Oxygen nonstoichiometry and magnetotransport properties of Sr-2(Y1-xCax)Co2O7+delta cobalt oxides

摘要

Tunability of oxygen nonstoichiometry of the Co-based Ruddlesden-Popper phase, Sr-2(Y1-xCax)CO2O7+delta, has been investigated using single-phase samples obtained by means of solid-state synthesis within 0.3 less than or equal to x less than or equal to 0.5. With cerimetric titrations and thermogravimetric measurements carried out in O-2 and Ar atmospheres, it is found that wide-range oxygen tuning is possible over the whole range of cation stoichiometry, 0.3 less than or equal to x less than or equal to 0.5. The minimum oxygen content corresponds to delta approximate to -1.2 for all the samples (with 0.3 less than or equal to x less than or equal to 0.5), while the maximum amount of oxygen loaded in the structure upon 1 atm O-2 annealing increases as x decreases, reaching delta = -0.52 at x = 0.3. The change in oxygen nonstoichiometry is reflected in the magnetic and magnetotransport properties of the phase. A small magnetoresistance effect (up to similar to3.5) is revealed for the oxygenated samples at low temperatures. (C) 2004 Elsevier B.V. All rights reserved.