Superconductivity of alkali metal intercalated beta-zirconium nitride chloride, A(x)ZrNCl (A = Li, Na, K)

Alkali metal intercalated compounds A(x)ZrNCl (A = Li, Na, K) were synthesized by the reaction of beta-zirconium nitride chloride with n-butyllithium or the respective alkali metal naphthalenes. All of the compounds became superconductors with a transition temperature (T-c) of ca. 15 K. Polar solvent molecules such as tetrahydrofuran, dimethylformamide, and propylene;carbonate were co-intercalated with the alkali metals, expanding the interlayer spacing. The T-c was dependent solely on the amount of intercalated alkali metals, or the doping level; the kind of intercalated alkali metals and the interlayer separation were not influential to the T-c. Although beta-ZrNCl is a semiconductor, only a small amount of doping of alkali metals was necessary for the superconductivity. Too much doping with alkali metals resulted in the decrease of T-c down to ca. 9 K.