Electron doping and superconductivity in layer-structured nitride chlorides, β-MNCL (M = Zr, Hf)

The layer-structured metal nitride chlorides, beta-MNCl (M = Zr, Hf) can be electron doped by intercalation of alkali metals between the layers. Upon intercalation, the crystals changed into superconductors with relatively high transition temperatures (T-c's). The highest T-c was observed at 25.5 K for the Li and tetrahydrofuran (THF) co-intercalated beta-HfNCl. A new electron-doping method has been developed by deintercalation of a part of chlorine atoms from the layers. The chlorine deficient compound beta-NINCl1-x showed superconductivity very similar to those of the alkali metal intercalated samples. (C) 2002 Published by Elsevier Science B.V.