Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references. Also available in electronic version.

Based in part on thesis-Massachusetts Institute of Technology. / "O.N.R. contract N5ori-078596." Bibliography: p.34.

The research carried out for this thesis has concentrated on Aurivillius bismuth oxide materials and the closely related Sillen and Bipox bismuth oxyhalides. X-ray and neutron powder diffraction techniques have been used to characterise precisely their structure and revealed several important features. The unexpected presence of a double phase transition scheme has been discovered for the Aurivillius phases Sr0.85Bi2.1Ta2O9 and SrBi4Ti4O15, both materials present the particularity of having an even number of perovskite layers n (n = 2 and n = 4 for Sr0.85Bi2.1Ta2O9 and SrBi4Ti4O15 respectively). The first transition from orthorhombic space group A21am to Amam, occurs at Tc (375deg.C and 550deg.C for Sr0.85Bi2.1Ta2O9 and SrBi4Ti4O15 respectively). The second transition from orthorhombic Amam to tetragonal I4/mmm, occurs at higher temperature (550deg.C and 650deg.C for Sr0.85Bi2.1Ta2O9 and SrBi4Ti4O15 respectively). These phase transitions have been understood in terms of specific octahedral tilt and displacive modes. In contrast, the n = 2 phase SrBi2Nb2O9 and the n = 3 phase Bi4Ti3O12 are shown to undergo a single-step transition from orthorhombic space group A21am to tetragonal I4/mmm at Tc = 440deg.C for SrBi2Nb2O9, and from orthorhombic space group B2cb to tetragonal I4/mmm at Tc = 675deg.C for Bi4Ti3O12. The atomic disorder of the Bi and A cations in the fluorite and perovskite sites of the Aurivillius phases has been demonstrated and thoroughly studied for the solid solutions Bi4-xSrxTi3-xNbxO12 and Bi4-xLaxTi3O12, and "size-matching" between the fluorite and the perovskite site has been found to be the key to understanding this disorder phenomenon. In the Sillen family, we extended the members of the Bi2MO4Cl group, where M = Lanthanide to the three following compounds: Bi2ErO4Cl, Bi2YbO4Cl, and Bi2LuO4Cl. We have demonstrated that in the Bi2MO4Cl group, the ionic radius of M must be greater than that of Sc3+ (r (Sc3+) = 0.87 Å for CN = 8). Another new compound with a novel ordering scheme for this family has been studied, viz. Bi5TeO8.5I2, crystallising in the orthorhombic space group Cmm2. Te4+ is shown to adopt only one of the three available M sites, thus inducing a polar structure. In the Bipox family, the crystal structures of two materials exhibiting ferroelectric properties, Bi4NbO8Cl and Bi4TaO8Cl have been determined to be orthorhombic, space group P21cn.

Ferroelectric materials have found a wide range of applications in data storage devices, sensors and actuators, capacitors, oscillators and filters, among others thanks to fabrication methods that allow integration into semiconductor devices at micro and nanoscales. As many of these materials also exhibit ferroelasticity, the interplay between ferroelectric and ferroelastic phenomena is a subject of intensive research. In earlier work on this topic, resonance enhanced piezoresponse force microscopy was introduced and theoretical models were developed to support quantitative imaging with PFM. The resonant PFM mechanism was thoroughly investigated, and functional materials including tetragonal polycrystalline PbZr0.3Ti0.7O3 and epitaxial PbZr0.2Ti0.8O3 thin films were studied at different length scales using resonant PFM. This technique was also used to study the ferroelectric/ferroelastic domains and their dynamics. In the current work, the interplay between ferroelectric and ferroelastic domains is investigated in both polycrystalline and epitaxial thin films, during which a type of unexpected controllable defects was proposed. It is shown that certain defects are controllable via an external electrical excitation and the strain associated with the defect can also be controlled. Lastly, ways to modify the thin film geometry with focused ion beam milling and broad beam milling and its impact on domain configurations is studied. The resulting changing geometry and the ferroelectric/ferroelectric domain modification has been compared.

