Search

Abstract: The physical property characterization of Al doped Mg1− x Al x B2 system with x =0.0 to 0.50 is reported. The results related to phase formation, structural transition, resistivity ρ(T) and magnetization M(T) measurements are discussed in detail. It is shown that the addition of electrons to MgB2 through Al results in loss of superconductivity. Also seen is a structural transition associated with the collapse of boron layers reflected by the continuous decrease in the c parameter. The main emphasis in this paper is on slow scan X-ray diffraction (XRD) results, which confirm the existence of a superstructure along the c-direction for the x =0.50 sample. The appearance of some additional peaks, viz. [103], [004], [104] and [112], results in doubling of the lattice parameter along the c-axis. This possibly indicates the alternative ordering of Al and Mg in MgAlB4 separated by hexagonal boron layers but still maintaining the same hexagonal AlB2 type structure. [Copyright &y& Elsevier]

Abstract: In this paper we investigate the properties of polycrystalline series of Ru1− x Cr x Sr2Eu1.5Ce0.5Cu2O10− δ (0.0⩽ x ⩽0.40) by resistivity, XRD and dc magnetization measurements. EuRu-1222 is a reported magneto superconductor with Ru spins magnetic ordering at temperatures near 100K and superconductivity occurs in Cu–O2 planes below T c ≅40K. The exact nature of Ru spins magnetic ordering is still being debated and no conclusion has been reached yet. In this work, we found the superconducting transition temperature T c =20K from resistivity and dc magnetization measurements for pristine sample. DC magnetization measurements exhibited ferromagnetic like transition for all samples. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we report the change in electronic structure of Cu0.3Co0.7Ba2−x Sr x YCu2O7+δ with change in structural pressure. Rietveld refined X-ray diffraction (XRD) pattern shows that the samples are phase pure. Decrease in lattice parameters with increasing x, confirms replacement by Sr ion at Ba ion site. The calculated tolerance factor of the systems is in accord with lattice parameter changes. The X-ray photoelectron spectroscopy (XPS) is made to find out the variation in ionic state of Co and Cu with ionic size variation in BaO/SrO layers. Effect of the same on the electronic structure and transport properties is explored. The XPS measurement reveals that Cu is in mixed 1+/2+ state and variation in valence state is non-monotonous with increasing x. Whereas Co is in mixed 3+/4+ state and with increasing x its valence state is increasing. The observed changes in electronic structure are subject of structural changes. The resistivity measurement shows that normal state conductivity decreases with increasing x. Resistivity behaviour indicates about holes in Cu/CoO x planes taking part in charge transport. The magnetic measurement (M–T and M–H) shows that paramagnetic nature for all the compositions. The presence of Cu ions in Cu/CoO x chains/planes results in paramagnetic behaviour. [Copyright &y& Elsevier]