Metal oxides crystallized in perovskite structure are generally modified in two different ways. According to the general structural formula ABO3, the two ways are A-site modification and B-site modification. The primary significance of perovskite metal oxides rests on their importance in electronic devices. A particular class of perovskites, namely Lead Zirconate or modified Lead Zirconate has received a special attention because of their unique antiferroelectricity and various applications in devices. Among the other modifications, A-site modification of PbZrO3 by La is rare and not much explored. Chapter 1 describes various applications of antiferroelectric thin films along with the synthesis and characterization of pure and La modified PbZrO3, which are relevant to the work presented in this thesis. Sol-gel processing and spin coating technique to deposit solid oxide thin films are well known for their low cost of deposition as well as for their ability to achieve better stoichiometric chemical composition. Common crack formation problem of sol-gel grown films can be prevented by ‘drying control chemical adhesive’ like polyvinylpyrrolidone (PVP). Heat treatment of sol-gel derived thin films is generally determined by TGA and DTA. Crystalline phase of deposited solid thin films is determined by XRD whereas effect of modification can be ascertained by XRD peak assignment and relative crystalline peak shifting. Sol-gel grown film thickness is measured by common cross sectional SEM whereas AFM can detail the surface morphology. Chapter 2 summarizes the deposition and characterization of pure and La modified PbZrO3 thin films. Any nonmetal, which is insulator, is dielectric material and show dielectric dispersion in a frequency domain of low field alternative current. Among the most common feature of dielectric dispersion, Maxwell – Wagner type dispersion is well known. Similar kind of dielectric dispersion, named Maxwell – Wagner like dispersion, can be observed while the equivalent circuit consists of parallel G – C along with a series R. Universal power law of ac conductivity is the deciding factor to distinguish the nature of dispersion. Structural phase transition can be determined by dielectric response and it is widely known as dielectric phase transition. Effect of La modification on dielectric phase transition of PbZrO3 thin films depends on stabilization or destabilization of antiferroelectricity. Maximum dielectric constants of pure and modified PbZrO3 thin films depend on the crystallographic orientations of the growth. Chapter 3 presents dielectric properties of pure and La modified PbZrO3 thin films and these properties are correlated to the stabilization or destabilization of antiferroelectricity, relative integrated intensity of (202)O film orientation and trapped electron charge due to oxygen vacancies. Charge storage property of a capacitor is determined by the polarization of the capacitor on application of electric field whereas field dependent integrated area of polarization on withdrawal of electric field determines the recoverable capacitive energy storage. Among the three kinds of capacitors like linear or paraelectric, ferroelectric and antiferroelectric capacitors, antiferroelectric capacitor is known to be best for their ability to store huge amount of recoverable energy. The recoverable energy in antiferroelectrics can be increased by increasing squareness of the P – E hysteresis loop, applicable electric field, polarization or by the all possible combinations of them. Chapter 4 describes the correlation of relative integrated intensity of (202)O [RI(202)O] with critical applied electric field of P – E saturation to provide enhanced squareness of the hysteresis loops. This chapter also describes the variation of charge and recoverable energy storage properties with respect to RI(202)O. Like magnetocaloric effect, electrocaloric effect is capable to alter the temperature of a system by adiabatic polarization or depolarization. From the Maxwell’s relation of thermodynamics, assuming, (∂p ) = (∂s )electrocaloric effect can be calculated from temperature dependent polarization value of a paraelectric, ferroelectric or an antiferroelectric. Chapter 5 presents the electrocaloric effect of pure and La modified PbZrO3 thin films. Summary of present study and discussion have been delineated in Chapter 6 along with the future work which can give more insight into the understanding of antiferroelectric PbZrO3 thin films with respect to Pb and Zr site modification and with respect to different electrodes. (For formulas pl see the pdf file of the thesis)

Les matériaux ferroélectriques non-linéaires à faibles pertes diélectriques présentent une permittivité ajustable sous champ électrique qui les destine à des applications de composants agiles hyperfréquences pour la microélectronique et les télécommunications (condensateurs et résonateurs accordables, déphaseurs, ...). Les performances requises - pertes diélectriques faibles, permittivité modérée, accordabilité maximale, stabilité thermique jusqu'aux hyperfréquences - imposent d'améliorer le matériau de base Ba0.6Sr0.4TiO3 (BST). Les céramiques élaborées à partir de BST et d'une phase à faibles pertes non-ferroélectrique telle MgO, MgTiO3, mais aussi les compositions inédites avec SnO2 et BaSnO3, sont caractérisées par des analyses physico-chimiques et électriques. Afin de réduire de manière significative les pertes diélectriques, de nouveaux composites à architecture contrôlée (coeur/écorce notamment BST@SiO2) sont développés par des procédés innovants de synthèse en chimie douce. Les essais de faisabilité et leurs propriétés électriques inédites ouvrent la voie à de nombreuses possibilités de maîtrise de l'agencement des phases dans les matériaux composites ferroélectriques.

