As fontes históricas disponíveis para área dos rios Nhamundá-Trombetas, no baixo Amazonas, relatam à existência de assentamentos populosos, formas hierarquizadas de organização social e cultos religiosos, indicando a existência de sociedades complexas a época dos primeiros contatos. Na segunda metade do século XIX, foram descobertas nessa área cerâmicas elaboradas e ídolos de pedra. Esses elementos associados aos relatos históricos induziram à hipótese sobre a existência de complexidade cultural nessa região desde antes do contato. Nesse contexto, a região do rio Trombetas adquiriu visibilidade para arqueologia da Amazônia. Estudos arqueológicos na região de Porto Trombetas realizados na década de 1970 demostratam a existência de duas ocupações ceramistas situadas ao longo dos rios e lagos: uma mais antiga - Pocó; e outra mais recente - Konduri. Pesquisas recentes na mesma região, realizadas no âmbito da arqueologia de contrato, permitiram identificar sítios com características distintas daqueles situados nas margens dos rios relacionados a ocupação Konduri. O estudo e a comparação entre os sítios ribeirinhos e do interflúvio irá mostrar que as sociedades pré-históricas daquela região exploravam e dominavam ambos os ambientes. / The available historical sources for the area of the Nhamundá-Trombetas rivers, in the lower Amazon, report the existence of populous settlings, hierarchical forms of social organization and religious cults, indicating the existence of complex societies during the time of the first contacts. In the second half of the 19th century, elaborated ceramic and stone idols were discovered in this area. These elements associated with the historical reports led to the hypothesis of the existence of cultural complexity in this region previous to the contact. In this context, the region of the Trombetas river acquired visibility for Amazon archaeology. Archaeological studies carried out in the Porto Trombetas region in the 1970s demonstrated the existence of two ceramist occupations spread along the rivers and the lakes: an older one - Pocó; and a more recent one - Konduri. Recent research, in the same region, carried out in the scope of contract archaeology, allowed the identification of small sites showing distinct characteristics from those located in the edges of the rivers and associated with Konduri occupation. The study and comparison between the sites located in the edges of the rivers and in the interfluve zone will show that the prehistoric societies from that region exploited and dominated both environments.

The presented diploma thesis deals with the issue of wire electrical discharge machining of SiSiC ceramics. The first part explains the principles of electrical discharge machining, describes the WEDM technology and presents the properties of the advanced ceramics. The second part consists of a detailed analysis of the cutting process of eighteen samples obtained with systematically changing process parameters. Based on the obtained results from EDX analysis, SEM electron microscopy and topography there was performed an analysis of the influence of process parameters on the cutting speed, surface roughness, kerf width and number of wire breaks with usage of the selected brass cutting wire. From the evaluated results it was possible to select a combination of parameters that ensured a stable machining process.

Tichá, E.: Tupesy ceramics traditions in the contemporary context. Education project from the beginning. /Diploma thesis/ Praha 2014, Univerzita Karlova v Praze, Pedagogická fakulta. The theses includes theoretical study and art project that are connected content by the theme of Tupesy pottery making. Based on the literature study and original sources it provides information about Tupesy ceramics, its history, tradition and technology, and puts this information into broader historical, cultural and artistic context. Own artefacts present traditional topic in the current context. The main contribution of this work is the author's proposal for a comprehensive pedagogical project based on traditional Tupesy ceramics, its implementation and evaluation. The results of five year work prove that Tupesy ceramic tradition is widely applicable in the current context of educational work with children. Powered by TCPDF (www.tcpdf.org)

Ceramic additive manufacturing is gaining popularity with methods like selective laser sintering (SLS), binder jetting, direct ink writing and stereolithography, despite their disadvantages. Laser sintering and binder jetting are too expensive, while direct ink writing lacks resolution and stereolithography lacks scalability. The project aims to combine one of the most versatile, affordable, and readily available 3D printing methods: fused filament fabrication (FFF) with polymer derived ceramics to produce cellular ceramics to overcome the disadvantages posed by the other methods. The process uses a two-step approach. The first step is to 3D print the part using a polymer FFF 3D printer with a thermoplastic polyurethane filament and the second step is to impregnate the part in a polysilazane preceramic polymer and then pyrolyze it in an inert environment up to 1200C. The resulting product is a high-resolution cellular ceramic of the composition SiOC(N). This type of cellular ceramic can find an application in several fields such as scaffolds for bone tissue regeneration, liquid metal filtering, chemical and gas filtering, catalytic converters and electric applications. The process can provide an affordable alternative to the products used in these fields currently.

