Solid State Phenomena Vol. 307

Abstract: This article reports the synthesis of cobalt ferrite (CoFe₂O₄) nanoparticles by low-cost sol-gel auto combustion method. The synthesized CoFe₂O₄ nanoparticles were characterized using X-ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray (EDX), UV-Visible (UV-Vis), Fourier Transform Infrared Spectroscopy (FTIR) and Vibrating Sample Magnetometry (VSM). The XRD pattern inferred the formation of cubic spinel structure with average crystallite size 35.3 nm. The crystallite size was obtained in the range 32-37.5 nm in FESEM analysis. The elemental composition was confirmed using EDX spectroscopy. The presence of spectral lines at positions 465.57 cm^-1 and 577.52 cm^-1 associated to stretching vibrations of Co-O in octahedral sites and Fe-O in tetrahedral sites confirmed the spinel structure. The magnetic properties such as saturation magnetization (Ms) 67.79 emu/g, coercivity (Oe) 874.76 Oe and remnant (Mr) 29.07 emu/g were obtained from the hysteresis curve. The bandgap 1.409 eV was obtained for synthesized CoFe₂O₄ using Tauc plot from UV-Vis absorption spectra.

Abstract: The present article reports the growth mechanism of zinc oxide (ZnO) nanowires grown on silicon substrate pre-coated with ZnO buffer layer by thermal evaporation method. ZnO nanowires are grown for different growth time of 0, 30, 90 and 120 mins with controlled supply of Ar and O₂ gas at 650 °C. The structural, morphological and crystallinity properties of ZnO nanowires are analyzed by field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) spectroscopy, high resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). FESEM images infers that, the nanowires growth is driven by self-catalysed vapor-liquid-solid mechanism, where the buffer layer serve as nucleation site. EDX spectra show the uniform composition and purity of ZnO nanowires. A strong (002) peak is detected in XRD spectra which indicates that the preferred growth orientation of the nanowires is toward the c-axis with a hexagonal wurtzite structure. The HRTEM microscopic graphs confirm the growth of nanowire along the preferred [0001] axis. Based on the analysis of grown ZnO nanowires, the probable growth mechanism is schematically presented.

Abstract: Plastic optical fiber sensing that coated with ZnO is developed and its interaction with ethanol and methanol solution is investigated. ZnO is synthesized sonochemically by using the bath type sonicator. The optical properties such as transmittance, absorbance and refractive index of ZnO is determined by using ultraviolet-visible (UV-Vis) spectrophotometer. Then, the cladding of plastic optical fiber (POF) is etched by using acetone solution, sand paper and deionized water. The unclad region is coated with ZnO and being immersed in the solution of ethanol and methanol in the range from 0 v/v% to 50 v/v%. The performance of ZnO coated POF is achieved by obtaining the power output value that transmitted via power meter. The result of this research is as the alcohol concentration increase, the power output value increase. Refractive index of ZnO is varied due to interaction between modified-cladding area and alcohol. Besides that, more light propagates inside the fiber when the sensor is tested under methanol solution compare to ethanol. Thus, the power output ratio increments as well as the sensor efficiency and shows the effectiveness of POF sensor to detect varied alcohol concentration.

Abstract: Partial unclad fibers with diameters ranging from d=121μm to d=125μm were fabricated using standard telecommunications optical fiber (SMF28) via low cost mechanical swipe-off technique. Graphene oxide (GO) was deposited using drop casting method on the outer side of the partial unclad SMF. IR laser with excitation wavelengths of λ=1310nm and λ=1550nm were launched along the graphene-coated SMF. The sensitivity of graphene based macrobend unclad SMFs were investigated by introducing two different pH of aqueous environment with values of 3.5 (acidic) and 12.5 (alkaline) that acted as sensing media. The optimum power loss was obtained as smallest diameter of partial unclad SMF with d=121μm was appointed. As uncoated SMF was replaced with the GO coated SMF which had been immersed into 3.5pH liquid solution, it was found that the optical power losses were increased about 6.79dBm and 5.15dBm using laser with λ₁=1310nm and λ₂=1550nm respectively. The uncoated SMFs experienced the increment of power losses about 2.11dBm and 5.15dBm as they were soaked into the solution with pH=12.5 using similar laser of λ₁ and λ₂. It is noteworthy to highlight the significant of graphene’s employment on macrobend unclad SMF by using λ₁=1310nm in which better sensitivity and selectivity represented by maximum changes of power losses were apparently observed for both solutions. The usage of λ=1550nm exhibited poor selectivity where the partial unclad SMF unable to differentiate two contrasting pH solution. In conclusion, graphene based macrobend fiber optic sensor for pH detection was successfully developed by employing partial unclad SMF with cladding diameter of d=121μm and laser wavelength of λ=1310nm due to the enhancement of evanescent field’s strength.

Abstract: An optimized study of tapered polymer optical fiber (POF) for measurement of different concentration of ethanol in deionized water (0.5%-3.5%) is proposed and demonstrated. This sensor operated based on evanescent wave absorption principle. The cladding of PMMA based POF is removed using organic solvents which can be used to create tapered POF. The unclad length around 1 cm and 3 cm as well as the waist diameters of POF in the range of 5 mm and 8 mm were compared for their efficiency as an ethanol sensor based on power output ratio values. Tapered POF with smaller waist diameter and longer tapered length showed higher sensitivity as ethanol sensor. Therefore, by tailoring the length and tapered diameter of POF, high sensitivity of ethanol sensor can be fabricated.

