Effects of Mn Substitution in YBa2Cu3O7-b Superconducting Ceramic
Ali Dihom, Mustafa Musa (2004) Effects of Mn Substitution in YBa2Cu3O7-b Superconducting Ceramic. Masters thesis, Universiti Putra Malaysia.
The influence of manganese (Mn) substitution in copper (Cu), barium (Ba) and yttrium (Y) sites in the Y-Ba-Cu-O system namely: YBa2Cu3-xMnxO7-δ (0.00 ≥ x ≥ 0.5), YBa2-x MnxCu3O7-δ (0.00 ≥ x ≥ 0.5) and Y1-xMnx Ba2Cu3O7-δ (0.00 ≥ x ≥ 0.5) were studied. The samples were prepared using the conventional solid state sintering technique. The sintered temperature and soaking time were 920ºC and 24 hours respectively. The transport properties of the samples were measured using the four-point probe electrical resistance measurement and the magnetic properties were measured by using ac susceptibility. Scanning electron microscope (SEM) was used to identify the surface morphology while the phase of the samples was determined using x-ray diffraction (XRD) technique. The pure sample, which exhibits TC(R=0) around 90 K and TConset around 94 K showed large flaky grains of ~ 25 µm in size with some gaps and voids. The effect of Mn substitution on the superconducting behaviour of YBCO shows that the transition temperature, TC was sharply reduced when the substitution site is at Ba. For the sample in which x=0.30 the values of TC are 80K, 72K and 60K for substitution in the Y, Cu and Ba sites, respectively. The dynamic magnetic properties of the samples show that the effect of Mn substitution is markedly decreased in the Ba substituted samples. The value of Josephson current Io for x=0.3 are 13.6µA, 14.1µA and 6.9µA for the substitution in Y, Ba and Cu sites, respectively. The XRD patterns showed that the orthorhombic structure was retained for all the samples. However, at higher concentration of Mn substitution, some unknown peaks were observed. There is a general trend of an increase of (102) peaks as Mn concentration increases at all sites, while the (003) and (006) peaks decreased. The morphology of the samples varies as Mn was substituted at different sites. At lower concentration, the shapes of the grains are sharper in Mn substituted the Y samples. When x=0.3, the grains are loosely packed and more rounded when Mn substituted the Ba sites. When manganese was incorporated in Y3+, Ba2+ and Cu2+ sites, the resistivity result showed the shifting in TC(R=0) towards low temperature as the Mn increases. The temperature dependence of ac susceptibility data χ΄ shows the shifting of the onset diamagnetism towards lower temperature as the Mn concentration increased due to the presence of low TC phase. The imaginary component, χ˝ shows a decrease in the intergranular coupling peak, TP towards lower temperature as the Mn concentration increased. XRD patterns showed the existence of the unknown peaks, which belong to the impurities. SEM micrographs showed the decrease in the grain size as the concentration increases.
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