Carnegie scientists are the first to discover the conditions under which nickel oxide can turn into an electricity-conducting metal. Nickel oxide is one of the first compounds to be studied for its electronic properties, but until now scientists have not been able to induce a metallic state. The compound becomes metallic at enormous pressures of 2.4 million times the atmospheric pressure (240 gigapascals). The finding is published in Physical Review Letters.
"Physicists have predicted for decades that the nickel oxide would transition from an insulator -- a compound that does not conduct electricity -- to a metal under compression, but their predictions have not previously been confirmed," remarked team leader Viktor Struzhkin of Carnegie's Geophysical Laboratory. "This new discovery has been a goal in physics that ranks as high as achieving metallic hydrogen, but for metal oxides."
The outer shells of atoms contain what are called valence electrons, which play a large role in electrical and chemical behavior. Metals generally have one to three of these valence electrons, while non-metals have between five and seven. Metals are good conductors of electricity because the valence electrons are loosely bound, so the electrons are free to flow through the material.