PhD thesis defense of Urszula Lewczuk-Jodłowiec
Structural, dielectric, optic, piezoelectric and ferroelectric properties of (1-x)Na0.5Bi0.5TiO3-xBaTiO3 solid solutions.
Polycrystalline solid solutions (1-x)NBT-xBT for x = 0, 0.04, 0.06, 0.08, 0.1, 0.12 and 0.125, obtained by solid phase reaction, were tested for their structural, optical, thermal, dielectric, pyroelectric and ferroelectric properties.
Microstructural studies indicate well-formed grains in the obtained materials, the size of which decreases as the content of Ba2+ ions increases. These studies have also shown a homogeneous spatial distribution of the elements in the samples. The analysis of the results of the study of mechanical properties indicates a slight decrease in the value of elastic parameters. This may be related to the increase in the size of the unit cell, which could lead to an increase in the length of chemical bonds. It was suggested that the anomalies observed in the thermal expansion study could be associated with a progressive change in the averaged unit cell volume as well as with the transition of crystal lattice dynamics from tetragonal to rhombohedral symmetry during cooling within the temperature range in which both phases coexist. The analysis of pyroelectric effect revealed the complex nature of depolarization process of the studied ceramics.
The results obtained in the present study indicate the similarity of the tested NBT-BT solid solution to pure NBT. The similarity is manifested, among others in:
(1) the occurrence of a diffused phase transition,
(2) identical character (electric order) of phases and the sequence of phase transformations from low temperature (rhombohedral or tetragonal) through the transition phase, which is a mixture of phases (rhombohedral with tetragonal or tetragonal with cubic), and
(3) the presence of relaxor features.