Key Engineering Materials Vol. 860

Abstract: Effect of difference silica source, namely commersial silica and silica from rice husk, as Si precursor on the synthesis of lanthanum silicate apatite (LSO) have been investigated. The conductivity of LSO was determined by impedance spectroscopy using LCR meter. The conductivity of LSO based on rice husk extraction (s_700°C = 2.13 ´ 10^-4 S.cm^-1) was ten times lower than that of LSO with commercial silica (s_700°C = 3.11´ 10^-5 S.cm^-1). Carbon content as an impurity on silica from rice husk extraction is suspected to decrease the homogeneity of its morphology so that it has an impact on its conductivity.

Abstract: Particle size analysis of synthesized Al₂O₃ by dissolution and alkali fusion-coprecipitation methods has been conducted. The formation of nano- or microparticles can be synthesized by the top-down (physically) and bottom-up (chemically) methods. In this study, the commercial alumina (Merck) with the particle size of 63 µm was synthesized through the bottom-up method. The dissolution method was done by reacting to alumina with ammonium hydroxide (NH₄OH). The alkali fusion method was carried out by reacting alumina with sodium hydroxide (NaOH) and it obtained by coprecipitation of the alkali fusion product with HCl and NH₄OH. The result from both methods were calcined at 600°C. The phase of synthesized Al₂O₃ was identified by using X-ray diffraction (XRD), whereas the morphology observed using a transmission electron microscope (TEM), and the particle sizes measured by particle sizes analyzer (PSA). The XRD pattern shows the γ-Al₂O₃ phases with particle sizes of ~33 nm and ~25 nm from TEM observations, while the PSA results revealed agglomerated particles with particle sizes of 1263 nm and 477 nm for the dissolution and alkali fusion-coprecipitation method, respectively. Therefore, both methods can be used to reduce the particle size of γ-Al₂O₃.

Abstract: The lower critical field of type-II organic layered superconductor l-(BETS)₂GaCl₄ has been estimated by magnetic measurements. The demagnetization factor of a needle-like sample shape has been taken into account for the measurements by applying the external field, parallel and perpendicular to the conducting plane. The lower critical field for the field parallel to the conducting plane is 5.5(2) G, in contrast with the previous studies. This allows us to discuss the anisotropy of lower critical field H_c1 in a quasi-two-dimensional organic layered superconductor l-(BETS)₂GaCl₄.

Abstract: We report the results of the resistivity measurement on La_2-xSr_xCuO₄ nanoparticles with x = 0, 0.05, and 0.20 evaluated by the four-point probe method. The high resistivity value shows the predominance of the inter-grain part. The temperature dependence of the conductivity can be analyzed by variable range hopping model showing the charge carriers are formed by thermal activation. There is no superconducting behavior that could be observed in La_2-xSr_xCuO₄ nanoparticles with x = 0.05 and 0.20.

Abstract: The partially substitution of magnetic impurity Ni for Cu in electron-doped superconducting cuprates of Eu_2-xCe_xCu_1-yNi_yO_4+a-d with x = 0.14 and y = 0, 0.01 and 0.02 has been studied in order to investigate the effect of Ni impurity on structure and the value of magnetic moments per unit volume extracted from susceptibility data in under-doped region. Magnetic-susceptibility measurements were carried out at low temperatures down to 2 K. For sample with y = 0, diamagnetic behavior is observed starting from about 9 K. The superconductivity disappeared at y ³ 0.01. The values of magnetic moment in every volume unit decreased with increasing Ni.

Abstract: Here we report spin-alignment contributions to muon coordinate calculated utilizing density functional theory (DFT) calculation. We estimated four different antiferromagnetic (AF) spin alignments in La₂CuO₄. We observed small changes by adjusting spin configurations in DFT calculations. Cu-spin value of 0.61 µB is constant in all calculations. The insulating gap of 1.9 eV is unchanged in all configurations. Muon coordinate was defined as the most minimum energy in atomic potential distribution. By assuming that Cu-spin is a point dipole for each atom, internal fields for muon were calculated and compared to known experimental results.

Abstract: The samples of Eu_2-xCe_xCuO₄ (ECCO) with x = 0.09 (Eu_1.91Ce_0.09CuO₄) and x = 0.16 (Eu_1.84Ce_0.16CuO₄) have been synthesized by the solid reaction method without annealing. Each sample is covered with CuO to prevent excess oxygen entering the sample. The purity and electrical resistivity were investigated by x-ray Diffraction (XRD) and resistivity measurements. From the XRD analysis, it was found that the purity of ECCO phase was 93.5% with tetragonal structure of T’ for x = 0.09 while 96.1% for x = 0.16. These results show that the synthesis method with CuO covering has succeeded in synthesizing materials with high purity. From the electrical measurements, the trace of superconductors was not observed in all samples. It is probably the existence of excess oxygen, which was not fully absorbed by CuO Covering.

Abstract: A modified dipole field equation proposed to reconstruct the μSR spectrum theoretically. Gaussian interaction weight added in dipole field calculation to investigate the effective interaction range between muon and its surrounding spin. The width of Gaussian interaction weight traced until the theoretical spectrum fit the data. The theoretical spectrum limited only to minima within the unit cell. By using the interaction weight the main peak spectrum can be reproduced without having a contradiction with the magnetic moment measured from neutron. Effective interaction between muon and surrounding spin estimated to be around which is relatively small.

Abstract: Water Hyacinth (WH) is a plant that can absorb various pollutants in water. However, this plant is categorized as an invasive plant that can become a weed in the waters. To improve the functionality of WH, processing of WH is needed to be used for various applications. One of modifications of WH is as porous carbon for battery cathode composite. In this paper, we reported a synthesis of a porous carbon from WH. WH is processed into carbon by carbonization at various temperatures of 400, 500 and 600 °C with various activators of KOH, H₃PO₄ and ZnCl₂ to obtain high quality porous carbon which has high electrical conductivity, large specific surface area and large porous volume. All synthesized carbons were characterized by proximate analysis measurements, scanning electron microscopy (SEM), and N₂ adsorption-desorption measurements. The highest carbon fixed content of 37.79% is obtained from charcoal with a carbonization temperature of 400 °C. The largest specific surface area of 264.77 m²/g was obtained from activated carbon with H₃PO₄ as activator. The values of pore volume and pore radius were 0.186 cm³/g and 1.56 nm, respectively.

Abstract: The purpose of this research is to observe the influence of carbon from rice husk charcoal composition at Unsaturated Polyester Resin/Carbon (UPR/C) composite as electromagnetic wave absorber. In this research, carbon has been synthesized from rice husk charcoal. Characterization with SEM-EDX and FT-IR showed that the carbon consists of C, O, and Si atoms. Characterization with XRD showed that carbon from rice husk charcoal is amorf with the maximum value of 2θ is 22,86^o, respectively. Carbon from rice husk charcoal then is used as a composite filler with UPR as the composite matrix with ratio filler/matrix such as 5:95; 10:90; 15:85; 20:80 and 25:75 (%w/w). Characterization with VNA is done at the frequency range of 8-12 GHz. It has been found that the composite which contains filler carbon 20% exhibits optimum reflection loss of peaks with-19,5909 dB at 10.60 GHz. The result showed that inside UPR/C composite can be used as an electromagnetic wave absorber.