Les principaux objectifs de cette thèse de doctorat ont été de réaliser la synthèse et la caractérisation structurale et dieléctrique des échantillons céramiques ferroélectriques appartenants au système Pb1-xRxZr0,40Ti0,60O3 avec R = Ba et La et x entre 0,00 à 0,50. Ce système a été choisi car il est un matériel ferroélectrique qui a des propriétés physiques intéressantes, comme haute constante diélectrique et piézo-électrique, ce qui les rend candidats potentiels pour des applications telles que les condensateurs à haute densité d'énergie et les actionneurs. Afin d'évaluer le comportement relaxor, les études ont été effectuées avec la variation de la composition, du type de dopage (par des atomes de la même ou différente valence - La ou Ba) et de la taille des particules de céramique, dès l'échelle micrométrique à l'échelle nanométrique. Les échantillons céramiques micrométriques ont été préparées par la méthode de réaction de l'état solide et la frittage dans un four électrique conventionnel. Les données fournies par la technique de diffraction des rayons X de cettes échantillons ont montré une transition de une phase tétragonal pour une phase cubique avec l'augmentation de la concentration de cations substituants. Ces changements ont été attribués à une diminution de distorsion dans le maille cristallographique en raison de l'apparition de défauts causés par l'incorporation de dopage. Les mesures électriques ont été obtenues par spectroscopie d'impédance et ont montré un comportement électrique relaxor à partir de compositions avec plus de 12% at. La et de 30% at. Ba pour les systèmes PLZT et PBZT, respectivement. Les mesures électriques de l'échantillon avec 12%, 13% et 14% at. La et 30% at. Ba présentent un comportement qui, selon la littérature, est liée à une transition de phase spontanée d'un comportement relaxor et au comportement d'un matérial ferroélectrique normal. La technique de diffraction des rayons X a également été utilisé pour surveiller le processus de transition de phase en fonction de la température pour échantillons PLZT et PBZT. Il est possible de voir le changement de structure tétragonal de groupe d'espace P4mm en structure cubique de groupe d'espace Pm-3m. En ce qui concerne la structure locale, nous avons effectué des mesures expérimentales avec la technique de spectroscopie d'absorption des rayons X dans le spectre XANES aux seuils d'absorption de différents éléments pour les échantillons PLZT et PBZT. Dans les cas de seuil d'absorption K du titane, l'intégration de La et Ba atomes de la structure du PZT entraîne une diminution dans le désordre local dans le octaèdre TiO6, vérifié par la réduction du déplacement statique de atome Ti au centre de l'octaèdre TiO6. Cette évolution est plus faible pour les échantillons que montrent le comportement relaxor. Les spectres d'absorption EXAFS au seuil LIII du plomb et seuil K du zirconium ont été effectués aussi et ces mesures indiquent que la structure locale autour des atomes de plomb ou de zirconium est également affectée par l'introduction des atomes de La et Ba dans la structure. Le comportement relaxor a été aussi étudié en fonction de la taille de grain dans une échelle nanométrique. Ainsi les échantillons de compostions PZT, PLZT11 et PBZT10 ont eté préparés en utilisant la méthode de synthèse chimique de polymères précurseurs et le processus de frittage par spark plasma. La caractérisation de ces échantillons par diffraction de rayons X montrent que les paramétres de maille réduisent en comparison avec les échantillons de même composition et taille de grain micrométrique. Pour l'échantillon de composition PLZT11, il est possible de constater le comportement relaxor par les mesures de la constante dieléctrique en fonction de la température. Les changements quand la taille de grain est dans une échelle nanométrique sont attribués à la limitation des frontières de grains, qui provoquent un systéme de tension, responsable de la diminuition des paramétres de maille, et provoquent l'apparition de domaines ferroélectriques nanométriques

The word piezo in greek means \to compress". Piezoelectric sensors work on the principle of direct piezoelectric effect, where a mechanical input generates a corresponding electric charge. The advantages of these sensors are wide fre-quency range of operation, high stiffness and small size. The main limitation of a piezoelectric sensor is that it cannot be used in measurements that are truly static. When a piezoelectric sensor is subjected to a static force, a fixed amount of charge is developed which would eventually decay at a rate dependent on the external impedance of the sensor circuitry. Operating sensors at resonance have been one of the methods to overcome the limitation of using piezoelectric sensors for static measurements. However, since both actuation and sensing are done by the same piezoelectric element, this results in a cross-talk of input and output signals. The drawback of using single piezoelectric element for actuation and sensing is overcome in this work by using two identical elements|one for actuation and one for sensing. The operating frequency is about 10 % of the natural frequency of the sensor, thus enabling to operate the sensor in non resonant mode. Since the actuation and sensing mechanisms are separated, static measurement can be carried out. The output signal from the sensing element is monitored by a Lock-in amplifier which works on the principle of phase sensitive detection. The advantage of this sensor design is high sensitivity along with narrow band detection. It can be shown that the voltage output of the sensor Vout / a1 + m(b1 + b2F + b3K) + c1F + d1K, where m and K are the external mass and interaction stiffness, respectively, F is the force acting on it. By maintaining any two of these three quantities constant, the remaining one can be measured without any difficulty. The non resonant mode of operation makes it possible to explore the potential of this sensor in investigating mechanics of solid-liquid (viscous), solid-solid (inelastic) and solid-tissue(viscoelastic) interactions. High sensitivity, wide range of measurement (1 g{1 g) and high resolutio(0.1 g) of the non resonant mass sensor makes it possible to use it in measure-ment of very small masses of the order 1 g. Typically, resonant sensors such as quartz crystal microbalance (QCM) are used for mass measurements at that range. However, since the performance of resonant sensors is controlled by damp-ing, a phenomenon known as `missing mass effect' arises. Operating a sensor in non resonant mode (stiffness controlled mode) is a way to overcome this problem, especially when the mass is viscous and/or