Synthesis and Oxidation States of 1-2-3 Superconductors

The non-stoichiometric amount of oxygen is a clear indication of lattice defects. 

Assigning oxidation states of —2 to oxygen, + 3 to yttrium and + 2 to barium, one would obtain an oxidation state 7/3 for copper when jc = 0. The non-integer oxidation state of copper is interpreted as if 2/3 of the ions are present as Cu2+ and 1/3 as Cu3 +. This mixed-valent composition seems to be determinant for the occurrence of superconductivity. In fact, as noted in Table 1, all the superconducting ceramic oxides contain Cu in a non-stoichiometric composition. 

It is noted that, as previously mentioned, there is a rapidly growing interest in the superconductivity of inorganic fullerene compounds. 

The larger Ca2+ ions are positioned at the corners of the cube, whereas the smaller Ti4+ ions are at the centre of the cube and bound to the six O2- ions forming a Ti06 group of octahedral geometry. 

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