PhD thesis defense of Monika Karpierz

Properties of the (1-x)K_0.5Bi_0.5TiO₃-xPbTiO₃ and (1-x)Na_0.5Bi_0.5TiO₃-xPbTiO₃ solid solutions

This dissertation concerns the properties of the (1-x)K_0.5Bi_0.5TiO₃-xPbTiO₃, (1-x)Na_0.5Bi_0.5TiO₃-xPbTiO₃ solid solutions. In this dissertation the studies of crystal structure and dielectric, piezoelectric, semiconducting (made for the first time) and ferroelectric properties of solid solutions (1-x)NBT-xPT (0≤x≤0.6) and (1-x)KBT-xPT (x = 0≤x≤0.8) have been carried out. These studies were aimed at determining the impact of introducing Pb²⁺ ions with unique features, including high polarizability and tendency to form chemical bonds by hybridization of electron orbitals, instead of ions (Na_0.5Bi_0.5)²⁺ or (K_0.5Bi_0.5)²⁺.
This treatment had a significant impact on the analyzed properties. It has strengthened the dielectric, piezoelectric and ferroelectric properties. It also modified electrical properties. The results discussed in this paper show the similarity of the behavior of NBT-PT and KBT-PT solid solutions to the basic compounds, i.e. NBT and KBT. The results of dielectric and ferroelectric properties under uniaxial pressure (for some materials measured for the first time), show their high mechanical strength, and the linear dependence of the dielectric permittivity value on the pressure of 0.2KBT-0.8PT solid solution promotes it for applications as a sensor in force/pressure meters. The dissertation was extended by a part containing ab initio calculations of electron density of states (DOS). DOS were calculated and compared with available data.