viscoelastic in nature. Drosophila fly, egg and larvae are the viscoelastic masses that are measured using this non res-onant sensor. Evaporating sessile drops of water and Cetyl trimethylammonium bromide (CTAB) surfactant solution from nominally flat surfaces are monitored to characterize the sensor for viscous mass measurement. Evaporation rate per unit surface area remains more or less constant, during the initial stages of evap-oration. When the surfactant concentration is varied, evaporation rate per unit surface area is highest for solutions around critical miscelle concentration (CMC). A study is carried out to understand the effect of concentrations on spreading of ink over inkjet printing paper. It is found that the spreading is least around CMC, since spreading is dependent on the rate of evaporation. The non resonant piezoelectric sensor which has high stiffness and quick re-sponse is also capable of measuring very small frictional forces. This sensor is configured to work as an inertial slider. Friction measurement at micro scales is important for designing microsystems such as stick-slip actuators. At such length scales, experiments have to performed at low loads and high excitation frequencies. The support stiffness of such systems should be high and the force of friction generated during slipping, when displacements are smaller than the contact radius, are of the order of few N. The displacement during slipping (S) is dependent on the amplitude of the input voltage to the actuation element. The frictional force measured during slipping by the sensor element indicates that the co-efficient of friction ( ) is independent of the sliding velocity. The developed non resonant sensor in this work under small amplitude exci-tation, can measure force gradient (i.e. stiffness). The total force generated when a needle is inserted into a viscoelastic material is a sum of force due to stiffness of the material, friction and the cutting force at the tip. The force due to stiffness is dominant when the needle is bending the tissue before the puncture occurs. Use of the non resonant sensor in tandem with strain gauge force sensor enables distinguishing the three components of the total force. The slope of the force-displacement (F -d) curve during the initial stages of needle penetration into the viscoelastic material, before puncture, is indicative of the stiffness of the mate-rial. The peak force measured during penetration is higher for needles with larger diameters and lower insertion velocities. The viscoelastic response (relaxation) of the material remains independent of the insertion velocity, for a given thickness of the material and a constant needle diameter. In summary, the sensor designed and developed in this work operates in stiffness controlled mode to eliminate the `missing mass effect' encountered dur-ing resonant mode of operation, has been clearly highlighted. Mass, force and stiffness measurements are possible over a wide range just by varying the ampli-tude of the input signal to the actuator element. The advantages such as high stiffness, small size and high response makes it advantageous to carry out in-situ micro scale studies in scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Non-centrosymmetric materials that can be polarized under applied mechanical stress or electric field are piezoelectric in nature and the phenomenon is called piezoelectric effect. They are broadly classified as direct and converse piezoelectric effects. Piezo-ceramics have a wide range of applications such as piezoelectric actuators, sensors, and transducers. Among piezoceramics, ferroelectric based materials are imperative owing to the existence of spontaneous polarization in these systems. Several materials are investigated starting from naturally occurring crystals to synthetic ceramics but are limited in their application range. The piezoelectric and ferroelectrics properties of the solid-solutions based on lead zirconate and lead titanate called lead zirconate titanate (PZT), lead magnesium niobate-lead titanate (PMN-PT), lead zinc niobate-lead titanate (PZN-PT) (near morphotrophic phase boundary (MPB)) demonstrate their potential for myriad device applications besides inciting a great deal of academic interest. They have been widely used for commercial applications such as ultra sound transducers, ultrasonic motors, fuel injector actuators, nano positioners in scanning electron microscope etc. However, these materials contain more than 60% lead by weight and volatization of Pb at higher temperature, and disposal of lead results in environmental pollution and are fatal to human health. This gave an insight to search for lead-free solid solutions covering a wide spectrum of applications akin to that of PZT. The search for alternatives to lead based piezoelectric materials is now being focused on modified barium titanates and alkali niobates in which the incidence of MPB was reported similar to that of PZT. In this thesis the results pertaining to the various investigations carried out on modified barium titanates, Ba(Zr0.2Ti0.8)O3- x(Ba0.7Ca0.3)TiO3(BCZT), and alkali niobates, potassium sodium niobate (KNN), are presented. Especially, lead-free piezoelectric material Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3(BCZT) with x= 0.5 has attracted great attention due to its excellent piezoelectric properties. Contrary to the other Pb-free systems, the BZT–BCT phase diagram shows a Morphotropic Phase Boundary (MPB) characterized by the existence of a tri-critical point (TCP), which is also the case for PZT and PMN–PT. One drawback of the BZT–xBCT (x=0.5) is its high sintering temperature (where it exhibits the largest d33 of 550 – 620pC/N). Several methods have been adopted and various additives are being added to bring down the sintering temperature, since high d33 requires an optimized sintering temperature of around 1540oC which also shows excellent ferroelectric properties. However, the methods that were reported in the literature to synthesize the above materials do not guarantee compositional homogeneity and also there is a limitation in obtaining ceramics of enhanced grain size as the ceramics comprising larger grains are demonstrated to exhibit high piezoelectric coefficients. Therefore to address these issues, the simple soft chemical route was adopted to synthesize chemically homogenous powder and the influence of microstructure (grain size) and ferroelectric domains on piezoelectric properties of the BCZT at nano and micron sized crystallites was studied. The results obtained are classified into chapter 3 and chapter 4 accordingly apart from introduction, materials, and methods. Another