Ferroelectric and piezoelectric ceramic reinforced metal matrix composites are new materials being explored for vibration damping purposes. The high damping ability of ferroelectric and piezoelectric ceramics such as barium titanate (BaTiO3) and lead zirconate titanate (PZT) is due to the anelastic response of ferroelastic domain walls to applied external stress. In piezoelectric ceramics, vibration energy can also be dissipated through the direct piezoelectric effect if the appropriate electric circuit is connected across the ceramic. In this work we have examined the vibration damping behavior of BaTiO3, nickel-barium titanate (Ni-BaTiO3) composites and nickel-lead zirconate titanate (Ni-PZT) composites. BaTiO3 ceramics were fabricated by a combination of uniaxial pressing and cold isostatic pressing followed by sintering in air. Low frequency (0.1Hz-10Hz) damping capacity of BaTiO3, tanδ has been measured in three-point bend configuration on a dynamic mechanical analyzer. Tanδ has been found to increase with temperature up to the Curie temperature (Tc) of BaTiO3, after which there was a drop in damping capacity values due to the disappearance of ferroelectric domains above Tc. Furthermore within the frequency range tested, tanδ has been found to decrease with increasing vibration frequency. We also observed that tanδ decays with the number of vibration cycles (N). The decrease in tanδ with N, however, is fully recovered if BaTiO3 is heated above the Tc. Ni-BaTiO3 composite composed of a layer of BaTiO3 ceramic sandwiched between two layers of Ni were fabricated using a combination of electroless plating and electroforming. The damping behavior of the composite was analyzed in terms of the damping mechanisms below Tc and the damping mechanisms above Tc of BaTiO3. Below Tc, vibration damping ability of the composite was highly influenced by ferroelastic damping in the BaTiO3 component. Above the Curie temperature, the damping capacity was influence more by the inherent damping mechanisms in the nickel matrix. The damping mechanisms in Ni-PZT composites were evaluated at a low vibration frequency of 1Hz. In these composites we identified ferroelastic domain wall motion as the main damping mechanism active below the Tc of PZT. Using a poled PZT ceramic enhanced the damping capacity of the composite because of favorable ferroelastic domain orientation in the direction of applied stress. Based on our experimental results, we found no evidence of a direct piezoelectric damping mechanism in the Ni-PZT composites. / Ph. D.

Ferroelectric-reinforced metal matrix composites (FR-MMCs) show promise as high damping materials for structural applications. Most structural materials are valued based on their stiffness and strength; however, stiff materials typically have limited inherent ability to dampen mechanical or acoustic vibrations. The addition of ferroelectric ceramic particles may also augment the strength of the matrix, creating a multifunctional composite. In this work, the damping behavior of FR-MMCs created by the addition of barium titanate (BaTiO3) discontinuous reinforcement in a bearing bronze (Cu-10w%Sn) matrix has been studied. It has been shown that even when combined with other traditional composite mechanisms, added damping ability has been achieved due to the ferroelectric nature of the reinforcement. FR-MMCs currently represent a material system capable of exhibiting increased damping ability, as compared to the structural metal matrix alone. / Master of Science

Metal matrix composites offer unique opportunities for achieving multi-functionality in materials. In an attempt to investigate the possibility of enhancing damping characteristics of structural metals, copper was reinforced with tetragonal ferroelectric BaTiO3 particulates (Cu-BaTiO3 composites) using powder metallurgy techniques. The effect of particulate size and three processing conditions, sintering atmosphere, cooling rate and, uniaxial compaction pressure on the tetragonality and hence the ferroelectric properties of barium titanate powder were investigated using differential scanning calorimetry (DSC) and x-ray diffraction (XRD). The results show that sintering atmosphere and cooling rates have little effect on the tetragonality of barium titanate powder. Tetragonality of barium titanate powder decreased gradually with decreasing particle size. The decrease in tetragonality with decreasing particle size, however, was only severe in the very fine powders. Although no direct relationship was found between uniaxial compaction pressure and tetragonality, uniaxial pressure may also decrease the tetragonality of barium titanate. Three Cu-BaTiO3 composites, D1, D2 and D3 reinforced with 40vol% barium titanate particles of average sizes 209μm, 66μm and 2μm were respectively fabricated. The retention of the ferroelectric tetragonal phase of barium titanate after composite processing was confirmed by DSC. Composite microstructures observed using optical and scanning electron microscopy revealed uniform dispersions of barium titanate particles in D1 and D2. In D3, the barium titanate formed a chain-like structure because of extensive agglomeration of the fine reinforcement particles. Damping characteristics of the composites were evaluated between 25oC and 165oC at a frequency of 1Hz using dynamic mechanical analysis (DMA). The relative damping capacities (tanδ) in the composites were higher than the unreinforced metal. The damping capacity of composites D1 and D2 was also found to be dependent on temperature. Damping capacity was high from room temperature up to the Curie point of barium titanate, after which there was a slight drop in damping values probably due to a loss in ferroelectric properties. The small drop in damping values recorded in excess of the Curie temperature is an indication that ferroelectricity contributes little to the overall damping capacity of the Cu-BaTiO3 composites. This results from either a reduced ferroelectric damping in barium titanate particles or, poor stress transfer from matrix to reinforcement because of the weak and porous copper-barium titanate interface. / Master of Science

