Crystal Structure and B-Site Ordering in Antiferroelectric Pb(Mg1/2W1/2)O3, Pb(Co1/2W1/2)O3 and Pb(Yb1/2Nb1/2)O3

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Abstract
The high-temperature phase of Pb(Mg1/2W1/2)O3, Pb(Co1/2W1/2)O3 and Pb(Yb1/2Nb1/2)O3 belongs to the space group Fm3m with the unit cell size of 2a c×2a c×2a c where a c is the lattice parameter of the cubic perovskite unit cell. All these complex perovskites undergo phase transition into low-temperature orthorhombic structures with a shrunken lattice parameter along the c-axis and the approximate √2a lattice parameters along the a 0- and b 0-axes, which are, respectively, parallel to the prototype [110] c and [11̄0] c directions. The symmetry along the b 0-axis of the perovskites is most prominently distinguished from that along the a 0-axis in that the low-temperature structure is modulated in the b 0-axis direction. For Pb(Mg1/2W1/2)O3, a diffraction pattern detrimental to the crystal structure determination well below the Curie temperature is presented. At the same time, the crystal structures of lock-in phases of the aforementioned oxides are compared with the well-known structure of PbZrO3.