Acute and obtuse rhombohedrons in the local structures of relaxor ferroelectric Pb(Mg sub(1/3)Nb sub(2/3)O sub(3)

The local structures around Nb and Pb in the prototypical relaxor ferroelectric Pb(Mg sub(1/3)Nb sub(2/3)O sub(3) (PMN) were investigated by x-ray fluorescence holography. The separate atomic images of nearest Pb around Nb revealed acute and obtuse rhombohedral structures of the crystal unit cells. The Pb-Pb correlated images showed a local structure of body-center-like 2a sub(0) x 2a sub(0) x 2a sub(0) superlattice, proving a rigid three-dimensional network structural model combining the two kinds of rhombohedrons. The Pb atoms in the networks are positionally stable, while the other Pb atoms are fluctuating. This superstructure and the fluctuating Pb and Nb atoms are believed to play an important role in the relaxor behavior of PMN at the atomic level.