Preparation, thermal stability and permeability behavior of substituted Z-type hexagonal ferrites for multilayer inductors

摘要

Co{sub}2Z-type hexagonal ferrites with iron excess Ba{sub}3Co{sub}(2-x)Fe{sub}(24+x)O{sub}41 (0≤x≤0.8) and deficiency Ba{sub}3Co{sub}(2+y) Fe{sub}(24-y)O{sub}41 (0≤y≤0.6) were prepared by an oxalate copre-cipitation technique. This synthesis route leads to almost single phase Z-type ferrites for x=0 after calcination and sintering at 1330 ℃. The Z-type formation is enhanced for x>0 and single phase ferrites are obtained for 0.4≤x≤0.8. The permeability of Z-type ferrites varies with composition x: Maximum permeability of μ'=28 is observed for 0.41 GHz. For iron deficient samples 0≤y≤0.6 multi-phase mixtures were obtained. For Ag-based multilayer inductor applications sintering at 950 ℃ is required. Co{sub}2Z ferrites with Fe excess are not stable at this temperature as demonstrated by XRD. The permeability of samples sintered at 950 ℃ is drastically reduced to Μ'=3. This demonstrates that these materials are not able to provide sufficient permeability for multilayer inductors for high-frequency operations since they are not compatible with the low temperature ceramic cofiring technology.