The Chemical Interaction of Silver-Palladium Alloy Electrodes with Bismuth-Based Piezomaterials

摘要

Multilayer technology relies heavily on the chemical compatibility of metal and ceramic. This work focuses on the ceramic-electrode interaction between 92Bi_(0.5)Na_(0.5)TiO_3-6 Ba TiO_3-2K_(0.5)Na_(0.5)NbO_3 [(Bi_(0.46)Na_(0.47)Ba_(0.06)K_(0.01))(Nb_(0.02)Ti_(0.98)) O_3], a promising actuator material and forerunner to an emerging class of lead-free actuator materials, and a silver-palladium alloy for inner electrodes, the only currently viable material for the firing temperatures necessary (1100℃). Of special concern was the high content of bismuth in the ceramic since prior investigations suggest that Bi_2O_3 (as well as various bismuth ti-tanates) used as a fluxor in electroceramics are prone to forming the intermediate-phase bismuth palladate (Bi_2PdO_4), which can lead to poor contacting and delamination of multilayer stacks. Remarkably, no evidence of bismuth palladate formation could be found. However, the phase relations of the bulk ceramic have proven to be quite complex. Potassium was being drained out of the bulk ceramic either constituting the secondary phase K_4Na_2(TiO_3)_3 in unmodified experiments or evaporating and being replaced by silver in samples in contact with Ag. Mechanisms for the formation of these phases or the lack thereof are proposed. These findings were obtained by XRD, TG-DSC, and SEM with EDX, and LA-ICPMS.