High-dielectric low-loss self-bias hexagonal ferrite material and preparation method thereof

Abstract

The invention discloses a high-dielectric low-loss self-biased hexagonal ferrite material and a preparation method thereof, and belongs to the technical field of ferrite material preparation. The ferrite material comprises BaM hexagonal ferrite and an additive, wherein the BaM hexagonal ferrite is Ba0. 9La0. 1Fe0. 9Cu0. 1O17.5, and the additive is Ba0. 9La0. 1Fe0. 9Cu0. 1O0. On the basis of the mass of the BaM hexagonal ferrite pre-sintering material, the doping agent comprises 0.3 wt% of SiO2, 0.3 wt% of H3BO3, 0.6 wt% of CaCO3 and 0.2 to 1 wt% of nanoscale BaTiO3. According to the invention, nanoscale BaTiO3 is adopted as a dopant and is enriched on a grain boundary, Ti < 4 + > in the nanoscale BaTiO3 diffuses into a BaM ferrite lattice and preferentially occupies a Fe vacancy to generate defect recombination, and meanwhile, a multi-step microwave sintering technology is adopted, so that excellent characteristics of high Hc, Mr / Ms and epsilon ', low delta H, tan delta epsilon and the like of the hexagonal ferrite material are realized; and the engineering requirements of low loss and large bandwidth of a miniature integrated device in a microwave frequency band range are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of ferrite material preparation, and specifically relates to a high permittivity and low loss self-biased hexagonal ferrite material and a preparation method thereof. Background Art

[0002] Active phased array radars are widely used in modern electronic countermeasures, and microwave devices with characteristics such as small size and low loss have become the research focus in the microwave / millimeter wave field. A microwave circulator is an indispensable important component in a Transmit / Receive (T / R) module. Traditional circulators require a relatively large permanent magnet (accounting for about 90% of the device weight and volume) built-in to provide a bias magnetic field, which poses a challenge to the miniaturization of the T / R module in realizing the whole machine. Self-biased hexagonal ferrite has excellent magnetocrystalline anisotropy, high coercivity H c and remanence ratio M r / M s and other excellent properties; by using the above properties, a self-bias field can be provided for the microwave circulator, thus getting rid of the bondage of the external magnetic field and achieving the purpose of miniaturization and light weight.

[0003] Regarding the self-biased hexagonal ferrite material, Patent CN202010630259.X discloses a self-biased hexagonal ferrite material and a preparation method thereof, with the main components being (6.5 - 7) mol Fe2O3, (1 - 1.17) mol BaCO3, (0 - 1) mol Ga2O3, and the performance indexes being: saturation magnetization intensity 4πM s = 4.32 kGs, remanence ratio M r / M s = 0.89, coercivity H c = 2.28 kOe, anisotropy field H a = 18.02 kOe, ferromagnetic resonance linewidth ΔH = 260 Oe, and the relative permittivity ε' and dielectric loss tanδ ε are not reported. The Adolfo University in Chile (Ceramics International, 2025) uses lanthanum (La) and cobalt (Co) co-doped BaM ferrite, with the performance indexes being: M s = 62 emu / g, H c = 1.9 kOe, H a = 9.39 kOe, ε' = 25, tanδ ε = 0.057, and the specific ΔH is not reported. The Federal University of Amazonas in Brazil (Journal of Alloys and Compounds, 2025, 1030) uses Al 3+ doped BaM ferrite, with the performance indexes being: M s= 53 emu / g, ε' = 25, tanδ ε = 0.4, no specific M reported r 、H c and H a 。The University of Bahawalpur, Islamabad, Pakistan (Ceramics International, 2023, 6487 - 6499) used Sr - Yb - Co to jointly replace BaM, and the performance indicators were: ε' = 2.4, tanδ ε = 10 -3 , no specific magnetic properties were reported. The University of Electronic Science and Technology of China, in collaboration with Northeastern University in the United States (Materials, 2022, 15, 8792), prepared Ba 0.8 La 0.2 Fe 11.8 Cu 0.2 O 19 hexagonal hexaferrite materials; the performance indicators were: M r / M s = 0.89, H c = 2.81 kOe, H a = 14.6 kOe, ΔH = 379 Oe, ε' and tanδ were not reported ε 。Although the above - mentioned materials can achieve high characteristics in terms of single performance (such as M r / M s , ΔH, etc.), the strong coupling relationship between their magnetic - dielectric properties makes it difficult to achieve collaborative optimization of key technical indicators: high ε' often accompanies the decrease of H c and M r / M s , resulting in the loss of the self - biasing property of the material; while lower ε' although helps to maintain excellent magnetic properties, it cannot meet the requirements of miniaturization and lightweight of microwave devices. Summary of the Invention

