Chemical tailoring of electronic doping in YSr/sub 2/Cu/sub 3/O/sub 7+or-d/ superconductor

With the aim to optimize the carrier concentration and T/sub c/ of YSr/sub 2/Cu/sub 3/O/sub 7+or-d/ (YSCO), we studied the effects of aliovalent substituents for Y and Cu1 in both as-prepared and annealed samples. Ca/sup 2+/ and Ce/sup 4+/ and Al/sup 3+/ were substituted for Y and Cu1, respectively. The samples were synthesized at 1050 degrees C, under a pressure of 30 Kbar, in a multi-anvil apparatus. The post-preparation annealings were carried out in static oxygen, nitrogen or under dynamic vacuum. The samples were characterized by X-ray diffraction and found to be almost single-phase at doping concentrations <or= 10%. T/sub c/ was determined by resistivity and magnetic susceptibility Vs temperature measurements. It was found to decrease in Ca-doped samples, to slightly increase for Al-doping or to remain almost constant for Ce-doping. These results seem to support the hypothesis that as-prepared YSCO is overdoped. For any substitution <10%, T/sub c/ decreased or vanished and the samples had a high content of secondary phases. T/sub c/ of doped compounds also decreases after post-preparation annealings.