Tuning the high-temperature properties of Pr2NiO4+δby simultaneous Pr- and Ni-cation replacement

S. Ya. Istomin, O. M. Karakulina, M. G. Rozova, S. M. Kazakov, A. A. Gippius, E. V. Antipov, I. A. Bobrikov, A. M. Balagurov, A. A. Tsirlin, A. Michau, J. J. Biendicho, G. Svensson
2016 RSC Advances  
Novel Pr 2Àx Sr x Ni 1Àx Co x O 4AEd (x ¼ 0.25; 0.5; 0.75) oxides with the tetragonal K 2 NiF 4 -type structure have been prepared. Room-temperature neutron powder diffraction (NPD) study of x ¼ 0.25 and 0.75 phases together with iodometric titration results have shown the formation of hyperstoichiometric oxide for x ¼ 0.25 (d ¼ 0.09(2)) and a stoichiometric one for x ¼ 0.75. High-temperature X-ray powder diffraction (HT XRPD) showed substantial anisotropy of the thermal expansion coefficient
more » ... EC) along the a-and c-axis of the crystal structure, which increases with increasing the Co content from TEC High-temperature NPD (HT NPD) study of the x ¼ 0.75 sample reveals that a very high expansion of the axial (Ni/Co)-O bonds (75.7 ppm K À1 in comparison with 9.1 ppm K À1 for equatorial ones) is responsible for such behaviour, and is caused by a temperature-induced transition between low-and high-spin states of Co 3+ . This scenario has been confirmed by high-temperature magnetization measurements on a series of Pr 2Àx Sr x Ni 1Àx Co x O 4AEd samples. For compositions with high Ni content (x ¼ 0.25 and 0.5) we synthesised K 2 NiF 4 -type oxides Pr 2ÀxÀy Sr x+y (Ni 1Àx Co The studies of the TEC, high-temperature electrical conductivity in air, chemical stability of the prepared compounds in oxygen and toward interaction with Ce 2Àx Gd x O 2Àx/2 (GDC) at high temperatures reveal optimal behaviour of Pr 1.35 Sr 0.65 Ni 0.75 Co 0.25 O 4+d . This compound shows stability in oxygen at 900 C and does not react with GDC at least up to 1200 C. It features low TEC of 13 ppm K À1 and high-temperature electrical conductivity in air of 280 S cm À1 at 900 C, thus representing a promising composition for use as a cathode material in intermediate temperature solid oxide fuel cells (IT-SOFC).
doi:10.1039/c6ra03099h fatcat:6mfds7mzmnakpk234rbycjtfuu