039] Step 8, grinding and polishing the sintered ceramic sheet at 300 mesh, 600 mesh, 1000 mesh and 2000 mesh respectively to obtain smooth and flat doped yttrium iron garnet magneto-optical ceramics.

[0040] Example 2 Step 1, take 15.1 parts of Y2O3, 44.4 parts of Fe2O3, 25.9 parts of Bi2O3, and 14.6 parts of CeO2 for mixing, and the average particle size is 0.45μm.

[0041] Step 2, put the weighed raw materials into the ball mill, add ball milling beads and an appropriate amount of anhydrous ethanol according to the mass ratio of raw materials: ball milling beads: anhydrous ethanol = 1:10:1.5. Then fix the ball mill on the planetary ball mill, rotate at 200r / min, and the ball milling program is forward rotation for 30min, stop for 10min, reverse rotation for 30min, stop for 10min, and the total ball milling time is 7h to fully mix the raw materials. The ball milling beads are made of zirconium dioxide (ZrO2), and the ball milling beads with a diameter of 2mm and 3mm are mixed in a ratio of 1:1 as the ball milling medium; anhydrous ethanol is used as a dispersant to improve the ball milling efficiency.

[0042] Step 3: Pour the ball-milled mixed slurry into a centrifuge tube and centrifuge at 10,000 r / min for 10 minutes. Pour off the supernatant containing impurities. Then put the mixed raw material precipitate into an electric hot air drying oven and bake it at 60° C. for 8 hours to remove ethanol.

[0043] Step 4: Place the dried and ground powder in an alumina crucible and pre-sinter it in a muffle furnace to allow the raw materials to fully react and generate the target product. The pre-sintering temperature is 900°C. First, heat it to 510°C at a heating rate of 5°C / min and sinter it for 2 hours. Then heat it to 900°C at a heating rate of 3°C / min and sinter it for 6 hours. After the pre-sintering, the sample is cooled naturally.

[0044] Step 5, grind the pre-burned sample into powder in an agate mortar, add 5% polyvinyl alcohol solution by weight of the powder, wherein the mass fraction of the polyvinyl alcohol (PVA) solution is 10wt%, mix and grind until "sand-like" particles are formed, and then sieve through a 150-mesh nylon sieve to obtain a powder with uniform particle size.

[0045] Step 6, pour the sieved powder into a tablet press mold, and press it into a green embryo at 4 MPa, wherein the holding time is 1 minute.

[0046] Step 7, place the pressed green embryo into an alumina crucible, and pad the bottom of the green embryo with powder of the same composition to prevent the ceramic sheet from sticking to the crucible, and sinter in a muffle furnace at a sintering temperature of 1100°C. First, heat it to 550°C at a heating rate of 5°C / min, and keep it warm for 2h, then heat it to 1100°C at a heating rate of 5°C / min, and keep it warm for 4h, then cool it to 600°C at a cooling rate of 4°C / min, and keep it warm for 2h for debinding. After sintering, the sample is cooled naturally.

[0047] Step 8, grinding and polishing the sintered ceramic sheet at 300 mesh, 600 mesh, 1000 mesh and 2000 mesh respectively to obtain smooth and flat doped yttrium iron garnet magneto-optical ceramics.

[0048] Reference Figure 2 (Dielectric frequency curve of ceramic sample at room temperature). The doped yttrium iron garnet magneto-optical ceramic obtained in Example 2 maintains good dielectric constant stability in the microwave frequency band of 300MHZ~600MHZ, changes little with frequency, and the dielectric constant value is always above 20, meeting the requirements of microwave devices for high dielectric properties.

[0049] Example 3 Step 1, take 21.6 parts of Y2O3, 45.0 parts of Fe2O3, 31.5 parts of Bi2O3, and 1.9 parts of CeO2 for mixing, and the average particle size is 0.45μm.

