Compatibility of RuO_2 electrodes with PZT ceramics

摘要

Because of its high electrical conductivity and good diffusion barrier properties ruthenium dioxide (RuO_2) is a good electrode material for use with ferroelectric lead zirconate-titanate (PZT) solid solutions. Under certain conditions, RuO_2can react with PZT to form lead ruthenate (Pb_2Ru_2O_(6.5)) during processing at elevated temperatures resulting in lead depletion from PZT. The standard Gibbs energies of formation of RuO_2 and Pb_2Ru_2O_(6.5) and activities of components of the PZT solid solution have been determined recently. Using this data along with older thermodynamic information on PbZrO_3 and PbTiO_3, the stability domain of Pb_2Ru_2O_(6.5) is computed as a function of PZT composition, temperature and oxygen partial pressure in the gas phase. The results show PbZr03-rich compositions are more prone to react with RuO_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.