Abstract
For many years it has been widely believed that structural vacancies exist in NiAl, CoGa, NiGa, and other CsCl-type intermetallic compounds. In formulating a theory of vacancy formation in ordered nonstoichiometric bcc alloys, we have found that such structural vacancies may not necessarily exist. It is shown that in CoGa, structural vacancies are indeed extremely unlikely and that purely thermal vacancies can account satisfactorily for the observed composition dependences of vacancy concentration.