Structure and superconducting properties of Ga-substituted YBa2Cu3O7−δ and YBaSrCu3O7−δ systems

Nagarajan, Rajamani ; Ramachandra Rao, C. N. (1993) Structure and superconducting properties of Ga-substituted YBa2Cu3O7−δ and YBaSrCu3O7−δ systems Journal of Materials Chemistry, 3 (9). pp. 969-973. ISSN 0959-9428

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Official URL: http://pubs.rsc.org/en/content/articlelanding/1993...

Related URL: http://dx.doi.org/10.1039/JM9930300969

Abstract

In YBa2Cu3−yGayO7−δ, Ga can be substituted at the Cu(1) site up to y=0.1 without change in structure, but this is accompanied by a slight decrease in the hole concentration and Tc; the same is true when Y is partly substituted by Ca, as in Y1−xCaxBa2Cu3−yGayO7−δ,(0 .0<x≤0.2). When one Ba is replaced by Sr as in YBaSrCu3−yGayO7−δ,, however, Ga can be substituted at the Cu(1) site to a much greater extent (up to y=0.6). In this system, Ga substitution changes the structure from orthorhombic to tetragonal, unlike in YBa2Cu3−yGayCu3O7−δ,. Both the hole concentration and Tc decrease with an increase in y and the material becomes non-superconducting for y>0.2. The y=0.3 and 0.4 compositions show metal-semiconductor transitions at 60 and 120 K, respectively, while the y=0.6 composition is a semiconductor. When Y is partly substituted by Ca as in Y1−xCaxBaSrCu3−yGayO7−δ,, the material is superconducting even when y=0.3. All these Ga-substituted cuprates are in the underdoped region and accordingly Tc increases with increase in hole concentration.

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