Study Of Low Temperature Co-fired LiZn Gyromagnetic Composite Ferrite Materials

Modern radar systems,antimissile systems,and satellite communication systems have been developed in the direction of microsystems and integration,and it is inevitable in high frequency,miniaturization,integration,high performance,stability and reliability of microwave devices and electronic components.So far,low temperature cofired microwave ferrites?LTCF?and microwave ceramics?LTCC?have become the international focus in these fields.They have also been a bottleneck technology for the realization of the passive phased array radar and antimissile systems.So far,it has been still unsolved in the low temperature co-fired ceramics technology?900 °C?of the gyromagnetic spinel ferrites applied in microwave and millimeter-wave bands,especially how to ensure a high saturation magnetization,a low ferromagnetic resonance linewidth,and a high remanence square ratio in the low temperature co-fired ferrites.In fact,it is still a challenge in our era.Meanwhile,it is also the most fundamental scientific problem in how to turn the low temperature co-sintered powders into gyromagnetic rawmaterial belts and integrated devices capable of application.This dissertation has been carried out for the international difficulties and technical bottlenecks of science and technology,as follows:Firstly,LiZnTi(Li_0.43Zn_0.27Ti_0.13Fe_2.17O₄)ferrites doped with a small amount of?0.35 wt.%-1.5 wt.%?H₃BO₃-Bi₂O₃-SiO₂-ZnO?BBSZ?glass were synthesized through a low temperature ceramic sintering process.BBSZ glass promoted grain growth via liquid phase sintering,and the optimum addition of BBSZ could reduce porosity of the samples.Meanwhile,selected parameters including saturation induction?Bs?,coercivity?Hc?and ferromagnetic resonance linewidth??H?were measured as functions of doping content,and their relationships with ferrite porosity and microstructure were also discussed.The addition of proper content of BBSZ glass can not only improve Bs,but also reduce Hc and ferromagnetic resonance linewidth??H?by low temperature?880⁹20 °C?liquid phase sintering.The sample sintered at 920 °C with 0.5 wt.% BBSZ glass addition exhibits a saturation induction of 340 mT,a coercivityof 104 A/m,a remanence square ratio of larger than 0.92 and a ferromagnetic resonance?FMR?linewidth??H?of about 158 Oe,suggesting that it is promising for LTCC phase shifters.Secondly,the effects of Li₂O-B₂O₃-SiO₂-CaO-Al₂O₃?LBSCA?glass on the microstructure evolution and gyromagnetic properties of low-temperature sintered Li Zn Ti ferrites were systematically investigated.The results revealed that the densification process of the samples was sensitive to the LBSCA glass content,and low LBSCA glass content was a precondition for sufficient densification,grain growth and magnetic and gyromagnetic properties.The ferromagnetic resonance?FMR?linewidth??H?was explained on the basis of spin wave theory of anisotropy and porosity broadening in polycrystalline materials,which helped to get the theoretical and experimental verification for a low magnetic loss.The sample sintered at 900 °C with 0.7 wt.% LBSCA glass addition exhibits a saturation magnetization of 65 emu/g,a coercivity of 170 A/m,a remanence square ratio of larger than 0.82 and a ferromagnetic resonance?FMR?linewidth of 168 Oe,suggesting that it is promising for LTCC phase shifters.Thirdly,a modified low-temperature liquid phase sintering technique was used to fabricate Li_0.43Zn_0.27Ti_0.13Fe_2.17O₄ ferrites.Fixed amount of Li₂O-B₂O₃-SiO₂-CaO-Al₂O₃?LBSCA?glass?0.3 wt.%?was added to Li_0.43Zn_0.27Ti_0.13Fe_2.17O₄ powders to decrease the sintering temperature below 950 °C,while the addition of Bi₂O₃ oxide contributed to optimizing the microstructure and densification and improving the magnetic and gyromagnetic properties.We have discussed the influence of the co-doping of LBSCA glass and Bi₂O₃ oxide on the microstructure evolution,magnetic and gyromagnetic properties of LiZnTi ferrite ceramicsas well as the relation between the microstructure and porosity and the physical parameters.The sample resintered at 940 °C with co-doping of 0.3 wt.% of LBSCA glass and 0.03 wt.% of Bi₂O₃ presented excellent magnetic and gyromagnetic properties of = 73.32 emu/g,= 120 A/m and ?H = 163 Oe,suggestingthat it is promising in the LTCC phase shifter fabrications.Fourthly,NiZn ferrite nanoparticles?2-20 wt.%?of composition Ni_0.4Zn_0.6Fe₂O₄ were introduced into Li ZnTi ferrite of composition Li_0.42Zn_0.27Ti_0.11Fe_2.2O₄ and sintered at a temperature of 920 °C for 2 h,well below that of the Ag melting point.Here,Li ZnTi ferrites were prepared by a solid-state reaction method,and NiZn ferrite nanoparticles were fabricated by a hydrothermal chemical technique.Low FMR linewidth,low coercivity and high magnetic moment were achieved after refining the heat treatment conditions of the mixture.Riveted full profile refinement of the X-ray powder diffraction patterns and analysis of M?ssbauer spectrawere employed to study the structure and captions distribution,while a chemical model of ions' partial substitution in?A?,[B] sites of Li ZnTi ferrites and Ni Zn ferrites was proposed and validated.The variation of physical parameters with the content of NiZn ferrite nanoparticles further confirmed the chemical model.The appropriate amount of NiZn ferrite nanoparticles contributed to improving the saturation magnetization,and decreasing the coercivity and ferromagnetic resonance linewidth.A narrow FMR linewidth of 152.5 Oe,reduced coercivity of 132.9 A/m and improved saturation magnetization of 74.23 emu/g were obtained by way of the addition of 8 wt.% NiZn ferrite nanoparticles.Therefore,the composite ferrite materials are promising in LTCC devices such as phase shifters,filters,and antenna substrates.Finally,V₂O₅ and Sb₂O₃ oxides were co-doped into the crystal structure of Li_0.43Zn_0.27Ti_0.13Fe_2.17O₄ ceramics fabricated by a solid-state reaction method.Here,Li Zn Ti ferrites doped with a small amount of V₂O₅ and Sb₂O₃ oxides could be well densified below 920 °C with excellent magnetic and gyromagnetic properties.XRD Rietveld refinement analyses proved that most of V⁵⁺ ions substituted Fe³⁺ ions from the?A?sites while most of Sb3+ ions substituted Ti⁴⁺ ions from the [B] sites within x?0.010.In the range composition of 0.020?x?0.040,part of V⁵⁺ ions substituted Fe³⁺ ions from the?A?sites leading to the creation of Fe²⁺ ions,meanwhile,part of Sb³⁺ ions substituted Fe³⁺ ions from the [B] sites,resulting in the occurrence of ?-Fe₂O₃ phase.A narrow FMR linewidth of ?150.6 Oe,a tremendously enhanced saturation induction of ?470 mT,a remanence square ratio of ?0.86 and an optimized coercivity of ?174 A/m were obtained in the Li0.43Zn0.27Ti0.11VxSbxFe2.17O4?x = 0.010?ceramics.The ceramic materials therefore are very promising in LTCC phase shifter applications.