Specific-heat study of the phonon-fracton crossover in glassy ionic conductors

Specific-heat measurements as a function of temperature in the range 1.2--40 K are reported for the ternary glassy ionic conductors (AgI)ₓ (Ag₂{0.2B}₂O₃{)}_{1{{-}}x}$ for x=0, 0.2, 0.5, and 0.65. A pronounced maximum in C/${T}³$ vs T is observed in the above temperature range. This anomaly and the anomalous temperature dependence observed previously at higher temperature are interpreted in terms of an energy spectrum typical of localized modes of fractal nature, which dominate over the long-wavelength elastic modes.