THE SOLID-STATE PROPERTIES OF URANIUM - A HISTORICAL-PERSPECTIVE AND REVIEW

We review our current understanding of the mechanical, electronic and structural properties of the element uranium, with the focus on the low-temperature regime in which the alpha-phase is stable. We start with a historical perspective, as the need for understanding the metallurgy of uranium so that its use as a nuclear fuel in the late 1940s could be optimized led to an increasing number of experiments aimed at exploring the solid-state properties. This was further accelerated when single crystals became available in the 1950s and when the superconductivity of the low-temperature alpha phase became the subject of controversy in the 1960s. The late 1960s and 1970s saw a considerable effort towards understanding the nature of the 5f electrons around the uranium nucleus. The increasing availability of sophisticated methods in computational physics first showed in the 1970s that the 5f electrons should be treated as itinerant, and the decade ended with the observation (by neutron diffraction) of a subtle periodic lattice distortion at 43 K in the alpha phase. The observation of this distortion, which is ascribed to a charge-density wave, leads to an explanation for many of the anomalies seen in over 30 years' work on the alpha phase. The review ends with a description of our current understanding and the problems still outstanding.