Some electrical and structural properties of Pr-Ce alloys

Abstract

The electrical resistivity of praseodymium-cerium (Pr-Ce) and lanthanum-cerium (La-Ce) alloys has been studied in the temperature range 1.3 - 1100 K and 0 - 900 C respectively. The present data have confirmed the existence of a conventional Kendo divergence at T = 0 K in double-hexagonal close packed Pr-Ce alloys. In addition to this, evidence has been found of structure at about 20 K and 90 K. This is tentatively ascribed to the presence of Kondo sidebands of the type discussed by Maranzana. These Kondo sidebands are related to the cerium crystalline electric field levels expected in the Pr-Ce alloys on the basis of Rainford's (1971) crystalline electric field parameters for pure praseodymium. Evidence has also been obtained, under certain conditions, for the existence of antiferromagnetic ordering in the alloys at around 26 K. In connection with the structural properties, the dhcp →← fee phase transition in the Pr-Ce alloys and the absence of this transition in pure praseodymium have been discussed on the basis of electrical resistivity and X-ray powder diffraetion data. At high temperatures, a hysteresis loop for the dhcp →← fcc transition in the Pr-Ce alloys has been observed which decreased in size with increasing praseodymium content and vanished in the Ce Pr alloy .(_10)Pr(_.90) alloy. No hysteresis was observed with alloys of higher praseodymium content. The similarity between the atomic volumes of the dhcp - Pr and the hypothetical fce-Pr phases and the disappearance of the dhcp →← fee transition in the Pr-Ce alloys containing more than 90 at.% Pr have indicated the possibility that there is a delicate relationship in favour of the dhcp phase towards the praseodymium end. The observed positive deviation from the line connecting the atomic volumes of the dhcp-Pr and dhcp-Ce has been attributed to the change of the effective valency of cerium from 3.1 to 3. A tentative phase diagram for the Pr-Ce system has been presented which is similar to the La-Nd phase diagram proposed by Gschneidner (1961).