Crystal structure and physical properties of microwave sintered Sr1−xLaxFe12−xCuxO19 (x=0–0.5) ferrites for LTCC applications

Abstract

The Sr1−xLaxFe12−xCuxO19 (x=0–0.5) ferrites for use in low temperature co-fired ceramics (LTCC) technology were prepared by improved solid phase method. Dependence of their crystal structure, magnetic, electrical, and dielectric properties on La–Cu substitution amount were investigated. Pure M-type phase is obtained for the ferrites with La–Cu substitution amount x≤0.3. With x further increasing to 0.5, the multiphase structure is formed, where the M-type phase coexists with the LaFeO3 phase and Sr2FeO4−x phase. In single M-type phase region with x≤0.3, the varied magnetic properties can be well explained considering the occupancy effects of La3+ and Cu2+ ions in magnetoplumbite structure. Their electrical transport behavior is found to be correlated with La–Cu substitution amount. Single metal–semiconductor (M–S) transition is clearly observed in the ferrites with a high doping amount as x=0.3. The polarization behavior from 1kHz to 10MHz follows the charge polarization mechanism, and the temperature dependence of real permittivity (ε′–T curves) and dielectric loss (tgδ–T curves) strongly suggests the complicated multiparticle polarization and relaxation.