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 sprctra of Cr-doped soda-lime-s ilicate and calcium-aluminate glasses of which the compositions were 15Na(2 )O-15CaO-70SiO(2) and 10MgO-55CaO-35AL(2)O(3) in mole%, respectively. It wa s estimated that the amount of Cr4+ formed in the aluminate glass was simil ar to 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 silic ate 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 similar to1.72 A, while [CrO6] polyhedra preva iled in the silicate glass with an average Cr-O length of similar to1.96 A. (C) 2000 Elsevier Science B.V. All rights reserved.