Solid State Phenomena Vol. 345

Abstract: Barium Hexaferrite is a permanent magnet material known for its excellent quality and relatively inexpensive manufacture. Barium hexaferrite has good stability and can be applied in various technologies. In this research, the synthesis of barium hexaferrite has been successfully made from the primary materials Fe (NO₃)₃ and Ba (NO₃)₂ using the sol-gel method, as well as other materials such as NaOH, chitosan, molasses, acetic acid and distilled water as the primary solvents for several materials. In addition, variations in aging time 0 hours, 2 hours, 4 hours and 6 hours were added to see the effect on morphology, crystal structure and the magnetic properties of barium hexaferrite magnets. The characterization process is carried out with three testing processes, namely X-Ray Diffraction testing (XRD), Scanning Electron Microscopy (SEM) and Vibrating Sample Magnetometer (VSM). From the XRD, it was found that the desired phase of Barium Hexaferrite (BaFe₁₂O₁₉) was formed, while in the SEM testing process, it was seen that the aging time of the barium hexaferrite sample decreased the particle size of the barium hexaferrite BaFe₁₂O₁₉ from an aging time of 0 hours seen 681.459 nm and at an aging time of 6 hours. Visible 538.859 nm particle size formed. The VSM characterization results showed that different aging times did not affect the barium hexaferrite nanomagnets' magnetic properties.

Abstract: The normal state of high-T_c superconducting cuprates is crucial to understanding of the mechanism in superconductivity. There are two main ways to remove superconductivity so that the sample is in a normal state, that is by applying a large magnetic field or adding impurities such as Zn to the sample. To investigate the crystal structure and magnetic properties in the normal state of electron-doped high-T_c cuprates in overdoped regime, Eu_2-xCe_xCu_0.97Zn_0.03O_4+α-δ (ECCZO) with x = 0.16, 0.17, 0.18, and 0.19 has been synthesized by the solid-state reaction method. The crystal structure and magnetic properties of the samples were characterized by XRD and SQUID measurements. The results of XRD measurements shows all samples have T’-structure and the values of lattice parameters a, CuO bond length, and crystallite size increased with increasing x. On other hand, the value of lattice parameters c decreased with increasing x, causing the expansion of the tetragonal unit cell in the horizontal direction. From susceptibility measurements, in the normal state with 3% of Zn impurity all samples have the paramagnetic behaviour. The magnetic parameters of these samples analysed by the Curie law. With increasing of Ce concentration, the C and the are increased. The increase in the magnetic parameters since the increasing in magnetic ordering.

Abstract: Electrical transport in materials have been studied extensively due to its great potential in spintronic technology. The introduction of the secondary phase into the manganite matrix can modify the electrical properties, subsequently improving the low-field magnetic resistance (LFMR). In this work, we study the change in electrical properties at different temperatures of polycrystalline (1-x)La_0.7Sr_0.2Ca_0.1MnO₃/xTiO₂ (LT) composites where x = 0, 0.05 and 0.1. Polycrystalline La_0.7Sr_0.2Ca_0.1MnO₃ (LSCMO) was synthesized by sol-gel method, calcined at 700 °C, and pre-sintered at 800 °C for 6 h before adding TiO₂. TiO₂ as filler was mixed with LSCMO by wet mixing and stirring for about 30 min until a homogeneous compound was formed. Composite LT was then inserted to oven up to 100 °C for 2h to remove the moisture, compacted at 10 MPa, and sintered at 1200°C for 12 h. All samples in the LSCMO phase have a rhombohedral crystal structure with space group R3c. The crystal structure parameters were studied using Rietveld refinement through GSAS II software. The sample was characterized by SEM to represent the morphology of the sample. As the TiO₂ content increased, the magnetization decreased, as observed by VSM analysis at room temperature. The electrical transport properties of pure LSCMO and LT were characterized by cryogenic from 195K to 260 K. The resistivity of LT10 is too high compared to that of LT5 and as the temperature increases, the resistivity in this range will decrease. For 200 K, the resistivity of LSCMO, LT5 and LT10 are 3.09 x 10^-2 ohm.cm, 4.40 x 10³ ohm.cm and 4.77 x 10⁴ ohm.cm respectively.

Abstract: Differences in particle size can affect the magnetic properties of superconductors. At the nanoscale, superconductors have different magnetic properties than those at the micro or submicron size. The difference in particle size in superconducting materials can be obtained by giving the sintering temperature difference. In this work, we focus only on the magnetic properties in Eu_1.85Ce_0.15CuO_4+α-δ (ECCO) in the optimal-doped regime prepared by the sol-gel method with various sintering temperatures 700 °C, 800 °C and 900 ° C sizes with an annealing temperature 800 °C to obtain different particle. The lattice parameters and crystallite size were obtained using XRD. Based on the XRD results, the higher the sintering temperature variation, the larger the crystallite size produced with lattice distortion and expansion with a decrease in particle size. The magnetic properties of these materials have been investigated using a superconducting quantum interference device (SQUID) at temperatures between 2 K and 30 K with the applied field at 5 Oe. Based on the SQUID measurement, the magnetic properties of samples sintering at 700 °C and 800 °C were found to be ferromagnetic-like behaviour, while sintering at 900 °C was found to be paramagnetic with no trace of the superconductivity phase. The differences response of magnetic properties can be associated with the effect of the differences size of the crystallites in each material, that can relate to uncompensated spins produced by the surface effect.

