SUPERCONDUCTIVITY IN ZN-DOPED TETRAGONAL LABACACU3O7-DELTA SYSTEMS

Resistivity and ac susceptibility of Zn-doped samples of the LaBaCaCu3 O7-delta (LBCCO) system have been measured for Zn content of 0.5%, 1.0 %, 1.5%, 2.0%, 2.5%, and 3.0% at. wt. X-ray diffraction has been used to find the lattice parameters of the samples. The samples remain tetr agonal for all the considered concentrations of Zn. Idometry and therm ogravimetric analyses have been done to estimate the oxygen content of different samples. Analyzing the resistivity and ac susceptibility da ta, the following conclusions are drawn about the role of Zn in the LB CCO samples. (1) The conduction mechanism of electrons appears to foll ow a crossover from the purely metallic regime to the localization reg ime due to either weak localization or electron-electron interaction e ffects after about 1.5% Zn (2) The superconducting transitions reveale d by the resistivity vs temperature curves or susceptibility vs temper ature curves becomes sharper with Zn increasing content of Zn up to 1. 0%. After 1.5% the resistive and ac susceptibility transitions become broader with increasing Zn. (3) T-c depression up to Zn content of 1.0 % seems due to direct suppression of the effective pairing interaction , while at and above 2.5% Zn Te depression is expected to be due to di sorder effects such as reduction of density of states at the Fermi ene rgy.