Abstract
NBT presents an orthorhombic to tetragonal second order phase transition that occurs near 320 °C. It corresponds to the so-called antiferroelectric-paraelectric phase transition. A model is presented in which the diffuse phase transition is achieved by the progressive canceling of the antiphase octahedra tilting prevailing within a - b + a - orthorhombic structure, whereas the in-phase tilting is maintained. This transformation gives finally rise to the a 0 a 0 c + octahedra tilting system of the tetragonal phase. Electron diffraction experiments show that a long-range ordering occurs within the tetragonal phase. It probably develops as P4 2 /mnm ordered nanoregions disseminated within a P4-/mbm disordered matrix. The order is still visible in the temperature domain of the cubic phase.
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