Molten salts activated by high-energy milling: A useful, low-temperature route for the synthesis of multiferroic compounds

There are only a few multiferroic compounds, among which BiFeO3 is the most important. Research the synthesis of bismuth ferrite, with novel and improved magnetic and electrical properties, has been mainly based on the use of hydrothermal or sol gel methods. However, these methods require either rather extreme conditions or several steps for synthesis. We demonstrate that the use of molten salts, activated by high energy milling, results in pure nanometric BiFeO3, LaFeO3 and intermediate phases in the Bi1−xLaxFeO3 system. The chemical reagents used are Bi(NO3)3⋅5H2O, La(NO3)3⋅6H2O, Fe(NO3)3⋅9H2O and NaOH. A brief milling process of the reagents creates an amorphous precursor and crystalline NaNO3. The thermal treatment of the precursors, at 500 °C for two hours, produces a crystalline mixture of Bi1−xLaxFeO3 and NaNO3. Simple washing eliminates the NaNO3. The characterization of intermediates and final products, through thermal analysis, X-ray diffraction and scanning electronic microscopy, allows the inference of possible mechanism. In addition, vibrating sample magnetometry (VSM) and ferroelectric tests show the typical magnetic and electric polarization loops characteristic of these materials even when formed at the nano-scale.