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(1 - 4 of 4)
- Title
- Rietveld analysis of powder diffraction data from a carbonate fluorapatite.
- Creator
- Moghaddam, Hadi Yazdani, Florida Atlantic University, Leventouri, Theodora
- Abstract/Description
-
The mechanism of the carbonate substitution in the apatite structure is unraveled through analysis of Rietveld refinements of powder diffraction data from a single-phase natural carbonate fluorapatite (francolite). The refined values of the P-O bond lengths give a ~1.6% distortion of the phosphate tetrahedron caused by the carbonate substitution. The two bond lengths P-O1 and P-O2 and their corresponding angles on the mirror plane of the phosphate tetrahedron are mainly disturbed by this...
Show moreThe mechanism of the carbonate substitution in the apatite structure is unraveled through analysis of Rietveld refinements of powder diffraction data from a single-phase natural carbonate fluorapatite (francolite). The refined values of the P-O bond lengths give a ~1.6% distortion of the phosphate tetrahedron caused by the carbonate substitution. The two bond lengths P-O1 and P-O2 and their corresponding angles on the mirror plane of the phosphate tetrahedron are mainly disturbed by this substitution. A static positional disorder, mainly of the atoms at the tetrahedral sites, is revealed from the temperature dependence of the atomic anisotropic displacement parameters. A model for the mechanism of the carbonate entrance in the apatite structure is proposed.
Show less - Date Issued
- 2000
- PURL
- http://purl.flvc.org/fcla/dt/12718
- Subject Headings
- Rietveld method, Apatite, X-rays--Diffraction
- Format
- Document (PDF)
- Title
- Structural, magnetic, and electrical properties of ruthenium oxides.
- Creator
- Leao, Juscelino Batista, Florida Atlantic University, Neumeier, John, Charles E. Schmidt College of Science, Department of Physics
- Abstract/Description
-
Early reports of antiferromagnetism in CaRuO3 will be discussed within the framework of our recent experiments. We have observed that slight Ru deficiency (∼4%) leads to a weak feature in the magnetic susceptibility. Temperature-dependant time-of-flight (TOF) neutron powder diffraction data revealed no long-range magnetic order in the Ruthenium deficient CaRu 0.96O3 sample. More careful analysis of magnetization data indicates that the feature in chi(T) can be attributed to a weak...
Show moreEarly reports of antiferromagnetism in CaRuO3 will be discussed within the framework of our recent experiments. We have observed that slight Ru deficiency (∼4%) leads to a weak feature in the magnetic susceptibility. Temperature-dependant time-of-flight (TOF) neutron powder diffraction data revealed no long-range magnetic order in the Ruthenium deficient CaRu 0.96O3 sample. More careful analysis of magnetization data indicates that the feature in chi(T) can be attributed to a weak ferromagnetic phase which forms below an ordering temperature of T = 147 K. This phase is destroyed with Lanthanum doping (∼2%) and annealing in reducing conditions dramatically shifts this feature. Measurements of the magnetic susceptibility versus temperature of the series Ca1-xLaxRu 0.96O3 (0 ≤ x ≤ 0.12) led to further study of CaRuO 3 and SrRuO3. The structural parameters of CaRuO 3 and SrRuO3 powder samples, obtained from neutron time-of-flight data analysis via Rietveld refinement, will be compared.
Show less - Date Issued
- 2002
- PURL
- http://purl.flvc.org/fcla/dt/12954
- Subject Headings
- Ferromagnetism, Ruthenium oxide superconductors, Rietveld method
- Format
- Document (PDF)
- Title
- Simultaneous x-ray and neutron diffraction Rietveld refinements of nanophase Fe substituted hydroxyapatite.
