A. Mekki

An XPS study of iron sodium silicate glass surfaces

Abstract A series of (SiO2)0.7−x(Na2O)0.3(Fe2O3)x glasses (0.0 ≤ x ≤ 0.18) were prepared and investigated by means of X-ray photoelectron spectroscopy (XPS). The quantitative ratio [Fe2+]/[Fetotal], for each glass has been determined from an analysis of the Fe 3p spectra. For low Fe2O3 content both iron valencies are present, however, it was found that Fe3+ is the dominant species for high Fe2O3. From an analysis of the O 1s spectra, it was possible to discriminate between bridging and non-bridging oxygen atoms. It was found that the ratio of the non-bridging oxygen content to the total oxygen content increases with increasing iron concentration. It has also been shown that the non-bridging oxygen contribution to the O 1s spectra can be simulated by summing the contributions from the SiONa, SiOFe(II) and SiOFe(III) components present in the glass.

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.

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.

XPS and magnetization studies of cobalt sodium silicate glasses

Cobalt sodium silicate glasses with the chemical composition (0.70 - x)SiO2-(0.30)Na2O-xCoO, where 0.0 ≤ x ≤ 0.20, have been investigated by means of X-ray photoelectron spectroscopy (XPS) and magnetization techniques. The Co 2p spectra show intense satellite structures ∼ 6 eV above the photoelectron peak and the Co 2p32-Co 2p12 separation was ∼ 15.9 eV for all the samples studied. These observations indicate the presence of high spin Co2+ ions in the glasses. The Co 3p spectra have been fitted with contributions from octahedral and tetrahedral Co2+ and the ratio [Co2+(oct)]/[CoTotal2+] increases with increasing CoO content. The O Is spectra also show composition-dependent changes. The fraction of non-bridging oxygen atoms was determined from these spectra and was found to increase with increasing cobalt oxide. Co(II) ions are found to be incorporated in the glass as network modifiers but the contribution from SiOCo(II) to the non-bridging part of the O Is signal could be separated from that from SiONa by simulating the spectrum. DC magnetic susceptibility measurements were performed on the same samples but these suggest that Co2+ exists mainly in octahedral coordination. The magnetic data indicate that the exchange interaction is antiferromagnetic and increases with increasing CoO in the glass.

X-ray photoelectron spectroscopy study of copper sodium silicate glass surfaces

Copper oxide-containing, sodium silicate glasses with composition (0.70 - x)SiO2-0.30Na2O-xCuO (x in the range 0–0.2), were prepared by conventional melting and casting. The surface structure has been investigated by X-ray photoelectron spectroscopy. Evidence for the presence of copper in the Cu+ state for glasses with x ≤ 0.14, and for both oxidation states (Cu+ and Cu2+) in the glass where x = 0.18, has been obtained from the “shake up” satellite structure of the Cu 2p core level spectra. A deconvolution procedure has been undertaken to determine quantitatively the [Cu2+]/[Cutotal] ratio. The non-bridging oxygen content, obtained from the deconvolution of the O 1s core level spectra, increases with increasing copper oxide content indicating that copper acts as a network modifier. The O 1s spectra were modelled in such a way as to separate the contribution from SiOCu and SiONa to the non-bridging oxygen signal.

Transition metal ions in ternary sodium silicate glasses: a Mössbauer and neutron study

Abstract The structure of transition metal (TM) sodium silicate glasses of formulae (Fe2O3)x(Na2O)0.3(SiO2)0.7−x and (CoO)x(Na2O)0.3(SiO2)0.7−x where the nominal x=0, 0.05, 0.10, 0.15 and 0.20, have been studied using neutron diffraction and Mossbauer spectroscopy. The Mossbauer spectra of the iron-containing series show that both Fe3+ and Fe2+ are present, the majority being Fe3+. The isomer shifts show that the coordination number of Fe3+ is low, probably 4, and of Fe2+ somewhat higher though the measurement is less accurate. The neutron data show that both the iron and the cobalt are 4-coordinated with bond lengths of about 1.90 and 1.95 A, respectively with O–TM–O bond angles approaching 90°. The Fe–O bond length decreases and the O–O bond length increases with increasing Fe2O3 content. The first sharp diffraction peak (FSDP) is split on addition of iron and cobalt, showing intermediate-range order (IRO) with a larger repeat distance. The effective Debye temperatures for Fe2+ and Fe3+ are 268 and 312 K, respectively, showing the different Fe–O bond strengths of the two oxidation states arising from their different charges. The shift in the Mossbauer spectra with temperature was not that expected from the second order Doppler shift and thermal expansion showing an intrinsic isomer shift dependence on temperature. An attempt was made to relate this to the possible changes in hybridization of the iron with the concentration of Fe2O3.

