  The origin of the functional properties of complex oxide superlattices can be
resolved using time-resolved synchrotron x-ray diffraction into contributions
from the component layers making up the repeating unit. The CaTiO3 layers of a
CaTiO3/BaTiO3 superlattice have a piezoelectric response to an applied electric
field, consistent with a large continuous polarization throughout the
superlattice. The overall piezoelectric coefficient at large strains, 54 pm/V,
agrees with first-principles predictions in which a tetragonal symmetry is
imposed on the superlattice by the SrTiO3 substrate.
