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Redox behaviour of polyvalent ions in phosphate glass melts and phosphate glasses
Glass melts and glasses with the basie composition NaPO₃ · 2Sr(PO₃)₂ doped with V₂O₅ and Fe₂O₃ were studied with the aid of square-wave voltammetry and spectroscopic methods. From the square-wave voltammetry in the glass melt, a linear dependence of the peak potentials on the temperature was obtained. The Standard enthalpy ΔH⁰, the Standard entropy ΔS⁰ and lg(C_ox/C_red) of the transitions Fe³⁺/Fe²⁺ and V⁴⁺/V³⁺ were calculated. The diffusion coefficients calculated from the peak currents measured follow Arrhenius' law. By means of electron spin resonance, the concentration of V⁴⁺ was determined. The corresponding extinction coefficients for the V⁴⁺ bands were calculated from the absorption spectra. Concerning the vanadium-containing glass, the results of square-wave voltammetry and spectroscopy were compared quantitatively. For the iron-doped glass, the comparison was only qualitative.