Abstract. The process of spontaneous thermal dissociation of the semiconducting nonstoichiometric compounds Cu2~X (X=S, Se) in vacuum has been investigated. Thermogravimetric, X-ray and electrochemical techniques reveal that the dissociation rates sharply decrease at 5 < 8~r (8~r.=f(T)) and the chalcogen fluxes from the compounds into the vacuum become immeasurably small. The results of the experiments are discussed in terms of the formation of a phasc at the surface with properties of a compound of constant composition. Possible reasons are the excess surface energy together with the high mobility of copper ions which results probably in the reconstruction of the subsurface layers.

Abstract.We have investigated the dissociation rates of nonstoichiometric semiconductors Ag2+_sX (X = S, Se) to the vacuum by means of solid-state electrochemical technique. The values of chalcogen fluxes from the sample's surface were measured versus compound's composition and temperature. There has been obtained experimental evidence of the surface reconstruction of silver chalcogenides when the exact phase composition 8~r.(T) is reached. This critical value 5or. correlates with the order-disorder transition in the silver sublattice for the Ag2• interface.