INVESTIGADORES
ASCOLANI Hugo Del Lujan
artículos
Título:
Synthesis, crystal chemistry, and physical properties of the Ruddlesden-Popper phases Sr3Fe2-xNixO7-(0 < x <1.0)
Autor/es:
F. PRADO; L. MOGNI; H. ASCOLANI; M. ABBATE; M.S. MORENO; ARUMUGAM MANTHIRAM; A. CANEIRO
Revista:
JOURNAL OF SOLID STATE CHEMISTRY
Referencias:
Año: 2005 vol. 178 p. 1559 - 1568
ISSN:
0022-4596
Resumen:
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 3d n+1L configuration with 2p holes (L) in the oxygen band. The insulator states are stabilized due to a pp type band gap that arises because the pd transfer integral Ts dominates over the O 2p bandwith. Although magnetic measurements reveal the presence of ferromagnetic interactions that lead to magnetic frustration at T£ 40K; no long-range magnetic order was observed for the samples with x³ 0. 3. The electrical resistivity decreases with increasing Ni content as the pp band gaptend to close due to the reduction of the Ts value. Negative magnetoresistance (» -24% for x= 0.6 and - 7% for x=1.0 at 20K and 9T) was observed for the Ni containing samples. 3Fe2_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 3d n+1L configuration with 2p holes (L) in the oxygen band. The insulator states are stabilized due to a pp type band gap that arises because the pd transfer integral Ts dominates over the O 2p bandwith. Although magnetic measurements reveal the presence of ferromagnetic interactions that lead to magnetic frustration at T£ 40K; no long-range magnetic order was observed for the samples with x³ 0. 3. The electrical resistivity decreases with increasing Ni content as the pp band gaptend to close due to the reduction of the Ts value. Negative magnetoresistance (» -24% for x= 0.6 and - 7% for x=1.0 at 20K and 9T) was observed for the Ni containing samples.