Abstract
A series of alkali silicate glasses of the composition 0.3 Na22O-0.5 Si02-x(MnO⋅Fe2O3); x=0.025-0.16, were heat-treated at temperatures from 200°to 800°C for 0.5-17 hrs, and ESR measurements were made on these glasses. Onlyg=2 line was observed in the ESR spectra both in the glass and the crystallized glass. The line width ΔH decreased with crystallization of the glass and increased with the growth of particle size of crystals. In the glassy state the line width shows a maximum at MnO⋅Fe2O3=7 mole percent, and the effective g-value shows a minimum at MnO⋅Fe2O3=10 mole percent. From these experimental results, the following implications are obtained on the change of distribution of Mn2+ and Fe3+ ions under the influence of heat-treatments;
(1) Mn2+ and Fe3+ ions are present not in isolation but in pairs by exchange or super-exchange interactions in the Na2O-SiO2-MnO Fe2O3 glass.
(2) The interactions between Mn2+ and Fe3+ ions are enhanced in the glass as the concentration of magnetic ions is increased. This is due to an increasing probability in finding shorter ion pairs with increasing population of magnetic ions in the glass.
(3) The interactions among the magnetic ions are enhanced as soon as nucleation takes place on heating. This is due to the atomic rearrangement in ion pairs from a disordered structure to an ordered structure.
