1/27/2024 0 Comments Helium electric conductivity![]() Fluid hydrogen becomes metallic at 1.4 Mbar at high temperature (>10 3 K) along the shock-wave Hugoniot ( 5), whereas at low temperature (≤300 K) crystalline hydrogen is expected to metallize only >4 Mbar ( 6). However, recent high-pressure results have revealed the role of temperature in metallization, particularly in the fluid state. Thus, one might expect helium to be insulating at giant-planetary conditions, for its solubility in metallic hydrogen to be limited and for addition of helium to limit the electrical conductivity of the gaseous envelope ( 4). Under compression, however, helium is predicted to metallize via closure of the energy gap at ≈100 Mbar (10 TPa) ( 2), a pressure greater than that at Jupiter's center ( 3). Helium is known to be an electrical insulator at low pressure, with a wide energy gap (19.8 eV) between occupied and unoccupied electron orbitals it exhibits almost no chemical bonding ( 1). The change in electronic structure of He at elevated pressures and temperatures has important implications for the miscibility of helium in hydrogen and for understanding the thermal histories of giant planets. Gap closure is achieved by a broadening of the valence band via increased s–p hydridization with increasing temperature, and this influences the equation of state: The Grüneisen parameter, which determines the adiabatic temperature–depth gradient inside a planet, changes only modestly, decreasing with compression up to the high-temperature metallization and then increasing upon further compression. The electronic energy gap (band gap) closes at 20,000 K at a density half that of zero-temperature metallization, resulting in electrical conductivities greater than the minimum metallic value. Using first-principles molecular dynamics simulations, we find that fluid helium undergoes temperature-induced metallization at high pressures. As the second most-abundant chemical element in the universe, helium makes up a large fraction of giant gaseous planets, including Jupiter, Saturn, and most extrasolar planets discovered to date.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |