Search

We report the preparation and characterization of YBa2Cu3O7 (YBCO) films grown onto SrTiO3 and YSZ substrates by the trifluoroacetates chemical solution deposition method and following sintering with oxygen atmosphere at 860 °C. The X-ray diffraction (XRD) reveals (00ℓ) – oriented crystallites indicating epitaxial growth of the films in the c-direction. Despite granular morphology and the presence of Y2BaCuO5 and CuO as minor secondary phases, the technique shows the successful formation of the superconducting YBCO and preventing the formation of the unwanted BaCO3 phase. Rocking curve measurements of the (005) reflection for the YBCO/SrTiO3 was fitted with one Gaussian function with full width at the half maximum (FWHM) of 0.44° confirming that it consists of YBCO crystallites with different texture. For the sample grown on YSZ, the rocking curve was fitted with two Gaussian functions, one corresponding to the YBCO layer (FWHM = 0.4°) and another to the substrate (FWHM = 0.3°). The magnetic measurements taken in zero field cooling and field cooling modes confirm the formation of the superconducting YBCO with critical temperatures (TC) 91.8 and 85.7 K for the samples grown onto YSZ and SrTiO3, respectively. The critical current density (JC) curves indirectly calculated by using the Bean´s model from the M(T) loops were JC ~ 109 A/cm2 for the sample deposited onto YSZ and JC ~ 107A/cm2 for the YBCO deposited onto SrTiO3. Overall, the difference in TC and JC values between both samples could be related to their difference in oxygen content, porosity, hole concentration per Cu ion and the presence of secondary phases.

The steel industry produces large amounts of slag coming from different stages during the steelmaking process every year. Currently, there are numerous attempts to recycle it or to use it in some other industry sectors and to preserve the environment. The characteristics of the slag depends on the steelmaking process and it is crucial to have it before any attempt of recycling. In this work, slag sample produced in the ladle furnace from SIDERPERU steel plant were collected and analyzed by using energy dispersion X-ray (EDX), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), SQUID magnetometer and Mössbauer spectroscopy. The chemical analysis obtained by EDX and XRF indicate that the main elemental composition of the material is Fe, Ca, Si and Cr. XRD identifies that these elements are in the phases: FeO, Fe3O4, α-Fe2O3, Ca2SiO4, and Ca2,32Mn0,68SiO7. Magnetometry measurements suggest the Verwey transition for magnetite and the Morin transition for hematite are screened by the presence of superparamagnetic phases. The Mössbauer spectrum shows two doublets related to Fe2+ and Fe3+ ions with hyperfine parameters belonging to that of non-stoichiometric wustite. Also, the presence of hyperfine fields characteristic of the Fe3O4 and Fe2O3 phase identified at room temperature verifies the magnetometry analysis. The analysis of the sample used in this work reveals details connected with the steel fabrication processes and are helpful for posterior recycling attempts.

In this work, we characterize the hollow hematite (α-Fe2O3) micro spheres obtained by two non-template techniques: i) sol gel and ii) spray roasting process. Both techniques allow the production of high yield hollow hematite spheres up to 100 g for the case of sol gel and up to 500 kg for the case of spray roaster process. The samples were characterized by X-ray diffraction, scanning electron microscopy and Mössbauer spectroscopy. The results indicate nearly uniform hollow spheres with diameters of around 1–1.5 μm and consisting of polycrystalline hematite. The Mӧssbauer spectroscopy reveals the signal change of quadrupole shift values evidencing the occurrence of the Morin transition and that the samples show an antiferromagnetic order at 77 K as in bulk hematite. The Morin temperature (TM) for both samples was obtained from the measurements of the magnetic moments as a function of the temperature in zero field cooling (ZFC) and field cooling (FC) modes. The values of TM for both samples are lower than that reported for bulk hematite (TM(bulk) = 263 K). Remarkably, the ZFC and FC loops do not overlap in both samples, revealing irreversible Morin transition. However, the sample obtained by sol gel presents thermal hysteresis with TM values of 260 K (in ZFC) and 248 K (FC). Whereas, the sample obtained by spray roaster process presents complete irreversibility and TM values of 252 K (in ZFC) and 242 K (in FC). Keywords: Hollow spheres, Hematite, Morin transition, Thermal hysteresis

Due to the current necessity to obtain epitaxial superconductor films at low cost, we report the growth of YBa2Cu3O7 (Y123) films by chemical deposition. The procedure involved simple steps such as precipitation of stoichiometric amounts of yttrium, barium and copper acetates in oxalic acid (H2C2O4). The precursor solution was dripped onto LaAlO3 (100) substrates with the help of a Fisher pipette. The films were annealed in oxygen atmosphere during 12 h at three different temperatures: 820 °C, 840 °C and 860 °C. After 820 °C and 860 °C annealing, X-ray diffraction (XRD) analysis revealed high intensity of the ( 00l ) reflections denoting that most of the Y123 grains were c-axis oriented. In addition, we also observed a-axis oriented grains (( h00 ) reflexion), minor randomly oriented grains and other phases (such as Y2BaCuO5 and CuO). In contrast, the sample treated at 840 °C, we noticed c – and a-axis oriented grains, very small amounts of randomly oriented grains without formation of other phases. From the magnetization versus temperature measurements, the critical temperatures were estimated at 70K and 90K for the samples annealed at 820 °C and 860 °C respectively.

We report the phase formation and superconductivity in [Y 1−x Ca x ]SrBaCu 2.80 (BO 3 ) 0.20 O y with 0.10≤x≤0.50 prepared at normal pressure and temperature. The X-ray diffraction pattern shows that all samples have a tetragonal P4/mmm structure, indicating that the BO 3 groups were incorporated in the structure. The ZFC magnetization versus temperature measurements under an applied field of 10 Oe using a SQUID magnetometer, show that the materials are superconductors, with T c ≈ 77K, almost independently of the Ca content. The observed differences are related to the volume fraction of Meissner effect. In the temperature range 100–300K all samples show a typical Curie - Weiss behavior, under an applied high field of 20 KOe.