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A series of compounds LaBa2Cu3-xNixO7±[delta] (0.0 < x < 0.3) and Ln Ba2Cu3-xNixO7-[delta] (Ln123; Ln = Pr, Nd, Sm, Gd, and Er; x = 0.1, 0.2) has been synthesized by a ceramic method and their structure characterized by X-ray and electron diffraction. The substitution of nickel in LaBa2Cu3O7±[delta](La123) induces an orthorhombic to tetragonal structural transition as well reducing the activation energy for oxygen desorption. Orthorhombicity increased with decreasing lanthanide ion radius in the Ln Ba2Cu2.9Ni0.1O7±[delta] system. Electrical resistivity measurements show metallic behavior down to 4.2 K for LaBa2Cu3-xNixO7±[delta] (0.1 < x < 0.3). The superconducting transition temperatures of Ni-doped Ln123 decreased with increasing rare earth ion radius, for the same nickel content. These properties are discussed in terms of the Ni3+ ion occupying the Cu(1) sites in La123 stabilized by a larger La3+ ion and Ni2+ ion occupying the Cu(2) sites in the Ln 123 system of oxides.
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