Novel inorganic materials generated by aliovalent anion substitution

Substitution of cations, as well as anions, in inorganic materials to change the structure and properties is generally carried out with ions of the same valency (e.g., S2− for O2− or Se2− for S2−). Such substitution does not give rise to marked changes in the properties. However, substitution with isoelectronic aliovalent anions (e.g., N3− for O2−) brings about a significant change in the electronic structure and properties, but this is associated with the creation of anion vacancies. It is, therefore, found fruitful to substitute two aliovalent anions (e.g., N3− and F− for O2−) to change the electronic structure and properties and also to avoid the anion vacancies. In this article, we discuss the effect of partial aliovalent anion substitution in metal oxides and metal sulfides. More importantly, we discuss the synthesis of materials where the oxide ion is fully substituted by the nitride (N3−) and fluoride (F−) ions as in the Zn2NF and TiNF. We also discuss the substitution of sulfide ion (S2−) by isoelectronic phosphide (P3−) and chloride (Cl−) ions. Results of recent studies on the synthesis and properties of cadmium phosphohalides of various compositions are discussed.