Thermoelectric Power of Cerium-Based Systems

Abstract

A study of the valence instability in the Ce_1-XTh_X system was carried out recently via resistance and volume measurements.⁽¹⁾ In this work we report measurements of the thermoelectric power (TEP) in the Ce_1-XTh_X and Ce_0.9-XTh_0.1La_X systems. Figure 1 shows the characteristic shape of TEP curves in the region of a continuous transition (x=0.290), at the second order instability (x=0.269) and across a first order instability (x=0.175). In all cases the TEP is large and positive with a cut-off occurring at the valence instability temperature. One can see the signature of critical rounding on the 0.269 curve, but it is not possible to separate the critical contribution from the normal background which is strongly temperature dependent. In addition, below the valence instability temperature, i.e., in the mixed valence phase, the TEP is small ≃7–8 µV/deg and weakly temperature dependent. To get more insight into the TEP of the y-phase we have tried to extend the γ-phase region by alloying CeTh with La. It is known that the addition of La lowers the instability temperature ∿9°K/at % La and that above 9 at % La the transition becomes continuous.(2) Figure 2 shows the TEP for a CeThLa sample.

Work supported in part by the U. S. Office of Naval Research and the U. S. Army Research Office.