Nichtstöchiometrische

Nichtstöchiometrische compounds are chemical compounds that do not have simple integer ratios of their constituent elements. This deviation from the ideal stoichiometric ratio is often due to the presence of crystal defects, such as vacancies or interstitial atoms, within the solid-state structure. These defects can alter the electronic and chemical properties of the material, making non-stoichiometric compounds interesting for various applications.

One common type of non-stoichiometry arises from missing atoms in the crystal lattice, known as vacancies. For example, in some metal oxides, oxygen atoms can be absent, leading to a deficiency of oxygen relative to the ideal formula. Conversely, interstitial atoms, where atoms occupy positions not normally part of the crystal lattice, can also cause non-stoichiometry. Another mechanism is the substitution of one element for another within the lattice, which can lead to a departure from the expected elemental ratio if the substituting element is present in a different proportion.

Non-stoichiometric compounds are prevalent in many areas of chemistry and materials science. They are particularly important in the study of solid-state chemistry, where their properties are closely linked to the nature and concentration of their defects. Examples include wustite (iron(II) oxide), which can have a range of compositions between FeO and Fe$_{0.95}$O, and various transition metal oxides and sulfides. The precise composition of a non-stoichiometric compound is often denoted by a variable subscript, indicating the departure from the ideal ratio. Understanding and controlling non-stoichiometry is crucial for tuning the performance of materials in applications such as catalysis, electronics, and solid-state electrolytes.