[0004] The purpose of the present invention is to propose a high - permittivity, low - loss, self - biasing hexagonal ferrite material and its preparation method in view of the problems existing in the background technology. The present invention uses nanoscale BaTiO3 as a dopant, and the nanoscale BaTiO3 enriches at the grain boundaries. The Ti 4+ diffuses into the BaM ferrite lattice and preferentially occupies the Fe vacancies, generating defect recombination. At the same time, a multi - step microwave sintering technology is adopted to achieve high H c , M r / M s and ε', low ΔH and tanδ ε and other excellent characteristics, meeting the engineering requirements of low - loss and large - bandwidth for micro - integrated devices in the microwave frequency range.

[0005] Core idea of the present invention: Based on problems such as high insertion loss and narrow bandwidth of self-biased circulators, the present invention proposes a high-dielectric low-loss self-biased hexagonal ferrite material and its preparation method. First, a partially Fe-deficient formula is adopted, resulting in an imbalance of positive charges and a reduction in the unit cell volume in the main formula. To compensate for the missing positive charges, positively charged oxygen vacancies are generated inside the crystal, which is beneficial to improving the dielectric constant of the BaM ferrite material. And nano-scale Fe2O3 powder is used to enhance the microwave absorption efficiency and promote the formation of the Fe-deficient BaM crystal phase. In addition, the lack of Fe in the main formula will drive Ti in BaTiO3 (enriched at the grain boundaries) 4+ to migrate towards the BaM ferrite grains. Second, nano-scale BaTiO3 is used as a dopant. Nano-scale BaTiO3 has strong Ti 4+ ion migration activity and is more likely to dissociate from the BaTiO3 lattice and diffuse into the interior of the BaM lattice. And when the temperature < 120 °C, BaTiO3 is in the tetragonal phase with low crystal symmetry. When the temperature is above 120 °C, BaTiO3 will undergo a phase change and transform into the cubic phase. Combining the growth characteristics of BaM ferrite and BaTiO3, a multi-step microwave sintering technique is adopted to promote the diffusion of Ti in BaTiO3 4+ into the BaM ferrite lattice and preferentially occupy the Fe vacancies, resulting in defect recombination. At the same time, at the BaM-BaTiO3 interface, the oxygen ions in BaTiO3 are shared, and the oxygen vacancies at the contact interface are reduced; Ti 4+ will simultaneously increase the ε' of both BaM ferrite and BaTiO3. The high-melting-point and high-resistance-state BaTiO3 is enriched at the grain boundaries of BaM ferrite, forming a steric hindrance effect and producing a grain growth inhibition effect, significantly reducing the tanδ of BaM ferrite ε , and making the BaM ferrite grains gradually approach the single-domain state, improving the coercivity. Finally, oxygen is introduced during the sintering holding stage to reduce the generation of Fe 2+ . At the same time, the holding time is appropriately extended to promote the uniform and dense growth of BaM ferrite, further reducing the dielectric loss and the ferromagnetic resonance linewidth.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A high-dielectric low-loss self-biased hexagonal ferrite material, comprising BaM hexagonal ferrite and additives, wherein the BaM hexagonal ferrite is Ba 0.9 La 0.1 Fe 10.9 Cu 0.1 O 17.5 ; Based on the mass of the BaM hexagonal ferrite pre-sintered material, the dopants include 0.3 wt% SiO2, 0.3 wt% H3BO3, 0.6 wt% CaCO3, and 0.2 - 1 wt% nano-scale BaTiO3.

[0008] A preparation method of a high-dielectric and low-loss self-biased hexagonal ferrite material, comprising the following steps:

[0009] (1) Ingredient preparation:

[0010] According to the chemical formula Ba 0.9 La 0.1 Fe 10.9 Cu 0.1 O 17.5 Calculate and weigh the raw material powders of BaCO3, CuO, La2O3, and nanoscale Fe2O3 to improve the microwave absorption efficiency of multi-step microwave sintering;

[0011] (2) Primary ball milling:

[0012] Mix the raw material powders obtained in step (1) evenly in a ball mill, and the ball milling time is 12 - 15 hours;

[0013] (3) Pre-sintering:

[0014] Dry the primary ball milled material obtained in step (2), and then perform pre-sintering at 1050 - 1150 °C, with a heating rate of 2 - 3 °C and a holding time of 2 - 4 hours, to obtain a BaM hexagonal ferrite pre-sintered material;

