The chromium site in doped glassy lithium tetraborate

• Adoption of the Li + site for chromium dopants in lithium tetraborate identified.
• Increased oxygen coordination for glass over the crystalline lithium tetraborate.
• Distortions about the doping chromium characterized.
• Local bond order is preserved in spite of the glassy nature.

Using extended X-ray absorption fine structure (EXAFS) spectroscopy, we find that Cr substitutes primarily in the Li+ site as a dopant in lithium tetraborate Li2B4O7 glasses, in this case 98.4Li2B4O7–1.6Cr2O3 or nominally Li1.98Cr0.025B4O7. This strong preference for a single site is nonetheless accompanied by site distortions and some site disorder, helping explain the optical properties of chromium doped Li2B4O7 glasses. The resulting O coordination shell has a contraction of the Cr–O bond lengths as compared to the Li–O bond lengths. There is also an increase in the O coordination number.

Lithium tetraborate: labeled are the B1 and B2 sites, where the latter correspond to BO3 and BO4 structures respectively.Figure optionsDownload as PowerPoint slide