G. Carini et al., LOW-TEMPERATURE SPECIFIC-HEATS OF LANTHANUM AND YTTRIUM PHOSPHATE-GLASSES, Nuovo cimento della Societa italiana di fisica. D, Condensed matter,atomic, molecular and chemical physics, biophysics, 16(8), 1994, pp. 1277-1284
The specific heats of (R(2)O(3))(x)(P2O5)(1-x) glasses containing high
concentrations of La3+ and Y3+ ions have been measured between 1.5 K
and 30 K. It is shown that, in addition to the usual Debye contributio
n, there is an excess specific heat arising from localized vibrational
states which has been discussed in terms of two distinct models. The
first predicts a maximum in the temperature dependence of the excess s
pecific heat associated with the crossover frequency from phonon to fr
acton behaviour. The phonon-fracton density of states used to fit the
excess specific heat gives rise to model parameters having the same ma
gnitudes as those found previously for other glasses including samariu
m phosphates. The second model, formulated on the basis of soft vibrat
ions in glasses, predicts a minimum in the excess specific heat, which
is also observed.