Invar Effect, Thermal Expansion, and Elastic Softening of δ-Phase Pu

摘要

Plutonium metal is famous for its variety of crystal structures; of these, the close-packed cubic δ phase is least understood because its surprisingly large atomic volume has resisted first-principles calculation. Unusual related properties―including the negative thermal expansion of the unalloyed δ phase, anomalous thermal expansion behavior of the alloys, pronounced elastic softening with increasing temperature, and the low melting point―have remained unexplained for more than 40 years. There has been some progress. Recently we explained the anomalous thermal expansion as the consequence of the invar effect. Figure 1 shows the energy level diagram for the invar effect.