Development of a lead-free copper co-fired BNT-based piezoceramic sintered at low temperature

Compatibility of Bi-based piezoelectric ceramic and copper electrodes is demonstrated by co-firing 0.88Bi(1/2)Na(1/2)TiO(3)-0.08Bi(1/2)K(1/2)TiO(3)-0.04BaTiO(3) (BNKBT88) with copper. A combination of Bi2O3, CuO, ZnO, Li2CO3, and B2O3 are used as additives to reduce firing temperature to 900 degrees C with minimal effect on the electromechanical properties compared to sintering at 1150 degrees C without additives. Co-firing with copper electrodes requires controlled oxygen sintering at low temperature. The atmosphere is controlled using carbon dioxide and hydrogen gas to maintain an oxygen partial pressure of 6.1x10(-8) atm, which is necessary for the coexistence of Cu metal and Bi2O3. The thermodynamic activity of bismuth oxide in BNKBT88 is calculated to be 0.38. BNKBT88 ceramics were successfully co-fired with internal as well as surface Cu metal electrodes. The copper co-fired ceramics were successfully polarized and the dielectric and piezoelectric properties are evaluated.