# 123, 247, and 124 cuprate superconductors: Investigations of thermodynamic stabilities, defect structures, and intergrowths

Rao, CNR and Subbanna, GN and Nagarajan, R and Ganguli, AK and Ganapathi, L and Vijayaraghavan, R and Bhat, SV and Raju, AR (1990) 123, 247, and 124 cuprate superconductors: Investigations of thermodynamic stabilities, defect structures, and intergrowths. In: Journal of Solid State Chemistry, 88 (1). pp. 163-176.

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## Abstract

Careful investigations employing nonresonant microwave or rf absorption, $Cu^{2+}$ EPR spectra, X-ray diffraction, and electron microscopy show that orthorhombic $Yba_2Cu_3O_{7-\delta}$ is thermodynamically stable and monophasic when $\delta$ is $0.0–0.2 (T_c = 90 K), 0.25 (T_c = 80 K)$, and $0.5 (T_c = 45 K)$. The last two compositions are associated with ordered oxygen-vacancy structures; in the $\delta = 0.0–0.2$ regime, $3b = c$. Compositions in the range $\delta = 0.3-0.4 (T_c = 60 K)$ do not appear to be thermodynamically stable and decompose on annealing, suggesting thereby that the so-called 60 K superconducting phase in the $YBa_2Cu_3O_{7-\delta}$system may not be genuine. 123 cuprates prepared with excess CuO often show fringes of 124 in lattice images. Both 124 and 247 cuprates prepared by the ceramic method in a flowing oxygen atmosphere frequently show intergrowths of each other or with 123. Such epitaxial relationships between 123, 124, and 247 cuprates could be of significance with respect to their superconducting properties. Both 124 and 247 cuprates undergo thermal decomposition to give 123 and CuO.

Item Type: Journal Article Journal of Solid State Chemistry Academic Press Inc. Copyright of this article belongs to Academic Press Inc. superconductors Division of Chemical Sciences > Solid State & Structural Chemistry Unit 03 Jan 2008 19 Sep 2010 04:41 http://eprints.iisc.ac.in/id/eprint/12604