Mixed “cobalt-nickel” layered oxides and oxyhydroxides of n = 2 members of the Ruddlesden–Popper family Sr2.5La0.5Co1.3Ni0.7(O,OH)7−y

Abstract

The crystal structure, transport and magnetic properties of Sr_2.5La_0.5Co_1.3Ni_0.7O_6.4 and Sr_2.5La_0.5Co_1.3Ni_0.7O_x(OH)_y·zH₂O samples are detailed. Contrary to the first compound, the second one is not strictly speaking a second member of the well-known Ruddlesden–Popper (RP) series, but it exhibits very close relationships. Indeed, due to topotactical reactions with air (hydrolysis and hydration), water molecules are included within the rock salt layer of the “perfect” RP oxide, Sr_2.5La_0.5Co_1.3Ni_0.7O_6.4, to form the hydrated oxyhydroxide phase presented in this paper. Cationic homogeneity of the samples was confirmed by energy dispersive spectroscopy analyses performed with a transmission electron microscope. The crystal structure of samples was determined by combined refinements of powder X-ray and electronic diffraction data. Physical properties of compounds are discussed, for instance the hydrated compound and the “perfect” RP oxide both exhibit typical magnetic frustrated systems and no long range order prevails at low temperature. Transport property measurements reveal a semi-conducting behavior for Sr_2.5La_0.5Co_1.3Ni_0.7O_6.4. Finally, relationships between structure and physical properties are described herein.