Crystallization enables suppressing thermal conduction in oxide glasses

Oxide glasses are important materials to overcome great societal challenges within energy and environment. The thermal conduction in oxide glasses is a key controlling factor for developing new materials used for fast heat transport or thermal insulation. Unfortunately, the thermal conductivity of oxide glasses is scarcely studied. It is well known that the thermal conductivity of glasses is usually lower than that of their crystalline counterparts due to the lack of long-range order in glasses, limiting the phonon mean free path. Thus, glasses are better thermal insulators than crystals. But how can we reduce the thermal conductivity of glasses even further? Here, we demonstrate a new way to suppress the thermal conduction in glasses. Specifically, the new way is based on our recent new finding, i.e., the thermal conductivity of glass-ceramics exhibits an abnormal trend with varying crystallinity. Upon initial crystallization, the thermal conductivity of a silicate glass system decreases by approx. 20 % compared to that of the pure glass phase. Upon further crystallization, as expected, it increases again due to the enhanced degree of long-range order. The initial reduction in thermal conductivity could be ascribed to an enhanced scattering effect caused by crystallites. This scattering effect exceeds that of the pure glass phase.