Investigating Phase and Electrical Properties of Calcium-Doped Yttrium Iron Garnet

Abstract

Literature studies have shown that Ca 0.5 Y 2.5 Fe 5 O 12-δ can be a promising cathode material for intermediate temperature solid oxide fuel cell (IT-SOFC) 1 . As it exhibits higher electrical and ionic conductivity compared to several other kinds of rare-earth garnets 2 . However, given the high resistivity (> 10 12 Ω cm at room temperature) and less-explored oxide ion conductivity of its parent phase yttrium iron garnet (Y 3 Fe 5 O 12 , YIG), the effect of calcium doping on the electronic and ionic properties has not been fully studied yet 3 . In this work, polycrystalline samples of Ca-doped YIG, with general chemical formula Ca x Y 3-x Fe 5 O 12-δ (x=0, 0.1, 0.3, 0.5 and 0.7), were prepared and phase characterized by powder X-ray diffractometer. The oxygen non-stoichiometry was determined by iodometric titration at room temperature and thermogravimetric analysis (TG) at elevated temperatures. Total electrical conductivity was measured by four-probe DC method, and ionic conductivity was calculated by using a modified Hebb-Wagner polarization method. As a result, the ionic transference number was calculated and discussed in relation to its potential applications. Reference: Zhong, W., Ling, Y., Rao, Y., Peng, R. & Lu, Y. Calcium doped Y 3 Fe 5 O 12 as a new cathode material for intermediate temperature solid oxide fuel cells. J. Power Sources 213, 140–144 (2012). Kharton, V. V. et al. Ionic Transport in Gd 3 Fe 5 O 12 - and Y 3 Fe 5 O 12 -Based Garnets. J. Electrochem. Soc. 150, J33 (2003). Lehmann-Szweykowska, A., Wojciechowski, R. J., Gehring, G. A. & Tobijaszewski, I. Quasiparticles in Calcium Doped Yttrium-Iron Garnets. Acta Phys. Pol. A 91, 423–426 (1997).