1,721,013 research outputs found
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
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
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
Heterostructured ceramic materials based on PZTN-CFO compounds
Full text linkMultiferroic composites are currently one of the hot research topics [1]. Particulate ceramic composites have the advantages of low cost, simple production technology, good magnetoelectric effect 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 due to the excellent piezoelectric properties showed by the PZT material class and the large magnetostrictive coefficient of the CF. Unfortunately unwanted reactions occur during densification of PZT-CF materials at 1100-1200 °C. They are promoted by initial PbO loss that is calculated through XRD analysis, considering the amount of ZrO2 and variation of perovskite's tetragonality. The resulting titania reacts with CF to form cobalt titanate [2]. The microstructure of the composites at 26-81 mol % CF content was thoroughly investigated; the CF grain size distribution can be mono- or bi-modal and overgrowth [3] occurs. By setting a quite-fast sintering full densification and prevention of unwanted reactions was achieved for the PZT:CF 74:26 composites. The high coercivity (789 Oe) shown by these composites is correlated to the good dispersion of euhedral CF grains (250 nm) in the PZT matrix that is affected as well by limited grain growth (240 nm). [1] G. Schileo, Recent developments in ceramic multiferroic composites based on core/shell and other heterostructures obtained by sol-gel routes. Prog. Solid State Ch. 41 (2013) 87-98. [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
Electrophoretic deposition of bilayer based on sacrificial titanium dioxide and lead zirconate titanate on bare silicon wafer
No full textBilayer thick films of sacrificial titanium dioxide and Nb-doped lead zirconate titanate (PZTN) have been deposited on bare silicon wafers using electrophoretic deposition (EPD) technique. Deposition of such ceramic particles, dispersed ethanol-based suspensions, on semiconductor substrate has been made possible after preparation of alloyed junctions Al/Si characterized by ohmic behaviour. Sintering of green TiO2/PZTN films was performed at 900 ◦C for 1 h. The composition of the films, the thickness and relative density of the deposited materials have been analysed by EDS-SEM analysis. The lead diffusion through the silicon wafer has been reduce
Multiple parallel twinning overgrowth in nanostructured dense cobalt ferrite
No full textCobalt ferrite powders were synthesized by solid state reaction of the nanosized oxides at different temperatures. The highly aggregated powders were milled, and the aggregate size was reduced from 25 - 40 μm to 12-20 μm, depending on the milling time. A correlation between milling media diameter and final granulometry, and an unexpected calcination temperature effect on the milling efficiency were found. Highly homogenous green bodies and fully dense materials were produced for the first time after conventional sintering. The crystallite size depends primarily on the heating conditions and decreases from 50 - 70 nm to 27-13 nm. Under the same sintering conditions, particle morphology and crystallite size control the final grain shape, producing twinned grains with increased multiple parallel twinning overgrowth for the finer powders. The sintered cobalt ferrite ceramics show a relative density of 96-99%. The higher the planar faults density and grain size, the lower is the induced magnetization due to increased domain walls pinning. The variation of initial susceptibility was explained by extending the Globus model to the case where the domain walls are pinned at twinning boundaries. A linear correlation between multiparallel-twinned grains fraction and initial susceptibility was foun
Magnetoelectric composite bilayer films 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 piezoelectric phases and cobalt ferrite. The deposition/co-depositionwere made from colloidal suspensions in ethanolkeeping 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 chemical activity between the two layers was controlled through the batches composition and it could lead to the synthesis of complex engineered structures.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. 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
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