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[en] Ferroelectrics 0.67Pb (Mg1/3Nb2/3)O3-0.33PbTiO3 (PMN-PT) + x mol% WO3 (x=0.1, 0.5, 1, 2) were prepared by columbite precursor method. Electrical properties of WO3-modified ferroelectrics were investigated. X-ray diffraction (XRD) was used to identify crystal structure, and pyrochlore phase were observed in 0.67Pb (Mg1/3Nb2/3)O3-0.33PbTiO3+2 mol% WO3. Dielectric peak temperature decreased with WO3 doping, indicating that W6+ incorporated into PMN-PT lattice. Lattice constant, pyrochlore phase and grain size contribute to the variation of Kmax. Both piezoelectric constant (d33) and electromechanical coupling factors (kp) were enhanced by doping 0.1 mol% WO3, which results from the introduction of 'soft' characteristics into PMN-PT, while further WO3 addition was detrimental. We consider that the two factors, introduction of 'soft' characteristics and the formation of pyrochlore phase, appear to act together to cause the variation of piezoelectric properties of 0.67PMN-0.33PT ceramics doping with WO3
[en] 0.67Pb(Mg1/3Nb2/3)O3 (PMN)-0.33PbTiO3 (PT) ferroelectric ceramics has been selected as base component. Different content of B-site substitute (0.1, 0.5 and 1 mol%) were used to modify the base component. The specimens were synthesized by the columbite precursor method, and pure perovskite phase were obtained for all the specimens. The dielectric behavior was examined to investigate the relaxor behavior of each component. It is found that the specimen undoped and modified with 0.1 mol% WO3 nearly behave as normal ferroelectric ceramics, while with the content of WO3 increasing, the degree of relaxor behavior for the composition increases. Thus, B-site substitute WO3 has a strong effect of inducing relaxor behavior of PMN-PT ferroelectric ceramics near morphotropic phase boundary (MPB)
[en] Thermochromic vanadium dioxide exhibits a semiconducting to metallic phase transition at Tt = 341 K, involving strong variations in electrical, magnetic, optical transmittance. Tungsten-doped vanadium dioxide nanopowders were synthesized by thermolysis with slight improvement and active white powdery tungstic acid (WPTA) used as a substitutional dopant. The results show that the phase transition temperature of the doped VO2 powders were decreased to 298.6 K, which is very close to the room temperature. Tungsten-doped has enhanced the IR properties of VO2 nanopowders because the contrast of its IR transmission below and above the room temperature is up to 92% in our experiment.
[en] Microstructure and dielectric properties of relaxor ferroelectrics in the solid solution, formulated 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 + 2 mol% RE (RE = Sm, Nd, Yb or Ce), have been investigated. The effects of these dopants on microstructure, maximum dielectric constant (K max) and degree of ordering, etc. have been studied. It was found that doping of Sm, Nd and Ce reduced K max from 23924 to 14921, 13466 and 12511 respectively, while the doping of Yb increased K max to 27759. The variation of K max is analyzed according to grain size, domain structure and order-disorder behavior. Diffuseness of the phase transition is calculated to indicate order-disorder behavior, which is roughly opposite to that of K max. The present results show that order-disorder behavior is the key factor on K max of PMN-PT ceramics near morphotropic phase boundary
[en] Colloidal zinc oxide (ZnO) quantum dots (QDs) with a uniform particle size of around 5 nm have been synthesized, purified and blended with polymethylmethacrylate (PMMA) by solution mixing to prepare PMMA/ZnO nanocomposite films. The structure and morphology of ZnO QDs and PMMA/ZnO nanocomposite films have been characterized using high-resolution transmission electron microscopy. The PMMA/ZnO nanocomposite films prepared are highly transparent. The UV-vis spectra and thermogravitational analysis results show that a small amount of colloidal ZnO QDs (<1 wt%) without further surface modification can greatly improve the thermal stability of PMMA along with UV-shielding capability
[en] Highlights: • ZrP nanoplatelets with various sizes were successfully exfoliated by the presented melt compounding method. • This fabrication method could be used to prepare polymer nanocomposites with exfoliated ZrP nanoplatelets in a large scale. • The improvement of modulus of elasticity of ZrP/POE-g-MA was attributed to the well-exfoliated nanoplatelets. • The ductility of ZrP/POE-g-MA compounds also became better, if ZrP nanoplatelets were first intercalated by diglycolamine. A melt compounding method to achieve the exfoliation of layered zirconium phosphate (ZrP) nanoplatelets was presented in this work. ZrP nanoplatelets were first intercalated by diglycolamine (DGA) to increase the interlayer distance and functionality. In the next melt compounding process, the cyclic anhydrides of maleic anhydride grafted polyolefin elastomers (POE-g-MA) reacted with the hydroxyls in DGA-ZrP. Subsequently, the long polyolefin chains of POE-g-MA intercalated into the interlayer of ZrP smoothly and exfoliated the nanoplatelets successfully. ZrP nanoplatelets with various sizes were fully exfoliated in POE-g-MA matrices. The modulus of elasticity of POE-g-MA was improved by the incorporation of ZrP nanoplatelets and further increased if the nanoplatelets are exfoliated. The ductility of ZrP/POE-g-MA compounds also became better, if ZrP nanoplatelets were first intercalated by DGA and then exfoliated, especially for the smaller nanoplatelets. Our work provides a general method to prepare polymer nanocomposites containing exfoliated ZrP nanoplatelets in a large scale.