Abstract: ZnO films were deposited by magnetron sputtering using RF power supply, in order to study the effect of substrates on quality of the prepared films. Then, growth of the ZnO films on thin AlN buffer layer and Si(100) substrates were characterized using different techniques. The surface morphology was investigated by means of scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The structural properties were investigated via X-ray diffraction (XRD) patterns, Rocking Curve as well as Pole figures. The ZnO films were textured and they had preferred orientation (002) and the crystallinity was better for ZnO/Si in the used growth conditions. The XRD results were confirmed by HRTEM. Optical properties were analyzed by photoluminescence (PL), as well as electrical characteristics were performed by C-V and I-V measurements. The dispersion orientation of these films, as indicated via the FWHM (rocking curves), is small for thin ZnO/Si. These results are considered as hopeful for piezoelectric applications.

Abstract: This paper attempts to evaluate the use of composite of polyaniline (PANI)/palm kernel shell-derived porous carbon (C-PKS) as alternative materials for supercapacitor electrodes. The preparation of PANI/C-PKS composites was carried out using an in-situ polymerization method. After the composite was formed, the structures and morphologies were characterized using an N2-sorption analyzer, SEM - EDX, and TGA. As for the performance of supercapacitor electrodes, the composite was tested using a three-electrode system. Structural and morphological characterization results showed that PANI was successfully deposited in C-PKS. The amount of PANI deposited in C-PKS was ca. 7.5%, obtained from TGA analysis. Meanwhile, the capacitance performance test results showed that the PANI/C-PKS composite featured a specific capacitance of ca. 116 F/g. There was an increase in specific capacitance compared to the blank material (C-PKS only) which showed only 94 F/g.

Abstract: Thermal oxidation of 4H-SiC to grow native-oxide SiO₂ is always followed by the generation of crystal defects and lattice distortion. We studied the relaxation of this distorted lattice on thermally-oxidized 4H-SiC surface by performing annealing process with several conditions. The surface distortion could be relaxed partially by annealing under argon, nitrogen monoxide, and H₂O gases, confirmed by in-plane X-ray diffractometer. This surface relaxation is possibly induced by the release of oxygen-related defects, as confirmed by thermal desorption analysis. The surface distortion caused by thermal oxidation is due to the existence of oxygen in 4H-SiC lattice, while the relaxation is caused by the migration of the oxygen-related defect structure, and emitted from 4H-SiC surface region as CO molecule.

Abstract: The study of formation energy and the vibrational effect on the vacancy concentration in the gray tin (α-Sn) using density functional theory has been successfully carried out. The vacancy is modeled by using a supercell consisting of 64 atoms. The vibrational effect is obtained by calculating the phonon density of states (P-DOS) of perfect and vacancy gray tin through the Gaussian-function approach. It is found that the formation energy of Sn-vacancy is 1.89 eV, and the vacancy concentration at the melting point is 3.68 × 10³ cm^-3. However, the vacancy concentration increases significantly to 6.48 × 10⁹ cm^-3 when the vibrational effect is considered. It is expected due to the softening of P-DOS on the vacancy case.

Abstract: The first principle density functional theory calculation has been done for calculating electronic and valleytronic properties on WS₂/CoO(111) heterointerface. We have performed the structural optimization of the WS₂/CoO(111) heterointerface and obtained the most stable structures by evaluating the binding energy between WS₂ and CoO(111) surface. Electronic and valleytronic properties can be understood by band structures, density of states, and spin texture of the crystal models. The results show that non-magnetic WS₂ becomes ferromagnetic because of the interfacial effect with the CoO(111) surface. The presence of CoO(111) near the WS₂ gives magnetic induction which breaks the time-reversal symmetry preserved on non-magnetic WS₂. Accordingly, the largest valley degeneracy is observed at Q and Q’ point in the unoccupied state, with the valley splitting up to 186 meV. Furthermore, the out-of-plane spin texture has also been calculated and the results show that spin configuration at Q and Q’ have opposite signs (up and down, respectively) indicating that the valley couple occurs on the heterointerface. Our results suggest that WS₂/CoO(111) is a promising candidate for valleytronic applications.

Abstract: This paper reports the synthesis and its application to the adsorption of methylene blue dye using graphene-oxide (GO) and reduced graphene-oxide (RGO). Among carbon-based nanomaterials, graphene and its derivatives have received remarkable attention due to their unique thermal, mechanical, and electronic properties and two-dimensional structure. The GO was synthesized by the modified Hummers method (chemical exfoliation) of graphite flake. This reaction produced graphite oxide (GrO) as an intermediate material. The synthesized materials, namely graphite, graphene oxide, and reduced graphene oxide, were characterized by XRD, FTIR, and Raman spectroscopy. These materials were tested to evaluate their adsorption capacity, concentration, contact time, and adsorbent weight on methylene blue, which was analyzed using a UV-vis spectrophotometer. The XRD pattern showed the formation of 2θ peaks at 24° to 26^o for graphite, graphene oxide, and reduced graphene oxide, respectively. Furthermore, characterization by FTIR showed the appearance of O-H groups with peaks of 3358 cm^-1 and 3342 cm^-1 for graphene and reduced graphene oxides. Raman characterization indicated that reduced graphene oxide has a wavelength at the D-band peak of about 1375 cm^-1 and the G-band peak reaching 1597 cm^-1 with an ID/IG intensity ratio of 0.8. The adsorption test of methylene blue showed that reduced graphene oxide had the best adsorption capacity with an adsorbent, concentration, optimum time, and highest adsorption capacity value of 25 mg, 30 ppm, 45 minutes, and 15.642 mg/g. The adsorption process followed the Langmuir isotherm rule, as evidenced by the R² value of 0.9881.