Key Engineering Materials Vol. 860

Abstract: LiFeSi_0.03P_0.97O₄/C composite materials with variations in duration of milling are 4, 8, 12, and 16 h have been synthesized successfully by solid-state process. The iron stone from Tanah Laut Kalimantan used as source of ion Fe and Glucose used as material coating. The result of XRD have shown all of the samples have a olivine LiFePO₄ phase except for milling 16 h. The largest electrical conductivity was 1.75x10^-8 S/cm observed in sample of 16 h.

Abstract: In the recent years, LiFePO₄ has been widely developed as a cathode for lithium ion batteries because it has high theoretical capacity (170 mAh/g), good stability and is also environmentally friendly. However, the poor electronic conductivity (~10^-9 S/cm) and low diffusion coefficient of lithium ion (~10^-15-10^-14 cm²/s) are limiting its application. Some solutions to overcome this problem are carbon coating and doping metal ions. This study aims to determine the effect of Gd³⁺ ion doping on the electronic conductivity of LiFePO₄/C. The synthesis method was used is carbothermal reduction with Fe₂O₃, Gd₂O₃, LiH₂PO₄ and carbon black reagents. The synthesized LiFe_1-xGd_xPO₄/C was characterized using XRD, SEM-EDS, and four point probes. The results obtained showed that gadolinium ion doping increased the conductivity of LiFePO₄/C from 1.8952 x10^-6 to 8.69x10^-6 Scm^-1 using 0.07 mol ion Gd³⁺.

Abstract: A cathode Lithium Ferro Phospate (LFP) composite material with variation doping ion Silicon (Si) with x = 0; 0,01; 0,03; 0.06 and carbon coating (LiFeSi_xP_1-xO₄/C) as lithium ion battery cathode were synthesized by a solid state reaction and wet milling methods. X-Ray Diffraction (XRD) pattern showed that the of olivine phase formed, and analysis characterization of Scanning Electron Microscopy (SEM) have shown average dimension particle of cathode in orde 1 micron. Analysis by Cyclic Voltammetry (CV) doping ion Si x = 0,03 have the best reversible electrochemical process than the other concentration, and have the highest charge and discharge capacity (78,745 mAh/g).

Abstract: Magnetic nanofluids are a category of nanomaterial which exhibit simultaneously liquid and superparamagnetic properties. These nanofluids are magnetic nanoparticles stably dispersed in liquid carrier. Magnetic nanoparticles with and without SiO₂ encapsulation have been successfully synthesized by co-precipitation method from ferrous and ferric precursors dispersed in various liquid. Fe₃O₄ nanoparticles were investigated by Zeta Potential and HR-TEM to determine the stability of nanoparticles, average particles size and microstructure of nanoparticles. From zeta potential measurements, is was found that the value of zeta potential for Fe₃O₄ dispersed in ethanol was ± 0,9 mV, while dispersed in di-water was ± 31,1 mV, indicating that nanoparticles Fe₃O₄ are more stable in DI-water. The increasing of zeta potential indicated the adsorption of negatively charged hydroxyl group to the surface of Fe₃O₄ nanoparticles. From XRD measurements, it was found that crystal quality of Fe₃O₄.SiO₂ sintering at 80 °C decreased by increasing the volume of tetraethyl orthosilicate (TEOS), while that samples sintering at 1000 °C have a good crystal quality with hexagonal phase of a-Fe₂O₃.SiO₂. From SQUID measurements, it was found that samples of Fe₃O₄.SiO₂ sintering at 80 °C with TEOS volumes of 1 ml and 2 ml showed a paramagnetic like while samples of a-Fe₂O₃.SiO₂ sintering at 1000 °C with the same TEOS volume showed ferrimagnetic properties.

Abstract: La_0.7Ba_0.25Nd_0.05MnO₃ (LBNMO) compounds were synthesized using two different methods, namely are solid-state reaction (SS) and sol-gel (SG). All samples were heat-treated at 1200 °C for 12 hours. The investigation on structural, morphological, and magnetic properties was carried out by X-Ray Diffractometer (XRD), Scanning Electron Microscope (SEM), and Vibrating Samples Magnetometer (VSM) at room temperature. From the Rietveld refinement, both samples have formed a rhombohedral structure with an R-3c (167) space group. The average crystallite size was calculated using the Scherrer formula and Williamson-Hall (W-H) method for comparison. It was shown that the crystallite size of the sample produced by the SG method has larger than the SS method. This result is fairly consistent with the result obtained from SEM analysis, which shows that the average grain for the SG sample is larger than of the grain of the SS samples. From the magnetic hysteresis curve, the magnetization saturation value for the SG was higher and sharper than that of the SS sample. These confirm the occurrence of the double exchange interaction in the samples, which is mainly associated with the reduction of bandwidth and grain size.

