Hole compensation by Nd, Ca and Zn substitutions in YBa₂Cu₃O_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, Tc. We address this question in terms of a proposed "master curve" on a Tc 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, Tc, in terms of the "master curve". We show that the Tc 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 CuO2 plane are less likely to fit the so-called "master curve" than non Cu-site substitutions such as Nd, Ca, La, etc. © 1990.