Study of the Semiconducting Behavior in Zr-Doped Bi_1.95Sr_1.65La_0.4CuO_{6+ Ceramic Cuprates}

The effect of zirconium substitution on copper sites in ceramic cuprates of the Bi1.95Sr1.65La0.4Cu1-xZrxO6+& delta; system, where x = 0.0, 0.2, and 0.4, on the structural and superconducting properties has been examined. Undoped and Zr-doped samples were synthesized using the traditional solid-state reaction technique. The x-ray diffraction analysis showed that the phase in the undoped sample is recognized as the Raveau phase, also known as a phase R-2201 superconductor, whereas it totally transforms to phase I, also known as a phase I-2201 semiconductor, in the Zr-doped samples. Electrical resistivity measurements using the four-probe method show a superconductor state in the undoped sample below T-C,T-Onset = 35 K. In the Zr-doped samples, the results demonstrate that superconductivity is suppressed, and a semi-conducting behavior is shown. The loss of superconductivity in the system may be attributed to the excess oxygen intercalation in the Bi-O double layers and to the localization of the charge carriers. The transport process in the Zr-doped samples is followed by a two-dimensional variable range hopping conduction.