Unusual Chemical Behavior for Potassium under Pressure: Potassium−Silver Compounds

At high pressures, there are large changes in the size and electron concentration of the alkali metals. As a result, significant changes should occur in the solid-state chemistry of these elements, allowing the formation of alkali metal−transition metal compounds. The formation of two alkali metal−transition metal compounds, K 3 Ag and K 2 Ag, is reported. These compounds rapidly form at room temperature upon compression of stoichiometric mixtures of the elements. K 3 Ag has a BiF 3 -type structure related to the bcc structure of potassium, with silver replacing some of the bcc potassium sites. The anisotropic ω-phase structure of K 2 Ag consists of graphite-like layers of potassium atoms with silver atoms between the layers. At ambient pressure, lithium is the only alkali metal that forms compounds with silver. Thus, under pressure, potassium can exhibit chemical behavior exhibited by lithium at atmospheric pressure.