Influence of Sintering Additive on the Electrical Conductivity, Chemical Stability and Sinterability of BaCe0.55Zr0.3Y0.15O3-δ

Ceramic proton conductors have regarded as an electrolyte materials for the next-generation intermediate-temperature solid oxide fuel cell (IT-SOFC) due to their lower activation energy than oxygen ion conductor in its operating condition. Among those candidates, Ba based perovskite-structured materials such as Yttrium doped BaCeO₃ and BaZrO₃ are frequently used because of their high proton conductivity. In addition, a discovery of BaCeO₃-BaZrO₃ solid solution (BCZYs) providing an acceptable compromise between chemical stability and proton conductivity consolidates its recognition as a promising electrolyte material. However, due to the refractory nature of BCZYs, a detrimental in electrical conductivity caused by an inevitable barium deficiency from the high temperature sintering, prohibits its practical utilization, and thus, many of studies were devoted to reduce sintering temperature of BCZYs. Recently it was reported that, even though the exact mechanism was not understood yet, the addition of some transition metal oxide such as nickel oxide, zinc oxide and copper oxide gives a tremendous enhancement in sintering of BCZYs. Moreover, sintering aid-assisted sintered BCZYs have some similarity in resulting feature such as reduced bulk electrical conductivity and enhanced chemical stability which has been expected due to barium deficiency in BCZYs. Recently, solid state reactive sintering (SSRS) in which synthesis and sintering of BCZYs occurs at the same time by employing nickel oxide as a sintering aid, was reported. According to their study, barium deficiency was induced by the formation of barium-transition metal compound (BaY₂NiO₅) consequently acting as a sintering aid during sintering. Therefore, addition of extra sintering aid with a form of BaY₂NiO₅ on BCZYs is supposed to be more efficient to prevent barium deficiency. Hence, in order to compare the effect of different form of sintering additives, we investigate the electrical conductivity, chemical stability and sinterability of BaCe_0.55Zr_0.3Y_0.15O_3-δ with various types of nickel oxide additives (simple oxide form, NiO and compound form, BaY₂NiO₅) via dilatometery, DC 4-probe, EIS, XRD and TG/DSC analysis. In this presentation, in addition to the experimental results, possibility and limitation of compound form of sintering aid will be also discussed.