LaFeO3-based nanopowders prepared by a soft–hard templating approach: the effect of silica texture†
A combined soft–hard templating (SHT) approach was used to prepare LaFeO3-based perovskite nanopowders with high surface area and porosity. In the SHT approach, a self-sustained combustion process between a soft fuel (citric acid) and an oxidant (metal nitrates) occurs in the presence of a silica hard template (amorphous, HMS or SBA-15 silica). The as-burned powders were then calcined, processed by basic etching and carefully characterized by X-ray diffraction combined with Rietveld refinement, small angle X-ray scattering, neutron activation analysis, N2-adsorption, X-ray photoelectron spectroscopy and transmission electron microscopy. It was observed that structural, microstructural and textural properties of the obtained nanopowders strongly depend on the hard template used and an excellent correlation was found between the samples' specific surface area and cumulative pore volume of the original hard template. The use of several complementary characterization techniques revealed the composite nature of the prepared materials, evidencing the presence of amorphous La and Fe silicates in all the LaFeO3 nanopowders. Furthermore, it was demonstrated that these silicates have an important function in the transmission of the microstructural-morphological-textural features from the template to the final powder.