Effect of sintering parameters on silver diffusion of (Zn, Mg)TiO3 based multilayer ceramic capacitors

In this study, the effects of heating rate and two-step sintering on the sintering behaviour, the microstructure and the silver diffusion of (Zn, Mg)TiO3 based multilayer ceramic capacitors (ZMT MLCCs) with pure silver electrodes were investigated. The energy dispersive spectroscopy results showed that the silver ions diffused into the dielectric layer significantly when ZMT MLCC was sintered directly up to 900 degrees C with a fixed heating rate (conventional sintering). However, ZMT MLCC was presintered (first step sintering) at 600-800 degrees C then sintered at 900 degrees C (second step sintering); it was found to effectively suppress silver ion diffusion into the dielectric layer. For example, the concentration of silver ions was identified by energy dispersive spectrometer, and both the Ag ion concentrations for conventional and two-step sintering are 2 and 0.1 at-% respectively. In addition, SEM observations showed that the silver electrode of ZMT MLCCs was greatly discontinuous by conventional sintering. Unlike the two-step sintering, this result shows that the silver electrode of ZMT MLCCs was completely discontinuous. To prove the effect of silver ion diffusion on the insulation resistance of ZMT MLCCs, the insulation resistance under different sintering conditions was measured at 85 degrees C and 95% relative humidity atmosphere. The insulation resistance of ZMT MLCCs with conventional sintering was degraded obviously, which was compared with that with the two-step sintering.