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

摘要: Abstract Ca-free single crystal and polycrystalline samples of Pb 2 Sr R Cu 3 O 8 have been prepared by a PbO/NaCl flux growth method fast solid state reaction, respectively. The electronic character the crystals this series can be roughly categorized into three groups: insulating (no carrier doping in CuO planes) for = La, Ce, Pr, Nd, semiconducting Sm, Eu, Gd, Tb, poorly metallic Dy, Ho, Y. Crystals with Eu to Ho are found superconducting exception Tb. these is likely promoted cation vacancy at rare-earth sites which has established structural chemical analyses. anomalous behavior Tb may originate from lower dopant level as inferred structure determination or possibly presence 4+ . fact that observed nonstoichiometric not stoichiometric ones seems consistent mechanism.