challenging area of research in lead free piezoceramics for nanoscale device application is to synthesize materials and to visualize the piezoelectric properties at nanoscale with controlled shapes and sizes. For that, Mg2+ ion was chosen as the dopant especially on Ba2+ sites to synthesize Ba0.95Mg0.05Zr0.1Ti0.9O3 (BMZT) nanocrystals, as MgO is known to be an effective grain growth inhibitor in many functional and structural ceramics. Therefore in the present thesis Mg2+ ion was chosen to exercise a strict control over the grain size. The results obtained from this title compound are discussed in chapter 5. Another class of material is K0.5Na0.5NbO3 (KNN), which has been considered a good candidate for lead-free piezoelectric materials. KNN exhibits an MPB around 50% K and 50% Na separating two orthorhombic phases from the complete solid solution of NaNbO3 (Anti-ferroelectric) and KNbO3 (ferroelectric). The major problem associated with KNN ceramic is its complex densification process; difficulty in processing and volatilization of sodium at higher sintering temperature leading to stoichiometric discrepancy. To overcome these difficulties, in the present investigations, an attempt has been made to fabricate KNN ceramics by employing the liquid phase sintering method. In this chapter, B2O3 and borate based glass (0.5 Li2O - 0.5K2O- 2B2O3) were chosen to improve the densification, grain size and their effects on the physical properties of the KNN ceramics are discussed in chapter 6. In chapter 7, KNN crystallites (with size varying from nano to micrometers) were dispersed in the Polyvinylidene fluoride (PVDF) matrix to obtain a polymer/nano or micro crystal composites and the effect of nano and micron sized KNN fillers on the structural, dielectric and piezoelectric properties were investigated. The results obtained pertaining to these aforementioned investigations are organized as follows. In Chapter 1, a brief introduction to the field of ferroelectricity, piezoelectricity, and piezoelectric materials. The emphasis has been on the ferroelectric based piezoelectric materials belonging to the perovskite family of oxides. A brief exposure to the conventional lead based piezoceramics, lead zirconate titanate (PZT) is discussed. Furthermore, drawbacks associated with lead based ceramics are highlighted and alternatives to PZT based ceramics such as modified barium titanate and alkali niobate solid solutions are focused, leading to the motivation and objectives of our work. Chapter 2 describes the various experimental techniques that are employed to synthesize and characterize the materials under investigation. Chapter 3 deals with details concerning the characterization of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) nanocrystals prepared via complex oxalate precursor route at a relatively low temperature (800°C/5h). The phase formation temperature of BCZT at nanoscale was confirmed by thermogravimetric (TG), differential thermal analysis (DTA) followed by X-ray powder diffraction (XRD) studies. Fourier Transform Infrared (FTIR) spectroscopy was carried out to confirm the complete decomposition of oxalate precursor into BCZT phase. The XRD and profile fitting revealed the coexistence of cubic and tetragonal phases and was also corroborated by Raman study. Transmission electron microscopy (TEM) studies carried out at 800°C and 1000°C/5h heat treated BCZT powder revealed the crystallite size to be in the range of 20 – 50 nm and 40 – 200 nm respectively. The optical band gap for BCZT nanocrystalline powder was obtained using Kubelka Munk function and was found to be around 3.12 ± 0.02 eV and 3.03± 0.02 eV respectively for 800°C (20 – 50 nm) and 1000°C/5h (40 – 200 nm) heat treated samples. The piezoelectric properties were studied for two different crystallite sizes (30 and 70 nm) using piezoresponse force microscope (PFM). The d33 coefficients obtained for 30 nm and 70 nm sized crystallites were 4 pm/V and 47 pm/V respectively. These were superior to those of BaTiO3 nanocrystal (≈ 50 nm) and promising from the technological/industrial applications perspective. Chapter 4 deals with the studies concerning the effect of microstructure (Grain size) and ferroelectric domains on physical properties of Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics. Fine powders comprising nanocrystallites of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) were synthesized via oxalate precursor method which facilitated to obtain homogenous and large grain sized ceramics at a lower sintering temperature. The compacted powders were sintered at various temperatures in the range of 1200°C - 1500°C for an optimized duration of 10h. Interestingly the one that was sintered at 1450°C/10h exhibited well resolved Morphotrophic Phase Boundary (MPB). The average grain size associated with this sample was 30 µm accompanied by higher domain density mostly with 90° twinning. These were believed to make a significant contribution towards obtaining large strain of about 0.2 % and piezoelectric coefficient as high as 563 pC/N. The maximum force that was generated by BCZT ceramic (having 30 µm grain size) was found to be 161 MPa which is much higher than that of known actuator materials such as PZT (40 MPa) and NKN-5-LT (7 MPa). Chapter 5 reports the details involving the synthesis, structural, optical, and piezoelectric response of lead free Ba0.95Mg0.05Zr0.1Ti0.9O3 nanocrystalline powder. Nanocrystalline powders of Ba1-xMgxZr0.1Ti0.9O3 (x=0.025 - 0.1) were synthesized via citrate assisted sol-gel method. Interestingly, the one with x=0.05 in the system Ba1-xMgxZr0.1Ti0.9O3 exhibited fairly good piezoelectric response apart from the other physical properties. The phase and structural confirmation of synthesized powder was established by X-ray powder diffraction (XRD) and Raman Spectroscopic techniques. Two distinct Raman bands i.e., 303 cm-1 and 723 cm-1 characteristic of the tetragonal phase were observed. Thermogravimetric analysis (TGA) was performed to evaluate the phase decomposition of the as-synthesized Ba0.95Mg0.05Zr0.1Ti0.9O3 sample as a function of temperature. The average crystallite size associated with Ba0.95Mg0.05Zr0.1Ti0.9O3 was calculated using Scherrer formula based on the XRD data and was found to be 25 nm. However, Scanning and Transmission Electron Microscopy studies revealed the average crystallite size to be in the range of 30-40 nm. Kubelka-Munk function was employed to determine the optical band gap of these nanocrystallites. The piezoelectric response of 26 pm/V was observed for Ba0.95Mg0.05Zr0.1Ti0.9O3 nanocrystal by Piezoresponse Force Microscopy (PFM) technique. Photoluminescence (PL) study carried