Advanced Materials Research Vol. 501

Abstract: Bismuth titanate solid solutions, Bi12+xTiO10+δ (0 ≤ x ≤ 0.6), were synthesized by conventional solid state method at sintering temperature of 700°C for 48 h. Structural studies were performed by powder X-ray diffraction (XRD) analysis and revealed that single-phase materials were obtained with a general formula of Bi12+xTiO10+δ (0 ≤ x ≤ 0.6). The electrical properties of all the single-phase samples were studied using the impedance spectroscopy technique. Further characterization of the materials was carried out using differential thermal analysis (DTA) and indicated that no phase transition was observed. The TGA analysis was observed and found that all the materials were thermally stable.

Abstract: In order to study the influence of deionized water and heat treatment on the structure of the crystal, a compositional series of 20Li2O:20SrO:30B2O3:30P2O5 with deionized water and without de-ionized water as a solvent were prepared at 800ᵒC for different sintering time from 7 to 24 h. The crystalline phase and structural of 20Li2O:20SrO:30B2O3:A 30P2O5 crystal was studied using X-ray powder diffraction (XRD) and Infrared (IR) Spectroscopy. From the XRD result, samples prepared with deionized water as solvent displayed better crystalline respond. The samples showed a better crystalline structure when it was sintered for 24 h as compared to 7 h. The infrared spectra of the samples showed three distinctive regions around 1200 – 650 cm-1, 650 – 360 cm-1 and 360 cm-1 showing clear signs of boron units as the major host structure.

Abstract: Samarium doped magnesium phosphate glass having a composition of [P2O5]50-x-[MgO]50-[Sm2O3]x, with 0≤x≤4 mol% were prepared by melt-quenching method. The emission spectra were recorded using the photoluminescence spectrometer in the range of 540-730 nm at room temperature after being excited at 403 nm. It was found that the emission spectrum of Sm3+consisted of four emission bands at ~559.76 nm, ~597.32 nm, ~641.55 nm and ~705.57 nm which were assign as a transition of 4G5/2→6H5/2, 4G5/2 →6H7/2, 4G5/2→6H9/2 and 4G5/2→6H11/2 respectively. The transition of 4G5/2→6H7/2 is detected as the strongest orange (597.32 nm) luminescence peaks thus dominates the transition.

Abstract: . The study of the crystallization kinetics of rare-earth doped glass stimulated much interest especially for crystallization process. In this work transparent Eu2O3 doped glasses with composition TeO2 - Na2O – MgO were prepared using conventional melt-quenching technique. The amorphous nature of glass was confirmed using X-ray diffraction method. The influence of Eu3+ content on the crystallization kinetics of the glass such as activation energy (Ea) was thoroughly evaluated under non-isothermal conditions using DTA. The crystallization kinetic at different heating rate from 5 °C min-1 to 25 °C min-1 at different crystallization temperature (Tp) were examined and verified using Ozawa method. The result showed that the activation energy (Ea) was decreased with the increasing of the dopant concentration from 319.8 eV to 93.5 eV.

Abstract: A tellurite glass of TeO2-PbO-Li2O doped with Nd2O3 has been successfully fabricated by using the conventional melt-quenched technique. The absorption and emission spectroscopy have been identified using UV-VIS-NIR and photoluminescence spectrometer, respectively. From the spectroscopy, ten significant spectra have been observed in the region of 400-900 nm. The absorption wavelength centered at 585 nm attributed to 4I9/2 → 4G5/2 transition is the predominant wavelength to be used as the excitation wavelength. Emission spectra have been determined by using 585 nm excitation wavelength at room temperature. From the emission spectra, seven distinctive upconversion bands contributed from Nd3+ were observed in the region of 400-1500 nm. It was found that the bands were centered at 450 nm (4G11/2 → 4I9/2), 485 nm (4G11/2 → 4I11/2), 605 nm (4G11/2 → 4I15/2), 665 nm (4G7/2 → 4I13/2), 880 nm (4F3/2 → 4I9/2), 1062 nm (4F3/2 → 4I11/2) and 1340 nm (4F3/2 → 4I11/2), respectively. Tthese emission bands showed the possibility of visible and near infrared emission spectra.

