Local structure study of the off-center displacement of Ti and Zr across the morphotropic phase boundary ofPbZr1−xTixO3(x=0.40,0.47,0.49,0.55)

Abstract

X-ray absorption fine structure (XAFS) experiments were carried out on a series of ferroelectric materials $\mathrm{Pb}{\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ (PZT) $(x=0.40,0.47,0.49,0.55)$ 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 $3\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ 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 $\mathrm{Zr}\phantom{\rule{0.3em}{0ex}}K$-edge EXAFS data suggest that at low temperature, the $\mathrm{Zr}{\mathrm{O}}_{6}$ 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 $\mathrm{Zr}{\mathrm{O}}_{6}$ local structure hardly changes with Ti concentration across the MPB region. Finally, the XAFS data also show that the sizes of the $\mathrm{Zr}{\mathrm{O}}_{6}$ octahedra are larger than that of the $\mathrm{Ti}{\mathrm{O}}_{6}$ octahedra which was also observed by experimental neutron pair distribution function analysis.