BRUNO SANTOS CORREA
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Artigo IPEN-doc 30205 Cobalt doping effects in zinc oxide2024 - PEREIRA, LUCIANO F.D.; FERREIRA, WANDERSON L.; CORREA, BRUNO S.; COSTA, MESSIAS S.; COSTA, CLEIDILANE S.; FILHO, ARNALDO A.M.; SALES, TATIANE S.N.; BOSCH-SANTOS, BRIANNA; SCHELL, JULIANA; BURIMOVA, ANASTASIA; SAXENA, RAJENDRA N.; CABRERA-PASCA, GABRIEL A.; CARBONARI, ARTUR W.In this paper, we investigate the solubility effects of Co in ZnO (Zn1−xCoxO, where x = 0, 0.03, 0.05, 0.1, 0.2, 0.25, 0.4, 0.8, and 1) by combining the results of perturbed angular correlation (PAC) spectroscopy using highly diluted 111Cd as probe nuclei and ab initio calculations based on spin-density functional theory (SDFT). This combined approach enables us to characterize the local structure around Cd ions, where, through PAC technique, it was possible to measure the EFG as a function of temperature and Co concentration and thereby monitor the changes in the structure and the Co solubility threshold in ZnO and the ZnO/CoO/Co3O4 mixed phase. The full-potential linear augmented plane wave plus local orbital (APW+lo) formalism were used here to describe the electronic structure of the supercells, including the atomic relaxations. These Ab initio calculations show an interesting behavior of the Cd and Co impurity levels in the band structure of ZnO, which explains the experimental results in terms of the origin of EFG and the evidence of ferromagnetic response.Artigo IPEN-doc 30219 Investigation of Ni/Ni3C nanoparticle synthesis for application as a catalyst in carbon nanostructure growth2023 - SILVA, CRYSTIAN W.C.; CABRERA-PASCA, GABRIEL A.; SOUZA, KATIUSSE S.; COSTA, CLEIDILANE S.; COSTA, MESSIAS S.; CORREA, BRUNA S.; FERREIRA, WANDERSON L.; FREITAS, RAFAEL S.; CARBONARI, ARTUR W.; OTUBO, LARISSAThe synthesis of functional Ni/Ni3C nanoparticles has attracted significant interest, especially in the field of electrocatalysis, where these promising nanoparticles are employed to develop sophisticated electrocatalysts, particularly for hydrogen production through the hydrogen evolution reaction. However, the significant reactivity of these systems makes them susceptible to degradation, compromising their catalyst performance. One solution explored to mitigate this problem involves the catalytic growth of carbon nanostructures to encapsulate and protect these nanoparticles. The mechanisms for the formation of carbon nanostructures from nanoparticles remain the subject of this study. Among the reported processes, the annealing of nanocatalysts has been described as a highly effective method for producing such systems. This process is influenced by parameters, such as the temperature, atmosphere, and structural and morphological characteristics of the nanocatalysts. In the work reported here, we evaluated the influence of different ligand pairs (oleylamine/oleic acid and oleylamine/palm kernel oil) on the structural, morphological, and magnetic properties of Ni/Ni3C nanoparticles obtained through thermal decomposition at 240 °C for 3 h. Additionally, we investigated the impact of annealing in a nitrogen atmosphere on the structural properties of these nanoparticles and the growth of carbon nanostructures as a protective mechanism. The analyses include conventional techniques such as X-ray diffraction, transmission electron microscopy (TEM), magnetization measurements, and thermogravimetric analysis with differential scanning calorimetry. Additionally, local analysis was conducted using perturbed angular correlation spectroscopy (PAC) across a broad temperature range (30–693 K), utilizing the radioactive tracer 111In(111Cd) for these measurements. The characterizations revealed that palm kernel oil contributes to the formation of nanoparticles with a higher Ni3C content, a broader size distribution, and a lower saturation magnetization. The PAC measurements in the range of 30–50 K, along with density functional theory calculations, indicated the absence of the Ni-hcp phase in the nanoparticles, a topic frequently discussed in the literature. Moreover, the presence of Ni3C regions with carbon deficiency was identified, characterized by a quadrupole frequency (νQ) of 23 MHz and a hyperfine field (Bhf) of 1 T. The temperature-dependent local analysis, combined with thermal analysis and TEM measurements, confirmed the development of carbon nano-onions around the nanoparticles during thermal treatment above 695 K in a nitrogen atmosphere. This observation demonstrates that nanoparticles obtained with palm kernel oil, which has the highest Ni3C content, offer superior encapsulation of Ni nuclei through these graphitic nanostructures.Resumo IPEN-doc 30169 Comparative local analysis of Ni/Ni3C nanoparticles synthed with oleylamine/oleic acid and oleylamine/palm kernel oil ligand pairs2023 - SILVA, CRYSTIAN W.C. da; OTUBO, LARISSA; SOUZA, KATIUSSE S. de; CARBONARI, ARTUR W.; CORREA, BRUNO S.; FREITAS, RAFAEL S. de; PASCA, GABRIEL A.; COSTA, CLEIDILANE S.In recent decades, Ni/Ni3C nanoparticles have been a topic of interest, especially for their catalytic and magnetic properties, promising as electrocatalysis, for example [1]. These systems are usually obtained by chemical methods, in the presence of ligands responsible for controlling their structure and morphology [2]. In this work, we carried out a comparative study of the hyperfine