X-ray photoelectron spectroscopy (XPS) and magnetic susceptibility studies of copper–vanadium phosphate glasses

Abstract

Vanadium phosphate glasses containing CuO with the chemical composition [(V 2O 5) 0.6− x (P 2O 5) 0.4(CuO) x ], where x=0.0, 0.1, 0.2 and 0.3, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS) and magnetization 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 shifting by about 2 eV towards lower binding energies in the CuO–vanadium phosphate glasses from their values in P 2O 5, while the V 2p peaks shift by ∼0.3 eV towards lower binding energies from V 2O 5 and the Cu 2p peaks shift by ∼0.8 eV towards higher binding energies from CuO. These shifts can be accounted for by changes in the next-nearest neighbor environment around the P, Cu and V atoms and the reduction in the valence state of the Cu and V ions. The O 1s spectrum is fitted to two peaks and the variation in the ratio of the peak areas is discussed in terms of the local structure 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 both Cu + and Cu 2+ in these glasses; although the XPS results indicate that more than 90% of the Cu ions exist in the Cu 2+ state. Likewise a multivalent state for the V ions is indicated by an asymmetry and broadening in the V 2p spectra as the CuO concentration in the glasses increases. This tendency is also observed in the magnetic susceptibility results as the ratios V 5+/V total determined from XPS are in qualitative agreement with those determined by using the susceptibility measurements combined with inductively coupled plasma (ICP) spectroscopy results. Furthermore the susceptibility data appear to follow a Curie–Weiss behavior ( χ= C/( T− θ)) for temperatures above ∼40 K with negative Curie temperatures indicating that the predominate magnetic interactions between the Cu 2+–Cu 2+ and Cu 2+–V 4+ exchange pairs are antiferromagnetic in nature.