The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
Mark T. Weller - One of the best experts on this subject based on the ideXlab platform.
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Hydrogenous materials using Powder Neutron Diffraction : full structural determination of adsorbed water molecules in a zeolite
Chemical communications (Cambridge England), 2008Co-Authors: Paul F. Henry, Mark T. Weller, Chick C. WilsonAbstract:A full structural description, including the adsorbed water molecules, of the zeolite goosecreekite CaAl(2)Si(6)O(16).5H(2)O, has been obtained from Powder Neutron Diffraction data in one hour, illustrating the potential of modern instrumentation for characterization of hydrogenous materials without deuteration.
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Rapid structure determination of the hydrogen-containing compound Cs2C2O4.H2O by joint single-crystal X-ray and Powder Neutron Diffraction.
Acta Crystallographica Section B Structural Science, 2007Co-Authors: Mark T. Weller, Paul F. Henry, Mark E. LightAbstract:The structure determination of caesium oxalate monohydrate using single-crystal X-ray Diffraction, Powder Neutron Diffraction data and a combination of both has been undertaken. Results show that even for hydrogen-containing materials data collected rapidly on a high-flux Neutron diffractometer improve the refinement such that accurate positional and thermal displacement parameters can be extracted for all atom types. This contrasts with structural models extracted from either data set alone that demonstrate the inherent limitations of the individual Diffraction methods. The rapidity with which useful Neutron Diffraction data has been collected from hydrogen-containing compounds, 10 min in this study, indicates that the technique should be widely applicable allowing the facile and accurate extraction of hydrogen positions for many compounds.
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Investigation of cancrinite structures by Powder Neutron Diffraction
Recent Advances in the Science and Technology of Zeolites and Related Materials Part B Proceedings of the 14th International Zeolite Conference, 2004Co-Authors: Mark T. Weller, N.j. KenyonAbstract:Deuterated forms of cancrinite, [Na-8(CO3)center dot(D2O)(n)] [AlSiO4](6) - CAN, and intermediate phase mixed disordered cancrinite-sodalite [Na8-y(CO3)(1-y/2)center dot(D2O)(n)] [AlSiO4](6) - CAN/SOD, have been synthesised and studied using variable temperature, high resolution Powder Neutron Diffraction. The structure of cancrinite shows anions are present only in the main 12-niembered ring channels, with water molecules co-ordinating to sodium in the 11-hedral epsilon-cages. In situ, Powder Neutron Diffraction, studies of the thermal decomposition of cancrinite and the disordered cancrinite/sodalite show marked differences in their behaviours. Both materials undergo a lattice contraction as water is lost between 100 and 300 degrees C though this process, and decomposition of the aluminosilicate framework, OCCUr at significantly lower temperatures for the disordered structure.
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Investigation of cancrinite structures by Powder Neutron Diffraction
Recent Advances in the Science and Technology of Zeolites and Related Materials Part B Proceedings of the 14th International Zeolite Conference, 2004Co-Authors: Mark T. Weller, N.j. KenyonAbstract:Deuterated forms of cancrinite, [Na(CO).(D O)] [AlSiO] - CAN, and intermediate phase mixed disordered cancrinite-sodalite [Na (CO).(DO)] [AlSiO] - CAN/SOD, have been synthesised and studied using variable temperature, high resolution Powder Neutron Diffraction. The structure of cancrinite shows anions are present only in the main 12-membered ring channels, with water molecules co-ordinating to sodium in the 11-hedral ε-cages. In situ, Powder Neutron Diffraction, studies of the thermal decomposition of cancrinite and the disordered cancrinite/sodalite show marked differences in their behaviours. Both materials undergo a lattice contraction as water is lost between 100 and 300 °C though this process, and decomposition of the aluminosilicate framework, occur at significantly lower temperatures for the disordered structure
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Determination of the cation distribution in Fe2Ni(PO4)2 using isotopic substitution and Powder Neutron Diffraction
Journal of Applied Crystallography, 2003Co-Authors: Paul F. Henry, Mark T. Weller, Chick C. WilsonAbstract:The distribution of divalent iron and nickel over the two metal sites with differing coordination geometry in Fe2Ni(PO4)2, sarcopside, has been investigated using time-of-flight Powder Neutron Diffraction of nickel isotopically substituted materials. Data from four separate samples were collected using HRPD at ISIS, containing natNi, 58Ni, 60Ni and 62Ni, under identical conditions. The occupancy of iron on the M(1) site was found to be 0.290 (1) from a combined-data-set Rietveld refinement of the three isotopically substituted samples, compared with 0.26 (4) and 0.26 (15) respectively from this and a previous time-of-flight Powder Neutron Diffraction study using natural-abundance nickel, and 0.366 (6) and 0.376 (3) using anomalous X-ray scattering techniques. A critical comparison of isotope substitution Neutron Diffraction and anomalous X-ray scattering methods for distinguishing nickel and iron from Powder data is presented.
