Marina Bastea

High Pressure Insulator-Metal Transition in Molecular Fluid Oxygen

We report the first experimental evidence for a metallic phase in fluid molecular oxygen. Our electrical conductivity measurements of fluid oxygen under dynamic quasi-isentropic compression show that a nonmetal-metal transition occurs at 3.4 fold compression, 4500 K, and 1.2 Mbar. We discuss the main features of the electrical conductivity dependence on density and temperature and give an interpretation of the nature of the electrical transport mechanisms in fluid oxygen at these extreme conditions.

Kinetics of Propagating Phase Transformation in Compressed Bismuth

We observed dynamically driven phase transitions in isentropically compressed bismuth. By changing the stress loading conditions we explored two distinct cases: one in which the experimental signature of the phase transformation corresponds to phase-boundary crossings initiated at both sample interfaces, and another in which the experimental trace is due to a single advancing transformation front in the bulk of the material. We introduce a coupled kinetics-hydrodynamics model that for this second case enables us, under suitable simplifying assumptions, to directly extract characteristic transition times from the experimental measurements.

High pressure phase transformation in iron under fast compression

We observe kinetic features—velocity loops—at the α to ϵ phase transformation of iron, similar with the ones reported when water is frozen into its ice VII phase under comparable experimental conditions. By using a phase nucleation and growth kinetic model with pressure dependent phase interface velocity we find that the thermodynamic path followed by the sample is strongly dependent on the drive conditions and sample characteristics. The velocity loops become broader and shallower at slower compressions, while on faster time–scales, e.g., for laser drivers, the loops form at higher velocities and may eventually disappear.

Electrical conductivity of lithium at megabar pressures

We report measurements of the electrical conductivity of a liquid alkali metal\char22{}lithium\char22{}at pressures up to 1.8 Mbar and fourfold compression, achieved through shock compression experiments. We find that the results are consistent with a departure of the electronic properties of lithium from the nearly free electron approximation at high pressures.

RAMP COMPRESSION EXPERIMENTS—A SENSITIVITY STUDY

We present the first sensitivity study of the material isentropes extracted from ramp compression experiments. We perform hydrodynamic simulations of representative experimental geometries associated with ramp compression experiments and discuss the major factors determining the accuracy of the equation of state information extracted from such data.

Near-equilibrium polymorphic phase transformations in Praseodymium under dynamic compression

The authors report the first experimental observation of sequential, multiple polymorphic phase transformations occurring in praseodymium dynamically compressed using a ramp wave. The experiments also display the signatures of reverse transformations occurring upon pressure release and reveal the presence of small hysteresis loops. The results are in very good agreement with equilibrium hydrodynamic calculations performed using a thermodynamically consistent, multiphase equation of state for praseodymium, suggesting a near-equilibrium transformation behavior.

Comment on "Metallization of Fluid Nitrogen and the Mott Transition in Highly Compressed Low-Z Fluids"

A Comment on the Letter by R. Chau et al., Phys. Rev. Lett. 90, 245501 (2003). The authors of the Letter offer a Reply.