- Creator
- Kyriacou, Andreas, Charles E. Schmidt College of Science, Department of Physics
- Abstract/Description
-
The effect of Fe substitution on the crystal structure of hydroxyapatite (HAp) is studied by applying simultaneous Rietveld refinements of powder x-ray and neutron diffraction patterns. Fe is one of the trace elements replacing Ca in HAp, which is the major mineral phase in bones and teeth. The morphology and magnetic properties of the Fe-HAp system are also studied by transmission electron microscopy and magnetization measurements. Samples of Ca(5-x)Fex(PO4)3OH with 0
Show moreThe effect of Fe substitution on the crystal structure of hydroxyapatite (HAp) is studied by applying simultaneous Rietveld refinements of powder x-ray and neutron diffraction patterns. Fe is one of the trace elements replacing Ca in HAp, which is the major mineral phase in bones and teeth. The morphology and magnetic properties of the Fe-HAp system are also studied by transmission electron microscopy and magnetization measurements. Samples of Ca(5-x)Fex(PO4)3OH with 0< x < 0.3 were prepared. Single phase HAp was identified in x-ray diffraction patterns (XRD) of samples with x < 0.1 inferring that the solubility limits are less than 0.1. Hematite ((Sa(B-Fe2O3) is identified as a secondary phase for higher Fe content. The refined parameters show that Fe is incorporated in the HAp structure by replacing Ca in the two crystallographic sites with a preference at the Ca2 site. This preference explains the small effect of the Fe substitution on the lattice constants of HAp. The overall decrease of the lattice constants is explained by the ionic vi size difference of Ca and Fe. The increasing trend of the a-lattice constant with x in the Fe substituted samples is attributed to a lattice relaxation caused by the substitution of the 4- and 6-fold Fe at the 7- and 9-fold Ca1 and Ca2 sites. This Ca local geometry reduction is indicated by a slight increase of the Ca1-O3 and Ca2-O1 bond lengths. Above the solubility limit x = 0.05, the Fe is partitioned in and out of the HAp structure with increasing nominal Fe content x. The excess Fe is oxidized to hematite. The TEM analysis and magnetic measurements support the results of the simultaneous Rietveld refinements. The TEM images show no significant effect on the morphology and size of the HAp particles upon Fe incorporation. The particles are either spheres or short rods of dimensions 20-60 nm. Hematite particles are imaged in the samples with x exceeding the solubility limit. These particles
Show less - Date Issued
- Florida Atlantic University
- PURL
- http://purl.flvc.org/FAU/3342204
- Subject Headings
- X-rays, Diffraction, Rietveld method, Nanostructured materials, Biomedical materials
- Format
- Document (PDF)
- Title
- Effect of Processing Temperature on the Properties of Nanophase Fe-substituted Hydroxypatite.
- Creator
- Kathriarachchi, Vindu, Leventouri, Theodora, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
- Abstract/Description
-
The effect of processing temperature on the crystal structure properties of the Fe-substituted Hydroxyapatite (Fe-HAp) was studied by using the Rietveld refinement method of powder x-ray (XRD) and neutron diffraction (NPD) patterns. Superconducting QUantum Interference Device (SQUID) magnetometry, transmission electron microscopy (TEM) and x-ray fluorescence spectroscopy (XRF) were used to study the magnetic properties, particle morphology and chemical composition of the prepared samples. Two...
Show moreThe effect of processing temperature on the crystal structure properties of the Fe-substituted Hydroxyapatite (Fe-HAp) was studied by using the Rietveld refinement method of powder x-ray (XRD) and neutron diffraction (NPD) patterns. Superconducting QUantum Interference Device (SQUID) magnetometry, transmission electron microscopy (TEM) and x-ray fluorescence spectroscopy (XRF) were used to study the magnetic properties, particle morphology and chemical composition of the prepared samples. Two sets of samples of chemical formula Ca5-xFex(PO4)3OH were prepared with x = 0, 0.05, 0.1, 0.2 and 0.3 by using processing temperatures of 37°C and 80°C, following a two-step co-precipitation method. A single phase HAp was identified in samples with x = 0 and 0.05. Processing temperature affects the type and percentage of secondary phases: hematite was detected in samples prepared at 37°C with x ≥ 0.1, hematite and maghemite were detected in samples prepared at 80°C with x = 0.2 and 0.3. Rietveld refinements of NPD and XRD patterns showed that the a lattice constants are greater in Fe-substituted samples prepared at 37°C, whereas the c lattice constants are greater in the 80°C samples for x ≥ 0.05. Fe preferentially substitutes at the Ca2 site in the 80°C samples, whereas Ca1 is the preferred substitution site in the 37°C samples. Fe substitution results to a decrease of the lattice constants at both preparation temperatures. The ratios Fe/(Fe + Ca) of the refined atomic fractions of the samples prepared at 80°C are greater than those of the 37°C samples. Further, more secondary phases form in samples prepared at 37°C compared to 80°C samples. The magnetic measurements reveal that pure HAp is diamagnetic, whereas samples with x = 0.05 and 0.1 are paramagnetic. Samples with x = 0.3 showed superparamagnetic behavior based on ZFC and FC measurements. Similar hysteresis loops in samples x = 0.2 and 0.3 indicate that the samples with x = 0.2 may show superparamagnetic properties. For x = 0.2 and 0.3, the samples prepared at 80°C showed higher magnetization compared to the 37°C samples, because of the maghemite secondary phase. Based on the TEM images, Fe substituted HAp nanoparticles prepared at 37°C are mainly spherically shaped, and the 80°C particles are mainly elongated. Increase of the Fe concentration favors formation of elongated particles and larger spherical particles. The XRF measurements confirm the Fe for Ca substitution in the HAp structure based on the decrease of the Ca/P and the increase of the Fe/(Fe + Ca) atomic ratios with the Fe concentration.
Show less - Date Issued
- 2015
- PURL
- http://purl.flvc.org/fau/fd/FA00004512, http://purl.flvc.org/fau/fd/FA00004512
- Subject Headings
- Biomedical materials, Nanostructured materials -- Environmental aspects, Nanostructured materials -- Mechanical properties, Pharmaceutical biotechnology, Rietveld method
- Format
- Document (PDF)
