Transition metal amorphous alloys

Inoue, A. Nakamura, N. Sugita, T. Zhang, T. Masumoto, T. (1993a). Bulky La-Al-TM (TM=Transition Metal) amorphous alloys with high tensile strength produced by a... 

All of the heavy lanthanide-transition metal amorphous alloys which are magnetic show antiferromagnetic coupling between the lanthanide and transition metal spins. The Curie temperatures as previously noted, are perturbed significantly from the crystalline values and may be either depressed (J -Fe alloys) or increased (R-Co alloys) due to fluctuations in exchange and anisotropy interactions or band structure effects. The latter has been ascribed by Tao et al. (1974) to explain the anomalous increase in the of R-Co alloys. They suggested a reduced electron transfer from the rare earth conduction bands to the Co d-band in the amorphous state compared to the crystalline. In the case of the RF z alloys the situation is more complex due to the population of both minority and majority spin bands of the Fe. 

A common feature of R-amorphous alloys and transition metal-metalloid alloys is that they show similar transport properties such as high resistivities with weak temperature dependence and often at low temperature a logarithmic variation with temperature (Kastner et al., 1980). The magnetic R-alloys often show additional transport behaviour. We will now discuss this in detail for several R-amorphous alloys. 

Fig. 80. Superconducting transition tent perature of transition metals and alloys of the 4d series in the amorphous and crystalline states, as a function of electron-to-atom ratio. The result obtained on amorphous La0j0AUo2o ( ) has been included for comparison (after Johnson, 1978).

Hellstem, E., and Schultz, L., Amorphization of transition metal Zr alloys by mechanical alloying, Appl. Phys. Lett., 48 (2), 124-126, 1986. 

Bellissent, R., Galli, G., Hyeon, T., MigUaido, R, Parette, G., Suslick, K.S. Magnetic and structural properties of amorphous transition metals and alloys. J. Non-Cryst. Solids 205-207, 656-659 (1996)... 

The formation of Al-based amorphous alloys by liquid quenching was first tried in binary systems of Al-metalloid and Al-transition-metal (M) alloys. As a result, it was found in... 

B. S. Berry and W. C. Pritchet, Effect of Hydrogen on the Magnetoelastic Behavior of Amorphous Transitional Metal-Metalloid Alloys, J. Appl. Phys. 52 1865 (1981). 

The above treatment assumes a single atomic component system whereas the rare earth transition metal amorphous materials (R-T) are two component and thus three pair correlation functions, G(r), exist, one each for the possible R-R, R-T, and T-T combinations. These are lumped together to produce the observed scattered intensity function, but may be separated by experiments on isotopically substituted alloys which have different neutron scattering amplitudes, or as in the case of Co-P by separating the magnetic components using polarized neutrons (Bletry and Sadoc, 1975). 

Self-diffusion in amorphous Fe35Co5oBi5 and FeegCo Bis alloys was investigated using radioactive Fe and Co tracer atoms by [1994Pav]. It was found that the diffusivity of Fe equals to that of Co and it is independent of mutual concentration of the transition metal in alloys. The mean activation enthalpy was calculated. 

Metallic Glasses. Under highly speciali2ed conditions, the crystalline stmcture of some metals and alloys can be suppressed and they form glasses. These amorphous metals can be made from transition-metal alloys, eg, nickel—2irconium, or transition or noble metals ia combination with metalloid elements, eg, alloys of palladium and siUcon or alloys of iron, phosphoms, and carbon. 

Perspectives for fabrication of improved oxygen electrodes at a low cost have been offered by non-noble, transition metal catalysts, although their intrinsic catalytic activity and stability are lower in comparison with those of Pt and Pt-alloys. The vast majority of these materials comprise (1) macrocyclic metal transition complexes of the N4-type having Fe or Co as the central metal ion, i.e., porphyrins, phthalocyanines, and tetraazaannulenes [6-8] (2) transition metal carbides, nitrides, and oxides (e.g., FeCjc, TaOjcNy, MnOx) and (3) transition metal chalcogenide cluster compounds based on Chevrel phases, and Ru-based cluster/amorphous systems that contain chalcogen elements, mostly selenium. 

A further method of producing amorphous phases is by a strain-driven solid-state reaction (Blatter and von Allmen 1985, 1988, Blatter et al. 1987, Gfeller et al. 1988). It appears that solid solutions of some transition metal-(Ti,Nb) binary systems, which are only stable at high temperatures, can be made amorphous. This is done by first quenching an alloy to retain the high-temperature solid solution. The alloy is then annealed at low temperatures where the amorphous phase appears transiently during the decomposition of the metastable crystalline phase. The effect was explained by the stabilisation of the liquid phase due to the liquid—>glass... 

Most amorphous metallic alloys do not show a metal-insulator transition. They do, however, show moderate changes in the resistivity with temperature, some of which can be interpreted in terms of the quantum interference effect, together with the interaction effect of Altshuler and Aronov (Chapter 5, Section 6). These will be described below. Amorphous alloys of the form Nb Six Au Six etc. do, however, show a metal-insulator transition of Anderson type, and some of those are treated in Chapter 1, Section 7. 

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... 

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