Preparation of LSGM electrolyte via fast combustion method and analysis of electrical properties for ReSOC

In this work, we prepared LaSrGaMgO (LSGM) by the fast combustion method and assessed the electrical properties with respect to the composition and sintering temperature (1200, 1300, and 1400 °C by 6 h) as an electrolyte material for the reversible solid oxide cells (ReSOCs). For the preparation of samples, two different fuels, such as tartaric acid (TA) and citric acid (CA), with corresponding nitrate salts as precursors, were adopted for the fast combustion method (at 500 °C for 10 min). From the X-ray diffractograms, two main phases corresponding to LSGM orthorhombic (space group Imma) and LSGM-cubic (space group Pm-3 m) were identified. From the literature, both structures are reported as high oxygen ion conductive species, but normally they are not reported to appear together. Additionally, in some cases, an isolating (secondary) phase of LaSrGaO in a low concentration < 1.98% was observed. The scanning electron microscopy (SEM) studies on samples sintered at 1200 and 1300 °C revealed the smaller grain size and irregular morphology. The SEM micrographs depicted a well-defined superficial morphology with less porosity for the samples sintered at 1400 °C. For comparative analysis, the conductivity (S.cm) was measured at varying temperatures (300–800 °C) for the samples sintered at 1300 and 1400 °C. Because of the large number of insulating phases produced by the incomplete sintering process, the samples sintered at 1300 °C had lower conductivities. A higher conductivity of 0.125 S.cm was observed for LaSrGaMgO (LSGM), which was obtained using the citric acid (sintered at 1400 °C), which is in the range of earlier reported similar studies. The observed variation in the conductivity with respect to different phases of LSGM, the influence of the secondary phase, and the wt% of the constituents of LSGM are discussed.The authors acknowledge the financial support of FONDECYT (ANID) Projects No.:1181703, 11220335 and DOCTORADO NACIONAL: 21202168, Government of Chile. The authors thank Mónica Uribe from Instituto de Geología Aplicada, UDEC; the Centro de Microscopía Avanzada, CMA BIO-BIO, Proyecto PIA-ANID ECM-12 for their contribution to this work

Size dependent magnetic and capacitive performance of MnFe2O4 magnetic nanoparticles

MnFe2O4 magnetic nanoparticles (MNPs) are prepared by simple chemical oxidation method with optimized experimental conditions. The particle size is reduced by introducing the ferric ions as a size reducing agent during the chemical reaction. The saturation magnetization of the MnFe2O4 MNPs are tuned between 45 and 67 emu/g. The shift in the particle size distribution is confirmed from the transmission electron microscope (TEM) micrograph. The highest specific capacitance of 415 F/g is achieved for the smaller sized MnFe2O4 MNPs prepared with higher concentration of ferric ions. The results suggest that the ferric ions could be used for the size control of ferrites through chemical oxidation method and the sized reduced MnFe2O4 MNPs could be a suitable choice for the electrochemical supercapacitor applications.University of ATACAMA Postdoctoral Research Projec

Evaluation of La0.8 Sr0·2MnO3 perovskite prepared by fast solution combustion

LaSrMnO (LSM) perovskite as oxygen electrode material for the reversible solid oxide fuel cells (ReSOFC) was synthesized by the fast solution combustion method and assessed for subsequent calcination influence. The microstructural, morphological, compositional and optical properties of the obtained material were analyzed with X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM) coupled with an energy-dispersive X-ray spectroscopy detector (EDS) and UV–visible spectroscopy techniques. The XRD results showed the coexistence of rhombohedral R-3c and Pm-3m polymorphs for the perovskite phase, with a decreased fraction of the cubic phase as the temperature and/or time used for the calcination were increased. The HR-TEM images confirmed the existence of the R-3c and Pm-3m polymorphs for the sample subjected to calcination at 1300 °C, showing that the rapid combustion method did not allow the pure formation of the LaSrMnO phase for the calcination temperatures below 1400 °C, due to the swiftness of the combustion synthesis 500 °C for 5 min. The average grain size was found to be increased with the calcination time. The EDS analysis depicted a better agreement in stoichiometry with the theoretical composition. The apparent porosity was decreased with the increase in the temperature and calcination time due to the coalescence of the sintering pores. The sample obtained after the calcination at 1400 °C for 8 h exhibited 1.6% of porosity. The hardness was improved with the higher calcination time and temperature and reached a maximum value of 5.7 GPa that merely matched the bulk density. A similar trend was observed in the temperature dependence resistivity studies and all the samples presented a low resistivity of ∼1.2 Ω cm in the temperature range of 600–700 °C. The optical characterization exhibited a broad absorption in 560–660 nm.The authors acknowledge the FONDECYT-ANID (Project No. 1181703) for the financial support. Ramón Cobo-Rendón thanks to ANID-Chile Grant No.: 21210463

