Pr and Y co-doped M-type hexaferrite material, preparation method and application thereof

Abstract

The application provides a praseodymium-yttrium co-doped M-type hexagonal ferrite material and a preparation method and application thereof. z Fe 12‑x‑ y Pr x Y y O 19 , wherein 0.05<=x<=2.0, 0.05<=y<=1.5, 0.9<=z<=1.4, and x / y>1 / 7. The praseodymium and yttrium are doped into the M-type hexagonal ferrite, the characteristics of variable valence and large ion radius of praseodymium are utilized, and the Fe-deficient 3+ and Sr-rich 2+ environments are combined, so that Pr 4+ is formed, thereby reducing the grain size and forming a polyhedral aggregate, and meanwhile, the praseodymium-yttrium doping forms multiple impurities, interfaces are formed between the impurities and the main phase, and the interface polarization is promoted. The conversion of Pr 3+ to Pr 4+ is beneficial to the formation of oxygen vacancies and Fe 2+ , thereby significantly improving the dielectric properties of the material and enhancing the microwave absorption performance, and the material can be applied as a wave-absorbing material.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electromagnetic wave absorbing materials, and particularly relates to a praseodymium-yttrium co-doped M-type hexaferrite material and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of wireless information technology, various frequency bands of electromagnetic waves are generated in modern society, and serious electromagnetic radiation not only interferes with the operation of sensitive electronic equipment, but also threatens human health, and unique nanomaterials need to be developed for electromagnetic wave absorption. Spinel and hexaferrite are traditional magnetic loss type microwave absorbing materials, and are the first choice for electromagnetic wave absorbing materials due to their strong magnetic loss, easy synthesis and low cost. Among them, M-type hexaferrite has been widely concerned due to its relatively low price, high saturation magnetization (MS) capacity, high coercivity, high resistivity, corrosion resistance and excellent chemical stability,

[0003] Ion doping is an important means to improve the wave absorbing performance of M-type hexaferrite. Lijun et al. synthesized Co-Ti co-doped hexagonal barium ferrite BaFe 12-2x Co x Ti x O 19 By controlling the substitution of Co and Ti elements in barium ferrite (x = 1.0, 1.2 and 1.4), satisfactory reflection loss was obtained in the range of 10 GHz (Li J, Xu TT, Liu L L, et al. Microstructure, magnetic and low-frequency microwave absorption properties of doped Co-Ti hexagonal barium ferrite nanoparticles [J]. Ceramics International, 2021, 47(13): 19247-19253.). Lijun et al. synthesized Ti 4+ doped barium ferrite BaFe 12-x Ti x O 19, by controlling the level of elements substituted for Ti in barium ferrite (x = 0.2, 0.4, 0.6 and 0.8), satisfactory reflection loss was obtained in the sample with x = 0.2 (Li J, Hong Y, He S, et al. A neutron diffraction investigation of high valent doped barium ferrite with wideband tunable microwave absorption[J]. Journal of Advanced Ceramics, 2022, 11(2): 263-272.). Sriramulu et al. prepared Co-Mg co-doped hexagonal strontium ferrite SrFe 12-2x Co x Mg x O 19 , by controlling the level of elements substituted for Co and Mg in strontium ferrite (x = 0.0-1.0), the minimum reflection loss was observed to be -23.86 dB at 10 GHz when x = 0.4 (Sriramulu G, Praveena K, Reddy B R, et al. Observation of rhombohedral CoFe2O4 phase in Co-Mg co-doped SrFe 12 O 19 hexaferrite[J]. Journal of Magnetism and Magnetic Materials, 2023, 583: 171046.).

[0004] However, the current M-type ferrite still has the problems of thick thickness, narrow absorption frequency band, and low absorption intensity. Therefore, it is urgent to develop a new M-type ferrite wave-absorbing material that can solve the above problems and simplify the process flow and reduce the production cost. SUMMARY

[0005] The purpose of the present application is to provide a praseodymium-yttrium co-doped M-type hexagonal ferrite material and its preparation method and application. The prepared wave-absorbing material can realize the characteristics of thin thickness, wide frequency band and strong absorption.

[0006] To achieve the purpose of the present application, the following technical solutions are adopted:

[0007] In the first aspect, the present application provides a praseodymium-yttrium co-doped M-type hexagonal ferrite material, the chemical formula of which comprises Sr z Fe 12-x-yPr x Y y O 19 , wherein 0.05≤x≤2.0, 0.05≤y≤1.5, 0.9≤z≤1.4, and x / y>1 / 7.

[0008] In the present application, by doping praseodymium and yttrium into M-type hexaferrite, the characteristics of praseodymium such as variable valence and large ion radius are utilized, and the environment of Fe deficiency 3+ and Sr-rich 2+ is combined to form Pr 4+ , thereby reducing the grain size and forming polyhedral aggregates, and the praseodymium and yttrium doping forms multiple impurities, which forms an interface between the impurities and the main phase, promoting the interface polarization. The conversion of Pr 3+ to Pr 4+ is conducive to the formation of oxygen vacancies and Fe 2+ , thereby significantly improving the dielectric properties and enhancing the microwave absorption performance of the material.

