A study of the effects of transition metal impurities on the properties of perovskite structure ferroelectrics

The study of the effects of substitutional atoms in the unit cell of potassium tantalate niobate (KTa1-xNbxO3 ) and other perovskite like structures such as potassium tantalate (KTaO 3) and barium titanate (BaTiO3) is of great importance in understanding the origins of structural phase transitions and long range order in such systems. This kind of long range order is at the origin of the theories that explain the appearance of spontaneous polarization in displasive type ferroelectrics.; The current study performed on potassium tantalate niobate (KTa 1-xNbxO3) doped with iron showed that a small amount of iron---as small as 10 ppm---had a large effect on both the electrical properties and the ferroelectric phase transition of KTN. The current study aimed at explaining the origins of such an effect. The current study included the addition of iron to KTN single crystals of ultra high purity through thermal diffusion. Electrical measurements (dielectric constant and dielectric loss) versus temperature were used to reveal the nature of the ferroelectric phase transition in the KTN:Fe system. A study of the structural variations with composition and temperature was also carried out using x-ray microanalysis, x-ray topography and high resolution photography. Refractive index variations were measured and used to reveal changes in the structure and composition of KTN. Finally, the results obtained were used to construct a model that would explain some of the properties of KTN phase transitions and their behavior with iron doping, and also explain some of the structural variations due to growth conditions.