Processamento e caracterização elétrica de perovisquitas hexagonais de ba5nb4o15 dopadas com titânio e zircônio

Abstract

Among the common materials used to produce solid oxide fuel cell’s (SOFC’s) electrolytes and electrodes areoxides with perovskite structures; they show desirable characteristics for this application, like good levels of ionic conduction. Nowadays, there are many different studies on this field, where developing new proton conduction materials to improve SOFC’s performance is one of them. Present work evaluated the viability of compound Ba5Nb4O15 (BNO) as a candidate to produce SOFC’s elements. This compound show a hexagonal perovskite structure and recent papers point this kind of structure is currently used can show some indications of proton conduction. At present study, it was evaluated BNO synthesis through an alternate method to solid-state reaction, based on Pechini method and using different oxides as precursors. Since there are many different processing routes to obtain this phase, it was compared sinterability of synthesized powders after pressing and sintering at two temperatures: 1400 and 1450ºC. The poisoning effect of titanium and zirconium on structure and electric properties was also studied. BNO phase was successful obtained in all synthesis, although non-stoichiometry phases were present on Pechini sample after first calcination; after sintering, these phases were no longer present though. A higher densification was obtained after milling synthesized powder previously to pressing: a bulk porosity smaller than 5% was achieved. Doping produce grain refinement, but it was not efficient improving electrical conductivity. However, sintered samples at 1450ºC had shown higher conductivity on humid atmosphere (H2O) than presented on heavy water atmosphere (D2O). This could be an indication of proton conductionin this structure. Keywords: proton conduction, hexagonal perovskites, Pechini method, solid oxide fuel cells.