A STUDY ON THE MIGRATION OF CO(II) AND FE(IN) IONS IN THE PROCESS OF THERMAL PHASE-SEPARATION OF AN ALKALI-BOROSILICATE GLASS CONTAINING COBALT AND UBIQUITOUS TRACE IRON

Absorption spectra of added Co(II) ions and EPR spectra of both Co(II) and ubiquitous Fe(III) ions in an alkali-borosilicate glass of vycor- type composition are studied both before and after thermal phase separ ation of the glass as well as in a silica glass derived from the phase -separated glass through vycorization. The results show that although almost all Co(II) ions migrate to the separated alkali-borate phase at the time of phase separation, only the interstitial ions in the case of Fe(III) take part in similar migration. The Fe(rn) ions in the subs titutional silicon sites, however, remain unaffected. It is also revea led that as a consequence of the process of phase separation a small f raction of the interstitial Fe(III) ions gets converted into substitut ional ions leading to a net increase in the concentration of substitut ional Fe(III) ions in the glass. Analysis of both absorption and EPR s pectra of the Co(II) ions suggests that a change of host of the ion du e its migration does not bring about any significant change in its coo rdination structure, which is typically a distorted tetrahedron both i n the parent glass as well as in the phase-separated berate glass.