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A systematic evaluation of the electrical conductivity of Sr-substituted YAlO3 system has been performed. A comparison between the Ca- and Sr-doped YAlO3 systems is reported. The samples have been synthesized by citrate gel route, and the electrical conductivity measurements have been conducted in air in the 300–800 °C temperature range. The influence of phase development of the compositions on the total conductivity has been investigated using the x-ray diffraction technique. Also, the effect of microstructure and composition of the phases evolved on the electrical conductivity has been analyzed using scanning electron microscopy and energy dispersive spectrum techniques. I. INTRODUCTION

The quest for a novel electrolyte for solid oxide fuel cells (SOFCs) has been a prime concern for researchers over the past few decades.1,2,3,4 Ceramic oxides based on various crystal structures have been explored for their suitability as electrolytes in SOFCs.5,6,7 Perovskite-type Sr- and Mg-doped lanthanum gallate (LSGM) is a new electrolyte material with high conductivity suitable for intermediate temperature solid oxide fuel cells.8 Divalent cation-doped LaGaO3 composition exhibits a conductivity of about 0.16 S/cm at 800 °C. This value is higher relative to the conductivity of yttria-stabilized zirconia, which is about 0.034 S/cm at 800 °C.9 Compared to CeO2-based electrolytes, the electrolytic domain of doped LaGaO3 extends to substantially lower oxygen chemical potentials. However, doped LaGaO3 system suffers from several disadvantages, namely, the high cost of gallium, reduction of gallium to lower valance states, vaporization of gallium, formation of secondary phases, lower mechanical strength, and significantly high reactivity with other components of the cell.10,11,12,13. In search of alternate electrolyte materials with relatively low cost, moderate thermal expansion, and higher stability with respect to reduction and volatilization compared to doped CeO2
d and LSGM, doped perovskite-based aluminates such as LnAlO3 have been investigated.14 In particular, the electrical properties of LaAlO3 have been investigated by several researchers, and the material is a potential candidate to overcome these limitations due to its stability and cost-effectiveness.15,16 The electrolyte, with different kinds of dopants either on the A- or on the B-site, is a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.197 J. Mater. Res., Vol. 27, No. 15, Aug 14, 2012

a mixed ionic and p-type electronic conductor at high oxygen partial pressures and ionic conductor at low partial pressures.17 It has been reported that Nd0.9Ca0.1AlO2.95 exhibits a rather high oxygen ion conduction and high transference number of oxide ions over a wide range of oxygen partial pressures.18 Electrical conductivity of SmAlO3 substituted by Ni, Mg, or Zn ions on Al site has been measured as a function of temperature and oxygen partial pressure. From the oxygen partial pressure dependence of electrical conductivity, SmAl0.95