Dominique Bazin - One of the best experts on this subject based on the ideXlab platform.
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Analysis of hydroxyapatite crystallites in subchondral bone by Fourier transform infrared spectroscopy and Powder Neutron Diffraction methods
Comptes Rendus Chimie, 2016Co-Authors: Christine Chappard, Michel Daudon, Gilles André, Dominique BazinAbstract:CR_Chimie_22_HAL_Chappard_8Juin2015 1 1 Analysis of hydroxyapatite crystallites in subchondral bone by Fourier transform infrared spectroscopy and Powder Neutron Diffraction methods Analyse des cristaux d'hydroxyapatite dans l'os sous chondral par spectroscopie infra-rouge a transformee de Fourier et Diffraction Neutronique sur poudres ABSTRACT English Fourier Transform Infrared (FTIR) spectroscopy and Powder Neutron Diffraction (PND) were performed in human subchondral bone covered (C+) or not covered by cartilage (C-) to study hydroxyapatite. With FTIR, the carbonation rate was 30% with identical spectra in C+ and C-. With PND, the width of the Diffraction peak (hkl=002) highlighted the anisotropy of nanocrystals (with needle and/or platelet-like shape) along the c-axis with average length of 50 nm and thickness of 10 nm and with no difference between C+ and C- .
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Analysis of hydroxyapatite crystallites in subchondral bone by Fourier transform infrared spectroscopy and Powder Neutron Diffraction methods
Comptes Rendus Chimie, 2016Co-Authors: Christine Chappard, Michel Daudon, Gilles André, Dominique BazinAbstract:CR_Chimie_22_HAL_Chappard_8Juin2015 1 1 Analysis of hydroxyapatite crystallites in subchondral bone by Fourier transform infrared spectroscopy and Powder Neutron Diffraction methods Analyse des cristaux d'hydroxyapatite dans l'os sous chondral par spectroscopie infra-rouge à transformée de Fourier et Diffraction Neutronique sur poudres ABSTRACT English Fourier Transform Infrared (FTIR) spectroscopy and Powder Neutron Diffraction (PND) were performed in human subchondral bone covered (C+) or not covered by cartilage (C-) to study hydroxyapatite. With FTIR, the carbonation rate was 30% with identical spectra in C+ and C-. With PND, the width of the Diffraction peak (hkl=002) highlighted the anisotropy of nanocrystals (with needle and/or platelet-like shape) along the c-axis with average length of 50 nm and thickness of 10 nm and with no difference between C+ and C- .
