Structural and magnetic studies of monophasic maghemite (γ-Fe2O3) magnetic nanocrystallites (MNCs) synthesized by the co-precipitation chemical route are reported in this paper. For the synthesis, a starting precursor of magnetite (Fe3O4) in basic medium was oxidized at room temperature by adjusting the pH = 3.5 at 80˚C in an acidic medium without surfactants. X-ray diffraction (XRD) pattern shows widened peaks indicating nanometric size and Rietveld Refinement confirms only one single-phase assigned to γ-Fe2O3 MNCs. High Resolution Transmission Electron Microscopy (HR-TEM) demonstrates the formation of nanoparticles with diameter around D ≈ 6.8 ± 0.1 nm which is in good agreement with Rietveld Refinement (6.4 ± 1 nm). A selected area electron diffraction pattern was carried out to complement the study of the crystalline structure of the γ-Fe2O3 MNCs. M(H) measurements taken at different temperatures show almost zero coercivity and remanence indicating superparamagnetic domain and high magnetic saturation.
The AC susceptibility of [Y 0.8 Ca 0.2 ](Ba 0.5 Sr 0.5 ) 2 Cu 3 O 7−δ was investigated as a function of frequency and amplitude of AC magnetic field. The susceptibilities of the sample display the field amplitude dependence. The peak temperature (T p ) of its imaginary part shows not frequency dependence but field amplitude dependence. The frequency effect on AC susceptibility was negligible. As the field amplitude increases, T p shifts to lower temperature.
En el presente trabajo se evaluó experimentalmente la degradación del colorante azul, Cibacron Navy-H2G a través de la acción fotocatalítica de nanopartículas industriales de TiO2 de la empresa española Avanzare. Las nanopartículas corresponden a la fase anatasa caracterizada por DR-X, tienen un tamaño aproximado de 26,6 nm, medidos con TEM y 20,4 nm, medidos con DLS. La degradación fotocatalítica se evaluó en función a la masa del fotocatalizador desde 0,1 g hasta 1,0 g; a la concentración del colorante desde 20 ppm hasta 100 ppm; y a pH desde 2 hasta 10. El tiempo de degradación fotocatalítica del colorante se monitoreo con espectrofotometría UV-Visible. Los mejores resultados del proceso se obtuvieron con una masa de 0,6 g de nanopartículas de TiO2 , concentración de colorante de 20 ppm y a un pH de 4.
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.
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