Conduction mechanism and magnetoresistance in Gd<Subscript>1-x</Subscript>Pr<Subscript>x</Subscript>BaCaCu<Subscript>3</Subscript>O<Subscript>7-δ</Subscript>

Tetragonal Gd<Subscript>1-x</Subscript>Pr<Subscript>x</Subscript>BaCaCu<Subscript>3</ Subscript>O<Subscript>7-δ</Subscript> (0≤x≤1) polycrystalline samples have been prepared by the standard solid-state reaction, and characterized by XRD and SEM. Rietveld analysis on X-ray diffraction pattern shows site mixing between rare earth (R) and Ca. Contrary to Gd<Subscript>1-x</Subscript>Pr<Subscript>x</Subscript>Ba<Subscript>2</Subs cript>Cu<Subscript>3</Subscript>O<Subscript>7-δ</Subscript>, a hump on the ρ(T) curve is observed at about 80 K. The normal state resistivity has been analyzed by the two and three dimensional variable range hopping (2&3D-VRH) and Coulomb gap. For low concentration of Pr (x>0.5–0.6, corresponding to the metal-insulator transition), 2D-VRH is the dominant mechanism, but with the increase of x, the 3D-VRH is dominant. Substitution of Ba by Ca highly increases the superconducting granularity. The magnetoresistance measurements have been analyzed by the Ambegaokar and Halperin phase slip model. The field dependences of the pinning energy and critical current density have been studied for different amounts of Pr doping. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005