Solution combustion synthesis of iron-deficient Sc2-xFexO3 (x = 0.17-0.47) nanocrystals with bixbyite structure: The effect of spatial constraints

Abstract

In this paper, nanopowders based on iron-deficient Sc2-xFexO3 (x = 0.17–0.47) nanocrystals with bixbyite structure and crystallite size of 3.7–38.9 nm were successfully synthesized via solution combustion. Variable glycine-to-nitrate (G/N) ratio was the main controlling factor. A wide range of experimental and computational methods were used to analyze the impact of spatial constraints on the resulting solid-state products. It was found that solution combustion mode greatly influenced on the temperature and gaseous products in the reaction zone. Volume (G/N = 0.4–0.8, Tmax = 1179–1511 °C), self-propagating (G/N = 1.0–1.4, Tmax = 614–957 °C) or smoldering (G/N = 0.2, Tmax = 443 °C) combustion modes were acquired during the synthesis depending on G/N ratio. It was shown that the formation of impurity phases of am-Fe2O3 (Tmax < 850 °C), c-Fe3O4 (900 °C < Tmax < 1500 °C) or c-FeO (Tmax > 1500 °C) was possible, depending on the combustion temperature. Besides, the combustion mode affected the porous and surfacial structure of resulting mesoporous nanopowders – specific surface area and total pore volume varied in ranges of 1.7–82.8 m2/g and 0.0088–0.1538 cm3/g, consequently. Chemical composition and unit cell parameters of Sc2-xFexO3 showed the positive deviation from Vegard's law. The average sizes of the interpore thickness (h) depending on G/N ratio were found from values of specific surface area and pycnometric density of nanopowders, which made it possible to establish the presence of spatial constraints for the crystals' growth of Sc2-xFexO3 at h values below 10 nm. Analysis of aspect (h/D) ratio allowed to determine synthetic parameters which led to mono- or polycrystalline structure of interpore space in resulting Sc2-xFexO3-based nanopowders. The results and patterns established in this paper allowed to synthesize a new type of foam-like functional materials based on rare-earth ferrites.