Development of silver–metal oxide reactive air braze alloys for electroding PZT ceramics

Existing multi-layer devices using lead-based piezoelectric ceramics utilize an internal electrode that does not bond the ceramic layers. Improvements in device performance and processing could be gained if the electrode also acted as a bond between the ceramic layers. In the current work, the feasibility of brazing lead zirconate titanate (PZT) in ambient conditions utilizing silver-based alloys containing low melting temperature metal oxides was investigated. Wettability, joint fracture strength, and microstructural analyses were conducted for various PZT/silver–metal oxide systems. The metal oxide additions included copper (II) oxide, vanadium pentoxide, lead (II) oxide, and eutectic lead oxide-titanium (IV) oxide. The silver–copper oxide (Ag–CuO) system demonstrated the most potential; exhibiting an apparent contact angle of approximately 64° and an average braze joint fracture strength that was approximately 62% of the monolithic PZT strength. In addition, no significant reaction product formation was observed at the silver/PZT interface. However, a preliminary investigation of multi-layer devices electroded with Ag–CuO alloys indicated a decrease in the resistivity of the brazed PZT by several orders of magnitude.