XPS, auger, electrical and optical studies of vanadium phosphate glasses doped with nickel oxide

X-ray photoelectron and X-ray excited Auger spectra, optical absorption and DC conductivity of vanadium phosphate glasses containing nickel oxide have been studied as a function of nickel content. The shift in the binding energy of the V 2p _{3 2} photoelectron peak with the change in nickel content provided evidence of a change in the valence states of vanadium. The Ni 2p _{3 2} core level in NiO powder is a doublet and is normally used as a fingerprint for NiO. However, a single peak, shifted to higher binding energy, was observed in the glasses. The Ni (LVV) Auger spectrum for NiO powder showed a doublet structure. In glasses, however, two well-separated peak were observed in this spectrum. The results suggest that Ni in the glass may exist in two different phases, viz. nickel oxide and nickel vanadate. Initial addition of nickel (2 wt% of NiO) increased the optical absorption and electric conductivity but large additions, (5 wt% of NiO) led to a small decrease. The conductivity had a minimum value for a concentration of about 10 wt% of NiO. An attempt has been made to account for the observed changes in optical and electrical properties in terms of the XPS and Auger results.