Microstructure and performance characterization of in-situ Co₂FeO₄ whiskers reinforced YIG/YIG joints

Bismuth-based glasses doped with different CoO contents were designed to realize the in-situ growth of Co₂FeO₄ whiskers in YIG/YIG joint. The microstructure, mechanical and dielectric properties of the joints were systematically investigated. The optimized processing joint with 23 mol% CoO doping, brazed at 725 °C for 15 min, under bonding pressure of 6 kPa was achieved. And the shear strength of joint reached a maximum of 72 MPa, which is attributed to the increased number and optimized spatial distribution of Co₂FeO₄ whiskers. The in-situ Co₂FeO₄ whiskers acted as effective hard phases in the glass matrix. The shear strength of YIG/YIG joint was enhanced by the crack propagation deflection and pulling out result from Co₂FeO₄ whiskers. The dielectric constant of YIG joints decreased from 16.2 to 15.3 at the frequency of 10 MHz, which is closer to that of the original YIG material with the CoO doping increasing. The dielectric loss tangent increased slightly with the growth of Co₂FeO₄ whiskers due to the hole hopping between Co³⁺⇔Co²⁺ ions. The effective bonding of YIG materials has broad application prospects for the integration of ferrite microwave devices.