[0009] In the present application, the chemical formula of the praseodymium and yttrium co-doped M-type hexaferrite material is Sr z Fe 12-x-y Pr x Y y O 19 , wherein 0.05≤x≤2.0, 0.05≤y≤1.5, 0.9≤z≤1.4. For example, x can be 0.05, 0.08, 0.1, 0.2, 0.4, 0.6, 0.8, 0.9, 1, 1.2, 1.3, 1.5, 1.7, 1.8, or 2, preferably 0.1≤x≤1.5; y can be 0.05, 0.15, 0.35, 0.5, 0.65, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5, preferably 0.05≤y≤1; z can be 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, or 1.4; and x / y>1 / 7, i.e., the ratio of x to y is greater than 1 / 7, for example, it can be 1 / 6, 1 / 5, 1 / 4, 1 / 3, 1 / 2, or 1 / 1, but is not limited to the listed values, and other values not listed within the above-mentioned value range are also applicable.

[0010] As a preferred technical scheme of the present application, the praseodymium-yttrium co-doped M-type hexaferrite material simultaneously absorbs in the C band and the Ku band, and has strong absorption in the C band and the X band; the C band is 4-8 GHz, the X band is 8-12 GHz, and the Ku band is 12-18 GHz. In the field of wave absorption, a reflection loss below -10 dB is considered to have an absorption effect, and a reflection loss below -20 dB is considered to have a strong absorption effect. -10 dB represents 90% absorption rate, and -20 dB represents 99% absorption rate.

[0011] Preferably, the working temperature of the praseodymium-yttrium co-doped M-type hexaferrite material is -40-400℃, for example, it can be -40℃, 0℃, 60℃, 100℃, 160℃, 200℃, 250℃, 300℃ or 400℃, etc., but is not limited to the listed values, and other values not listed in the above value range are also applicable.

[0012] In a second aspect, the present application provides a preparation method of the praseodymium-yttrium co-doped M-type hexaferrite material of the first aspect, which comprises the following steps:

[0013] Mixing a strontium source, an iron source, a praseodymium source, a yttrium source, a complexing agent and a solvent to obtain a mixed solution;

[0014] Adjusting the pH of the mixed solution and heating the reaction to obtain a viscous gel;

[0015] Sequentially performing heat treatment and calcination on the viscous gel to obtain the praseodymium-yttrium co-doped M-type hexaferrite material.

[0016] As a preferred technical scheme of the present application, the ratio of the total molar amount of the praseodymium source, the yttrium source and the iron source to the molar amount of the strontium source is 12:(0.9-1.4), for example, it can be 12:0.9, 12:0.95, 12:1, 12:1.05, 12:1.1, 12:1.15, 12:1.2, 12:1.25, 12:1.3, 12:1.35 or 12:1.4, etc., but is not limited to the listed values, and other values not listed in the above value range are also applicable.

[0017] Preferably, the molar ratio of the praseodymium source, the yttrium source and the iron source is (0.05-2.0):(0.05-1.5):(9.0-11.9), for example, it can be 0.05:0.05:11.9, 0.1:0.3:11.6, 0.35:0.05:11.6, 0.8:0.8:10.4, 1.5:1.5:9.0, etc., but is not limited to the listed values, and other values not listed in the above value range are also applicable.

[0018] In the present application, the molar ratio of praseodymium source, yttrium source and iron source is adjusted to realize the exchange of tetravalent praseodymium and trivalent praseodymium, and increase the oxygen vacancies and dielectric loss.

[0019] Preferably, the strontium source, iron source, praseodymium source and yttrium source include any one or a combination of at least two of nitrate, acetate or chloride of the corresponding metal elements, and the purity of the raw materials is analytical pure or above.

[0020] As a preferred technical solution of the present application, the complexing agent includes citric acid.

[0021] Preferably, the molar ratio of the complexing agent to the total molar amount of the strontium source, iron source, praseodymium source and yttrium source is (1-5):1, for example, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4.5:1 or 5:1, etc., preferably (1-3):1, but not limited to the listed values, and other values not listed in the above value range are also applicable.

[0022] As a preferred technical solution of the present application, the method of mixing the strontium source, iron source, praseodymium source, yttrium source, complexing agent and solvent includes first stirring and mixing the strontium source, iron source, praseodymium source, yttrium source and solvent, and then adding a complexing agent solution thereto.

[0023] As a preferred technical solution of the present application, the pH adjustment uses a pH adjuster, and the pH adjuster includes ammonia water.

[0024] In the present application, the concentration of the ammonia water is 25%-50%, for example, it can be 25%, 30%, 35%, 40%, 45% or 50%, etc., but not limited to the listed values, and other values not listed in the above value range are also applicable.

[0025] Preferably, the pH range for adjusting the pH is 5-8.5, for example, it can be 5, 5.5, 6, 6.5, 7, 7.5, 8 or 8.5, etc., but not limited to the listed values, and other values not listed in the above value range are also applicable.

[0026] Preferably, the constant temperature for the heating reaction is 75-95℃, for example, it can be 75℃, 80℃, 85℃, 90℃, 95℃, etc., but not limited to the listed values, and other values not listed in the above value range are also applicable.

[0027] Preferably, the heating reaction uses water bath or oil bath heating, and stirring is maintained.

[0028] Preferably, before the heat treatment, the viscous gel is first dried;

[0029] Preferably, the temperature of the drying is 95-125℃, for example, it can be 95℃, 100℃, 105℃, 110℃, 115℃ or 125℃, etc., but not limited to the listed values, other values not listed in the range of values are also applicable.

