Hole compensation by Nd, Ca and Zn substitutions in YBa 2Cu 3O y

Abstract

An important and not completely resolved question regarding the high temperature superconductors is the relationship between the hole concentration and the transition temperature, T c. We address this question in terms of a proposed “master curve” on a T c versus hole concentration plot. This curve shows a maximum at 90 K at a hole concentration of approximately 0.2–0.22 holes per plane copper for the 1-2-3 type systems. Here we report on hole compensation studies where we selectively substituted Nd, Ca and Zn into the 1-2-3 structure. We used chemical and Hall measurements to determine the hole concentrations and looked at their relationship to the superconducting transition temperatures, T c, in terms of the “master curve”. We show that the T c lowerin g by Zn cannot be attributed to hole concentration changes alone. Although Zn substituted materials appear to be the most obvious examples, we expect that substitutions on the CuO 2 plane are less likely to fit the so-called “master curve” than non Cu-site substitutions such as Nd, Ca, La, etc.