G.D. Khattak

Structure of molybdenum-phosphate glasses by X-ray photoelectron spectroscopy (XPS)

Highly-concentrated molybdenum-phosphate glasses with analyzed compositions of Mo greater than 0.65 have been studied by X-ray photoelectron spectroscopy (XPS) and magnetization measurements. 1 eV shifts in the binding energies of P2p, P2s, Mo3d, and Mo3p from their respective values in P2O5 and MoO3 can be accounted for by changes in the next nearest neighbor environment of the P and Mo atoms upon the mixing of the two glass formers. The O1s spectrum is deconvoluted into two peaks with the lower-energy peak being associated with the oxygen atoms of the non-bridging PO structure as well as from various MO bonds and the higher-energy peak with the bridging oxygen atoms of the POP structure. From the amount of Mo6+ reduced to Mo5+, as determined from the magnetization results, the variations in the areas of these O1s peaks are discussed in terms of an existing structural model based on this binary glass being composed of a mixture of the structural groupings which occur in the crystalline phases of the MoO3:P2O5 system.

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

Vanadium phosphate glasses with the nominal chemical composition [(V2O5)x(P2O5)1 x], where x = 0.30, 0.40, 0.50, and 0.60, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS) and magnetization measurements. Asymmetries found in the O 1s, P 2p, and V 2p core level spectra indicate the presence of primarily P–O–P, P–O–V, and V–O–V structural bonds, a spin–orbit splitting of the P 2p core level, and more than one valence state of V ions being present. The magnetic susceptibility data for these glasses follow a Curie–Weiss behavior which also indicates the presence of some V ions existing in a magnetic state, i.e., a valence state other than that of the non-magnetic V. From qualitative comparisons of the abundance of the bridging oxygen or P–O–P sites as determined from the areas under the various O 1s peaks with the abundances of differing phosphate structural groups associated with the presence of different valence states of the vanadium ions, a glass structure model consisting of a mixture of vanadate phosphate phases is proposed for these glass samples. These include V2O5, VOPO4, (VO)2P2O7, VO(PO3), and V(PO3)3 with the abundance of orthophosphate (PO4) 3 units increasing with increasing vanadium content. 2009 Elsevier B.V. All rights reserved.

X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and electrical conductivity studies of copper phosphate glasses

Phosphate glasses containing CuO with composition (CuO)x(P2O5)1-x, where x = 0.1, 0.2, 0.3, 0.4 and 0.5, were studied by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and room temperature electrical conductivity, σ. The spin orbit components Cu 2p32 and Cu 2p12 show doublet structures which may be associated with Cu+ and Cu2+. The ratio C = Cu+Cutotal as a function of x was determined using the Cu 2p32 spectra. It is observed that the ratio, C, initially decreases with x, becomes minimum at x = 0.3 and then increases. Although the variation of σ with C was very small, it is close to the uncertainty in the measurement of its value; nevertheless it was maximum at C = 0.5, in agreement with the previous prediction. The FT-IR spectra indicated a maximum shift in the P = O absorption at 30% CuO contents in the glasses, which essentially follows the same pattern as the shift for the POP absorption. Further, the development of the high energy component peak in the O 1s (associated with POP oxygen) spectra follows a trend similar to the 760 cm−1 (also associated with POP) absorption band in the FT-IR spectra.

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

Abstract 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 2 p 3 2 photoelectron peak with the change in nickel content provided evidence of a change in the valence states of vanadium. The Ni 2 p 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.

Structure and magnetic properties of vanadium-sodium silicate glasses

Abstract Vanadium–sodium silicate glasses with the chemical composition [(V2O5)x(Na2O)0.30(SiO2)0.70−x] (0.0⩽x⩽0.10) have been studied by X-ray photoelectron spectroscopy (XPS) and magnetization measurements. The core-level binding energies of O 1s, V 2p and Si 2p in these glasses have been measured for surfaces produced by in vacuo fracture. The peak position and width of the V 2p3/2 peak are independent of the V2O5 content while the O 1s core-level spectra show significant composition-dependent changes. Two distinct peaks are resolvable arising from the bridging oxygen and non-bridging oxygen (NBO) atoms in the silicate glasses. The fraction of NBO, determined from these spectra is found to increase with increasing V2O5 content in the glass and are consistent with the formation of predominantly alkali metavanadate species. The magnetic susceptibility data of these glasses indicate a large, temperature-independent diamagnetic contribution arising from the glass matrix as well as small paramagnetic contribution from the V4+ ions. The V4+ content deduced from the magnetization results (∼2%) is below the detection limit of XPS analysis.

