Synthesis and Characterization of Rare Earth Barium Copper Oxide [(RE₁₋xMx)Ba₂Cu₃O₇₋d] via Coprecipitation and Electrophoretic Deposition Methods

Preparation of superconducting material was usually carried out via the solid state reaction technique where oxides and carbonates metal precursors were mixed thoroughly followed by heat treatment. Alternatively, the materials can be prepared via the wet chemistry technique, in which higher homogeneity could be achieved due to initial mixture of cations at atomic scale. In this study, superconductors were prepared via co-precipitation technique from metal acetates which were reacted with oxalic acid as a precipitating agent to form metal oxalates. Transmission Electron Microscopy (TEM) analysis shows that ultra fine powders of metal oxalates were obtained with the particle size in the range of 9 to 12 nanometers. X-ray diffraction (XRD) analyses confirmed the phases of the metal oxalates. Thermal decomposition and phase formation stages of samples were determined via Thermogravimetric (TG), Differential Thermal Analysis (DTA) and XRD analysis at different heat treatment temperatures. Minute traces of BaCuO2 phase was discernible in the X-ray diffraction patterns of sample obtained after sintering at 880 oC for 15 hours. By increasing the sintering temperature up to 970 oC, elimination of the BaCuO2 phase in YNdBCO samples has succeeded. However, this phase remained in YGdBCO and NdGdBCO samples. Electrical resistivity measurement via 4-point probe technique shows zero resistance temperature, TC(R=0) and TC-onset are (86 K, 95 K), (88 K, 92 K) and (90 K, 98 K) for samples YNdBCO, YGdBCO and NdGdBCO, respectively. In addition, preparation of superconductor coating were also carried out in this study. Numerous efforts have been reported in fabricating superconductors into certain shapes namely, wires, thin films and many more. The Electrophoretic Deposition (EPD) method is an attractive method where it is low cost, requires simple apparatus, large surface area with uniform thickness of deposits could be obtained and deposits could be designed according to the shape of substrate. In this study, the superconductor coatings were prepared via the EPD method. Several parameters such as colloidal suspension behaviour, voltage of deposition, grinding time, substrate and sintering conditions were investigated in order to obtain good quality coatings. Colloidal suspension behaviour was investigated via Nanophox particle size analyzer. Smallest particle size distribution was ~ 15 nm by dispersing in acetone. Meanwhile, in order to enhance the deposition of the powders, particle size of the powders need to be reduced. After grinding the powders, deposition was improved and TEM analysis shows that deposited powders are in the range f 30 – 40 nm. To avoid the melting of silver substrates, sintering in argon atmosphere was carried out followed by slow cooling in oxygen atmosphere. XRD analyses of deposited samples show that orthorhombic 123 phase was obtained YBCO, GdBCO and NdBCO samples however, for YBCO samples the orthorhombicity value was relatively low. Meanwhile, improvement in microstructure was achieved where more dense films were successfully obtained by performing the multi-deposition technique

Preparation of RF/Brij 58 mesoporous carbon film as supercapacitor electrode

Mesoporous carbon (MC) film was prepared using carbon precursor of resorcinol and formaldehyde via self-assembly soft templating method for supercapacitor application with high electrochemical performance. A neutral surfactant of Brij 58 was used as structure directing agent for the pore structure geometry tuning while preparing the MCs. It was then carbonized to obtain the ordered mesoporous carbon (OMC) films or namely as RF/Brij58 film. The mesostructure was characterized by X-ray diffraction patterns (XRD) and electrochemical analysis. The carbonized RF/Brij58 film show excellent electrochemical property for supercapacitor application and the specific capacitance up to 10.57 mFcm-1 at 5 mV s−1 scan rate was obtained

Preparation of TiO2 compact layer by heat treatment of electrospun TiO2 composite for dye-sensitized solar cells

The power conversion efficiency (PCE) of the dye-sensitized solar cell was improved by using titanium dioxide (TiO2) compact layer prepared via heat treatment assisted electrospinning. Titanium tetraisopropoxide mixed with polyvinyl-alcohol was used as the electrospun solution. In this study, TiO2 photoanode with TiO2 compact layer was compared with TiO2 photoanode without TiO2 compact layer where the PCE was improved by 76.88%. Electrochemical impedance spectroscopy proved that the TiO2 compact layer can reduce the series resistance and improved the short circuit current density, resulting in a low recombination effect that leads to a higher PCE. The electron lifetime and charge collection efficiency of TiO2 nanoparticles with TiO2 compact layer displayed a higher value compared to TiO2 nanoparticles without TiO2 compact layer

