Investigation of a peculiar relaxor ferroelectric:: Na0.5Bi0.5TiO3.

The relaxor ferroelectric, Sodium Bismuth Titanate, (Na0.5Bi0.5TiO3), NBT is an A-site substituted distorted perovskite. An extensive temperature-, pressure- and substitution-dependent study of the crystal structure and phase transitions in this compound has been carried out using neutron/x-ray diffraction techniques. This has been complemented with optical, Raman and computational modelling studies. The temperature-dependent investigation shows that NBT undergoes a first phase transition from the high-temperature cubic prototype (Pm (3) over bar m) Phase I to Phase II of tetragonal symmetry (P4bm) and then a second one with strong diffuse character to Phase III of rhombohedral symmetry (R3c). The high-pressure study of NBT has revealed an interesting and unusual relaxor-to-antiferroelectric (R3c --> Pnma) phase transition. Structural variations as a function of temperature and doping across the (Na1-xKx)(0.5)Bi0.5TiO3 (NKBT) series have also been established.