The prime objective of this dissertation is to design, synthesize and characterize lead-free piezoelectric based magnetostrictive components based magnetoelectric (ME) composites that exhibit self-bias characteristics and high amplitude of ME coupling. The secondary goal of this thesis was to lay down the foundation for nanoscale and flexible magnetoelectric devices. Self-biased ME effect was investigated in lead-free three-phase laminate composites. This effect is characterized by non-zero remanent ME responses at zero magnetic bias field (Hbias). It was revealed that the self-biased ME effects can be observed in three-phase laminate composites consisting of piezoelectric material and two dissimilar magnetostrictive materials. On applying Hbias to the laminates in bending mode configuration, the ME responses were found to exhibit hysteretic behaviors with remanent ME responses. The shape of hysteretic ME response could be controlled by adjusting the magnetic interactions and piezoelectric properties. Further, converse magnetoelectric (CME) responses in bending-mode three-phase laminates exhibited hysteretic behaviors with similar magnitudes during Hbias sweep as it was generated directly by applying ac voltage (Vac) without any external Hbias. Lead-free (1 - x) [0.948 K0.5Na0.5NbO3 - 0.052 LiSbO3] - x Ni0.8Zn0.2Fe2O4 (KNNLS-NZF) compositions were synthesized for optimizing ME properties of particulate composites. Island-matrix microstructure was developed to improve the magnitude of ME coupling effect by overcoming the problems found in conventional particulate composites. The structure lead to improvement of ME coefficient with maximum magnitude of 20.14 mV/cm ae as well as decrease of optimum Hbias of < 500 Oe in the composition of 0.7 KNNLS - 0.3 NZF particulate composites. Room-temperature ME phase diagram of (1 - x) BaTiO3 - x BiFeO3 materials (BT - x BFO, x = 0.025 - 1.0) was investigated for designing compositions suitable for thin film devices. The BT - x BFO compositions in narrow range of x = 0.71 - 0.8 were found to exhibit good piezoelectric, dielectric and magnetic properties simultaneously. The room temperature ME coefficient was found to be maximum with high magnitude of 0.87 mV/cmOe in the optimized composition of x = 0.725.This composition was found to consist of local monoclinic distortions with average rhombohedral symmetry as confirmed by detailed structural analysis through Raman spectroscopy and atomic pair distribution functions (PDFs). MnFe2O4 (MFO)-Ni core-shell nanoparticles were synthesized and characterized for developing tunable devices such as memristor. The MFO nanoparticles synthesized by solvothermal method exhibited diameter of 200 nm, mean primary particle size of 15 nm, high saturation magnetization of 74 emu/g and coercivity of 89 Oe. Ni encapsulation on MFO nanoparticles was performed by aqueous ionic coating method. Ni shells with uniform thickness of 1 nm were coated on MFO nanoparticles by this method. In order to develop future nanoscale dual phase energy harvesters and magnetic field sensors, vertically-aligned piezoelectric nanorods were synthesized. In the initial attempt, Pb(Zr0.52Ti0.48)O3 (PZT) was used to verify the feasibility of developing one dimensional (1D) piezoelectric nanostructures with controlled diameter and height. For the 1D nanostructure, well-ordered anodic aluminum oxide (AAO) templates were prepared by two step aluminum anodizing. The PZT nanorods were synthesized by vacuum infiltration of PZT precursor solutions and exhibited uniform diameter of 90 nm and aspect ratio of 10 with vertical in respect to the Pt-Si substrate. The piezo-response of PZT nanorods showed good magnitude owing to the reduced clamping effect from the substrate. Attempt towards the development of flexible tunable devices that possess magnetic field sensing and actuation ability was made in the later part of the thesis. The electroactive polymeric actuators in the form of Polypyrrole (PPy) / Au / Polyvinylidene fluoride (PVDF) / Au / Polypyrrole (PPy) were synthesized and the process flow was optimized. Pore size and thickness of PVDF layer was adjusted by changing the solvent, viscosity and drying temperature. Different types of electrolyte solutions were investigated to improve the strain and response time. The actuators exhibited high deflection of 90 % with fast response of 50% deflection per second. Dual-functional structure in the form of  PPy-MFO / Au / PVDF / Au / PPy-MFO was developed by PPy polymerization including MFO nanoparticles via cyclovoltammetric method. / Ph. D.