Optimization of power conversion efficiency of polyvinyl-alcohol/titanium dioxide as light scattering layer in DSSC using response surface methodology/central composite design

This study focused on the optimization of polyvinyl-alcohol/titanium dioxide (PVA/TiO2) nanofibers as a light scattering layer in the dye-sensitized solar cell. The experiment was designed by response surface methodology with central composite design (RSM/CCD). Two parameters were studied i.e. electrospinning time and concentration of titanium tetraisopropoxide (TTIP). A quadratic model was used to determine the significance of each parameter studied towards the surface response which is power conversion efficiency (PCE). The statistical analysis showed that the electrospinning time and concentration of TTIP were significantly affected the PCE with the coefficient of variance (R2) of 0.9756. The RSM was able to predict the optimum condition of each parameter with less than 5% residual standard error

Light scattering effect of polyvinyl-alcohol/titanium dioxide nanofibers in the dye-sensitized solar cell

In the present work, polyvinyl-alcohol/titanium dioxide (PVA/TiO2) nanofbers are utilized as a light scattering layer (LSL) on top of the TiO2 nanoparticles photoanode. The TiO2 nanoparticles decorated PVA/TiO2 nanofbers display a power conversion efciency (PCE) of 4.06%, which is 33% higher than TiO2 nanoparticles without LSL, demonstrating the incorporation of PVA/TiO2 nanofbers as LSL reduces the radiation loss and increases the excitation of the electron that leads to high PCE. The incorporation of PVA/TiO2 nanofbers as LSL also increases the electron life time and charge collection efciency in comparison to the TiO2 nanoparticles without LSL

Controlled concentration of Mn salt for the synthesis of manganese oxide/mesoporous carbon film as potential

Manganese oxide (Mn2O3) mesoporous carbon (MPC) was synthesized by the incipient wetness of impregnation at room temperature and followed by calcination of 300 °C. The structure and morphology of Mn2O3/MPC were characterized by Fourier transform infrared (FTIR) spectrum, atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). The electrochemical performance of synthesized composites was evaluated by cyclic voltammetry (CV), galvanostatic measurement of charge-discharge (GCD) as well as power and energy density characteristics. The specific capacitance of the composite electrode when 10 wt.% Mn salt was coated on the surface of MPC film could reach 53.59 mF cm-2 as compared to MPC film at only 15.23 mF cm-2. These are in good agreement with the electrochemical performance improvement results of the energy and power density recorded for Mn2O3/MPC, which lead to higher specific capacitance as supported by the CV and GCD results in 1 M potassium chloride (KCl) of electrolyte. This enhanced capacitance was attributed to the outstanding electric properties of MPC film as well as the faradaic redox reactions of manganese oxide as proven by FESEM and EDX analysis. The results indicate the promising application of the fabricated Mn2O3/MPC composite as electrodes for supercapacitors

Preparation and characterization of p-sulfonated calix[4]arene functionalized chitosan hydrogel beads and their preliminary adsorption study towards removal of lead(II) and zinc(II) ions

p-sulfonated calix[4]arene functionalized chitosan hydrogel beads have been successfully prepared by mixing p-sulfonated calix[4]arene and chitosan in dilute acetic acid solution (1% v/v), followed by dropping the mixture into sodium hydroxide solution to form beads with diameters of ~0.1 cm. The presence of the active sulfonate groups and the unique structure of calixarene render the material useful as an adsorbent for heavy metal ions. Metal adsorption on p-sulfonated calix[4]arene is possible through a combination of physical and ionic interactions. Atomic Absorption Spectroscopy (AAS) results showed that the amount of adsorbed metal ion is optimum at 10 ppm for all samples. The overall percentage of metal ion removal shows that p-sulfonated calix[4]arene modified chitosan is the best adsorbent with up to 98% removal achieved for Pb(II) and 90% removal for Zn(II). This is followed by p-sulfonated calix[4]arene and graphene oxide (GO) modified chitosan with up to 90% removal for Pb(II) and 89% removal for Zn(II) and pure chitosan hydrogel beads with up to 60% removal for both Pb(II) and Zn(II). The results clearly prove that the presence of p-sulfonated calix[4]arene can enhance the adsorption of heavy metal ions. In addition, the adsorbent shows higher Pb(II) removal compared to Zn(II)