[0015] (4) Doping:

[0016] Add 0.3 wt% SiO2, 0.3 wt% H3BO3, 0.6 wt% CaCO3, and 0.2 - 1 wt% nanoscale BaTiO3 equivalent to the mass of the pre-sintered material to the BaM hexagonal ferrite pre-sintered material obtained in step (3);

[0017] (5) Secondary ball milling:

[0018] Ball mill the mixed powder obtained in step (4) for 12 - 20 hours, and the average particle size of the powder after ball milling is 0.6 - 1.0 μm;

[0019] (6) Forming:

[0020] Perform dehydration treatment on the slurry obtained in step (5) to control the water content of the slurry between 3.0 - 3.5 wt%; then press the dehydrated slurry into a green body in a magnetic field - electric field dual-field coupling forming machine, with a forming magnetic field strength of 0.6 - 1.0 T, apply a 10 kV / m DC electric field in the vertical direction, a forming pressure of 80 - 120 MPa, and a pressure holding time of 90 s, and use the ferroelectricity of BaTiO3 to induce multi-level grain orientation to form a 3D texture;

[0021] (7) Multi-step microwave sintering in an oxygen atmosphere:

[0022] Place the green body obtained in step (6) into an oxygen atmosphere microwave sintering furnace, and use intermittent microwave heating to raise the temperature in the furnace to 120 - 900 °C, accelerate the discharge of moisture in the green body, and inhibit the cracking of the green body; among them, the heating rate is 1 - 2 °C / min, and the microwave power is 5 - 8 kW;

[0023] Then use continuous microwave heating to continuously raise the temperature in the furnace to 900 - 1060 °C, so that the additives are uniformly enriched at the grain boundaries, fully wrap the crystal lattice, and promote Ti 4+ to rapidly diffuse along the grain boundaries into the crystal lattice; among them, the heating rate is 1.5 - 3 °C / min, and the microwave power is 7 - 9 kW;

[0024] Finally, apply high-frequency pulsed microwaves at 1060 °C and keep it warm for 4 - 8 hours in an oxygen atmosphere of 0.02 - 0.04 MPa to reduce the generation of Fe 2+ and use the thermo-mechanical coupling effect to eliminate closed pores and make the grains uniformly densified; among them, the microwave power is 14 - 16 kW.

[0025] Furthermore, in step (1), the particle size of the nano-scale Fe2O3 is 50 - 100 nm.

[0026] For the sample obtained in step (7), use an X-ray diffractometer to analyze the phase composition of the sample; use a scanning electron microscope to observe the microscopic morphology of the sample; use a LakeShore 8604 vibrating sample magnetometer in the United States to measure 4πM s 、4πM r 、H c ; use a CK-XW-100 high-frequency comprehensive measurement system to measure ΔH, ε' and tanδ ε , and the anisotropy field H a is derived through the Kittel formula. After testing, the indicators of the sample are:

[0027] Saturation magnetization 4πM s ≥4.6 kGs;

[0028] Remanence ratio M r / M s ≥0.82;

[0029] Coercivity H c ≥2.8 kOe;

[0030] Ferromagnetic resonance linewidth ΔH ≤ 390 Oe;

[0031] Dielectric constant ε' ≥ 24;

[0032] Dielectric loss tanδ ε ≤4×10 -4 .

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] The high-dielectric low-loss self-biased hexagonal ferrite material provided by the present invention can bring the following technical effects to fields such as microwave device design: (1) A high saturation magnetization intensity (4πM s ≥4.6 kGs) can meet the engineering requirements for bandwidth expansion of microwave devices; (2) A high remanence ratio (M r / M s ≥0.82) and coercivity (H c ≥2.8 kOe) can make the magnetic moment tend to precess in the direction of strong anisotropy, forming a built-in field, completely getting rid of the bondage of external permanent magnets, and realizing miniaturization and integration; (3) A high and adjustable dielectric constant (ε'≥24) can reduce the radius of the central gyromagnetic medium of the self-biased circulator; (4) A low ferromagnetic resonance linewidth (ΔH≤400 Oe) and dielectric loss (tanδ ε ≤4×10 -4 ) can meet the engineering requirements for low insertion loss of miniaturized integrated devices. Description of the Drawings

[0035] Figure 1 It is the X-ray diffraction pattern of the high-dielectric low-loss self-biased hexagonal ferrite material in Examples 1 to 6;

[0036] Figure 2 It is the scanning electron microscope photograph of the high-dielectric low-loss self-biased hexagonal ferrite material in Examples 1 to 6;

[0037] Figure 3 It is the ferromagnetic resonance linewidth fitting diagram of the high-dielectric low-loss self-biased hexagonal ferrite material in Examples 1 to 6;

[0038] Figure 4 It is the hysteresis loop of the high-dielectric low-loss self-biased hexagonal ferrite material in Examples 1 to 6. Detailed Embodiments

[0039] The following further illustrates the core idea and technical solutions of the present invention through examples, but the present invention is not limited to these examples.

