Raman spectroscopy and density functional theory analyses of the melt structure in a Li2B4O7 crystal growth system

Melt structure, a fundamental and challenging subject for borate crystal growth, has not been solved for many years. In this paper, a new method has been employed to study the Li2B4O7 melt structure. High-temperature Raman spectroscopy has been used to investigate the structural evolvement from a Li2B4O7 crystal to a Li2B4O7 melt. Based on the investigation, a model was proposed to describe the Li2B4O7 melt. The melt is made up of polymer-like boron–oxygen chains; the minimal repeated unit is the B4O6O22− (O = bridging oxygen) group which is formed by a B3O4O2− six-membered ring and a BOO2− triangle linked by a bridging oxygen atom. DFT calculations have verified the melt structure and provided accurate assignments for the vibrational bands present in the Li2B4O7 melt Raman spectrum.