Papers by Keyword: Rietveld Analysis

Abstract: Iron substituted Lead zirconate titanate nanoparticles Pb (Zr_0.52Ti_0.48) _1-x Fe_xO_3-x (PZTFx) (for (x=0.00, 0.025, 0.05, 0.075, 0.10, 0.15 and 0.20) was prepared using the sol-gel route in the morphotropic phase boundary (MPB) region. The X-ray diffraction data revealed the formation of both rhombohedral and tetragonal structures. The microstructural properties of the compounds were examined through the scanning electron microscopy (SEM) technique. The impedance spectroscopy and conductivity spectroscopy were carried out over a wide range of temperatures (RT–400°C) and frequencies (100 Hz–2 MHz) to investigate the grain and grain boundary effect on the electrical properties of PZTFx. The complex impedance analysis data have been presented in the Nyquist plot which is used to identify the corresponding equivalent circuit and fundamental circuit parameters. Cole– Cole plots indicate Debye-type dielectric relaxation and the grain boundaries resistance is dominant at room temperature. The Nyquist plot showed the negative temperature coefficient of resistance (NTCR) character of PZTFx ceramics. The dielectric properties of (PZTFx) ceramics as a function of temperature are studied and displayed a resonance phenomenon for all samples. Temperature-dependent conductivity behavior indicated an Arrhenius type of thermally activated process in the low-temperature region. Activation energy has been calculated from the temperature-dependent DC electrical conductivity measurements for all the samples.

Abstract: Preparation conditions of titanium oxide (TiO₂) powders were examined by the hydrolysis of titanium potassium oxalate (K₂TiO(C₂O₄)₂), through the homogeneous precipitation method (80oC for 24 h) and hydrothermal treatment (160 or 170oC for 1 h). According to the Rietveld analysis, almost a single phase of anatase TiO₂ could be obtained by the hydrothermal treatment at 160oC for 1 h, followed by the heating at 900oC for 10 min in air. The molar ratio of anatase to rutile TiO₂ was found to be controlled by optimizing the hydrothermal conditions in the solution and the heating conditions in air for the photocatalytic activity.

Abstract: A facile method was successfully developed to prepare Ternary oxynitride of iron and gallium. Initially mixed oxyhydroxides of Iron and gallium were prepared by co-precipitation method. Then this was nitrided using urea and agar in presence of ammonia at 900°C, which gave mixed cation oxynitride . This mixed oxynitride was characterized using XRD, XPS and SEM. The X-ray diffraction pattern of the Fe_x’Ga_xO_yN_z phase was refined within the cubic spinel structure (space group Fd-3m), using the fullprof program. On assuming 3⁺ oxidation state for half of iron and whole of gallium, the chemical composition of the oxynitride spinel determined by the X-ray analysis is Fe₂GaN₂O₂. The refinement using these parameters resulted in a good fit to the observed diffraction data, with a crystallographic R factor of 5.92. This ternary oxynitride of iron and gallium is a novel material which can give unique optical and magnetic properties.

Abstract: Small pellets with differing mullite contents were prepared by a conventional ball-milling and dry-powder pressing technique, followed by firing at temperature of 1300°C and 1600°C for four hours. Kaolin processing waste and high purity aluminum hydroxide were used as starting materials. The sintered samples were examined using X-ray diffraction to determine the weight percent of each identified phase. The results showed that the percentage of mullite in kaolin processing waste can be increased by introducing additional aluminum hydroxide. It was found that sintered samples yielded best results when derived from both types of kaolin processing waste with 40wt% of aluminum hydroxide and a firing temperature of 1600°C.

Abstract: La-doped barium titanate (BaTiO₃) was prepared using conventional solid state synthesis route. All peaks for sample x=0 are approaching the phase pure of BaTiO₃ structure with tetragonal crystal structure (P4mm). Sintering of pressed powder are performed at 1300oC, 1400oC and 1450oC for overnight for pure BaTiO₃ and 1350oC for 3 days for BaTiO₃ doped lanthanum with intermittent grinding. Phase transition was studied by different x composition. The changes in the crystal structure of the composition x=0.1 and 0.2 were detected by using X-ray diffraction (XRD). The phase changes between tetragonal-cubic and cubic-tetragonal depending on the temperature. Rietveld Refinement analysis is carried out to determine the lattice parameter and unit cell for BaTiO₃.