X-ray Photoelectron Spectroscopy (XPS) and Magnetization Studies of Iron–Vanadium Phosphate Glasses

Abstract Iron–sodium borate glasses with the chemical composition [(B2O3)0.70−x(Na2O)0.3(Fe2O3)x], where 0.00⩽x⩽0.15, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS) and magnetization measurements. The core-level binding energies of O 1s, B 1s, and Fe 2p have been measured with both O 1s and B 1s peaks shifting by about 2 eV towards smaller binding energies in the Fe-containing borate glasses while the Fe 2p3/2 and 2p1/2 core levels for the glasses remain essentially unchanged from those of Fe2O3 powder. The O 1s spectrum is deconvoluted into two peaks and the variation in the ratio of the peak areas is discussed in terms of the local iron structure. We suggest that both X-ray photoelectron spectroscopy and magnetization measurements show that the Fe ions remain essentially in one oxidation state, probably Fe3+, for the Fe borate glasses. In addition, the appearance of a large hysteresis between the zero field-cooled and field-cooled magnetization data indicate that the Fe moments are clustered and that the predominant interaction is antiferromagnetic.

Composition-dependent loss of phosphorus in the formation of transition-metal phosphate glasses

Abstract Phosphate glasses containing MnO2, Co3O4 and CuO analyzed by Rutherford backscattering spectroscopy (RBS) have higher transition-metal (TM) concentrations in the glass than the initial batch composition. These compositional changes result from vaporization of phosphorus during the melt and are greater for the lower TM oxide batch composition glasses. X-ray photoelectron spectroscopy (XPS) shows that the copper ions exist as Cu+ and Cu2+, while cobalt ions exist as high-spin Co2+. The oxidation states for the Mn phosphate glasses could not be determined by XPS. The magnetization results, combined with RBS, indicate that more than 90% of the Cu ions occur as Cu2+, that all Co ions are in the high-spin Co2+ state and that more than half the manganese ions exist in the Mn2+ state. In addition to the measured phosphorus-to-metal atomic ratios, R, for the glasses being much less than those for the initial batch compositions, the R(glass) are essentially constant for R(batch) greater than ∼ 2.5, independent of the TM ion and the initial batch composition. This suggests that phosphate glasses containing relatively small quantities of cations probably exist as ultraphosphate networks.

X-ray photoelectron spectroscopic studies of zinc-tellurite glasses

Zinc–tellurite glasses with chemical composition [(ZnO)x(TeO2)100−x], where x=25, 30 and 35 have been prepared and investigated by X-ray photoelectron spectroscopy (XPS). Zn 2p peaks shift by about 0.25 eV towards higher binding energy in the zinc–tellurite glasses in comparison to its value in ZnO powder, while the Te 3p, Te 3d, and O 1s core levels for the glasses remain essentially unchanged from those of TeO2 powder. Each O 1s spectrum is deconvoluted into two peaks, in which the higher energy one is due to oxygen atoms in the hydroxides covering the sample surface. Although both bridging oxygen (BO) and non-bridging oxygen (NBO) atoms should certainly exist in these tellurite glasses, the electrons are delocalised in the NBO–Te–BO bonds which equalize the electronic density of the valence shell between BO and NBO atoms and make it difficult to distinguish.

X-Ray photoelectron spectroscopy (XPS) studies of copper–sodium tellurite glasses

Abstract Sodium tellurite glasses containing CuO with the nominal composition [(Na2O)0.3(TeO2)0.7−x (CuO)x], where x=0.00, 0.05, 0.15, and 0.20, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS). The binding energies of Te 3p, Te 3d, O 1s, and Cu 2p core levels in these glasses have been measured and compared to the corresponding binding energies in TeO2 and CuO powders. The Te 3p and Te 3d core levels for the glasses were essentially unchanged from those of TeO2 powder and have little dependence upon the CuO content. Although the O 1s peak showed a small asymmetry on the higher energy side of the peak in the glasses, it was primarily the result of hydroxide contamination on the glass surface rather than the appearance of non-bridging oxygen atoms arising from a structural change in the TeO4. For glasses with x=0.05 and 0.15, the Cu 2p peaks were shifted by more than 1 eV towards lower binding energies in comparison to their values in CuO powder, which suggests the presence of Cu+ ions in these glasses. The appearance of satellite peaks in the Cu 2p spectra, however, provided definitive evidence for the presence of Cu2+ ions in these glass samples as well. The broadened Cu 2p3/2 peaks were correspondingly decomposed into two distinct peaks separated by approximately 1.25 eV, with the lower energy peak being associated with Cu+ and the higher one with Cu2+. The relative Cu2+ content estimated from the spectral analysis was found to vary from 15% for the x=0.05 glass sample to over 70% for the x=0.20 sample.

Investigation of the magnetic properties in strontium–borate vanadate glasses

To further elucidate the nature of the valence state of V ions in vanadate glasses, magnetic susceptibility measurements in the temperature range of 5 to 300 K have been performed on a series of vanadium–strontium–borate (V2O5+SrO+B2O3) oxide glasses with V2O5 concentrations greater than 50 mol %. The magnetic susceptibility for these oxide glasses is found to consist of a temperature-independent paramagnetic contribution arising from V2O5 and a Curie–Weiss temperature-dependent contribution associated with magnetic V4+ ions being present in concentrations between 2% and 10% of the total V concentration. The negative Curie–Weiss temperatures in the range of 0 to −2.8 K indicate a weak antiferromagnetic interaction between the V4+ ions. These results are consistent with a glass network structure consisting of VO5 polyhedra in which the V4+ would be predominantly isolated species, and any interactions between the V4+ ions would result from superexchange interactions through V–O–V bonds.