Structural Study of PbZn1/3Nb2/3O3 by Single Crystal X-ray Diffraction and EXAFS.

Abstract

The structure of PbZn1/3Nb2/3O3 ferroelectric relaxor was investigated by the single crystal X-ray diffraction and the extended X-ray absorption fine structure (EXAFS) techniques at room temperature. The crystal has a rhombohedral R3m symmetry with a=0.40620(4)nm and α=89.93 (1)°. The metal atoms are displaced from the cubic prototype positions by 0.035(1)nm for Pb, and 0.012(2)nm for Zn and Nb. The Pb atoms are statistically distributed 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). Single crystal X-ray diffraction and EXAFS data suggested a pyramidal coordination for the local structure around Pb, which is similar to PbO4 in PbO. The 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 aperiodic distortion of the corner-shared octahedral network.