Abstract
We have investigated the effect of partial substitution of Ca for Y and/or Mg for Cu on structural, compositional and magnetic properties in γBa2Cu3O7-δ polycrystalline compounds. 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 Spectroscopy (EDS) revealed that the distribution of Ca in the sample is quite homogenous. DC susceptibility measurements show that superconducting transition temperature Tc is reduced much more by Ca than Mg. Hysteresis loops reveal that magnetic irreversibility is decreased by Ca and Mg content. The deduced critical current density Jc does not follow the same variation. Ca alone reduces Jc for x=0.1 and x=0.2. Together with Ca, Mg compensates the reduction of Jc and increasing its content near the solubility limit gives higher Jc than in the undoped sample.
Highlights
The analysis of impurity effects in high temperature superconductors (HTSC) gained additional interest upon confirmation that this subject could provide a crucial test for d-wave symmetry of the order parameter in high Tc copper oxides [1,2]
The magnetic properties were obtained from Zero Field Cooled (ZFC) and Field Cooled (FC) M(T) DC magnetization measurements, and M(H), using a Physical Properties of Materials System (PPMS) of Quantum Design working in a vibrating samples magnetometer (V.S.M.) mode
All prepared samples show a small fraction of Ba-secondary phases at values of 2θ between 28° and 31° indicating a partial substitution of Ca at the Ba sites
Summary
The analysis of impurity effects in high temperature superconductors (HTSC) gained additional interest upon confirmation that this subject could provide a crucial test for d-wave symmetry of the order parameter in high Tc copper oxides [1,2]. It is realized that the superconducting transition temperature, Tc, sensitively depends on both the hole concentration in the CuO2 planes and the relative electric charge of the oxygen within the planes [3,4] The level of this charge can be controlled either by manipulating the oxygen stoichiometry in the Cu–O chains, by application of pressure or by ionic substitution [5,6]. The study of non-magnetic cation substitution in HTSC has generated a thoroughly interest in the last years due to the observation of a very high efficiency in depressing Tc in these materials This is known to be an indication primarily of the d-wave symmetry of the superconducting order parameter [9,10]. The magnetic properties were obtained from Zero Field Cooled (ZFC) and Field Cooled (FC) M(T) DC magnetization measurements, and M(H), using a Physical Properties of Materials System (PPMS) of Quantum Design working in a vibrating samples magnetometer (V.S.M.) mode
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