Pearly layers in seashells, also known as nacreous layers, are reported to be three orders of magnitude tougher than their primary constituent, aragonite. Their high toughness is attributed to a particular structure of alternating layers of natural ceramic and polymer materials. This work tries to emulate it using engineering materials. The thickness, strength, and stiffness of the ceramic layer; the thickness, stiffness, strength, and toughness of the polymer interface layer; and the number of layers are the factors that contribute to different degrees. Furthermore, understanding the relative contribution of different toughening mechanisms in nacre would enable identification of key parameters to design tough engineered ceramics. As a step towards that, in this thesis, layered ceramic beams replicating nacre were studied analytically, computationally, and experimentally. The insights and findings from these studies were then used to develop a new method to make tough layered ceramics mimicking nacre. Subsequently, the use of layered ceramics for armour applications was evaluated. Based on analytical numerical and experimental studies, we observed that the strength of the layers is a key factor to replicate the high toughness of nacre in engineered ceramics. We also demonstrated that, crack deflection and bridging observed in nacre in studies elsewhere, occur due to the high strength of platelets. Based on these findings, the new method developed in this study uses green alumina-based ceramic tapes stacked with screen printed stripes of graphite. During sintering, graphite oxidizes leaving empty channels in the stack. These channels were filled with tough interface materials afterwards. As a result, a ceramic- polymer composite with more than 2-fold increase in toughness was developed. Subsequently, we evaluated layered ceramics for armour applications based on numerical analysis validated with experiments. Consistent to the trends in literature, we observed that layers degrade the resistance to ballistic impact. However, improved energy absorption is demonstrated in layered ceramics. These conflicting dual trends were not presented and quantified in any earlier studies conducted elsewhere. Another new observation not documented earlier is the effect of interface strength. Using an interface material of sufficient strength, penetration resistance of layered ceramics can be improved beyond monolithic ceramics. Using these findings, new layered ceramic armour can be designed that is cost- effective and better performing than monolithic ceramics.