out on these nanocrystals exhibited a blue emission (470 nm) at room temperature. Chapter 6 describes the effect of the addition of B2O3 on the density, microstructure, dielectric, piezoelectric and ferroelectric properties of K0.5Na0.5NbO3 ceramics. Boron oxide (B2O3) addition to pre-reacted K0.5Na0.5NbO3 (KNN) powders facilitated swift densification at relatively low sintering temperatures which was believed to be a key to minimize potassium and sodium loss. The base KNN powder was synthesized via solid-state reaction route. The different amounts (0.1 to 1 wt %) of B2O3 were added, and ceramics were sintered at different temperatures and durations to optimize the amount of B2O3 needed to obtain KNN pellets with the highest possible density and grain size. The 0.1 wt% B2O3 added KNN ceramics sintered at 1100°C for 7h exhibited higher density (98%) with grain size of ~5 µm. Scanning electron microscopy (SEM) studies confirmed an increase in average grain size with increasing B2O3 content at the appropriate temperature of sintering and duration. The B2O3 added KNN ceramics exhibited improved dielectric and piezoelectric properties at room temperature. For instance, 0.1 wt% B2O3 added KNN ceramic exhibited d33 value of 116 pC/N which is much higher than that of pure KNN ceramics. Interestingly, all the B2O3 added (0.1 to 1wt %) KNN ceramics exhibited polarization – electric field (P vs E) hysteresis loops at room temperature. The remnant polarization (Pr) and coercive field (Ec) values are dependent on the B2O3 content and crystallite size. The details pertaining to the effect of the addition of borate based glass (0.5 Li2O - 0.5K2O- 2B2O3) on the physical properties of K0.5Na0.5NbO3 ceramics are also reported in this chapter. The addition of powdered 0.5 Li2O - 0.5K2O- 2B2O3 (LKBO) glass (0.5 to 2 wt%) to potassium sodium niobate, K0.5Na0.5NbO3 (KNN) powder facilitated higher densification which resulted in improved physical properties that include dielectric, piezoelectric and ferroelectric. The required polycrystalline powders of KNN were synthesized through solid-state reaction route, while LKBO glass was obtained via the conventional melt-quenching technique. Pulverized glass was added to KNN powders in different wt% and compacted at room temperature and these were sintered around 1100°C. Indeed the addition of optimum amount (1 wt %) of LKBO glass to KNN ceramics facilitated lowering of sintering temperature accompanied by larger grains (8 µm) with improved density. The dielectric constant (εr) measured at room temperature was 475 (at 10 kHz), whereas it was only 199 for the LKBO glass free KNN. The piezoelectric coefficient (d33) was found to be 130 pC/N for 1wt% LKBO added glass, which was much higher than that of pure KNN ceramics (85 pC/N). Indeed, the LKBO glass added samples did exhibit well saturated P versus E hysteresis loops at room temperature. Though there was no particular trend observed in the variation of Pr with the increase in glass content, the Pr values were higher than those obtained for KNN ceramics. The improved physical properties of KNN ceramics encountered in these studies were primarily attributed to enhancement in density and grain size. Chapter 7 presents a comparative study on the structural, dielectric and piezoelectric properties of nano and micron sized K0.5Na0.5NbO3 fillers in PVDF composites. Polymer nanocrystal composites were fabricated by embedding polyvinylidene fluoride (PVDF) with different vol% of K0.5Na0.5NbO3 (KNN) nanocrystallites using hot-pressing technique. For comparison, PVDF-KNN microcrystal composites of the same compositions were also fabricated which facilitated the crystallite size (wide range) effect studies on the dielectric and piezoelectric properties. The structural, morphological, dielectric, and piezoelectric properties of these nano and micro crystal composites were investigated. The incorporation of KNN fillers in PVDF at both nano and micrometer scale above 10vol% resulted in the formation of polar β-form of PVDF. The room temperature dielectric constant as high as 3273 at 100Hz was obtained for PVDF comprising 40 vol% KNN nanocrystallites due to dipole –dipole interactions (as the presence of β-PVDF is prominent), whereas it was only 236 for PVDF containing the same amount (40 vol%) of micron sized crystallites of KNN at the same frequency. Various theoretical models were employed to predict the dielectric constants of the PVDF-KNN nano and microcrystal composites. PVDF comprising 70 vol% micronmeter sized crystallites of KNN exhibited d33 value of 35pC/N, while the nanocrystal composites of PVDF-KNN did not exhibit any piezoelectric response perhaps due to unrelieved internal stress within each grain besides having less number of domain walls. The Thesis ends with summary and conclusions, though each chapter is provided with conclusions and a complete list of references.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2015-01-27T13:24:18Z No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Maysa de Melo Paranhos - 2014.pdf: 2355457 bytes, checksum: 7b3e122ce6fe59cb047d8e835e921f53 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2015-01-28T11:04:11Z (GMT) No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Maysa de Melo Paranhos - 2014.pdf: 2355457 bytes, checksum: 7b3e122ce6fe59cb047d8e835e921f53 (MD5) / Made available in DSpace on 2015-01-28T11:04:11Z (GMT). No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Maysa de Melo Paranhos - 2014.pdf: 2355457 bytes, checksum: 7b3e122ce6fe59cb047d8e835e921f53 (MD5) Previous issue date: 2014-01-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG / DSA® electrodes modified with films ErYZrO2 or YZrO2 and boron-doped diamond electrodes (BDD) were tested as electrochemical sensors detect front of the neurotransmitter epinephrine and its interfering ascorbic acid (AA) and uric acid (UA), which coexist with epinephrine in biological fluids and are also electroactive, rusting in the same potential that epinephrine. The physical and morphological characterization of the films of ZrO2 were performed using the techniques of XRD, SEM / FEG, EDXS and Open circuit potential. For electrochemical characterization of the sensor in developing were used the techniques of cyclic voltammetry (CV), differential pulse voltammetry (DPV) and Flow Injection Analysis with Amperometric Detection. The analyzes used for physical and morphological characterization of the ZrO2 films demonstrated that the technique of spin coating together with the methodology used for the deposition of ZrO2 films on the surface of substrate DSA® showed films were obtained satisfactory. The BDD electrodes showed good