Low-temperature thermal conductivity of sodium borate glasses

The thermal conductivity of glassy (${\mathrm{B}}_2$ ${\mathrm{O}}_3$ ${)}_{0.99}$(${\mathrm{Na}}_2$ O${)}_{0.01}$ and (${\mathrm{B}}_2$ ${\mathrm{O}}_3$ ${)}_{0.90}$(${\mathrm{Na}}_2$ O${)}_{0.10}$ has been measured in the temperature range 0.3–15 K. We find a strong influence of the addition of ${\mathrm{Na}}_2$O, as opposed to the behavior of silica glasses. In borate glasses there exists a strong decrease of conductivity with soda content while the plateau gradually fades away.