1,721,008 research outputs found
Production and characterization of morphological and microstructural composite bulk or film for the study of interactions multiphysics
Full text linkProduction and morphological and microstructural characterization of bulk composites or thick films for the study of multiphysics interactions
Full text linkThe surge of interest in multifunctional materials over the past 15 years has been driven by their fascinating physical properties and huge potential for technological applications such as sensors, microwave devices, energy harvesting, photovoltaic technologies, solid-state refrigeration, and data storage recording technologies. Among the others, magnetoelectric multiferroic composites are a special class of advanced solid-state compounds with coupled ferromagnetic and ferroelectric ferroic orders which allow to perform more than one task by combining electronic, magnetic and mechanical properties into a single device component. The production and characterization of lead zirconate titanate (PZT)- cobalt ferrite composites was the main topic of the thesis. During the PhD activity different ceramic processing and characterization technologies were studied and involved in order to optimize the produced materials as a function of the final microstructural and functional properties. The synthesis of cobalt ferrite (CF) and niobium-doped lead zirconate titanate (PZTN) powders by solid state reaction method and sol-gel technique, to control the particle size distributions and their microstructural and functional properties through calcination and milling treatments has been addressed first, followed by the mixing of the PZT and CF powders to produce particulate composites. The dispersion of PZT and CF in a liquid media, to produce layered composites by depositing the particles by electrophoretic deposition was an objective of the work as well. Key issues such as the lead loss during the sintering of PZTN-CF composites and the reaction between CF and titania have been addressed and have resulted in improvements in the sintering and characterization techniques leading to the production of fully dense PZTN-CF dual-particulate composites. In particular, the optimized sintering parameters have configured a new paradigm of ceramic sintering, which has been called quite-fast sintering, in respect to the traditional one, and the study of the PbO loss has led to propose an equation to calculate the PbO loss through XRD analysis. Further important achieved results were: the production of nanocobalt ferrite particles by multi-step milling, the correlation between the spin-canting angle with the microstrain and the average crystallite size of nanocobalt ferrite particles, the understanding of the CF growth mechanisms, the extension of the Globus model from small ferromagnetic grains "having no defect inside" to multiparallel-twinned overgrown ones, the understanding of heating rate effect on the interface nucleation onset of the anatase-to-rutile transformation and the anatase particle size, and the reaction products between CF and rutile at 1200 °C at the variation of CF/rutile ratio
Magnetoelectric composite bilayer film by electrophoretic deposition
Full text linkIn the recent years the interest of the research community towards multiferroic composite materials was growing fast [1,2]. A number of papers relates to bulk materials while less attention is focused on films. Electrophoretic deposition (EPD) was applied to prepare magnetoelectric (ME) composite bilayer thick films based on perovskite phase and spinel cobalt ferrite as some of the best piezoelectric and magnetostrictive oxides belong these crystal groups. The co-deposition of titanium oxide (TO) and cobalt ferrite (CFO) nanoparticles and the deposition of niobium-doped lead titanate zirconate (PZTN) were made from colloidal suspensions in ethanol keeping constant voltage and recording the current. Good adhesion and compaction of the green film were achieved by optimization of deposition voltage and time while high density of the film and minimized interphase reactions occurred after sintering. The deposited volume, the mixing of dielectric and magnetic phases and the density and ordering of the films have been verified by electron scanning microscopy after heat treatment. No reactions between the different phases was found. The piezoelectric properties were measured on the sintered films. [1] N.A. Spaldin, M. Fiebig, Science 309 (2005) 391. [2] R. Ramesh, N.A. Spaldin, Nat. Mater. 6 (2007) 2
Thick dielectric films produced by electrophoretic deposition
No full textElectrophoretic deposition (EPD) from colloidal suspensions was utilized for the
preparation of lead zirconate titanate films (PZT) on PZT based substrates. The present
process is developed as a convenient forming process for the development of devices
based on thick ceramic films. The deposition parameters - using EPD - such as colloidal
parameters, deposition voltage and deposition time and the post process parameters, such
as drying velocity and sintering will be controlled. Conductive materials are customarily
used as deposition substrates, but the possibility of depositing on semiconductors (SC)
has recently been demonstrated in this laboratory [1]. This work wants to continue the
research started by Baldisserri et al. that puts emphasis on the analysis of current
transients during constant-voltage deposition as a diagnostic tool for the assessment of
some crucial features of the EPD process [2,3]; the correlations between the above
parameters and final microstructure, by checking the salient features like the film
adhesion, compaction and functionality, will be investigated.
