Bismuth layer structure ferroelectrics (BLSFs) have attracted intensive investigation for the potential use in nonvolatile ferroelectric random access memory (NvRAM/FeRAM) and high temperature piezoelectric devices. In this thesis, there are three kinds of Bi-layered structure ferroelectric ceramics materials prepared by solid-state reaction methods. Investigations have been made on the crystal structure, surface morphology, and dielectric properties of these ferroelectric materials. In the chapter3 of this thesis, ferroelectric materials are SrBi2Ta2O9-based ceramics. One of the materials is SrBi2Ta2O9 composition with excess x wt% Bi2O3 (x=0, 2, and 4). Even 1280oC is used as the sintering temperature of stoichiometric SrBi2Ta2O9 composition, the X-ray diffraction patterns will show that the SrBi2Ta2O9 phase is coexisted with the raw material of Ta2O5 and the secondary phases of SrBi2O4 and BiTaO4. For SrBi2Ta2O9 composition with excess 2wt%- or 4wt%-Bi2O3-doped and sintered at 1040oC, the Ta2O5, SrBi2O4, and BiTaO4 phases are eliminated and only the SrBi2Ta2O9 phase is observed in the X-ray diffraction patterns. The other of SrBi2Ta2O9-based ceramics was doped with V2O5. V2O5 is used to substitute Ta2O5 of the SrBi2Ta2O9 ceramics to form SrBi2Ta2-xVxO9 composition, where x=0.1, 0.2, 0.3, and 0.4. For all SrBi2Ta2-xVxO9 composition, the crystal intensities of the (00l) planes (l =6, 8, 10, 12, and 14) increase with the increase of sintering temperature and saturate at 1050oC-sintered ceramics, and the increase in the crystal intensities of the (008) and (0010) planes are more obvious. For the same sintering temperature, the crystal intensities of the (00l) planes increase with the increase of V2O5 content and saturate at SrBi2Ta1.7V0.3O9 ceramics. In the chapter4, ferroelectric materials are SrBi4Ti4O15-based ceramics. One of the materials is (Sr1-xBax)Bi4Ti4O15 (x=0, 005, 0.1, 0.15, and 0.02), and BaO is used to substitute SrO. Dielectric properties were investigated in the temperature of 25oC~ 805oC at 1MHz. It is found that Curie temperatures are shifted to higher temperature as the BaO content increased. For (Sr1-xBax)Bi4Ti4O15 ceramics sintered at 1150oC, the Curie temperature for x=0, 0.05, 0.1, 0.15, and 0.2 are 645oC, 665oC, 705oC, 725oC, and 745oC, respectively. The other is non-stoichiometric compositions SrBi4Ti4O15+x Bi2O3, (x= -0.04, -0.02, 0, 0.02, and 0.04). From the observations of SEM, the SrBi3.92Ti4O14.88 and the SrBi3.96Ti4O14.94 ceramics reveal a two-phased grain growth, the bar-typed and the irregularly disk-typed grains coexist; The other ceramics will reveal the irregularly disk-typed grains. From the X-ray diffraction patterns, Bi2Ti2O7 and SrTiO3 phases are observed in the SrBi3.92Ti4O14.88 and the SrBi3.96Ti4O14.94 ceramics. Except the SrBi3.96Ti4O14.94 ceramics, the other ceramics have revealed an unapparent splitting peak in the (119) plane. In the chapter5, ferroelectric materials are (Na0.5Bi0.5)TiO3-BaTiO3-based ceramics. The 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 + x wt% Bi2O3 (x= 0, 1, 2, and 3) ceramics were fabricated by two different processes. The first process is that (Na0.5Bi0.5)TiO3 and BaTiO3 composition was calcined at 850oC and 1100oC, respectly, and then the calcined (Na0.5Bi0.5)TiO3 and BaTiO3 powders were mixed in according to 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 + x wt% Bi2O3 compositions. The second process was that the raw materials were mixed in accordance to the 0.95 (Na0.5Bi0.5)TiO3-0.05 BaTiO3 + x wt% Bi2O3 compositions and then calcined at 900oC. The sintering process was carried out in air for 2h from 1120oC to 1240oC. As the sintering temperatures are higher than 1160oC, the maximum dielectric constants of ceramics made by the second method are higher than those of ceramics by the first method, and the maximum dielectric constant of this ceramics will reveal in the x =1 ceramics. Both ceramics reveal a broaden dielectric constant-temperature curves. The other is (1-x) (Na0.5Bi0.5)TiO3-x BaTiO3 compositions, where x= 0.03, 0.05, and 0.07, formatted by two different methods given above. The dielectric-temperature curves of (1-x) (Na0.5Bi0.5)TiO3-x BaTiO3-based ceramics are almost unchanged as the measured frequency changed from 10 kHz to 1MHz.