Abstract: The thermoelectric materials based on p-type Bi2Se3xTe3 (1-x) bulk products and dispersed with x compositions of Se (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were fabricated using standard solid-state microwave synthesis procedures. The products were characterized by X-ray diffraction (XRD). The XRD characterizations revealed that these products are pure Bi2Te3 and Bi2Se3 with uniform structures. The electrical properties of the Bi2Te3, Bi2Se3 and Bi2Se3xTe3 (1-x) samples were measured in the temperature range of 303–523 K. The highest value of the Seebeck coefficient was 176.3 μV/ K for the Bi2Se0.6Te2.4 sample, but only 149.5 and 87.4 μV/K for the Bi2Te3 and Bi2Se3 samples, respectively.

Abstract: Preparation of LiTaO3 was done using the sol-gel method which is also known as the wet chemical technique. Thermal analysis (TG-DSC) of LiTaO3 precursor was studied to determine an optimized heating temperature. LiTaO3 was heated at 550 °C with different sintering time of 12, 24, 48 and 72 h. The formation of pure LiTaO3 occurred during sintering time of 72 h which was confirmed using X-ray diffraction (XRD). The morphology of pure LiTaO3 was recorded using a Scanning Electron Microscope (SEM). Pure LiTaO3 can only be formed at a longer heating time in order to complete the oxidation process.

Abstract: LiCoO₂ has been used as a cathode material in commercial Li-ion batteries. This is due to advantageous properties of the LiCoO₂ like ease of preparation and good electrochemical characteristics. However, the high cost and toxicity of Co has limited its use. Therefore, the substitution of Co in the LiCoO₂ by non-toxic and inexpensive transition metallic element is needed. Mn is considered as one of the promising candidates to fulfill all the requirements. Partial substitution of Co by Mn has also been considered to enhance the stability of LiCoO₂ lattice, minimize capacity fading and increase cycle life of the Li-ion battery. LiCo_(1-x)Mn_xO₂ (x= 0.1, 0.2, 0.3) were prepared by using a self-propagating combustion (SPC) method. X-ray diffraction (XRD) of the samples were carried out for phase analysis and showed that all the materials are pure. The samples were also analyzed using the Field Emission Scanning Electron Microscope (FESEM) to study its morphology and particle size. Finally cathodes were fabricated and assembled in an inert gas-filled fabrication box. Discharge profiles of the materials were carried out in the voltage range of 4.3 V – 3 V. The materials obtained were phase pure and improved the capacity fading of the materials compared to LiCoO₂. All of the materials exhibited less than 10% capacity loss even though it does not improve the first cycle discharge capacity.

Abstract: Phosphate glasses containing fixed concentration of rare-earth with and without metallic nanoparticles (NPs) having compositions (59.5-x) P2O5-MgO-xAgCl-0.5Er2O3, where 0 ≤ x ≤ 1.5 mol% was prepared using melt-quenching technique. Spectral characterizations were made using UV-VIS-IR spectroscopy and photoluminescence spectroscopy. Addition of silver NPs enhanced the corresponding absorption and was optimum at 1.5 mol% AgCl. Infrared to visible frequency upconversion (UC) emission were observed in the glass on pumping with 797 nm radiation. Furthermore, it was found that the emission at 540 nm, due to Er3+transition (4S3/2-4I15/2) was much more influenced by the silver NPs in comparison to the emission at 632 nm (4F9/2 - 4I15/2). These enhancements were attributed to the local fields present in the vicinity of silver NPs. Moreover, the rapid increase in the intensity of the green band as compared to the red band was due to the charge cloud effect of the plasmon band. Since green band lie more close to the plasmon frequency band of Ag and hence showed rapid increase compared to the far lying red bands. Our findings may contribute towards the development of solid state laser and sensors

Abstract: Friction stir welding (FSW) is a new and promising welding process which can produce low cost and high quality joints of heat-treatable aluminum alloys. This is because it does not require the consumable filler materials and can eliminate some welding defects such as crack and porosity. The main objective of the present work was to evaluate the processing parameter of friction stir welding (FSW) process for 6061-T6 alloy and to determine the properties of the obtained joints. Experiments have been conducted by varying the friction stir welding processing parameter ; tool rotational speed, in rpm (410, 865, 1140) and feed rate, in mm/min (22, 32, 45). The shoulder diameter of the tool for FSW was 18 mm. Microstructure, microhardness and tensile properties were investigated in this studied. The results showed that there was a variation of grain size in each weld zone which depends on the material and process parameters of FSW in the joint itself. The coarsest grain size was observed in the heat affect zone (HAZ), followed by the Thermo Mechanically Affected Zone (TMAZ) and the nugget zone. The highest hardness was reported on the nugget zone and maximum tensile strength was obtained on the sample with processing parameter 865 rpm rotational speed.