References
[1] C. Baldisserri, D. Gardini, C. Galassi, Sensors & Actuators A 174 (2012) 123.
[2] C. Baldisserri, D. Gardini, C. Galassi, J. Colloid Interface Sci., 347 (2010) 102.
[3] H. Farnoush, J.A. Mohandesi, D. H. Fatmehsari, Ceram. Int., 38 (2012) 6753
Milling and quite-fast sintering as key production steps to obtain fully dense PZTN-CF particulate composites
No full textIn the near future (within ten years) magnetoelectric multiferroics could be implemented into the emerging technologies such as wireless power, internet of things, machine-to-machine communication services, mesh network, etc. Remarkable efforts have been done to develop laminated bi-layer and multilayer multiferroic composites as bulk or thin films. These structures lead to remarkable magneto-electric coupling coefficients of a few Volts / cm∙Oe because the ferroic layer is a "full dielectric" which can be completely poled in the conventional way. On the other hand in the particulate ceramic composites the requirement for "full dielectric" is no longer applicable, since the ferroic phases are fully separated within the composite. The strengths of particulate ceramic composites are low cost, simple production technology, higher strain mediated magneto-electric coupling (since electric order phase/magnetic phase interface density can be higher) and easy control of electrical and magnetic properties if the ferroelectric phase (generally a perovskite) and the ferromagnetic one (a ferrite with spinel structure) are mixed in a favourable proportion under the percolation threshold of the ferromagnetic phase. A great research effort is in progress to improve the fabrication of PZT-CoFe2O4 (PZT- CF) composites in order to avoid the unwanted reactions, which occur during densification of PZT-CF materials at 1100-1200 °C, and to achieve the electric saturation during the poling. Up to date, by setting a quite-fast sintering, full densification and prevention of unwanted reactions were achieved for the PZT:CF 74:26 composites,1 but achieving electric saturation is still a challenge. Further important results were: the understanding that the main cause of reactions is the PbO loss;1 the proposal of an equation to calculate the PbO loss through XRD analysis, considering the amount of ZrO2 and variation of perovskite's tetragonality;1 and the ability to design the ceramic process (milling of the CF powers in particularly) to control the CF grain size distribution, which can be mono- or bi-modal, and overgrowth.1,2 References 1. P. Galizia, C.E. Ciomaga, L. Mitoseriu and C. Galassi, "PZT-cobalt ferrite particulate composites: Densification and lead loss controlled by quite-fast sintering", J. Eur. Ceram. Soc., 37, pp. 161-168, 2016. 2. P. Galizia, C. Baldisserri, C. Capiani and C. Galassi, "Multiple parallel twinning overgrowth in nanostructured dense cobalt ferrite", Mater. Design, 109, pp. 19-26, 2016
Thick composite magnetoelectric films by electrophoretic deposition
Full text linkElectrophoretic deposition (EPD) from colloidal suspensions was utilized for the preparation of composite magneto-dielectric films on a conductive substrate. The present process is developed as a convenient forming process for the development of devices based on thick magneto-dielectric films [1]. The deposition parameters - using EPD - such as colloidal parameters, deposition voltage and deposition time and the post process parameters, such as drying velocity and sintering will be controlled. This work aims to control the fillers/matrix ratio during the deposition and obtain a good adhesion, compaction and functionality of the composite film after the heat treatment. Measurements results for the current transients during constant-voltage deposition and the correlated deposited mass are presented [2, 3].1] A.O. Karilainen, P.M.T. Ikonen, C.R. Simovski, S.A. Tretyakov, A.N. Lagarkov, S.A. Maklakov, K.N. Rozanov, and S.N. Starostenko, Experimental studies on antenna miniaturisation using magneto-dielectric and dielectric materials, IET Microw. Antennas Propag., vol. 5, no. 4, pp. 495-502, 2011. 2] C. Baldisserri, D. Gardini and C. Galassi, An analysis of current transients during electrophoretic deposition (EPD) from colloidal TiO2 suspensions, Journal of Colloid and Interface Science 347 (2010) 102-111 3] H. Farnoush, J.A. Mohandesi, D. H. Fatmehsari and F. Moztarzadeh, A kinetic study on the electrophoretic deposition of hydroxyapatite-titania nanocomposite based on a statistical approach, Ceramics International 38 (2012), 6753-676
Microstructure development in novel titania-cobalt ferrite ceramic materials
