Low-temperature behavior of potassium and sodium silicate glasses

In a study of the low-temperature anomalies which appear in disordered solids we have measured the specific heat, thermal conductivity, thermal expansion, and dielectric dispersion for a carefully prepared series of (SiO₂{)}_{1{{-}}x}$(${K}₂O{)}ₓ$ and (${SiO}₂)_1-x(Na₂O)ₓ glasses. Each sample had a known glass transition temperature Tg, mass density, phonon velocities, covalency, and density and concentration fluctuations. The only significant correlation occurred between the phonon mean free path and the glass-transition temperature. No explicit support was found for any model developed to explain the specific heat and/or thermal conductivity of glasses.