Critical region and metal–nonmetal transition in expanded fluid mercury: advanced evaluation of small-angle X-ray scattering data

Metal-non-metal transition in lead-bismuth eutectic

Thermodynamic functions and electrical resistivity of Pb-Bi eutectic alloy have been measured over wide ranges of specific volume and pressure in the liquid and gaseous state. The experimental data show a crossover from metallic to insulating behavior in the electrical resistivity of the alloy when its specific volume increases. It is found that in the crossover region the constant volume temperature coefficient of resistivity changes sign from positive to negative and passes through zero at a value of the specific volume which is 2.4 times larger than that in normal state. The second salient feature of the alloy revealed by these experiments is that the isochores plotted in the specific internal energy-pressure plane are straight lines. Based on these experimental data and using an earlier developed approach, an equation of state (EOS) of the alloy has been constructed whose accuracy is determined mainly by the errors of the measurements. It is shown that this EOS can be used to obtain direct estimates of the specific volume and pressure at the critical point of the liquid-gas transition as well as the critical volume for the metal-non-metal (M-NM) transition observed in this eutectic. The results indicate that the critical specific volumes for these two transitions are equal, and the M-NM transition can be described by the classical percolation theory.

An equation of state for expanded metals

We present a model equation of states for expanded metals, which contains a pressure term due to a screened-Coulomb potential with a screening parameter reflecting the Mott-Anderson metal-to-nonmetal transition. As anticipated almost 80 years ago by Zel'dovich and Landau, this term gives rise to a second coexistence line in the phase diagram, indicating a phase separation between a metallic and a nonmetallic liquid.

Structural studies on fluid Hg and fluid Se at high temperatures and high pressures by means of X-ray diffraction and small angle X-ray scattering

X-ray diffraction (XRD) and small angle X-ray scattering (SAXS) measurements for fluid Hg and fluid Se up to the supercritical region have been carried out using synchrotron radiation at SPring-8. We obtained the structure factor, S ( Q ) $S\left(Q\right)$ , including a small angle region, and the pair distribution function, g ( r ) $g\left(r\right)$ , for both fluids from the liquid to the dense vapor region. Change of the local structure and medium-range correlations at the metal-insulator transition in fluid Hg were revealed. On the other, the average coordination number of two was preserved at the semiconductor-metal transition in fluid Se. From a SAXS experiment of fluid Se in 2012, SAXS spectra near the semiconductor-metal transition region show the Ornstein–Zernike profile and the SAXS intensity is reduced with increasing pressure. These results indicate difficulties of separating fluctuations intrinsic to the semiconductor-metal transition from those arising from the liquid-vapor critical point in fluid Se, although fluctuations intrinsic to the electronic transitions are largely expected in both fluids.

Structure and energetics of microscopically inhomogeneous nanoplasmas in exploding clusters

We present a theoretical-computational study of the formation, structure, composition, energetics, dynamics and expansion of nanoplasmas consisting of high-energy matter on the nanoscale of ions and electrons. Molecular dynamics simulations explored the structure and energetics of hydrogen and neon persistent nanoplasmas formed under the condition of incomplete outer ionization by the laser field. We observed a marked microscopic inhomogeneity of the structure and the charge distribution of exploding nanoplasmas on the nanoscale. This is characterized by a nearly neutral, uniform, interior domain observed for the first time, and a highly positively charged, exterior domain, with these two domains being separated by a transition domain. We established the universality of the general features of the shape of the charge distribution, as well as of the energetics and dynamics of individual ions in expanding persistent nanoplasmas containing different positive ions. The inhomogeneous three-domain shell structure of exploding nanoplasmas exerts major effects on the local ion energies, which are larger by one order of magnitude in the exterior, electron-depleted domain than in the interior, electron-rich domain, with the major contribution to the ion energies originating from electrostatic interactions. The radial structural inhomogeneity of exploding nanoplasmas bears analogy to the inhomogeneous transport regime in expanded and supercritical metals undergoing metal-nonmetal transition.

Small-angle X-ray scattering of two-phase systems: significance of polydispersity

Evaluation of the small-angle X-ray scattering of two-phase systems leads to the determination of the Porod lengthlpand the correlation lengthlc. In dilute systems, the parameter κl=lc/lp− 1 is a measure of the polydispersity of the chord lengthslwithin the dilute phase, which depends on the size distribution and the shape of the particles forming this phase. As an example, the change of κlwith the size distribution is calculated for spheres and spheroids. For dense two-phase systems, κldepends not only on the polydispersities of the chord lengthsl1andl2of the two phases but also on the spatial order in the system. This is demonstrated by examples related to microemulsions. The appendix contains a short discussion on the relationship between chord-length distributions and Bertrand's paradox.