[0030] Preferably, the time of the drying is 10-48h, for example, it can be 10h, 16h, 20h, 24h, 30h, 36h or 48h, etc., but not limited to the listed values, other values not listed in the range of values are also applicable.

[0031] Preferably, the holding temperature of the heat treatment is 100-350℃, for example, it can be 100℃, 120℃, 140℃, 160℃, 180℃, 200℃, 220℃, 240℃, 260℃, 280℃, 300℃, 330℃ or 350℃, etc., but not limited to the listed values, other values not listed in the range of values are also applicable.

[0032] Preferably, the time of the heat treatment in step (3) is 0.1-3h, for example, it can be 0.1h, 0.5h, 0.8h, 1h, 1.4h, 1.8h, 2.2h, 2.5h, 2.8h or 3h, etc., but not limited to the listed values, other values not listed in the range of values are also applicable.

[0033] As a preferred technical solution of the present application, the holding temperature of the calcination is 900-1300℃, for example, it can be 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃ or 1300℃, etc., preferably 1100-1300℃, but not limited to the listed values, other values not listed in the range of values are also applicable.

[0034] Preferably, the heating rate of the calcination is 2-10℃ / min, for example, it can be 2℃ / min, 3.5℃ / min, 5℃ / min, 7.5℃ / min, 8.5℃ / min or 10℃ / min, etc., preferably 2-5℃ / min, but not limited to the listed values, other values not listed in the range of values are also applicable.

[0035] Preferably, the time of the calcination is 3-21h, for example, it can be 3h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h or 21h, etc., but not limited to the listed values, other values not listed in the range of values are also applicable.

[0036] It is worth mentioning that by controlling the heating rate of the calcination within a certain range, the crystal growth time can be increased, larger grains are formed, the dielectric loss of the material is increased, and the wave absorption effect is better.

[0037] Preferably, the heating mode of the calcination comprises microwave heating and / or electric heating.

[0038] As a preferred technical scheme of the present application, the preparation method comprises the following steps:

[0039] (1) mixing a strontium source, an iron source, a praseodymium source, a yttrium source, a complexing agent and a solvent to obtain a mixed solution;

[0040] The ratio of the total molar amount of the praseodymium source, the yttrium source and the iron source to the molar amount of the strontium source is 12:(0.9-1.4); the molar ratio of the praseodymium source, the yttrium source and the iron source is (0.05-2.0):(0.05-1.5):(9.0-11.9); and the ratio of the molar amount of the complexing agent to the total molar amount of the strontium source, the iron source, the praseodymium source and the yttrium source is (1-5):1;

[0041] (2) mixing a pH regulator and the mixed solution of step (1) to adjust the pH to 5-8.5, and then performing a heating reaction by water bath or oil bath heating, constant temperature stirring at 75-95℃ to obtain a viscous gel;

[0042] (3) drying the viscous gel of step (2) at 95-125℃ for 10-48h, then heat treating at 100-350℃ for 0.1-3h, and then calcining by microwave heating and / or electric heating and heating at a heating rate of 2-10℃ / min to 900-1300℃ for 3-21h to obtain the praseodymium-yttrium co-doped M-type hexagonal ferrite material.

[0043] In a third aspect, the present application provides an application of the praseodymium-yttrium co-doped M-type hexagonal ferrite material of the first aspect, and the application comprises a wave-absorbing material, a permanent magnet material, a microwave device and a catalysis field.

[0044] The numerical range of the present application includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed, and the present application does not list the specific point values included in the range for the sake of brevity and simplicity.

[0045] Compared with the prior art, the present application has the following beneficial effects:

[0046] (1) The present application incorporates praseodymium and yttrium into M-type hexagonal ferrite, controls the molar ratio of praseodymium and iron, realizes the conversion of Pr 3+ to Pr 4+ , and is beneficial to oxygen vacancies and Fe 2+The formation of the material has strong absorption in C-band and X-band, and can realize simultaneous absorption in C-band and Ku-band, widen the absorption frequency band, significantly improve the dielectric performance of the material and enhance the microwave absorption performance;

[0047] (2) The preparation method has low production cost and simple process, and the prepared praseodymium and yttrium co-doped M-type hexaferrite material has the advantages of adjustable wave absorption frequency band, large wave absorption intensity and high working temperature.

[0048] (3) The prepared hexaferrite material maintains the relative stability of the wave absorption performance in a large doping range of praseodymium and yttrium, which makes it can be used as a basic material of other composite materials. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 The X-ray diffraction pattern of the praseodymium and yttrium co-doped strontium ferrite material of Example 1 and Comparative Example 2;

[0050] Figure 2 The wave absorption effect diagram of the praseodymium and yttrium co-doped strontium ferrite material of Example 1;

[0051] Figure 3 and Figure 4 The scanning electron microscope image and the wave absorption effect diagram of the praseodymium and yttrium co-doped strontium ferrite material of Example 2, respectively;

[0052] Figure 5 and Figure 6 The scanning electron microscope image and the wave absorption effect diagram of the praseodymium and yttrium co-doped strontium ferrite material of Example 3, respectively;

[0053] Figure 7 and Figure 8 The scanning electron microscope image and the wave absorption effect diagram of the praseodymium and yttrium co-doped strontium ferrite material of Example 4, respectively;