catalytic activity for both analyzed substances (EP, AA and UA). While BDD electrode showed good sensitivity for detection of EP in the presence of AA, electrodes ZrO2 addition to good sensitivity and selectivity showed good reproducibility for the detection of EP without interference from UA and AA. / Eletrodos a base de DSA® modificados com filmes de ErYZrO2 e YZrO2 bem como eletrodos de Diamante Dopado com Boro (DDB) foram testados como sensores eletroquímicos para a detecção eletroquímica do neurotransmissor Epinefrina (EP) e de seus interferentes ácido ascórbico (AA) e ácido úrico (AU), os quais coexistem com a EP nos fluidos biológicos oxidando-se praticamente no mesmo potencial. As caracterizações física, química e morfológica dos filmes a base de ZrO2 foram realizadas por meio das técnicas de DRX, MEV/FEG, EDXS e potencial de circuito aberto. Para caracterização eletroquímica do sensor produzido foram utilizadas as técnicas de Voltametria Cíclica (VC), Voltametria de Pulso Diferencial (VPD) e Análise por Injeção em Fluxo em modo Amperométrico. As análises utilizadas para caracterização física e morfológica dos filmes a base de ZrO2 mostraram que a técnica de spin-coating juntamente com a metodologia utilizada para deposição dos filmes a base de ZrO2 sobre substrato de DSA® permitiu a obtenção dos filmes espessos e com boa homogeneidade. O eletrodo de DDB apresentou boa atividade eletroquímica para as substâncias analisadas (EP, AA e AU). Enquanto eletrodos de DDB apresentaram boa sensibilidade para detecção de EP na presença de AA, eletrodos de ZrO2, além de boa sensibilidade, apresentaram seletividade e boa reprodutibilidade para detecção de EP sem interferência de AU e AA.

Perovskite based artificial superlattices has recently been extensively investigated due to the immense promise in various device applications. The major applications include non-volatile random access memories, microwave devices, phase shifters voltage tunable capacitor applications etc. In this thesis we have taken up the investigation of two different types of symmetric superlattices, viz. BaZrO3/BaTiO3 and SrTiO3/BaZrO3, with possible applicability to voltage tunable devices. Chapter 1 deals with the introduction to the perovskite based functional oxides. Their various applications and the specific requirements for voltage tunable device applications has also been discussed in detail. The basic properties of BaTiO3 and SrTiO3, which are well documented in the literature, have been reviewed. The fundamental physics of interfacial interactions that influence the properties of superlattices is also discussed using existing models. The reason behind the choice of constructing artificial superlattices of BaZrO3/BaTiO3 and SrTiO3/BaZrO3 and the motivation behind this thesis is outlined. Chapter 2 gives a brief description of the basic characterization techniques that has been employed for studying the thin films. These include pulsed laser deposition of oxide thin films, structural characterization using X-Ray Diffraction and Atomic Force Microscope and electrical characterization of thin film metal-insulator-metal structures. The basic principle behind the techniques has also been included in various sections of this chapter. Chapter 3 introduces the reader to basic properties of the less studied perovskite material BaZrO3, one of the parent components of Ba(Zr,Ti)O3 based ceramics for high frequency applications. BaZrO3 is the common material in both the types of superlattices studied in this thesis. Initially the growth of polycrystalline BaZrO3 on (111)Pt/TiO2/SiO2/Si has been elaborated in this chapter. After characterizing the crystalline quality of the films and optimizing the growth conditions, epitaxial BaZrO3 films has been grown on (001) SrTiO3 substates. Dielectric properties of epitaxial BaZrO3 film have been measured as a function of temperature and frequencies. The electric field tunability of BaZrO3 films has been calculated from capacitance-voltage data for comparison with superlattice structures. Chapter 4 deals with the basic considerations involving growth of artificial superlattices and multilayers using pulsed laser ablation technique. The fundamental differences between formation of multilayers and superlattices have also been discussed, and the basic considerations for optimizing growth parameters are analyzed in this chapter. X-ray θ-2θ and φ-scans have been performed to investigate crystal quality of superlattices. The growth rates calculated from the satellite reflections in X-ray θ-2θ scans indicate fair degree of control over the growth and φ-scans confirms epitaxial cube-on cube growth of both types of superlattices. Atomic Force microscopy has been used to hcaracterize the film quality and surface morphology of superlattice structures and it has been found that the films have a very smooth surface with rms roughness of the order of few nanometres. Chapter5 deals with the detailed electrical characterization of both types of superlattices structures. Dielectric response showed nearly temperature invariance for both types of superlattices. Polarization measurements show that the heterostructures are in paraelectric state. Even for paraelectric/ferroelectric BaZrO3/BaTiO3 superlattices, stress induced stabilization of the paraelectric state is exhibited in low period superlattices. Paraelectric/paraelectric-SrTiO3/BaZrO3 superlattices exhibited a tunability of ~20% at intermediate modulation periods and an extremely stable dissipation factor with respect to temperature which is very attractive for device application point of view. A maximum tunability of ~40% has been observed for lowest period BaZrO3/BaTiO3 superlattice. Relatively high Quality Factors has been observed for both type of superlattices and their dependence on the modulation periods has been analyzed. Dielectric relaxation data showed that Maxwell-Wanger type of behaviour is exhibited but the presence of a conductance component G had to be realized in the equivalent circuit representation, which originates from the observation of a square law dependence of the alternating current on the frequency. Finally DC electrical characteristics were investigated as a function of temperature to determine the type of conduction mechanism that is involoved. The data has been analyzed using existing theories of high field conduction in thin dielectric films and it has been found that at different temperature ranges, the conduction mechanism varied from bulk limited Poole-Frenkel to Space Charge limited conduction. The activation energy calculation indicate that the physical processes responsible for dielectric relaxation and dc conduction are identical.