interactions occurring in Ni/Ni3C nanoparticles, synthed by thermal decomposition in the presence of oleylamine/oleic acid and oleylamine/palm kernel oil ligand pairs, at 513 K, for 3 hours. The local analysis was performed using perturbed correlation spectroscopy (PAC) in the temperature range from 30K to 300K, using the 111Cd probe, implanted in the samples by diffusion, during the synthesis. The parameters of the hyperfine interactions were compared to the results obtained by XRD, TEM and magnetization, indicating the obtainment of Ni/Ni3c nanoparticles of the core-shell type, showing a higher Ni3C content, greater distribution and lower saturation magnetization for nanoparticles synthed with palm kernel oil compared to those obtained with oleic acid. In addition, the hyperfine parameters showed the existence of regions with a quadrupole frequency of 24 MHz and a magnetic hyperfine field of 1T in both samples, which may be indicative of carbon-deficient Ni3C regions, predicted in the literature [3].Artigo IPEN-doc 29041 Local crystalline structure of doped semiconductor oxides characterized by perturbed angular correlations2022 - BURIMOVA, ANASTASIA; CARBONARI, ARTUR W.; LIMA, NICOLE P. de; MIRANDA FILHO, ARNALDO A.; SOUZA, ALEXANDRE P. dos S.; SALES, TATIANE da S.N.; FERREIRA, WANDERSON L.; PEREIRA, LUCIANO F.D.; CORREA, BRUNO S.; SAXENA, RAJENDRA N.Doping semiconductor oxides with trace amounts of non-native elements can improve their properties such as bandgap and conductivity. The lack of local techniques makes the precise characterization of these materials difficult. Among the few techniques capable of providing local characterization, those based on hyperfine interactions at probe nuclei have the advantage of being well established, probing the material homogeneously and completely, thus investigating different regions of material. Some of these techniques are also quite sensitive even at extremely low dopant concentrations. The perturbed angular correlation technique, combined with first-principles calculations, has recently been shown to be a powerful method for characterizing doped semiconductor oxides. In this paper, we present a brief review of the unique information extracted from the semiconductor investigation with such a complex approach, including semiconductor oxides doped with cadmium and other elements. A strong relationship between the local environment, including electronic structure, and the nature of the dopant and the native element of the doped oxides is also shown.Artigo IPEN-doc 28524 Magnetic and structural properties of the intermetallic Ce(1−x)LaxCrGe3 series of compounds2021 - BOSCH-SANTOS, B.; CABRERA-PASCA, G.A.; CORREA, E.L.; CORREA, B.S.; SALES, T.N.S.; MOON, K-W.; DENNIS, C.L.; HUANG, Q.; LEAO, J.B.; LYNN, J.W.; CARBONARI, A.W.The Ce(1−x)LaxCrGe3 (x = 0, 0.19, 0.43, 0.58, and 1) intermetallic compound system has been investigated by magnetization measurements and neutron scattering techniques to determine the effect of La doping on the magnetic ordering and exchange interaction between Cr ions. The structural and magnetic characterization in this series was first verified by x-ray diffraction and bulk magnetization measurements. The samples exhibit the known hexagonal perovskite structure (P63/mmc space group) and have a single magnetic phase according to magnetizationmeasurements. In this paper, the ferromagnetic ordering temperature for Cr evolves smoothly from a range of 68 K to 77 K for CeCrGe3 to a range of 91 K to 96 K for LaCrGe3 as La replaces Ce. Magnetization results indicate the formation of domain walls below the transition temperature for all Ce(1−x)LaxCrGe3 systems investigated. Neutron results indicate ordered magnetic Cr moments aligned along the c axis for the x = 1 LaCrGe3 system, as well as for x = 0.19, 0.43, and 0.58, which contrasts with the x = 0 CeCrGe3 where the moments order in the ab plane.Artigo IPEN-doc 28161 Crystalline and magnetic properties of CoO nanoparticles locally investigated by using radioactive indium tracer2021 - SANTOS, RENATA V.; CABRERA-PASCA, GABRIEL A.; COSTA, CLEIDILANE S.; BOSCH-SANTOS, BRIANNA; OTUBO, LARISSA; PEREIRA, LUCIANO F.D.; CORREA, BRUNO S.; EFFENBERGER, FERNANDO B.; BURIMOVA, ANASTASIA; FREITAS, RAFAEL S.; CARBONARI, ARTUR W.We herein report a comprehensive investigation on the magnetic, structural, and electric properties of CoO nanoparticles with different sizes by local inspection through hyperfine interactions measured in a wide range of temperatures (10–670 K) by using radioactive 111In(111Cd) tracers with the perturbed angular correlations technique. Small cobalt oxide nanoparticles with the characteristic size of 6.5 nm have been prepared by the wet chemical route that turned out to be essential to incorporate radioactivity tracers during nucleation and growth of the particles. Nanocrystalline samples with 22.1 nm size were obtained by thermal treatments under low pressure of helium at 670 K. The hyperfine data were correlated with X-ray diffraction, ZFC–FC magnetic measurements, and transmission electron microscopy to describe the structure, magnetic properties, size, and shape of samples. An analysis of the temperature evolution of hyperfine parameters revealed that the structural distortion and the magnetic disorder in the core and on the surface layer play an important role in the magnetic behavior of CoO nanoparticles.