AVS 46th International Symposium
    Applied Surface Science Division Wednesday Sessions
       Session AS-WeA

Paper AS-WeA3
Surface Segregation in NixCo(1-x)O and MnxCo(1-x)O Solid Solutions

Wednesday, October 27, 1999, 2:40 pm, Room 6A

Session: Oxides and Insulators
Presenter: M.A. Langell, University of Nebraska
Authors: M.A. Langell, University of Nebraska
M.W. Nydegger, Pace Analytical Corporation
F. Gevrey, Univ. Framche Comte, France
G. Couderc, Univ. Lyon, France
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Because of the similarity in crystal structure and compatible nature of their cations, many transition metal oxides systems are miscible over a wide range of composition. For these systems, the bulk structure was investigated by powder x-ray diffraction as early as the mid 1940's, and they are generally observed to follow Vegard's law. We have measured the surface composition of two rocksalt monoxide systems, NiO/CoO and MnO/CoO, which form bulk homogeneous solid solutions over the entire range M@subx@Co@sub(1-x)@O (M =Ni or Mn) of 0@<=@x@<=@1. Surface analysis has been performed with Auger and x-ray photoelectron spectroscopy, the latter of which also provides information on the chemical nature of the cations at the surface of the solid solution. Unlike the bulk material, the surface of both systems shows distinct evidence for segregation of one cation at the expense of the other and appears to be related to the formation of a spinel phase. In the case of the NiO/CoO system the spinel composition is NiCo@sub2@O@sub4@, and for the MnO/CoO system the composition agree with the spinel CoMn@sub2@O@sub4@. Information is also obtained on the octahedral and tetrahedral site occupancy of the cations and on their formal oxidation states.