Effect of salt type on the particle size of LaMn_1-xFe_xO₃ (0.1≤x≤0.5) synthesized in molten chlorides

LaMn_1-xFe_xO₃ perovskites were successfully synthesized via molten salt synthesis in NaCl-KCl and LiCl-KCl, for the first time. The effect of salt type on the size of the obtained perovskite particles was investigated using two procedures. The first, corresponding to the common “mixing” synthesis procedure, included heating the La-, Mn- and Fe-nitrates and chlorides mixture above the melting point of the chloride mixture. While the synthesis temperature (600–850 °C) and perovskite composition (0.1 ≤ x ≤ 0.5) had no significant effect on the LaMn_1-xFe_xO₃ particle size, the effect of molten salt type was dramatic. The average size of LaMn_1-xFe_xO₃ particles synthesized in LiCl-KCl was 0.7–0.8 μm, while more than twice smaller particles were obtained in NaCl-KCl. Since different salts have both different melting points as well as different chemical and physical properties, it is impossible to distinguish between the individual contributions of these characteristics to the observed size difference. In order to address this problem, a second “feeding” procedure was employed, which skips the melting event by feeding the metal nitrates into already molten salt. Particles obtained using “feeding” procedure in LiCl-KCl (∼0.5 μm) were still larger than those obtained in NaCl-KCl (∼0.3 μm). The remnant effect, attributed solely to the salt properties, is explained by the nucleation and crystal growth model, with respect to higher perovskite solubility in LiCl-KCl. The suggested “feeding” procedure renders the separate analysis of synthesis conditions (e.g. the sole effect of salt type) for the first time, and can assist in the unraveling of molten salt synthesis mechanistic aspects.