Ferroelectric materials, especially the polycrystalline ceramics, are very promising material for a variety of applications such as high permittivity dielectrics, ferroelectric memories, piezoelectric sensors, piezoelectric/electrostrictive transducers, electrooptic devices and PTC thermistors. Among the ferroelectric based piezoelectric ceramics the lead–zirconate-titanate Pb(Zr1-xTix)O3 (PZT) have dominated transducer and actuator market due to its excellent piezoelectric and dielectric properties, high electromechanical coupling, large piezoelectric anisotropy, ease of processing and low cost. However, the toxicity of lead based compounds has raised serious environmental concerns and therefore has compelled the researchers to look for new lead free alternatives with good piezoelectric and ferroelectric properties. (Na0.5Bi0.5)TiO3 (NBT) and its solid solution is one of the leading lead free piezoceramic ceramics due to their interesting ferroelectric, piezoelectric, electromechanical and dielectric property. The parent compound NBT is a ferroelectric with a moderately high Curie temperature (~250 oC), large ferroelectric polarization (~40µC/cm2) polarization, promising piezoelectric properties with 0.08% strain and longitudinal piezoelectric coefficient (d33) ~ 80 pC/N. X-ray and neutron diffraction studies in the past have shown that NBT exhibits rhombohedral (R3c) at room temperature. Neutron diffraction studies have suggested that NBT undergo a gradual rhombohedral to tetragonal (P4bm) transformation in a temperature region 200-320 ºC. Though the structure and phase transition behavior of NBT has been extensively investigated for over six decades now, this subject has again become debatable in recent few years, with some group reporting formation of orthorhombic phase above room temperature and another group suggesting monoclinic distortion at room temperature using high resolution x-ray diffraction technique. Interestingly the intermediate orthorhombic instability, reported by electron diffraction studies, has never been captured by neutron diffraction method though neutron diffraction is an equally powerful tool for studying (oxygen) octahedral tilts in perovskites. Needless to mention, the understanding of the subtle structural distortions have great significance with regard to the determination of the structure-piezoelectric property correlations in NBT based piezoceramics. The present thesis deals with such subtle structural issues in great detail. The systems investigated in the thesis are Ca and Ba modified NBT. While the Ca modified system was chosen to understand the subtle orthorhombic instability that has been reported above room temperature (only) by detailed electron diffraction work, Ba-modified NBT is the most investigated among the NBT-derived piezoelectric material systems and this thesis attempts to address some of the very complex nature of the structure-piezoelectric property correlation of this system. The first chapter of the thesis provides a brief introduction to the field of ferroelectrics, perovskite structure and their phase transition. A brief exposure to the conventional lead based relaxor ferroelectric and piezoelectric material is provided. A detailed overview of the existing knowledge related to room temperature structure of NBT and its phase transition studies with temperature has been discussed in the later part of this chapter. The second chapter includes various the experimental techniques that have been employed to synthesis and characterize the specimens under investigation. The third chapter deals with the phase transition behaviour of Ca modified NBT as a function of composition and temperature in the dilute concentration region. This work was carried out with the view to obtain a better understanding and compliment the intrinsic high temperature orthorhombic instability in NBT reported by electron diffraction technique. Interestingly, inspite of the fact that neutron diffraction method is a very sensitive tool for investigating subtle change in the nature of octahedral tilt in oxide perovskites, the intermediate orthorhombic distortion proposed by the electron diffraction studies has so far never been captured in any of the neutron diffraction studies. In this work we have verified the genuineness of the intrinsic instability with regard to the non-polar orthorhombic structure using neutron powder diffraction by adopting a special strategy which helped in capturing the characteristic signatures (the superlattice reflections) of the orthorhombic phase in the neutron powder diffraction patterns. It was found that small fraction of Ca-substitution (8-10 mol %) was good enough to amplify the magnitude of the orthorhombic (Pbnm) distortion, without altering the sequence of the structural evolution with temperature of the parent compound (NBT) itself, and stabilizing it at the global length scale at lower temperatures than pure NBT. This chapter presents the innovative approach that was used to extract reliable information about the very complex phase transition behaviour, involving coexistence of the various similar looking but crystallographically different phases in different temperature regimes by Rietveld analysis of temperature dependent neutron powder diffraction pattern in conjunction with temperature dependent dielectric and ferroelectric characterization of the specimens. The detailed study revealed the following sequence of structural evolution with temperature: Cc+Pbnm →Pbnm + P4/mbm → P4/mbm →Pm3 m. The fourth chapter gives a detail account of the structure-property correlations and the phase transition behaviour of (1-x)(Na0.5Bi0.5)TiO3 – (x)BaTiO3 (0≤x≤0.10), the most important solid solution series with NBT as reported in the literature. The phase transformation behaviour of this system has been investigated as a function of composition (0<x≤0.10), temperature, electric field and mechanical-impact by Raman scattering, ferroelectric, piezoelectric measurements, x-ray and neutron powder diffraction methods. The structure of the morphotropic phase boundary (MPB) compositions of this system, which is interesting from the piezoelectric property point of view, has been under controversy for long. While some groups report the structure to be pseudocubic, other groups suggest it to be combination of rhombohedral and tetragonal. A perusal of the literature suggests that the reported nature and composition range of MPB is dependent on the method of synthesis and characterization technique used. In the present study, crystal structure of the NBT-BT solid solution has been investigated at the close interval near the MPB (0.05≤x≤0.10). Though x-ray diffraction study revealed three distinct composition ranges characterizing different structural features in the equilibrium state at room temperature: (i) monoclinic (Cc) + rhombohedral (R3c) for 0≤x≤0.05, (ii) “cubic-like” for 0.06≤x≤0.0675 and (iii) MPB like for 0.07≤x<0.10, Raman and neutron powder diffraction studies revealed identical symmetry for the cubic like and the MPB compositions. Both the cubic like compositions and the MPB compositions exhibit comparatively large d33. In the later part of this chapter this apparent contradiction is resolved by the fact that the cubic like structure transforms irreversibly to MPB after electric poling, a procedure which involves applying high dc electric field (well above the coercive field) to the pellet before carrying out the piezoelectric measurements. The effect of electrical field and mechanical impact has been studied for all the three different composition range, and it was found that electric field and mechanical impact both led to irreversible phase transformation in the same direction, though the transformation with mechanical impact remains incomplete in comparison to electric field. The most pronounced effect was observed for the cubic like compositions 0.06≤x≤0.0675 – they undergo phase separation to rhombohedral and tetragonal phases by electrical and mechanical perturbations. In the non-perturbed state the cubic-like critical compositions mimics features of relaxor ferroelectrics and extremely short coherence length (~ 40-50 Å) of the out-of-phase octahedral tilts. In the poled state this coherence length grows considerably and the system behaves like a normal ferroelectric. This confirmed a strong coupling between the lattice, octahedral tilts and polarization degrees of freedom. Neutron diffraction study of compositions exhibiting cubic-like and the MPB like revealed that the traditional P4bm tetragonal structure model fails to account for the intensity of the superlattice reflections. Thus the tetragonal structure stabilized above room temperature in pure NBT is different from the tetragonal phase observed at room temperature in the NBT-BT system. The results of the effect of mechanical impact and electric field has also been reported in this chapter for the critical composition exhibiting MPB (x=0.07). A detailed structural analysis of the precritical compositions, x≤0.05, revealed coexistence of ferroelectric phases (Cc+R3c) in equilibrium state (annealed specimens). This transforms to single phase (R3c) state after poling. Thus though the precritical (x≤0.05) and critical compositions (0.06≤x<0.10) of NBT-BT exhibits coexistence of ferroelectric phases in the equilibrium state, the fact that the electric poling makes the specimen single phase, R3c, after poling for the precritical compositions and retains the two phase nature of the critical compositions makes the critical compositions exhibit considerably higher piezoelectric response than the precritical compositions. Chapter five is dedicated to phase transition behaviour of the post critical compositions of (1-x)(Na0.5Bi0.5)TiO3–(x)BaTiO3 (0.16≤x≤1) using temperature dependent XRD, dielectric and ferroelectric studies. Though structurally the entire composition range is tetragonal, several notable features were revealed during detailed examination of the structural and dielectric behaviour. This study is also important from the view point that pure BT is a major component of multilayer ceramic capacitors and that an increase in the Curie point would be a welcome step for better temperature stability of the device. NBT does this. The transition temperature increases from 120 ºC for pure BT to 275 ºC for x=0.30 along with simultaneous increase in c/a ratio from 1.009 (pure BT) to 1.02 (x=0.30). Detailed analysis of temperature and frequency dependent dielectric data revealed deviation from Curie-Weiss and suggests a gradual transformation to relaxor-ferroelectric state as the NBT concentration increases in BT. The measure of frequency dispersion ‘γ’ parameter was determined from modified Curie-Weiss law for various compositions in the system. The ferroelectric and piezoelectric properties have also been investigated in detail for this composition range and an attempt has been made to correlate the composition variation of these properties with their structural parameters. This chapter shows a systematic correlation between all physical quantities such as Curie point, piezoelectric coefficient, polarization and tetragonality as a function of composition.

