Structural anomalies in RBa2Cu3-xCoxO7±δ (R= rare earth) defect perovskites

Ramesh, S. ; Vasanthacharya, N. Y. ; Hegde, M. S. ; Subbanna, G. N. ; Rajagopal, H. ; Sequiera, A. ; Paranjpe, S. K. (1995) Structural anomalies in RBa2Cu3-xCoxO7±δ (R= rare earth) defect perovskites Physica C: Superconductivity, 253 (3-4). pp. 243-253. ISSN 0921-4534

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A series of oxides RBa2Cu2CoO7+δ(R = La, Pr, Nd, Sm, Gd and Er) has been synthesized and found to crystallize in an orthorhombic YBa2Cu3O7-δ(123)-like structure. X-ray electron and neutron diffraction studies of LaBa2Cu3-xCoxO7±δ showed that for smaller concentrations of Co (0.05≤x≤0.3) the oxides crystallize in a tetragonal structure, and for higher concentrations, (0.3≤x≤1), in an orthorhombic structure. LaBa2Cu2CoO7+δ showed an orthorhombic to tetragonal structural transition with decreasing oxygen content, and thermal desorption of oxygen from LaBa2Cu2CoO7.35 supported the presence of two types of labile oxygens, O(1) at (0½0) and O(6) at ( 00½). All members of RBa2Cu2CoO7+δ were semiconducting and the degree of orthorhombicity decreased with decreasing size of the central rare earth ion. Superconductivity was quenched faster in LaBa2Cu3-xCoxO7±δ for a lower value of x = 0.1, unlike in the case of YBa2Cu3-xCoxO7±δ where superconductivity persists up to x = 0.35. The compounds with x ≥0.2 were all semiconducting. Magnetic susceptibility studies on LaBa2Cu3-xCoxO7±δ suggest a mixed valent state for cobalt.

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Deposited On:13 Nov 2010 12:32
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