[0054] Figure 9 and Figure 10 The scanning electron microscope image and the wave absorption effect diagram of the praseodymium and yttrium co-doped strontium ferrite material of Example 5, respectively;

[0055] Figure 11 and Figure 12 The scanning electron microscope image and the wave absorption effect diagram of the praseodymium and yttrium co-doped strontium ferrite material of Example 6, respectively;

[0056] Figure 13 and Figure 14 The scanning electron microscope image and the wave absorption effect diagram of the praseodymium and yttrium co-doped strontium ferrite material of Example 7, respectively;

[0057] Figure 15 The wave absorption effect diagram of the praseodymium and yttrium co-doped strontium ferrite material of Example 8;

[0058] Figure 16 This is a microwave absorption effect diagram of the praseodymium-yttrium co-doped strontium ferrite material in Example 9;

[0059] Figure 17 and Figure 18 The images shown are scanning electron microscope (SEM) images and microwave absorption effect diagrams of the praseodymium-yttrium co-doped strontium ferrite material of Example 10.

[0060] Figure 19 The image shows the microwave absorption effect of the praseodymium-yttrium co-doped strontium ferrite material in Example 11.

[0061] Figure 20 The image shows the microwave absorption effect of the praseodymium-yttrium co-doped strontium ferrite material in Example 12.

[0062] Figure 21 The image shows the microwave absorption effect of the praseodymium-yttrium co-doped strontium ferrite material in Example 13.

[0063] Figure 22 and Figure 23 The images shown are scanning electron microscope (SEM) images and absorption effect diagrams of the praseodymium-yttrium co-doped strontium ferrite material from Example 17. Detailed Implementation

[0064] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0065] All raw materials used in the examples and comparative examples were of analytical grade.

[0066] Example 1

[0067] This embodiment provides a praseodymium-yttrium co-doped M-type hexagonal ferrite material with the chemical formula SrFe. 11.9 Pr 0.05 Y 0.05 O 19 Its preparation method includes the following steps:

[0068] (1) Ferric nitrate nonahydrate, praseodymium nitrate hexahydrate, yttrium nitrate hexahydrate and strontium nitrate were mixed in deionized water at a molar ratio of 11.9:0.05:0.05:1.0. Then, an aqueous solution of citric acid monohydrate was added, and the ratio of the molar amount of citric acid monohydrate to the total molar amount of iron source, praseodymium source, yttrium source and strontium source was controlled to be 1:1. The mixture was stirred for 3 hours to obtain a mixed solution.

[0069] (2) Add 25% ammonia water to the mixed solution in step (1) until the pH value of the mixed solution is 7.0, and then place it in an oil bath constant temperature bath and stir at 95°C for more than 8 hours to carry out the heating reaction and obtain a viscous gel.

[0070] (3) The viscous gel prepared in step (2) is dried in a blast drying oven at 100°C for more than 24 hours, then heat treated at 300°C for 0.3 hours, ground, and then baked at 1250°C for 3 hours at a temperature rising rate of 5°C / min to obtain the praseodymium-yttrium co-doped M-type hexaferrite material.

[0071] Figure 1 The curve (b) is the X-ray diffraction result of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 1. As can be seen from the figure, when the doping amount of praseodymium is x = 0.05, a pure M phase can be formed. Figure 2 The figure is the wave absorption effect diagram of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 1. As can be seen from the figure, it has strong absorption in the low frequency band, and the minimum reflection loss is -48.95 dB. In the high frequency band, the matching thickness is small, reaching 2.0 mm.

[0072] Example 2

[0073] The praseodymium-yttrium co-doped M-type hexaferrite material provided in the embodiment has a chemical formula of SrFe 11.8 Pr 0.1 Y 0.1 O 19 The preparation method is the same as that of Example 1 except that the molar ratio of iron nitrate nine hydrate, praseodymium nitrate six hydrate, yttrium nitrate six hydrate and strontium nitrate in step (1) is adjusted from 11.9:0.05:0.05:1.0 to 11.8:0.1:0.1:1.0.

[0074] Figure 3 The figure is the scanning electron microscope image of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 2, Figure 3 (a) and Figure 3 (b) are images with magnifications of 25,000 times and 10,000 times, respectively. As can be seen from the figure, the particles of the prepared material are mostly hexagonal. Figure 4 The figure is the wave absorption effect diagram of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 2. As can be seen from the figure, it has strong absorption in the low frequency band, and the minimum reflection loss is -51.57 dB. In the high frequency band, the matching thickness is small, reaching 2.0 mm.

[0075] Example 3

[0076] The praseodymium-yttrium co-doped M-type hexaferrite material provided in the embodiment has a chemical formula of SrFe 11.6 Pr 0.2 Y 0.2 O 19 ​The preparation method is same as that of Example 1 except that the molar ratio of iron nitrate nine hydrate, praseodymium nitrate six hydrate, yttrium nitrate six hydrate and strontium nitrate in step (1) is adjusted from 11.9:0.05:0.05:1.0 to 11.6:0.2:0.2:1.0.

[0077] Figure 5 The scanning electron microscope images of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 3 are shown in Figs. 3(a) and 3(b), respectively. Figure 5 (a) and Figure 5 (b) are images with magnifications of 25,000 times and 10,000 times, respectively. As can be seen from the images, the particles of the prepared material are mostly hexagonal. Figure 6 The wave absorption effect diagram of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 3 is shown in Fig. 3(c). It is shown in the diagram that the material has strong absorption in the low frequency band, and the matching thickness is small, reaching 1.5 mm in the high frequency band.

