Effect of double substitution on structural and magnetic properties of Y1-xCaxBa2(Cu1-yMgy)(3)O7-delta

The effect of the double substitution of Ca and Mg on structural, compositional and magnetic properties in YBa2Cu3O7-? polycrystalline compounds are investigated. All prepared samples were found to be single phase with small fraction of Ba-secondary phases. Substitution by more than 2% of magnesium causes an increase of spurious phases. Energy Dispersive Spectrometry (EDS) has been made to analyse the distribution of Ca and Mg in the samples. DC susceptibility measurements show that superconducting transition temperature Tc is reduced by Ca alone and much more when there is also Mg. These measurements have been analysed accurately in order to determine the variations, versus the content of Ca and Mg, of the width of the transition, the temperature of irreversibility Tirr and the difference between the ZFC and FC magnetisations. The critical current density Jc, deduced from the M(H) hysteresis loops, does not follow the same variation versus the content of Ca when the content of Mg is changed. Ca alone reduces Jc for x = 0.1; 0.2. Together with Ca, Mg seems to compensate the reduction of Jc and increasing its content near the solubility limit gives higher Jc than in the undoped sample.