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Type 2 diabetes and uric acid stones: A Powder Neutron Diffraction investigation
Comptes Rendus Chimie, 2016Co-Authors: Michel Daudon, Emmanuel Véron, Gilles André, Emmanuel Letavernier, Raphaël Weil, Guy Matzen, Dominique BazinAbstract:AbstractRecent epidemiologic investigations have identified an association between type 2 diabetes and uric acid kidney stones. This association was more apparent in women than in men. In this paper, we show through Powder Neutron Diffraction that particle sizes of uric acid kidney stones were significantly different between male and female patients (84.7±5.3 vs. 140.2±6.7 nm, p=0.000003). Interestingly, when type 2 diabetes appeared, this structural difference between male and female vanished (76.1±3.9 vs. 78.8±4.2 nm, not significant). Thus, the complete set of structural data is in line with observations regarding epidemiological data. Some explanations based on supersaturation are discussed
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Analysis of hydroxyapatite crystallites in subchondral bone by Fourier transform infrared spectroscopy and Powder Neutron Diffraction methods
Comptes Rendus Chimie, 2016Co-Authors: Christine Chappard, Michel Daudon, Gilles André, Dominique BazinAbstract:International audienceCR_Chimie_22_HAL_Chappard_8Juin2015 1 1 Analysis of hydroxyapatite crystallites in subchondral bone by Fourier transform infrared spectroscopy and Powder Neutron Diffraction methods Analyse des cristaux d'hydroxyapatite dans l'os sous chondral par spectroscopie infra-rouge à transformée de Fourier et Diffraction Neutronique sur poudres ABSTRACT English Fourier Transform Infrared (FTIR) spectroscopy and Powder Neutron Diffraction (PND) were performed in human subchondral bone covered (C+) or not covered by cartilage (C-) to study hydroxyapatite. With FTIR, the carbonation rate was 30% with identical spectra in C+ and C-. With PND, the width of the Diffraction peak (hkl=002) highlighted the anisotropy of nanocrystals (with needle and/or platelet-like shape) along the c-axis with average length of 50 nm and thickness of 10 nm and with no difference between C+ and C- .Des expérimentations par spectroscopie infrarouge à transformée de Fourier (FTIR) et par Diffraction Neutronique sur poudres (PND) ont été réalisées sur de l’os sous-chondral humain recouvert (C+) ou non recouvert par le cartilage (C) pour étudier l’hydroxyapatite (HAP).En FTIR, le taux de carbonatation est de 30% avec des spectres identiques pour C+ et C−. Avec la PND, la largeur du pic de Diffraction (hkl = 002) a mis en évidence l'anisotropie des nanocristaux (en forme aiguille et/ou de plaquettes) le long de l'axe c, avec une longueur moyenne de 50 nm et une épaisseur de 10 nm, sans différence entre C+ et C−
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Type 2 diabetes and uric acid stones: A Powder Neutron Diffraction investigation
Comptes Rendus Chimie, 2015Co-Authors: Michel Daudon, Emmanuel Véron, Gilles André, Emmanuel Letavernier, Raphaël Weil, Guy Matzen, Dominique BazinAbstract:Background: Recent epidemiologic investigations have identified an association between type 2 diabetes and uric acid kidney stones. This association was more apparent in women than in men. However, male patients are more prone than women to form uric acid stones in upper and lower urinary tract. In addition, uric acid stone morphology may be different according to stone location. Finally, it was shown that uric acid stone prevalence is increasing with the patient’s age. Aim of the study: To compare uric acid crystal size as determined by Powder Neutron Diffraction with clinical data and the gender of patients. Material and methods: Uric acid stones from 43 patients (24 males, 19 females) identified by Fourier transform infrared spectroscopy were investigated using Environmental Scanning Electron Microscopy and Powder Neutron Diffraction. Results: Uric acid anhydrous was the main crystalline form of the stones. The mean size of the crystals was 91.3 ± 28.5 nm. No significant differences were found regarding uric acid crystal size in the stones by comparison to the stone location or the patient’s age. However, particle sizes of uric acid kidney stones were significantly different between male and female patients (84.7 ± 5.3 vs. 140.2 ± 6.7 nm, p < 0.000003) in the absence of diabetes mellitus. Interestingly, when type 2 diabetes appeared, this structural difference between male and female vanished (76.1 ± 3.9 vs. 78.8 ± 4.2 nm, not significant). Thus, the complete set of structural data is in line with observations regarding epidemiological data. Some explanations based on supersaturation are discussed.
Michel Daudon - One of the best experts on this subject based on the ideXlab platform.
