Microstructure and magnetic properties of low-temperature sintered CoTi-substituted barium ferrite for LTCC application

In this article, the influences of the BaCu(B2O5) (BCB) additive on sintering behavior, structure and magnetic properties of iron deficient M-type barium ferrite Ba(CoTi)xFe11.8−2xO19 (BaM) have been investigated. It is found that the maximum sintered densities of BaM change from 86% to 94% as the BCB content varies from 1 to 4 wt%. Single-phase BaM can be detected by the XRD analysis in the sample with 3 wt% BCB sintered at 900 °C, and the microstructure is hexagonal platelets with few intragranular pores. This is attributed to the formation of the BCB liquid phase. Meanwhile, the experimental results illuminate that the CoTi ions prefer to occupy the 4f2 and 2b sites and the magnetic properties depend on the amount of CoTi-substitution. In addition, the chemical compatibility between BaM and silver paste is also investigated; it can be seen that BaM is co-fired well with the silver paste and no other second phase is observed. Especially, the 3 wt% BCB-added Ba(CoTi)0.9Fe11O19 sintered at 900 °C has good properties with the sintered density of 4.9 g/cm3, saturation magnetization of 49.7 emu/g and coercivity of 656.6 Oe. These results indicate that it is cost effective in the production of Low Temperature Co-fired Ceramics (LTCC) multilayer devices.

Research highlights
► Systematic investigation on the ion substitution and low-temperature sintering of barium ferrite.
► BaCu(B2O5) is first successfully used to lower the sintering temperature of barium ferrite.
► Densification of BaFe12O19 was speeded up by the BaCu(B2O5) liquid phase.