Effects of composition and processing on the superconductivity of La1+zBa2-zCu3Oy

✍ Scribed by T.B. Lindemer; B.C. Chakoumakos; E.D. Specht; R.K. Williams; Y.J. Chen

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 847 KB
• Volume: 231
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(94)90144-9

✦ Synopsis

The effects of composition, processing time (t), temperature (T) and 02 partial pressure (Po~) on the superconducting transition temperature, To, were investigated for La~ +zBa2_:Cu30 r Tallon and Flower's prediction of Tc -~ 100 K [Physiea C 204 (1993) 237] at z =0 could not be attained. Instead, the T¢ maximum of 93-94 K is similar to that of the yttria analog. As z was increased, the T¢ values increased gradually by a few kelvin until z = 0.2, which is at the orthorhombic to tetragonal transition, and then decreased more abruptly, with no superconductivity for z > 0.5. Crucial steps in the process at all z values include the highest temperature anneal (1065°C) in 0.1 MPa 02, reduction of the oxygen content at 950°C and cooling to 300--400"C, both at 100-1000 Pa O 2, and reoxygenation at 0. i MPa 02 during slow cooling (5-20°C/min) to < 1500C. Additional experiments demonstrated that the intragranular critical current was less than that for the yttria analog. Values of Tc decreased fairly monotonically with decreasing y at z = 0.08, and a La excess of 0.2 and Cu nonstoichiometry on both sides of Cu/(La + Ba) = 1 generally depressed To.