Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1820787 | Physica C: Superconductivity and its Applications | 2006 | 7 Pages |
Abstract
We report on the results of systematic studies of Sr substitution effect for R(Ba1âxSrx)2Cu3O6+δ (where R = Nd, Pr) with 0 ⩽ x ⩽ 0.5, prepared under reducing atmosphere. Single phases were obtained for a wide range of x for both systems of Nd(Ba1âxSrx)2Cu3O6+δ and Pr(Ba1âxSrx)2Cu3O6+δ by means of synthesis at high-temperature under reducing atmosphere (Ar:O2 = 100:0.1). In particular, solubility as high as x = 0.5 was successfully achieved for the first time in the Pr(Ba1âxSrx)2Cu3O6+δ. For R = Nd, the superconducting transition temperature, Tc, decreases from 95 to 50 K as x increases from 0 to 0.5. From the Rietveld refinement of powder X-ray diffraction (XRD) data, occupancy of Sr at the Nd site is found, gSr/Nd (=2 Ã gNd/Ba), and the value of gSr/Nd increases with x from 0 (x = 0) to 0.11 (x = 0.5). Occupancy of O(4), gO(4), decreases and O(5), gO(5), increases with x. It is demonstrated that the depression of Tc with x is caused by the replacement of Ba2+ by Sr2+ and Nd3+ and also by the replacement of Nd3+ by Sr2+. Disorder in the BaO plane induce the disorder in the CuO plane, which results in the decrease of the orthorhombicity. For R = Pr, both of the electrical resistivity and antiferromagnetic ordering temperature, TN, increase with x until x = 0.3, then decreases with x. Refinement results do not show intermixing of Sr and Pr; Sr ions occupy only the Ba site and Pr ions does not occupy the Ba site. The dependence of the orthorhombicity on x is quite different from that of Nd-system. The crystal becomes tetragonal at x = 0.4, which is smaller than that of Nd-system. The hybridization between the Pr 4f and the O 2p orbitals which prefers the tetragonal symmetry is considered to advances the transition to the tetragonal structure.
Related Topics
Physical Sciences and Engineering
Physics and Astronomy
Condensed Matter Physics
Authors
Tuerxun Wuernisha, Fumihiko Sano, Yumiko Takahashi, Takashi Kamiyama, Yoshiki Takano, Kazuko Sekizawa,