Vapor diffusion of silver in cofired silver/palladium–ferroelectric ceramic multilayer

The mechanism of silver interfacial migration was investigated during cofiring multilayer structures of Pb-based relaxor ferroelectric ceramics and Ag/Pd alloy electrode. A several-micron depth of silver diffusion could be confirmed by energy dispersive X-ray spectroscopy measurements. Scanning electron microscopy and transmission electron microscopy observations indicated that the silver migration was not attributed to a single factor. This involved the electrode composition, the sintering characteristic of the ceramics, and the related sintering procedure. All these results have demonstrated that the vapor-phase diffusion via open pores on the surface of the ceramics at the early period of sintering was the most important reason for the silver migration even though the migration along grain boundaries or into grains occurs at the final stage of sintering. Based on an evaporation–condensation vapor-phase mass transport mechanism, a rate-controlled sintering process or a low-temperature sintering route of the materials was suggested to effectively inhibit the interfacial diffusion of silver.