The Research On Low-Temperature Sintering And Magnetic Properties Of Co₂Z-type Hexagonal Ferrites

Co₂Z-type hexaferrite with high initial permeability, high quality factor, high themal stablity and low loss tangent is a prominsing material for multilayer chip inductors (MLCIs) for very-high frenquency (300 Hz¹G Hz) application. But the sintering temperature of Co₂Z is sufficiently higher than 1250℃, which limits the use in MLCIs because so high sintering temperature is difficulty to co-fire with metal internal electode material of lower melting point. To low sintering temperatue of Co₂Z-type hexaferrite with excellent properties has been a key technology to make MLCIs for very-high frenquency application.To lower the sintering temperature of Co₂Z-type hexaferrite, we incorporated Co₂Z-type hexaferrite with B₂O₃, B₂O₂-Bi₂O₃ and Cu²⁺ ion respectively. And the effects of concentration of B₂O₃, B₂O₃-Bi₂O₃ and Cu²⁺ -substition on the densification, phase structure and magnetic properties of Co₂Z hexaferrite were investigated in this paper.The results show that the sintering temperature of Co₂Z-type hexaferrite could be decreased from 1250℃ to 1000℃ by incorporating with B₂O₃ only or by co-doping B₂O₃-Bi₂O₃ aids. The bulk density is 4.75 g/cm3 and relative density is 88.68% with 2.0wt% B₂O₃ dopant. The B₂O₃ aids was not reacte with Co₂Z by XRD identified, the M-type phase and the Z-type phase were co-existed in the sample when the B₂O₃ concentration <5.0wt% and the sintering temperature below 1000℃. By co-doping 3.0wt% B₂O₃-Bi₂O₃ aids with B₂O₃-Bi₂O₃ mol proportion is 1:4, the bulk density is 4.81 g/cm3 and relative density is 90%. When the B₂O₃-Bi₂O₃ mol proportion was changed from 1:4, 1:1 to 4:1 the main phase consists of the Z-type phase in the sample. By co-doping B₂O₃+xBi₂O₃(x=0.25¹.0wt%) aids, when x=0.75 wt% the bulk density is 4.93 g/cm3 and the relative density is up to 93%. The grains are typically of platelet morphology, fine and perfectly homogeneous by co-dopingB₂O₃-Bi₂O₃The effects of B₂O₃ concentration on the densification, phase structure and magnetic properties of Co_1.4Cu_0.6Z-type hexaferrite were investigated. The results show that Z-type phase and M-type phase were co-existed in the sample and the volume of M-type phase increased and initial permeability decreased with the increasing of B₂O₃ concentration. By incorporating with B₂O₃ and Cu²⁺-dopants the Co₂Z-type hexaferrite could be well sintered at 950℃ with bulk density of 5.02g/cm3, μ=2.5 and the relative density is up to 94%. These improvements make the material suitable for fabrication low-temperature sintering of Multilayer Chip Inductors for very-high frequency application.