If the static disorder in a system is increased the conductivity and the electron mean free path decreases to the limit where it reaches the Ioffe-Regal criterion. In this paper experimental results are presented which show that dynamic disorder (produced by electronphonon interaction) can produce similar effects as static disorder. In certain metallic glasses it has been found that when the resistivity as a function of temperature reaches a critical value (almost equal to the maximum metallic resistivity value) the TCR changes from positive to negative values.

As a result of strong electron-phonon interaction, the enhancement of scattering with increasing temperature may decrease the mean free pathl in crystals down to interatomic distances:l≈a. This means that with respect to the electron wave the degree of the atomic disorder in these crystals is approximately the same as in amorphous metal. Because of a high electron velocity the dynamic character of the disorder seems to be unimportant. At the same time, the degree of disorder can be easily changed by varying the temperature. This makes it possible to simulate and study the transport properties of the disordered media on highquality crystals with strong phonon scattering. The sign that indicates the fitness of a crystalline metallic material for such studies is the saturation of its resistivityρ that ceases to grow as the temperature is increased.

The saturation of resistivity was investigated experimentally on (i) Cu-Zr alloys in the crystalline state, (ii) single crystals of WO₂, which is a metal with well-defined Fermi surface.

The samples of Cu-Zr were produced by the recrystallization of amorphous ribbon. Some of these samples reveal resistivity saturation. With further increase ofT a maximum in theρ(T) dependence was observed at those compositions which slightly decreased theirρ value under recrystallization. This unusual dependence can be explained in terms of the two-band model assuming that thed-electrons reach the minimal free path,l≈a, while thes-electrons do not.

The WO₂ crystals were used to study the anisotropy of (T). In the directions, whereρ is high, there is a tendency to saturation. Whereρ is low, no tendency to saturation is observed. The quantitative analysis of the curves has shown that not only the absolute value but also the relative value of the deviation from the Boltzmann lawρ∼T decreases down as the resistivity decreases.