Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5397252 | Journal of Electron Spectroscopy and Related Phenomena | 2006 | 7 Pages |
Abstract
Local atomic and crystal structures around Cu and Mn atoms in Mn1.68Cu0.6Ni0.48Co0.24O4 spinel samples fabricated by metal-organic decomposition synthesis at different annealing temperatures were investigated by X-ray absorption fine structure analysis. There are two distinct copper cations, Cu1+ and Cu2+, both of which maintain tetrahedral coordination. The bond-length distances are Cu1+-OÂ =Â 2.00Â Ã
and Cu2+-OÂ =Â 1.80Â Ã
. The manganese cations are for the most part octahedral. The spinels prepared at low temperature (600 °C) contain smaller (Mn4+-O = 1.88 Ã
) undistorted MnO6 octahedrons corresponding to Mn4+ valence, whereas the manganese octahedrons in high-temperature materials (800 °C and higher) were larger and had a pronounced tetragonal distortion pertaining to Mn3+ oxidation state (Mn3+-O = 1.93 Ã
and 2.11Â Ã
). By rising the fabrication temperatures, relative concentration of the species of Mn4+ and Mn3+ varies as a result of the reaction represented by Cu1+ + Mn4+ â Cu2+ + Mn3+, implying irreversible temperature-induced structural transformation. Atomic coordinates in the low-temperature phase are similar to those found in the ideal cubic spinel with oxygen parameter u = 0.27, whereas local environments of the Cu and Mn atom correspond to the tetragonal CuMn2O4 phase (space group I41/amd). Unlike in CuMn2O4, orientation of the lattice distortions is random, however, the long-range cubic spinel structure is retained at all time.
Related Topics
Physical Sciences and Engineering
Chemistry
Physical and Theoretical Chemistry
Authors
Dmitry A. Kukuruznyak, Jerome G. Moyer, Nam T. Nguyen, Edward A. Stern, Fumio S. Ohuchi,