Synthesis and Properties of New Layr Structured Superconductors

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In a previous study, we derived a new type of superconductor from the layer structured beta-ZrNC1 by electron doping of the nitride layers through lithium intercalation. This finding suggests that the nitride layers may become good matrices of superconductivity like CuO_2 layers of copper oxide superconductors. In this study, a series of beta-ZrNCl type layered nitrides have been prepared and the possibility of superconductivity has been examined after electron doping. Developments of new layer structured nitride superconductors have also been studied. Some important results of this study are the following :1. A new high Tc superconductor with Tc as high as 25.5 K was obtained by intercalation of lithium in beta-HfNCl. Note that the Tc (25.5 K) is much higher than the Tc of HfN with the rock-salt structure.2. All combinations of MNX ( M = Zr, Hf ; X = C1, Br, I) crystals were prepared by using high pressure and high temperature conditions. All of the crystals showed superconductivity by electron doping. The Tcs were mainly determined by the kinds of metal nitride layers concerned.3. Intercalation compounds of alpha-TiNCI having a different type of nitride layers from that of beta ZrNCl structure were prepared by the reaction with pyridine. The intercalation compounds showed superconductivity with Tc at 6 K.This is the first superconductor derived from a layered semiconductor by intercalation of an organic base as electron donor.4. Artificial superlattice films of ZrN/Si_3N_4 were prepared on Si(111) substrate by a laser abration technique. The electron doping into the films is now under investigation.