Gabriel Adolfo Cabrera Pasca

Understanding how lattice effects tune magnetic exchange in intermetallic alloys is essential for controlling functional magnetic properties. Here we investigate Ce _(1-x) La _(x) CrGe ₃ (x = 0, 0.19, 0.43, 0.58, and 1) hexagonal perovskite-type intermetallics using perturbed angular correlation (PAC) spectroscopy combined with structural characterization. La substitution induces a systematic lattice expansion while simultaneously increasing the Curie temperature from 69 K (CeCrGe 3 ) to 84 K (LaCrGe ₃ ). PAC measurements using ¹¹¹ In( ¹¹¹ Cd) reveal a pronounced increase of the magnetic hyperfine field at the Cr site with increasing La content, despite larger Cr-Cr distances.This counterintuitive behavior suggests a crossover from a relatively itinerant regime in Ce-rich compositions toward a more localized Cr 3d state in La-rich compounds, consistent with lattice-induced band narrowing and modified Cr-Ge-Cr exchange interactions. No magnetic contribution from Ce is detected within experimental sensitivity, confirming that ferromagnetism is governed by the Cr sublattice. These results indicate that lattice expansion is an important parameter for exchange enhancement in RECrGe ₃ intermetallic alloys.

The design of hierarchical copper oxide microstructures with tailored nanomorphologies is essential for next-generation electrocatalytic, sensing, and nanoelectronic applications. Here, we report an atmosphere-controlled thermal oxidation route for the sustainable synthesis of hollow Cu/Cu₂O/CuO microtubes decorated with a dense array of vertically aligned CuO nanowires. The synthesis uses recycled copper microwires from electronic waste (e-waste) coated with a polyurethane (PU) polymer. Comparative analysis under ambient air and high-purity synthetic air reveals that the thermal degradation of the polymeric coating forms a carbon-rich layer, crucial for regulating asymmetric cation transport and inducing mass transport that drives void formation via the Kirkendall effect. This mechanism transforms the solid microwire into a concentric hollow microtube structure. Critically, oxidation under synthetic air promotes the extensive growth of long CuO nanowires (up to 20 μm), guided by anisotropic diffusion along twin boundaries and sustained by a strong chemical potential gradient. These findings establish atmosphere control as a powerful strategy to fine-tune the multiscale architecture of sustainable metal oxide nanostructures from e-waste precursors, opening pathways for the scalable production of multifunctional materials.

This work investigates the incorporation of Vismia guianensis alcoholic extract (EAVG) into cassava starch, with the aim of improving its bioplastic properties. Cassava starch was dissolved into distilled water and doped with 0.2%, 0.5%, and 1.0% EAVG under a temperature controlled at the gelatinization point (∼70 °C) and then cast to form bioplastics. The resulting samples were characterized via attenuated total reflectance/Fourier transform infrared spectroscopy (ATR/FTIR), thermogravimetric and differential thermal analysis (TGA-DTA), X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), atomic force microscopy (AFM), and mechanical essays, providing insights into chemical composition, thermal stability, crystallinity, surface morphology, and mechanical properties. The results demonstrated that EAVG played an effective role, enhancing the flexibility and stability of the bioplastic with potential use in biomedical applications. Moreover, the results also showed significant improvements in mechanical and thermal properties, suggesting that EAVG is a valuable addition to bioplastics. Therefore, EAVG presents a pathway for advancing bioplastics with enhanced mechanical, thermal, and functional characteristics, with the potential for further advancements in these fields.

The advancement of functional nanomaterials has become a major focus of recent research, driven by the exceptional properties these materials display compared to their macroscopic (bulk) counterparts. Cobalt oxide nanoparticles (CoO-NPs) stand out primarily for their catalytic and magnetic properties, which can enable a range of technological applications, such as advanced catalysts, drug delivery systems, implants, prosthetics, sensors. However, in addition to the dependence on factors such as size, morphology, and functionalization, the properties of CoO-NPs are significantly influenced by the crystal structure. Therefore, local investigation into the polymorphic structures of CoO at the nanometric scale may provide new insights into the local structural and magnetic characteristics of these systems. In this report, we address the synthesis and local characterization of cobalt oxide (CoO) nanoparticles in the rock-salt cubic fcc-CoO and Wurtzite hpc-CoO phases, obtained through thermal decomposition. We analyze the influence of oleylamine and oleic acid ligands on the structural and morphological control of these systems. The obtained nanoparticles were characterized using conventional techniques such as X-ray diffraction (XRD), transmission electron microscopy, Raman spectroscopy, and Fourier-transform infrared spectroscopy. Local characterization was carried out by the perturbed angular correlation (PAC) nuclear technique using the radioactive tracer ¹¹¹In(¹¹¹Cd). Measurements were conducted at 295 and 10 K to investigate possible magnetic phase transitions in these systems. XRD results confirmed the formation of fcc-CoO and hcp-CoO phases. The phase fcc was obtained with the pair of oleylamine and oleic acid ligands, while the phase hcp phase was synthesized using only oleylamine. Additionally, nanoparticles synthesized with oleylamine and oleic acid exhibited better morphological control compared to those produced with only oleylamine. Raman spectroscopy analyses suggest a phase transformation process resulting in Co₃O₄. PAC results for hyperfine interactions at the ¹¹¹In(¹¹¹Cd) probe nucleus, indicate that the hcp-CoO phase shows smaller hyperfine magnetic interactions (B _hf = 1 T) compared to the fcc-CoO phase (B _hf = 17 T). This suggests the mechanism of superexchange interactions, which are strongly influenced by the Co-O-Co bond angle, which is 110° for the hpc-CoO phase and 180° for the fcc-CoO phase due to the geometries of the systems.

In this paper, we investigate the solubility effects of Co in ZnO (Zn_1−xCo_xO, 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.

In the work here reported, we have calculated magnetic hyperfine interactions in rare-earth (R) intermetallic compounds by using the free open-source all-electron ELK code. The RCd (R = Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) series was chosen as a test system because an almost complete set of experimental data on the hyperfine parameters at Cd sites was acquired through the time differential perturbed angular correlation (TDPAC) spectroscopy as previously reported. Moreover, results on magnetic hyperfine field (B_hf) from WIEN2k code were also reported allowing a qualitative comparison analysis. We emphasize that the utilized version of ELK accounted for the contact field only. Yet, as it is the only contribution expected for Cd site in RCd compounds, the calculated B_hf values are in reasonable agreement with the experimental results. The Spin-orbit coupling when taken into account led to a decrease in deviation from experimental data. Addition, the Hubbard-like term was revealed crucial in order to make B_hf predictions for CeCd, suggesting that this behavior may be associated with a weaker 4f electron localization in Ce.