Liquid metal cooled reactor Clementine was the first liquid metal cooled nuclear reactor and used mercury coolant, thought to be the obvious choice since it is liquid at room temperature. However, because of disadvantages including high toxicity, high vapor pressure even at room temperature, low boiling point, producing noxious fumes when heated, relatively low thermal conductivity, and a high neutron cross-section, it has fallen out of favor. Sodium and NaK (a eutectic sodium-potassium alloy) do not corrode steel to any significant degree and are compatible with many nuclear fuels, allowing for a wide choice of structural materials. They do, however, ignite spontaneously on contact
Polar metal and a polar material at room temperature. The resistivity of this system, however, shows an upturn with decreasing temperature, hence does not strictly adhere to the definition of a metal. Also, when grown 3 or 4 unit cells thick (1-2 nm) on the (100) crystal face of LaAlO, the LaNiO can be a polar insulator or polar metal depending on the atomic termination of the surface. Lithium osmate, LiOsO also undergoes a ferrorelectric transition when it is cooled below 140K. The point group changes from "Rc" to "R3c" losing its centrosymmetry. At room temperature and below lithium osmate is an