Energy spectrum of one-particle excitations in liquid dielectrics under high pressures and temperatures
- PDF / 254,287 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 54 Downloads / 224 Views
SORDER, AND PHASE TRANSITION IN CONDENSED SYSTEMS
Energy Spectrum of One-Particle Excitations in Liquid Dielectrics under High Pressures and Temperatures A. G. Khrapak and V. E. Fortov Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, 125412 Russia e-mail: [email protected] Received October 15, 2007
Abstract—The effect of pressure on the conductivity of molecular liquids (hydrogen, oxygen, and nitrogen) and alkali metals (cesium and rubidium) in the region of the experimentally observed dielectric–metal transition is investigated. It is shown that capture of free electrons by atoms or molecules (resulting in the formation of negative ions) is advantageous from the point of view of energy in liquids under moderately high pressures and temperatures. In spite of the fact that the ionization potential increases with density, the energy of an electron transition to the level of the negative ion decreases and, hence, the forbidden gap also decreases. For high densities, the level of negative ions is broadened and transformed into the conduction band. It is assumed that the exponential dependence of conductivity on density and temperature in the transition region is associated with transfer of quasi-free electrons located at the level of atomic negative ions. The spectrum of negative ions of hydrogen, oxygen, and cesium in the strongly compressed state is determined, and the forbidden gap calculated for these substances is found to be in good agreement with the results obtained for hydrogen and oxygen in single shock-wave experiments. PACS numbers: 72.20.-i, 52.27.Gr DOI: 10.1134/S1063776108050099
1. INTRODUCTION Under high pressures produced in shock-wave experiments, transition of liquid hydrogen, oxygen, and nitrogen to a state with a high conductivity close to that of metals is observed [1–3]. At low pressures and temperatures, these molecular liquids are good dielectrics. As the pressure and temperature increase, a part of molecules are ionized, leading to the emergence of conductivity that exponentially increases with density. Under a pressure on the order of 100 GPa at a temperature of about 2000 K, the conductivity of all three “supercritical” liquids becomes a constant value on the order of 103 Ω–1 cm–1, which corresponds to “minimum metallic conductivity” [3, 4]. The high conductivity of these substances is usually attributed to almost complete ionization of atoms and is explained using theoretical models in the physics of strongly nonideal Coulomb systems. At the same time, electrophysical properties of these liquids in the transient semiconductor region have been almost completely neglected in the literature. Here, we propose a simple model for estimating the electron forbidden energy gap in a wide range of pressures (from the triple point to the metallization threshold). It will be shown that electrons under low pressures are localized at molecular negative ions. In this case, conduction is associated with transport of positively charged clusters and negatively charged ion bubbles. Th
Data Loading...
