Materials Science Forum Vol. 1023

Abstract: Rare-earth element of gadolinium (Gd) were successfully doped into zinc oxide (ZnO) using dual sputter source of DC and RF sputtering. The substrate rotation speed was controlled from 1 rpm to 9 rpm to investigate their effects on the properties of the films in order to achieve a great feature of thin film. XRD profiles confirmed the c-axis orientation with structure of ZnO hexagonal wurtzite. No peaks related to secondary phases were observed. The intensity of dominant peak showed increment upon improvement of substrate rotation speed. The incorporation of Gd into ZnO structure was further confirmed by composition element form EDX with average atomic percentage of 3 at. % for all the films. Surface topology from AFM images showed the grain size has increased with the higher speed of substrate rotation. Gd-doped ZnO thin films indicated good transparency with an average transmittance above 90 % regardless of substrate rotation speed. The bandgap has a slight decrease from 3.06 eV to 3.03 eV with an increment speed of rotational substrate. These findings further imply that the substrate rotation speed has a significant influence on the structural and optical properties of the sputtered thin films.

Abstract: We have presented the evidence of hole self-doping due to excess oxygen addition in polycrystal LaMnO₃ (LMO). The polycrystal LMO samples were prepared by use of a solid-state reaction method. Powder mixtures with a molar ratio of 1:1 between La₂O₃ and Mn₂O₃ were pre-annealed at 1100oC for 18 hours in the atmospheres of oxygen gas, helium gas and vacuum. By this heat treatment, non-crystalline LMO samples were produced. After that, the non-crystalline LMO samples were grinded and were pressed into pellets at the pressure of 3t/cm³. The pellets were annealed at 1100oC and 1300oC for 18 hours in the same atmospheres as the pre-annealing. Through these processes, polycrystal LMO samples were finally produced. To investigate crystallographic structure of the LMO samples, X-ray diffraction (XRD) measurements were performed by use of Cu-K radiation. From the experimental results of XRD measurements, we have found that all LMO samples have perovskite structure and are polycrystals. In addition, to investigate surface structure of the LMO samples, scanning electron microscope (SEM) measurements were carried out. Electrical resistivities (ERs) of the polycrystal LMO samples were measured as a function of temperature (4K-300K). The ERs of polycrystal LMO samples produced in an oxygen gas atmosphere show lower values as compared with other LMO ones in He gas and vacuum atmospheres. Especially, the temperature dependence of the ER for a polycrystal LMO sample produced at the annealing temperature of 1100oC in an oxygen atmosphere shows a metallic behavior. Thus, we have considered that this LMO sample has the largest hole self-doping concentration in all LMO ones.

Abstract: MXene is the new family of two-dimensional (2D) transition metal carbides, carbonitrides and nitrides discovered in 2011. The unique properties of 2D MXene such as excellent mechanical properties, hydrophilic surfaces and metallic conductivity made it interesting for application in electrodes of rechargeable batteries, supercapacitors, photocatalysts, catalysts, transparent conducting films, and flexible high-strength composites. The MXene can be synthesized through a selective etching process by using either in-situ HF (hydrofluoric acid) or direct HF methods. This study reports on the effect of the in-situ HF and direct HF etching procedures on the morphology of the synthesis Ti₂C₃ MXene using titanium aluminum carbide (Ti₂AlC₃) as precursor. The morphology and elements presence were evaluated by using variable pressure field emission scanning electron microscope (FESEM) and energy dispersion X-ray (EDX) spectroscopy analyses, respectively. The analysis shows that the MXene synthesized through the direct HF method was successfully delaminated compared to the in-situ HF procedures.

Abstract: Sodium-ion batteries (SIBs) as low-cost alternatives to expensive lithium-ion batteries become a hot R&D topic in the recent days due to the natural abundancy of sodium in the Earth’s crust and also in the oceans. As far as solid electrolytes for SIBs are concerned, larger size of Na⁺ ions compared to that of Li⁺ ions hinders the ionic mobility resulting to insufficient ionic conductivity for practical applications. Development of quasi-solid state gel-polymer electrolytes (GPEs) would be a feasible solution to overcome this challenge. In this work, we developed Poly (methyl methacrylate) (PMMA) based GPEs with six different compositions dissolved in EC:PC (ethylene carbonate and propylene carbonate, 1:1 wt%) mixture. Among six different GPE samples investigated by Electrochemical Impedance Spectroscopic and Raman Spectroscopic techniques, the best ambient temperature ionic conductivity of 4.2 mS cm^-1 was obtained for 9PMMA:9NaPF₆:41EC:41PC (wt%). Variation of ionic conductivity with inverse temperature showed Arrhenius behavior with almost constant activation energies. The best conducting GPE showed an activation energy of 0.14 eV. In the Raman spectra, very sharp crystalline peaks (400-850 cm^-1 wave number range) of NaPF₆ disappear in the gel state of the electrolytes confirming the non-crystalline nature of the GPEs. Boson modes remain almost constant in intensity for all the six different compositions. The best conducting GPE seems to be highly suitable for practical applications in SIBs as it has sufficient ambient temperature ionic conductivity.

