Synchrotron x-ray diffraction study of the surface layer in poled ceramic BaTiO3

Both unpoled and poled BaTiO3 were studied by laboratory and synchrotron x-ray sources. The shorter-wavelength synchrotron radiation was used to probe deeper below the specimen surface. Diffraction patterns revealed a distinctive surface layer of the same tetragonal structure as the main BaTiO3 fraction. A sin(2) Psi analysis of peak shift confirmed that no measurable change of elastic strain occurs upon poling. This indicates that poling may induce excessive strain that was relieved by microcracking or that a majority of domains reverse orientation. However, domain switching and possible microcracking may induce inhomogeneous strain (microstrain) and alter domain-size distribution. Line-broadening analysis showed large anisotropy of both coherently diffracting domain size and microstrain. The poled specimen shows a larger microstrain and smaller average domain size, which indicates possible effects of microcracking and additional defects created during poling.