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Analysis of hydroxyapatite crystallites in subchondral bone by Fourier transform infrared spectroscopy and Powder Neutron Diffraction methods
Comptes Rendus Chimie, 2016Co-Authors: Christine Chappard, Michel Daudon, Gilles André, Dominique BazinAbstract:CR_Chimie_22_HAL_Chappard_8Juin2015 1 1 Analysis of hydroxyapatite crystallites in subchondral bone by Fourier transform infrared spectroscopy and Powder Neutron Diffraction methods Analyse des cristaux d'hydroxyapatite dans l'os sous chondral par spectroscopie infra-rouge a transformee de Fourier et Diffraction Neutronique sur poudres ABSTRACT English Fourier Transform Infrared (FTIR) spectroscopy and Powder Neutron Diffraction (PND) were performed in human subchondral bone covered (C+) or not covered by cartilage (C-) to study hydroxyapatite. With FTIR, the carbonation rate was 30% with identical spectra in C+ and C-. With PND, the width of the Diffraction peak (hkl=002) highlighted the anisotropy of nanocrystals (with needle and/or platelet-like shape) along the c-axis with average length of 50 nm and thickness of 10 nm and with no difference between C+ and C- .
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Analysis of hydroxyapatite crystallites in subchondral bone by Fourier transform infrared spectroscopy and Powder Neutron Diffraction methods
Comptes Rendus Chimie, 2016Co-Authors: Christine Chappard, Michel Daudon, Gilles André, Dominique BazinAbstract:CR_Chimie_22_HAL_Chappard_8Juin2015 1 1 Analysis of hydroxyapatite crystallites in subchondral bone by Fourier transform infrared spectroscopy and Powder Neutron Diffraction methods Analyse des cristaux d'hydroxyapatite dans l'os sous chondral par spectroscopie infra-rouge à transformée de Fourier et Diffraction Neutronique sur poudres ABSTRACT English Fourier Transform Infrared (FTIR) spectroscopy and Powder Neutron Diffraction (PND) were performed in human subchondral bone covered (C+) or not covered by cartilage (C-) to study hydroxyapatite. With FTIR, the carbonation rate was 30% with identical spectra in C+ and C-. With PND, the width of the Diffraction peak (hkl=002) highlighted the anisotropy of nanocrystals (with needle and/or platelet-like shape) along the c-axis with average length of 50 nm and thickness of 10 nm and with no difference between C+ and C- .
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Type 2 diabetes and uric acid stones: A Powder Neutron Diffraction investigation
Comptes Rendus Chimie, 2016Co-Authors: Michel Daudon, Emmanuel Véron, Gilles André, Emmanuel Letavernier, Raphaël Weil, Guy Matzen, Dominique BazinAbstract:AbstractRecent epidemiologic investigations have identified an association between type 2 diabetes and uric acid kidney stones. This association was more apparent in women than in men. In this paper, we show through Powder Neutron Diffraction that particle sizes of uric acid kidney stones were significantly different between male and female patients (84.7±5.3 vs. 140.2±6.7 nm, p=0.000003). Interestingly, when type 2 diabetes appeared, this structural difference between male and female vanished (76.1±3.9 vs. 78.8±4.2 nm, not significant). Thus, the complete set of structural data is in line with observations regarding epidemiological data. Some explanations based on supersaturation are discussed
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Analysis of hydroxyapatite crystallites in subchondral bone by Fourier transform infrared spectroscopy and Powder Neutron Diffraction methods
Comptes Rendus Chimie, 2016Co-Authors: Christine Chappard, Michel Daudon, Gilles André, Dominique BazinAbstract:International audienceCR_Chimie_22_HAL_Chappard_8Juin2015 1 1 Analysis of hydroxyapatite crystallites in subchondral bone by Fourier transform infrared spectroscopy and Powder Neutron Diffraction methods Analyse des cristaux d'hydroxyapatite dans l'os sous chondral par spectroscopie infra-rouge à transformée de Fourier et Diffraction Neutronique sur poudres ABSTRACT English Fourier Transform Infrared (FTIR) spectroscopy and Powder Neutron Diffraction (PND) were performed in human subchondral bone covered (C+) or not covered by cartilage (C-) to study hydroxyapatite. With FTIR, the carbonation rate was 30% with identical spectra in C+ and C-. With PND, the width of the Diffraction peak (hkl=002) highlighted the anisotropy of nanocrystals (with needle and/or platelet-like shape) along the c-axis with average length of 50 nm and thickness of 10 nm and with no difference between C+ and C- .Des expérimentations par spectroscopie infrarouge à transformée de Fourier (FTIR) et par Diffraction Neutronique sur poudres (PND) ont été réalisées sur de l’os sous-chondral humain recouvert (C+) ou non recouvert par le cartilage (C) pour étudier l’hydroxyapatite (HAP).En FTIR, le taux de carbonatation est de 30% avec des spectres identiques pour C+ et C−. Avec la PND, la largeur du pic de Diffraction (hkl = 002) a mis en évidence l'anisotropie des nanocristaux (en forme aiguille et/ou de plaquettes) le long de l'axe c, avec une longueur moyenne de 50 nm et une épaisseur de 10 nm, sans différence entre C+ et C−
