| Research Abstract |
We have reported that layer structured nitride halides β-MNX (M = Zr, Hf ; X = Cl, Br, I) electron-doped by intercalation of alkali metals became superconductors. In particular, the compound cointercalated with Li and THF (tetrahydrofuran), Lio_<48>(THF)_yHfNCl, showed a high critical temperature of Tc = 25.5 K. In this study, we have collaborated with solid state physicists to investigate the superconducting mechanism, and new types of layer structured nitrides have been developed. The main results obtained are the followings;
1. Single crystals of β-MNX were successfully prepared using ammonium halides as fluxes under high-pressure conditions, and their structures were determined by the single crystal X-ray analysis.
2. A new electron-doping method was developed by partial deintercalation of chlorine atoms to form β-ZrNCl_<1-x> and β-HfNCl_<1-x>, which were stable in air for pretty long time. The deintercalated samples showed similar superconductivity with those electron doped by alkali metal intercalation.
3. Isotope substituted β-Hf^<15>NCl was prepared, and its superconductors were derived by electron doping.
4. ^<15>N NMR study revealed that the layer structured nitride superconductors were two-dimensional ones with very low carrier densities and weak phonon enhancement. The mechanism of the new superconductors cannot be interpreted in the conventional BCS theory.
5. The superconducting gap was successfully measured by a break-junction method.
6. Layer structured Sr_2N oriented films were prepared by MBE method in a high vacuum chamber with a nitrogen radical source.
|
