Oxidation state and local coordination of chromium dopant in soda-lime-silicate and calcium-aluminate glasses

We have analyzed Cr K-edge X-ray absorption spectra of Cr-doped soda-lime-silicate and calcium-aluminate glasses of which the compositions were 15Na2O–15CaO–70SiO2 and 10MgO–55CaO–35Al2O3 in mole%, respectively. It was estimated that the amount of Cr4+ formed in the aluminate glass was ∼85±10% out of the total nominal chromium content, i.e., 0.06 mole%, and the remaining chromium ions were in 6+ oxidation state. In the silicate glass, Cr3+ was accompanied by Cr6+ the portion of which was relatively small compared to that in aluminate glass. Short-range structural units of chromium in the aluminate glass were [CrO4] and severely distorted [CrO6] with a Cr–O bond distance of ∼1.72 Å, while [CrO6] polyhedra prevailed in the silicate glass with an average Cr–O length of ∼1.96 Å.