Interfacial Structure Evolution and Co-Firing Compatibility in BTN/NZF Laminated Ceramics

A critical challenge in developing multifunctional ceramic components is the integration of different functional units, which necessitates solving the problem of co-firing incompatibility between dissimilar ceramics. Here, warpage-free and crack-free Ba₃Ti₄Nb₄O₂₁ (BTN) ceramic/Ni0.6Zn0.4Fe1.98O₄ (NZF) ferrite laminates with strong interfacial bonding were successfully co-fired using the solid-state reaction method. The co-firing compatibility was achieved by investigating the sintering shrinkage behavior of NZF ferrites with different particle sizes while preserving the magnetic properties of NZF. The internal stress distribution within the heterostructure was analyzed via finite element simulation, which indicated that BTN and L-NZF (with a relatively large particle size) possess excellent co-firing matchability. Moreover, the phase composition, elemental distribution, and microstructure of the BTN/L-NZF interface were systematically investigated, and the reaction zone induced by direct co-firing was identified. The results demonstrate a tightly bonded interface with minimal elemental interdiffusion. A thin (18.6 nm) M-type barium ferrite (BaM) interphase layer formed at the interface due to the reaction between BTN and L-NZF, which significantly strengthened the interfacial adhesion through the introduction of semicoherent interface at the initially incoherent boundary. Ion interdiffusion was suppressed by the BaM layer. Among the ions, Fe³⁺ diffused the farthest but with a limited distance of only 63 nm, which did not noticeably affect the dielectric properties of BTN. This work demonstrates the potential of BTN/NZF for multilayer devices such as filters and offers an approach to tailoring interfacial properties in co-fired ceramics.