X-ray photoelectron spectroscopy (XPS) and magnetic susceptibility studiesof copper-vanadium phosphate glasses

Vanadium phosphate glasses containing CuO with the chemical composition [(V 2O5)(0.6-x)(P2O5)(0.4)(CuO)(x)], where chi = 0.0. 0.1, 0.2 and 0.3, have be en prepared and investigated by X-ray photoelectron spectroscopy (XPS) and mag netization measurements. The core-level binding energies of O 1s, P 2p, P 2s. Cu 2p and V 2p have been measured with the P 2p and P 2s peaks shift ing by about 2 eV towards lower binding energies ill the CuO-vanadium phosp hate glasses from their values in P2O5, while the V 2p peaks shift by simil ar to 0.3 eV towards lower binding energies from V2O5 and the Cu 2p peaks s hift by similar to 0.8 eV towards higher binding energies from CuO. These s hifts can be accounted for by changes in the next-nearest neighbor. environ ment around the P, Cu and V atoms and the reduction in the valence state of the Cu and V ions. The O is spectrum is fitted to two peaks and the variat ion in the ratio of the peak areas is discussed in terms of the local struc ture as well. In addition, the Cu 2p(3/2) and Cu 2p(1/2) peak show doublet structures in the XPS spectra which are associated with the presence of bot h Cu+ and Cu2+ in these glasses; although the XPS results indicate that mor e than 90% of the Cu ions exist ill the Cu2+ state. Likewise a multivalent state for the V ions is indicated by an asymmetry and broadening in the V 2 p spectra as the CuO concentration in the glasses increases. This tendency is also observed in the magnetic susceptibility results as the ratios V5+/V -total determined from XPS are in qualitative agreement with those determin ed by using the susceptibility measurements combined with inductively coupl ed plasma (ICP) spectroscopy results. Furthermore the susceptibility data a ppear to follow a Curie-Weiss behavior (chi = C/(T - 0)) for temperatures a bove similar to 40 K with negative Curie temperatures indicating that the p redominate magnetic interactions between the Cu2+-Cu2- and Cu2+-V4+ exchang e pairs are antiferromagnetic in nature. (C) 2000 Elsevier Science B.V. All rights reserved.