New AES measurements on chlorinated tetragonal YBa2Cu3O7−x phases

✍ Scribed by T. Olesch; E. Kemnitz; A.M. Gas'kov; T.A. Kouznetsova; G.N. Maso

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 395 KB
• Volume: 218
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(93)90048-u

✦ Synopsis

Effects of oxidative chlorination on tetragonal YBa2Cu307_x are studied. After reaction with gaseous chlorine at 415-435 K nonsuperconducting YBa2Cu3Or.~ becomes superconducting. The formation of BaO2 and CUC12.2 H20 is shown by X-ray diffraction analysis. The C1/element ratio in the chlorinated-product phase determined by Auger electron spectroscopy steadily decreases with sputtering time as a result of a topotactical solid-gas reaction. The chloride concentration on the grain surface approaches values similar to pure binary metal chlorides. Hence, a partial substitution of chlorine for oxygen in the 123 lattice in this region can be excluded. Based on the experimental results a two-step mechanism of the formation of superconducting 123 phase is discussed. First, oxygen is released by oxidative chlorination especially in the surface. In a second step the released oxygen is incorporated into tmreacted CuO2 layers forming the orthorhombic structure. Raman spectroscopy and the isotope-exchange behaviour support this mechanism.