1.6 Determining the chemical formula of nonstoichiometric iron

Chemical formula determination

Magnetite (Fe ₃ O ₄ ) nanoparticles (n-Mag) are nanometer sized, superparamagnetic, have high saturation magnetization, high magnetic susceptibility, and low toxicity. These properties could be utilized for many possible applications; hence, n-Mag has attracted much attention in the scientific community. Some of the potential applications include drug delivery, hyperthermia agents, MRI contrast agents, cell labeling, and cell separation to name a few.

The crystal structure of n-Mag is cubic inverse spinel with Fe ³⁺ cations occupying the interstitial tetrahedral sites(A) and Fe ³⁺ along with Fe ²⁺ occupying the interstitial octahedral sites(B) of an FCC latticed of O ^2- . Including the site occupation and charge of Fe, the n-Mag chemical formula can be written (Fe ³⁺ ) _A (Fe ²⁺ Fe ³⁺ ) _B O ₄ . Non-stoichiometric iron oxide results from B-site vacancies in the crystal structure. To maintain balanced charge and take into account the degree of B-site vacancies the iron oxide formula is written (Fe ³⁺ ) _A (Fe _(1-3x) ²⁺ Fe _(1+2X) ³⁺ Ø _x ) _B O ₄ where Ø represents B-site vacancy. The extent of B-site vacancy has a significant effect on the magnetic properties of iron oxide and in the synthesis of n-Mag stoichiometric iron oxide is not guaranteed; therefore, B-site vacancy warrants attention in iron oxide characterization, and can be addressed using Mossbauer spectroscopy.