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One significant application of donor doped barium titanate (BaTiO3) is in the manufacture of Positive Temperature Coefficient of Resistance (PTCR) thermistors. Combined synthesis, phase diagram and electrical studies were undertaken on donor doped barium titanate with a view to understanding the factors responsible for PTCR phenomena. A range of materials, both commercial PTCR devices and in-house lanthanum-doped barium titanate samples, have been studied. All three commercial PTCR samples measured were found to be electrically inhomogeneous with two PTCR-exhibiting regions and a conductive grain core. The conductive core resistance had a characteristic temperature dependence, with a minimum occurring in the vicinity of the tetragonal to cubic phase transition (Tc) of barium titanate. The phase relations and electrical behaviour of two joins in the lanthanum-doped BaTiO3 system, join A (Ba4-4xLa4xTi4-xO12) and join B (Ba1-yLayTiO3+), were also studied. Compositions on joins A and B for 0x0.195 and 0y0.1 respectively, crystallised as single phase barium titanate. Charge compensation on both joins (at these concentrations) was achieved by a mixture of both titanium vacancies and free electrons. The electron compensation mechanism, Ba_1-yLa_yTi. 4+_1-yTi. 3+O_3, significantly complicates determination of phase relations in this system, since it occurs off the BaO-TiO_2-La_2O_3 ternary phase diagram. Ac impedance measurements indicated that samples on join A were electrically inhomogeneous resulting in the presence of different regions with variable Tx values; furthermore, the phase transitions in each region were themselves complex. The tetragonal to cubic phase transition was studied by a combination of x-ray diffraction, ac impedance and by varying dopant concentration. The resulting behaviour was complex, with both first order and continuous transitions occurring. There was also evidence of a two phase, (i.e. both cubic and tetragonal barium titanate) region associated with a distribution in particle size: small particles (&60 2m) were cubic; larger ones were tetragonal. It is apparent that the combined, complicating effects of grain size and segregation phenomena make it inappropriate to give an explanation for the phase relations and electrical behaviour of lanthanum-doped barium titanate in terms of classical phase equilibria and phase transition theories.

Donor doped barium titanate ceramics are well known for their Positive Temperature Coefficient of Resistance (PTCR) characteristic above the crystallographic transition temperature, T° '130°C, where the material changes from the ferroelectric state to paraelectric. The shape and magnitude of the PTCR characteristic are known to be dependent on the composition and preparation of the ceramic, the presence of impurities, particularly donor dopant concentration and acceptor ions, and the sintering conditions. Thirty years ago Heywang proposed a model based on the presence of two-dimensional resistive grain boundary layers consisting of discrete electron traps located in energy between the conduction and valence bands, to explain the PTCR effect. Donor doped barium titanate samples were prepared in a number of different ways: the variation of donor concentration, the addition of impurity acceptor ions, reduction of the sintering temperature and variation of the sintering atmosphere. These samples were investigated by examining their microstructure and their electric and dielectric properties, both at room temperature and above the transition. Theoretical analysis of the experimental results, based on the Heywang model, was then performed to investigate the effects of preparation on the grain boundary layer characteristics. Resistivity - temperature measurements were carried out to find the effect of composition and sintering conditions on the PTCR characteristic and capacitance - temperature measurements demonstrated the effects of donor and acceptor incorporation on the dielectric properties of barium titanate. Grain boundary and grain bulk resistance were separated by means of a. c. impedance methods at room temperature, where the effects of composition and sintering on each were observed. Finally, current - voltage measurements between TT and the resistivity maximum were made for samples containing different donor concentrations, to examine the current conduction mechanism. Detailed analysis of the electric and dielectric measurements permitted the effects of composition and sintering on the grain boundary layer characteristics to be determined. Acceptor state densities were estimated using the resistivity - temperature measurements and capacitance - temperature results, between TT and the resistivity maximum. Resistivity - temperature measurements above the maximum enabled acceptor energies to be estimated. Analysis of the dielectric properties showed that neither the composition nor sintering atmosphere affected the dielectric properties of the grain boundary layers, which were found to obey the Curie-Weiss law above the transition temperature in the same way as the grain bulk. The observed effects of the changes in the preparative conditions to the electric and dielectric properties were explained in terms of the Heywang model and microstructural development, resulting from modifications to the grain boundary layers. The conduction mechanism was examined by means of current - voltage measurements above the transition temperature and below the resistivity maximum. In contrast to the prediction of Heywang. this was found to be predominantly diffusion limited.

