The influence of acceptor doping, stoichiometry and processing on the mechanical properties and microstructure of PZT ceramics

Lead zirconium titanate (PZT) is the most widely used ferroelectric ceramic material on the market. The majority of published research revolves around its piezoelectric and dielectric properties. This thesis is focused on the complex dependencies between the material’s composition (Sr^{2+}, Fe^{3+} doping and Zr/Ti ratio), microstructure, structure, physical, functional and mechanical properties. The goal was to identify the most important strength-controlling factors to create stronger and more reliable PZT products and reduce their manufacturing waste. PZT specimens were prepared from metal oxides using an optimised conventional powder processing route and industrial processing parameters. Fracture strength was tested under equibiaxial flexural stress using a custom-designed ring-on-ring fixture and the results were evaluated using a 2-parameter Weibull distribution. Large pores and machining-induced damage were identified as the weakest flaws. The pore size distribution was affected by all studied factors. The most notable increase in strength was caused by the acceptor doping, which was linked to the changes in grain boundary strength; and by an increase in the sintering temperature (for pure PZT). The strength of the acceptor-doped PZT showed no significant change with Zr/Ti ratio or sintering temperature, unlike the undoped PZT

Microstructure, nanostructure, and local crystallography in perovskite ferroelectrics and antiferroelectrics

Selected area and Kikuchi diraction patterns, traditional bright eld and dark eld imaging techniques in electron microscopy as well as high resolution TEM and STEM techniques, together with electron backscattered electron diraction technique have been used to study the domain structures, local crystallography and atomic structures in PZT-based materials. Reliable EBSD mapping of 90 degrees domains in a tetragonal Pb(Zrx; Ti1-x)O3 with x = 0.5 ferroelectric perovskite has been achieved for the rst time, together with reliable automated orientation determination from TEM-Kikuchi patterns. This has been used to assess the local crystallography of domains by determining misorientation angles at 90 degrees domain boundaries and thus local c/a ratios. In most cases, a good agreement is found between local c/a ratios and global measurements by X-ray diraction, but some clear discrepancies have also been found suggesting that real local variations are present, perhaps as a consequence of compositional inhomogeneities. The details of the domain structure of the incommensurate antiferroelectric struc- ture in La-doped zirconium-rich lead zirconate titanate have been revealed in detail for the rst time. The structure is dominated by 60 degrees domain boundaries close to {101} planes of the primitive perovskite cell; and tilts of the perovskite sublattice of about 0.5 degrees are also noted at such boundaries consistent with a small tetragonal distortion of the primitive cell. Within each domain a streaked nanostructure is revealed under weak diraction conditions perpendicular to the long b-axis of the incommensurate supercell, which appears to be a consequence of planar faulting perpendicular to this b-axis. 90 degrees domain boundaries are also observed but are less frequent than 60 degrees boundaries and in con- trast to previous reports, these often have rather curved and irregular boundary planes. The atomic arrangement of these 90 degrees boundaries was studied by aberration corrected HRSTEM. Dierent stackings and periodicities were identied.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Fabrication of Lead Iron Niobate Thin Films Focusing on Sol-Gel Method

