Proton-conducting BaCe0.5Zr0.3Ln0.2O3-δ (Ln = Yb, Gd, Sm, Nd, la or Y) ceramics for solid oxide fuel cell applications: Effects of acceptor-doping on microstructure, thermal and electrical properties

Abstract

Six materials belonging to Ln-doped BaCeO3-BaZrO3 system (Ln = Yb, Y, Gd, Sm, Nd, La) are prepared and characterized in the present work. The impact of the type of the acceptor dopant on (i) the microstructure (relative density, size and type of grains), (ii) the thermal properties (linear expansion, thermal expansion coefficient) and (iii) the electrical properties (nature and value of conductivity) is identified. The modified citrate-nitrate combustion synthesis method is adopted in order to achieve single-phase ceramic samples with relative density higher than 94% at reduced sintering regime (1450°C for 5 h). It is found that: i) the mean grain size increases (from 1.4 to 3.8 μm), ii) the thermal expansion coefficient tends to growth (from 7.610-6 to 11.310-6 K-1 in the high temperature range), iii) the ionic conductivity decreases (from 10.2 to 0.3 mS cm-1 at 800°C) with increasing ionic radius of acceptor Ln-dopant. It is also found that BaCeZr0.3Y0.2O3-δ electrolyte can be considered as the most optimal one for IT-SOFC applications from the view point of electrical properties. However, in the temperature interval of 550-700°C, this sample possesses non-uniform thermal expansion.