Elastic and dielectric measurements of the structural transformations in the ferroelectric perovskite (Na1/2Bi1/2)1-xBaxTiO3

The perovskite (Na1/2Bi1/2)TiO3 (NBT) undergoes a series of structural and polar transitions starting from the high temperature paraelectric phase: tetragonal paraelectric, tetragonal antiferroelectric, rhombohedral antiferroelectric and finally rhombohedral ferroelectric, according to neutron diffraction and dielectric spectroscopy. In solid solution with BaTiO3 (BT) the ferroelectric phase changes from rhombohedral to tetragonal, at the so-called morphotropic phase boundary, and the phases at higher temperature become ill-defined, also because of the large lattice disorder induced by the coexistence of differently charged cations in the same sublattice. Combined dielectric and anelastic spectroscopy measurements are presented, which clarify some issues related to the phase transitions in NBT-BT. The influence of Ba substitution on the tetragonal antiferroelectric phase is determined for the first time, and the possibility that a monoclinic phase, although with very short coherence length, exists near the morphotropic phase boundary is discussed in view of a large maximum of the elastic compliance.