Abstract: The relationship of geometrical properties and mechanical properties of carbon nanotubes (CNTs) was investigated by using high-throughput molecular simulation. Geometrical properties such as diameter, number of walls, chirality, and crosslink density were considered. As a key factor in determining the mechanical properties of composites reinforced with CNTs, nominal tensile strength is the focus in this study, which can be calculated by fracture force divided by the full cross-sectional area including the hollow core and the wall thickness. The fracture mode, nominal tensile strength, and nominal Young’s modulus under the condition of CNTs outermost tube loading axial tensile test were evaluated. Three types of fracture modes led by different crosslink densities of CNTs were obtained. By data-mining through large amounts of datasets, we showed that CNTs with small diameter, large number of walls, and crosslinks between walls can have high nominal tensile strength. We demonstrated that zigzag-type CNTs with crosslink density of approximately 1.5% - 2.5%, armchair-type CNTs with crosslink density of approximately 3% - 4% can help improve the load transfer from the outer tube to the inner tube the most.

Abstract: In this work, PVDF/BaTiO₃ nanocomposites consisting of polyvinylidene fluoride (PVDF) as matrix and BaTiO₃ (BT) as fillers were prepared by ball milling and hot-pressing process. It is known that nanofillers content and frequency affect the effective dielectric permittivity of the nanocomposites materials. Therefore, a developed model based on deep neural network (DNN) was used to study the effect of the input parameters on the dielectric permittivity of the nanocomposites. The volume fraction (vol%) of BT and frequency of alternating current (AC) were selected as the input parameters and the effective dielectric permittivity as the output response. The results show that the developed DNN model was able to predict the effective dielectric permittivity of PVDF/BT nanocomposites with a correlation coefficient (R) of 0.997. Thus, our study confirmed the accuracy and efficiency of the developed DNN model for predicting the relative dielectric permittivity of PVDF/BT nanocomposites.

Abstract: After solid solution treatment at 1335°C for 4 hours and cooling to room temperature at different rate, the nickel-based single crystal superalloy were made into three kinds of nickel-based single crystal superalloy materials containing different size γ′ phases, respectively. The tensile test of I-shaped specimens was carried out at 980°C, and their effect of γ′ phase microstructure on the tensile properties was studied. The results show that the yielding strength of the material air-cooled to room temperature was lower than that with cooling rate at 0.15°C/s, but both of them were lower than the yielding strength of original material. Little difference was found on the elastic modulus of I-shaped specimens made of three kinds of materials. When the cubic degree of the γ′ phase is higher and the size is larger, the tensile properties of the material is better, which can be attributed to the larger size and narrower channel of the matrix phase that lead to higher dislocation resistance.

Abstract: Texture characteristics of compressed 1235 Al-alloy treated by different purification methods are studied by electron backscattered diffraction. The effects of oxide inclusions on texture components of material are studied as well. The main textures in hot-compressed 1235 Al-alloy are Cube texture, R texture, Gross texture, Brass texture, and Rotated cube texture. The lower the content of oxide inclusions in the material, the smaller the total relative ratio of textures. The total relative ratio of textures goes to the smallest by 1.8 % in high-efficient purified 1235 Al-alloy by oxide inclusion content of 0.051 %. The purification results have obvious effects on types and percentage of texture in the deformed alloy. With the decreasing content of oxide inclusion, the ratio of deformation texture decreases and recrystallization texture increases. Brass texture is gradually replaced by Goss texture in the deformation textures. R texture is the main texture in recrystallization textures. Therefore, reducing the content of oxide inclusions is effective for improving the hot deformation properties of 1235 Al-alloy.

Abstract: This research investigates the nickel content added by 1.1wt%, 2.2wt%, 3.7wt% and 4.5wt% on the microstructure and mechanical properties in the nodular cast iron. The results demonstrate that the microstructure of nickel addition consists of nodule graphite, ferrite and pearlite phase while nickel was added to 4.5 wt% the microstructure becomes ferrite transform to fully pearlite phase. In addition the ductile iron has the highest nodularity (0.79%), followed by 1.1%Ni (0.75%), 2.2%Ni (0.71%), 3.7%Ni (0.69%) and 4.5%Ni (0.58%). The hardness and tensile strength increase when increasing the nickel content. Elongation is enhanced with nickel increasing and reaches a maximum of 12% at 1.1 wt% Ni, then decreases with the further increase of nickel.