Investigation into sintering and melt-growing of high temperature superconducting 123 materials

The dependence of transport Jc and sinter temperature on grain size of YBa2Cu3O7-x samples prepared with different initial powder precursor sizes (dpr) has been investigated, with a view to improving on their low Jc values. It was found that during the sintering process at a given temperature, for a given initial particle size of YBa2Cu3O7-x powder precursor, grains grow to an asymptotic equilibrium grain size, de, which is only temperature dependent. Therefore, low sintering temperatures produced small grain size samples while high sintering temperatures produced large grain size samples. For each batch of increasing precursor grain size there was found to be a characteristic curve for the Jc dependence on grain size. Each curve followed the same trend such that, at small grain sizes, i.e. low sintering temperatures, the Jc increases. This was attributed to incomplete sintering. The Jc for each precursor batch then peaks at a different grain size, which corresponds to optimal sintering. The grain size at which the maximum Jc occurs increases for samples of a larger precursor size. Beyond the maximum J, all the samples follow an intrinsic curve of a sharp decrease in Jc with increasing equilibrium grain size, de, of the sample. This was attributed to an intrinsic grain size dependence of Jc for larger grains.A recent report by Jin et al [1] showed both a six fold enhancement in intergranular Jc and an acceleration of the kinetics of oxygen absorption during the tetragonal-orthorhombic transformation, by doping YBa2Cu3O7-x with 1%wt Sb2O3. Work presented in this thesis demonstrates that the reported increase in Jc is apparently not due to an intrinsic enhancement but is likely to be due to the modification in grain size produced by Sb2O3 doping. It also shown that the reported acceleration of oxygen absorption is probably due to the increased porosity produced by Sb2O3 doping.