Anomalous peak structure of specific heat around Tc of Ba2YCu3Oy

✍ Scribed by Y. Nakazawa; J. Takeya; M. Ishikawa

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 547 KB
• Volume: 225
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(94)90327-1

✦ Synopsis

Through a systematic study of the effects of oxygen stoichiometry on the specific heat of the Ba2YCu3Oy system, we have confirmed that a double-peak structure around Tc is disclosed only for well-annealed samples in a narrow region near y= 6.92 and that the double-peak structure merges to a distinct single peak of mean-field type as the oxygen concentration is slightly decreased to y= 6.88-6.90. Evidence for such a double transition was also obtained in resistivity and magnetic susceptibility measurements. These results imply that each grain in polycrystalline samples containing more oxygen than y= 6.90 consists of two different superconducting portions with different To's, probably the portion of lower To( ~ 89 K) surrounding the higher To( ~ 92 K) portion. We propose that this difference of Tc results from a different oxygen configuration around CuO chains, implying the important role of such a local arrangement of oxygen around CuO chains in determining the superconductive nature in the Ba2YCu3Oy system. In contrast, only a broad anomaly was observed in ortho-II phase samples which no longer possess such a CuO chain structure.