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Rendon, R. C., Salvo, C., Sepulveda, E., Arulraj, A., Sanhueza, F., Rodriguez, J. J., et al. (2022). Evaluation of Structural and Functional Properties of La0.6Sr0.4MnO3 Perovskite Prepared by the Fast Solution Combustion Approach. Catalysts, 12(12), 1636.
Abstract: A series of La0.6Sr0.4MnO3 (LSM) perovskite was made using the rapid solution combustion method, which was calcined by varying the temperatures. In order to determine how the calcination temperature affected the nanopowders produced and calcined at various temperatures, their microstructural, morphological, compositional, optical, and electrical properties were analyzed using corresponding characterization tools. The XRD results showed the coexistence of the rhombohedral polymorphs R-3c and Pm-3m for the perovskite phase under a calcination temperature of 1400 degrees C, which were eliminated with increased calcination temperature. The average grain size was found to increase with increasing calcination temperature. The EDS analysis showed better agreement of the stoichiometry with the theoretical composition. The apparent porosity decreased with increasing temperature due to the coalescence of sintering pores. The sample obtained after calcination at 1500 degrees C showed 10.3% porosity. The hardness also improved with increasing calcination temperature and reached a maximum value of 0.4 GPa, which matched the bulk density. A similar trend was observed in the resistivity studies as a function of temperature, and all the samples exhibited a low resistivity of similar to 1.4 Omega.cm in the temperature range of 500-600 degrees C. The optical characterization showed broad absorption at 560-660 nm and bandwidth values between 3.70 and 3.95 eV, according to the applied heat treatment.
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Sahlevani, S. F., Pandiyarajan, T., Arulraj, A., Valdes, H., Sanhueza, F., Contreras, D., et al. (2024). Tailored engineering of rod-shaped core@shell ZnO@CeO2 nanostructures as an optical stimuli-responsive in sunscreen cream. Mater. Today Commun., 38, 107959.
Abstract: The catalytic efficiency of the materials can be boosted with the selective designing (nanostructures) including the core@shell which aids in attaining the separation of photoinduced charge carriers. However, to effectively separate the carriers and reduce the rate of recombination, tuning the thickness of the shell wall is a vital one. The one-dimensional (1D) rod-like shell wall-controlled ZnO@CeO2 core@shell structures were successfully prepared via co-precipitation and hydrothermal methods using the hexamethylenetetramine (HMTA) as a reagent. The CeO2 shell wall thickness was fine-tuned between 15 and 70 nm with a variation in the concentration of HMTA reagent. The results revealed that the concentration of HMTA played a significant role in the formation of ZnO@CeO2 core@shell structures and in tuning their thickness. The FE-SEM images evidenced the core-shell structures formation with the specific thickness and uniformity. The HR-TEM images confirmed the homogeneity and regular form of the shell thickness. The unit cell and crystallite size were identified from the XRD analysis. The constructed core-shell structures were further employed in the formula of the prototypes of sunscreen and their photoprotective performance was analyzed in the view to cut the solar light irradiation in a new sunscreen formulation. The developed core-shell ZnO@CeO2 structures showed the excellent optical absorption in both the UV as well as visible regions.
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Sepulveda, E., Mangalaraja, R. V., Troncoso, L., Jimenez, J., Salvo, C., & Sanhueza, F. (2022). Effect of barium on LSGM electrolyte prepared by fast combustion method for solid oxide fuel cells (SOFC). MRS Adv., Early Access.
Abstract: In this work, La0.85Sr0.15-xBaxGa0.85Mg0.15O3-delta (LSBGM), with 0 <= x <= 0.075, were prepared as electrolytes for solid oxide fuel cells applications. The effect of barium and sintering temperature on the structure and electrical properties was studied. A fast combustion method was used, starting with nitrate salts and citric acid as fuel. The XRD spectra showed two main phases corresponding to LSGM orthorhombic (space group Imma) and LSGM-cubic (space group Pm-3 m). From literature, both structures are reported as high oxygen ion conductive species, but normally, they are not reported to appear together. Major secondary phases were LaSrGaO4, BaLaGaO4, and BaLaGaO7. SEM revealed a material with low porosity, indicating incomplete densification. The sample La0.85Sr0.75Ba0.075Ga0.85Mg0.15O3-delta showed a conductivity of 0.016 and 0.058 S cm(-1) at 600 degrees C and 800 degrees C, respectively. This means an improvement of 34% compared to the non-barium sample La0.85Sr0.15Ga0.85Mg0.15O3-delta at 600 degrees C. Thus, this composition could be used in SOFC.
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Sepúlveda, E., Sanhueza, F., Cobo, R., Jiménez, J., & Mangalaraja, R. V. (2024). Relationship among the powder mass, press charge, and final properties of an LSGM electrolyte for solid oxide cells. MRS Adv., Early Access.
Abstract: In this work, La0.85Sr0.15Ga0.85Mg0.15O3-delta (LSGM) was prepared as an electrolyte for solid oxide cell (SOC) applications. A fast combustion method was used, starting with nitrate salts and citric acid as fuel. Different parameters, such as mass and pressing load, in the pre-sintering step were used to obtain a highly ionic conductive material at intermediate temperatures. The aim is to find optimal processing conditions for energy savings. SEM analysis showed similar grain sizes and distributions for all samples. The XRD spectra showed two main phases corresponding to LSGM orthorhombic (space group Imma) and LSGM cubic (space group Pm-3m). LaSrGaO4 appeared in lighter samples. The EIS revealed that heavier samples present high conductivity, showing a clear relationship between conductivity, sample mass (during the pre-sintering step), and the LSGM phase amount. The effect of pressure was less evident. The highest conductivity was 0.013 and 0.063 S cm-1 at 600 and 800 degrees C, respectively.
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