Impact of transient liquid phase on the cold sintering of multiferroic BiFeO3

Cold sintering of perovskite materials is still, despite years of research, challenging. The key objective when cold-sintering oxide materials is finding an appropriate liquid phase that triggers pressure-dissolution process and mechano-chemical compaction and densification of ceramics. In this study, cold sintering of the multiferroic BiFeO3 perovskite is reported for the first time. When organic additives or solvents are used, these effectively sinter the compound, but cause precipitation of secondary phases that impede grain-to-grain contacts and the polarization coupling, and result in electrically conductive samples. We found that it is critical to carefully select the sintering additives based on their reactivity, decomposition temperature and products, while ensuring a significant level of wettability and matrix solubility. NaOH/KOH mixture was found to be the best sintering aid, resulting in remanent polarization and strain responses of cold-sintered BFO comparable to those reported for conventionally sintered ceramics.