Compositional dependence of the valency state of Cr ions in oxide glasses

Absorption spectra of Cr ions in multi-component oxide glasses melted in Ar were measured. The integrated extinction coefficient is used as a parameter to analyze the redox reaction of Cr3+ and Cr6+ in glass samples. The relative content of Cr6+ increased and that of Cr3+ decreased with increasing basicity in silicate and borate glasses; this result is consistent with previous studies. On the contrary, only Cr3+ exist in phosphate glasses. Cr4+ ions were found only in aluminate, gallate and alumino-silicate glasses with modifier contents ≥ 60 mol%. The relationship between point defects and Cr4+ formation is examined on the basis of electron spin resonance measurements. We concluded that the superoxide ion radical (O2−) and the peroxy bonding (-O-O-) oxidize Cr3+ to Cr4+ in aluminate, gallate, and alumino-silicate glasses.

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