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

• Published in: Journal of electroceramics 2009-02, Vol.22 (1-3), p.227-232
• Main Authors: Kracunovska, S, Topfer, J
• Format: Article
• Language: English
• Subjects: Ceramics; Characterization and Evaluation of Materials; Chemistry and Materials Science; Composites; Crystallography and Scattering Methods; Dispersions; Electrochemistry; Ferrites; Glass; Inductors; Iron; Materials Science; Multilayers; Natural Materials; Optical and Electronic Materials; Permeability; Sintering
• ISSN: 1385-3449; 1573-8663
• DOI: 10.1007/s10832-007-9387-9

Co 2 Z-type hexagonal ferrites with iron excess Ba 3 Co 2 −  x Fe 24 +  x O 41 (0 ≤  x  ≤ 0.8) and deficiency Ba 3 Co 2 +  y Fe 24 −  y O 41 (0 ≤  y  ≤ 0.6) were prepared by an oxalate coprecipitation technique. This synthesis route leads to almost single phase Z-type ferrites for x  = 0 after calcination and sintering at 1330 °C. 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 0.4 ≤  x  ≤ 0.6 for samples sintered at 1330 °C. The frequency dispersion shows broad peaks of μ ″ stretching from 200 MHz to >1 GHz. For iron deficient samples 0 ≤  y  ≤ 0.6 multi-phase mixtures were obtained. For Ag-based multilayer inductor applications sintering at 950 °C is required. Co 2 Z ferrites with Fe excess are not stable at this temperature as demonstrated by XRD. The permeability of samples sintered at 950 °C 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.