This thesis deals with the investigations on the atomic composition, chemical surface states and microstructural features of barium titanate and other electronic ceramics namely barium polytitantes, calcium manganites and magnesium calcium titanate by surface analytical techniques. After presenting a brief introduction on the ceramic materials studied in terms of their crystal structures, electrical properties, nonstoichiometry and interfacial characteristics, the thesis describes the synthesis of the ceramics and the methodology of the different surface analytical techniques utilized such as backscattering spectrometry (BS), an ion beam analysis (IBA) technique, X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDS). The XPS investigations on the chemical surface states of polycrystalline barium titanate having well-defined electrical characteristics reveal the prevalence of Ba in two distinct chemical environments : the one corresponding to the lower binding energy is related to the dielectric while the other having higher binding energy is correlated to semiconducting properties of the ceramics. Processes such as abrasion or polishing make the surfaces more reactive and susceptible to atmospheric contamination. Sputter cleaning causes surface modification leading to changes in the Ba (3d) and Ti (2p) spectra. Studies on the surface atomic composition by BS and microstructural features of doped barium titanate ceramics reveal their interfacial characteristics in terms segregation of dopants or metal ion constituents. Surfaces of these ceramics exhibit cationic as well as anionic nonstoichiometry depending on the processing steps involved. Ceramics synthesized by oxalate precursor route are Ti-rich while those prepared by gel-to-crystallite method are Ba-rich. These are correlated to the chemical processes and background impurities which in turn control the microstructures. Barium titanate substitued with > 1 at. % Mn are deficient in oxygen and exist as the hexagonal polymorph. Acceptors segregate at the grain boundaries accompanied by the enrichment of Ti leading to PTCR or GBLC characteristics. The oxygen nonstoichiometry prevailing in the surface regions of differently processed calcium manganites is investigated by way of depth profile measurements involving 16O(a,a) 16O resonant scattering. These studies reveal extensive compositional heterogeneity across the surface layers particularly in the manganite specimens annealed in lower po2 leading to the stabilization of brownmillerite phase. Two of the microwave dielectric ceramics namely dibarium nona-titanate and barium tetra-titanate with suitable variations in Ba:Ti ratios have been synthesized by the carbonate-gel precipitation. The corresponding dense ceramics have high permittivity (~ 52) and low temperature coefficient of permittivity (TCK ~ 5 ppm /0C). Extensive miscibility between the ilmenite-type MgTiO3 and perovskite-type CaTiO3 over a wide compositional range is brought about by the simultaneous equivalent substitution of Al3+ + La3+. The resulting (Mg1-(x+y)CaxLay)(Ti1-yAly)O3 ceramics exhibit improved microwave dielectric properties by way of high permittivity, low TCK and high quality factor. The microarea elemental distribution and chemical surface state studies reveal the complexity in the Mg/Ca distribution and its correlation with the solid state miscibility as well as dielectric properties. The discontinuous changes in the local site symmetry of the cationic substituents in these ceramics have been investigated by the photoluminescence spectra using Pr3+ as the emission probe.