Effects of HoMnO3 nanoparticles addition on microstructural, superconducting and dielectric properties of YBa2Cu3O7–δ

(YBa2Cu3O7–δ)1-x(HoMnO3)x (x = 0.0, 0.0025, 0.005, 0.01, 0.03 and 0.05) ceramics were fabricated by introducing co-precipitation synthesized HoMnO3 (HMO) nanoparticles during solid state reaction process of YBa2Cu3O7–δ (Y-123) superconductors. (Y-123)1-x(HMO)x samples were characterized using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) attached with energy Dispersive X-ray spectrometer (EDX), four-point probe measurement, AC susceptometer and impedance analyzer. Majority of XRD patterns were indexed to orthorhombic Y-123 phase. Besides, YBaMn2O5 (1.5–3.6%) and YBaMn2O6 (2.4–7.4%) phases were detected. FESEM images and EDX analysis showed the presence of agglomerated particulates related to Mn and Ho based phases residing in between the Y-123 grains. The superconducting behavior was significantly enhanced at x = 0.0025 while there was no major depression noticed in critical temperature (Tc-R=0) as the addition increased till x = 0.03 (Tc-R=0 = 88 K). AC susceptibility curves of composites samples manifested sharp transitions for samples with x = 0.0025 and 0.005. Dielectric parameters εr′ and εr′ʹ decreased as the frequency increased for all samples. The εr versus frequency measurements showed increment in εr′ and εr′ʹ values for all added samples as compared to Y-123 sample. The highest values for εr′ and εr′ʹ were obtained for sample x = 0.05 with the highest loss at lower frequency. The Nyquist plots of complex impedance were analyzed where two semi-arc circulars represent grain and grain boundary effect were deduced

Phase formation of REBa2Cu3O7−δ (RE: Y0.5Gd0.5, Y0.5Nd0.5, Nd0.5Gd0.5) superconductors from nanopowders synthesised via co-precipitation

Phase formation of REBa2Cu3O7−δ (RE: Y0.5Gd0.5, Y0.5Nd0.5, Nd0.5Gd0.5) superconductors synthesised via co-precipitation (COP) method were investigated by thermogravimetric analysis (TGA), differential thermal analysis (DTA) and X-ray diffraction (XRD) analysis. All samples showed identical thermal decomposition behaviour from the thermogram in which 5 major weight losses were observed. However, XRD of the samples at different heat treatment temperatures showed different diffraction patterns indicating different thermolytic processes. Meanwhile, transmission electron microscopy and surface area analysis revealed that the powders obtained from COP have particle sizes ranging from 7 to 12 nm with relatively large surface area. Molar ratios of prepared samples obtained were near to the theoretical values as confirmed by elemental analyses using X-ray fluorescence (XRF). The TC(R=0) for sintered YGd, YNd and NdGd were 87 K, 86 K and 90 K, respectively. Surface morphological study via scanning electron microscope showed the structures of samples were dense and non porous

Passively Q-switched of EDFL employing multi-walled carbon nanotubes with diameter less than 8 nm as saturable absorber

The paper demonstrates passively Q-switched erbium-doped fiber laser implementing multiwalled carbon nanotubes (MWCNTs) based saturable absorber. The paper is the first to report the use of the MWCNTs with diameter less than 8 nm as typically, the diameter used is 10 to 20 nm. The MWCNTs is incorporated with water soluble host polymer, polyvinyl alcohol (PVA) to produce a MWCNTs polymer composite thin film which is then sandwiched between two fiber connectors. The fabricated SA is employed in the laser experimental setup in ring cavity. The Q-switching regime started at threshold pump power of 103 mW and increasable to 215 mW. The stable pulse train from 41.6 kHz to 76.92 kHz with maximum average output power and pulse energy of 0.17 mW and 3.39 nJ are produced. The shortest pulse width of 1.9 μs is obtained in the proposed experimental work, making it the lowest pulse width ever reported using MWCNTs-based saturable absorber