Electronic states disordered alloys

Abstract. We compute the velocity correlation function of electronic states close to the Fermi energy, in approximants of quasicrystals. As we show the long time value of this correlation function is small. This means a small Fermi velocity, in agreement with previous band structure studies. Furthermore the correlation function is negative on a large time interval which means a phenomenon of backscattering. As shown in previous studies the backscattering can explain unusual conduction properties, observed in these alloys, such as for example the increase of conductivity with disorder. 

Figure 5.22 shows p, i H, and S ( T)/T for disordered (Au, Ag, Cu)-Sn systems versus x. TK and the MDOS have already been presented above (Fig. 5.13 and Fig. 5.17). A close overall similarity exists among the different alloys as well as to the corresponding liquid state. For alloys with 27-30 at. % Sn, where Kpe = 2fcF is fulfilled, p is maximal while RH and S ( T)/T deviate from the corresponding free-electron value. These deviations are obviously related to FsBz-effects showing that f or fcF cannot be deduced from Hall-effect data in alloys with a high peak at Kpc as mentioned above. Equations (5.7) and (5.8) are always found to be a better approach.

Discussing the electronic properties of fluids, we cannot ignore the basic fact that these materials are structurally disordered. When the electron-ion interaction is weak, as in the NFE limit, structural disorder is not too important. But Anderson (1958) showed that in the presence of a sufficiently strong disordered ionic potential, electrons inevitably become localized. The localized wave functions decay exponentially with distance from specific atomic sites and, at T = 0, an electron will not diffuse to another part of the material, even given an arbitrarily long time. In his original paper, Anderson considered a specific disordered model structure—a crystalline alloy having a random distribution of potential well depths. He showed that there exists a critical ratio of the width of the potential distribution V to the band width W of the ordered system. If V/W 1, the electronic states are localized. 

THEORY OF ELECTRONIC STATES IN DISORDERED ALLOY HYDRIDES... 

Very few results on the adsorption of H on UHV clean surfaces of intermetallic compounds and ordered or disordered alloys are known. The surface electronic structure of e,g, FeTi and LaNi are essentially those of a d-transition metal with a high density of states at E, Accordingly,... 

Various interesting properties of 4f-electron systems such as CK and HF compounds have been generally studied using crystalline materials, where there is also periodicity of 4f electrons. The formation of the Fermi surface from 4f-electron bands is essential to many, if not all of these cooperative properties. Therefore, such behaviors are not expected to occur in disordered alloys without translational symmetry where the 4f electrons have non-Bloch-type states. However, interesting behaviors have recently been observed in Ce-based structurally disordered materials. Here, we introduce amorphous CeRu system as a typical example. Crystalline CeRu2 compoimd is one of the famous itinerant 4f-electron materials to show SC (T = 6.3 K, y = 27 mj/mol K ) (Hedo et al., 1998 Matthias et al., 1958). On the other hand, amorphous fl-CeRu also shows FlF-like behavior in the Ce-rich side and SC in the Ru-rich side (Homma et al., 1997). 

Che72] Chen, A.-B., Weisz, G., and Sher, A., Temperature Dependence of the Electron States and dc Electrical Resistivity of Disordered Binary Alloys, Phys. Rev.,Vol 5,1972, p. 2897-2924... 

Amorphous alloys are characterised by a structural disorder where each atom constitutes a structural unit. In this state, the low mass density and the loss of the periodicity enhance the localisation of the 3d electrons in the rare earth-transition metal alloys. In... 

Solid-state nuclear magnetic resonance (NMR) has been extensively used to assess structural properties, electronic parameters and diffusion behavior of the hydride phases of numerous metals and alloys using mostly transient NMR techniques or low-resolution spectroscopy [3]. The NMR relaxation times are extremely useful to assess various diffusion processes over very wide ranges of hydrogen mobility in crystalline and amorphous phases [3]. In addition, several borohydrides [4-6] and alanates [7-11] have also been characterized by these conventional solid-state NMR methods over the years where most attention was on rotation dynamics of the BHT, A1H4, and AlHe anions detection of order-disorder phase transitions or thermal decomposition. There has been little indication of fast long-range diffusion behavior in any complex hydride studied by NMR to date [4-11]. 

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