Electron-doped cuprates as high-temperature superconductors
M. Naito, Tokyo University of Agriculture and Technology, Japan
The divalent copper ion in high-Tc copper oxides takes three different oxygen coordinations: 6-fold octahedral, 5-fold pyramidal, and 4-fold square-planar coordinations, which is different from other 3d transition-metal ions taking only the 6-fold octahedral coordination in most cases. Copper oxides with the 4-fold square-planar coordination may be the least familiar but the most distinguished compounds. Only two families are known at present: ‘Nd2CuO4’ compounds and ‘infinite-layer’ compounds. The two families have been categorized as ‘electron-doped’ superconductors since superconductivity appears only ...