We determined the crossover frequency ${\mathrm{\omega }}_{\mathrm{co}}$ between phonon and fracton regimes from the study of the low-frequency inelastic light scattering in superionic borate glasses of the type (AgI${)}_{\mathit{x}}$(${\mathrm{Ag}}_2$O⋅${\mathrm{B}}_2$${\mathrm{O}}_3$${)}_{1\mathrm{-}\mathit{x}}$. The scaling of ${\mathrm{\omega }}_{\mathrm{co}}$ with the fractal characteristic length was studied by variation of the AgI concentration x. We thus obtained the diffusion coefficient scaling exponent theta and the spectral dimensionality d̃ which characterizes energy diffusion on a fractal.

• Received 12 August 1986

DOI:https://doi.org/10.1103/PhysRevLett.58.503