Compatibility of RuO sub(2) electrodes with PZT ceramics

Because of its high electrical conductivity and good diffusion barrier properties ruthenium dioxide (RuO sub(2)) is a good electrode material for use with ferroelectric lead zirconate-titanate (PZT) solid solutions. Under certain conditions, RuO sub(2) can react with PZT to form lead ruthenate (Pb sub(2)Ru sub(2)O sub(6& #x00B7; 5)) during processing at elevated temperatures resulting in lead depletion from PZT. The standard Gibbs energies of formation of RuO sub(2) and Pb sub(2)Ru sub(2)O sub(6&# x00B7; 5) and activities of components of the PZT solid solution have been determined recently. Using this data along with older thermodynamic information on PbZrO sub(3) and PbTiO sub(3), the stability domain of Pb sub(2)Ru sub(2)O sub(6&# x00B7; 5) is computed as a function of PZT composition, temperature and oxygen partial pressure in the gas phase. The results show PbZrO sub(3)-rich compositions are more prone to react with RuO sub(2) at all temperatures. Increasing temperature and decreasing oxygen partial pressure suppress the reaction. Graphically displayed are the reaction zones as a function of oxygen partial pressure and PZT composition at temperatures 973,1173 and 1373 K.