Abstract
Abstract Small changes of the stoichiometric ratio can significantly influence the physical properties of compounds. This is well known for the electrical properties, but lately examples where the magnetic properties are influenced have been discovered, such as FeCr 2 S 4 and Fe 3 O 4 . Non-stoichiometry is similar to chemical impurity but differences exist: direct detection is not possible; on the onther hand, control of stoichiometry is somewhat more direct than control of chemical impurity. In this talk we shall concentrate on oxides; we shall define stoichiometry and establish the connection with atomic defects in the material. The stoichiometric ratio is established by equilibration with the atmosphere, but depends at room temperature usually on the history of the sample. The stoichiometric ratio is easiest to measure at high temperature while equilibration is reasonably fast, and we shall review some of the applicable methods; conductivity, weighing titration of oxygen and others.
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