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.

Surface integrity is of great significance in grinding performance since grinding process is often used as a finishing step. For metallic materials, residual stresses play an important role in surface integrity for its strong effect on fatigue life, corrosion resistance, and part distortion. For ceramic materials, the surface damage induced by grinding process could greatly affect the mechanical strength and surface finish of the component. The functional behavior of machined components can be enhanced or impaired by the grinding process. Because of this, understanding the surface integrity imparted by grinding is very important. The use of fluid is common in grinding process, however, the high cost and environmental impact of the conventional flood cooling is very undesirable. The minimum quantity lubrication (MQL) have been introduced in industry for about two decades as a promising alternative to conventional flood cooling for economical and environmental advantages. A comprehensive understanding of the MQL effect on the process performances and surface integrity is of great value to the implementation of MQL technique in industrial situation. Grinding-induced residual stress prediction has been a topic of research since the 1970’s while the studies of MQL grinding is still on the early stage with experimental investigations. A comprehensive study and quantitative description of MQL effect on the residual stress generation in grinding is highly demanded. On the other hand, although there has been significant research in the area of surface damage in ceramic grinding, there are still opportunities for advancing predictive methods. Therefore, the objectives of the current research are set as follows: (1) develop a method of predicting residual stress based on an analytical description of the grinding process under MQL condition, (2) develop a method of predicting surface finish and damage in ceramic grinding, and (3) validate the model with experimental data. The research will first focus on predicting residual stresses in MQL grinding based on first principles. This includes predictive models of grinding forces, and grinding temperature stemmed from grinding kinematics and dynamics principles as part of the overall modeling effort. The effect of MQL on both lubrication and cooling aspects has been integrated into these models. The mechanical and thermal output parameters will serve as the basis for determining the loading history which generate residual stresses. The research will also aim at surface roughness modeling in ceramic grinding. A ductile-brittle mixed surface generation is predicted based on the nature of ceramic materials and grinding kinematics. The crack system developed from indentation fracture mechanics approach will be utilized in evaluating the brittle mode surface generation. The modeling techniques will be applied to a range of grinding conditions and materials. This research would aid in evaluating various surface integrities in grinding of metallic and ceramic materials with little experimental efforts. The output could be used to machine these materials effectively to order to improve the functionality of the component.

This investigation was initiated by IBM to determine the types of cracks formed in hot-isostatic-pressed (HIP) Ni-Zn ferrite under impact and static loading conditions. A 1/8-inch tungsten carbide (WC) ball was used to apply the load in both cases. The impact loading condition was accomplished by dropping the WC ball from various heights between 40 and 200 cm. The static loading condition was accomplished by applying loads of 10 kg, 15 kg, and 30 kg on a Rockwell Hardness Tester. The response of HIP Ni-Zn ferrite to impact and static loading was elastic/plastic yielding permanent indentations. "Dimple" impressions, Hertzian-ring cracks, and radial cracks were formed upon applying increasing loads to the HIP Ni-Zn ferrite. As the grain size of the material was increased, both the Hertzian-ring and radial cracks were formed at lower loads compared to the as-received samples. The "dimple" impressions were not observed to follow this trend.