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In flux-grown (1-x)NaNbO3-(x)Gd⅓NbO3 solid solution crystals a diffusion of the dielectric permittivity ε maximum grows with x and increases dramatically when x exceeds a threshold value x0 ≈ 0.1. Optical studies by the rotating-polarizer method show that Gd-doping results in a very small mean size of twins and the distribution of the birefringence image becomes very messy. In the x < x0 range the changes of lattice parameters and birefringence corresponding to the ε(T) anomaly were revealed. The results obtained are in line with the assumption that phase transition diffusion in NaNbO3 is a result of the local strains stemmed from the impurities. [ABSTRACT FROM AUTHOR]

The relaxor ferroelectric, Sodium Bismuth Titanate, (Na 0.5 Bi 0.5 TiO 3 ), 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 &3macr; 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 (Na 1-x K x ) 0.5 Bi 0.5 TiO 3 (NKBT) series have also been established. [ABSTRACT FROM AUTHOR]