Hematite (α-Fe2O3) is one of the most important, stable, non-toxic, nature-friendly and corrosion-resistant metal oxides.

Hematite crystallizes in the rhombohedral lattice system, and it has the same crystal structure as ilmenite and corundum(Al2O3). Hematite and ilmenite form a complete solid solution at temperatures above 950 °C (1,740 °F).

Fe2O3 has many other phases like beta-Fe2O3, epsilon-Fe2O3 and gamma-Fe2O3(maghemite). But alpha-Fe2O3 is the most stable of all the phases.

Structural Properties:

Crystal System: Hexagonal(trigonal)

Lattice Parameters:

a=b=5.03 Angstroms

c=13.74 Angstroms

alpha=beta=90 degrees

and gamma= 120 degrees.

I am also attaching a .cif(Crystallographic Information File) here(fe2o3 alpha hematite.zip).

You can download it and open it using softwares like Avogadro or Vesta.

These are good visualization tools to build and visualize the crystal structures.

Color:  black to steel or silver-gray, brown to reddish brown, or red.

The following are some of the pictures of the Alpha-Fe2O3 crystal:

The following is a simulated XRD(X-Ray Diffraction) Pattern for the Alpha-Fe2O3 crystal:

The following is a picture of the Density of States for alpha-Fe2O3 calculated using DFT+U(Density Functional Theory+Hubbard Parameter). The plot has been obtained from materialsproject.org.The following is a calculated electronic band structure found using DFT+U:

Band Gap: 2.1-2.3 eV (lies in the visible range)
Therefore, Alpha-Fe2O3 is an n-type semiconductor.

Magnetism:

Hematite is an antiferromagnetic material below the Morin transition at 250 kelvin (K) or -9.7 degrees Fahrenheit (°F), and a canted antiferromagnet or weakly ferromagnetic above the Morin transition and below its Néel temperature at 948 K, above which it is paramagnetic.

The magnetic structure of a-hematite was the subject of considerable discussion and debate in the 1950s because it appeared to be ferromagnetic with a Curie temperature of around 1000 K, but with an extremely tiny magnetic moment (0.002 µ_B).

Applications:

Hematite (alpha-Fe2O3) possesses extensive applications in pigments, magnetic devices and as anticorrosive agents,
catalysts, gas sensors and as photoanodes for photo-assisted electrolysis.

Iron oxide nano-particles (NPs ) are of considerable interest due to their wide range of applications in fields such as magnetic storage, medicine, chemical industries and water purification.

The magnetic nano-crystals are receiving much attention as these are now emerging in biomedical applications with new possibilities.

 

Synthesis:

Typical nano-particle synthesis methodologies involve routes including precipitation, sol-gel, hydrothermal, dry vapor deposition, surfactant mediation, microemulsion, electro-deposition and sonochemical. 3. The above mentioned synthetic methods have several advantages and disadvantages for preparing iron oxide nano particles (NPs). While these methods often furnish particles with narrow size distributions they tend to require re-optimization for each desired particle size, shape, or surface functional groups. 4. In terms of size and morphology control of the iron oxide NPs, thermal decomposition and hydrothermal synthetic route seems the optimal methods. For obtaining the water-soluble and biocompatible iron oxide NPs, co-precipitation was often employed, but this method presents low control of the particle shape, broad distributions of sizes and aggregation of particles. As a time competitive alternative, sonochemical route can also be used to synthesis iron oxide NPs with unusual magnetic properties.

References:

https://en.wikipedia.org/wiki/Hematite

https://materialsproject.org/materials/mp-24972/

https://www.researchgate.net/profile/Mamata_mohapatra/publication/49613341_Synthesis_and_applications_of_nano-structured_iron_oxideshydroxides_-_A_review/links/0c9605391c53dbb42e000000/Synthesis-and-applications-of-nano-structured-iron-oxides-hydroxides-A-review.pdf?origin=publication_detail

http://www.sciencedirect.com/science/article/pii/S0169433214019722

http://pubs.acs.org/doi/abs/10.1021/jp102243g