Magnetoelectric (ME) effect is defined as the change in dielectric polarization (P) of a material under an applied magnetic field (H) or an induced magnetization (M) under an external electric field (E). ME materials have attracted number of investigators due to their potential for improving applications such as magnetic field sensors, filters, transformers, memory devices and energy harvesters. It has been shown both experimentally and theoretically that the composite structures consisting of piezoelectric and magnetostrictive phases possess stronger ME coupling in comparison to that of single phase materials. Giant magnetoelectric effect has been reported in variety of composites consisting of bulk-sized ME composites and thin film ME nanostructures. In this dissertation, novel ME composite systems are proposed, synthesized and characterized in both bulk and thin films to address the existing challenges in meeting the needs of practical applications. Two applications were the focused upon in this study, tunable transformer and dual phase energy harvester, where requirements can be summarized as: high ME coefficient under both on-resonance and off-resonance conditions, broad bandwidth, and low applied DC bias. In the first chapter, three challenges related to the conventional ME behavior in bulk ME composites have been addressed (1) The optimized ME coefficient can be achieved without external DC magnetic field by using a self-biased ME composite with a homogenous magnetostrictive material. The mechanism of such effect and its tunability are studied; (2) A near-flat ME response regardless of external magnetic field is obtained in a self-biased ME composite with geometry gradient structure; (3) By optimizing interfacial coupling with co-firing techniques, the ME coefficient can be dramatically enhanced. Theses co-fired ME laminates not only exhibit high coupling coefficient due to direct bonding, but also illustrate a self-biased effect due to the built-in stress during co-sintering process. These results present significant advancement toward the development of multifunctional ME devices since it eliminates the need for DC bias, expands the working bandwidth and enhances the ME voltage coefficient. Next, magnetoelectric nanocomposites were developed for understanding the nature of the growth of anisotropic thin film structures. In this chapter following aspects were addressed: (1) Controlled growth of nanostructures with well-defined morphology was obtained. Microstructure and surface morphology evolution of the piezoelectric BaTiO3 films was systematically analyzed. A growth model was proposed by considering the anisotropy of surface energy and the formation of twin lamellae structure within the frame work of Structure Zone Model (SZM) and Dynamic Scaling Theory (DST). In parallel to BaTiO3 films, well-ordered nanocomposite arrays [Pb1.1(Zr0.6Ti0.4)O3/CoFe2O4] with controlled grain orientation were developed and investigated by a novel hybrid deposition method. The influence of the pre-deposited template film orientation on the growth of ME composite array was studied. (2) PZT/CFO/PZT thick composite film and BTO/CFO thin film were synthesized using sol-gel deposition (SGD) and pulsed laser deposition (PLD) techniques, respectively. The HRTEM analysis revealed local microstructure at the interface of consecutive constituents. The interfacial property variation of these films was found to affect the coupling coefficient of corresponding ME nanocomposites. Subsequently, a novel complex three-dimensional ME composite with highly anisotropic structure was developed using a hybrid synthesis method. The influence of growth condition on the microstructure and property of the grown complex composites was studied. The film with highly anisotropic structure was found to possess tailored ferroelectric response indicating the promise of this synthesis method and microstructure. Based on the laminated ME composites, three types of ME tunable transformer designs were designed and fabricated. The goal was to develop a novel ME transformer with tunable performance (voltage gain and/or working resonance frequency) under applied DC magnetic field. Conventional ME transformers need either winding coil or large external magnetic field to achieve the tunable feature. Considering the high ME coupling of ME laminate, two ME transformers were developed by epoxy bonding Metglas with transversely/longitudinally poled piezoelectric ceramic transformer. The influence of different operation modes toward magnetoelectric tunability was analyzed. In addressing the concern of the epoxy bonding interface, a co-fired ME transformer with unique piezoelectric transformer/magnetostrictive layer/piezoelectric transformer trilayer structure was designed. The design and development strategy of thin film ME transformer was discussed to illustrate the potential for ME transformer miniaturization and on-chip integration. Lastly, motivated by the increasing demand of energy harvesting (EH) systems to support self-powered sensor nodes in structural health monitoring system, a magnetoelectric composite based energy harvester was developed. The development and design concept of the magnetoelectric energy harvester was systematically discussed. In particular, the first dual-phase self-biased ME energy harvester was designed which can simultaneously harness both vibration and stray magnetic field (Hac) in the absence of DC magnetic field. Strain distribution of the EH was simulated using the finite element model (FEM) at the first three resonance frequencies. Additionally, the potential of transferring this simple EH structure into MEMS scalable components was mentioned. These results provide significant advancement toward high energy density multimode energy harvesting system. / Ph. D.

