Rare electrical transport

The electrical transport properties of rare earth manganites with perovskite-type structure have been extensively studied in recent years because of the colossal magnetoresistance (CMR) effect or potential applications as catalysts. In most cases the general formula of rare earth manganites used in these studies are Ln,, (A,(Mn03, where A is a divalent ion (A = Ba, Sr, Ca, Pb) substituting for La. 

In these oxides, the 6s and 5d and, to a lesser extent, the 4f electrons of the rare earth atom are mainly responsible for electrical transport and structural properties, whereas the localized 4f electrons govern the magnetic properties. X-ray absorption spectroscopy (XAS) offers the important advantage of simultaneously probing the 4f and the ds conduction states in these oxides. In XAS, the dipole selection rules are strictly obeyed and this facilitates the identification of the spectral features. Generally, the 3d—>4f (Mjv-v) or 4d—>4f (Niv-v) absorption transitions are studied. In these absorption processes the excited 4f electron participates directly in the transition. The resulting multiplet structure is observed to provide a finger-print of the 4f population of the rare earth atom. The modification in the valence band electron distribution introduced by the delocalization of a 4f electron is probed by the transition of a 2p (Ln-m) electron in the vacant sd conduction states. In this case the 4f electron does not participate direct in the transition. 

Electrical transport characteristics of rare-earth oxides. 

Sharma Indu, B., Singh, D., Magotra, S.K. Effect of substitution of magnetic rare earths for La on the structure, electric transport and magnetic properties of La2SrFc207. J. Alloys Comp. 1998,269,13-16. 

E. Gratz and M.J. Zuckermann, Transport properties (electrical resitivity, thermoelectric power thermal conductivity) of rare earth intermetallic compounds 117... 

Friederich et al. (1979) have reported the first data obtained by EPR for non-s rare earth ions (Nd ), e.g. NdnAggs, which is paramagnetic down to 4.2 K. The experiments were done at 293,100 and 4.2 K in a magnetic field of 1000 to 5000 G, and showed the presence of some complicated structure. The results are discussed in terms of the g factor. The resonance observed above 100 K indicates the existence of sites having a non-axial crystal field. The authors think that EPR is promising for investigation of the electrical field gradients (or crystal fields) in amorphous rare earth alloys (see next section for transport properties). 

TRANSPORT PROPERTIES (ELECTRICAL RESISTIVITY, THERMOELECTRIC POWER AND THERMAL CONDUCTIVITY) OF RARE EARTH INTERMETALLIC COMPOUNDS... 

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