CONTRIBUTION A L'ETUDE DE L'INFLUENCE DU DOPAGE SUR LES PROPRIETES ELECTRONIQUES DES CUPRATES SUPRACONDUCTEURS

摘要

In this work, we have investigated the phase diagram (T,p) through the effects of doping on the electronics properties of two systems La2-xSrxCuO4 and Bi2Sr2Ca1-xYxCu2-yZnyO8+d. First, the optical conductivity in two configurations, in-plane and out-of-plane, for two La2-xSrxCuO4 compounds (an under-doped with x = 0.08 and the optimally doped with x = 0.15) was analyzed. For under-doped case, along the c-axis and at low frequencies, we observed a decrease of the optical conductivity as temperature decreases. Moreover, with the in-plane configuration and at low frequencies, we have found a suppression of the scattering rate, which was accompanied by an increase of the effective mass when the temperature decreases. Since these results are only obtained in the under-doped one, they might be attributed to a signature of the pseudo-gap phase. In order to compare and to study the behavior of the Bi-2212 cuprate, we have synthesized Bi2Sr2Ca1-xYxCu2-yZnyO8+d samples. The yttrium substitution modifies the charge carriers concentration and the zinc substitution leads to a suppression of the superconductivity. At first, we have studied ceramics samples. Two ways of synthesis were used : the conventional solid-state reaction and the modified citrate process. The latter one has shown an improved purity and cristallinity. Transport measurements have shown that at high temperature, samples turn from a metallic state to a semi-conductive state upon the yttrium and zinc substitutions. We have grown Bi2Sr2Ca1-xYxCu2-yZnyO8+d crystals in an image furnace. The tests have shown that the growth is complex. After having optimized the parameters of the fusion on the un-doped composition, we have obtained single crystals with a typical size 15 x 5 x 0.2 mm3. For the substitutions, the yttrium prevents the growth of big crystals (i.e. the size could not exceed 3 x 1.5 x 0.2 mm3). The solubility limit of the zinc substitution on the copper site has been found to be equal to 0.03. Finally, we have grown and characterized single crystals with composition Bi1.99Sr2.01Ca0,76Y0.3Cu1.9Zn0.03O8+d