Does metallic ammonium exist?

Abstract

The ammonium ion NH_4^+ behaves in many ways like an alkali metal ion. This led Ramsey to propose that monovalent ammonium metal (NH_4^+ ions immersed in an almost uniform, degenerate sea of electrons) is stable at pressures much lower than typical insulator–metal transition pressures of megabars ~10^(11) Pa (10^5 Pa = 1 bar). Subsequently, it was estimated that the transition from a mixture of NH_3 and H_2 molecules to metallic ammonium, occurs at a pressure of less than 2.5×10^(10) Pa. If this estimate were correct, metallic ammonium would be of great interest to experimental high pressure physicists, and to planetary physicists. Indeed, metallic ammonium has been invoked in some but not all models for the interiors of Uranus and Neptune; and its existence could be of importance for calculations of the interior magnetic fields of these planets.

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