Crystal structure and domain-wall orientations of antiferroelectric Pb(Yb1/2Nb1/2)O3

The crystal structure of antiferroelectric Pb(Yb1/2Nb1/2)O-3 with ordered complex perovskite structure was reexamined by TEM (transmission electron microscope). Its domain-wall orientations were investigated by the spontaneous strain method. From the CBED (convergent-beam electron diffraction) patterns, its point group was determined to be orthorhombic mmm. During transition from the high-temperature cubic to low-temperature orthorhombic phase, the prototype cubic cell is monoclinically distorted. The monoclinic cell was found to be contracted along the direction of Pb2+ shifts. The reduced symmetry of the orthorhombic phase transformed from the prototypic phase allows the existence of ten species of domain walls, i.e, six W-walls and four W'-walls. The breaking of reflection symmetry during transition occurred at (1 0 0), (0 1 0), (0 1 1), (0 (1) over bar 1), ((1) over bar 0 1) and (1 0 1) planes of the cubic prototype. These high-symmetry planes correspond to the W-walls in the ferroelastic phase. Taking into account the domain geometry, the (1 0 0)(m) and (0 1 0)(m) planes art: the 90 degrees domain-boundaries and the others can be both 60 degrees and 120 degrees ones. The orientations of W'-walls calculated from the strain components were approximately ((2) over bar 3 3)(m), (2 (3) over bar 3)(m), ((3) over bar 2 3)(m) and (3 (2) over bar 3)(m) planes at room temperature. On approaching the transition these W'-walls tend to orient themselves toward the direction of 60 degrees or 120 degrees domain W-walls.