Tracking the Effects of Rigidity Percolation Down to the Liquid State: Relaxational Dynamics of Binary Chalcogen Melts

The stochastic dynamics of binary liquids with formula $A_x{B}_{1-x}$, $x=0–0.4$ is investigated by neutron spin-echo spectroscopy. These compositions comprise samples of varying chemical connectivity, ranging from twofold-coordinated liquid Se to higher average coordinated ${\mathrm{As}}_2{S}_3$. The parameters giving the temperature dependence of the relaxation patterns show a quasilinear dependence on the average coordination number. The results thus extend the validity of the rigidity concept into the normal liquid state and emphasize the role played by the fine details of atomic bonding on the dynamics at 10 ps–1 ns scales.

Figure 1

Selected NSE spectra which were measured at the lowest and highest momentum transfer value, respectively. The data were measured on the ${\mathrm{Se}}_{92}{\mathrm{Ge}}_{08}$ sample. The solid lines are fits of KWW relaxation functions.

Figure 2

Wave-vector dependence of the relaxation times for a set of temperatures (left-hand side graphs) and temperature dependence of the relaxation times for a set of wave vectors (right-hand side graphs). Data for liquid Se correspond to the two uppermost graphs. The wave-vector values are given in the insets in reciprocal angstrom units. Data for liquid ${\mathrm{Se}}_{92}{\mathrm{Ge}}_{08}$ are shown in the two middle frames. Data for liquid ${\mathrm{As}}_{25}{\mathrm{Se}}_{75}$ are given in the two lowest frames.

Figure 3

The activation energies calculated from the Arrhenius plots versus average coordination number. The inset displays the dependence of the thermodynamic glass-transition temperature on the same parameter. Data pertaining the calorimetric glass-transition temperatures are taken from Ref. 2.

Figure 4

Compositional dependence of the parameter $C_{\beta }$ characterizing the strength of the temperature dependence of $\beta$. The inset displays the temperature dependence of data pertaining to several different compositions.