Preparation and physical properties of the GdPr-123 system

The Gd-Pr solid solution of the '123' crystal structure, Gd1-xPrxBa2Cu3O7-y (GdPr-123) with 0.0 ≤ x ≤ 1.0 has been prepared by the standard solid-state reaction technique. Details of sample preparation and results of XRD, SEM, TGA, DT, M(μ0H), and X(T) measurements are reported. For x ≥ 0.45, GdPr-123 is non-superconducting down to 10 K and does not show 'metallic' conduction. Samples have a predominantly single-phase orthorhombic structure with Pmmm symmetry and a small percentage (approx. 1%) of the Ba sites are occupied by Pr ions in some Pr-rich samples. The lower critical field value measured lies in the range of 10 mT. The nominal valence of the Cu ion in the whole range of x is determined; at the metal - semiconductor boundary xcr approx. 0.45, which is smaller by only 0.18 than the value 2.33 of the fully oxygenated GdBa2Cu3O7-y (Gd-123) system. However, the valence of Pr is 3.86+. We suggest that the increasing band filling and localization of states due to the disorder effects together with Pr doping could cause the observed metal-semiconducting transition; qualitatively this is the same as the oxygen depletion case. (author)