IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Wednesday Sessions
       Session SS3-WeA

Paper SS3-WeA5
Electronic Structure of Complex Manganite Spinels Studied by XPS, XANES, EXAFS and Nanoprobe EELS

Wednesday, October 31, 2001, 3:20 pm, Room 122

Session: Electronic Structure I
Presenter: D.A. KuKuruznyak, University of Washington
Authors: D.A. KuKuruznyak, University of Washington
B.W. Reed, University of Washington
J.G. Moyer, University of Washington
M.C. Gregg, University of Washington
S.-W. Han, University of Washington
E.A. Stern, University of Washington
M. Sarikaya, University of Washington
F.S. Ohuchi, University of Washington
Correspondent: Click to Email
Ni-Co-Cu-Mn-O spinels, owing to their strong temperature influence on resistivity, are technologically important oxide materials for thermistor applications, among which Ni@sub 0.48@Co@sub 0.24@Cu@sub x@Mn@sub 2.28-x@O@sub 4@ (x = 0.6, and 1.2) are the compositions of specific industrial interests. In this study, we synthesized nanocrystalline thin films and powders using low temperature metallorganic decomposition technique, rather than conventional solid state sintering. The materials were subsequently annealed at temperatures between 500 and 800°C, and it was found that annealing temperature was a decisive factor in controlling transport properties. Electronic structure of the bulk and surface was investigated by combinations of XPS, XANES, and nanoprobe EELS. The analysis revealed that the annealing caused change of the oxidation state from Cu@super 1+@ to Cu@super 2+@, which was accompanied by reduction of manganese cations from Mn@super 4+@ to Mn@super 3+@. EXAFS analysis showed that both the Cu@super 1+@ and Cu@super 2+@ ions occupied the tetrahedral lattice sites, whereas both the Mn@super 4+@ and Mn@super 3+@ were in the octahedral sites in the spinel structure. During the course of annealing, an unusually large negative binding energy shift in both Cu 2p and Cu 3d levels for the Cu@super 1+@ state was observed. This negative shift appears to be unique to this system, and was attributed to the change in the Fermi surface topology due to strong 3d-4p hybridization which occurs in the in the tetrahedral coordination because of the completely filled 3d@super 10@ orbital of Cu@super 1+@ ion.