[0078] Example 4

[0079] The present example provides a preparation method of a praseodymium-yttrium co-doped M-type hexaferrite material, which has a chemical formula of Sr1Fe 11.4 Pr 0.3 Y 0.3 O 19 The preparation method is same as that of Example 1 except that the molar ratio of iron nitrate nine hydrate, praseodymium nitrate six hydrate, yttrium nitrate six hydrate and strontium nitrate in step (1) is adjusted from 11.9:0.05:0.05:1.0 to 11.4:0.3:0.3:1.0.

[0080] Figure 7 The scanning electron microscope images of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 4 are shown in Figs. 4(a) and 4(b), respectively. Figure 7 (a) and Figure 7 (b) are images with magnifications of 25,000 times and 10,000 times, respectively. As can be seen from the images, the particles of the prepared material are mostly hexagonal. Figure 8 The wave absorption effect diagram of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 4 is shown in Fig. 4(c). It is shown in the diagram that the material has strong absorption in the low frequency band, and the matching thickness is small, reaching 1.5 mm in the high frequency band.

[0081] Example 5

[0082] The present example provides a praseodymium-yttrium co-doped M-type hexaferrite material, which has a chemical formula of SrFe 11.2 Pr 0.4 Y 0.4 O 19The preparation method is same as that of Example 1 except that the molar ratio of iron nitrate nine hydrate, praseodymium nitrate six hydrate, yttrium nitrate six hydrate and strontium nitrate in step (1) is adjusted from 11.9:0.05:0.05:1.0 to 11.2:0.4:0.4:1.0.

[0083] Figure 9 The scanning electron microscope images of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 5 are shown in Figs. 5(a) and 5(b), Figure 9 (a) and Figure 9 (b) are images with magnifications of 25,000 times and 10,000 times, respectively. As can be seen from the images, the particles of the prepared material are mostly hexagonal and spherical. Figure 10 The wave absorption effect diagram of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 5 is shown in Fig. 5(c). It can be seen from the diagram that the material has strong absorption in the low frequency band, and the matching thickness is small, reaching 2.0 mm in the high frequency band.

[0084] Example 6

[0085] The present example provides a preparation method of a praseodymium-yttrium co-doped M-type hexaferrite material, which has a chemical formula of SrFe 11 Pr 0.5 Y 0.5 O 19 The preparation method is same as that of Example 1 except that the molar ratio of iron nitrate nine hydrate, praseodymium nitrate six hydrate, yttrium nitrate six hydrate and strontium nitrate in step (1) is adjusted from 11.9:0.05:0.05:1.0 to 11:0.5:0.5:1.0.

[0086] Figure 11 The scanning electron microscope images of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 6 are shown in Figs. 6(a) and 6(b), Figure 11 (a) and Figure 11 (b) are images with magnifications of 25,000 times and 10,000 times, respectively. As can be seen from the images, the particles of the prepared material are mostly hexagonal. Figure 12 The wave absorption effect diagram of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 6 is shown in Fig. 6(c). It can be seen from the diagram that the material has strong absorption in the low frequency band, and the minimum reflection loss is -45.20 dB, and the matching thickness is small, reaching 1.5 mm in the high frequency band.

[0087] Example 7

[0088] The present example provides a preparation method of a praseodymium-yttrium co-doped M-type hexaferrite material, which has a chemical formula of SrFe 10.8 Pr 0.6 Y 0.6 O 19The preparation method is same as that of Example 1 except that the molar ratio of iron nitrate nine hydrate, praseodymium nitrate six hydrate, yttrium nitrate six hydrate and strontium nitrate in step (1) is adjusted from 11.9:0.05:0.05:1.0 to 10.8:0.6:0.6:1.0.

[0089] Figure 13 The scanning electron microscope images of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 7, Figure 13 (a) and Figure 13 (b) are images with magnification of 25,000 times and 10,000 times, respectively. As can be seen from the images, the particles of the prepared material are mostly hexagonal and spherical. Figure 14 The wave absorption effect image of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 7 shows that it has strong absorption in the low frequency band, and the matching thickness is small, reaching 2.0 mm in the high frequency band.

[0090] Example 8

[0091] The present example provides a preparation method of a praseodymium-yttrium co-doped M-type hexaferrite material, which has a chemical formula of SrFe 10.2 Pr 0.9 Y 0.9 O 19 The preparation method is same as that of Example 1 except that the molar ratio of iron nitrate nine hydrate, praseodymium nitrate six hydrate, yttrium nitrate six hydrate and strontium nitrate in step (1) is adjusted from 11.9:0.05:0.05:1.0 to 10.2:0.9:0.9:1.0.

[0092] Figure 15 The wave absorption effect image of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 8 shows that it has good absorption in the low frequency band, and the matching thickness is small, reaching 2.0 mm in the high frequency band.

[0093] Example 9

[0094] The present example provides a praseodymium-yttrium co-doped M-type hexaferrite material, which has a chemical formula of SrFe 1.5 Y 1.5 O 19 The preparation method is same as that of Example 1 except that the molar ratio of iron nitrate nine hydrate, praseodymium nitrate six hydrate, yttrium nitrate six hydrate and strontium nitrate in step (1) is adjusted from 11.9:0.05:0.05:1.0 to 9:1.5:1.5:1.0.

