Bonding Mechanisms of BTO-NZF Laminated Cofired Bodies Featuring High-Quality Heterojunctions

The shrinkage rate of Ni 0.6 Zn 0.4 Fe 1.8 O 4 (NZF) ferrite was controlled to enable cofiring with BaTiO 3 (BTO) at 1250 °C, forming BTO-NZF laminated structures. Postcofiring microstructural analysis revealed a well-bonded interface with minimal elemental interdiffusion. Notably, Ti 4+ exhibited the highest diffusion coefficient (1.60 ± 0.05 × 10 –12 cm 2 /s). Unidentified phases on the NZF side effectively restricted Ba 2+ and Ti 4+ diffusion. The BTO-NZF heterojunction consisted primarily of nanoscale amorphous layers containing Ba 2+ and coherent crystalline regions. The dense amorphous barrier layer not only ensured strong interfacial bonding but also significantly suppressed interdiffusion. High-quality heterojunction formation was influenced by four primary factors, including the presence of similar ionic radii and interplanar spacings, amorphous barrier layers, and a certain concentration of large-radius ions. Magnetic characterization showed that NZF had a saturation magnetization ( M s ) of 70.29 ± 0.50 emu/g, a coercivity ( H c ) of 8.89 ± 0.50 Oe, and a remanent magnetization ( M r ) of 1.01 emu/g. The relative dielectric constant (ε r ) of BTO ranged from 1490 to 2500 (at 1 MHz), while the dielectric loss tangent (tanδ) varied between 4 × 10 –3 and 1.25 × 10 –2 . These findings offer valuable guidance for selecting cofired laminated substrates and designing high-performance heterojunctions. Moreover, the resulting cofired laminates exhibit excellent electromagnetic properties, demonstrating strong potential for magnetoelectric coupling applications.