Yttria stabilized zirconia (YSZ) is the state of the art ceramic top coat material used for TBC applications. The desire to achieve a higher engine efficiency of agas turbine engine by increasing the turbine inlet temperature has pushed YSZ toits upper limit. Above 1200°C, issues such as poor phase stability, high sinteringrates, and susceptibility to CMAS (calcium magnesium alumino silicates) degradation have been reported for YSZ based TBCs. Among the new materials,gadolinium zirconate (GZ) is an interesting alternative since it has shown attractive properties including resistance to CMAS attack. However, GZ has a poor thermo-chemical compatibility with the thermally grown oxide leading to poor thermal cyclic performance of GZ TBCs and that is why a multi-layered coating design seems feasible.This work presents a new approach of depositing GZ/YSZ multi-layered TBCs by the suspension plasma spray (SPS) process. Single layer YSZ TBCs were also deposited by SPS and used as a reference.The primary aim of the work was to compare the thermal conductivity and thermal cyclic life of the two coating designs. Thermal diffusivity of the YSZ single layer and GZ based multi-layered TBCs was measured using laser flash analysis (LFA). Thermal cyclic life of as sprayed coatings was evaluated at 1100°C, 1200°C and 1300°C respectively. It was shown that GZ based multi-layered TBCs had a lower thermal conductivity and higher thermal cyclic life compared to the single layer YSZ at all test temperatures. The second aim was to investigate the isothermal oxidation behaviour and erosion resistance of the two coating designs. The as sprayed TBCs were subjected toisothermal oxidation test at 1150°C. The GZ based multi-layered TBCs showed a lower weight gain than the single layer YSZ TBC. However, in the erosion test,the GZ based TBCs showed lower erosion resistance compared to the YSZ singlelayer TBC. In this work, it was shown that SPS is a promising production technique and that GZ is a promising material for TBCs.

O titanato e zirconato de chumbo \'PB\'(\'ZR\'1-y\'TI\'y)\'O IND.3\' é um material ferroelétrico de estrutura perovskita que tem sido aplicado como transdutores, amplificadores, sensores piezoelétricos, piroelétricos e memórias ferroelétricas. É bem estabelecido que a incorporação de íons de \'LA POT.3+\' ou \'BA POT.2+\' nos sítios ocupados pelo \'PB\' no sistema \'PB\'(\'ZR\'1-y\'TI\'y)\'O\' (PZT), formando os sistemas \'PB\'1-x\'LA\'x\'ZR\'1-y\'TI\'y\'O IND.3\' (PLZT) e \'PB\'1-x\'BA\'x\'ZR\'1-y\'TI\'y\'O IND.3\' (PBZT), provoca mudanças significativas nas suas propriedades. No entanto, poucos trabalhos tem sido dedicados a esses sistemas contendo altas concentrações de \'TI\', principalmente no que se refere à estrutura desses materiais. Assim, este trabalho teve por objetivo analisar as propriedades estruturais e suas correlações com as propriedades dielétricas dos sistemas \'PB\'1-x\'LA\'x\'ZR\'0,40\'TI\'0,60\'O IND.3\' (PLZT100x) e \'PB\'1-x\'BA\'x\'ZR\'0,40\'TI\'0,60\'O IND.3\' (PBZT100x) em função da composição e da temperatura. Foram preparadas amostras cerâmicas por meio de sinterização convencional com x variando entre 0,05 e 0,21 para o sistema PLZT e entre 0,10 e 0,50 para o sistema PBZT. Em relação à estrutura a longa distância, medidas de difração de raios X mostraram uma diminuição no grau de tetragonalidade com o aumento da concentração dos cátions substituintes, que foi atribuída à formação de vacâncias no sítio A (caso do \'LA\') e diferença entre o raio iônico (caso do \'BA\'). Estas alterações estruturais em função da composição foram também responsáveis pelo aumento do grau de difusidade das curvas de permissividade dielétrica e pela observação de um estado ferroelétrico relaxor nas amostras contendo altas concentrações de \'LA\' e \'BA\'. Em relação à estrutural local, os resultados obtidos através da técnica de espectroscopia de absorção de raios X (XAS) nas bordas \'K\' do \'TI\' e LIII do \'PB\' mostraram que a incorporação de átomos de \'LA\' ou \'BA\' à estrutura do PZT leva a uma redução no deslocamento do átomo de \'TI\' em relação ao centro do octaedro \'TI\'O IND.6\' e mudanças na ordem local do átomo de \'PB\'. No que tange as composições contendo 21% at. de \'LA\' e 50% at. de \'BA\', diferentemente dos resultados de DRX que mostraram uma simetria cúbica, a técnica de XAS mostrou uma simetria local tetragonal. Em bom acordo com os resultados obtidos pela técnica de espectroscopia Raman, espectros EXAFS medidos em altas temperaturas mostraram também que a estrutura local não é compatível com uma estrutura de simetria cúbica. Espectros XANES medidos na borda \'K\' do oxigênio revelaram uma redução no grau de hibridização entre os estados 2p do \'O\' com 6sp do \'PB\' à medida que a concentração de \'LA\' ou \'BA\' aumenta, que estaria relacionada com o surgimento de comportamento relaxor. Amostras cerâmicas densas nanoestruturadas de composição PZT, PLZT11 e PBZT10 foram preparadas pelo método de spark plasma sintering (SPS) a fim de analisar a influência do tamanho de grão. Foi verificado que as amostras sinterizadas por SPS apresentam tamanho de grão em torno de 60 nm. A caracterização dielétrica destas amostras mostra que a redução do tamanho de grão causa uma redução no valor de máximo da permissividade dielétrica e características difusas da permissividade em função da temperatura devido ao aumento das regiões de contorno de grão. / Lead titanate zirconate (\'PB\'(\'ZR\'1-x\'TI\'x)\'O IND.3\') are ferroelectric materials with perovskite structure which has been used as transducers, capacitors, piezoelectric and pyroelectric sensors and ferroelectric memories. The substitution of \'PB POT.