Synthesis, crystal chemistry and physical properties of the Ruddlesden–Popper phases Sr3Fe2
xNixO7
d (0pxp1.0)

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

JOURNAL OF SOLID STATE CHEMISTRY

ACADEMIC PRESS INC ELSEVIER SCIENCE

Lugar: Amsterdam; 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 oxidesSr3Fe2xNixO7d with 0pxp1:0 have been studied. X-ray diffraction and selected area electron diffraction (ED) data indicate thatthe samples have a tetragonal (Space group I4/mmm) structure. ED patterns and high-resolution images reveal the presence of aregular stacking along the c-axis for the x ¼ 1:0 sample. The lattice parameters, oxygen content, and average oxidation state of ironand nickel decrease with increasing Ni content. The electronic structure of the x ¼ 1:0 sample was studied by M 2p X-rayphotoelectron spectroscopy (XPS). An analysis of the spectra using the cluster model indicates that this material is in the negativecharge-transfer regime and the ground state is dominated by the 3d n+1L configuration with 2p holes (L) in the oxygen band. Theinsulator states are stabilized due to a p–p type band gap that arises because the p–d transfer integral Ts dominates over the O 2pbandwith. Although magnetic measurements reveal the presence of ferromagnetic interactions that lead to magnetic frustration atTp40K; no long-range magnetic order was observed for the samples with xX0:3: The electrical resistivity decreases with increasingNi content as the p–p band gaptend to close due to the reduction of the Ts value. Negative magnetoresistance (24% for x ¼ 0:6and 7% for x ¼ 1:0 at 20K and 9T) was observed for the Ni containing samples.