Foi desenvolvido um novo método para a determinação da polarização ferroelétrica de polímeros ferroelétricos, em particular do PVDF estirado biaxialmente. A técnica consiste em manter constante a corrente através da amostra e medir a evolução da tensão (V versus t) entre os eletrodos da mesma. As medidas foram realizadas em ambiente com atmosfera de ar superseco o que permite desprezar a condução elétrica das amostras, simplificando sobremaneira as equações do problema. Considera-se a existência de dois tipos de polarização: a ferroelétrica, com tempo de chavamento desprezível, e uma polarização elétrica foram realizados em duas situações distintas: com chaveamento e sem chaveamento ferroelétrico. O procedimento permite avaliar a dependência da polarização ferroelétrica com o campo, determinada a partir da equação geral da corrente. Para se descrever a resposta da polarização elétrica dependente do tempo, usa-se o princípio da superposição e assume-se que ela está em fase com o campo elétrico aplicado (processo lento). Será mostrado que é possível determinar a polarização ferroelétrica do polímero PVDF estirado biaxialmente sem a necessidade de determinar a formas funcionais da polarização dependente do tempo e de se conhecer o valor da capacitância da amostra. / In this work a novel method was developed for the determination of the ferroelectric polarization of ferroelectric polymers, in particular of biaxially stretched PVDF. The technique consists of maintaining constant the current through the sample and to measure the evolution of the bias voltage (V versus t) on the electrodes. Measurements were performed in super-dry air, which allows one to neglect the electric surface and volumetric conduction of the samples, simplifying the equations of the problem. It is considered the existence of two polarization types: the ferroelectric, with a very short switching time, and a another polarization dependent of the time. The processes for studying the electric polarization were accomplished in two different situations: with switching and without ferroelectric switching. The procedure allows evaluating the dependence of the ferroelectric polarization on the electric field, determined starting from the general equation of the current. To describe the time dependent polarization it is used the principle of superposition and the polarization value assumed to be in phase with the applied electric field (slow process). It will be shown that it is possible to determine the ferroelectric polarization of the material without the need of the functional form of the polarization and the value of the capacitance of the sample.

