A THEORY OF OXIDE-COATED CATHODE

A new model is presented in order to explain a variety of previous observations on the oxide-coated thermionic cathode, as well as the behaviour of a number of other oxide layer structures. It is supposed that, during the activation process, conducting filaments of molecular dimensions are developed through the oxide coating, and that these are directly responsible for the electrical conductivity of the oxide and its high thermionic emission efficiency. A possible structure is suggested for such conducting filaments, consisting of a chain of metal atoms separated by oxygen vacancies, probably clustered along grain boundaries in the oxide. Earlier theories of oxide-coated cathode behaviour are summarized and their relation to the new theory is discussed. © 1969.