Epästoikiometrioita

Epästoikiometrioita refers to deviations from the ideal stoichiometric composition in chemical compounds. In a perfectly stoichiometric compound, the ratio of atoms of each element is exactly as represented by its chemical formula. However, in many solid-state materials, particularly non-metal deficient compounds and metal oxides, vacancies or excess atoms can lead to a non-integer ratio of elements, hence the term non-stoichiometry.

These deviations arise due to defects in the crystal lattice, such as Schottky defects (pairs of vacancies) or Frenkel defects (an atom displaced from its lattice site into an interstitial position). For instance, in some metal oxides, oxygen can be missing, leading to a metal-to-oxygen ratio that is less than ideal. Conversely, excess metal atoms or interstitial anions can also cause non-stoichiometry.

Non-stoichiometry significantly influences the physical and chemical properties of materials. These include electrical conductivity, optical properties, catalytic activity, and mechanical strength. For example, the non-stoichiometry in iron oxides affects their magnetic properties and color. Understanding and controlling non-stoichiometry is crucial in the development and application of many advanced materials, including semiconductors, ceramics, and catalysts. The presence of these defects allows for tuning material properties for specific technological applications.