Perovskite-like layered structured (PLS) compounds display a range of interesting physical and chemical properties, including photocatalysis, photoluminescence, ion conductivity, electrochemical stability, magnetic properties, ferroelectricity and piezoelectricity. There are mainly three homologous series of PLS compounds distinguished by their different BO6 octahedra orientation: the Dion-Jacobson phase (A'An-1BnO3n+1); the AnBnO3n+2 phase; and the hexagonal phase (AnBn-1O3n). Some of the 4-layer AnBnO3n+2 compounds, like La2Ti2O7 and Sr2Nb2O7, have been reported to be ferroelectrics with super high Curie point (above 1300 °C), but no ferroelectric properties have been reported for the 2-layer and 3-layer AnBnO3n+2 compounds, and also there are few reports on the ferroelectric properties of compounds with Dion-Jacobson structure and hexagonal structure. Consequently, in this work, the crystallographic structures, microstructures, dielectric, ferroelectric and piezoelectric properties of (AxLa1-x)Ti2O7 (A = Sm and Eu) solid solutions with 4-layer AnBnO3n+2 structure, Pr3Ti2TaO11 with 3-layer AnBnO3n+2 structure, LaTaO4 with 2-layer AnBnO3n+2 structure, ABiNb2O7 (A = Rb and Cs) with Dion-Jacobson structure and Sr6TiNb4O18 with hexagonal structure were studied. Spark plasma sintering (SPS) was used to sinter ceramics with high density and preferred orientation. X-ray diffraction refinement (XRD) and transmission electron microscopy (TEM) were used to study the crystallographic structures and microstructures of the layer structured compounds. The ferroelectricity was studied using the current-electric field and polarization-electric field hysteresis loops. The Curie point and phase transitions were studied using the temperature dependence of the dielectric constant and loss. Piezoresponse force microscopy (PFM) was also used to study the ferroelectric domain structure of some layer structured compounds. In the first part of this work, the piezoelectric constant of La2Ti2O7 was improved by doping Sm. The crystallographic structure of (Eu1-xLax) 2Ti2O7 and (Sm1-xLax) 2Ti2O7 solid solutions were well studied. (AxLa1-x)Ti2O7 solid solutions were isomorphous with La2Ti2O7 when x was less than 0.5 for (EuxLa1-x)Ti2O7 and 0.8 for (SmxLa1-x)Ti2O7. When x was above their solubility limit, a biphase was observed. The XRD and Raman data suggested that the biphase consisted of (AxLa1-x)2Ti2O7 perovskite-like layered structure and pure Sm2Ti2O7 pyrochlore structure. Ferroelectric domain switching was observed in the I-E and P-E hysteresis loops for textured (SmxLa1-x)Ti2O7 (x < 0.2). The highest d33 was 2.8 pC/N for (Sm0.1La0.9)Ti2O7. In the second part, The Pr3Ti2TaO11 compound was demonstrated to have a 3-layer type II AnBnO3n+2 PLS structure belonging to space group Pmc21 with unit cell parameters a = 3.8689(3) Å, b = 20.389(2) Å, c = 5.5046(5) Å, and its ferroelectric properties were investigated. Analysis of the XRD and TEM results showed that Pr3Ti2TaO11 ceramics have an n = 3 (type II) heteroblock structure consisting of alternating n = 2 and n = 4 octahedral oxide layers. High resolution electron microscopy revealed the layered structure to be highly disordered, with faulting of the heteroblock structure and the coexistence of a n = 4 phase on a fine scale (nm), which was evident as a broadening of the XRD peaks of the ceramics. Pr3Ti2TaO11 ceramic exhibits a super-high Curie point (1415±5 °C). A small, but measurable piezoelectric constant d33 between 0.1 and 0.2 pC/N was detected for the samples poled above 900 °C under an electric field of 100~200 V/cm. Pure LaTaO4 powders with orthorhombic phase were be prepared by co-precipitation method. The orthorhombic LaTaO4 powders have a 2-layer perovskite-like layered structure with space group A21am, which was refined using Rietveld method. The single phase O-LaTaO4 ceramic was prepared using SPS with a slow cooling rate (20 °C/min). A d33 of 0.3 pC/N was obtained from the electric field induced orthorhombic phase. In the second part of this work, the ferroelectricity and piezoelectricity of CsBiNb2O7 with Dion-Jacobson type PLS structure was successfully demonstrated for the first time. The ferroelectricity and piezoelectricity of RbBiNb2O7, which have similar structure with CsBiNb2O7, were also fully studied. Highly textured 2-layer Dion-Jacobson ceramics ABiNb2O7 (A = Rb and Cs) were prepared by one-step SPS. High resolution TEM showed well ordered (0 0 1) lattice planes. Striped ferroelectric domains were observed using PFM. The ferroelectricity and piezoelectricity of CsBiNb2O7 has been demonstrated for the first time. The Tc of RbBiNb2O7 and CsBiNb2O7 are 1098±5 and 1033±5 °C, respectively. The piezoelectric constant of RbBiNb2O7 and CsBiNb2O7 were approximately 5 and 8 pC/N. Thermal depoling studies confirmed the Curie point and the stability of the piezoelectricity. Sr6Nb4TiO18 ceramics with non-centrosymmetric structure were successfully prepared, but no obvious evidence was found to prove its ferroelectricity. The untextured and textured 6-layer Hexagonal compound Sr6Nb4TiO18 was prepared by solid state reaction and spark plasma sintering. Its Curie point was found to be greater than 1500 °C. No ferroelectric properties were observed by studying of I-E and P-E loops, and no d33 was observed after poling.