Nous explorons la variété des types d'interactions électrostatiques entre les charges dans des films minces à haute permittivité diélectrique, en analysant le cas particulier de l'interaction de Coulomb bidimensionnel logarithmique. Pour ce système, nous proposons une méthode de réglage du régime d'interaction à l'aide de l'électrode externe. Nous étudions ensuite les électrostatiques des charges étendues dans les matériaux diélectriques: des fils et des bandes chargés de manière homogène ou périodique. En s'appuyant sur les potentiels électrostatiques calculés de ces objets, nous abordons plusieurs applications possibles. Tout d'abord, nous suggérons la méthode non destructive pour mesurer la constante diélectrique des films minces déposés par un substrat par un condensateur à deux fils. Ensuite, nous étudions la formation des domaines dans des films ferroélectriques avec la polarisation dans le plan. L'apparition de la texture en domaines est causée soit par le bord chargé d'un échantillon de taille finie, soit par l'existence d'une paroi de domaine chargé dans le film. Les deux phénomènes augmentent l'énergie électrostatique de l'échantillon, ce qui stimule l'apparence des domaines pour minimiser l'énergie totale. Nous montrons que la taille équilibre du domaine dépend de la géométrie de l'échantillon et, pour les domaines dans le plan, elle viole la loi racine carrée de Kittel, étant inversement proportionnelle à l'épaisseur du film / We explore the various types of electrostatic interaction between charges in thin films with high dielectric permittivity, including the special case of the two-dimensional logarithmic Coulomb interaction, and propose a method of tuning the interaction regime using the external gate electrode. Changing the gate-to-film distance, one may alter the electrostatic screening length of the dielectric sample and control the ranges of different interaction types. We investigate next the electrostatics of extended charges in dielectric media, modeling the electrostatic potential distribution for charged wires, stripes and domain walls, with either homogeneous or periodic linear charge density. Basing on the calculated dependencies of the potential on the system geometry and material parameters, we discuss several possible applications: i ) we suggest the non-destructive method for measuring the dielectric constant of substrate deposited thin films by a two-wire capacitor; ii ) we study the domain structure formation in ferroelectric films with in-plane polarization. We show that for the in-plane striped 180˚ domain structure, induced by the discontinuity of the order parameter at the film edge, the equilibrium domain width violates the Kittel's square root law, being instead inversely proportional to the film thickness. The calculations for the in-plane domains, generated by the microscope tip or charged domain wall in the ferroelectric slab, demonstrate the conformity of the optimal domain length to the characteristic electrostatic length of the sample, and accord with the experimental data

Xu Chicheng = 光折变掺铁铌酸锂晶体中的二波耦合和光伏空间孤子 / 徐赤诚. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 113-114). / Text in English; abstracts in English and Chinese. / Xu Chicheng = guang zhe bian shan tie ni suan li jing ti zhong de er bo ou he he guang fu kong jian gu zi / Xu Chicheng. / Acknowledgements --- p.i / Abstract --- p.ii / Table of Contents --- p.v / Chapter Chapter 1 --- Introduction --- p.1 / Chapter Chapter 2 --- Background --- p.5 / Chapter 2.1 --- Band Transport Model --- p.5 / Chapter 2.2 --- Two-wave Mixing --- p.9 / Chapter 2.3 --- Fanning --- p.12 / Chapter 2.4 --- Photovoltaic Effect --- p.16 / Chapter 2.5 --- Spatial Solitons --- p.19 / References --- p.22 / Appendix Refractive Index perturbation in LiNb03 crystal --- p.25 / Chapter Chapter 3 --- Single Laser Beam Interactions with Fe:LiNb03 Crystals / Chapter 3.1 --- Fe:LiNb03 Crystals --- p.30 / Chapter 3.2 --- Interferometric Studies of Refractive Index Perturbations --- p.32 / Chapter 3.3 --- Fanning --- p.47 / Chapter 3.4 --- Self-defocusing --- p.53 / Chapter 3.5 --- Surface Charge Recombination --- p.58 / References --- p.67 / Chapter Chapter 4 --- Photovoltaic Spatial Soliton in Fe:LiNb03 Crystal --- p.69 / Chapter 4.1 --- Introduction --- p.69 / Chapter 4.2 --- Experimental Setup --- p.73 / Chapter 4.3 --- Results and Discussion --- p.75 / Chapter 4.4 --- Conclusion --- p.82 / References --- p.83 / Chapter Chapter 5 --- Two-wave Mixing in Fe:LiNbO3 Crystals --- p.84 / Chapter 5.1 --- Introduction --- p.84 / Chapter 5.2 --- Experimental Setup --- p.87 / Chapter 5.3 --- Results and Discussion I - Without Background Beam --- p.89 / Chapter 5.4 --- Result and Discussion II - With Background Beam --- p.96 / Chapter 5.5 --- Origin of Temporal oscillations during TWM in Fe:LiNb03 Crystal --- p.100 / Chapter 5.6 --- Conclusion --- p.108 / References --- p.109 / Chapter Chapter 6 --- Conclusion and Future Outlook --- p.111

