X-ray photoelectron spectroscopy (XPS) and magnetization studies of iron-vanadium phosphate glasses

Vanadium phosphate glasses containing Fe2O3 with the chemical composition [(Fe2O3)x(V2O5) 0.6-x(P2O5)0.4], where x = 0.00, 0.10, 0.20, 0.25 and 0.30, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS) and magnetic susceptibility measurements. The core level binding energies of V 2p, Fe 2p, P 2p and P 2s in the Fe2O3-vanadium phosphate glasses have been measured and shifts from the corresponding binding energies measured for V2O5, Fe2O3 and P2O5 powders are accounted for by changes in the next-nearest neighbor environment of these atoms in the P4O10 local structure. The O 1s spectra for the glasses are single, symmetric peaks arising from nearly 95% of the oxygen sites being occupied by non-bridging oxygen atoms. In addition, the broadened V 2p3/2 and Fe 2p3/2 spectra for the glass samples are decomposed into two peaks that are associated with the presence of V5+ and V4+ and Fe3+ and Fe2+, respectively. The magnetic susceptibility data appear to follow a Curie-Weiss behavior (χ = C/(T - θ)) for temperatures above ∼15 K with negative paramagnetic Curie temperatures indicative of antiferromagnetic interactions between the magnetic Fe3+, Fe2+ and V4+ ions. The experimentally determined Curie constants from the susceptibility data are in good agreement with the calculated values based on the Fe3+, Fe2+ and V4+ concentrations determined from the XPS analyses. Other qualitative features in the magnetic susceptibility results can be explained in terms of the formation of various magnetic clusters (single, dimer and trimer) with the introduction of the magnetic ions onto the P sites of the P4O10 str ucture. © 2001 Elsevier Science B.V. All rights reserved.