[0050] Step 2, put the weighed raw materials into the ball mill, add ball milling beads and an appropriate amount of anhydrous ethanol according to the mass ratio of raw materials: ball milling beads: anhydrous ethanol = 1:10:1.5. Then fix the ball mill on the planetary ball mill, rotate at 300r / min, and the ball milling program is forward rotation for 30min, stop for 10min, reverse rotation for 30min, stop for 10min, and the total ball milling time is 6h to fully mix the raw materials. The ball milling beads are made of zirconium dioxide (ZrO2), and the ball milling beads with a diameter of 2mm and 3mm are mixed in a ratio of 1:1 as the ball milling medium; anhydrous ethanol is used as a dispersant to improve the ball milling efficiency.

[0051] Step 3: Pour the ball-milled mixed slurry into a centrifuge tube and centrifuge at 10,000 r / min for 10 minutes. Pour off the supernatant containing impurities. Then put the mixed raw material precipitate into an electric hot air drying oven and bake it at 60° C. for 8 hours to remove ethanol.

[0052] Step 4: Place the dried and ground powder in an alumina crucible and pre-sinter it in a muffle furnace to allow the raw materials to fully react and generate the target product. The pre-sintering temperature is 900°C. First, heat it to 540°C at a heating rate of 5°C / min and sinter it for 2 hours. Then heat it to 900°C at a heating rate of 3°C / min and sinter it for 6 hours. After the pre-sintering, the sample is cooled naturally.

[0053] Step 5, grind the pre-burned sample into powder in an agate mortar, add 5% polyvinyl alcohol solution by weight of the powder, wherein the mass fraction of the polyvinyl alcohol (PVA) solution is 10wt%, mix and grind until "sand-like" particles are formed, and then sieve through a 150-mesh nylon sieve to obtain a powder with uniform particle size.

[0054] Step 6, pour the sieved powder into a tablet press mold, and press it into a green embryo at 4 MPa, wherein the holding time is 1 minute.

[0055] Step 7, place the pressed green embryo into an alumina crucible, and pad the bottom of the green embryo with powder of the same composition to prevent the ceramic sheet from sticking to the crucible, and sinter in a muffle furnace at a sintering temperature of 1100°C. First, heat it to 500°C at a heating rate of 5°C / min, and keep it warm for 2h, then heat it to 1100°C at a heating rate of 5°C / min, and keep it warm for 4h, then cool it to 600°C at a cooling rate of 4°C / min, and keep it warm for 2h for debinding. After sintering, the sample cools naturally.

[0056] Step 8, grinding and polishing the sintered ceramic sheet at 300 mesh, 600 mesh, 1000 mesh and 2000 mesh respectively to obtain smooth and flat doped yttrium iron garnet magneto-optical ceramics.

[0057] For the doped yttrium iron garnet magneto-optical ceramic obtained in Example 3, the XRD spectrum of the ceramic sample (such as Figure 3 ) is highly consistent with the YIG standard PDF card, indicating that the prepared doped YIG ceramic has a single yttrium iron garnet phase with high crystal purity. Figure 4 ) It can be seen that typical garnet-type crystals have been formed, with regular crystal structure, uniform particle size, moderate size, and close arrangement, indicating that its crystal structure is complete and dense. Its VSM curve (such as Figure 5 ) It can be seen that with the change of magnetic field intensity, a classic hysteresis loop of soft magnetic materials is formed, in which the saturation intensity value is a medium saturation intensity, the coercive force is small, within 20Oe, and the magnetic properties are relatively good.

[0058] Comparative Example 1 Step 1, take 21.6 parts of Y2O3, 45.0 parts of Fe2O3, 31.5 parts of Bi2O3, and 1.9 parts of CeO2 for mixing, and the average particle size is 0.45μm.

[0059] Step 2, put the weighed raw materials into the ball mill, add ball milling beads and an appropriate amount of anhydrous ethanol according to the mass ratio of raw materials: ball milling beads: anhydrous ethanol = 1:10:1.5. Then fix the ball mill on the planetary ball mill, rotate at 300 r / min, and the ball milling program is forward rotation for 30 minutes, stop for 10 minutes, reverse rotation for 30 minutes, stop for 10 minutes, and the total ball milling time is 6 hours to fully mix the raw materials. The ball milling beads are made of zirconium dioxide (ZrO2), and the ball milling beads with a diameter of 2mm and 3mm are mixed in a ratio of 1:1 as the ball milling medium; anhydrous ethanol is used as a dispersant to improve the ball milling efficiency.

