Low Temperature Sintering Of Y - Type Hexagonal Ferrite And Its Properties

Hexagonal ferrites with planar magnetic structure become an ideal material for the chip inductor because of its much higher cut-off frequency than that of the traditional spinel ferrites and exceptional magnetic properties in high frequency region. The soft magnetic materials used for multilayer chip inductor not only require excellent magnetic properties in high frequency, but also can co-firing with silver electrodes below950℃. Thus, hexagonal ferrites with low sintering temperature and high relative density are most important in high frequency multilayer chip inductor applications.Combined with the existing research results in our laboratory, we use chemical coprecipitation method to synthesis Y-type hexagonal ferrite precursor (Ba2Co0.4Zn1.0Cu0.6Fei2O22).Laser particle size analyzer (LPS), scanning electron microscopy (SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and Agilent E4991A RF Impedance/Material Analyzer were used to investigate the effect of reaction time on particle sizes, surface morphology, crystal structure, magnetic properties of the powders and sintered samples. The results show that, the precursor with90h coprecipitation reaction time has uniform particle size distribution, the average particle diameter has a value of about1μm. A near single-phase Y-type hexagonal ferrite was obtained after sintering at900℃. The sintered sample shows a relative density above95%, an initial permeability of3.7, a quality factor of5.8in the1GHz frequency, a resonant frequency above2.5GHZ and a cutoff frequency around3GHz.The precursor with90h coprecipitation reaction time was heat treated at different calcination temperatures (850～950℃) and sintering temperatures (900～950℃). Experimental results show that the sample calcined at850℃and sintered at950℃exhibits excellent electromagnetic properties with an initial permeability of3.65, a quality factor of132in the100MHz frequency. The sintered sample shows a relative density about94%, a dielectric constant of7.12, a dielectric loss(tanδ) at10-3magnitude in the30MHz frequency, and a DC resistivity of5.53×105Ω·mm at1MHz frequency. It was found that severe agglomeration occurred in the drying process of the precursors. We choose different washing systems for precursor slurry in order to suppress agglomeration. The results indicated that the solution of SDBS can suppress the agglomeration of powder during the washing and drying process, but has a bad effect on the formation of Y-phase due to the introducing of impurity ions. Using anhydrous ethanol replaced distilled water in the particle surface before the drying of the precursor slurry can reduce the agglomeration of the powder during the drying process and improve the dispersibility of the powder. A uniform fine powder can be obtained after drying. This method can also decrease the difficulty of grinding and sieving of the precursor powders greatly. The electromagnetic properties of the final sample have a certain improvement and will not affect the crystal structure of the sample.