Antiferrodistortive reconstruction of the PbTiO3(001) surface

We present in situ x-ray scattering measurements of the surface structures of PbTiO{sub 3} (001) in equilibrium with PbO vapor. At 875 to 1025 K, a reconstruction having c(2x2) symmetry is present under most conditions, while a 1x6 reconstruction occurs under PbO-poor conditions. The atomic structure of the c(2x2) phase is found to consist of a single layer of an antiferrodistortive structure with oxygen cages counter-rotated by 10 degrees about the titanium ions.