Abstract: This paper presents the synthesis and characterization of Bi₂Sr₂Ca₂Cu₃O_8+x superconducting nanowires. Bi₂Sr₂Ca₂Cu₃O_8+x nanowires with T_c = 68 K were synthesized using the electrospinning process employing sol–gel precursors. A sol–gel methodology was used to obtain a homogeneous PVP solution containing Bi, Sr, Ca, and Cu oxalates. Samples were heat-treated at 120 °C to remove excess moisture, and then at 850 °C in box furnace. Bulk sample was also prepared using coprecipitation method for comparison. Based on XRD, the nanowire sample showed minimal Bi-2223 phases and apparent Bi-2212 phases. The morphology, microstructure, and crystal structure of these nanowires were examined using field emission scanning electron microscopy (FESEM) to reveal a rectangular morphology having typical wire thickness in the range of 150–1000 nm. Electrospun Bi-2223 were grinded and pressed at 0.9 GPa into pellets. DC measurements were conducted to investigate the critical transition temperature (T_c) of Bi-2223 nanowires and to compare their magnetic properties to those of coprecipitated Bi-2223 pellets. The T_c for the bulk sample is observed at 101 K and electrospun Bi-2223 at 68 K. Coprecipitated Bi-2223 was added with Pb whereas electrospun Bi-2223 does not employ Pb. These results point to the existence of utilizing of the substitution of Pb with Bi; Bi-2223 phases in pressed nanowire are less, and the potential of using electrospinning to synthesis functional Bi-2233 superconductors.

Abstract: The effects of Ni_0.5Zn_0.5Fe₂O₄ nanoparticle addition on the superconducting and transport properties of (Tl_0.85Cr_0.15)Sr₂CaCu₂O₇ (Tl-1212) superconductor were investigated in this paper. The Tl-1212 samples were produced by mixing high purity oxide powders through a solid-state reaction method. Nano Ni_0.5Zn_0.5Fe₂O₄ particles with compositions of 0.001 wt.%, 0.003 wt.%, 0.005 wt.%, 0.01 wt.% and 0.02wt.% with average size of 60 nm were added into the Tl-1212 powders. The transition temperatures (T_c-zero and T_c-onset) were measured using a four-point probe method. The highest T_c-zero recorded was 97 K which was exhibited by the pure Tl-1212 sample. The transport critical current, I_c, of the Tl-1212 samples were found through the 1 µV/cm criterion with temperature ranging from 30 K to 77 K. The sample with a composition of 0.003 wt.% displayed the highest value of J_c at 77 K with a value ranging up to 1780 mA/cm². The Tl-1212 samples were characterised using scanning electron microscopy (SEM), powder X-ray diffraction method (XRD), energy dispersive X-Ray analysis (EDX), electrical resistance measurements and transport critical current density measurements. The J_c of the Tl-1212 superconductor has been improved through the addition of Ni_0.5Zn_0.5Fe₂O₄ nanoparticles but adding an excessive amount has caused its J_c to degrade.

Abstract: A study of the effects of Cerium oxide nanoparticle doped with BSCCO-2223 on the microstructure and superconducting properties was carried out. All samples were synthesized using solid state reaction method. Ce concentration is varied from x = 0.0 up to 0.1 in a general stoichiometry of Bi_1.6Pb_0.4Sr₂Ca_1-xCe_xCu₃O_y. The samples were characterized structurally and electrically by X-Ray Diffraction (XRD) and four-point probe method respectively. XRD analysis shows that both (Bi,Pb)-2212 and (Bi,Pb)-2223 phases coexist in the samples having tetragonal crystal structure but changed to orthorhombic when x=0.10. The values of critical transition temperature, T_C and critical current density, J_C of the samples decreased with the increase in Ce concentration. The possible reasons for the observed degradation in superconducting and structural properties of Bi-2223 due to Ce nanoparticles addition were discussed.

Abstract: The effect of Cr and Ni substitution on electrochemical performance of layered LiCo_0.9M_0.1O₂ (M=Cr and Ni) has been investigated. Partial substituted of LiCo_0.9Cr_0.1O₂ and LiCo_0.9Ni_0.1O₂ has been synthesized using a self-propagating combustion (SPC) method with annealing temperature of 700 ̊ C for 24 h. The starting materials used were metal nitrates and citric acid act as a combustion agent. The phase and crystalinity of the materials were characterized using X-Ray Diffraction (XRD) and results showed that the single phase and pure materials were obtained with no impurity peaks were detected. The morphology and particle sizes of samples also analyzed using Field Emission Scanning Electron Microcopy (FESEM). The electrochemical performances of the materials were measured by its charge-discharge cycling which carried out in the voltage range of 2.5 V to 4.5 V. The results from charge-discharge studies found that LiCo_0.9Ni_0.1O₂ has better specific discharge capacity compared with LiCo_0.9Cr_0.1O₂.

Abstract: Fourier Transform Infrared (FT-IR), was applied to investigate the complexation, structural, ionic transport properties and dominant charge carrier species in Chitosan (CS) / Methyl Cellulose (MC) blend doped with 1 – butyl – 3 – methylimidazolium bis (trifluorosulfonyl) imide (BMIMTFSI) solid biopolymer electrolytes (SBEs) which have been prepared via solution casting technique. Samples were partially opaque in appearance with no phase separation. The occurrence of interactions between the host polymer CS/MC blend and ionic dopant BMIMTFSI were proven by FT-IR analysis from the shift in C-O band in 1049 cm^-1. The FTIR spectrum in the region between 1080 and 980 cm⁻¹ were deconvoluted using Origin 8 software to disclose the percentage of free mobile ions and contact ion of the samples. Ionic transport properties analysis reveals that the ionic conductivity is dependent on the ionic mobility (μ) and diffusion of ions (D).Keywords: Biopolymer Electrolyte; Polymer Blend; Chitosan, Methylcellulose; BMITFSI; Ion transport.