Papers by Keyword: Crystal Structure

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: Ga₂O₃ is a hopeful wide-band-gap semiconductor material for a next-generation power semiconductor. We performed crystal structure analysis on Ga₂O₃ film on sapphire substrate using cross-sectional transmission electron microscope (TEM) and atomic resolution plan-view scanning transmission electron microscopy (STEM). The TEM analysis suggested that the main Ga₂O₃ film is composed of κ-Ga₂O₃ or mixed crystal of κ-Ga₂O₃ and ε-Ga₂O₃. But, it is difficult to distinguish these two possibilities only by cross-sectional TEM. Contrast modulation of Ga atomic columns in the atomic resolution HAADF-STEM image showed that the main part of the Ga₂O₃ film was κ-Ga₂O₃ monolayer grown along the c-axis direction, and twins are formed.

Abstract: In this study, effect of La substitution on the microstructure, magnetic properties and microwave absorption characteristics of Ba_1-xLa_xFe₁₂O₁₉ (x=0, 0.1, 0.2, 0.3, 0.5, 0.7) is reported. The samples were synthesized through mechanical alloying and solid reaction a temperature 1200 °C for 2 hours. A single-phase material occurred only at x = 0 and 0.1. Additional second phases were existing in all samples with x ≥ 0.2 which led to multi-phase materials. The single phase (x = 0 and 0.1) has a relatively uniform particle size distribution with a mean crystallite size 138 nm. Additional phases of respectively Fe₂O₃ and LaFe₂O₃ were identified in all samples with x ≥ 0.2. Effect of La substitution is to decrease the magneto crystalline anisotropy constant and the saturation magnetization. The latter is due to a decrease in mass fraction of the main magnetic phase. All Ba_1-xLa_xFe₁₂O₁₉ samples have superior microwave characteristics which able to absorb more than 99 % the incoming electromagnetic wave entering the material. The absorption bandwidth is found relatively wide within the frequency range 8-12 GHz.

Abstract: Bismuth ferrite (BiFeO₃) nanoparticles has been synthesized by coprecipitation method with various NaOH concentration (4, 6, 8, and 10 M) and temperature (RT, 60, 80, and 100 C). X-ray diffraction patterns showed the emergence of Bi(OH)₃ and Bi₂₅FeO₄₀ structures with crystallite size in the range of 15.1 nm to 35.6 nm. The particles sample was agglomerated. Hysterisis loop showed the linear M–H loops behaviour with no magnetization saturation in 15 kOe maximum field applied which indicates the antiferromagnetic properties. The coercivity field tends to increase by the increasing of the NaOH concentration and synthesis temperature. In addition, the annealing treatment could leads the increasing of coercivity fields while decreasing the magnetization of BFO sampel.

Abstract: In this research, CoFe_2-xLa_xO₄-based smart magnetic material has been developed which will be applied as a microwave absorbing material. This smart magnetic material is an artificial advanced material which has properties such as electromagnetic waves so that it is able to respond to the presence of microwaves through the mechanism of spin electron resonance and wall resonance domain. This smart magnetic material consists of a combination of rare earth metal elements (spin magnetic in the f orbital configuration) and transition metal elements (spin magnetic in the d orbital configuration) with a semi-hard magnetic structure. This semi-hard is a characteristic of magnetic properties which is between hard magnetic and soft magnetic properties. This characteristic of the semi-hard magnetic properties is needed so that this material has the ability to absorb microwaves. Substitution of lanthanum into cobalt ferrite CoFe_2-xLa_xO₄ for La³⁺ (x = 0 - 0.8) has been synthesized using the solid reaction method through mechanical deformation techniques. The refinement result of X-ray diffraction shows that the sample contains 2 phases with increasing of x compositions. Particle morphology and elementary analysis were observed respectively by using a scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). It was concluded that the effect of La substitution on CoFe_2-xLa_xO₄ resulted in changes in the crystal structure parameters and phase transformation as a function of composition.

