Local structure in BaTi1-xZrxO3 relaxors from neutron pair distribution function analysis

The pair distribution functions (PDF) of BaTi1-xZrxO3 (BTZ) relaxors (x=0.25,0.32,0.35), as well as those of the end members BaTiO3 and BaZrO3, were determined at 300 K from neutron powder scattering data. In the relaxors, the PDF provides direct evidence that the Ti and Zr atoms do not occupy the equivalent octahedral sites expected from the crystallographic cubic perovskite structure. It is shown that the TiO6 and ZrO6 octahedra in BTZ relaxors are instead similar to those observed in BaTiO3 and BaZrO3, respectively. In BaZrO3, the Zr atoms lie at the center of regular oxygen octahedra, forming nonpolar ZrO6 units. In the tetragonal ferroelectric phase of BaTiO3, the distribution of Ti-O distances within TiO6 octahedra is found compatible with a displacement of the Ti atoms in the [111](p) direction of the pseudocubic perovskite cell. We conclude that the local polarization in BTZ relaxors is mainly due to the displacements of the Ti atoms and that moreover the Ti displacements are very similar in BTZ relaxors and in the classical ferroelectric BaTiO3.