D.A. Landinez Tellez

Structure, microstructure, magnetic properties and chemical stability of HoBa2SbO6 with Yba2Cu3O7−δ superconductor

Abstract A complex perovskite oxide HoBa 2 SbO 6 in the Ho–Ba–Hf–O, rare-earth based oxide system, has been synthesised and sintered as a single phase material. The structure, microstructure, quantitative elemental analysis and magnetic properties of this material have been studied by X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) techniques and magnetic susceptibility measurements. Significant presence of superstructure reflection lines in the XRD spectra of HoBa 2 SbO 6 reveals that it is an ordered complex perovskite oxide. Magnetic susceptibility measurements show that HoBa 2 SbO 6 presents a paramagnetic behaviour at low temperature (5–300 K). Microstructure and EDX analysis show that sintered HoBa 2 SbO 6 has homogeneous surface morphology with uniform particle size (1–2 μm) distribution and there is no evidence of impurity in the single phase sintered HoBa 2 SbO 6 . The chemical stability of HoBa 2 SbO 6 with YBa 2 Cu 3 O 7− δ superconductor was studied. This study shows that HoBa 2 SbO 6 is chemically compatible with YBa 2 Cu 3 O 7− δ and it did not have deleterious effect on the superconducting transition temperature of YBa 2 Cu 3 O 7− δ . Also, HoBa 2 SbO 6 melts congruently and single crystals could be grown from the melt. In view of these favourable characteristics, HoBa 2 SbO 6 could be used as a potential substrate material for YBa 2 Cu 3 O 7− δ superconductor film.

Structural aspects, superconductivity and thermal properties of Pr in the La1-xPrxCaBaCu3O7-δ system with 1.0 ≥ x ≥ 0.0

Abstract We report on the structural aspects and superconductivity of the La 1− x Pr x CaBaCu 3 O 7− δ system (RE: 1113) with x =0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 1.0. X-ray diffraction studies show that Pr substitutes isostructurally in LaBaCaCu 3 O 7− δ (La: 1113) until complete replacement of La. The superconducting transition temperature, T c , determined from AC susceptibility measurements decreases with x . The relative T c depression due to Pr in the LaBaCaCu 3 O 7− δ system is less in comparison to that found for La site Pr substituted LaBa 2 Cu 3 O 7 system. Normal state DC magnetism of the Pr substituted samples show a Curie–Weiss paramagnetic susceptibility with deviations below about 10xa0K. The non-superconducting compounds ( x =0.7, 1.0) display Schottky-type anomalies which are attributed to crystalline electric field effects (CEF). The related entropy change for x =1.0 sample amounts to Δ S =7.75xa0J/molxa0K. Rietveld analysis on neutron diffraction pattern of x =0.0 sample shows that 46xa0at% of the La is occupying the Ba site, in normal Re: 123 unit cell. A similar situation is suppose to occur in case of PrBaCaCu 3 O 7 , for which the refinement of Ba and Pr sites is near impossible due to their similar scattering cross-sections for neutrons. Ba site sitting Pr does not contribute to the Pr-4f hybridization with Cu–O conduction band, giving rise to a lower T N and less effect of Pr on superconductivity of La: 1113 system than for La: 123. The results strengthen extended Pr-4f hybridisation with Cu–O conduction band.

Chemical and physical stability of MgO with superconductors

Chemical and physical compatibility of MgO with (LBCCO) high- superconductors have been studied by x-ray diffractometry and magnetic measurements on composites containing 0-100 vol% of MgO component. X-ray diffractometry studies carried out on composite show that MgO is chemically non-reactive with LBCCO superconductors even up to 80 vol% addition of MgO and severe heat treatment at for 30 h. Lattice matching between MgO and unit cells is fairly well (lattice mismatch ). Magnetization measurements carried out on composite show that no deleterious effect on the superconducting properties of is caused by MgO addition. Thus we infer that MgO is chemically and physically compatible with superconductors and MgO substrates could be used for the fabrication of high- LBCCO superconducting films.