Abstract: Nd₂Fe₁₄B permanent magnet manufacturing technology in some developing countries is still relatively difficult because it is constrained by limited equipment facilities and dependence on imports of raw materials. In the context of efforts to build national independence, the concrete step is to try to study the process of making permanent Nd₂Fe₁₄B magnets with conventional facilities and technology. In this research an attempt was made to make and characterize Nd₂Fe₁₄B permanent magnets substituted with praseodymium Pr metal using conventional technology through the arc melting method. The success parameter of the results of this sample making is the formation of the Nd₂Fe₁₄B phase in the sample. The formation of this phase can be fundamentally studied the number of mass fractions of formed phases and structure crystallography using X-ray diffraction facilities and is supported by spectroscopy facilities and their magnetic properties. So the purpose of this research in general is to study the manufacturing process and the fundamental formation of the phases of the NdPrFe₁₄B sample making through the arc melting method, while specifically wanting to know the relationship between phase analysis and the magnetic anisotropic properties of NdPrFe₁₄B. The coercivity field appears to increase significantly after the sample is substituted with Pr and has a fairly small crystallite size distribution. So it was concluded that the presence of Pr was able to withstand the growth of grain, causing the anisotropic magnetocrystalline field to increase.

Abstract: Tungsten trioxide (WO₃) nanostructures were synthesized by a hydrothermal method, and the influence of essential hydrothermal conditions, temperature and time, on their crystal structure, morphology and visible-light driven photocatalysis was studied. The hydrothermal temperature was varied from 120 °C to 200 °C, and the hydrothermal time changed from 12 h to 32 h. The crystal structure, morphology and photocatalytic performance of WO₃ nanostructures were characterized by XRD, SEM and UV-Vis. The crystal structure of WO₃ nanostructure was triclinic phase and their morphology was mainly one dimensional nanorods. Methylene blue was used as the target to evaluate their photocatalytic performance under visible light (λ>420 nm). The photocatalytic results suggest the suitable hydrothermal conditions to synthesize WO₃ nanostructures for the wastewater treatment application.

Abstract: Nanocrystalline bismuth ferrite BFO; BiFeO₃ and manganese sillenite, BMO; Bi₁₂MnO₂₀ (BMO) powders have been successfully elaborated using a facile co-precipitation approach. The formed materials were examined using X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FE-SEM). Furthermore, the change in the optical properties was performed based on Fourier transform infrared spectroscopy (FT-IR) and UV-visible spectrophotometer. Typical, pure BiFeO₃ and Bi₁₂MnO₂₀ phases were detected for the precursors precipitated at pH 10 based on ammonium hydroxide as a base then annealed at 500°C for 2h. Eventually, the optical band gap energy of BFO and BMO using Kubelka–Munk function based on Tauc’s plot was found to be 2.12 and 2.79 eV, respectively.

Abstract: High entropy alloys (HEAs) generally exhibit either high resistance to deformation or high toughness due to the presence of body-centered or face-centered cubic structure, respectively. To overcome these limitations, new high entropy alloys have been developed in the present study. This investigation aims to synthesis and characterization of novel CoCrFeNi₃Si, CoCrFe₂Ni₂Si, and Co₂CrFeNi₂Si high entropy alloys. The mechanical alloying route is used to synthesize these alloys. Grinding was carried out to 20h and X-ray diffraction (XRD) analysis was done at different time intervals of grinding. The face-centered cubic structure along with the intermetallic compound of Ni-Si was observed after 20h of grinding. Furthermore, a pseudo binary strategy based on the valence electron concentration and mixing enthalpy is also employed to design the high entropy alloys considered in the present study. Carefully analysis of the XRD pattern indicates that from 5 to 20h of mechanical alloying there is a decrement in the initial peaks of elements observed.

Abstract: Theoretical and experimental materials for analyzing the technical capabilities of concrete are generalized and the physicochemical basis for the strength and durability of concrete is developed on the basis of the recent advances in building materials science and other sciences. That may increase the traditional concrete potential use and most importantly – to create the most firm and durable concrete of the new generation.