[en] Highlights: • Porous BDD/Ta sensor constructed using a Ni-assisted plasma etching method. • Sensor was applied to detection of dopamine and pyridoxine in human serum. • Electrochemical sensor has high sensitivity, selectivity, and long-term stability. • Selectivity of sensor is dependent on plane activity and surface chemistry. - Abstract: A porous boron-doped diamond (PBDD)/Ta sensing electrode was prepared for the fast, sensitive, stable, and discriminative detection of dopamine (DA) and pyridoxine (vitamin B6) in human serum. All the exposed surfaces of the diamond grains of the BDD layer were etched into a porous form, with pore sizes of less than 500 nm and an average depth of about 200 nm. The electrochemical performance characteristics of the PBDD layer and the reaction mechanisms enabling the detection of DA and vitamin B6 were studied. Large numbers of oxygen-containing groups on the PBDD surface, as well as the activity difference of the different planes, enabled us to successfully distinguish between DA and B6 by using the PBDD/Ta electrode. The low background current of PBDD, the large active area of the porous surface, and the high electron transfer properties led to the PBDD electrode having a high sensitivity. Therefore, this sensor can be used to stably detect DA and B6 in serum. Aberrant levels of DA and vitamin B6 in body fluids are key risk indicators for some diseases; thus, monitoring the levels of both and other species in serum is of great significance to clinical diagnoses.
[en] In present work, a multifunctional piezoelectric/photoluminescence effect, which originated from the combination of the piezoelectric properties and the photoluminescence effect, was realized in one-dimensional Er3 + doped lead-free BaTiO3 nanofibers prepared by a sol-gel based electrospinning method. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) were utilized to characterize the morphologies and phase structures. The effect of the host crystallization and rare-earth concentration on the structure and photoluminescence properties was studied. In addition, temperature-dependent PL spectrum exhibited a piezoelectric/photoluminescence coupling effect, characterized by the enhanced photoluminescence intensity around the ferroelectric-paraelectric phase transition temperature of BaTiO3.
[en] In this paper, we describe a method for fabricating dry electrodes for use in recording electroencephalograms (EEGs), which are based on the use of chitosan (Ch), gold (Au) particles, and titanium dioxide (TiO2) nanotube arrays deposited on titanium (Ti) thin sheets. The samples were characterized by scanning electron microscopy, X-ray diffraction, electrochemical impedance spectroscopy, and EEG signal collection. The TiO2 nanotube arrays were grown on the Ti thin sheet by an electrochemical anodic oxidation method. The Au particles were deposited on the bottom and surface layers of the TiO2 nanotube array using an electrochemistry-based multi-potential step technology. The fabricated dry Ch/Au-TiO2 electrodes have an efficient conversion interface for ion current/electron current, a high biocompatible contact surface, and a fast electron transfer channel. To confirm that the Ch/Au-TiO2 layer can be used in dry EEG electrodes, the impedance spectra of the electrodes in solution and skin were analyzed. The mean impedance values for skin were found to be approximately 169 ± 33.0 kΩ at 2.15 Hz and 67.4 ± 8.9 kΩ at 100 Hz. In addition, EEG signals from the forehead and sites with hair were collected using both the dry Ch/Au-TiO2 electrode and a wet Ag/AgCl electrode for comparison purposes. It was found that high quality EEG signal recordings could be obtained using the dry electrodes. The fact that electrolytes are not required means that the electrodes are suitable for use in long-term bio-potential testing. - Graphical abstract: We prepared dry electrodes based on chitosan, Au micro/nano-particles, and TiO2-nanotube-coated Ti films for use in the accurate monitoring of EEG bio-potentials on the forehead and sites with hair. - Highlights: • Chitosan (Ch)/Au-TiO2/Ti thin films have been successfully prepared. • The Ch/Au-TiO2/Ti thin films were used as dry electrodes and applied to EEG monitoring. • The EEG signal quality from the dry electrode is similar to that from wet electrode. • The Ch and Au-TiO2 nanotubes improved the interfacial stability and electron flow. • The dry electrode has applications in the recording of various bio-potentials.