Positron annihilation study of the O–T phase transition for Eu1+xBa2−xCu3O7−δ superconductors

✍ Scribed by Yang Li; Yang Liu; Ruifei Duan; Xiaotao Xiong; Baoyi Wang; Guohui Cao; Long Wei; D.N. Zheng; Z.X. Zhao; Joseph H. Ross Jr.

• Book ID: 103889917
• Publisher: Elsevier Science
• Year: 2004
• Tongue: English
• Weight: 827 KB
• Volume: 402
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/j.physc.2003.09.081

✦ Synopsis

The effects of Eu substituting for Ba on structural and superconducting properties were investigated for a series of superconductors Eu 1þx Ba 2Àx Cu 3 O 7Àd (x ¼ 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, and 0.2). With Eu content increasing, the random substitution of excessive Eu for Ba ion forms a Eu-Ba non-stoichiometric distribution on Ba site, which deviates from the ideal 123 phase stoichiometry. The analysis of crystallographic structure shows that the solid solubility x of Eu on Ba site is over 0.2. Eu 1þx Ba 2Àx Cu 3 O 7Àd take on an orthorhombic-tetragonal (O-T) phase transition from x ¼ 0:06, and end in x ¼ 0:18. Corresponding to the O-T phase transition, superconducting critical temperature T c rapidly decreases with Eu content increasing, which is attributed to the decline of carrier density and the proximity effects of non-superconducting clusters. The positron annihilation measurements show anomalous changes for lifetime spectra and Doppler-broadened radiation spectra when the O-T phase transition occurs. By the model of excessive oxygen defects in Cu-O chain regions, we discuss effects of Eu-Ba non-stoichiometric distribution on structural and superconducting properties.