No full textThe system cobalt ferrite (CFO)–titania (TO) has been studied in view to produce new in situ ceramic composites by conventional solid state reaction. To synthesize the CFO–TO composite, the processing parameters are optimized to yield a reliable and repeatable homogeneous distribution of the phases. Composition, crystalline structure and microstructure of the sintered bodies were investigated by XRD, SEM, microprobe analysis; the image analysis was performed to quantify the phase volume content and grain size. The final compositions after sintering differ significantly from the starting ones as a consequence of the reaction of titania with the ferrite and the formation of a new ternary compound Fe2CoTi3O10 (FCTO). In this work we report for the first time the preparation of almost pure (about 95 vol%) single phase FCTO ceramics, its XRD patterns, and the microstructural characterization
PZT film on silicon by electrophoretic deposition
No full textIn recent times direct integration of ferroelectrics on silicon wafer has been attracting interest [1]. Electrophoretic deposition (EPD) was investigated in this laboratory [2] as an alternative mean to produce lead zirconate titanate (PZT) film on silicon wafers followed by sintering at 850-950°C. EPD is an easily implemented deposition technique that requires only basic laboratory gear and a sufficiently stable colloidal suspension to produce ceramic and electroceramic films with thickness in the 100 nm - 10 mm range3 . It has been found that the EPD of niobium-doped lead zirconate titanate (PZTN), performed in ethanol-based suspensions of PZT on bare silicon wafers on which Al/Si alloyed ohmic contacts were made, produced smooth green films that strongly pinned to the silicon substrate after sintering. Thick and well-adhered sintered PZT films on silicon having thickness about 50 µm were thus obtained. Such structures could be the core of novel on-chip sensors/actuators. The results of the production of thick PZT films by EPD and sintering and some characterizations of the same are reported. [1] M. Y. Gureev, A. K. Tangatsev, N. Setter; IEEE T Ultrason Ferr, 58, 1959 (2011) [2] C. Baldisserri, D. Gardini, C. Galassi; Sensor Actuat A-Phys, 174, 123 (2012) [3] P. Sarkar, P.S. Nicholson; J Am Ceram Soc, 79, 1987 (1996
Reduction of PbO loss in PZT-cobalt ferrite composites through quite-fast sintering and its quantification by means of XRD analysis
Full text linkNowadays, considerable efforts have been devoted to design and control the fabrication of multifunctional materials in order to fulfil the needs of modern technology for novel sensors, microwave devices, energy harvesting, photovoltaic technologies, solid-state refrigeration, data storage recording technologies and multiferroic random access multistate memories (MFRAM) [1]. Particulate ceramic composites are low cost, simple production technology, higher strain mediated magnetoelectric coupling (since electric order phase/magnetic phase interface density can be higher) and easy control of electrical and magnetic properties if the ferroelectric phase and the ferromagnetic one are mixed in a favourable proportion under the percolation threshold of the ferromagnetic phase. A great research effort is in progress to improve the fabrication of PZT-CoFe2O4 (PZT-CF) composites due to the excellent piezoelectric properties showed by the PZT material class and the large magnetostrictive coefficient of the CF. Unfortunately, during the sintering process particulate PZT-CF composites, side reactions do occur that are detrimental to the properties of the so-obtained material. In this study, we have avoided such reactions and PbO loss by setting a quite-fast sintering process [2]. The extent of PbO loss was determined by means of XRD analysis of the densified samples taking into account the amount of ZrO2 and the variations of the perovskite's tetragonality [2]. The calculated PbO loss values are in agreement with the final density and the microstructure of PZT-CF composites. In particular, microstructural characterization showed that CF grain size distribution can be mono- or bi-modal, and CF overgrowth was found to affect the coercivity of the material [3]. [1] M. M. Vopson, Fundamentals of Multiferroic Materials and Their Possible Applications. Crit. Rev. Solid State 4:40 (2015) 223-250 doi:10.1080/10408436.2014.992584 [2] P. Galizia, et al., PZT-cobalt ferrite particulate composites: Densification and lead loss controlled by quite-fast sintering. J. Eur. Ceram. Soc. (2016). doi:10.1016/j.jeurceramsoc.2016.08.025 [3] P. Galizia, C. Baldisserri, C. Capiani, C. Galassi, Multiple parallel twinning overgrowth in nanostructured dense cobalt ferrite. Mater. Design 109 (2016) 19-26. doi:10.1016/j.matdes.2016.07.05
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