Experimental Studies of Several Cerium-Aluminide - Kondo Compounds.

Cerium metal is known to undergo an isostructural volume collapse concurrent with a first order electronic transition driven by temperature or pressure. The system passes from an ambient temperature and pressure Curie-Weiss paramagnetic (gamma)-phase to a low temperature or high pressure Pauli paramagnetic (alpha)-phase. The models which have been historically proposed to explain the (gamma) -(alpha) transition in Ce are discussed. The intermetallic (gamma)-like compound CeAl(,2) is employed to investigate this (gamma)-(alpha) transition. Volume reduction via chemical substitution is the experimental method used to controllably drive Ce through its volume collapse. Lattice parameter measurements point to an alloy -induced volume collapse for x > 0.5 in Ce(,1-x)Sc(,x)Al(,2). CeAl(,2) is magnetically non-dilute and is included in the class concentrated Kondo systems which exhibit a Kondo effect. Electrical resistivity measurements on (Ce,Sc)Al(,2) and (Ce,Y)Al(,2) systems were performed and the results are interpreted in the context of a crystalline electric field-modified Kondo effect. The characteristic energy scale, the spin fluctuation (Kondo) temperature T(,SF), is seen to dramatically increase upon the approach of the volume collapse. The resistivity results plotted versus ln T/T(,SF) of these alloys were empirically scaled and normalized and show a universal low temperature resistivity form. Another Ce based system, CePd(,3) is similarly studied. CeAl(,2) enters an antiferromagnetic phase with ordering temperature T(,N) of about 3.85K. Thermal expansion measurements via capacitive dilatometry were performed on the Ce(,1-x)Th(,x)Al(,2) and Ce(,1-y)Eu(,y)Al(,2) systems. The dependence of T(,N) on Th addition is discussed in terms of magnetic dilution and spin fluctuation effects with ideas consistent with those of the single-impurity Anderson model.