Effect of composition on valence states of iron cations in some borate glasses

We present the results of magnetic studies and Mössbauer effect measurements on 20Fe₂O₃80[3B₂O₃(1?x)PbOxA_uO_v] glasses with A_uO_v = CaO, As₂O₃ or GeO₂. The fraction r of ferrous ions is not dependent on CaO content, while in case of glasses with As₂O₃ and GeO₂ a linear variation is observed. The increase of the number of ferric ions is proportional to the difference between the valences of A ions and that of lead as well as on A_uO_v content. The magnetic measurements show that the reciprocal susceptibility for T ? 50 K has a nonlinear variation, typical for systems with random distribution of exchange interactions. At T > 50 K, a Curie-Weiss behaviour is evidenced. The Curie constants show a composition dependence similar to that of r values. Finally, the influence of the glass matrix composition on the iron valence states is discussed.