Unusual redox response of M=Ni in YBa2(Cu1-xMx)3Oy

✍ Scribed by Donggeun Ko; H. Oesterreicher

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 448 KB
• Volume: 231
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(94)90630-0

✦ Synopsis

We report here on the changes in behavior, including transitions from superconducting to semiconducting, as a function of heat treatment of YBa2 (Cu~_xNix) 3Oy with x = 0.05. In particular, conventional materials prepared by slow cooling from ~ 1200 K (designated OP for oxygenating preparations), show superconducting onset temperatures of To~ 75 K. This is also the case when materials are quenched from air annealing temperatures TA > 1123 K and subsequently reoxygenated at Ta = 673 K. However, when OP are air annealed at TA = 1023 K, quenched to liquid N2 (designated K parent or Kp in this state ), and subsequently reoxygenated at T~ = 673 K (designated as Ko compound), no superconductivity is observed in the resistivities down to 4.2 K. Also, magnetic susceptibilities of Ko compounds show relatively large effective magnetic moments and either no, or only trace amounts of, superconductivity. Both Kp (quenched from TA= 1023 K) and Ko were orthorhombic, while the conventional parents (quenched from TA > 1123 K) were tetragonal. Possible origins for this unusual Ko phenomenology are discussed and comparisons are drawn with other cases where thermal treatment results in loss of superconductivity.