Chemical characterization and superconductivity of Tl2Ba2−xLaxCuOy with the orthorhombic and tetragonal structures

✍ Scribed by Saturo Nakajima; Takeo Oku; Reiko Suzuki; Masae Kikuchi; Kenji Hiraga; Yasuhiko Syono

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 463 KB
• Volume: 214
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(93)90110-c

✦ Synopsis

Oxygen contents and metal ratios of oxygen-annealed Tl2Ba2CuOy were determined by iodometric titration and energy dispersive X-ray spectroscopy (EDX) analysis, respectively. Tc and unit cell dimensions ofTl2Ba 2_xLaxCuOJ~ phase with two structures, orthorhombic and tetragonal, have been investigated for a wide substitution range of La for Eta. The discrepancies between the orthorhombic and tetregonal phases are explained by the difference in the T1 content, but are not related to the superconductivity. Oxygen-annealed TI2Ba2CuOj, was not superconducting due to overdoping and Tc increased to about 50 K with increasing x up to x=0.2-0.4. The average Cu valence of TI2Ba2_xl.,axCuOy calculated by assuming TI (III) was about 1.8-2.1 +, which might be too low for a Tc about 50 K. It was suggested that the over-doping state in Tl2Ba2CuOy was ascribable to charge transfer TP -t-(Cu-O)p.