The electronic and atomic structures of interstitial H impurities were investigated, with regard to their effect upon ferroelectric polarization, by means of first-principles total-energy calculations. Interstitial H was found to bond to O and to act as a shallow donor impurity. At equilibrium, H did not greatly affect nearby Ti-O bonds, and the H-O dipole increased the polarization. The barrier to reversing the defect dipole could give rise to imprinting (extra stabilization of one of the 2 polarization modes).

Effect of Interstitial Hydrogen Impurities on Ferroelectric Polarization in PbTiO3. C.H.Park, D.J.Chadi: Physical Review Letters, 2000, 84[20], 4717-20