Submitted by Daniele Amaral (daniee_ni@hotmail.com) on 2016-10-07T19:22:08Z No. of bitstreams: 1 TeseRRGP.pdf: 3041523 bytes, checksum: f8585bab1f9c1565717516794f4e8831 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-20T19:31:28Z (GMT) No. of bitstreams: 1 TeseRRGP.pdf: 3041523 bytes, checksum: f8585bab1f9c1565717516794f4e8831 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-20T19:31:35Z (GMT) No. of bitstreams: 1 TeseRRGP.pdf: 3041523 bytes, checksum: f8585bab1f9c1565717516794f4e8831 (MD5) / Made available in DSpace on 2016-10-20T19:31:43Z (GMT). No. of bitstreams: 1 TeseRRGP.pdf: 3041523 bytes, checksum: f8585bab1f9c1565717516794f4e8831 (MD5) Previous issue date: 2015-09-04 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / This study analyses the relationships between synthesis routes and physical properties of the composite system 67.5(PbMg1/3Nb2/3O3) +32.5(PbTiO3), or simply PMN-PT, as ferroelectric phase and BaFe12O19, or BaM, as magnetic phase. The choice of phases was based on the exceptional properties that both PMN-PT and BaM possess: solid solutions of the complex perovskite PMN-PT in both monocrystalline and polycrystalline forms, particularly those whose composition lies within the region of morphotropic boundary phases, have the largest known piezoelectric coefficients. BaM, or barium hexaferrite, presents relatively high property anisotropy due to its hexagonal crystal structure (expressed in particles that grow in nonequiaxed format) and easy magnetization along the c-Crystallographic axis. Thus, the main objective of this work was to obtain and characterize magnetoelectric composites (either volumetric or as two-dimensional nanostructures) textured from PMN-PT/BaM, by exploiting the quasi-piezomagnectic characteristics and the microstructural, crystallographic and magnetic anisotropyof the BaM phase. With a molar ratio of 80/20 between the ferroelectric and magnetic phases, different routes of synthesis and processing were used for the production of threedimensional ceramic composites with 0-3 connectivity, or thin films with 0-3 and 2-2 connectivity.The Pechini, sol-gel, co-precipitation,and solid state reaction techniques were applied for the synthesis of powders and/or solutions; the pressure-assisted sintering method was used for the densification of three-dimensional bodies; and the spin-coating technique was employed for the deposition of films. Physical, electrical, magnetic and magnetoelectric characterizations were performed in order to clarify the influence of the BaM phase upon composites of different configurations. In a prospective yet not exhaustive manner, relations were assessed among the experimental parameters of the various synthesis routes (with greater focus on the barium hexaferrite phase) and the production of ceramic composites of PMNPT/ BaM system. It was found that the final characteristics of the prepared materials, particularly the hysteresis behavior of the magnetoelectric coefficient as a function of applied magnetic field, were highly susceptible to variations in the morphology, size and orientation of barium hexaferrite grains, which, in turn, depended on the synthesis and sintering routes applied. / Realizaram-se estudos de síntese e de caracterização das propriedades físicas do sistema compósito 67,5(PbMg1/3Nb2/3O3) +32,5(PbTiO3), ou simplesmente PMN-PT, como fase ferroelétrica, e da BaFe12O19, ou BaM, como fase magnética. A escolha dessas fases baseou-se nas propriedades excepcionais que ambas apresentam. A perovskita complexa PMN-PT, tanto na forma monocristalina como policristalina, apresenta soluções sólidas com os maiores coeficientes piezoelétricos conhecidos, particularmente as de composição na região do contorno morfotrópico de fases, como é o caso da 32,5%mol de PT. A fase BaM, ou hexaferrita de bário, apresenta relativamente alta anisotropia de propriedades magnéticas devido à sua estrutura cristalográfica hexagonal (refletida em partículas que crescem em formato não equiaxial) e fácil magnetização ao longo do eixo cristalográfico-c. O objetivo principal deste trabalho foi a obtenção e a caracterização de compósitos magnetoelétricos (volumétricos ou como nanoestruturas bidimensionais) texturados de PMN-PT/BaM, explorando-se as características quasi-piezomagnéticas e a anisotropia microestrutural/cristalográfica/magnética da fase BaM. Com uma proporção molar de 80/20 entre a fase ferroelétrica e a magnética, foram utilizadas diferentes rotas de síntese e de processamento de materiais para a produção de compósitos com conectividade 0-3, quando no caso de corpos cerâmicos volumétricos; ou 0-3 e 2-2, quando no caso de filmes finos. Os métodos Pechini, sol-gel, de copreciptação e de reação no estado sólido foram utilizadas na síntese dos pós e/ou soluções; o método de sinterização assistida por pressão, para a densificação dos corpos volumétricos, e a técnica “spin-coating”, para a deposição dos filmes. As caracterizações físicas, elétricas, magnéticas e magnetoelétricas buscaram evidenciar a influência das propriedades da fase BaM nas diferentes configurações de compósitos. De forma prospectiva e ainda não exaustiva, foram avaliadas as relações entre os parâmetros experimentais das diversas rotas de síntese (com maior foco na fase hexaferrita de bário) e a produção de compósitos cerâmicos do sistema PMN-PT/BaM. Encontrou-se que as características finais dos materiais preparados, em especial o comportamento histerético do coeficiente magnetoelétrico em função do campo magnético aplicado, foram altamente susceptíveis às variações da morfologia, tamanho e orientação dos grãos da hexaferrita de bário, que, por sua vez, dependem das rotas de síntese e de sinterização aplicadas.

In a conventional charge-pump based PLL design, the loop parameters such as the band-width, jitter performance, charge-pump current, pull-in range among others govern the ar-chitecture and implementation details of the PLL. Different loop parameter specificationschange with a change in the reference frequency and inmost cases, requires careful re-designof some of the PLL blocks. This thesis describes the implementation of a semi-digital PLLfor high bandwidth applications, which is self-compensated, low-power and exhibits band-width tracking for all reference frequencies between 40 MHz and 1.6 GHz in 65nm CMOStechnology.This design can be used for a wide range of reference frequencies without redesigning anyblock. The bandwidth can be fixed to some fraction of the reference frequency during designtime. In this thesis, the PLL is designed to make the bandwidth track 5% of the referencefrequency. Since this PLL is self-compensated, the PLL performance and the bandwidthremains same over PVT corners.