[0060] Step 3: Pour the ball-milled mixed slurry into a centrifuge tube and centrifuge at 10,000 r / min for 10 minutes. Pour off the supernatant containing impurities. Then put the mixed raw material precipitate into an electric hot air drying oven and bake it at 60° C. for 8 hours to remove ethanol.

[0061] Step 4: Place the dried and ground powder in an alumina crucible and pre-sinter it in a muffle furnace to allow the raw materials to fully react and generate the target product. The pre-sintering temperature is 900°C. First, heat it to 400°C at a heating rate of 5°C / min and sinter it for 2 hours. Then heat it to 900°C at a heating rate of 5°C / min and sinter it for 6 hours. After the pre-sintering, the sample is cooled naturally.

[0062] Step 5, grind the pre-burned sample into powder in an agate mortar, add 5% polyvinyl alcohol solution by weight of the powder, wherein the mass fraction of the polyvinyl alcohol (PVA) solution is 10wt%, mix and grind until "sand-like" particles are formed, and then sieve through a 150-mesh nylon sieve to obtain a powder with uniform particle size.

[0063] Step 6, pour the sieved powder into a tablet press mold, and press it into a green embryo at 4 MPa, wherein the holding time is 1 minute.

[0064] Step 7, place the pressed green embryo into an alumina crucible, and pad the bottom of the green embryo with powder of the same composition to prevent the ceramic sheet from sticking to the crucible, and sinter in a muffle furnace at a sintering temperature of 1300°C. First, heat it to 500°C at a heating rate of 5°C / min, and keep it warm for 2 hours, then heat it to 1300°C at a heating rate of 5°C / min, and keep it warm for 4 hours, then cool it to 600°C at a cooling rate of 4°C / min, and keep it warm for 2 hours for debinding. After sintering, the sample is cooled naturally.

[0065] Step 8, grinding and polishing the sintered ceramic sheet at 300 mesh, 600 mesh, 1000 mesh and 2000 mesh respectively to obtain smooth and flat doped yttrium iron garnet magneto-optical ceramics.

[0066] The yttrium iron garnet magneto-optical ceramic materials prepared in Examples 1 to 3 and Comparative Example 1 were tested, and the results are shown in Table 1 below. The results show that the yttrium iron garnet magneto-optical ceramic materials prepared by the present invention have completed high-concentration ion doping, a single crystal phase, a uniform grain size and a complete morphology, and have the characteristics of high density, high magnetism, and high dielectric properties. The application ability of ferrite materials in the magneto-optical field and the microwave field is effectively improved, and the problem of low density or poor dielectric properties of yttrium iron garnet materials is solved.

[0067] When the temperature exceeds 1200°C (especially, the temperature is 1300°C in Comparative Example 1), the dielectric constant of the obtained product shows a downward trend compared with Examples 1 to 3, which not only illustrates the important influence of sintering temperature on the dielectric properties of yttrium iron garnet magneto-optical ceramic materials, but also proves the unique advantages of the preparation method proposed in the present invention in reducing the sintering temperature. The yttrium iron garnet magneto-optical ceramic material obtained by the method proposed in the present invention can not only be obtained at a lower sintering temperature, but also has better dielectric properties, that is, the dielectric constant of the yttrium iron garnet magneto-optical ceramic material obtained by the present invention is higher than that of the product obtained at a higher sintering temperature under 300MHZ conditions, and the dielectric loss is also smaller, which fully demonstrates the advancement and practicality of the preparation method of the present invention, and also provides a broader space and possibility for the application of yttrium iron garnet magneto-optical ceramic materials in high-frequency circuits, microwave devices and other fields.

[0068] Table 1 Test results of yttrium iron garnet magneto-optical ceramic materials prepared in Examples 1 to 3 and Comparative Example 1

[0069] The above description is only a preferred embodiment of the present invention and is not intended to impose any limitation on the technical solution of the present invention. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can also be subjected to several simple modifications and substitutions, and these modifications and substitutions are also within the scope of protection covered by the claims.

