Wastite (Fq_xO) ß A Review of Its Defect Structure and Physical Properties

Wiistite, a complex nonstoichiometric oxide of iron, exhibits varied structural forms and physical properties depending on its defect structure and degree of non-stoichiometry. This review examines the intricacies of wiistite's defect structure, highlighting the significance of octahedral versus tetrahedral cation distribution and the implications of exsolution. The study reveals that while wiistite is compositionally between pure FeO and magnetite, it does not form a solid solution and is characterized by unique physical traits such as cation diffusion, electrical conductivity, and magnetism, all influenced by defect types and clustering. The exploration of simple relationships between stoichiometry, molar volume, and bulk modulus demonstrates that predictive models are insufficient for the complexities involved. To fully understand wiistite's physical properties, this review stresses the necessity of comprehensive experimental investigations that encompass synthesis conditions and structural assessments pre- and post-experimentation. Such insights are crucial for advancing knowledge in geophysics and materials science, particularly regarding the behavior of nonstoichiometric minerals.