The optical and electron spin resonance (ESR) spectra of barium borate glasses, containing the oxides of V, Fe and Cu separately and in mixed proportions, have been studied. The optical spectra of the single transition metal (TM) oxide glasses showed the usual features, while those for the mixed glasses showed single bands without showing individual features of the single TM oxide glasses. However, the linear plots of optical density against composition revealed the presence of two valence states for each TM element, and this was confirmed by ESR results as well. The ESR spectra of the mixed glasses showed a complicated interaction pattern for two different TM ions, in comparison with those of the glasses containing a single TM ion. For the Fe-V glasses, the progressively vanishing hyperfine structure of the VO2+ complex with increasing addition of iron oxide is discussed in terms of nuclear spin relaxation, cross-relaxation between two spin systems and spin diffusion within the vanadium spin system. The covalency of the VO2+ complex and the number of distorted Fe3+ ions were found to decrease with increasing addition of Fe2O3 replacing V2O5. Similar features were noted for the Cu-V glasses; the spectra of Cu-Fe glass also showed a strong interaction between two different TM ions. It has been suggested that all the possible four valence states (for a given mixed glass) from two different TM elements are present, and that pairing of two different TM ions from two dissimilar TM elements occurs, facilitating the formation of “associates” (e.g. V4+-O-Fe3+).

Optical and ESR investigation of borate glasses containing single and mixed transition metal oxides

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.

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

Barium borate glasses containing 0-35 mole% V2O5 were found to be homogeneous. Optical absorption spectra indicated that only V4+ of the lower valence states of vanadium was present. The molar volume data suggested that a change in the structure associated with vanadium ions occurred at around 22% V2O5. ESR spectra showed that a more continuous change occurred in the electron structure associated with the V4+ ions as the V2O5 content was varied. Resistivity and activation energy decreased rapidly with decreasing vanadium-vanadium separation, while, at constant % V2O5, they showed a minimum at V4+/(V4++V5+)=0.45. Thermoelectric power of glasses with 25-30% V2O5 showed very low activation energies, in agreement with a polaron hopping mechanism.

http://iopscience.iop.org/article/10.1088/0022-3727/11/18/015/pdf

Polaronic conduction and spectroscopy of borate glasses containing vanadium

The electrical resistivities and activation energies for electric conduction in glasses of the system Na2O-V2O5-B2O3 with V2O5<15 mol.%, have been measured. Two types of conductivities are postulated: ionic conductivity in the higher temperature region and electronic conductivity in the lower temperature region. V2O5 is assumed to be introduced into such glasses as a network former and also as a network modifier. It is deduced that the electronic conductivity in glasses with low concentrations of V2O5 is strongly affected by the concentration and the structural form of V2O5 in the glass. The dependence of the activation energy for electronic conduction on V2O5 content, for the glasses studied, is found to differ from that for glasses with high V2O5 content. It is assumed that the activation energy depends on the continuity of the V2O5 network.

Mixed ionic-electronic conduction in sodium borate glasses with low V2O5 content

Electrical characterization of lithium bismuth borate glasses containing cobalt/vanadium ions

The resistivities and activation energies of borate glasses containing oxides of both V and Fe, and both V and Cu are lower than those of glasses containing the same amounts of each TM oxide separately. Optical and ESR spectra suggest that the proportions of ions in reduced valence states are not greatly affected by mixing the oxides. It is concluded that polaron-hopping between ions of different TM elements occurs readily in these mixed glasses.

J O Isard

Papers

Electrical conductivity of barium borate glasses containing mixed transition metal oxides