FeO1x

FeO1-x is a non-stoichiometric iron oxide, meaning its chemical formula does not represent a fixed ratio of iron to oxygen. The 'x' indicates a variable deficiency of oxygen atoms in the crystal lattice compared to the ideal FeO (wüstite) structure. This deficiency is typically small, with 'x' usually ranging from 0.05 to 0.15. The precise value of 'x' is influenced by factors such as temperature and oxygen partial pressure during its formation.

FeO1-x crystallizes in the rock-salt structure, similar to pure FeO. However, the oxygen vacancies create defects within this structure, which significantly impact its properties. These defects can influence electrical conductivity, magnetic behavior, and reactivity. For instance, the presence of these vacancies can lead to a p-type semiconductor behavior.

Wüstite, the end member of this non-stoichiometric series, is the only stable iron oxide between approximately 575 °C and 1550 °C under standard atmospheric pressure. Below this temperature range, it disproportionates into a mixture of Fe3O4 (magnetite) and Fe. The non-stoichiometric nature of FeO1-x is a key characteristic studied in materials science and solid-state chemistry due to its relevance in areas like catalysis, battery materials, and high-temperature oxidation processes of iron and steel.