[0095] Figure 16 The wave absorption effect image of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 9 shows that it still has wave absorption effect at this doping concentration, and has good absorption in the high frequency band.

[0096] Example 10

[0097] This example provides a praseodymium-yttrium co-doped M-type hexaferrite material with a chemical formula of SrFe 11.8 Pr 0.1 Y 0.1 O 19 The preparation method thereof is the same as that of Example 1 except that the molar ratio of iron nitrate nine hydrate, praseodymium nitrate six hydrate, yttrium nitrate six hydrate and strontium nitrate in step (1) is adjusted from 11.9:0.05:0.05:1.0 to 11.8:0.1:0.1:1.0, and the holding temperature of calcination in step (3) is adjusted from 1250°C to 1200°C.

[0098] Figure 17 The scanning electron microscope images of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 10, Figure 17 (a) and Figure 17 (b) are images with magnifications of 25,000 times and 10,000 times, respectively. As can be seen from the images, the particles of the prepared material are mostly hexagonal. Figure 18 The wave absorption effect diagram of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 10 shows that it has strong absorption in the low frequency band, and the matching thickness is small in the high frequency band, which can reach 2.0 mm.

[0099] Example 11

[0100] This example provides a praseodymium-yttrium co-doped M-type hexaferrite material with a chemical formula of SrFe 11.2 Pr 0.4 Y 0.4 O 19 The preparation method thereof is the same as that of Example 1 except that the molar ratio of iron nitrate nine hydrate, praseodymium nitrate six hydrate, yttrium nitrate six hydrate and strontium nitrate in step (1) is adjusted from 11.9:0.05:0.05:1.0 to 11.2:0.4:0.4:1.0, and the holding temperature of calcination in step (3) is adjusted from 1250°C to 1200°C.

[0101] Figure 19 The scanning electron microscope images of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 11, Figure 19 (a) and Figure 19 (b) are images with magnifications of 25,000 times and 10,000 times, respectively. As can be seen from the images, the particles of the prepared material are mostly hexagonal and spherical. Figure 20 The wave absorption effect diagram of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 11 shows that it has strong absorption in the low frequency band, and the minimum reflection loss is -41.74 dB, and the matching thickness is small in the high frequency band, which can reach 1.5 mm.

[0102] Example 12

[0103] This example provides a praseodymium-yttrium co-doped M-type hexaferrite material with a chemical formula of SrFe 11.8 Pr 0.1 Y 0.1 O 19 The preparation method thereof is the same as in Example 1 except that in step (1), the molar ratio of iron nitrate nine hydrate, praseodymium nitrate six hydrate, yttrium nitrate six hydrate and strontium nitrate is adjusted from 11.9:0.05:0.05:1.0 to 11.8:0.1:0.1:1.0, and the holding temperature of calcination in step (3) is adjusted from 1250°C to 1300°C.

[0104] Example 13

[0105] This example provides a praseodymium-yttrium co-doped M-type hexaferrite material with a chemical formula of SrFe 11.6 Pr 0.2 Y 0.2 O 19 The preparation method thereof is the same as in Example 1 except that in step (1), the molar ratio of iron nitrate nine hydrate, praseodymium nitrate six hydrate, yttrium nitrate six hydrate and strontium nitrate is adjusted from 11.9:0.05:0.05:1.0 to 11.6:0.2:0.2:1.0, and the holding temperature of calcination in step (3) is adjusted from 1250°C to 1300°C.

[0106] Figure 21 The wave absorption effect diagram of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in Example 13 is shown in the figure, which shows that it has strong absorption in the low frequency band, and the minimum reflection loss is -42.59 dB. In the high frequency band, the matching thickness is small, which can reach 2.0 mm.

[0107] Example 14

[0108] This example provides a praseodymium-yttrium co-doped M-type hexaferrite material with a chemical formula of Sr 1.1 Fe 11.8 Pr 0.1 Y 0.1 O 19 The preparation method thereof is the same as in Example 1 except that in step (1), the molar ratio of iron nitrate nine hydrate, praseodymium nitrate six hydrate, yttrium nitrate six hydrate and strontium nitrate is adjusted from 11.9:0.05:0.05:1.0 to 11.8:0.1:0.1:1.1, and the holding temperature of calcination in step (3) is adjusted from 1250°C to 1200°C.

[0109] Example 15

[0110] The embodiment provides a praseodymium-yttrium co-doped M-type hexaferrite material, which has a chemical formula of SrFe 1.2 Fe 11.8 Pr 0.1 Y 0.1 O 19 The preparation method is same to that of the embodiment 1 except that the molar ratio of the iron nitrate nine hydrate, the praseodymium nitrate six hydrate, the yttrium nitrate six hydrate and the strontium nitrate in the step (1) is adjusted from 11.9:0.05:0.05:1.0 to 11.8:0.1:0.1:1.2, and the holding temperature of the calcination in the step (3) is adjusted from 1250 DEG C to 1200 DEG C.

