Theoretical model for oxygen vacancy dependence of T/sub c/ in the YBa2Cu3O/sub x/ system (6 ≤ x ≤ 8)

With a view to understanding the relationship between oxygen content, oxygen vacancy ordering, and T/sub c/ in the YBa2Cu3O/sub x/ system, the electronic structure of these materials has been calculated for x = 6, 7, and 8 using the first-principles pseudofunction method. Employing a simple interpolation scheme, the electronic density of states has been estimated at the Fermi level, N(E/sub F/), for materials containing varying numbers of oxygen vacancies and varying degrees of oxygen vacancy disorder. Adopting a simplified BCS model according to which T/sub c/ depends only on N(E/sub F/), it is shown that T/sub c/ increases monotonically as the oxygen content, x, increases from 6 to 8. Moreover, for a fixed x, the more highly ordered the oxygen vacancies, the higher is T/sub c/. In this paper the essential features of their theoretical model are summarized and used to interpret recent experimental results reported at this conference by Batlogg