Control of the oxygen doping in Bi-2212 whiskers by means of their synthesis process

Direct evidence of oxygen doping control in single phase Bi2Sr2CaCu2O8+δ (Bi-2212) whiskers is reported, along with the changes in their structural properties obtained by varying the growth temperature of the synthesis process in the range from 843 to 872 °C. The as-grown whiskers were investigated by means of x-ray powder diffraction (XRPD), electrical transport measurements, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). The XRPD measurements showed that the value of the c-axis lattice parameter increases from 30.556 to 30.640 Å when increasing the growth temperature, which indicates different oxygen doping levels spanning from the slightly overdoped to the nearly optimally doped regimes. Such results are also confirmed by the electrical characterizations, which revealed a typical relationship among resistivity (ρab), superconducting critical temperature (Tc), and c-axis value. The growth of CuO crystals has also been identified during this study, with a maximum yield in the range 860–864 °C, where also a slope change in the c-axis behavior has been found, implying a possible correlation between the two phenomena. Therefore, by changing the synthesis growth temperature, one can provide an effective way to tune the whisker electrical transport properties.