Papers by Keyword: Rietveld Refinement

Abstract: Colossal magnetoresistive (CMR) materials have been widely studied because of their huge potential in spintronic technology. An introduction of secondary phase to the manganite matrix is able to improve the low field magnetoresistance (LFMR). This method is favoured by recent research works as it requires a lower magnetic field compared to intrinsic magnetoresistance. Structural, magnetic properties and magnetotransport properties of polycrystalline (1-x) La_0.67Ca_0.33MnO₃ (LCMO): x TiO₂ composites where x = 0.00, 0.05, 0.10, 0.15 and 0.20 were investigated in this work. Polycrystalline La_0.67Ca_0.33MnO₃ (LCMO) was synthesized via sol-gel method and pre-sintered at 800 °C before appending with nano-sized TiO₂. All samples are in LCMO phase having an orthorhombic structure with space group Pnma. The crystal structural parameter is studied by using Rietveld refinement. As TiO₂ content increases, the magnetization is getting higher as observed via vibrating sample magnetometer (VSM) analysis at room temperature. Magnetotransport properties of the pure LCMO sample have been studied from 80 – 220 K. The LFMR is enhanced as the temperature drops. The results have shown LCMO: TiO₂ manganite composite is an excellent candidate for future magnetic sensors and memory devices.

Abstract: Perovskite manganites have always been the research interest attributed to its intriguing colossal magnetoresistive (CMR) properties. Incorporation of an insulating secondary phase into the manganite composites has proven as an effective measure to enhance the low field magnetoresistance (LFMR). This paper reports the structural, microstructural and magnetic properties of (1-x) Pr_0.7Sr_0.3MnO₃ (PSMO): x Al₂O₃ composites synthesized by the solid-state reaction method. Different compositions of nano-sized Al₂O₃ (x = 0.00, 0.05, 0.10, 0.15 and 0.20) were appended into the samples to investigate its effect on the physical properties. X-ray diffraction patterns show all samples exhibit polycrystalline PSMO as the major phase and strong orientation along (121) direction throughout the series. The crystal structural parameter is presented by Rietveld refinement. Nano-sized of Al₂O₃ has distorted the pure PSMO as changes have been observed in bond length and bond angle observed. Surface roughness and particle size show the increment along with increasing Al₂O₃ composition from the atomic force microscope (AFM) analysis. All samples possess the narrow hysteresis loop with weak ferromagnetic nature. The PSMO: Al₂O₃ presented in this study is a promising manganite composite which can be utilized in the magnetic sensor applications.

Abstract: Current study deals with the microstructural characterization of five different plates of steel with carbon concentration ranging from ultra-low to moderately high. Phase analysis was carried out using XRD technique. The XRD results were analyzed through Rietveld refinement and Williamson Hall plots. Rietveld refinement was carried out to understand the effect of carbon concentration on the lattice parameters of the above steel samples in as-received condition and also after deformation under uni-axial tensile loading. Lattice parameters obtained from refinement showed the strong dependence on carbon concentration of the given steels. But the failed specimens showed somewhat complex results as Spheroidized high carbon steel, Low carbon steel and IF steel showed an increase in lattice parameter whereas Medium carbon steel and Microalloyed steel showed a contraction in lattice parameter. Williamson Hall plot gave the crystallite size, microstrain and dislocation density in the steels. For IF and Microalloyed steels the dislocation density in the material is found to be higher after deformation whereas dislocation density decreased in Spheroidized high carbon steel, Medium carbon steel and Low carbon steel.

Abstract: This work is focused on a development and research of a new lead-free Sn-Mg solder, alloy compatible with the human body. Tin and magnesium are biocompatible elements which do not cause an inflammation or allergic reactions with living tissues. We have prepared the Sn₉₇Mg₃ solder (wt. %) by a rapid solidification of its melt on a copper wheel (melt-spinning technique). This solder may find applications in electronic devices for intracorporeal utilisation. The microstructure of the prepared solder exhibits a heterogeneous distribution of the SnMg₂ intermetallic particles within the β-Sn matrix. Structure of the solder was studied by an in-situ high energy X-ray diffraction experiment (energy of an X-ray photon: 60 keV) where 2D XRD patterns were collected from the sample in the temperature range from 298 K to 566 K. The experiment was performed at a high brilliance 3^rd generation synchrotron source of radiation (PETRA III storage ring, DESY, Hamburg, Germany) at the P02 undulator beamline. From the measured X-ray diffraction data by applying the Rietveld refinement technique we have obtained thermal volume expansion data, mean positions of atoms as well as isotropic atomic displacement parameters of the constituent SnMg₂ and the β-Sn crystalline phases. Thermal behaviour was studied by differential scanning calorimetry at heating rates of 5, 15, 30 and 60 K.min^-1 and compared with the measured X-ray data. Our main goal lies in a preparation of a lead-free solder with fine grain structure made exclusively of biocompatible elements. We demonstrated that the rapid melt solidification technique leads to in an improvement and better thermal stability of this alloy.

Abstract: A facile strategy was proposed to incorporate the dopant Fe into 8YSZ-based material, which can be potentially applied as solid electrode materials for Solid Oxide Fuel Cells (SOFC). In this study, 8YSZ powder was investigated in terms of densification, conductivity and thecrystal structure as a solid electrolytes. Therefore, varying mol% of Fe included 1, 2, and 3 were prepared for investigation. The crystalline structure of the pristine and Fe doped samples were characterized by X-ray diffraction (XRD) and the phase contents were evaluated by using the Rietveld method. Rietveld quantitative phase analysis demonstrates that the monoclinic-ZrO₂phase increases (12.8 wt% to 39.7 wt%) as the concentration of Fe increases, while the amount of tetragonal-ZrO₂ phase drop (40.4 wt% to 11.9 wt%) dramatically. Sintering activity was applied to improve incorporation of the 8YSZ powder and the dopant Fe where the relative density increases from 77% to 92%. Sample YSZ-2Fe has been fitted with CPE equivalent circuit and achieved 6.251 x 10^-6S/cm at 300 °C in air. However, it was found that conductivity levels decreased as the mol% of Fe increased. In short, sample YSZ-2Fe ceramic demonstrated good results in terms of densification (92.09%), cubic ZrO₂ phase (22 wt%) and conductivity 6.251 x 10^-6 S/cm.

