Amorphous lanthanide metal

Magnetism in amorphous lanthanide-transition metal alloys... 

It has been shown that all the properties of T, Hy, 0 and electrical resistivity at room temperature (Prt) for the Al-R amorphous alloys were essentially independent of the atomic number of the R metals. The atomic size of the R metals varies systematically with the atomic number and hence the atomic size factor also seems to have little effect on the above-mentioned properties. On the other hand, it is generally known that the inherent chemical nature of the lanthanide metals results from 4f-electrons which lie at the inner side in their atoms. Although the number of 4f-electrons varies systematically with the atomic number, the electrons are screened by 5s - and 5p -electrons which lie at the outer side of the atoms, resulting in a similarity in chemical properties of the lanthanide metals. Accordingly, it may reasonably be assumed that the independence of the properties of the Al-R amorphous alloys as a function of atomic number is due to the unique electronic structure in which the 4f-electrons are screened by 5s- and 5p-electrons. 

Quite a different scenario is expected for a lanthanide metal ion, where the valence orbitals are buried inside. Thus, a lanthanide ion has less preference for a particular coordination geometry. This can sometime allow ready transformation of coordination geometry around the metal center, leading to drastic changes in the overall structure and making it amorphous. Unlike MOFs built with transition metals, lanthanide MOFs rarely exhibit SC-SC transformation. One example is reported in a thermally... 

Preparation and Characterization of Lanthanide and Actinide Solids. Crystalline / element phosphates were prepared as standards for comparison to the solids produced in the conversion of metal phytates to phosphates. The europium standard prepared was identified by X-ray powder diffiaction as hexagonal EuP04 H20 (JCPDS card number 20-1044), which was dehydrated at 204-234 °C and converted to monoclinic EUPO4 (with the monazite structure) at 500-600 °C. The standard uranyl phosphate solid prepared was the acid phosphate, U02HP04 2H20 (JCPDS card number 13-61). All attempts to prepare a crystalline thorium phosphate failed, though thorium solubility was low. In the latter case the solids were identified as amorphous Th(OH)4 with some minor crystalline inclusions of Th02. 

The amorphous alloys are characterised by a structural disorder where each atom constitutes a structural unit. In this state, the small mass density and the loss of the periodicity enhance the localisation of the 3d electrons in the lanthanide-transition metal alloys. In amorphous alloys, at a certain concentration, the 3d magnetic moment... 

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. 

Liu and Hong, 2007] X. R. Liu and S. M. Hong. Evidence for a pressure-induced phase transition of amorphous to amorphous in two lanthanide-based bulk metallic glasses. Applied... 

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