SITES FOR HOSTED METAL-IONS IN GLASSES AND MELTS

Glass forming compositions in alkali phosphate systems exist where the glass is molten below 500 degrees C. This temperature is approximatel y the limit for recording optical (ultraviolet/visible) spectra using a conventional spectrophotometer. Some glasses, e.g. Na2O-K2O-P2O5 (1: 1:3) undergo limited physical change so that spectra can be recorded f or the melt on cooling or for the cold glass on heating. Spectra recor ded for Ni2+, Mn3+ and Cr3+ indicated octahedral coordination. The sli ght spectral changes occurring with temperature are discussed and the data obtained should be useful for studying these metal ions when they undergo redox or stereochemical change in other glass systems. Spectr al changes for Tl+ and Pb2+ indicated a basicity decrease as the melt cooled, with the rate being less below T-g. For Co2+ there was evidenc e for an octahedral/tetrahedral equilibrium which was found to undergo a displacement more or less in accordance with the basicity change si gnalled by Tl+ and Pb2+.