We report an experimental determination of the phonon dispersion curves in a face-centered cubic (fcc) delta-plutonium-0.6 weight % gallium alloy. Several unusual features, including a large elastic anisotropy, a small-shear elastic modulus C', a Kohn-like anomaly in the T1[011] branch, and a pronounced softening of the [111] transverse modes, are found. These features can be related to the phase transitions of plutonium and to strong coupling between the lattice structure and the 5f valence instabilities. Our results also provide a critical test for theoretical treatments of highly correlated 5f electron systems as exemplified by recent dynamical mean field theory calculations for delta-plutonium.

We present the design of a contact atomic force microscope (AFM) that can be used to image solid surfaces in aqueous solution up to 150 °C and 6 atm. The main features of this unique AFM are: (1) an inert gas pressurized microscope base containing stepper motor for coarse advance and the piezoelectric tube scanner; (2) a chemically inert membrane separating these parts from the fluid cell; (3) a titanium fluid cell with fluid inlet–outlet ports, a thermocouple port, and a sapphire optical window; (4) a resistively heated ceramic booster heater for the fluid cell to maintain the temperature of solutions sourced from a hydrothermal bomb; and (5) mass flow control. The design overcomes current limitations on the temperature and pressure range accessible to AFM imaging in aqueous solutions. Images taken at temperature and pressure are presented, demonstrating the unit-cell scale (<1 nm) vertical resolution of the AFM under hydrothermal conditions.

Several of the high‐pressure crystalline forms of ice exist in the interiors of the larger icy moons of the outer planets. Guided by the phase relations established by Bridgman 75 years ago, we have transformed ordinary water ice I to ices II, III, V, and perhaps VI. We subsequently deformed those phases in a gas deformation apparatus designed for these experiments. We found ice II to be the strongest of the high‐pressure phases, having a strength roughly comparable to that of ice I. Ice III is very weak: at fixed levels of stress, ice III flows 102‐103 times faster than ice II. We confirm Bridgman's (1912) findings that ices III and V can exist metastably within the ice II field and, in addition, find that these phases may be deformed plastically within much of the metastable region without reverting to ice II. The most persistent metastable existence of ice III occurs in the warmer portions of the ice II field, through which historical and present‐day temperature‐pressure profiles in the icy moons pass. Thus, although the stability field of ice III is small, the weakness of this phase may have profoundly influenced the evolution and present‐day behavior of the icy moons.

Plutonium (Pu) is well known to have complex and unique physico-chemical properties [1]. Notably, the pure metal exhibits six solid-state phase transformations with large volume expansions and contractions along the way to the liquid state:

No abstract