ABSTRACT
Single-phase La0.8Sr0.2MnO3 (LSM) has been synthesized using a volatilized molten salt synthesis (vMSS) method for the first time with a LiCl-KCl eutectic with diameters of up to 300 nm, with the majority ranging from 50 to 100 nm. While deleterious to LSM formation when the MSS takes place in the liquid phase, a LiCl-KCl eutectic successfully facilitates LSM formation when volatilized. Specifically, KCl evaporates more readily than LiCl and promotes the formation of LSM via the vapor phase. As time progresses, LiCl volatilization increases and contributes negatively to Sr stoichiometry in the perovskite phase in accordance with Lux-Flood chemistry and to product phase purity. The vMSS is therefore a way to obviate the more immediate restrictions of Lux-Flood chemistry in the liquid phase. These results demonstrate the surprising versatility and flexibility of the MSS method to synthesize numerous potential energy-relevant materials with greater ease than previously thought.
ABSTRACT
In this work, we investigate the synthesis of (La0.8Sr0.2)MnO3 (LSM) in various molten salts to gain insight on the influence of molten salt ions for synthesizing materials critical for energy applications. LSM nanoparticles with a size range of â¼10-200 nm and with target stoichiometries were formed from oxide precursors via feeding into KNO3. Furthermore, feeding precursors into the melt compared to mixing and heating from room temperature results in complete formation of LSM that was otherwise unattainable using conventional molten salt synthesis methods. In LiCl-KCl eutectic, the high Lux acidity of Li+ and Cl- establishes a thermodynamic barrier that impedes Sr from reacting with other precursors in solution and increases Sr stability in the melt compared to the perovskite phase. As a result, LSM will not form in a LiCl-KCl eutectic under ambient conditions. Thus, this study further explicates the molten salt synthesis for perovskites and can serve as a guide for future syntheses.
ABSTRACT
Strontium-doped lanthanum cobalt ferrite (LSCF) is a widely used cathode material due to its high electronic and ionic conductivity, and reasonable oxygen surface exchange coefficient. However, LSCF can have long-term stability issues such as surface segregation of Sr during solid oxide fuel cell (SOFC) operation, which can adversely affect the electrochemical performance. Thus, understanding the nature of the Sr surface segregation phenomenon and how it is affected by the composition of LSCF and strain are critical. In this research, heteroepitaxial thin films of La1-x SrxCo0.2Fe0.8O3-δ with varying Sr content (x = 0.4, 0.3, 0.2) were deposited by pulsed laser deposition (PLD) on single-crystal NdGaO3, SrTiO3, and GdScO3 substrates, leading to different levels of strain in the films. The extent of Sr segregation at the film surface was quantified using synchrotron-based total-reflection X-ray fluorescence (TXRF) and atomic force microscopy (AFM). The electronic structure of the Sr-rich phases formed on the surface was investigated by hard X-ray photoelectron spectroscopy (HAXPES). The extent of Sr segregation was found to be a function of the Sr content in bulk. Lowering the Sr content from 40% to 30% reduced the surface segregation, but further lowering the Sr content to 20% increased the segregation. The strain of LSCF thin films on various substrates was measured using high-resolution X-ray diffraction (HRXRD), and the Sr surface segregation was found to be reduced with compressive strain and enhanced with tensile strain present within the thin films. A model was developed correlating the Sr surface segregation with Sr content and strain effects to explain the experimental results.
