Low-temperature behavior of potassium borate glasses

Abstract

The addition of 25 mol % ${\mathrm{K}}_2$O to amorphous ${\mathrm{B}}_2$ ${\mathrm{O}}_3$ increases the glass-transition temperature $T_g$ by 50%, increases the specific heat for T≊4, but leaves the low-temperature phonon mean free path essentially unchanged. The increase in specific heat with increasing $T_g$ is not in agreement with the free-volume model of a glass, which would predict a ≳50% decrease in specific heat.