[0040] The specific preparation methods of Examples 1 to 6 include the following steps:

[0041] (1) Batching: According to the chemical formula Ba 0.9 La 0.1 Fe 10.9 Cu 0.1 O 17.5Calculate and weigh the raw material powders of BaCO3, CuO, La2O3, nanoscale Fe2O3, 0.3 wt% of SiO2, 0.3 wt% of H3BO3, 0.6 wt% of CaCO3, and 0 - 1 wt% of nanoscale BaTiO3; the formulations of the raw material powders in Examples 1 - 6 are as follows in the table:

[0042]

[0043] (2) Primary ball milling: Mix the raw material powders obtained in step (1) evenly in a ball mill, and the ball milling time is 12 - 15 hours;

[0044] (3) Pre - sintering: Dry the primary ball - milled material obtained in step (2), and then conduct pre - sintering at 1050 - 1150 °C, with a heating rate of 2 - 3 °C, and a holding time of 2 - 4 hours to obtain the BaM hexagonal ferrite pre - sintered material;

[0045] (4) Doping:

[0046] Add 0.3 wt% of SiO2, 0.3 wt% of H3BO3, 0.6 wt% of CaCO3, and 0 - 1 wt% of nanoscale BaTiO3 equivalent to the mass of the pre - sintered material to the BaM hexagonal ferrite pre - sintered material obtained in step (3), as shown in the above table;

[0047] (5) Secondary ball milling: Ball mill the mixed powder obtained in step (4) for 12 - 20 hours, and the average particle size of the powder after ball milling is 0.6 - 1.0 μm;

[0048] (6) Forming: Conduct dehydration treatment on the slurry obtained in step (5) to control the water content of the slurry between 3.0 - 3.5 wt%; then press the dehydrated slurry into a green body in a magnetic - electric field dual - field coupling forming machine. The forming magnetic field strength is 0.6 - 1.0 T, apply a DC electric field of 10 kV / m in the vertical direction, the forming pressure is 80 - 120 MPa, and the pressure - holding time is 90 s. Utilize the ferroelectricity of BaTiO3 to induce multi - level grain orientation and form a 3D texture;

[0049] (7) Multi - step microwave sintering in oxygen atmosphere:

[0050] Place the green body obtained in step (6) in an oxygen - atmosphere microwave sintering furnace, and use intermittent microwave heating to raise the temperature in the furnace to 700 °C to accelerate the discharge of moisture in the green body and inhibit the cracking of the green body; among them, the heating rate is 1.5 °C / min, and the microwave power is 6 kW;

[0051] Then use continuous microwave heating to continuously raise the temperature in the furnace to 1000 °C, so that the additives are evenly enriched at the grain boundaries, fully wrap the crystal lattice, and promote Ti 4+Diffuse rapidly along the grain boundaries into the lattice; among them, the heating rate is 2 °C / min and the microwave power is 8 kW;

[0052] Finally, microwave heat to 1060 °C, apply high-frequency pulsed microwaves at 1060 °C and hold for 6 hours in an oxygen atmosphere of 0.04 MPa to reduce Fe 2+ generation, and utilize the thermo-mechanical coupling effect to eliminate closed pores and make the grains uniformly dense; among them, the microwave power is 15 kW.

[0053] Characterize and test the phase composition, microstructure, and magnetic properties of the sample obtained in step 7. Analyze the phase composition of the sample using an X-ray diffractometer; observe the microstructure of the sample using a scanning electron microscope; measure 4πM using a LakeShore 8604 vibrating sample magnetometer in the United States s 、4πM r 、H c ; Measure ΔH, ε', and tanδ using a CK-XW-100 high-frequency comprehensive measurement system ε , and the anisotropy field H a is derived through the Kittel formula.

[0054] It can be known through testing that the ε', tanδ ε 、4πM s 、M r / M s 、H c 、H a 、and ΔH are as follows in the table.

