Research On Preparation Technology Of M-type Hexaferrites For X-band Quasi-planarized Circulator

When traditional X-band circulators operate,it is required to provide the external permanent magnets?its volume and weight account for more than 80%of the microwave device?for ferrite substrates as indispensable biasing fields to achieve the circular function which will increase the weight and volume of the device,and it is difficult to meet the miniaturization and lightweight demand of the microwave integrated circuit system.Magnetite-type hexagonal ferrite materials have high coercive force,high remanence ratio,and high anisotropic field,which can form a self-built"internal field"inside the ferrite to provide self-biased field,completely get rid of the constraints of external magnetic steel,and achieve quasi-planarization characteristics,which will greatly reduce the weight and volume of the circulator,and achieve the purpose of device miniaturization,light weight and integration.Therefore,it is of great strategic significance to study the preparation technology of M-type hexagonal ferrite materials for X-band quasi-planarized circulators.This paper is based on the performance requirements of quasi-planarized circulator substrate materials,and uses traditional oxide ceramics to prepare BaM hexagonal ferrite.The ion occupancy of BaM hexagonal ferrite was calculated based on the first-principles,and the relationship between the ion substitution of BaM hexagonal ferrite,the preparation process,and the relationship between additives and properties were thoroughly explored.Firstly,the traditional oxide ceramics method was used to prepare Sc substituted BaM hexagonal ferrite,and the effect of Sc substitution on the properties of BaM hexagonal ferrite was studied.The results show that:?1?The phases of BaM hexagonal ferrite substituted by Sc are pure phases,indicating that Sc ions completely enter the crystal lattice,but Sc substitution inhibits the growth of crystal grains,resulting in deterioration of the microstructure of the material;?2?Through the first-principles and Maxwell-The Boltzmann distribution jointly calculates the theoretical probability that Sc occupies each crystal position in the temperature range of 0-1500 K,and combined with Raman analysis,we know that Sc preferentially occupies 2a and 12k crystal positions.?3?Within the range of Sc substitutions studied,Sc substitution can significantly reduce the anisotropy field H_a,saturation magnetization 4?M_s,residual magnetism ratio M_r/M_s,and density d of BaM hexagonal ferrite.The proper amount of Sc substitution can get the lowest ferromagnetic resonance linewidth?H.When the amount of Sc substitution is 0.5,the material has the best synthesis performance:4?M_s=3.65 kGs,M_r/M_s=0.84,d=5.11 g/cm³,H_c=528 Oe,H_a=13.9 kOe,?H=482 Oe,f_r=43.0 GHz.?4?Based on Néel's ferrimagnetic molecular field theory,calculations by Brillouin function fitting show that Sc substitution will weaken the molecular field interactions between 2b-4f₂?12k-4f₁?2a-4f₁?12k-4f₂and 2b-12k crystal positions,so that the Curie temperature T_c is reduced,thereby reducing the material temperature stability.Then,based on BaFe_11.5Sc_0.5O₁₉9 as the main formula,the influence of the preparation process?pre-calcination temperature and secondary ball milling time?on the properties of BaM hexagonal ferrite was studied.The results show that:?1?The appropriate pre-firing temperature can promote the densification and uniform growth of the crystal grains,thereby improving the comprehensive properties of the sintered sample.When the pre-firing temperature is 1250°C,the comprehensive properties of the material are the best;?2?The secondary ball milling time can improve the microstructure and properties of BaM hexagonal ferrite.If the secondary ball milling is too long,the microstructure and performance of the material will be deteriorated.When the secondary milling time is 18 h,the sintered samples have the best overall performance:4?M_s=3.07 kGs,M_r/M_s=0.90,H_c=510 Oe,H_a=13.2 kOe,?H=393 Oe,f_r=40.8 GHz.Finally,the microstructure and properties of the BaM hexagonal ferrite doped with Bi₂O₃+CuO and Bi₂O₃+CuO+SiO₂ were studied.The results show that:?1?In the combined doping of Bi₂O₃+CuO,the melting point of the mixed phase of bismuth copper oxide formed at the grain boundary is lower,which can further promote the growth of grain densification,thereby increasing the density of the sintered sample;?2?In the combined doping of Bi₂O₃+CuO+SiO₂,a large amount of SiO₂ is concentrated at the grain boundaries,which suppresses the growth of the grains,thereby refining the grains and increasing the coercive force.When the doped amount of SiO₂ is 0.6 wt%,the coercive force?H_c=668 Oe?of the sintered sample is the highest,and the ferromagnetic resonance line width??H=280 Oe?of the material is better than the current literature report on BaM hexagonal ferrite bulk materials.