Oxygen non-stoichiometry and hole distribution in multi-layered copper oxides: understanding of the magnetic-irreversibility characteristics

Abstract

The dependence of the magnetic-irreversibility characteristics on the amount of excess oxygen and the hole distribution in superconductive multi-layered copper oxides, M m A 2 Q n−1 Cu n O m+2+2 n± δ or M– m ( A) 2 ( Q) ( n−1) n:P/RS, is discussed with relevant examples of such phases, i.e. Cu−1 (Ba,Sr)2 (Yb)12:P, Bi-2 (Sr)2 (Ca,Y)12:RS, Hg-1 (Ba)2 (Ca)23:RS, Cu-1 (Ba)2 (Ca)23:P and Cu-1 (Ba)2 (Ca)34:P. At a fixed cation stoichiometry, the irreversibility-field line, H irr( T), is shifted in a continuous manner to higher magnetic fields with increasing oxygen content. This trend applies not only to the M– m ( A) 2 ( Q) ( n−1) n:P/RS phases with a perovskite-type (P) charge reservoir but also to those with a rock-salt-type (RS) charge reservoir, and furthermore, in both cases to both under- and overdoped regions. However, when the increase in the oxygen content is accompanied with aliovalent cation substitution, e.g. trivalent-Y-for-divalent-Ca substitution in the Bi-2 (Sr)2 (Ca,Y)12:RS system, the H irr characteristics are not necessarily enhanced with increasing oxygen content but may rather be depressed. This provides us with one of the experimental evidences supporting the general conclusion that it is not the oxygen content but the concentration and the distribution of holes which control the H irr characteristics.