Microstructural evolution and growth behavior of Bi5Ti3FeO15 whiskers in the lithium ferrite joints with different Ti substitution

The Bi2O3-B2O3-SiO2-ZnO glass was used to join Li-Ti ferrites with three different Ti substitutions. The microstructural evolution and the resulting mechanical strength of the joints were systematically investigated. Needle-like, strip-like, rob-like and plate-like Bi5Ti3FeO15 phases were observed within the joint domain. The Ti concentration gradient decreased as the Ti substitution increased. A sufficiently pronounced Ti concentration gradient promotes the Bi5Ti3FeO15 nucleuses grow into whiskers along the c-axis orientation. The orientational distribution of Bi5Ti3FeO15 whiskers is consistent with the Ti concentration gradient. When the Ti concentration gradient is small enough, the Bi5Ti3FeO15 nucleuses evolve into plates due to a preferential growth of the ab crystalline plane of Aurivillius compounds. The resulting distribution of Bi5Ti3FeO15 plates is random. The layered Bi5Ti3FeO15 strip or rob phase represents a transition from a whisker to a plate. The Bi5Ti3FeO15 whiskers offer a better joint strength enhancement effect when compared with the Bi5Ti3FeO15 strips or robs.