1 3
Topics in Current Chemistry (2020) 378:6
empty space left around the A cation (Fig. 3). In this structure, the Fe cations occupy
octahedral sites and are sixfold coordinated to oxygen anions, while the larger M
cation is 12-fold coordinated to anions [9]. While the ideal perovskite-type structure
displays a cubic symmetry with a unit cell composed of four formula units in which
the atoms are touching one another, the deviation from the ideal perovskite structure
to give pseudo-cubic—mainly orthorhombic—symmetry has been rationalized by
Goodenough [10]. He introduced a tolerance factor t applicable at room temperature
to the empirical ionic radii and materializing the stability and the distortion of the
crystal structure within the following range:
For instance, lanthanum orthoferrite LaFeO 3 shows a high Goldschmidt tolerance
factor of 0.954, indicating that the distorted structure maintains a high level of symmetry, while the yttrium orthoferrite YFeO 3 structure displays a far lower symmetry
with a lower tolerance factor of 0.855 [11].
1.2 Preparation Methods
Progress in the synthesis of orthoferrites and spinel ferrites has been driven in the
last decades by the technological interest aroused by the ferrite materials in various
interdisciplinary application fields and by that derived from their tunable magnetic
properties. Whether they are categorized as bottom-up or top-down approaches, or
as chemical or physical methods, a large variety of preparation methods have been
investigated for synthesizing ferrite nanoparticles. Among them, co-precipitation,
sol–gel methods, thermal methods and solid-state reactions remain the most popular strategies implemented for elaborating catalysts for heterogeneous photo-Fenton
or photocatalysis, whereas a large (non-exhaustive) panel of methods such as sonochemical, microemulsion, reverse micelle, electrospinning, polyol, electrochemical,
0.75 < t =
(r A + r O )
√
2(r B + r O )
< 1.
Fig. 3 Crystallographic structure of MFeO 3 orthoferrites with
distorted perovskite structure
(orthorhombic crystal symmetry). Adapted and reproduced
with permission from Ref. [12].
Copyright AIP Publishing
111
Reprinted from the journal
Topics in Current Chemistry (2020) 378:6
empty space left around the A cation (Fig. 3). In this structure, the Fe cations occupy
octahedral sites and are sixfold coordinated to oxygen anions, while the larger M
cation is 12-fold coordinated to anions [9]. While the ideal perovskite-type structure
displays a cubic symmetry with a unit cell composed of four formula units in which
the atoms are touching one another, the deviation from the ideal perovskite structure
to give pseudo-cubic—mainly orthorhombic—symmetry has been rationalized by
Goodenough [10]. He introduced a tolerance factor t applicable at room temperature
to the empirical ionic radii and materializing the stability and the distortion of the
crystal structure within the following range:
For instance, lanthanum orthoferrite LaFeO 3 shows a high Goldschmidt tolerance
factor of 0.954, indicating that the distorted structure maintains a high level of symmetry, while the yttrium orthoferrite YFeO 3 structure displays a far lower symmetry
with a lower tolerance factor of 0.855 [11].
1.2 Preparation Methods
Progress in the synthesis of orthoferrites and spinel ferrites has been driven in the
last decades by the technological interest aroused by the ferrite materials in various
interdisciplinary application fields and by that derived from their tunable magnetic
properties. Whether they are categorized as bottom-up or top-down approaches, or
as chemical or physical methods, a large variety of preparation methods have been
investigated for synthesizing ferrite nanoparticles. Among them, co-precipitation,
sol–gel methods, thermal methods and solid-state reactions remain the most popular strategies implemented for elaborating catalysts for heterogeneous photo-Fenton
or photocatalysis, whereas a large (non-exhaustive) panel of methods such as sonochemical, microemulsion, reverse micelle, electrospinning, polyol, electrochemical,
0.75 < t =
(r A + r O )
√
2(r B + r O )
< 1.
Fig. 3 Crystallographic structure of MFeO 3 orthoferrites with
distorted perovskite structure
(orthorhombic crystal symmetry). Adapted and reproduced
with permission from Ref. [12].
Copyright AIP Publishing
111
Reprinted from the journal