Synthesis, crystal Chemistry and physical properties of the Ruddlesden-Popper phases Sr3Fe2-xNixO7-d ( 0< x<1)

MOGNI, L.; PRADO, F.; ABBATE, M.; MORENO, M.S.; MANTHIRAM, A.; CANEIRO, A.

JOURNAL OF SOLID STATE CHEMISTRY

Elsevier

Año: 2005 vol. 178 p. 1559 - 1568

0022-4596

The crystal chemistry, electronic structure, and electrical and magnetic properties of the novel perovskite-related nickel oxides Sr3Fe2-xNixO7-d with 0 < x < 1.0 have been studied. X-ray diffraction and selected area electron diffraction (ED) data indicate that the samples have a tetragonal (Space group I4/mmm) structure. ED patterns and high-resolution images reveal the presence of a regular stacking along the c-axis for the x=1.0 sample. The lattice parameters, oxygen content, and average oxidation state of iron and nickel decrease with increasing Ni content. The electronic structure of the x=1.0 sample was studied by M 2p X-ray photoelectron spectroscopy (XPS). An analysis of the spectra using the cluster model indicates that this material is in the negative charge-transfer regime and the ground state is dominated by the 3dn+1L configuration with 2p holes (L) in the oxygen band. The insulator states are stabilized due to a p–p type band gap that arises because the p–d transfer integral T(sigma) dominates over the O 2p bandwith. Although magnetic measurements reveal the presence of ferromagnetic interactions that lead to magnetic frustration at T < 40 K, no long-range magnetic order was observed for the samples with x > 0.3. The electrical resistivity decreases with increasing Ni content as the p–p band gap tend to close due to the reduction of the T(sigma) value. Negative magnetoresistance (aprox. −24% for x=0.6 and -7% for x=1.0 at 20 K and 9 T) was observed for the Ni containing samples.