ИСТИНА

Solid Oxide Fuel Cells (SOFCs) are considered as one of the alternative to traditional hydrocarbons sources of energy due to their high efficiency and excellent fuel flexibility [1]. They are operating at high temperature up to 1273 K and this creates numerous problems such as chemical stability, matching of the thermal expansion coefficients (TEC) between the components of the SOFC etc. [2]. Therefore efforts are directed to the creation of the so-called intermediate temperature SOFC (IT-SOFC) with operation temperatures down to 773 K [3]. Recently layered cuprates have attracted attention for the application in high-temperature electrochemical devices. Although the high-temperature properties of the La2CuO4 are well studied, much less information is available for other Ln2CuO4 cuprates. However, one can expect that these compounds could be of interest since Ce-doped Nd2CuO4 with T’-structure was found to exhibit promising properties for SOFC cathode application [4]. High-temperature crystal structure of the layered cuprates Ln2CuO4, Ln=Pr, Nd and Sm with tetragonal T’-structure was refined using X-ray powder diffraction data. Substantial anisotropy of the thermal expansion behavior was observed in their crystal structures with thermal expansion coefficients (TEC) along a- and c- axes changing from TEC(a)/TEC(c) =1.37 (Pr) to 0.89 (Nd) and 0.72 (Sm). Temperature dependence of the interatomic distances in Ln2CuO4 shows significantly lower expansion rate of the chemical bond between Pr and oxygen atoms (O1) belonging to CuO2-planes (TEC(Pr-O1) =11.7 ppm K-1) in comparison with other cuprates: TEC (Nd-O1)=15.2 ppm K-1 and TEC (Sm-O1)=15.1 ppm K-1. High-temperature electrical conductivity of Pr2CuO4 is the highest one in the whole studied temperature range (298-1173K). The trace diffusion coefficient (DT) of oxygen for Pr2CuO4 determined by isotopic exchange depth profile (IEDP) technique using secondary ion mass spectrometry (SIMS) varies in the range 7.2*10-13 cm2/s (973K) and 3.8*10-10 cm2/s (1173K) which are in between those observed for the manganese and cobalt-based perovskites. References 1. B.C.H. Steele, A. Heinzel, Nature 414 (2001) 345-352. 2. H. Tu, U. Stimming, J. Power Sources 127 (2004) 284–293. 3. J. M. Ralph, A. C. Schoeler, M. Krumpelt, J. Mater. Sci. 36 (2001) 1161 – 1172. 4. M. Soorie, S.J. Skinner, Solid State Ionics 177 (2006) 2081–2086.