Superconducting and Nonsuperconducting Ca-Free Single Crystals of Pb2Sr2RCu3O8 (R = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Y): Effect of Cation Vacancies and the Metal/Insulator Transition

✍ Scribed by J.S. Xue; M. Reedyk; J.E. Greedan; T. Timusk

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 354 KB
• Volume: 102
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1993.1061

✦ Synopsis

Ci-free single erystal and polycrystalline samples of (\mathrm{Pb}{2} \mathrm{Sr}{2} \mathrm{RCu}{3} \mathrm{O}{k}) have been prepared by a (\mathrm{PbO} / \mathrm{NaCl}) flux growth method and a fast solid state reaction, respectively. The electronic character of the single crystals of this series can be roughly categorized into three groups: insulating (no carrier doping in the (\mathrm{CuO}_{2}) planes) for (R=\mathrm{La}, \mathrm{Ce}). (\mathrm{Pr}), and (\mathrm{Nd}), semiconducting for (R=\mathrm{Sm}), Eu, Gd, and (\mathrm{Tb}), and poorly metallic for (R=) Dy, Ho, and Y. Crystals with (R=) Eu to Ho are found to be superconducting with the exception of (\mathrm{Tb}). The metallic character in these crystals is likely promoted by a cation vacancy at the rare-earth sites which has been established by crystal structural and chemical analyses. The anomalous behavior of the (\mathrm{Tb}) crystals may originate from a lower dopant level as inferred from the structure determination or possibly from the presence of (\mathrm{Tb}^{4+}). The fact that metallic behavior is observed in nonstoichiometric polycrystalline samples and not in stoichiometric ones seems consistent with the cation vacancy carrier doping mechanism. 1993 Academic Press. Inc.