Isotope-induced ferroelectricity

Although it is well known that for hydrogen-bonded ferro- and antiferroelec tric systems the replacement of hydrogen by deuterium induces a large isoto pe effect on the ferroelectric transition temperature T-c, similar findings have not been reported for perovskite type ferroelectrics until recently w hen it has been shown experimentally that the incipient quantum paraelectri c SrTiO3 can be driven to a ferroelectric state by replacing O-16 by its is otope O-18 [Phys. Rev. Lett. 28, 3540 (1999)]. The experimental data have b een analyzed within an anharmonic electron-phonon interaction model and con sistent quantitative agreement with the corresponding experiment is achieve d. In addition, it is shown that the origin of the isotope effect in perovs kite type quantum paraelectrics differs substantially from the one observed in hydrogen-bonded systems.