Blocking effect in promising proton conductors based on Ba3Ca1.18Nb1.82-xRxO9-d (R = Y3+, Gd3+, Sm3+, Nd3+) ordered perovskites for PC-SOFCs

Reference	Presenter	Authors (Institution)	Abstract
06-156	João Elias F. S. Rodrigues	Rodrigues, J.E.(Universidade de São Paulo); Francisco, L.H.(Universidade de São Paulo); Correr, W.R.(Universidade de São Paulo); Hernandes, A.C.(Universidade de São Paulo);	High proton conductivity and good chemical stability are keys to development of new electrolytes for PC-SOFCs as the next-future energy generation systems. However, the extensive use of new polycrystalline materials as solid electrolytes is still avoided, since the grain boundary response usually leads to a decreased total conductivity. The grain boundary acts as blocking surface that limits the achievement of high proton conductivity, opening up opportunities for studies on the intrinsic origin of the blocking effect in novel proton conducting materials. Here we present our results on the space-charge modeling of the impedance spectroscopy data obtained for Ba${}_3$Ca${}_{1.18}$Nb${}_{1.82-x}$R${}_{\mathit{x}}$O${}_{9-\delta }$ proton conductor ceramics, where $x$ = 0, 0.30 and R = Y${}^{3+}$, Gd${}^{3+}$, Sm${}^{3+}$, Nd${}^{3+}$ are doping agents. Non-stoichiometric barium calcium niobate perovskites have received much attention as potential solid electrolytes for proton conduction solid oxide fuel cells. We show that the doped ceramics have increased grain conductivity and their Schottky barriers are higher than that for undoped Ba${}_3$Ca${}_{1.18}$Nb${}_{1.82}$O${}_{9-\delta }$. In view of the space-charge model, the proton depletion in the space-charge layer is the reason for the reduction of the grain boundary conductivity in the doped compositions. Our findings are important in understanding proton conduction mechanism and in optimizing new doped electrolytes based on barium calcium niobate perovskites.
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