Electronic Spectra and Coordination of Ni²⁺ in Potassium Borate Glass and Melt to 1000°C

A quantitative visible‐uv spectroscopic study of local structure‐sensitive electronic transitions resulting from Ni²⁺ doped into sodium borate in the glassy and liquid states up to 1000°C was conducted using a simple windowless Pt‐cell technique with a high‐temperature spectrophotometer. Analysis of the spectra shows that Ni²⁺ is distributed between distorted tetrahedral and octahedral sites in a temperature‐dependent equilibrium with ΔH =44.4 kJ. mol⁻¹ in the liquid and a much smaller but nonvanishing value in the glass.