[0111] Example 16

[0112] The embodiment provides a praseodymium-yttrium co-doped M-type hexaferrite material, which has a chemical formula of SrFe 11.6 Pr 0.15 Y 0.25 O 19 The preparation method is same to that of the embodiment 1 except that the molar ratio of the iron nitrate nine hydrate, the praseodymium nitrate six hydrate, the yttrium nitrate six hydrate and the strontium nitrate in the step (1) is adjusted from 11.9:0.05:0.05:1.0 to 11.6:0.15:0.25:1.0.

[0113] Example 17

[0114] The embodiment provides a praseodymium-yttrium co-doped M-type hexaferrite material, which has a chemical formula of SrFe 11.6 Pr 0.25 Y 0.15 O 19 The preparation method is same to that of the embodiment 1 except that the molar ratio of the iron nitrate nine hydrate, the praseodymium nitrate six hydrate, the yttrium nitrate six hydrate and the strontium nitrate in the step (1) is adjusted from 11.9:0.05:0.05:1.0 to 11.6:0.25:0.25:1.0.

[0115] Figure 22 The scanning electron microscope (SEM) photos of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in the example 17, Figure 22 (a) and Figure 22 (b) are photos with magnifications of 25,000 times and 10,000 times respectively. Figure 23 The wave absorption effect photo of the praseodymium-yttrium co-doped M-type hexaferrite material prepared in the example 17 shows that the material has strong absorption in a low frequency band, and the minimum reflection loss is-50.10dB; in a high frequency band, the matching thickness is small, and reaches 2.0mm.

[0116] Comparative Example 1

[0117] The present comparative example provides a yttrium-doped M-type hexaferrite material with a chemical formula of SrFe 11.8 Y 0.2 O 19 The preparation method thereof is the same as that of Example 1 except that the molar ratio of iron nitrate nonahydrate, praseodymium nitrate hexahydrate, yttrium nitrate hexahydrate and strontium nitrate in step (1) is adjusted from 11.9:0.05:0.05:1.0 to 11.8:0:0.2:1.0.

[0118] The material prepared in Comparative Example 1 has poor wave absorption effect. In the matching thickness range of 1-5.5 mm, there is no reflection loss less than -10 dB.

[0119] Comparative Example 2

[0120] The present comparative example provides a strontium ferrite material with a chemical formula of SrFe 12 O 19 The preparation method thereof is the same as that of Example 1 except that praseodymium nitrate hexahydrate and yttrium nitrate hexahydrate are not used in step (1).

[0121] Figure 1 The curve (a) in the middle is the XRD ray diffraction pattern of the strontium ferrite material obtained in Comparative Example 2. The material prepared in Comparative Example 2 has poor wave absorption effect. In the matching thickness range of 1-5.5 mm, there is no reflection loss less than -10 dB.

[0122] Comparative Example 3

[0123] The present comparative example provides a praseodymium-yttrium co-doped M-type hexaferrite material with a chemical formula of SrFe 11.6 Pr 0.05 Y 0.35 O 19 The preparation method thereof is the same as that of Example 1 except that the molar ratio of iron nitrate nonahydrate, praseodymium nitrate hexahydrate, yttrium nitrate hexahydrate and strontium nitrate in step (1) is adjusted from 11.9:0.05:0.05:1.0 to 11.6:0.05:0.35:1.0.

[0124] The material prepared in Comparative Example 3 has poor wave absorption effect. In the matching thickness range of 1-5.5 mm, there is no reflection loss less than -10 dB.

[0125] The materials prepared in the above examples and comparative examples were subjected to performance tests. The specific test method was as follows: the sample was mixed with 20 wt% paraffin, and then they were pressed into a ring-shaped device. The inner diameter / outer diameter of the device was 3 / 7 mm, and the thickness was about 2 mm. Then a vector network analyzer (VNA, Agilent N5222A) was used to measure the dynamic electromagnetic parameters in the frequency range of 2-18 GHz using the transmission-reflection coaxial line method. And the reflection loss (RL) of a certain thickness was calculated according to the transmission line theory. The test results are shown in Table 1.

[0126] Table 1

[0127]

[0128]

[0129] In Table 1, " / " represents that the strongest absorption that meets 90% absorption is not met when the thickness is less than 6 mm.

[0130] The following points can be drawn from Table 1:

[0131] (1) The praseodymium-yttrium co-doped M-type hexaferrite material prepared by the preparation method provided in Examples 1-9 is mostly hexagonal and spherical in shape, and is in a close distribution state, has high dielectric loss and good impedance matching, has strong absorption in the C band and the X band, and can achieve simultaneous absorption in the C band and the Ku band;

[0132] (2) As can be known by comprehensively comparing Examples 1-8, Example 9, Comparative Examples 2 and 3, when the molar ratio of the praseodymium source, the yttrium source, the iron source and the strontium source is not reasonable, the conversion of Pr 3+ to Pr 4+ is less, which is not conducive to the formation of oxygen vacancies and Fe 2+ , resulting in reduced wave-absorbing performance, so that the coating with a thickness of less than 6 mm cannot effectively absorb electromagnetic waves (meet 90% absorption);

[0133] (3) As can be known by comprehensively comparing Example 16, Example 17 and Comparative Example 3, when the total molar amount of doping is constant and praseodymium and yttrium are not doped in equal proportions, the wave-absorbing effect can be obviously improved. With the gradual increase of the doping amount of the praseodymium source, the conversion of Pr 3+ to Pr 4+ is increased, which promotes the formation of oxygen vacancies and Fe 2+ , improves the dielectric loss, and improves the wave-absorbing performance. When the yttrium doping amount is dominant, simultaneous absorption in the C band and the Ku band is achieved. When the praseodymium doping amount is dominant, the matching thickness is reduced, and the frequency band is adjustable;

[0134] (4) From the comprehensive comparative example 1 and comparative example 2, when the praseodymium element is not doped, the material has a low dielectric loss, which results in poor wave absorption performance, i.e. the coating with a thickness less than 6 mm cannot effectively absorb electromagnetic waves (satisfying 90% absorption).

