Pressure—temperature—resistance Properties of Lanthanum, Bismuth, Neptunium, Plutonium, and Americium to 450° and 30 Kb.

Abstract

ponent 1 do not appear to be satisfactorily described component 1 is less than M,, to obtain sufficiently by the molecular theory in its present form. It may direct and precise information for a complete analysis. be necessary to measure them by diff ereiit experi-Acknowledgment.-This work was supported in mental means, especially when the molecular weight of part by a grant from the National ScTence Foundation.The actinide elements neptunium,.plutonium, and americium are materials of considerable interest to the high pressure investigator. The possibility of pressure-induced electronic transitions such as those in cerium and cesium is suggested by the electronic configurations of the actinides. Such transitions are usually detectable by a discontinuous change in the electrical resistance of the sample. A matter of additional interest is the known one atmosphere polymorphism of plutonium with six allotropic forms between room temperature and its melting point, of neptunium with two allotropic forms, and a suspected allotropism in americium. The program therefore involved the development of apparatus capable of developing high pressures and temperatures which could allow electrical resistance measurements to be made on milligram quantities of metal. In addition, the apparatus was t o be resistant t o breakage or blowout which could contaminate the laboratory, permanent equipment, and, of course, laboratory personnel.

Behavior of the Elements at High Pressures

“…The RT La(I-II) transition was first observed by Bridgman [72,73] during V(p) studies, although similar studies by Vaidya and Kennedy [385] did not reveal the transition. It has since been confirmed by R(p) [75,231,277] and superconductivity [266,337,427] measurements, and X-ray studies [279,313] have shown that La(JI) has a fcc structure. A unique feature of this transition is that it apparently consists of two separable events that-occur at roughly the same pressure.…”

“…The data are shown in figure 58. McWhan [277] did some R(p) work on this element but found no reproducible features in the data at RT to about 36 khar.…”

“…The Pu(l-II) boundary has been investigated five times [79,252,277,329, 34SJ with fair agreement. Three of these investigators [252, 329, 34S] 34S] with poor agreement, but considering the small amount of data upon which these boundaries are based, this is not surprising.…”

The Electrical Resistance of Bismuth From 25 to 80 Kilobars

“…There are systems which, do not exhibit a discontinuity in the resistance accompanying a phase chane;e. Lanthanum is such a case. 5 .. A.…”