Structure evolution of nanoparticulate Fe₂O₃

Abstract

The atomic structure and properties of nanoparticulate Fe2O3 are characterized starting from its smallest Fe2O3 building unit through (Fe2O3)n clusters to nanometer-sized Fe2O3 particles. This is achieved by combining global structure optimizations at the density functional theory level, molecular dynamics simulations by employing tailored, ab initio parameterized interatomic potential functions and experiments. With the exception of nearly tetrahedral, adamantane-like (Fe2O3)2 small (Fe2O3)n clusters assume compact, virtually amorphous structures with little or no symmetry. For n = 2-5 (Fe2O3)n clusters consist mainly of two- and three-membered Fe-O rings. Starting from n = 5 they increasingly assume tetrahedral shape with the adamantane-like (Fe2O3)2 unit as the main building block. However, the small energy differences between different isomers of the same cluster-size make precise structural assignment for larger (Fe2O3)n clusters difficult. The tetrahedral morphology persists for Fe2O3 nanoparticles with up to 3 nm in diameter. Simulated crystallization of larger nanoparticles with diameters of about 5 nm demonstrates pronounced melting point depression and leads to formation of ε-Fe2O3 single crystals with hexagonal morphology. This finding is in excellent agreement with the results obtained for Fe2O3 nanopowders generated by laser vaporization and provides the first direct indication that ε-Fe2O3 may be thermodynamically the most stable phase in this size regime.

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

“…Recently, e-iron oxide (e-Fe 2 O 3 )has drawn attention because it exhibits ah uge coercive field (H c ). [2][3][4][5][6][7] e-Fe 2 O 3 is ap olymorph of ferric oxide Fe 2 O 3 (a-phase, [8][9][10] b-phase, [11,12] g-phase, [13,14] e-phase, [2][3][4][5][6][7][15][16][17][18][19] and z-phase). [20] Due to its strong magnetic anisotropy, e-Fe 2 O 3 exhibits ferromagnetic ordering even in the single nanometer size (superparamagnetic limit = 7.5 nm), which is the smallest value among ferrites.…”

Geometric, electronic, and magnetic structure ofFexOy+clusters

“…4,6,9,10,[13][14][15][16][17][20][21][22][23][24]26 The number of works in which Fe m O n clusters were studied with methods beyond DFT is very limited and restricted to very small cluster sizes. For FeO + its reactivity towards H 2 was studied on a wave-function-based CASPT2D level.…”

Increased UV absorption properties of natural hydroxyapatite‐based sunscreen through laser ablation modification in liquid

“…Fe, on the other hand, could react to form α‐Fe 2 O 3 . As both HAp and α‐Fe 2 O 3 have quite high melting points (>1400°C), their evaporation is less likely to take place.…”