Overcoming the sensitivity of sodium bismuth titanate towards sintering in a reducing atmosphere by defect chemistry engineering

There has recently been a surge in demand for lead-free multilayer ceramic actuators and capacitors. A central concern has been controlling manufacturing costs, primarily attributed to the use of precious metal electrodes, such as Pt, Pd, and Ag, as internal electrode materials. To address this challenge, the incorporation of base metal electrodes such as Cu and Ni has emerged as a desirable option. For these electrode materials to be utilised successfully, the co-sintering of both the electrode and dielectric must take place within a lower oxygen partial pressure (PO2) range. This step is crucial to prevent the oxidation of Cu or Ni electrodes. Sodium-bismuth-titanate (NBT)-based ceramics have proven to be excellent candidates for ferroelectric applications. However, NBT’s sensitivity to the formation of oxygen vacancies or reduction of Bi at lower
poses a significant challenge to achieving this goal. Consequently, in this research, donor dopants such as Nb, Ta, V, Wo, and Mo were used to induce the pinning of defect levels. The results showed that Nb and Ta help suppress the formation of oxygen vacancies and increase the phase stability during sintering in low PO2 whereas V, Wo, and Mo failed to do so. Without Nb and Ta, NBT becomes conductive (three orders of magnitude higher) when sintered in low PO2 and its polarization and strain are severely suppressed. The modified NBT retains its electrical properties and is therefore an excellent candidate for co-sintering with Cu.