XPS studies on WO2.90 and WO2.72 and the influence of metallic impurities

The excess electrons in reduced tungsten oxides appear in the X-ray induced photoelectron spectrum of WO2.90 as W5+ signals. The ratio of the integrated intensities of the W5+4f and W6+4f peaks vary with chemical composition. A further increase in the W5+4f density of states appears for the doped crystals in proportion to the density of dopants. In WO2.72 the charge carriers produce fivevalent tungsten only fractionally, the remaining electrons filling up the conduction band. A structural interpretation is proposed. The introduction of metallic impurities of V, Ni, and Nb increases the density of the fivevalent states.