Abstract: Phase pure olivine LiNiPO₄ and doped LiNi_0.8Mn_0.1Co_0.1PO₄ powders have been prepared by conventional solid state route. X-ray diffraction (XRD) combined with Rietveld refinements analysis reveals the formation of LiNiPO₄ and doped LiNi_0.8Mn_0.1Co_0.1PO₄ with high crystalline nature at high temperature of 950 °C and 1000 °C. The lattice parameters of doped LiNi_0.8Mn_0.1Co_0.1PO₄ are significantly larger than LiNiPO₄. It has been found out that the estimated crystallite size is in the order of nanometres for both samples. SEM analysis confirms that the particles have connected with each other in random shape and sub-microns size. The particle size has increased as small amount of Mn and Co are doped into LiNiPO₄. The AC impedance spectroscopy measurements have revealed that the conductivity of LiNiPO₄ is enhanced by around one order of magnitude by doping Mn and Co.

Abstract: The sintering behaviour of low cost 8 mol% yttria stabilized zirconia powders has been studied. The effect of sintering holding time of the sintered granulated and milled 8YSZ were determined using density measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The elemental composition, particle size and morphology of the as-received 8YSZ powder and proceed for milling was investigated. 48 hours of ball milling on granulated 8YSZ resulted rises in specific surface area and sintered at 1550°C with the various period of time (4, 5, 6 and 7 hours). The milled 8YSZ sample with 5h sintering holding period coded as F5, sintering activity improved and the relative density came up to 98.3%. But then, granulated 8YSZ achieved only 62.7% with 5 hours holding time. Crystal structure analysis for milled 8YSZ powder consists of 59.6% of cubic ZrO₂ phase, 40.1% of tetragonal ZrO₂ and 0.3% of monoclinic ZrO₂. Meanwhile, granulated 8YSZ indicated low content in cubic ZrO₂ but high amount in monoclinic ZrO₂ phase. In brief, low cost 8YSZ reached higher densification of 98% successfully.

Abstract: The novel perovskite oxide series of Sm_1-xZr_xFe_1-yMg_yO₃ (x,y = 0.5, 0.7, 0.9) were synthesized by solid state reaction method. X-ray diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and conductivity analysis were carried out. XRD patterns of sintered materials revealed the shifted Bragg reflection to higher angle for the higher content of Zr and Mg. This is related to the ionic size of the dopant elements. Rietveld refinement showed that all compounds crystallized in cubic space group of Fm-3m. SEM images showed that the grains were well defined with highly dense surfaces makes it potential as an electrolyte material in solid oxide fuel cells (SOFCs) or gases sensors. Impedance spectroscopy at 550-800 °C shows that conductivity is higher at higher temperature. Sm_0.5Zr_0.5Fe_0.5Mg_0.5O₃ shows the highest conductivity of 5.451 × 10^-3 S cm^-1 at 800 °C. It was observed that 50% molar ratio of Mg and Zr doping performed highest conductivity.

Abstract: Metallic sample preparation process from cutting to polishing introduces defects into the subsurface layers by plastic deformation. Methods of bulk sample characterization are usually sensitive to the microstructure and presence of defects e.g. dislocations, grain boundaries, etc. near the surface. The X-ray diffraction technique (XRD) is a unique method used primarily for phase identification and quantification of crystalline materials. The extending of the method by the whole pattern fitting using Rietveld refinement analysis enables also utilisation for other purposes such as determination of the size of coherently diffracting domains (CDD). This property quantifies the degree of disorder in material and is usually correlated with mean crystallite size, i.e. subgrain size. However, since the penetration depth of the laboratory X-ray radiation is limited to the order of tens of micrometers (depending on the material), the observed result is highly affected by the density of defects such as dislocations in the surface area of the specimen and thus by their surface condition. The effect of the different final steps of grinding and polishing on the observed size of CDD was studied and discussed for two materials - aluminum Al7075 alloy and high entropy alloy HfNbTaTiZr. The reasonable finishing for the optimal results was found for both materials.

Abstract: The carbides of refractory metals like tungsten carbide (WC), tantalum carbide (TaC) and niobium carbide (NbC), has been extensively studied due to their applications in several areas of industry, because of their specific properties; such as high melting point, high hardness, wear resistance, oxidation resistance and good electrical conductivity. The tungsten carbide, particularly, is generally used at hardmetal industries due to its high hardness and wear resistance. New synthesis techniques have been developed to reduce the synthesis temperature of refractory metal carbides using more reactive precursors and gas-solid reactions for carbon reduction. The result is producing pure carbides suitable properties for production of high quality cemented carbides and more selective catalysts. In this work, pure and nanostructured WC was obtained from the ammonium paratungstate hydrate (APT), at low temperature and short reaction time. Hydrogen (H₂) and methane (CH₄) were used as a reducing gas and carbon source, respectively. The precursor and obtained product were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results obtained by diffraction of X-rays showed that complete reduction and carburization of APT have been took place resulted in pure WC formation. The average crystallite size was in nanometer order reaching values of approximately 20.8 nm and a surface area (BET) of 26.9 m2/g.