Claims

1. A doped yttrium iron garnet magneto-optical ceramic, characterized in that: Its chemical formula is Bi x Ce y Y 3-x-y Fe5O 12 ,1.0≤x≤1.2,0.1≤y≤0.8,it belongs to yttrium iron garnet ferrite co-doped with bismuth ions and rare earth ions.

2. A method for simply preparing the doped yttrium iron garnet magneto-optical ceramic according to claim 1, characterized in that: The following steps are involved: Step 1, ingredients: weigh different masses of yttrium oxide, iron oxide, bismuth oxide and cerium oxide raw materials according to molar ratio; Step 2, ball milling: mixing the raw materials and performing wet ball milling; Step 3, centrifugation and drying: centrifuging the ball-milled mixed slurry at high speed and drying; Step 4, pre-burning: pre-burning the dried mixed raw material and cooling it with the furnace to obtain a pre-burned raw material; Step 5, granulation and sieving: grinding the pre-burned raw material, adding polyvinyl alcohol solution to granulate, and then sieving to obtain powder with uniform particle size; Step 6, dry pressing: pressing the granulated and sieved powder into a blank; Step 7, high temperature sintering: sintering the green embryo, and then cooling it in the furnace to obtain a sintered doped yttrium iron garnet magneto-optical ceramic sheet; Step 8, grinding and polishing: grinding and polishing the sintered doped yttrium iron garnet magneto-optical ceramic sheet to obtain doped yttrium iron garnet magneto-optical ceramic.

3. The method for simply preparing doped yttrium iron garnet magneto-optical ceramics according to claim 2, characterized in that: In step 1, the ratio of each raw material is 12.2~24.9 parts of Y2O3, 43.3~46.3 parts of Fe2O3, 25.9~31.5 parts of Bi2O3, and 1.9~15.3 parts of CeO2; the average particle size of Y2O3, Fe2O3, Bi2O3 and CeO2 is 0.45μm.

4. The method for simply preparing doped yttrium iron garnet magneto-optical ceramics according to claim 2, characterized in that: In step 2, during wet ball milling, the medium is anhydrous ethanol, the mass ratio of raw materials, ball milling beads and anhydrous ethanol is 1:10:1.5, the rotation speed is 200-300 r / min, the ball milling procedure is alternating forward and reverse, and the time is 6-7 h.

5. The method for simply preparing doped yttrium iron garnet magneto-optical ceramics according to claim 2, characterized in that: In step 3, during high-speed centrifugation, the speed is 10000r / min and the time is 5-10min; During drying, the temperature is 60~70℃ and the time is 6~8h.

6. The method for simply preparing doped yttrium iron garnet magneto-optical ceramics according to claim 2, characterized in that: In step 4, the specific steps of pre-sintering are as follows: first, heat up to 450-550°C at a heating rate of 3-5°C / min, and sinter at this temperature for 2 hours; then heat up to 900°C at a heating rate of 3-5°C / min, and sinter at this temperature for 4-6 hours.

7. The method for simply preparing doped yttrium iron garnet magneto-optical ceramics according to claim 2, characterized in that: In step 5, the concentration of the polyvinyl alcohol solution added during the granulation process is 10 wt %, and the amount added is 5% of the mass of the powder; a nylon sieve with a specification of 150 mesh is used for sieving.

8. The method for simply preparing doped yttrium iron garnet magneto-optical ceramics according to claim 2, characterized in that: Step 6, during dry pressing, the pressure is 4-6 MPa and the holding time is 0.5-1 min.

9. The method for simply preparing doped yttrium iron garnet magneto-optical ceramics according to claim 2, characterized in that: In step 7, before sintering, a powder with the same composition is placed on the bottom of the green embryo; The specific steps of sintering are: first increase the temperature to 500-600°C at a heating rate of 3-5°C / min, then increase the temperature to 1000-1200°C at a heating rate of 3-5°C / min, and sinter at this temperature for 3-4 hours.

10. An application of the simply prepared doped yttrium iron garnet magneto-optical ceramic as claimed in claim 1 in the fields of wireless microwave and radio frequency.

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