Papers by Francisco Ascencio
Magnetic and optical properties of ZnO nanoparticles and nanorods synthesized by green chemistry
Nano express, Apr 11, 2024
Structural and Vibrational Study of Porous Ceo2 Nanoparticles
Journal of superconductivity and novel magnetism, Feb 2, 2024
In this research work, we report the synthesis, crystal structure, Raman Study, and magnetic prop... more In this research work, we report the synthesis, crystal structure, Raman Study, and magnetic properties at low temperatures of TaC x (x = 0.00, 1.25, and 1.50) compounds. The experiments are performed on polycrystalline samples synthesized by an arc melting method. The samples show a cubic phase with FFC structure measurements by XRD and were further analyzed by Rietveld refinements in which the small impurity of the Ta 2 C and T 2 O 5 was detected. Raman spectroscopy shows the characteristics of TaC peaks being associated with disordered band (D) and graphitic band (G). The transmission electron microscopy study was performed to obtain the morphology, size, and microstructure of the samples. The magnetic property magnetization curves in zero field cooling (ZFC) and field cooling (FC) modes reveal that the system is characterized as a type II superconductor. The most important aspect of this study is observed with the increase of C doping amount; the T c presents a slightly increasing tendency from 9 K to 9.5 K.
Clear antiferromagnetism induced by vacancies in ZnO nanoparticles synthesized by alkali salt method
Journal of Nanoparticle Research
Herein, the synthesis, structural characterization, and magnetic characteristics of ZnO nanoparti... more Herein, the synthesis, structural characterization, and magnetic characteristics of ZnO nanoparticles were studied. Pure wurtzite nanoparticles were grown into an alkali salt environment with a size of 10.37 ± 0.4 nm, determined by transmission electron microscopy. X-ray diffraction, Rietveld refinement, Raman, UV–Vis, photoluminescence spectroscopy, and atomic-resolution electron microscopy were performed to verify the structure and purity of the produced nanoparticles. Additionally, magnetization versus temperature measurements showed a low-temperature peak related to an antiferromagnetic transition of oxygen. This peak changes its shape with the rise of the magnetic field, and it practically disappears at 10,000 Oe. In addition, we observed that the transition to diamagnetism occurred at a lower temperature. Magnetization as a function of magnetic field curves presents the coexistence of antiferromagnetic and ferromagnetic behavior at 2 K. Meanwhile, diamagnetism was observed at magnetic fields over 1500 Oe and ferromagnetism between ± 1500 Oe at 300 K; these features were related to the vacancies of O and Zn.
Journal of Superconductivity and Novel Magnetism, 2021
We studied the physical behavior of PdO nanoparticles at low temperatures, which presents an unus... more We studied the physical behavior of PdO nanoparticles at low temperatures, which presents an unusual behavior clearly related to macroscopic quantum tunneling. The samples show a tetragonal single phase with P42/mmc space group. Most importantly, the particle size was estimated at about 5.07 ± 1.97 nm. Appropriate techniques were used to determine the characteristic of these nanoparticles. The most important aspect of this study is the magnetic characterization performed at low temperatures. It shows a peak at 50 K in zero field cooling (ZFC) mode that corresponds to the blocking temperature (TB). These measurements in ZFC and field cooling (FC) indicate that the peak behavior is due to different relaxation times of the asymmetrical barriers when the electron changes from a metastable state to another. Below TB in FC mode, the magnetization decreases with temperature until 36 K; this temperature is the crossover temperature TCr related to the anisotropy of the barriers, indicative o...
Applied Physics A, 2019
NiO nanoparticles with different sizes were synthesized at different temperatures from 300 to 700... more NiO nanoparticles with different sizes were synthesized at different temperatures from 300 to 700 • C to the study of behavior related to size. The nanoparticles show dimensions in the range 5.07-68.29 nm, which were determined by transmission electron microscopy images. The nanoparticles present an irregular morphology from 300 to 600 • C, while the observed structure is a truncated octahedron with FCC structure only for samples at 700 • C. X-ray diffraction measurements and Rietveld analysis verify this crystal structure, the crystal size, and the lattice parameters. Raman spectroscopy of the nanoparticles shows the normal modes of proposed truncated octahedrons related to longitudinal optical, transverse optical phonons, and a combination of both. Optical properties were measured by UV-visible spectroscopy to analyze the variation of the band gap in function of the size. In addition, magnetic measurements, magnetization versus temperature, and magnetization versus magnetic field present ferromagnetic behavior. M-H hysteresis curves show the coercive field with anisotropic characteristics that we related to the competition between two magnetic orders coexisting in the samples.
Nanoscale, 2017
Catalysts have been widely used in industries and can be optimized by tuning the composition and ... more Catalysts have been widely used in industries and can be optimized by tuning the composition and chemical ordering of the elements involved in the nano-alloy.
Superconductivity and Magnetism in In $ _ {2} $ O $ _ {3} $-ZnO Observed in Bulk and Nano Samples
Bulletin of the American Physical …, 2010
We prepared and studied compounds with In$_{2}$O$_{3}$ powders and ZnO nanoparticles. Samples wer... more We prepared and studied compounds with In$_{2}$O$_{3}$ powders and ZnO nanoparticles. Samples were prepared under different stoichiometric conditions and reacted at different temperatures. The initial temperatures where the oxides are mixed were in the ...
A comparative study of the synthesis and cathodoluminescence of BiOCl nanostructures using synthetic tannins
Materials Today Communications, 2020
Abstract Bismuth oxychlorides (BiOCl) nanostructures have attracted much attention due to their p... more Abstract Bismuth oxychlorides (BiOCl) nanostructures have attracted much attention due to their physicochemical properties with applications in pharmaceuticals and electronics; hence, its efficient production is considered to be of great importance. In this regard, polyphenols have emerged as excellent growth directing agents for the synthesis of nanomaterials, representing a soft and cleaner alternative for their controlled production. In this work, we compared the efficiencies of two synthetic tannins, tannic and gallic acid, for the soft chemistry production of BiOCl nanoflakes at room temperature. The morphology, chemical composition, and crystal structure of the produced nanocompounds were determined and compared in both cases. One phase BiOCl nanoflakes were produced when tannic acid was used, while a mixture of BiOCl and Bi2O3 phases was present in case of using gallic acid. The results reveal a phase stabilizing role of the glucose core present in tannic acid compared to gallic acid. Finally, optical absorption measurements revealed the band gap tuning of the produced nanostructures, and blue emission was observed through cathodoluminescence measurements in the 350−450 nm region.
Superconductivity and Magnetism in In2O3ZnO Observed in Bulk and Nano Samples
We prepared and studied compounds with In2O3 powders and ZnO nanoparticles. Samples were prepared... more We prepared and studied compounds with In2O3 powders and ZnO nanoparticles. Samples were prepared under different stoichiometric conditions and reacted at different temperatures. The initial temperatures where the oxides are mixed were in the range of 300 ^oC, final temperatures are close to 1100 ^oC. Samples were annealed in oxygen and argon atmospheres. The resulting black compounds present superconducting behavior with maximum transition temperatures above 4.5 K. Magnetic measurements show bulk superconducting diamagnetism to the maximum value about -1/4π. This type II superconducting material presents a critical magnetic file HC1 of 55 Oe and HC2 of 345 Oe, at 1.7 K. Isothermal magnetic measurements, below and above the superconducting transition temperature show that the compounds are also ferromagnetic.
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Papers by Francisco Ascencio