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

Abstract : 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
Document type :
Theses
Superconductivity [cond-mat.supr-con]. Université François Rabelais - Tours, 2005. French


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Submitted on : Friday, February 3, 2006 - 6:29:33 PM
Last modification on : Friday, April 24, 2015 - 1:14:01 AM

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Bruno Pignon. CONTRIBUTION A L'ETUDE DE L'INFLUENCE DU DOPAGE SUR LES PROPRIETES ELECTRONIQUES DES CUPRATES SUPRACONDUCTEURS. Superconductivity [cond-mat.supr-con]. Université François Rabelais - Tours, 2005. French. <tel-00011536>

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