Sol–Gel Synthesis and Micro-Raman Characterization of ε-Fe₂O₃ Micro- and Nanoparticles

Abstract

In this work, we present a sol–gel synthesis of ε-Fe2O3 nano and microparticles stabilized in silica thin films. Thanks to the relatively high size of the synthesized particles, we have been able to discriminate the Raman signal of the ε- and α-Fe2O3 phases, thus presenting the first Confocal Raman Microscopy study of isolated ε-Fe2O3 particles. The vibrational modes of each phase are identified at room temperature. The phase transition from ε- to α-Fe2O3 and the morphological modifications are analyzed as a function of the in situ output laser power. A complete study of the Raman spectra for ε-Fe2O3 particles has been performed for a wide range of temperatures (80–570 K). The phonon frequencies and line widths show a behavior in which the contributions from lattice thermal expansion and anharmonic interactions have to be considered. We have also identified a two-magnon mode in the ε-Fe2O3 phase. Its intensity increases close to the Néel transition (TN) and persists well above it. This observation could be one of the few experimental examples of a paramagnon, i.e., a magnetic excitation in a paramagnetic state.

The morphology and structure of crystals in Qing Dynasty purple‐gold glaze excavated from the Forbidden City

“…In addition to the dendritic-shaped crystals with sizes on the orders of tens of micrometers, a large number of leafshaped e-Fe 2 O 3 particles with lengths of 1-3 lm, widths of less than 1 lm, and thicknesses of approximately 150 nm are found in the glaze surface to a depth of tens of micrometers. Based on previous studies, e-Fe 2 O 3 crystals show a dark brown color, 12,22 which is basically similar to the color of purple-gold glaze. This finding demonstrates that e-Fe 2 O 3 crystals play a key role in the optical properties and are directly related to the reddish-brown color of such types of glaze.…”

“…In modern material studies, ε‐Fe 2 O 3 is a rare and metastable polymorph that is difficult to synthesize up to micrometers with a high purity and high yield because of its low surface energy . Thus far, the ε‐Fe 2 O 3 phase can be synthesized only as nanoscale objects, such as nanoparticles, nanowires, thin films and nanospheres, using the γ‐Fe 2 O 3 → ε‐Fe 2 O 3 → α‐Fe 2 O 3 phase transformation pathway. Although ancient ceramics kiln artists did not understand the underlying mechanisms and processes that occur during the firing of the purple‐gold glaze, these individuals could be expected to control the various factors, such as the right composition, firing temperature and atmosphere, and cooling rate, of the kiln depending on their experience for a particular effect to obtain the desired ε‐Fe 2 O 3 crystals.…”

“…In modern material studies, e-Fe 2 O 3 is a rare and metastable polymorph that is difficult to synthesize up to micrometers with a high purity and high yield because of its low surface energy. 8,10 Thus far, the e-Fe 2 O 3 phase can be synthesized only as nanoscale objects, such as nanoparticles, 8,12,13,[21][22][23][24][25][26][27][28] nanowires, 29,30 thin films 14 ceramics kiln artists did not understand the underlying mechanisms and processes that occur during the firing of the purple-gold glaze, these individuals could be expected to control the various factors, such as the right composition, firing temperature and atmosphere, and cooling rate, of the kiln depending on their experience for a particular effect to obtain the desired e-Fe 2 O 3 crystals. In view of the strong relationship between the purple-gold glaze color and the e-Fe 2 O 3 phase crystals, the underlying manufacturing technology of purple-gold glaze porcelain could provide useful information for improving the synthesis method to obtain e-Fe 2 O 3 crystals with large sizes and high yields.…”

Crystal Structure and Magnetic Properties of ϵ‐RuxFe2‐xO3 Nanosize Hard Ferrite

“…[21] Additionally, e-Fe 2 O 3 shows various functionalities such as high-frequency millimeter wave absorption, optical transparency,n onlinear magneto-optice ffect, ferroelectricity,a nd catalytic properties. [21][22][23][24][25][26][27] Severals ynthetic methods have been developed using wet and dry processes. [2-7, 21, 28-31] Metal substitution on magnetic materials is effective to control the magnetic properties.…”

Room-Temperature Magnetic Order in Air-Stable Ultrathin Iron Oxide

“…To date, -Fe2O3 has been prepared as nanoparticles with sol-gel methods 19,20 , thermal annealing 21 and as thin films with pulsed laser deposition 22 , electrodeposition 23 , and atomic layer deposition (ALD) 24 . While these important advances have enabled research into the properties of -Fe2O3, the morphology of the materials produced in these ways prevents potential incorporation into 2D spintronic devices.…”