Structural and magnetic properties of sodium iron germanate glasses

A series of sodium iron germanate glasses, with general composition 0.3Na2O‐xFe2O3‐(0.7 ) x)GeO2 (06 x6 0:15), has been prepared by conventional melting and casting. The chemical states of the various elemental components have been investigated by X-ray photoelectron spectroscopy (XPS) from fracture surfaces produced in situ. The analysis of the Fe 3p core level spectra of the glasses which contain iron oxide revealed the presence of both Fe 2a and Fe 3a oxidation states, with the proportion of the Fe 3a ions found to increase with increasing Fe2O3 content. The O 1s spectra also show composition-dependent changes, with the fraction of non-bridging oxygen atoms also increasing with iron oxide content. Direct current magnetic susceptibility and magnetisation (M) vs magnetic field (H) measurements were also performed on the same samples. The magnetic data support the conclusion that the exchange interaction is antiferromagnetic and increases with increasing Fe2O3 content. The fraction of Fe 2a ions determined from XPS was found to be in good agreement with values obtained from fitting the M vs H data with a standard Brillouin function. ” 2000 Elsevier Science B.V. All rights reserved.

Magnetic properties of praseodymium ions in Na2O–Pr2O3–SiO2 glasses

Sodium praseodymium silicate glasses of nominal composition 0.3Na2O xPr2O3 (0.7� x)SiO2, where 0pxp0:10; have been studied by magnetisation and X-ray photoelectron spectroscopy (XPS). The magnetisation data fail to collapse to a single curve in the M versus H=T representation for all values of x and the spread increases with x; indicating an increase in the magnetic exchange interaction. The M versus H data acquired at different temperatures have been fitted with a Brillouin function by refining the number of Pr 3+ ions in each glass sample. It was found that most of the Pr ions are in Pr 3+ valence state and only a small fraction (p5%) in the Pr 4+ state. Analysis of the XPS line shape indicates only the presence of Pr 3+ ions in these glasses.

XPS study of transition metal doped silicate glasses

Abstract X-ray photoelectron spectroscopy (XPS) has been used to study the redox state of transition metal oxides in sodium silicate glasses with compositions 0.30Na 2 O–0.70SiO 2 and 0.3Na 2 O–0.6SiO 2 –0.1TMO, where TMO=Fe 2 O 3 , CuO and CoO. From the analysis of the core level spectra of the transition metals, it was found that both Fe 2+ and Fe 3+ exist simultaneously in the iron doped glass, while Cu + was the only species present in the copper doped glass. In the cobalt doped glass, Co 2+ was found to exist in both tetrahedral (tet) and octahedral (oct) co-ordinations. From the analysis of the O 1s spectra, it was possible to discriminate between bridging and non-bridging oxygen atoms in each glass sample. It was also shown that the non-bridging oxygen contribution to the O 1s spectra can be simulated by summing the contributions from SiONa, SiOFe 2+ and SiOFe 3+ for the iron doped glass, SiONa and SiOCu + for the copper doped glass and SiONa, SiOCo 2+ (tet) and SiOCo 2+ (oct) for the cobalt doped glass. The quantitative values for the [Fe 2+ ]/[Fe] and [Co 2+ (tet)]/[Co] concentrations ratios were found from the analysis of the Fe 3p and Co 3p core level spectra, respectively.

Influence of rare-earth ions on SiO2–Na2O–RE2O3glass structure

Praseodymium and europium sodium silicate glasses of nominal composition (SiO(2))(0.70 - x)(Na(2)O)(0.30)(RE(2)O(3))(x), where RE is the rare earth and 0 ≤ x ≤ 0.10, were studied by neutron and high-energy x-ray scattering and classical molecular dynamics simulations. The observation of a significant x-ray intensity in doped as compared to un-doped glasses is indicative of RE-RE correlations at a distance of ∼ 3.7-3.9 Å, much shorter than would be expected for a homogeneous distribution, suggesting that clustering of the rare-earth cations occurs in both these glass systems at low concentrations. Above x = 0.075 (nominal), minimal changes in this region indicate that the RE atoms are incorporated much more randomly into the glass structure. The molecular dynamics simulations suggest that the rare-earth ions enter the sodium-rich regions in the sodium silicate glasses and act as modifiers. A cluster analysis performed on the model systems indicates that the tendency for clustering is higher in praseodymium-containing glasses than in the europium glasses.