In recent years, BiFeO3 (BFO) has attracted much attention due to that exhibits ferroelectric and antiferromagnetic properties at room temperature. It potentially develops the spintronics and multiple-state memories. BFO suffered from serious leakage, therefore the BFO discussed in this report has doped 10% Pb to reduce the leakage problem. The thin films are synthesized by radio frequency (RF) sputtering technique. The conductive SrRuO3 (SRO) thin film is deposited on the SrTiO3 (STO) substrate as a buffer layer and bottom electrode for piezoelectric measurements and subsequently deposited the multiferroics- BFO thin film. Atomic force microscopy (AFM) and piezoresponse force microscopy (PFM) are used to observe the morphologies and domain images in nanometer scale by different parameters and avoid the disturbance of leakage reasonably. The variations of piezoelectric properties through grain-grain boundary and domain-domain boundary are also studied in this report.

No description available.

Two groups of ferroelectric oxides have been studied using a.c. impedance techniques. These were donor-doped BaTiO₃ ceramics showing the positive temperature of resistance, PTCR, effect and single crystal LiTaO₃. Existing theories of the PTCR effect in BaTiO₃ ceramics assume that it is associated with the grain boundary regions. An in-depth analysis of a.c. data, using combined impedance and modulus spectroscopy revealed the presence of at least two components, both of which exhibited PTCR effects. These were attributed to bulk and grain boundary effects because of the different temperature dependence of their associated capacitances: grain boundary effects have temperature independent capacitances whereas bulk effects show a capacitance maximum at the Curie pont and Curie-Weiss behaviour above the Curie point. An explanation for the bulk PTCR effect is proposed. The a.c. data handling techniques used and developed here provide information regarding the inhomogeneous nature of the grain boundary and bulk components which cannot be obtained from d.c. measurements. An equivalent circuit to model the a.c. response of PTCR BaTiO₃ ceramics is presented. The influence of processing conditions on the various bulk and grain boundary PTCR effects, such as the sample cooling rate from the sintering temperature and low temperature anneals, < 400 °C, in various reducing and oxidising atmospheres is discussed. For quickly cooled samples, the PTCR response is dominated by the bulk impedance, whereas for slowly cooled samples, the grain boundary component dominates. Annealing in reducing atmospheres destroys the grain boundary PTCR effect whereas bulk PTCR effects are relatively insensitive to the atmosphere at low temperatures. Information regarding the conductive core of the grains and the behaviour of component resistances below the Curie point for slowly cooled samples is presented. A general model is proposed which explains the PTCR behaviour of BaTiO₃ ceramics. The effects of both cooling rate and atmosphere are incorporated in this model. A.c. impedance data for single crystal LiTaO₃ with the crystal c axis oriented parallel and perpendicular to the electric field were recorded above and below the Curie point, 590^oC. With the polar c axis parallel to the electric field, the following were measured: the charge polarisation associated with the ferroelectric domains, the intrinsic lattice polarisation, the resistance associated with domain re-orientation and the resistance due to lithium ion migration. The correct choice of equivalent circuit is crucial to the determination of these parameters. With the c axis parallel to the electric field, no ferroelectric behaviour was observed and the crystal was a modest electronic conductor at elevated tempeatures, 500-700^oC. The LiTaO₃ results presented indicate the potential of a.c. impedance techniques for probing the electrical properties of ferroelectric single crystals. Domain re-orientation may be characterised by macroscopic resistance and capacitance values. This allows the temperature dependence of domain re-orientation phenomena to be characterised as the crystal is heated through the Curie point. Such detailed characterisation cannot be obtained from existing fixed-frequency or d.c. measurements.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2007. / Title from title screen (site viewed June 17, 2008). PDF text: vi, 94 p. : ill. (some col.) ; 3 Mb. UMI publication number: AAT 3293918. Includes bibliographical references. Also available in microfilm and microfiche formats.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, June 1990. / Thesis Advisor(s): Panholzer, R. Second Reader: Neighbours, J.R. "June 1990." Description based on signature page. DTIC Identifiers(s): Nonvolitile memories, ferroelectric materials. Author(s) subject terms: Ferrorelectric, nonvolatile memory, radiation hard. Includes bibliographical references (p. 80-86). Also available online.

Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 119-121).