Peculiarities of optical behaviour of Na0.5Bi0.5TiO3 single crystals

Results of polarising-microscope study of Na0.5Bi0.5TiO3 (NBT) crystals obtained by the Czochralski method are reported. The nature of the observed domain structure is ferroelastic and the position of domain walls is stable in the range 20–540 °C. The temperature dependence of extinguishing angle ϕ between adjacent orientational states in the range ∼200–350 °C is observed. Possibility of appearance of strong internal mechanical stresses in NBT crystals at tetragonal–rhombohedral phase transition due to the different arrangement of Na1+ and Bi3+ ions in the A-position in these phases is discussed.