+2\' ions by \'LA POT.+3\' or \'BA POT.+2\' ions in the \'PB\'(\'ZR\'1-x\'TI\'x)\'O IND.3\' (PZT) system, which leads to the formation of the \'PB\'1-x\'LA\'x\'ZR\'1-y\'TI\'y\'O IND.3\' (PLZT) and the \'PB\'1-x\'BA\'x\'ZR\'1-y\'TI\'y\'O IND.3\' (PBZT) systems, induces several changes in the electric and structural properties of these materials. However, PLZT or PBZT systems based on \'TI\'-rich compositions have not been thoroughly investigated and the literature contains few reports concerning their structure. Thus, the main objectives of this doctoral thesis were the synthesis and structural characterization of \'PB\'1-x\'R\'x\'ZR\'0.40\'TI\'0.60\'O IND.3\' ferroelectric ceramic samples, with R = \'BA\' and \'LA\' and x between 0.00 to 0.50 (PLZT100x and PBZT100x). The characterization with X-ray diffraction technique of these samples showed a decrease of the tetragonality degree with increase of the doping cation concentration, which was related to the appearance of defects caused by the incorporation of \'LA\' or \'BA\' cations. These structural modifications were also responsible by the increase of the diffuseness at the dielectric permittivity and a relaxor behavior as a function of the \'LA\' or \'BA\' concentration. Concerning the local structure, XANES spectra in the absorption edge of various elements in PLZT and PBZT samples were performed. In the cases of \'TI\' \'K\'-edge absorption, the doping of \'LA\' and \'BA\' atoms in the PZT structure leads to a reduction of the displacement of \'TI\' atom in the center of the \'TI\'O IND.6\' octahedron. However, even when the crystal structure is cubic, a local octahedron distortion remains. EXAFS measurements in \'PB\' LIII-edge and \'ZR\' \'K\'-edge were performed and also indicate that local structure around lead or zirconium atoms is also affected by the introduction of \'LA\' and \'BA\' atoms in the PZT structure. In addition, XANES spectra measured at \'O\' \'K\'-edge revealed a reduction in the hybridization degree between \'O\' 2p and \'PB\' 6sp states with the addition of \'LA\' or \'BA\' atoms to the structure of PZT. It has been shown that hybridization between these states is essential to ferroelectricity and this reduction would be related to the relaxor behavior. PLZT and PBZT systems were also studied depending on the size of particle size in a nanometer scale. Thus samples PZT, PLZT11 and PBZT10 compositions were prepared using the synthesis method of precursor polymers and the process of sintering by spark plasma. A pronounced decrease in the values of maximum permittivity was observed and the dielectric curve as a function of the temperature exhibits a diffuse behavior. This size-induced diffuse phase transition and the reduction of the permittivity magnitude could be related to the differences between the core grain and the grain boundaries.

La menace d'une attaque bactériologique massive et létale visant les armées ou les populations civiles ont obligé les institutions de recherche militaire à investir massivement dans la préparation à une telle éventualité. La réponse à donner à une attaque bactériologique est conditionnée par les capacités de perception et d'indentification de cette attaque. Ainsi, le besoin en solution de détection et de reconnaissance biologique fiables, peu chères, facilement manipulables est crucial. Nous abordons dans ces travaux de thèse le cas de biocapteurs basés sur des micromembranes résonantes en silicium, assemblées par des technologies de microfabrication classiques. Nous montrons tout d'abord les avantages comparés de ce type de capteur pour répondre à la problématique donnée. Puis, nous rapportons l'étude théorique permettant le dimensionnement des micromembranes en fonction d'objectifs initialement formulés en termes de sensibilité et de limite de détection. La mise en vibration des membranes est assurée par l'action d'une pastille piézoélectrique déposée sur sa surface, la détection du mouvement est effectuée par une jauge piézorésistive positionnée à l'encastrement de la membrane. Nous abordons par la suite, la fabrication du microsystème, son conditionnement ainsi que la fabrication de l'électronique de détection associée. Enfin la caractérisation électrique, mécano-électrique puis biologique des membranes nous permet de mettre en relief les principaux résultats obtenus par rapport à l'état de l'art. Le premier point réside dans la démonstration de la co-intégration physique des phénomènes piézoélectrique et piézorésistif au sein d'une même structure résonante. Est démontrée ensuite la capacité à suivre en temps réel la fréquence de résonance des membranes par détection piézorésistive, lorsque celles-ci sont immergées dans un milieu biologique aqueux. Pour terminer, les résultats biologiques quant à la détection d'agents simulant la menace biologique sont présentés