Leang Po Shan = 利用飛行時間散射反衝符號測量譜儀研究LiTaO3(001)單晶之表面電荷動態特性 / 梁寶珊. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 50-51). / Text in English; abstracts in English and Chinese. / Leang Po Shan = Li yong fei xing shi jian san she fan chong fu hao ce liang pu yi yan jiu LiTaO3(001) dan jing zhi biao mian dian he dong tai te xing / Liang Baoshan. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Ferroelectricity and pyroelectricity of LiTαO3 --- p.1 / Chapter 1.2 --- Surface Studies of Ferroelectrics --- p.5 / Chapter 1.2.1 --- Size Effect and Importantce of Surface Properties --- p.5 / Chapter 1.2.2 --- General Difficulties in Surface Studies of Ferroelectrics --- p.5 / Chapter 1.2.3 --- Applicability of TOF-SARS in the Analysis of Ferro- electrics --- p.6 / Chapter 1.3 --- Surface Charge Dynamics on Ferroelectrics --- p.7 / Chapter 1.3.1 --- Surface Charge Screening of Spontaneous Polarization --- p.7 / Chapter 1.3.2 --- Discharge of Excessive Surface Charge --- p.7 / Chapter 1.4 --- Objectives of the Thesis Work: TOF-SARS Study of Surface Charge Dynamics of LiTαO3 --- p.11 / Chapter 2 --- Ion-Surface Interaction --- p.13 / Chapter 3 --- Time-of-Flight (TOF) Ion Scattering and Recoiling Spectrom- eter --- p.17 / Chapter 3.1 --- TOF Ion Scattering and Recoiling Spectrometer --- p.18 / Chapter 3.2 --- Ion Column --- p.19 / Chapter 3.2.1 --- Ion Source --- p.19 / Chapter 3.2.2 --- Pulsing System --- p.19 / Chapter 3.2.3 --- ExB Wien Filter Mass Analyzer --- p.20 / Chapter 3.2.4 --- Einzel Lens --- p.20 / Chapter 3.2.5 --- Neutral Beam Trap --- p.20 / Chapter 3.2.6 --- Vacuum Chamber and Manipulator --- p.20 / Chapter 3.3 --- Variable Angle Detector --- p.23 / Chapter 3.3.1 --- Setup --- p.23 / Chapter 3.3.2 --- Beam Alignment --- p.24 / Chapter 4 --- Results and Analysis --- p.25 / Chapter 5 --- Study of Charge Relaxation Process --- p.35 / Chapter 5.1 --- Derivation of Surface Electric Potential --- p.35 / Chapter 5.2 --- Data Analysis --- p.40 / Chapter 6 --- Conclusion --- p.49 / Bibliography --- p.50

Ce manuscrit présente la synthèse de nouveaux réseaux hybrides organiques/inorganiques à base de différents ligands imidazoliums. Trois ligands imidazoliums possédant chacun des caractéristiques spécifiques ont été synthétisés et utilisés avec l’objectif de parvenir à la formation de réseaux hybrides multiferroïques c’est-à-dire des réseaux qui possède à la fois un ordre magnétique et un ordre électrique. La modification du ligand a ainsi permis d’obtenir des composés répondant aux critères (de symétrie en particulier) à remplir pour la présence d’un ordre électrique. Pour construire le réseau inorganique magnétique nous avons travaillé sur la synthèse de composés à base de métaux de transition de la première série ou de lanthanides. L’ensemble des composés obtenus a été caractérisé par un ensemble de techniques (diffraction des rayons X, spectroscopie FTIR et UV-Vis, analyses thermiques et élémentaires). Les propriétés magnétiques, de luminescence et de ferroélectricité des composés ont aussi été étudiées. / This thesis presents the syntheses of new hybrid coordination networks based on imidazolium ligands. Three kinds of ligands possessing their own features were synthesized and used with the main objective to obtain multiferroic hybrid networks meaning networks which display a magnetic order and a ferroelectric order. The modification of the ligand allowed to obtain compounds filling criteria (on the symmetry) for a ferroelectric order. The magnetic inorganic network was built due to the synthesis of compounds based on first row metals or lanthanides. All compounds were characterized by several techniques (X-rays diffraction, spectroscopic measurements, thermal and elemental analyses). Magnetic, luminescence and ferroelectric properties were also studied.