[0135] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details of the above-described embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0136] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0137] In addition, various different embodiments of the present application can also be combined in any manner, as long as it does not deviate from the idea of the present application, and it should also be considered as disclosed by the present application.

Claims

1. A praseodymium-yttrium co-doped M-type hexagonal ferrite material, characterized in that, The chemical formula of the praseodymium-yttrium co-doped M-type hexagonal ferrite material includes Sr z Fe 12-x-y Pr x Y y O 19 Where 0.05≤x≤2.0, 0.05≤y≤1.5, 0.9≤z≤1.4, and x / y>1 / 7.

2. A method for preparing the praseodymium-yttrium co-doped M-type hexagonal ferrite material according to claim 1, characterized in that, The preparation method includes the following steps: A mixed solution is obtained by mixing a strontium source, an iron source, a praseodymium source, a yttrium source, a complexing agent, and a solvent. The pH of the mixed solution was adjusted and the reaction was carried out by heating to obtain a viscous gel; The viscous gel was subjected to heat treatment and calcination in sequence to obtain the praseodymium-yttrium co-doped M-type hexagonal ferrite material.

3. The preparation method according to claim 2, characterized in that, The ratio of the total molar amount of the praseodymium source, yttrium source, and iron source to the molar amount of the strontium source is 12:(0.9~1.4).

4. The preparation method according to claim 3, characterized in that, The molar ratio of the praseodymium source, yttrium source, and iron source is (0.05~2.0):(0.05~1.5):(9.0~11.9).

5. The preparation method according to claim 2, characterized in that, The strontium source, iron source, praseodymium source, and yttrium source include any one or a combination of at least two of the nitrate, acetate, or chloride salts of the corresponding metal element.

6. The preparation method according to claim 2, characterized in that, The molar ratio of the complexing agent to the total molar ratio of the strontium source, iron source, praseodymium source and yttrium source is (1~5):

1.

7. The preparation method according to claim 2, characterized in that, The complexing agent includes citric acid.

8. The preparation method according to claim 2, characterized in that, The preparation method includes: first stirring and mixing a strontium source, an iron source, a praseodymium source, a yttrium source, and a solvent, and then adding a complexing agent solution to the mixture.

9. The preparation method according to claim 2, characterized in that, The pH range for pH adjustment is 5 to 8.

5.

10. The preparation method according to claim 2, characterized in that, The pH adjustment uses a pH adjuster, which includes ammonia.

11. The preparation method according to claim 10, characterized in that, The concentration of the ammonia water is 25% to 50%.

12. The preparation method according to claim 2, characterized in that, The constant temperature for the heating reaction is 75~95℃.

13. The preparation method according to claim 2, characterized in that, The heating reaction is carried out using a water bath or oil bath while maintaining stirring.

14. The preparation method according to claim 2, characterized in that, Before the heat treatment, the viscous gel is dried.

15. The preparation method according to claim 14, characterized in that, The drying temperature is 95~125℃, and the time is 10~48h.

16. The preparation method according to claim 2, characterized in that, The heat treatment is held at a temperature of 100~350℃ for 0.1~3h.

17. The preparation method according to claim 2, characterized in that, The calcination heating rate is 2~10℃ / min, the holding temperature is 900~1300℃, and the time is 3~21h.

18. The preparation method according to claim 2, characterized in that, The heating method for roasting includes microwave heating and / or electric heating.

19. The preparation method according to claim 2, characterized in that, The preparation method includes the following steps: (1) Mix the strontium source, iron source, praseodymium source, yttrium source, complexing agent and solvent to obtain a mixed solution; The ratio of the total molar amount of the praseodymium source, yttrium source, and iron source to the molar amount of the strontium source is controlled to be 12:(0.9~1.4); the molar ratio of the praseodymium source, yttrium source, and iron source is controlled to be (0.05~2.0):(0.05~1.5):(9.0~11.9); the molar amount of the complexing agent to the total molar amount of the strontium source, iron source, praseodymium source, and yttrium source is controlled to be (1~5):1; (2) Mix the pH adjuster and the mixed solution described in step (1) to adjust the pH to 5~8.5, and then heat the solution by water bath or oil bath, stirring at a constant temperature of 75~95℃ to carry out the heating reaction and obtain a viscous gel. (3) The viscous gel described in step (2) is dried at 95~125℃ for 10~48h, then heat-treated at 100~350℃ for 0.1~3h, and then calcined at 900~1300℃ for 3~21h by microwave heating and / or electric heating at a heating rate of 2~10℃ / min to obtain the praseodymium-yttrium co-doped M-type hexagonal ferrite material.

20. An application of the praseodymium-yttrium co-doped M-type hexagonal ferrite material according to claim 1, characterized in that, The applications include microwave absorbing materials, permanent magnet materials, microwave devices, and catalysis.

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