Thermodynamic properties of small amorphous and crystalline silica particles at low temperatures

We have measured the low-temperature (T less than or equal to 1 K) specific heat and heat release of small amorphous and crystalline SiO2 particles em bedded in Teflon and of Vycor. The temperature and time dependence of these properties have been interpreted in terms of the tunneling model. We found that the particle size influences the density of states of tunneling syste ms of the composite. The smaller the size of the particles the larger is th e density of states of tunneling systems P-0. Quartz grains with dimensions in the micrometer range show similar glass-like properties as vitreous sil ica. In comparison with bulk vitreous silica, Vycor shows a much larger P-0 in agreement with the behavior we found for small SiO2 particles. We discu ss the implication of our results on the origin of the universal low-temper ature properties of glasses.