Roles of the blocking layer in high temperature copper-oxide superconductors

Abstract

Roles of the blocking layer that we named the layer which separates Cu−O2 layers more than 6A have been studied by comparing two kinds of highTc copperoxide superconductors such as Bi(2212) and La(2126) compound. These following results have been obtained. The hole concentration decreases when Sr is substituted by La and increases when Bi is substituted by Pb in Bi(2212), and it can be optimized by these substitution. In La(2126)Tc becomes up to 43K and the hole concentration (p;[Cu−O]+p) increases to 0.09 by the substitution of Ca for La and heat treatment under high oxygen partial pressure. The distance between Cu−O2 layers in both Bi(2212) and La(2126) are not changed by these substitution and heat treatment. We have found that the blocking layer has not direct roles for the maximumTc value of the material though by supplying carriers to Cu−O2 layers, it affects the actualTc value.