Surface Ferroelectricity in BaTiO3

There are conflicting reports in the literature about the existence of surface ferroelectricity. Pyroelectric measurements suggest that a surface polarization develops above the bulk Curie temperature, but TEM studies failed to observe anomalous surface properties. Recent time resolved x-ray studies of the field induced ferroelectric phase revealed a delay time before the onset of nucleation and a possible explanation is that the delay time is the time to form a surface ferroelectric layer prior to bulk nucleation. To test this idea we have used a varient of surface sensitive x-ray scattering in which the (330) planes in a [100] plate are used and the x-ray wavelength tuned so that the incident beam is normal and the scattered beam is arbitrarily close to the critical angle for total external reflection. We find that unelectroded crystals show no surface ordering but that samples with a single electrode have a surface transition and a reduced bulk Curie Temperature.