Probing the defect-induced magnetocaloric effect on ferrite/graphene functional nanocomposites and their magnetic hyperthermia

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULORecently, the development of an alternative magnetic refrigerant for the conventional fossil fuels attracts the researchers. We discussed the structural defect-induced magnetocaloric effect (MCE) in Ni0.3Zn0.7Fe2O4/graphene (NZF/G) nanocomposites for the first time. Single-phase spinel ferrite nanocomposites with an average size of 7-11.4 nm were achieved by using the microwave-assisted coprecipitation method. The effect of graphene loading on the structural and magnetism of NZF/G nanocomposites was elaborated. Raman analysis proved that the interface interaction between NZF and graphene yielded different densities of structural defects. In view of magnetism, superparamagnetic NZF nanoparticles showed a magnetic entropy change (-Delta S-M(max)) of -0.678 J.kg(-1) K-1 at 135 K, whereas the NZF/G nanocomposites exhibited superior -Delta S-M(max) at cryogenic temperatures and the defect-induced MCE change was indeed similar to the I-D/I-G intensity ratio. The nanocomposites exhibited different magnetic orderings between 5 and 295 K, and it was varying for I-D/I-G, 1.83 gt; 1.68 gt; 1.57 as antiferromagnetic (AFM) gt; AFM/ferrimagnetic (FiM) gt; FiM, respectively. Till now, NZF/G nanocomposites showed an inverse MCE of 4.378 J.kg(-1) K-1 at 35 K and a refrigerant capacity of 88 J.kg(-1) for 40 kOe, which was greater than the ferrites reported so far. Finally, MCE and magnetic hyperthermia were correlated at ambient conditions. These results pave the way for ferrite/graphene nanocomposites for cooling applications.123422584425855FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO2018/19096-1The authors greatly acknowledge FONDECYT Postdoctoral Research project no.: 3160170, CONICYT PIA/APOYO CCTE AFB170007 and CONICYT BASAL CEDENNA FB0807, Government of Chile and FAPESP Postdoctoral Fellowship Process Number (2018) 19096-1, Government of Brazil for financial assistance. We extend our gratitude to Prof. Lorena, Universidad Austral de Chile, Valdivia, for the Raman spectral measurements (FONDEQUIP EQM 160050 project)

Altered electrochemical properties of iron oxide nanoparticles by carbon enhance molecular biocompatibility through discrepant atomic interaction

Recent advancement in nanotechnology seeks exploration of new techniques for improvement in the molecular, chemical, and biological properties of nanoparticles. In this study, carbon modification of octahedral-shaped magnetic nanoparticles (MNPs) was done using two-step chemical processes with sucrose as a carbon source for improvement in their electrochemical application and higher molecular biocompatibility. X-ray diffraction analysis and electron microscopy confirmed the alteration in single-phase octahedral morphology and carbon attachment in Fe3O4 structure. The magnetization saturation and BET surface area for Fe3O4, Fe3O4/C, and alpha-Fe2O3/C were measured as 90, 86, and 27 emu/g and 16, 56, and 89 m2/g with an average pore size less than 7 nm. Cyclic voltammogram and galvanostatic charge/discharge studies showed the highest specific capacitance of carbon-modified Fe3O4 and alpha-Fe2O3 as 213 F/g and 192 F/g. The in vivo biological effect of altered physicochemical properties of Fe3O4 and alpha-Fe2O3 was assessed at the cellular and molecular level with embryonic zebrafish. Mechanistic in vivo toxicity analysis showed a reduction in oxidative stress in carbon-modified alpha-Fe2O3 exposed zebrafish embryos compared to Fe3O4 due to despaired infiuential atomic interaction with sod1 protein along with significant less morphological abnormalities and apoptosis. The study provided insight into improving the characteristic of MNPs for electrochemical application and higher biological biocompatibility