abstract
The oxygen deficiency of iron-substituted nickelates Ln(4)Ni(2.7)Fe(0.3)O(10-delta) (Ln = La, Pr) with the orthorhombic Ruddlesden-Popper structure was Studied by thermogravimetric analysis and coulometric titration in the oxygen partial pressure range 6 x 10(-5) to 0.7 atm at 973-1223 K. In air, the non-stoichiometry values vary in the relatively narrow ranges (2.4-4.2) x 10(-2) for La- and (0.01-2.0) x 10-2 for Pr-containing compositions, increasing with temperature. Due to the smaller size of praseodymium cations, Pr4Ni.7FeO.3010-6 exhibits a substantially lower thermodynamic stability in comparison with La4Ni2.7Fe0.3O10-delta and La4Ni3O10-delta, although the oxygen content in Pr4Ni2.7Fe0.3O10-delta lattice is higher. The partial substitution of iron for nickel has no essential effect on the low-p(O-2) stability limit corresponding to the transition of Pr4Ni3O10-delta into K2NiF4-type Pr2NiO4+delta. On the contrary, doping of La4Ni3O10-delta with iron decreases the oxygen vacancy concentration and shifts the phase stability boundary towards lower oxygen chemical potentials, suggesting a stabilization of the transition metal-oxygen octahedra in lanthanum nickelate lattice. The Mossbauer spectroscopy showed that the predominant state of iron cations, statistically distributed between the nickel sites, is trivalent. (c) 2007 Elsevier Inc. All rights reserved.
keywords
NI-O SYSTEM; K2NIF4-TYPE STRUCTURE; TRANSPORT-PROPERTIES; NEUTRON-DIFFRACTION; OXIDES; TEMPERATURE; CONDUCTORS; STABILITY; PHASES; CO
subject category
Chemistry
authors
Tsipis, EV; Patrakeev, MV; Waerenborgh, JC; Pivak, YV; Markov, AA; Gaczynski, P; Naumovich, EN; Kharton, VV
our authors
Vladislav Kharton
Invited Principal ResearcherGroups