Off-stoichiometry mechanism of the isotope effect in manganites - art. no.144409

A theory of the O-16 --> O-18 isotope effect in the manganites is developed . It is based on the facts that an excess in the oxygen content is a thermo dynamic necessity, and that it is isotope-dependent. As the excess oxygen a cts as an acceptor, the charge-carrier density is isotope-dependent. On the other hand, the excess oxygen creates an internal pressure in the crystal which is also isotope-dependent. Using a realistic model for the manganites and accounting for the phonon contribution, one obtains excellent agreemen t with experiment and predicts the inversion of the isotope effect at eleva ted temperatures. The former fact makes it possible to discard the assumpti on that the electron-phonon coupling in the manganites is anomalously stron g.