"March 2002." / The numerals in title are subscript. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Made available in DSpace on 2014-06-11T19:31:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-04-17Bitstream added on 2014-06-13T19:40:52Z : No. of bitstreams: 1 guarany_ca_dr_bauru.pdf: 3222268 bytes, checksum: 6e2051c16073f3ad22fc2a82421a6a90 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O Sistema ferroelétrico Pb'Z IND. 1-x''Ti IND. x''O IND. 3'(PZT) vem sendo amplamente estudado devido a interessantes propriedades físicas para composições próximas ao contorno de fase morfotrópico (CFM). No PZT o CFM se encontra em composições próximas a x = 0,50 no diagrama de fases, e separa a fase tetragonal da monoclínica. Nesta região é onde o PZT exibe elevado coeficiente eletromecânico. Comportamento e características similares também são exibidos no sistema 'Pb('Mg IND. 1/3''Nb IND. 2/3''O IND. 3) IND. (1-x)'Ti IND. x''O IND. 3' (PMN-PT), com propriedades eletromecânicas uma ordem de magnitude superior ao das cerâmicas de PZT. Desde a descoberta de uma fase ferroelétrica monoclínica nas proximidades do CFM para sistemas PZT e PMN-PT, estes ferroelétricos vem atraindo a atenção de diversos pesquisadores na tentativa de compreender a relação entre as características estruturais e as propriedades piezelétricas. Além disso, a descoberta de uma transição de fase estrutural induzida pela aplicação de um campo elétrico externo no PMN-PT realça o importante papel da fase intermediária monoclínica na alta resposta eletromecânica destes materiais. Nesta tese, transições de fases estruturais nos sistemas PZT e PMN-PT foram investigadas utilizando a técnica de espectroscopia de infravermelho em função da temperatura. Os estudos em função da temperatura foram centrados nos modos 'v IND. 1'-stretching, dos octaedros 'BO IND. 6' na estrutura 'AB IND. 3', e nas correspondentes larguras a meia altura 'W IND. i' para os sistemas PZT e PMN-PT. A ocorrência de anomalias no modo 'v IND. 1'-stretching foi associada à transição de fase estrutural. Um estudo suplementar, da influência de campos elétricos contínuos e alternados, nas propriedades dielétricas em função da temperatura para cerâmicas de PMN-35PT foi conduzido utilizando espectroscopia de impedância. / The Pb'Z IND. 1-x''Ti IND. x''O IND. 3'(PZT) ferroelectric system has been extensively studied because of its interesting physical proprieties close to the morphotropic phase boundary (MPB), the nearly vertical phase boundary between the tretragonal and monoclinic regions of the phase diagram to x = 0.50, where the material exhibits outstanding electromechanical proprieties. Similar behavior and features are also present in 'Pb('Mg IND. 1/3''Nb IND. 2/3''O IND. 3) IND. (1-x)'Ti IND. x''O IND. 3' (PMN-PT), with electromechanical proprieties sometimes one order of magnitude large than PZT ceramics. Since the discovery of a ferroelectric monoclinic phase in the PZT and PMN-PT system, for composition close to MPB that was not predicted on the original phase diagram, these ferroelectrics attained the attention of several researches due to the possibility of understanding the relatonship between structural features and piezoelectric properties. Moreover, interesting electric field induced phase transitions were discovered in PMN-PT highlighting the important role of the intermediate monoclinic phase for high electromechanical response of this material. In this thesis, structural phase transition was PZT and PMN-PT system were investigated by infrared spectroscopy as a function of temperature. Studies were centered on monitoring the behavior of the 'v IND. 1'-stretching modes and corresponding half width 'W IND. i' as a function of temperature in 'BO IND. 6' octahedron in 'AB IND. 3' structure of the PZT and PMN-PT. The occurrences of the anomalies in the 'v IND. 1'-stretching modes were associated to a structural phase transition. Additional temperature dependence of dielectric properties for PMN-0.35PT ceramics under different dc bias and ac driving electric fields were investigated by impedance spectroscopy.

ABSTRACT In this study, the rf magnetron sputtering was used to deposit (Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 (BSTZ) ferroelectric thin films on SiO2/Si substrates, and MFIS structure was also fabricated. The effects of various sputtering parameters effects on the characteristics of BSTZ thin films, such as the oxygen concentrations, deposition temperature, rf power, chamber pressure and deposition time were be discussed. As deposited on Pt/Ti/SiO2/Si substrate, the electrical and physical properties of BSTZ thin films after RTA and CTA thermal treatment were be also discussed. In XRD and SEM analysis, the crystal structure and grain size of as-deposited BSTZ thin film could be observed. From the C-V and J-E curves obtained, the memory window and leakage current density of MFIS structure were about 9.5V and 2.76¡Ñ 10-9 A/cm2, respectively. After RTA and CTA post-treatment, the capacitances of MFM structure were about 2.06nF and 1.93nF. We found that dielectric constant of as-deposited BSTZ thin film increased to 183 and 194, respectively. In addition, the leakage current density of RTA and CTA treated BSTZ films were about 3.82¡Ñ 10-6 A/cm2 and 1.16¡Ñ 10-6 A/cm2. Finally, the one-transistor-capacitor (1TC) structure of ferroelectric random access memory (FeRAM) with the gate oxide of BSTZ thin films on the polysilicon TFT structure have been fabricated and investigated.From the experimental results, the on/off drain current ratio is two orders, and its value is much smaller than those of the most reported bottom-gated TFTs devices by using different ferroelectric materials as gate oxide. From these results in this study, the BSTZ thin films for top-gate polysilicon thin-film transistor will be an excellent candidate to fabricate higher storage capacitance ferroelectric random access memory (FeRAM) devices for system on panel (SOP) applications.