Browsing by Author "Zirkelbach, Karl"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Electrical conductivity of semiconducting barium aluminophosphate glasses containing single and double redox pairs
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1988) Zirkelbach, Karl; Brückner, Rolf
    A steep increase of conductivity with increasing vanadium oxide concentration up to values 10^-1 S/m at 150 °C is observed in barium-rich glasses of the pseudo-binary systems TM(Transition Metal)-oxide-Ba(PO3)2-Al(PO3)3 with TM-transition metals vanadium, iron, manganese which is similar to that in pure vanadium phosphate glasses. For high concentrations (25 to 80 mol% vanadium oxide) an adiabatic hopping process between V4+ and V5+ ions is found. No hopping process takes place between V4+ and V3+ ions. The system with iron oxide content also shows a steep increase of conductivity. Maximum values around 10^-4 S/m are reached at 150 °C, because only 30 mol% iron oxide are soluble without crystallization. The hopping process between Fe2+ and Fe3+ ions is a non-adiabatic one. No or negligibly small hopping processes seem to exist in the manganese oxide-containing system. In systems with TM-oxides incorporated in pairs the probability of hopping processes significantly depends on the oxidation potential or on the electrochemical series of the redox pairs, respectively, because the electronic charge carrier concentration depends on the mutual shift of the redox equilibria. Those hopping processes which are not conform to this shift have a very low probability. Therefore, increasing or decreasing conductivity in those mixed redox pairs containing systems depends primarily on the electrochemical series and on the initial redox situation of that redox pair and its redox shift, which dominates the electrical conductivity. In the case of Fe2+ ions it was found that an increase in conductivity additionally takes place by a coordination change from 4- to 6-fold in the presence of manganese, favouring the hopping process between 6-fold coordinated Fe2+ and 6-fold coordinated Fe3+ ions.
  • Thumbnail Image
    Item
    Spectroscopic investigations of barium aluminophosphate glasses containing pairs of transition elements
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1987) Zirkelbach, Karl; Brückner, Rolf
    In barium-aluminophosphate glasses containing two transition elements (two redox pairs) vanadium and iron ions are oxidized by manganese (combinations vanadium-manganese and iron-manganese), iron ions by vanadium (combination iron-vanadium). For low and intermediate concentrations of transition metal ions the redox equliibrium shift is complete during cooling from the melting temperatures, but for high concentrations it remains mostly incomplete (depending on the specific combination). The influence on Tg is given as an example for medium concentrations of Fe-V (8 mol).
  • Thumbnail Image
    Item
    Spectroscopic investigations of barium aluminophosphate glasses containing vanadium, iron and manganese oxides
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1987) Zirkelbach, Karl; Brückner, Rolf
    In three ternary systems Ba(PO3)2-Al(PO3)3-T-oxide (T = Transhion element = vanadium, iron, manganese) the Ba/Al phosphate ratio was varied at constant T-oxide content, as well as the T-oxide content at constant Ba/Al phosphate ratio. Optical and ESR spectroscopic investigations as well as thermal expansion and Tg measurements were carried out. The relationship between glass composition and network strength differs principally from that in silicate glasses in some respects and finds corresponding interpretation. At low T-oxide concentrations the interaction between the T-ions and the surrounding oxygen ions decreases with increasing network strength (i.e. with increasing substitution of aluminum for barium). T-complexes are generally present in glasses in strongly distorted symmetry. Thus, for V^4+O6- octahedra distortions exhibit besides tetragonal distortion a significant share of orthorhombic asymmetry. For higher T-oxide concentrations glass properties and structure are characteristically influenced by valence ratios and coordination changes.