LOW-FREQUENCY VIBRATIONAL-STATES IN SPECTROSIL-B

The heat capacity of Spectrosil-B (vitreous silica containing 1200 ppm of OH) has been measured in the temperature range from 2 to 20 K. The heat capacity is closely similar to that of Spectrosil-WF (vitreous silica containing less than 20 ppm of OH). Therefore the heat capacities in the temperature range explored in this work do not depend upon OH concentration. The low-frequency density of vibrational states, g(nu), has been determined. It has been found that the form of g(nu) is non-quadratic which can be explained on the basis of the rotational motion of SiO4 rigid tetrahedra. The Raman and infrared coupling constants have been determined and these are similar. It is found that the form of the Raman coupling constant cannot be explained on the basis of Martin-Brenig theory.