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TITLE: Synthesis of Lathanum Chromite-Lathanum Manganite and LSCF-Lanthanum Manganite Core-Shell Particles via Molten Salt Route

ABSTRACT: Lanthanum chromite (LaCrO3), Lanthanum manganite (LaMnO3) and 40% strontium doped lanthanum cobalt iron oxide, La0.6Sr0.4 Co0.2Fe0.8O3 (LSCF-6428) as perovskite oxides are widely used as interconnect or cathode materials in solid oxide fuel cells(SOFCs) due to their high electrical conductivity, oxygen reduction kinetics, and good chemical stability. The solid state reaction route is the most commonly used method for synthesis of these materials. However, the solid state reaction method usually involves long-time mixing and high synthesis temperature (typically, >1200°C), which makes it time-consuming and costly. Molten salt synthesis, which occurs at much lower temperatures (350°C -550°C) can offer better particle size and compositional control and reduced energy usage during materials synthesis.

In this study, LaCrO3, LaMnO3, and LSCF were synthesized in a molten salt eutectic of LiCl-KCl. A reaction temperature ranges of 370-600°C was investigated. It was found that a pure LaMnO3 perovskite phase can be formed at temperatures as low as 400°C. In addition to LaCrO3 perovskite, LaOCl was also formed besides LaCrO3 at or above 400°C. LSCF powders were successfully synthesized at 500°C. The X-ray diffraction(XRD) results show this is an attractive alternative route of synthesis to decrease the reaction temperature. Scanning Electron Microscopy (SEM) images matched with XRD patterns also show that for microstructure of LaCrO3 particles, only cubic structures were formed at low temperature (400°C and 450°C) then hexagonal structures started to appear at temperatures above 500 °C.

The molten salt synthesis method was then used to prepare core-shell structures with LaCrO3 or LSCF particles as core and LaMnO3 as shell. Core-shell structures were characterized by Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscope (STEM) and Energy Dispersive X-ray Spectroscopy(EDS). It was found that the expected core-shell structures were successfully formed with the overall cubic structures.

Therefore, the molten salt synthesis method is a feasible method to decrease the operation temperature and form the core-shell structure.

COMMITTEE: Advisor: Srikanth Gopalan (ME, MSE); Emily Ryan (ME, MSE); Michael Gevelber (ME, MSE, SE)