Stabilization of ferroelectricity in quantum paraelectrics by isotopic substitution

SrTiO 3 and KTaO 3 are incipient ferroelectrics whose phase transition temperature is suppressed by quantum fluctuations. The recent observation of induced ferroelectricity due to exchange of 16 O by 18 O (1999 Phys. Rev. Lett. 82 3540) is reproduced for the dielectric data by an anharmonic electron-phonon interaction model, and a first order phase transition is predicted. Furthermore it is shown that this isotope effect does not occur in KTaO 3 since its local double-well potential is much shallower than that in SrTiO 3 .