Skin Layer ofBiFeO3Single Crystals

A surface layer (“skin”) different from the bulk was found in single crystals of ${\mathrm{BiFeO}}_3$. Impedance analysis and grazing incidence x-ray diffraction reveal a phase transition at $T^{*}\sim 275\pm 5°\mathrm{C}$ that is confined within the surface of ${\mathrm{BiFeO}}_3$. X-ray photoelectron spectroscopy and refraction-corrected x-ray diffraction as a function of incidence angle and photon wavelength indicate a reduced electron density and an elongated out-of-plane lattice parameter within a few nanometers of the surface. The skin will affect samples with large surface to volume ratios, as well as devices that rely on interfacial coupling such as exchange bias.