Abstract: Bulk polycrystalline samples La_0.85-xBa_xNa_0.15MnO₃ (x = 0, 0.05, 0.10 and 0.15) manganites were synthesized by the sol-gel route. The effect of Barium (Ba) existence on the structural and morphological was investigated by X-ray diffraction (XRD) and Scanning Electron Microscope (SEM). The structural parameters were obtained using Rietveld refinement of the XRD pattern. It was revealed the structures of compounds have rhombohedral with R-3c space group without any impurities phase. Furthermore, several changes are found to exist due to Ba substitution such as the lattice parameter, unit cells volume, average crystallite size, average Mn-O bond length (<Mn – O>) and average Mn-O-Mn bond angle (<Mn – O – Mn>). The changes in <Mn – O> and <Mn – O – Mn> due to Ba substitution, affects the double exchange interaction of the samples. SEM images reveal the existence of Ba also affects the morphology of the studied samples, which consisted of polygonal grains with homogeneous chemical composition.

Abstract: A perovskite manganate material La_0,667Ba_0,333Mn_1-xCu_xO₃ (x = 0.35 and 0.40) were prepared. The samples were synthesized by sol gel method. The samples were sintered at 1000^OC for 6 hours. Rietveld refinement shows that both samples are crystallized in orthorhombic structure with Pnma space group. This results is in accordance with Goldschmidt’s tolerance factor value which are 0.8698 and 0.8701 for x = 0.35 and 0.4, respectively. Subtitutions with large amount of copper ions in B-sites caused the unit cell to decrease from 236.234 ų to 236.088 ų . Futher calculation from crystallography Refinement also shows that copper subtitutions increase the crystallite size of the samples from 74.8 nm to 94.49 nm. It has been found from the SEM results that copper subtitutions also alter the morphology of the samples.

Abstract: Nanosized La_0.75K_0.05Ba_0.05Sr_0.15MnO₃ manganite have been synthesized using sol-gel method. Afterwards, the samples were sintered at eight different temperature ranging from 650 to 1000 °C. Phase purity, crystal structure and the morphology of the sample have been examined using X-Ray Diffractometer (XRD) and Scanning Electron Microscope. It has been found that different higher sintering temperature greatly affect the phase purity and crystallite size of the sample. Regardless of the sintering temperature, all the samples crystallized in rhombohedral structure with R-3c space group. The crystallite size of the samples is found to increase from 41.59 nm up to 73.42 nm as the sintering temperature increases. Further analysis from XRD result shows that sintering temperature also affect the average Mn-O bond length and Mn-O-Mn bond angle of the sample. The average Mn-O bond length is found to increase while the average Mn-O-Mn bond angle tends to decrease as sintering temperature increases. SEM measurement shows that various grain size ranging from ~100 nm up to ~ 350 nm exists in all the sample regardless the sintering temperature.

Abstract: The sequence of Cu substituted Ca_0.9La_0.05Bi_0.05Mn_1-XCu_xO₃ ( x = 0, 0.025, 0.05, 0.075, and 0.1) manganite has been studied and it has effect in the structure. The samples was synthesized using the citric acid sol-gel method. The samples was sintered at 800 °C for 5 hours. The crystallography and morphological of all samples was investigated using X-Ray Diffractometer (XRD) and Scanning Electron Microscope (SEM). The Rietveld analysis of the powder x-ray diffraction shows that all the samples crystallize in orthorhombic structure with pnma space group symmetry without any impurity phase. The Cu substitution does not change the crystal structure, but it changes the grain size. SEM results showed a valid different morphological structure. The increasing Cu concentration, it made the grain size larger, dispite all the samples had the same treatment.

Abstract: The polycrystalline Ca_0.9La_0.05Bi_0.05Mn_1-xNi_xO₃ (x = 0.025, 0.05, 0.075) samples were synthesized by sol-gel method. All samples were calcined at 650°C for 8 hours and sintered at 900°C for 8 hours. The structural and morphological properties of the samples were measured by X-ray diffraction (XRD) and Scanning electron microscope (SEM). The rietveld refinement shows that all samples were having an orthorhombic structure with pnma space group despite having different Ni content. Furthermore, the average crystallite size decreases with Ni substituion. SEM result shows the average grain size decreases with increasing Ni substitution regardless of the same heat treatment. This result will affect other properties like electrical and magnetic properties.