| Dielectric and ferroelectric materials are widely used in many applications, such as energy storage capacitors, actuators in micro-positioning devices, and ultrasound medical therapy devices. The demands of advanced materials with multi-functionalities, precise responses under different stimuli, or stable performance in harsh conditions, are growing nowadays. Usually such advanced materials have complex structures such as the deviation of local structure from long-range structures, non-equilibrium states, phase co-existence, and complicated microstructures. These complex structures result from a variety of reasons, e.g. the competing internal forces, flattened Gibbs free energy profiles, specific synthesis routes, etc. Since the dielectric and ferroelectric property of a material is a function of its structures, and the structures strongly depend on the processing methods, it is crucial to have a good understanding of the processing-structure-property relationships of these complex dielectrics and ferroelectrics. However, due to lack of sophisticated characterization techniques and data analysis methods, there are only limited studies on the comprehensive structural characterization of these complex materials.;The work in this dissertation characterizes the crystallographic structures of multiple complex dielectrics and ferroelectrics. These fundamentally important materials of interest are: lead-free ferroelectric Na1/2Bi 1/2TiO3-xBaTiO3 (NBT-xBT), Si-doped HfO2 fluorite, spinel compound CoxMn3-xO4 (CMO), high temperature dielectric BaTiO3-xBi(Zn1/2Ti1/2)O3 (BT xBZT), and Pb(Mg1/3Nb2/3)O3-xPbTiO 3 (PMN-xPT) relaxor. Each material exhibits unique functional properties associated with the structures at different length scales. Advanced scattering techniques, e.g. high energy X-ray diffraction (XRD), high resolution XRD, neutron diffraction, and X-ray total scattering, were used to construct the processing-structure-property relationships.;To elucidate the role of processing factors on the structures of NBT- xBT, in situ XRD during reaction was conducted. A new formation mechanism is proposed. Studying the processing in situ helps in understanding the reaction sequences, also helps in designing new processing route.;The processing-structure relationship study of Si-doped HfO2 was conducted using high resolution XRD. The calcination temperature and SiO 2 particle size play important roles in the incorporation of Si into HfO2 and the diffusion of Si out of (Hf,Si)O2 solid solution. The obtained (Hf,Si)O2 is confirmed as a non-equilibrium state. This work demonstrates that the processing conditions can be optimized to control the phases in Si-doped HfO2 final products.;The structures of CMO ceramics are characterized using combined analysis of neutron and X-ray diffraction. A tetragonal to cubic spinel transition was observed by addition of Co on B-sites. The lattice parameters, phase fraction, and atom-atom bond lengths were obtained by Rietveld method. This study contributes to a more thorough understanding of the structures in CMO spinel oxides.;To investigate the fundamental origin of the temperature stable properties of BT-xBZT, the local and long-range structures are characterized by in situ high temperature X-ray total scattering. The results show evidence of an enhanced tetragonal distortion at local scale, suggesting there are tetragonal polar clusters embedded in non-polar matrix. These tetragonal distortions can persist to at least 225°C, even though the average structure transforms to a paraelectric phase. These results indicate these nanoscale clusters may be responsible for the observed large permittivity at high temperatures. |
