Harrison N, Betts J B, Wartenbe M R, Balakirev F F, Richmond S, Jaime M, Tobash P H
Los Alamos National Laboratory, Los Alamos, Mail Stop E536, Los Alamos, NM, 87545, USA.
Los Alamos National Laboratory, Los Alamos, Mail Stop E574, Los Alamos, NM, 87545, USA.
Nat Commun. 2019 Jul 18;10(1):3159. doi: 10.1038/s41467-019-11166-0.
Plutonium metal undergoes an anomalously large 25% collapse in volume from its largest volume δ phase (δ-Pu) to its low temperature α phase, yet the underlying thermodynamic mechanism has largely remained a mystery. Here we use magnetostriction measurements to isolate a previously hidden yet substantial electronic contribution to the entropy of δ-Pu, which we show to be crucial for the stabilization of this phase. The entropy originates from two competing instabilities of the 5f-electron shell, which we show to drive the volume of Pu in opposing directions, depending on the temperature and volume. Using calorimetry measurements, we establish a robust thermodynamic connection between the two excitation energies, the atomic volume, and the previously reported excess entropy of δ-Pu at elevated temperatures.
钚金属从其最大体积的δ相（δ-Pu）转变为低温α相时，体积会异常大幅地收缩25%，但其潜在的热力学机制在很大程度上仍是个谜。在此，我们利用磁致伸缩测量来分离出此前隐藏但对δ-Pu熵有显著贡献的电子成分，我们证明这一成分对于该相的稳定性至关重要。这种熵源于5f电子壳层的两种相互竞争的不稳定性，我们发现这两种不稳定性会根据温度和体积以相反方向驱动钚的体积变化。通过量热法测量，我们在两种激发能、原子体积以及之前报道的高温下δ-Pu的过剩熵之间建立了稳固的热力学联系。
