Li-Mg, a Nearly Free-Electron Alloy

The momentum distributions of electron-positron pairs annihilating in polycrystalline Li, ${\mathrm{Li}}_{81}$ ${\mathrm{Mg}}_{19}$, and ${\mathrm{Li}}_{42}$ ${\mathrm{Mg}}_{58}$ have been measured. The results show that the alloy is a good, nearly-free-electron metal with an electron concentration determined by counting one electron per Li atom and two per Mg atom. The data lead to speculations about the description of metallic electrons in this alloy.