Doctor of Philosophy, Case Western Reserve University, 2017, Materials Science and Engineering

Bi(B'B")O3 - PbTiO3 type solid solutions in the morphotropic phase boundary region (MPB) are currently the most promising systems for high temperature piezoelectric applications. Bi-based systems have been shown to have enhanced Curie temperatures (Tc), which is an intrinsic limit for piezoelectricity, coupled with excellent piezoelectric properties at temperatures greater than the highest operating temperature for state-of-the-art Pb(Zr,Ti)O3 systems. However, as the Tc increases, thermal depoling becomes a key aspect in the characterization of the operating range of these systems targeted for high temperature applications. In this thesis, a multifaceted approach is pursued to elucidate the thermal effects on structure-property relationships through the use of impedance spectroscopy, X-ray diffraction (XRD) and high field measurements. A new ternary MPB system with the formulation BiScO3-Bi(Zn0.5Zr0.5)O3-PbTiO3 has been developed which improved upon the base BiScO3-PbTiO3 by reducing the loss tangent as a function of temperature while maintaining both a high Curie temperature (420°C) and stable properties up to the depoling temperature (380°C). The loss characteristics were improved further through the introduction of aliovalent dopants that affect the domain wall mobility. It was also observed that the phase ratio, which has a large effect on the dielectric and electromechanical properties, could be controlled through sintering temperature. The temperature stability of the newly developed piezoelectrics were investigated though thermal cycling in impedance spectroscopy. It was discovered that there is actually a range of temperature over which these materials depole, rather than at a single point, which can limit the operation even further. This work provides a guideline for studying high temperature piezoelectrics and emphasizes application limiting factors beyond the typical motivation to increase Tc. Hence, characterizing and improving the thermal depoling and (open full item for complete abstract)

Committee: Alp Sehirlioglu (Advisor); Mark De Guire (Committee Chair); Peter Lagerlof (Committee Chair); Christian Zorman (Committee Chair) Subjects: Materials Science