Local structure study of the off - center displacement of Ti and Zr across the morphotropic phase boundary of PbZr

X-ray absorption fine structure (XAFS) experiments were carried out on a series of ferroelectric materials PbZr1−xTixO3 (PZT) sx=0.40,0.47,0.49,0.55d to study the local structure around Ti and Zr atoms in each sample. Based on the fact that PZT has a single phase in the morphotropic phase boundary (MPB) from the x-ray diffraction measurements, both extended XAFS (EXAFS) and x-ray absorption near-edge structure results suggest that at 3 K the orientation of the Ti off-center displacement in these materials changes gradually from the [001] to [111] direction (in pseudocubic notation) as the Ti concentration x decreases from 0.55 to 0.40. This is evidence for a continuous rotation of the local electrical polarization across the MPB region in PZT. The Zr K-edge EXAFS data suggest that at low temperature, the ZrO6 octahedra in PZT are less distorted than indicated from the average structure for all samples, though a small Zr displacement relative to the O atoms may exist. This possible small Zr displacement is also much less than that found in density functional theory calculations. The ZrO6 local structure hardly changes with Ti concentration across the MPB region. Finally, the XAFS data also show that the sizes of the ZrO6 octahedra are larger than that of the TiO6 octahedra which was also observed by experimental neutron pair distribution function analysis.