Abstract
The purpose of a reactive atmosphere process (RAP) is to remove impurities, especially, polyatomic anion impurities, the most difficult of which is OH -. The latter, a pseudo-halide, is shown to be close in property to the fluoride. The two are far removed in reactivity and stability from the other halides. Thermodynamic arguments are presented to demonstrate that the practice of using the respective hydrogen halide gas as the sole RAP agent does not meet the defined objective of RAP. The criterion for the use of halogen as the RAP agent to clean up OH - impurity from metal oxides is given. The unusually large activity coefficient of OH - which influences melting behavior and solid-solid transitions is also shown to exert a limiting role on the purity of vapor-transported films. The unusually low electron affinity of OH - is made the basis of a model for color-center formation.
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