Nanoscale ferroelectric materials have numerous possible applications such as actively tunable photonic crystals, terahertz emitters, ultrasound transducers, and energy harvesters. One of most technologically relevant ferroelectric materials is lead zirconate titanate (PZT) due to its large piezoelectric response. However, there are limited methods currently available for creating nanoscale PZT structures. Current top-down patterning methods include material removal via a high energy beam, which damages the piezoelectric's properties, and wet etching, which is an isotropic process that results in poor edge definition. Similarly, current bottom-up approaches such as hard template-growth and hydrothermal processing have limited control over the aspect ratio of the structures produced and lack site specific registry. In this work, a bottom-up approach for creating PbZr₀.₅₂Ti₀.₄₈O₃ nanotubes was developed using soft-template infiltration by a sol-gel solution. This method allows excellent control of the structures produced, overcoming current manufacturing limitations. PZT nanotubes were fabricated with diameters ranging from 100 to 200 nm, aspect ratios (height to diameter) from 1.25:1 to 5:1, and wall thicknesses from 5 to 25 nm. The piezoelectric and ferroelectric nature of the nanotubes was characterized via scanning probe microscopy in order to investigate nanoscale phenomena. Specifically, the effects of lateral constraint, substrate clamping, and critical size on the extrinsic contribution to the piezoelectric response were studied and the results are discussed.

Ferroelectric and ferromagnetic alloy clusters are produced and studied in molecular beams. Nb clusters doped with 1-3 impurity atoms are ferroelectric with low transition temperatures. The alloy clusters with an even number of valence electrons have larger dipole moments than those with odd number of valence electrons. The ferroelectricity is suppressed by magnetic impurities or thermal excitations, and is enhanced by Au and Al doping. The observations strongly suggest that electron-pairing interactions exist in Nb clusters, which indicates Cooper pairing in clusters. The magnetic moments of Co clusters doped with small fraction of Mn,V and Al are studied and compared with those of the bulk alloys. CoMn alloy clusters have enhanced average magnetic moments with Mn doping, which is opposite to the behavior of bulk CoMn. CoV and CoAl alloy clusters behave similarly to their bulk counterparts. We explain the experimental results using the virtual-bound-state model. Finally, the magnetic properties of BiMn clusters are studied in molecular beams. The Mn local moments are found to couple ferromagnetically or ferrimagnetically depending on the composition of the clusters.

Electron emission from ferroelectrics (FEE) is a promising source for electrons. Although extensive studies have shown that the emission is inititated by a variation of the spontaneous polarization, the exact underlying emission process remained unclear to date. The focus of this work is to analyze and improve the electron emission process from ferroelectric materials. To achieve low operation voltages thin films and low coercive voltage ferroelectric relaxor single crystals were used. The emission was measured under ultrahigh vacuum (UHV) conditions with a single electron detector. The ferroelectric thin films were prepared with a structured top electrode, with nanometer-sized regularly arranged apertures. The emission from lead zirconate titanate (PZT) thin films was achieved at excitation voltages as low as 10 V. The voltage dependent polarization state within the emission apertures of PZT was imaged using piezoresponse force microscopy (PFM). The PFM measurements revealed that an increased fraction of the free surface area is switched by an increased applied voltage. Additional, as a thin film electron emitter, bismuth ferrite (BFO) films were investigated. Ferroelectric relaxor lead magnesium niobate - lead titanate (PMN-PT) was used as single crystal electron emitter due to its low coercive field. The time-dependent electron emission process from PMN-PT was clarified with the help of exciting voltage pulses of variable duration. It is demonstrated that FEE from PMN-PT can be described in the framework of a random field model for relaxors, with the measured electron flux correlating with the amount of reversed polarization. The time-resolved analysis gives insight into the polarization switching and screening processes within PMN-PT. The local electron emission from PMN-PT single crystals has been investigated, in the nanometer regime, with the help of an AFM tip serving as an electron detector. Additionally, the influence of the aperture size in the top electrode on the emission has been investigated. It is found that the electron emission is strongly influenced by the electric field distribution in the aperture. An optimum aperture width for electron emission from PMN-PT, which is much smaller than the apertures used so far, was found. Comparative investigations of the electron emission process from relaxors with barium titanate showed that the emission from PMN-PT is much more complex than the emission from a conventional ferroelectric. General conclusions on the future applications of FEE can be drawn.