[0055]

[0056] To sum up, the present invention is based on BaM hexagonal ferrite, and combines the high melting point and high dielectric BaTiO3 additive co-doping technology to prepare a BaM hexagonal ferrite material suitable for self-biased circulators with high coercivity (H c ≥2.8 kOe) and remanence ratio (M r / M s ≥0.82), high dielectric constant (ε'≥24) and low dielectric loss (tanδ ε ≤2.8×10 -4 ). Its dielectric constant is higher than that of most known polycrystalline hexagonal ferrites. These results provide a material basis for designing miniaturized self-biased circulators based on magnetodielectric materials. The larger dielectric constant, low dielectric loss, and narrow ferromagnetic resonance linewidth improve the bandwidth and insertion loss characteristics of the circulator.

[0057] It will be understood that the present invention is described by way of some embodiments, and those skilled in the art will know that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. Additionally, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A high permittivity and low loss self - biased hexagonal ferrite material, characterized in that, Comprising BaM hexagonal ferrite and additives, wherein the BaM hexagonal ferrite is Ba 0.9 La 0.1 Fe 10.9 Cu 0.1 O 17.5 ; Based on the mass of the BaM hexagonal ferrite pre-sintered material, the dopants include 0.3 wt% SiO2, 0.3 wt% H3BO3, 0.6 wt% CaCO3, and 0.2 - 1 wt% nano-sized BaTiO3.

2. The high-permittivity and low-loss self-biased hexagonal ferrite material according to claim 1, wherein The BaM hexagonal ferrite pre-sintered material is prepared by the following steps: (1) Ingredients: According to the chemical formula Ba 0.9 La 0.1 Fe 10.9 Cu 0.1 O 17.5 Calculate and weigh the raw material powders of BaCO3, CuO, La2O3 and nanoscale Fe2O3; (2) Ball milling: Ball milling the raw material powder obtained in step (1); (3) Pre-burning: The ball mill material obtained in step (2) is dried, and then pre-fired at 1050-1150° C. for 2-4 hours to obtain BaM hexagonal ferrite pre-fired material.

3. A preparation method of a high-permittivity and low-loss self-biased hexagonal ferrite material, characterized in that, The following steps are involved: (1) Ingredients: According to the chemical formula Ba 0.9 La 0.1 Fe 10.9 Cu 0.1 O 17.5 Calculate and weigh the raw material powders of BaCO3, CuO, La2O3 and nanoscale Fe2O3; (2) Primary ball milling: Ball milling the raw material powder obtained in step (1); (3) Pre-burning: The primary ball milled material obtained in step (2) is dried, and then pre-fired at 1050-1150° C. for 2-4 hours to obtain a BaM hexagonal ferrite pre-fired material; (4) Doping: Add 0.3wt% SiO2, 0.3wt% H3BO3, 0.6wt% CaCO3 and 0.2-1wt% nano-grade BaTiO3 equivalent to the mass of the pre-sintered material to the BaM hexagonal ferrite pre-sintered material obtained in step (3); (5) Secondary ball milling: The mixed powder obtained in step (4) is subjected to secondary ball milling, and the average particle size of the powder after ball milling is 0.6 to 1.0 μm; (6) Molding: Dehydrating and pressing the slurry obtained in step (5) to obtain a green body; (7) Multi-step microwave oxygen atmosphere sintering: The green body obtained in step (6) is placed in an oxygen atmosphere microwave sintering furnace, and intermittent microwave heating is used to raise the temperature in the furnace to 120-900° C., wherein the heating rate is 1-2° C. / min, and the microwave power is 5-8 kW; Then, continuous microwave heating is used to raise the temperature in the furnace to 900-1060°C, wherein the heating rate is 1.5-3°C / min and the microwave power is 7-9kW; Finally, high-frequency pulse microwaves are applied at 1060° C. and kept warm in an oxygen atmosphere of 0.02-0.04 MPa for 4-8 hours to obtain the high-dielectric-low-loss self-biased hexagonal ferrite material; wherein the microwave power is 14-16 kW.

4. The preparation method of the high-permittivity and low-loss self-biased hexagonal ferrite material according to claim 3, characterized in that, In step (1), the particle size of nano-sized Fe2O3 is 50 to 100 nm.

5. The preparation method of the high-permittivity and low-loss self-biased hexagonal ferrite material according to claim 3, characterized in that, The specific process of step (6) is as follows: dehydrating the slurry obtained in step (5) to control the water content of the slurry between 3.0 and 3.5 wt%; then pressing the dehydrated slurry into a green body under a magnetic field-electric field dual field coupling molding machine, the molding magnetic field strength is 0.6 to 1.0 T, a 10 kV / m DC electric field is applied in the vertical direction, the molding pressure is 80 to 120 MPa, and the holding time is 90 s.

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