Abstract
Substantial effort has been devoted to fabricating nanocrystalline lanthanum ferrite (LaFeO3), and calcination is the crucial process of crystallization in both high-temperature strategies and wet chemical methods. Lowering the calcination temperature gives the ability to resist the growth and agglomeration of nanoparticles, therefore contributing to preserve their unique nanostructures and properties. In this work, we prepared crystalline LaFeO3 nanoparticles with a calcination process at 500 °C, lower than the calcination temperature required in most wet chemistry methods. Correspondingly, the experimental conditions, including stoichiometric ratios, pH values, precipitants, complexant regent, and the calcination temperatures, were investigated. We found that the crystalline LaFeO3 was formed with crystalline NaFeO2 after calcination at 500 °C. Furthermore, the structure of FeO6 octahedra that formed in coprecipitation was associated with the process of crystallization, which was predominantly determined by calcination temperature. Moreover, an illusion of pure-phase LaFeO3 was observed when investigated by X-ray diffraction spectroscopy, which involves amorphous sodium ferrite or potassium ferrite, respectively. These findings can help prepare nanostructured perovskite oxides at low calcination temperatures.
Highlights
IntroductionA large number of synthetic methods to fabricate LFO-based perovskite oxides have been developed, including high-temperature strategies
We investigated the effects of stoichiometric ratio, pH value, precipitants, complexant regent, and calcination temperature
Through investigating the experimental conditions, including stoichiometric ratio, pH value, precipitants, complexant regents, and the calcination temperature, we concluded the following: (1) crystalline LaFeO3 nanoparticles could be formed after calcination at 500 ◦ C when the stoichiometric ratio La/Fe was higher than 3:7, coupling with the formation of crystalline NaFeO2 ; (2) coprecipitation at a high pH value was conducive to the crystallization of LaFeO3 at low calcination temperatures; (3) crystalline LaFeO3 nanoparticles could be formed after calcination at 500 ◦ C when using either NaOH or KOH
Summary
A large number of synthetic methods to fabricate LFO-based perovskite oxides have been developed, including high-temperature strategies Molten salt synthesis [3,4,5]) and wet chemical methods such as electrochemical deposition [6,7], electrospinning [8], microwave plasma [9], sol–gel [10,11,12,13,14,15,16], combustion [17], hydrothermal [18,19,20], and precipitation [21,22]. High-temperature strategies have been widely utilized for the fabrication of bulk LFO-based oxides that often require a calcination process at high temperatures (above 800 ◦ C). Wet chemical methods are extensively utilized to fabricate LFO-based perovskite nanostructures that usually involve a sol–gel or coprecipitation process for precursor preparation and a calcination process for crystallization
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