COORDINATION CHANGE AROUND 2WT-PERCENT NI IN NA2SI2O5 GLASS MELT SYSTEMS

The coordination environment around Ni at minor concentration levels (2 wt% NiO) in Na2Si2O5 glass and melt has been investigated by high temperature (293-1250 K) X-ray absorption fine structure (XAFS) spectroscopy. The derived average anharmonic Ni-O distances for the glass at 293 K and the melt above 1150 K are 1.99 (1) and 1.97 (1)Angstrom, respectively. The Ni-O distance in the glass is consistent with a mixture of Ni-IV and Ni-V, whereas that in the melt is consistent with dominantly Ni-IV. The significant reorganization of the melt during quenching may help explain the enrichment of Ni in, early-formed igneous minerals. These data also suggest the possibility of a pressure-induced coordination change around Ni, which may influence significantly the geochemical modeling of the Earth.