Department of Materials Science and EngineeringThe aim of this study was to synthesize a single-phase PFN thin film using Monoethanolamine(MEA) as a chelating agent through the sol-gel method. The PFN thin film was deposited onto a substrate using a spin-coating technique, where the solution was coated and rotated. In this process, the presence of MEA prevented the formation of secondary phases by promoting the reaction between the Nb precursor and the Fe precursor before reacting with the Pb precursor. The presence of MEA is speculated to be the reason why the Nb precursor reacted with the Fe precursor before the Pb precursor, thereby preventing the formation of secondary phases and lowering the crystallization temperature to around 150??C instead of 250-325??C. Furthermore, X-ray diffraction patterns demonstrate that the addition of MEA allowed the PFN thin film to grow as a single phase at low temperatures, while in the absence of MEA, a single phase could only be achieved at temperatures above 800??C. Scanning electron microscope images reveal that the presence of MEA eliminates porosity and cracks, resulting in a uniform film. Analysis of the ferroelectric properties, indicated by the P-E hysteresis loop, shows that the PFN thin film fabricated with the chelating agent at 500??C exhibits minimal leakage current and exhibits strong ferroelectric characteristics. However, for the PFN thin film fabricated without the chelating agent, the presence of secondary phases leads to significant leakage current, resulting in a large coercive field and reduced saturation polarization. In this study, an abnormal phenomenon was observed during the process of measuring the P-E polarization loop and permittivity as a function of temperature. as the temperature increased, the PFN thin film fabricated with the chelating agent exhibited a rapid increase in internal bias field around 150??C, but did not show a distinct Curie temperature. Unlike the reported PFN films with a Curie temperature around 110??C, the fabricated PFN films in this study did not exhibit the abrupt increase and decrease in permittivity, indicating an anomalous behavior. The exact cause of this phenomenon has not been determined yet, but it is believed to be a comprehensive effect of defect dipoles caused by the acceptor effect based on the relative amounts of Fe2+ and Fe3+ ions, and an increase in the concentration of defect charge carriers due to the temperature-induced increase. The comparison of the relative quantities of Fe2+ and Fe3+ based on the presence or absence of the chelating agent was conducted using XPS. However, further research is needed to elucidate the underlying causes of this phenomenon. To precisely identify these causes, additional analysis is required, but continuous improvement and research are necessary due to limitations in the resolution of measurement equipment and sample constraints. PFN is a multiferroic material that exhibits both ferroelectricity and antiferromagnetism, which has recently attracted significant attention. However, due to its relatively high Curie temperature, it displays ferroelectric properties at room temperature. Nonetheless, observing magnetic properties at room temperature is challenging due to its low Neel temperature. Additionally, PFN primarily demonstrates antiferromagnetic characteristics below the Neel temperature, attributed to the formation of Fe-O-Fe and Fe-O-Nb-O-Fe bonds at angles of 180??. In PFN, Pb2+ occupies the A-site while Nb5+ occupies the B-site, favoring electrical alignment. On the other hand, Fe3+ at the octahedral B-site provides the necessary magnetic moment for magnetic alignment, contributing to both ferroelectric and magnetic alignments in the material. Based on these principles, the coupling between electrical and magnetic alignments was investigated in order to study the ferroelectric and magnetic properties within complex perovskite structures. However, unfortunately, in this study, magnetic properties were not observed in the fabricated samples, indicating the need for further research. Nevertheless, in an attempt to induce coupling between electrical and magnetic alignments, the concept of A-site engineering was employed. A two-step method was implemented, involving the separate preparation of A-site and B-site solutions, followed by their mixture, to manufacture A-site engineered PFN thin films with a close-to-single-phase structure. Additionally, the introduction of a PbO layer on the substrate was employed to prevent the orientation of the upper film and the volatilization of Pb during sintering, as well as to mitigate the crystalline phase changes in the film caused by the diffusion of Pb ions from the electrode. This approach demonstrated the potential for the fabrication of A-site engineered PFN thin films at lower sintering temperatures. In this study, the observation of abnormal ferroelectric properties for the first time was achieved. By applying the A-site engineered PFN concept, previously reported in PFN bulk systems, to thin films, the potential for various applications, particularly in the field of memory, was demonstrated. Further research on the abnormal phenomena will continue in the future. Moreover, there is room for process improvement in the fabrication of single-phase multiferroic thin films that can be sintered at low temperatures, opening up endless possibilities for future advancements.clos

Advanced materials from gels. Proceedings of the Sixth International Workshop on Glasses and Ceramics from Gels

International workshop on glasses and ceramics from gels (6th. 1991. Sevilla

Low-toxic chemical solution deposition methods for the preparation of multi-functional (Pb1-xCax)TiO3 thin films

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid. Facultad de Ciencias. Departamento de Química Inorgánica. Fecha de lectura: 18-09-200

Nanoscale Ferroic Materials—Ferroelectric, Piezoelectric, Magnetic, and Multiferroic Materials

Ferroic materials, including ferroelectric, piezoelectric, magnetic, and multiferroic materials, are receiving great scientific attention due to their rich physical properties. They have shown their great advantages in diverse fields of application, such as information storage, sensor/actuator/transducers, energy harvesters/storage, and even environmental pollution control. At present, ferroic nanostructures have been widely acknowledged to advance and improve currently existing electronic devices as well as to develop future ones. This Special Issue covers the characterization of crystal and microstructure, the design and tailoring of ferro/piezo/dielectric, magnetic, and multiferroic properties, and the presentation of related applications. These papers present various kinds of nanomaterials, such as ferroelectric/piezoelectric thin films, dielectric storage thin film, dielectric gate layer, and magnonic metamaterials. These nanomaterials are expected to have applications in ferroelectric non-volatile memory, ferroelectric tunneling junction memory, energy-storage pulsed-power capacitors, metal oxide semiconductor field-effect-transistor devices, humidity sensors, environmental pollutant remediation, and spin-wave devices. The purpose of this Special Issue is to communicate the recent developments in research on nanoscale ferroic materials