Metastable liquid-liquid phase transition in a single-component system with only one crystal phase and no density anomaly

We investigate the phase behavior of a single-component system in 3 dimensions with spherically-symmetric, pairwise-additive, soft-core interactions with an attractive well at a long distance, a repulsive soft-core shoulder at an intermediate distance, and a hard-core repulsion at a short distance, similar to potentials used to describe liquid systems such as colloids, protein solutions, or liquid metals. We showed [Nature {\bf 409}, 692 (2001)] that, even with no evidences of the density anomaly, the phase diagram has two first-order fluid-fluid phase transitions, one ending in a gas--low-density liquid (LDL) critical point, and the other in a gas--high-density liquid (HDL) critical point, with a LDL-HDL phase transition at low temperatures. Here we use integral equation calculations to explore the 3-parameter space of the soft-core potential and we perform molecular dynamics simulations in the interesting region of parameters. For the equilibrium phase diagram we analyze the structure of the crystal phase and find that, within the considered range of densities, the structure is independent of the density. Then, we analyze in detail the fluid metastable phases and, by explicit thermodynamic calculation in the supercooled phase, we show the absence of the density anomaly. We suggest that this absence is related to the presence of only one stable crystal structure.Comment: 15 pages, 21 figure

Experimental evidence of the ferroelectric phase transition near the λ−\lambda-point in liquid water

We studied dielectric properties of nano-sized liquid water samples confined in polymerized silicates MCM-41 characterized by the porous sizes \sim 3-10nm. We report the direct measurements of the dielectric constant by the dielectric spectroscopy method at frequencies 25Hz-1MHz and demonstrate clear signatures of the second-order phase transition of ferroelectric nature at temperatures next to the \lambda- point in the bulk supercooled water. The presented results support the previously developed polar liquid phenomenology and hence establish its applicability to model actual phenomena in liquid water.Comment: 4 pages, single figur

Structural investigations of the amorphous alloy Al30Ge70Al_{30} Ge_{70} under high pressure

The structural behavior of the amorphous phase Al30Ge70, obtained by pressure quenching, has been investigated under pressure by in situ energy dispersive x-ray diffraction (EDXD) using synchrotron radiation. At p≊5 GPa there is a reversible transition from the amorphous state to a crystalline state with simple hexagonal (sh) structure. This γ phase is stable up to 47 GPa. At this pressure a transition to a hexagonal closed-packed structure takes place. The behavior of Al30Ge70under pressure is discussed in connection with structural transformations of group-IV elements and III-V compound

Effect of pressure on the superconducting TcT_c of lanthanum

The effect of pressure on the superconducting transition temperature Tc of La was studied up to 50 GPa. Tc(P) shows a rather complicated variation with a discontinuous increase in Tc at about 2.2 GPa due to the first-order phase transition from dhcp to fcc structure. At about 5.4 GPa a sharp peak is observed due to the soft-mode phase transition from fcc to the distorted fcc structure and two broad maxima are found within the stability region of the distorted fcc structure around 12 and 39 GPa. Some differences between these and previous low-pressure data for metastable fcc La are noticed. The results are discussed in connection with pressure-induced structural phase transitions found in earlier x-ray-diffraction experiments and band-structure calculations giving evidences for van Hove singularities in the density of states

Superconductivity and crystallographic transitions of InBi under pressure

Measurements of the superconducting transition temperature of the compound InBi under pressures up to 40 GPa reveal three different regions corresponding to the observed structural transitions I-II-III from the initial phase I of InBi type to phase II of type and to a body-centred tetragonal phase III . Some similarities and distinct differences in the superconducting and structural behaviour of the III-V compound InBi in comparison with the isoelectronic group IV element Sn point to some differences in the possible mechanisms for the crystallographic transformations under pressure