With combination of the both ferroelectric and ferromagnetic and mutural coupling properties, multiferroics attracts a lot of researcher¡¦s attentions. Among these very popular materials, such as REMnO (113 series, 125 series), BiFeO3 etc¡K , the BiFeO3 interests us the most for it manifests multiferroic effects above the room temperature. However, the pure BiFeO3 phase is very difficult to form and a serious lost of Bi creates complex grain boundaries that produces enormous electric leaking. In this study, Pb is doped into BiFeO3 in Bi sites and we hope this doping effect may increase the stability and the ferroelectricity of Bi1-xPbxFeO3. It is found that the crystal structure is changed dramatically, because of the doping of Pb, from the rhombohedra structure of the parent pure BiFeO3 to the cubic structure of Bi0.85Pb0.15FeO3. By the Pb doping, the compounds exhibit free from impurity phases and the dielectric constants are enhanced qualitatively to the doping levels.

<p>High tunability and low loss tangent of ferroelectric thinfilms offer unique opportunity for the development of variousmicrowave devices. Silver tantalate niobate, which showsexcellent microwave properties, was selected for this study.Ag(Ta,Nb)O₃(ATN) showed week dielectric dispersion in a widefrequency range from 1 kHz up to 100 GHz, negligible losses upto 30 GHz, and ease to tailor paraelectric state in a widetemperature range by Ta:Nb ratio.</p><p>This thesis is mainly based on the synthesis andcharacterization of niobate ferroelectric ATN thin films. Thinfilms for various measurements were prepared by pulsed laserdeposition and rf-magnetron sputtering techniques.</p><p>X-ray diffraction (XRD) pattern show that ATN/Pt₈₀Ir₂₀films have been found to be (001) preferentiallyoriented, while the epitaxial quality of ATN/LaAlO₃heterostructures have been ascertained. Dielectricproperties were analyzed by measuring the relationship betweendielectric permittivity and frequency as well as dielectricpermittivity and temperature. Reliable tracing of theferroelectric hysteresis polarization versus electric loopsindicate the ferroelectric state in ATN films at temperaturebelow 125 K and yields the remanant polarization of 0.4µC/cm²@ 77 K.</p><p>The fundamental current-voltage behavior in Ag(Ta,Nb)O₃ferroelectric films was measured usingMe/Ag(Ta,Nb)O₃/Pt₈₀Ir₂₀, Me = Pd, Au, Cr, and Al, vertical capacitivecell structures with different top electrodes. Various kinds ofconduction mechanisms such as Schottky emission, Poole-Frenkel,Fowler-Nordheim, and ionic conduction were classified.</p><p>Finally, by fabricating interdigital capacitors on the oxidesubstrates, the characteristics and performances of Ag(Ta,Nb)O₃varactors were examined. Au/Cr/ATN/LaAlO₃interdigital capacitors exhibited loss tangent aslow as 0.0033 @ 1 MHz, weak frequency dispersion of 5.8 % in 1kHz to 1 MHz range, tunability as high as 16.4 %,<i>K</i>-factor (tunability/tanδ) higher than 48.</p>

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Physics and Astronomy." Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 71-80).

Thesis (Ph. D.)--Lehigh University, 2003. / Includes bibliographical references and vita.

No description available.

Ferroelectric liquid crystals (FLCs) exhibit a bulk electric polarization (PS) that can be coupled to an electric field to produce an ON-OFF light shutter, and are being investigated as an alternative to nematic liquid crystals in display applications. Commercial FLC mixtures normally consist of a small amount of chiral dopant in an achiral smectic C (SmC) liquid crystal host. Because the switching time of FLC display is inversely proportional to the induced polarization, the design of chiral dopants with high polarization powers (p) is a key aspect of FLC research. Such work requires an understanding of the relationship between molecular structure and polar order in the chiral SmC* phase. Previous work in the Lemieux group focused on 2,2’-spirobiindan-1,1’-diones dopants, and a conformational model was proposed to explain the observed host dependence of the polarization power (p) of these dopants. In order to test this model, the 2,2’-spirobiindan-1,1’-dione core has been modified by introducing polar substituents and by modifying the functional groups linking the core to the alkyl side-chains. Specifically, this thesis focuses on implementing this approach via the synthesis and characterization of chloro- and methyl-substituted 2,2’-spirobiindan-1,1’-dione dopants. Four chiral dopants (2.1a, 2.1b, 2.2a and 2.2b) were synthesized, resolved and their absolute configurations assigned by CD spectroscopy. Their polarization powers were measured in four SmC hosts with different core structures. For both the ether-linked and ester-linked dopants, the addition of a substituent at the 6-position of one indanone ring results in lower polarization powers regardless of the size and polarity of the substituent, which is contrary to the original conformational distribution model. A comparative study of the data suggests that the ester-linked dopants exert much stronger perturbations on the host environment than the ether-linked dopants, especially when the 6-position is substituted. We postulate that this perturbation is chiral in nature, and that the feedback effect of chirality transfer causes a shift in the conformational distribution of the dopant favoring conformers with negative polarity. Probe experiments were performed to detect the effect of chirality transfer feedback (CTF) in the case of the chloro-substituted diester dopant (2.1b), showing consistent results with the postulate. / Thesis (Master, Chemistry) -- Queen's University, 2007-09-28 12:26:06.486

