Structural study of PbZn1/3Nb2/3O3 by single crystal X-ray diffraction andEXAFS

The structure of PbZn1/3Nb2/3O3 ferroelectric relaxer was investigated by t he single crystal X-ray diffraction and the extended X-ray absorption fine structure (EXAFS) techniques at room temperature. The crystal has a rhomboh edral R3m symmetry with a=0.40620(4) nm and alpha=89.93 (1)degrees. The met al atoms are displaced from the cubic prototype positions by 0.035(1) nm fo r Pb, and 0.012(2) nm for Zn and Nb. The Pb atoms are statistically distrib uted at the 9b positions in the hexagonal setting. EXAFS analysis gave mean bond distances of 0.235(1) nm for Pb-O, 0.204(1) nm for Zn-O, and 0.194(1) nm for Nb-O. The coordination number of Pb was estimated to be 3.8(2). Sin gle crystal X-ray diffraction and EXAFS data suggested a pyramidal coordina tion for the local structure around Pb, which is similar to PbO4 in PbO. Th e different bond distances of Zn-O and Nb-O imply a concurrent constriction of NbO6 and expansion of ZnO6 octahedra in the crystal, leading to an aper iodic distortion of the corner-shared octahedral network.