Influence of phase separation on the thermal conductivity of potassium borosilicate glasses between 1 and 10 K

The thermal conductivities of five potassium borosilicate samples which had undergone thermal treatment for different periods of time, were measured between 1 and 10 K. The results showed that, initially, as the particles grow bigger, thermal conductivity decreases until it reaches a minimum corresponding to an average dimension of 900 Å, thereafter increasing. An attempt was made to analyse the results in terms of a resonant scattering theory, which proved to be insufficient. As an alternative, a phenomenological model taking into account Kapitza's resistance was developed. This effect being important mainly during the first stage of the thermal treatment when the boundaries between phases are not yet well defined, it could explain the existence of a minimum of the thermal conductivity.