On the use of structural probe ions for relaxation studies in glasses. I. Spectroscopic properties of cobalt(II) in chloride-doped potassium nitrate-calcium nitrate glasses

As a preliminary to studies of the relaxation kinetics of processes involving temperature-induced coordination changes for transition metal ions dissolved in glasses, it has been necessary to determine the equilibrium spectroscopic and structural characteristics of these systems. For the particular case of the equilibrium between the tetrahedral and dodecahedral forms of Co(II) in 3:2 KNO₃-Ca(NO₃)₂ glasses containing 0-9 mol % KCl, the enthalpy change is found to be (5.2 ± 0.2) kcal/mol. Decreases in temperature and increases in KCl content shift the equilibrium in favor of more tetrahedral Co(II) formation. The molar absorptivities of the two forms were determined. Preliminary relaxation measurements indicate that at the glass transition temperature the relaxation time of the local Co(II) environment is of the same order as the structural relaxation time characteristic of the whole system.