Three different B-site additives, Mg1/3Nb2/3, Zr4+, and Cu1/2W1/2, were added to BNT ceramics in varying concentrations. These were abbreviated as BNMN, BNZ, and BNCW, respectively. The compositions were calcined to form a perovskite structure, ground to a fine powder, pressed into tablets and sintered to form dense ceramics. XRD analysis confirmed the formation of the perovskite phase. The electro-mechanical properties of the ceramics were evaluated. There were improvements in the low-field room temperature dielectric constant of 30% with 25% BNMN, 13% with 10% BNZ, and 16% with 2% BNCW. Higher concentrations of the additives degraded the dielectric performance. The conductivity of the BNT ceramics was reduced with very small concentrations (0.25 to 0.5%) of each of the additives. This reduction was maintained at the higher concentrations of the additives, which allowed for higher electric fields to be applied during both the poling process and the strain measurements. Improvements of approximately 30% in the d33 values were found at concentrations of 0.5% of each of the additives, but higher concentrations of the additives degraded the d33 values. The coercive field was affected by the additions to BNT. Increasing concentrations of BNMN reduced the coercive field in bipolar strain measurements. This was accompanied by a reduction in the remanent strain. Small additions (0.5 to 1.5%) of BNZ resulted in an increase in the coercive field by about 12%, followed by a 25% decrease at 5% BNZ. The remanent strain followed the same pattern. All concentrations of BNCW studied reduced the coercive field by about 12%. The remanent strain increased by 25% at 0.5% BNCW, and decreased by 42% at 2.5% BNCW. The electro-mechanical results for the BNMN and BNZ additives were compared to the behaviours of their lead-based counterparts, PMN and PZ. There was no consistent trend in the response of the electromechanical properties to the additions between the current lead-free and the lead-based systems. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2008-10-03 15:13:24.791

In this thesis, ferroelastic domain switching behaviour of lead zirconate titanate ceramics, as used in devices such as actuators, was studied. In particular, the effect of cyclic frequency and amplitude were assessed to develop a correlation between macrostructural changes and fatigue behaviour, both in the bulk and in crack-tip process zones. A variety of experimental methods were used. Raman scattering enabled the poling state of the ceramics can be determined. However, it could not distinguish between the different preferred orientations of in-plane c-domains. Conversely, neutron and X-ray diffraction technique can detect domain orientation distribution and the preferred direction of c-domains. In this study, neutron diffraction was used to probe domain switching behaviour in bulk samples while high spatial resolution X-rays were employed to analyse a switching zone near a crack tip. Under cyclic mechanical loading, domain switching and the accumulation of ferroelastic strain becomes saturated with increasing number of cycles. Moreover, time-dependent deformation was investigated. The results show that a domain forward-switching process occurs during creep deformation while a domain backward-switching process takes place during recovery. In addition, it was found that the frequency of applied stress affects the saturation of the ferroelastic strain while its magnitude has an influence on the level of strain accumulated. Under static mechanical loading, it was found that the size of the crack-tip zone where stress-induced domain switching occurs with increase in the stress intensity factor but the degree of domain switching around the crack tip changes only slightly. Under cyclic electrical loading, the results present a strong link between the frequency of the applied field, remnant polarisation, domain switching and the resultant crack growth. The results show that polarisation fatigue, the size of the switching zone, and the crack growth rate is greater at lower loading frequency. The quantitative analysis of the time dependent mechanism as well as the effect of loading frequency and amplitude on domain switching was achieved by applying viscoelastic models. Importantly, these models can be used to explain domain switching behaviour and domain wall movement under cyclic loading and link these processes to macroscopic deformation.