Microstructure evolution and properties of dielectric magnesium titanate ceramic joints fabricated with bismuth glasses

Bismuth glasses with different Bi₂O₃ and ZnO contents (designated as Bi15, Bi25, Bi36) were designed to investigate the interfacial microstructure evolution of magnesium titanate ceramic (MTC) joints. The mechanical and dielectric properties of joints were also studied. (Zn,Mg)₂TiO₄ layer formed at the interface by the substitution reaction of Zn. Bi₄Ti₃O₁₂ blocks generated at the interface of Bi15 glass seam due to low Bi₂O₃ content, while Bi₄Ti₃O₁₂ whiskers formed at the interface of Bi25 glass seam owing to the concentration gradient of Ti. Small Bi₄Ti₃O₁₂ plate-like phases formed with a high concentration of [BiO₆] and Ti, dispersing in the Bi36 glass seam. Rod-like MgSiO₃ were produced at the interfaces of all glass seams. Besides, MgO phases formed in the Bi36 glass seam, owning to the increase of O²⁻ concentration. The shear strength of MTC/Bi36/MTC joints reached a maximum of 86.1 MPa under a combined effect of excellent matching and strengthening of small rod-like MgSiO₃ and plate-like Bi₄Ti₃O₁₂. The dielectric and microwave dielectric properties were evaluated by the impedance analyser and the vector network analyser. The dielectric characteristics of MTC joints were similar to those of MTC base material. The microwave dielectric loss tangent of MTC joints was less than 0.09.