Observation of the antiferroelectric order parameter in surface layers of SrTiO3

Abstract

X-ray diffraction from the antiferroelectric superlattice of SrTiO3 has been observed in a grazing geometry for several values of the X-ray penetration depth. The samples were a polished single crystal grown by the Verneuil technique and a polished and etched single crystal grown from a top-seeded solution. The variation with temperature of the order parameter was found to depend strongly on the penetration depth for the Verneuil-grown sample. This dependence was much less for the sample grown from a top-seeded solution. The observed X-ray intensities for both samples have been fitted by a mean-field theory that takes into account a surface free-energy density that is different from that in the bulk, such as might arise from a strain localised in the surface.