Electronic structures of two-dimensional metallic oxides and bronzes

The electronic structures of some molybdenum and tungsten oxides or bronzes exhibiting Peierls transitions are investigated at room temperature. The d etection of a weak conduction band, well separated from a large valence ban d, evidences the metallic character of each oxide. The distributions of the valences of the different transition metals are analyzed by XPS. In each o xide, the presence of atleast two contributive components to the main core levels reveals a mixed valence state of the transition metal. But the propo rtions of the different components do not reflect the distribution of the c ationic valences. as expected from the crystallographic structures. To unde rstand this disagreement, we suggest that two alternative ways, including o r rejecting a screening effect generated by the conduction electrons contri bute to the photoemission processes and alter the real distribution of the cationic charges. (C) 2001 Elsevier Science B.V. All rights reserved.