Search

We have performed a systematic study on the occurrence of superconductivity in Nb1− x Mg x B2 (0.0≤ x≤0.40). X-ray diffraction and magnetization measurements are carried out to determine the changes in lattice parameters, superconducting transition temperature ( T c ) and critical field ( H c1). The substitution of Mg at Nb site results in considerable stretching of c-parameter with only a slight change in a parameter. Rietveld analysis on X-ray diffraction patterns gives a=3.11 Å and c=3.26 Å for pure NbB2 while a=3.10 Å and c=3.32 Å for Nb0.60Mg0.40B2. This increased c-parameter introduces superconductivity in niobium diboride. Magnetization measurements though indicate the absence of superconductivity in NbB2, the same shows a clear diamagnetic signal at about 10 K for Nb0.60Mg0.40B2 sample. The magnetization M( H) plots exhibit weak superconductivity like hysteresis loops. The stretching of c-parameter from around 3.26 to 3.32 i.e. by 0.06 cannot be explained solely by substitution of Nb by Mg in the lattice. It seems that some Nb deficiencies are introduced in the Nb1− x Mg x B2 as Mg is not substituted completely at the vacant Nb sites. This could be seen from XRD results, where one can clearly notice the presence of small amount of MgO in Nb1− x Mg x B2 samples. [ABSTRACT FROM AUTHOR]

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: We report synthesis and superconductivity of Pb-1212–Cu1− x Pb x Sr2Y0.6Ca0.4Cu2O7 (x =0.5–0.9) compounds. These compounds were synthesized through solid-state reaction route with optimized sintering temperatures and conditions. In particular, one needs to employ reducing atmosphere conditions to achieve superconductivity in higher Pb content samples. The X-ray diffraction (XRD) patterns reveals that all the compounds are crystallized in space group P4/mmm RE-123 structure. Superconductivity at 56K (onset) is achieved for Pb content as high as 90%. Our study reveals that superconductivity and structure stabilization in Pb-based are more critical to synthesizing conditions than other cuprates. It is concluded that superconductivity can be introduced in Pb-1212 compounds by synthesizing the same in reducing atmosphere and thus the Pb in lower (<+4) valence state. This ensures the replacement of Cu–O x chains of RE-123 by Pb–O x sheets acting as charge reservoir carrier donating blocks. [ABSTRACT FROM AUTHOR]

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: Synthesis and structural details of MSr2RECu2O z (M-1212) compounds with M=Ga, Nb, Fe, Al and Co) and RE=Eu, Y are reported. Reitveld refinement of X-ray diffraction (XRD) patterns shows that all compounds are crystallized in single phase. Nb-, Fe- and Al-1212 possess tetragonal P4/mmm space group structure while the Ga-1212 and Co-1212 are crystallized in orthorhombic Ima2 space group. The change of space group from P4/mmm to Ima2 indicating towards the doubling of unit cell. The buckling angle [Cu(2)–O(2)–Cu(2) angle] shows that most of the studied samples are heavily under doped and hence they could not exhibit superconductivity. Thermogravimetric (TGA) analysis shows the M-1212 compounds to be more stable than widely studied 90K superconductor Cu-1212 (RE-123). [ABSTRACT FROM AUTHOR]