A medium range order structural connection to the configurational heat capacity of borate–silicate mixed glasses

Abstract

It has been reported that the configurational heat capacity (C_p,conf) first increases and then becomes saturated with increasing B₂O₃/SiO₂ ratio in borate–silicate mixed glasses. Through Raman spectroscopy measurements, we have, in this work, found an implication for the intermediate range order (IRO) structural connection to the composition dependence of the C_p,conf of borate–silicate mixed glasses. In the silica-rich compositions, the C_p,conf rapidly increases with increasing B₂O₃ content. This is attributed to the increase of the content of the B–O–Si network units ([B₂Si₂O₈]²⁻) and 6-membered borate rings with 1 or 2 B⁴. In the boron-rich compositions, the C_p,conf is almost constant, independent of the increase in the B₂O₃/SiO₂ ratio. This is likely attributed to the counteraction between the decrease of the fraction of two types of metaborate groups and the increase of the fraction of other borate superstructural units (particularly 6-membered borate rings). The overall results suggest that the glasses containing more types of superstructural units have a larger C_p,conf.