Abstract: In this work, the effect of Pd addition on nanostructured TiO₂ powders is studied. The materials were obtained by the sol-gel method and characterized by XRD, Rietveld refinement, TEM, Raman and UV-vis spectroscopies. The crystal structure and the nature of the different TiO₂ phases were modified by varying the palladium/TiO₂ ratio: 0.01, 0.03, and 0.05. The XRD results revealed the presence of different combinations of TiO₂ (B), anatase, rutile and PdO phases as well as their coexistence in the different samples. The Rietveld analysis showed that the composition of the phases is rather affected by the amount of Pd added to the TiO₂ structure. The Raman spectroscopy confirmed the characteristic bands of the TiO₂ phases in the samples and their variation depending on the Pd/TiO₂ ratio. The TEM results indicated that the as-prepared samples displayed crystal sizes of nanometric order (˂ 80nm). The observed reduction of the band gap was also correlated with the combination of phases due to the palladium addition. All the Pd/TiO₂ samples showed a significant improvement in the elimination of 4-chlorophenol during the application of water treatment technology.

Abstract: Two polyphase gneiss samples (Western Alps, Switzerland) consisting of quartz, albite, muscovite and microcline have been investigated with respect to anisotropic physical properties - residual and applied strain - and crystallographic preferred orientations. The samples were taken in close vicinity to a fault structure. For texture evaluation the 'Rietveld texture analysis' has been applied, because reliable texture analysis of polyphase rocks from pole figures is problematic due to multiple peak overlaps. The quartz textures of both samples are strong and rather similar, whereas albite and microcline show a nearly random distribution. In contrast, the mica texture is pronounced and complex. The basal plane normals of muscovite are preferably oriented parallel to [-direction of the structural reference frame and switch to [-direction with residual orientations in [ and a transition into the [-[-plane within the fault. This might be the result of quartz recrystallization, if mica is used as reference according the applied stress field. A residual strain scan has been carried out along the axis of a cylindrical sample (d = 30 mm, l = 60 mm). Residual strain values of quartz have been detected with a minimum of-1.6×10^-3, and maximum strain values of 1.2×10^-3. Uniaxial compression experiments in discrete steps up to 53 MPa were performed, for each step the applied and residual strains were determined. The strain increases up to 28 MPa; surprisingly, lower strain values are detected at higher applied stresses.

Abstract: The crystal structure of (La,Mg,Nd)₅Ni₁₉ alloy has been investigated using powder x-ray diffraction. A Rietveld refinement is used to determine the phase structures for tying to find out the correlations of lattices among the phases in this hydrogen storage alloy. The results show that the alloy consists of three phases, which correspond to (La,Mg)₃Nd₂Ni₁₉ with a Pr₅Co₁₉-type structure, La (Mg,Nd)Ni₇ phase with a Ce₂Ni₇-type structure and (La,Mg)₃Nd₂Ni₁₉ with a Ce₅Co₁₉-type structure. Mg and Nd substitute for La atom at the 4f position for Pr₅Co₁₉-type and Ce₂Ni₇-type structures and the 6c position for Ce₅Co₁₉-type structure, respectively. It induces a good lattice match along the a-axisand b-axis among the three phases. The three kinds of structures might form a rod-like shape structural unit by stacking along the c-axis. This phase constitution seems to be beneficial for the cyclic stability of the hydrogen storage alloys.

Abstract: The influence of heat treatment on phase decomposition of Co-10 at. pct. Cu alloy was studied. The materials and phase compositions were studied by using energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) techniques. XRD analysis showed that the samples contained Co, Cu, CuO and CoCu2O3 phases depending on the heat treatment regimes. Moreover it is found that the formation of dendrite Co phase render the spinodal decomposition even for deep long aging inside the miscibility gap. The crystal structural parameters were refined with FULLPROF program. 2-D computer simulation indicates that the morphology and the shape of the microstructure agree with experimental SEM micrographs for the Cu rich phase.

Abstract: An experimental and theoretical investigation of defect modes in tin-doped cupric oxide (Sn-doped CuO) nanoparticles synthesized via a one-step solid-state reaction was reported. The defect mode at 455 cm^-1 due to Sn doping in CuO nanoparticles, calculated using a molecular model, was compared with the experimental value of 458 cm^-1 obtained from the FTIR vibrational spectrum. The Debye-Waller factor (DWF) of CuO nanoparticles was determined using Rietveld refinement of the XRD pattern and the Wilson’s plot, and the results were discussed on the basis of the number of surface atoms and thermal vibrations. The effect of defect modes upon the DWF of Sn-doped CuO nanoparticles was also discussed.