Resistivity, electrical rare earth elements

Other rare earth elements 767 R = electrical resistance... 

More than one boride phase can be formed with most metals, and in many cases a continuous series of solid solutions may be formed. Several methods have been used for the relatively large-scale preparation of metal borides. One that is commonly used is carbon reduction of boric oxide and the appropriate metal oxide at temperatures up to 2000 °C. Fused salt electrolysis of borax or boric oxide and a metal oxide at 700 1000 °C have also been used. Small-scale methods available include direct reaction of the elements at temperatures above 1000 °C and the reaction of elemental boron with metal oxides at temperatures approaching 2000 °C. One commercial use of borides is in titanium boride-aluminum nitride crucibles or boats for evaporation of aluminum by resistance heating in the aluminizing process, and for rare earth hexaborides as electronic cathodes. Borides have also been used in sliding electrical contacts and as cathodes in HaU cells for aluminum processing. 

The electrical resistivity of the rare earth metals has been studied in detail. We refer the reader to review articles by McEwen (1978) and Koskenmaki and Gschneidner (1978) for a more detailed discussion. De Gennes and Friedel (1958) developed their well-known model (see sect. 2.3.4) in order to explain the spin-disorder resistivity in lanthanides for T > As can be seen in fig. 9, PmaJiT>Tc), as determined from the resistivity in the c-axis direction for the heavy lanthanide elements, follows the de Gennes factor, (g — + 1). Refinements of that model have been made taking... 

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