Superconductivity and normal-state magnetism of CaLaBaCu3− xCoxO7 superconductor

Abstract The results of superconductivity and normal-state magnetism of the CaLaBaCu3 − xCoxO7 superconductor for x = 0.0–0.24 are studied by X-ray diffraction and SQUID magnetization. The transition temperature Tc of the samples, determined from AC susceptibility measurements decreases with an increase in the dopant Co concentration. The normal-state high-field (5 kOe) DC magnetism inferred that the pure sample (x = 0.0) has a small and nearly temperature-independent molar susceptibility, while the Co-doped samples follows the Curie-Weiss relation in terms of the paramagnetic moment on the dopant Co.

Pinning-force measurements in Bi2Sr2CaCu2O8+ y

Abstract We report on the applied field and temperature dependence of the pinning force in Bi 2 Sr 2 CaCu 2 O 8+ y single crystals. The pinning force was obtained from the hysteresis curves in magnetization measurements. The field dependence of the pinning force presents a maximum at nonzero applied field. The temperature dependence of the field for maximum pinning force shows three different behaviours: For temperatures between 10 and 25 K it decreases steeply with temperature; this behaviour is changed for a smooth temperature dependence for temperatures in the range 25–40 K and then it approaches to zero above 40 K. This behaviour suggest the existence of different pinning mechanisms for different temperature regions.

Synthesis, structural and morphological characterization of the perovskite LaYbO3

In this work we report synthesis of the LaYbO3 ceramics material by the solid state reaction technique and its structural and morphological characterization from X-ray diffraction and Scanning Electron Microscopy experiments. Rietveld refinement of the diffraction patterns reveals that this material crystallizes in an orthorhombic perovskite, Pnma space group (#62) with lattice parameters a=6.0233A, b=8.2080A and c=5.7203A. Systematic monitoring of the synthesis process is carried out through analysis of results of X-ray diffraction. The surface morphology of the samples was qualitatively analysed as a function of the sintering process.

Structural refinement of [Y1-xCax]SrBaCu2.80(PO4)0.20Oy

Abstract [Y 1− x Ca x ]SrBaCu 2.80 (PO 4 ) 0.20 O y samples with 0.10⩽ x ⩽0.40 were synthesized using the solid state reaction technique. X-ray diffraction patterns show that all the compounds crystallized into a 123 tetragonal structure. The analyses of the structure with Rietveld refinement were made using a model that contain one Cu(2) in a four coordination and not in five coordination as the other 123 tetragonal structures. This fact permits that the T c increases with Ca concentration. All samples are superconductors as reported previously.

Study of transport properties of CaLaBa[Cu1-xZnx]3O7-δ superconductors

Abstract In this work, the effect of substitution of Zn for Cu on the superconducting properties of CaLaBaCu3O7−δ has been studied. CaLaBa[Cu1−xZnx]3O7−δ samples present a sharp superconducting transition with a transition width that increases with x. The depletion of Tc with x is consistent with a non magnetic disordering model.

Superconductivity, synthesis and magnetism of CaLaBaCu3−x(Zn,Fe)xO7 tetragonal system

Abstract The results of superconductivity, structure and normal state magnetism of the CaLaBaCu3−x(Zn,Fe)xO7 are studies by x-ray diffraction and SQUID magnetization measurements. X-ray diffraction results show that both Zn-and Fe substitute isostructurally in CaLabaCu3O7 system. The superconducting transition temperature Tc of the samples, determined from ac susceptibility measurements decreases with increasing Zn or Fe concentration. The relative Tc depression rate (dTc/dx), is larger (12K/at%) for Zn than the Fe (6Kk/at%) substituted samples. For both the Zn and Fe substituted samples a Curie-Weiss behaviour is observed due to the presumed creation of local moments on Cu for Zn doped samples, and to the magnetic moment of Fe3+/Fe4+ ions in case of Fe substituted samples.

EDX analysis and microstructural properties of the Yba2Cu3O7−δ-Ba2HoSbO6 superconducting composites

We have fabricated and characterized Yba2Cu3O7−δ-Ba2HoSbO6a realized high Tcsuperconductor - ceramic insulator composite system in which particles of the superconductor and ceramic insulator could coexist with well defined separated phases left intact by stringent processing conditions. All the composites exhibit superconductivity at 92K. EDX analysis show that element% and atomic% of the composites are in a good agreement with those of their respective components. SEM studies show homogenous surface morphology and particle size distribution. There is no detectable interface interaction between component grains and Ba2HoSbO6grains are distinguishably distributed in the Yba2Cu3O7−δmatrix.