A possible re-entrant phase transition at the (001) surface in L1(2) structure

The relative stability of the different terminations of the (001) surface o f A(3)B compounds with the L1(2) structure is investigated as a function of both the temperature and the relevant energetic parameters. This is perfor med using the Ising model and a mean-field approximation. For a strong tend ency to A surface segregation, the termination of the A(3)B compound is an almost pure A surface plane in the whole range of temperatures correspondin g to the bulk ordered state. Conversely, for a large tendency to B segregat ion, the stability of the mixed AB termination is predicted. However, betwe en these two domains, a complex behavior is predicted. One or even two tran sitions, leading to a re-entrant behavior, can occur as a function of the t emperature between the pure A and the mixed AB termination, all these trans itions being located in the bulk ordered state. It is suggested that Ir3V i s a good candidate to exhibit such a rather surprising behavior. We also in vestigate the influence of some deviation with respect to the stoichiometry . A transition from the mixed AB to the pure A termination is predicted whe n the bulk concentration in A element increases. (C) 2000 Elsevier Science B.V. All rights reserved.