# Structure and superconducting properties of Ga-substituted $YBa_2Cu_3O_{7-\delta}$ and $YBaSrCu_3O_{7-\delta}$ systems

Nagarajan, Rajamani and Rao, Ramachandra CN (1993) Structure and superconducting properties of Ga-substituted $YBa_2Cu_3O_{7-\delta}$ and $YBaSrCu_3O_{7-\delta}$ systems. In: Journal of Materials Chemistry, 3 (9). pp. 969-973.

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## Abstract

In $YBa_2Cu_{3-y}Ga_yO_{7-\delta}$, 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 $T_c$; the same is true when Y is partly substituted by Ca, as in $Y_{1-x}Ca_xBa_2Cu_{3-y}Ga_yO_{7-\delta}$ $(0.0 < x \leq 0.2)$. When one Ba is replaced by Sr as in $YBaSrCu_{3-y}Ga_yO_{7-\delta}$, 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 $YBa_2Cu_{3-y}Ga_yCu_3O_{7-\delta}$. Both the hole concentration and $T_c$ 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 $Y_{1-x}Ca_xBaSrCu_{3-y}Ga_yO_{7-\delta}$, the material is superconducting even when y = 0.3. All these Ga-substituted cuprates are in the underdoped region and accordingly $T_c$ increases with increase in hole concentration.

Item Type: Journal Article Copyrigh of this article belongs to the Royal Society of Chemistry. Superconductivity;Oxide superconductor;Yetrium-barium-copper-oxygen system Division of Chemical Sciences > Solid State & Structural Chemistry Unit 27 Jun 2008 06 Jan 2011 07:32 http://eprints.iisc.ernet.in/id/eprint/14707