Y3 Ba4 Cu7 Ox bileşiğinin sentezlenerek yapısal ve elektriksel özelliklerinin incelenmesi

Abstract

VI ABSTRACT In this work, the preparation conditions and the properties of Y3Ba4Cu7Oj, prepared by solid-state reaction technique were investigated. The effect of i- Annealing temperature between 850-1000°C and ii-Stoichiometry were investigated. Moreover, the phases with close thermodynamic properties were tried to be seperated employing spesific heat treatment whose conditions were extracted from their DTA/TGA data. Resistance, x-ray, ER absorbance and SEM-EDAX data all indicate that the samples are multiphase and contain as the main phase with some Y2BaCu05 and CuO impurities. Data obtained from the samples annealed at different temperatures indicate that the reactions favor the route which yields YBa2Cu3Ox +impurities. It also suggest that the partial melting zone in the ternary phase diagram of Y203, BaC03 and CuO is an open surface with a minumum at 925°C. The resistance data of the samples annealed at 925 and 990°C show thermally unstable steppy resistive transitions at 110, 132 and 138K besides the main superconductive transition of around 90K. Among the samples having different stoichiometries the compound with the nominal composition of Y3Ba4Cu7Ox shows the lowest resistance value in the metallic region and the narrowest transition region despite the fact that IR data suggest that it contains the highest amount of impurities. In one case, Y2Ba3Cu5Ox and YBaCu2Ox phases were detected by EDAX inspection. VII DTA results of some samples reveal that the endothermic peaks around 950°C consist of 2 or 3 overlapped peaks. Closely oriented phases were attempted to be seperated employing a slow cooling rate(0.l°C/min) in each characteristic temperature range on the endothermic peaks. Outside this region a cooling rate of 20°C/min was utilised. Most of such heat treated samples showed either step-like resistive transition or discreate changes in the slope of resistance between 125-260K. These transitti ons were found to be unstable under thermal cycling and disappeared at high current(>lmA). Gaussian peak analysis employed to IR spectra reveals some unidentified peaks at 401, 405, 488-489, 526, 533, 539 and 541-543 cm"1 ; Y2Ba2Cu3Ox and Y3Ba4Cu7Ox as well as YBaCu2Ox and Y2Ba3Cu5Ox stoichiometrics were identified by EDAX investigation. The unidentified IR peaks may be attributed to these new phases. Observation of Y3Ba4Cu7Ox became more frequent after employing the specific heat treatment

VI ABSTRACT In this work, the preparation conditions and the properties of Y3Ba4Cu7Oj, prepared by solid-state reaction technique were investigated. The effect of i- Annealing temperature between 850-1000°C and ii-Stoichiometry were investigated. Moreover, the phases with close thermodynamic properties were tried to be seperated employing spesific heat treatment whose conditions were extracted from their DTA/TGA data. Resistance, x-ray, ER absorbance and SEM-EDAX data all indicate that the samples are multiphase and contain as the main phase with some Y2BaCu05 and CuO impurities. Data obtained from the samples annealed at different temperatures indicate that the reactions favor the route which yields YBa2Cu3Ox +impurities. It also suggest that the partial melting zone in the ternary phase diagram of Y203, BaC03 and CuO is an open surface with a minumum at 925°C. The resistance data of the samples annealed at 925 and 990°C show thermally unstable steppy resistive transitions at 110, 132 and 138K besides the main superconductive transition of around 90K. Among the samples having different stoichiometries the compound with the nominal composition of Y3Ba4Cu7Ox shows the lowest resistance value in the metallic region and the narrowest transition region despite the fact that IR data suggest that it contains the highest amount of impurities. In one case, Y2Ba3Cu5Ox and YBaCu2Ox phases were detected by EDAX inspection. VII DTA results of some samples reveal that the endothermic peaks around 950°C consist of 2 or 3 overlapped peaks. Closely oriented phases were attempted to be seperated employing a slow cooling rate(0.l°C/min) in each characteristic temperature range on the endothermic peaks. Outside this region a cooling rate of 20°C/min was utilised. Most of such heat treated samples showed either step-like resistive transition or discreate changes in the slope of resistance between 125-260K. These transitti ons were found to be unstable under thermal cycling and disappeared at high current(>lmA). Gaussian peak analysis employed to IR spectra reveals some unidentified peaks at 401, 405, 488-489, 526, 533, 539 and 541-543 cm"1 ; Y2Ba2Cu3Ox and Y3Ba4Cu7Ox as well as YBaCu2Ox and Y2Ba3Cu5Ox stoichiometrics were identified by EDAX investigation. The unidentified IR peaks may be attributed to these new phases. Observation of Y3Ba4Cu7Ox became more frequent after employing the specific heat treatment