## Universality of anomalous excitations and diffusion effects in amorphous solids and glasses

### professor M. Schulz (Ulm University)

### Abstract

Thermodynamic and electric properties of glasses were intensively
investigated during the last decades. An important result of this research
was the discovery of several universal properties that are only weakly
dependent on the special structure of the amorphous solid. These
`anomalous' properties are normally unknown for crystals.
Such properties can be observed in the low temperature behavior of the
specific heat, the thermal conductivity, the propagation of ultrasound,
dielectric loss of glasses as well as in phenomena related to the
transport and diffusion of ions close to and below the glass transition
point. Firstly, we will give a general proof for the universal existence
of anomalous, non-Debye excitations in amorphous is proposed. Starting
from an ideal amorphous solid with fixed mean positions of all atoms and
harmonic interactions, it was demonstrated that any increase of disorder
leads stringently to an increase of the spectral density for low (and also
very high) frequencies. That means, the density of states shows additional
contributions to the low frequency part of the standard Debye density,
even the wave length of corresponding phonon like excitations is of an
order of magnitude on which the amorphous solid is still homogeneous.
Secondly, a mesoscopic model will be presented which allows the
description of anomalous transport effects in glasses at and below the
glass transition point. Such effects are known as mixed alkali or mixed
mobile ion effect and they dominate the AC and DC properties of several
glasses. It will be shown that the interplay of an effectively short
ranged two particle interaction between the typical charge carriers and a
local, component-sensitive interaction between the charged particles and
their disordered environment leads above a critical interaction strength
to a universal anomalous dependence of the conductivity on the composition
ratio of the mobile charge carriers. The consideration of possible
structural relaxations of the glassy environment supports these effects
essentially, so that especially the difference between the conductivity of
glasses obtained from an partial ion exchange above and below the glass
transition point can be explained.