R.A. Montani

Democratic particle motion for metabasin transitions in simple glass formers.

We use molecular dynamics computer simulations to investigate the local motion of the particles in a supercooled binary liquid. Using the concept of the distance matrix, we find that the alpha relaxation corresponds to a small number of crossings from one metabasin to a neighboring one. Each crossing is very rapid and involves the collective motion of O(40) particles that form a relatively compact cluster, whereas stringlike motions seem not to be relevant for these transitions. These compact clusters are thus potential candidates for the cooperatively rearranging regions proposed a long time ago by Adam and Gibbs.

An electrothermal model for high-field conduction and switching phenomena in TeO2V2O5 glasses

Abstract The electrical behaviour of 0.4TeO2–0.6V2O5 glass samples was studied by determining the current-voltage dependence with constant current. The results show increasing deviations from the Ohms law with increasing current density, leading to a maximum voltage at large current densities. This electrical behaviour, described in literature as a switching phenomenon, is interpreted assuming that the Joule effect resulting from the current passing through, induces large increases of the glass conductivities.

Effect of Ag2O on the conductive behaviour of silver vanadium tellurite glasses

Abstract The effect of the Ag 2 O on the conductivity of vanadium tellurite glasses has been studied by using the impedance spectroscopy in a wide range of temperature. The obtained results confirm the existence of a transition from a typically electronic (polaronic) conductive regime when the molar fraction ( X ) of Ag 2 O is equal to 0, to a ionic conductive regime when X tends to 1. This transition is characterized by a deep minimum in the electrical conductivity of about 3 orders of magnitude.

The conductive behaviour of silver vanadium-molybdenum tellurite glasses

Abstract In a previous paper, the effect of the Ag 2 O on the electrical conductivity of vanadium tellurite glasses of the form X Ag 2 O·(1− X )V 2 O 5 ·2TeO 2 has been studied by using the impedance spectroscopy in a wide range of temperature and composition. The obtained results confirm the existence of a transition from a typically electronic (polaronic) conductive regime when the molar fraction ( X ) of Ag 2 O is equal to 0 to an ionic conductive regime when X tends to 1. This transition is characterised by a deep minimum in the electrical conductivity of about three orders of magnitude. In the present paper, a complementary study of the system of the form X Ag 2 O·(1− X )[0.5V 2 O 5 –0.5MoO 3 ]2TeO 2 is reported. The correlated behaviour between conductivity and the mean distance between silver ions and between vanadium ions for these two systems reinforces the idea of two independent migrating paths for both electrons and ions, respectively.

On the Monte Carlo simulation in the α-AgI system: The influence of the maximum displacement allowed to particles

Abstract Monte Carlo calculations on the α-AgI system were performed. The partial pair distribution function, the mean square displacement and the energy associated to Ag ion migration were obtained. The calculations make it evident that the maximum displacement allowed to the particles when exploring the configurational space should be taken into consideration.

On the deviation from the theoretical behavior in applying Wagner's polarization method to the solid electrolyte cuprous iodide

Abstract An interpretation of the deviations from the theoretical behavior by the application of Wagners polarization method to CuI is presented. It is based on the effect of high polarization potentials on the defect concentration, which leads to a modification of the slope of the logarithm of the hole current versus applied potential curves.

Time evolution of clusters of mobile particles in a model glass former

In this work we investigate by means of molecular dynamics simulations the detailed time evolution of string-like cooperative motions in a binary Lennard–Jones system at temperatures close to its mode-coupling temperature, Tc. The strings will be fully geometrically and dynamically characterised, making evident the correlated and concerted nature of the motions of the particles comprised. We shall show that at low temperature each string occurs in a sharp time window within the time interval [0,t∗], where t∗ is a characteristic time related to the lifetime of the global clusters of mobile particles. Moreover, the different strings that comprise a given global cluster will be shown to take place independently and asynchronically, thus providing further support to the heterogeneous scenario of relaxation, but in which different independent string-like sub-regions relax at different timescales. Finally, we shall also demonstrate that as temperature is increased the strings evolve during an increasing fraction of the time interval [0,t∗] and that for T∼0.55 the lifetimes of the strings and of the global clusters become akin to each other.

On the potential range of applicability of Wagner's polarization method

Abstract A previously proposed model for explaining deviations from the theoretical electronic current vs applied potential behavior predicted by Wagners polarization method is extended to include higher valence compounds. New supporting experimental observations are also presented.

A variational approach to relaxation in rugged free energy landscapes

We develop a variational principle governing the relaxation behavior of hierarchical systems. Limiting ourselves to a particular class of models amenable of a variational treatment, we study the relaxation of rugged systems whose conformation space topology deviates from ultrametricity under selective controllable conditions. While the Debye law is obtained in the ultrametric limit, Kohlrausch relaxation is shown to be directly related to the level of ruggedness beyond the ultrametric limit.

Monte Carlo simulation of the CaF2

A Monte Carlo simulation of CaF2 in the canonical ensemble was carried out using the Metropolis algorithm and the Soft‐Core and Born–Mayer–Huggins potentials. By studying the behavior of the mean square displacement and the specific heat, the existence of a transition to a superionic phase at about 1470 K was confirmed. A partial occupation of the interstitial sites in this superionic phase was also found.