Rare earth conductivities

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. 

In the above simplified picture, the position of the bare f level relative to the Fermi level is not subject to any restrictions. For Ce compounds and alloys, Ef may be fixed by consideration of the observed valence, so that the f density of states is expected to cut across the Fermi energy. This does indicate that the effects of the hybridization with the conduction band should also be included, in any more realistic model of Ce systems. However, the model should be equally applicable to other light rare earths as both experiment and band structure calculations show that the width and filling of the rare earth conduction band is roughly similar all across the lanthanide row. Also, from considerations of charge neutrality, the value of C/fj is expected to be only slowly varying across the row. Hence the observation of similar satellite structures in Pr and Nd compounds may be taken to be an affirmation of the above pictures. 

Fig. 9. A modem fluorescent lamp coating including a conductive layer of Sn02 F, then a protective coating of finely divided alumina, followed by the inexpensive halophosphate phosphor, and finally a thin layer of the triphosphor rare-earth blend.

Figure 7.6. A filled. skutterudite antimonide crystal structure. A transition niclal atom (Fc or Co) at the centre of each octahedron is bonded to antimony atoms at each corner. The rare earth atoms (small spheres) are located in cages made by eight octahedra. The large thermal motion of rattling of the rare earth atoms in their cages is believed be responsible for the strikingly low thermal conductivity of these materials (Sales 1997).

UCS, rare earth, and sodium are just three of the parameters that are readily available to characterize the zeolite properties. They provide valuable information about catalyst behavior in the cat cracker. If required, additional tests can be conducted to examine other zeolite properties. 

Much of this study was conducted on LaNi5-based alloys [13-20] and TiNir-based alloys [21-23], Sanyo Electric, Matsushita Battery and most other battery manufacturers have been using LaNi5-based rare earth-nickel-type alloys [24,... 

Rare earth elements, with relatively high thermal neutron activation cross-sections, have been tested or considered as tagging species for this purpose. At GA (Ref 8), preliminary expts were conducted with 0.38 cal ammo using dysprosium (Dy) and europium (Eu) deposited on the wall of the cartridge case and in the gunpowder, and Dy, hoKnium (Ho) and indium (In) in the primer. 

It has been noted that the conductivity and activation energy can be correlated with the ionic radius of the dopant ions, with a minimum in activation energy occurring for those dopants whose radius most closely matches that of Ce4+. Kilner et al. [83] suggested that it would be more appropriate to evaluate the relative ion mismatch of dopant and host by comparing the cubic lattice parameter of the relevant rare-earth oxide. Kim [84] extended this approach by a systematic analysis of the effect of dopant ionic radius upon the relevant host lattice and gave the following empirical relation between the lattice constant of doped-ceria solid solutions and the ionic radius of the dopants. 

The most well-studied and useful materials to date are those with fluorite-related structures, especially ones based on ZrOj, ThOj, CeOj and Bi203 (Steele, 1989). To achieve high oxide ion conductivity in ZrOj, CeOj and ThOj, aliovalent dopants are required that lead to creation of oxide vacancies. Fig. 2.2, scheme 4. The dopants are usually alkaline earth or trivalent rare earth oxides. 

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