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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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Sepulveda, E., Mangalaraja, R. V., Udayabhaskar, R., Cobo, R., Berzal, M. E., Jimenez, J., et al. (2022). Preparation of LSGM electrolyte via fast combustion method and analysis of electrical properties for ReSOC. J. Electroceramics, 49(2), 85–93.
Abstract: In this work, we prepared La1 – xSrxGa1-yMgyO3 (LSGM) by the fast combustion method and assessed the electrical properties with respect to the composition and sintering temperature (1200, 1300, and 1400 degrees 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 degrees 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 LaSrGaO4 in a low concentration < 1.98% was observed. The scanning electron microscopy (SEM) studies on samples sintered at 1200 and 1300 degrees 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 degrees C. For comparative analysis, the conductivity (S.cm(- 1)) was measured at varying temperatures (300-800 degrees C) for the samples sintered at 1300 and 1400 degrees C. Because of the large number of insulating phases produced by the incomplete sintering process, the samples sintered at 1300 degrees C had lower conductivities. A higher conductivity of 0.125 S.cm(- 1) was observed for La0.80Sr0.20Ga0.80Mg0.20O3 (LSGM), which was obtained using the citric acid (sintered at 1400 degrees 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.
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Thandapani, P., Aepuru, R., Beron, F., Mangalaraja, R. V., Varaprasad, K., Zabotto, F. L., et al. (2023). Multiferroic Electroactive Polymer Blend/Ferrite Nanocomposite Flexible Films for Cooling Devices. ACS Appl. Polym. Mater., 5(8), 5926–5936.
Abstract: In recent days, the interest toward the development ofmulticaloricmaterials for cooling application is increasing, whereas multiferroicmaterials would be the suitable alternative to the conventional refrigerants.To explore them, the poly(methyl methacrylate)/poly(vinylidenefluoride-co-hexafluoropropylene) (PMMA/PVDF-HFP) blend and PMMA/PVDF-HFP/Zn0.5Cu0.5Fe2O4 flexible multiferroicnanocomposite films were fabricated by the solution casting method.The structural analyses prove that the strong interfacial interactionbetween the PMMA/PVDF-HFP blend and the Zn0.5Cu0.5Fe2O4 (ZCF) through hydroxyl (-OH) andcarbonyl group bonding with PVDF-HFP enhanced the thermal stabilityand suppressed the electroactive & beta; phase from 67 to 62%. Experimentalresults show that 10 wt % of superparamagnetic ZCF nanoparticles witha particle size of 6.8 nm induced both the magnetocaloric and magnetoelectriceffects in a nonmagnetic PMMA/PVDF-HFP ferroelectric matrix at roomtemperature. A set of isothermal magnetization curves were recordedin the magnetic field strength of 0-40 kOe and a temperaturerange of 2-400 K. The maximum magnetic entropy changes (& UDelta;S (M)) of -0.69 J & BULL;kg(-1) K-1 of ZCF nanoparticles and -0.094 J & BULL;kg(-1) K-1 of PMMA/PVDF-HFP/ZCF nanocompositesshowed an interesting table-like flat variation in the temperaturerange of 100-400 K as a function of the magnetic field. Thesamples display a large temperature span with a relative cooling power of 293 and 40 J & BULL;kg(-1) for ZCF and PMMA/PVDF-HFP/ZCF,respectively. The magnetoelectric effect of the PMMA/PVDF-HFP/ZCFcomposite was proved, but it generated only 1.42 mV/m & BULL;Oe in theapplied field of 5 kOe. Hence, the entropy change of the present nanocompositewas only due to the magnetocaloric effect, where the magnetoelectriccross-coupling coefficient was negligible. The multicaloric effectcould be established if the nanocomposite showed a larger magnetoelectriccross-coupling in addition to the magnetocaloric effect. This approachprovides the research findings in functional multiferroic polymernanocomposites for miniaturized cooling devices.
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