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Type 2 diabetes and uric acid stones: A Powder Neutron Diffraction investigation
Comptes Rendus Chimie, 2015Co-Authors: Michel Daudon, Emmanuel Véron, Gilles André, Emmanuel Letavernier, Raphaël Weil, Guy Matzen, Dominique BazinAbstract:Background: Recent epidemiologic investigations have identified an association between type 2 diabetes and uric acid kidney stones. This association was more apparent in women than in men. However, male patients are more prone than women to form uric acid stones in upper and lower urinary tract. In addition, uric acid stone morphology may be different according to stone location. Finally, it was shown that uric acid stone prevalence is increasing with the patient’s age. Aim of the study: To compare uric acid crystal size as determined by Powder Neutron Diffraction with clinical data and the gender of patients. Material and methods: Uric acid stones from 43 patients (24 males, 19 females) identified by Fourier transform infrared spectroscopy were investigated using Environmental Scanning Electron Microscopy and Powder Neutron Diffraction. Results: Uric acid anhydrous was the main crystalline form of the stones. The mean size of the crystals was 91.3 ± 28.5 nm. No significant differences were found regarding uric acid crystal size in the stones by comparison to the stone location or the patient’s age. However, particle sizes of uric acid kidney stones were significantly different between male and female patients (84.7 ± 5.3 vs. 140.2 ± 6.7 nm, p < 0.000003) in the absence of diabetes mellitus. Interestingly, when type 2 diabetes appeared, this structural difference between male and female vanished (76.1 ± 3.9 vs. 78.8 ± 4.2 nm, not significant). Thus, the complete set of structural data is in line with observations regarding epidemiological data. Some explanations based on supersaturation are discussed.
Paul F. Henry - One of the best experts on this subject based on the ideXlab platform.
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Towards routine study of hydrogenous materials using Powder Neutron Diffraction
Acta Crystallographica Section A Foundations and Advances, 2014Co-Authors: Paul F. HenryAbstract:Hydrogen (1H) is an element that is ubiquitous in chemistry and materials science. Neutron Diffraction is the preferred technique for studying 1H-containing compounds, but is complicated by the high incoherent scattering cross section, which also varies with wavelength. This variation of scattering cross section as a function of wavelength/energy and chemical environment is not well understood.[1-2] This is surprising as it is the largest contributing factor to the scattering properties used in single crystal and Powder Neutron Diffraction experiments to calculate the optimal sample size for hydrogen containing compounds and the tabulated data are given for fixed Neutron velocity of 2200 m s-1 (approximately 1.8 Å). The use and current limitations of certain current generation Neutron Diffraction instruments to probe 1H materials has recently been described.[3] Here, I present work to validate an empirical correction for the incoherent scattering cross section of 1H as a function of incident Neutron wavelength in the range 0.5 - 10 Å using continuous source, monochromatic wavelength measurements. The practical use of this is that a, potentially quantitative, correction for all Neutron Diffraction data, including time-of-flight (TOF) from pulsed sources, as a function of scattering angle and Neutron path length will become possible. Implementation of methodology that allows routine H position definition from easily synthesised material (i.e. non-isotopically enriched, and in polycrystalline or small single crystal (≤ 50 μm) form) for both TOF and monochromatic Neutron instruments would be both of widespread application. Additionally, i will present work on an instrument concept for a pulsed monochromatic Powder diffractometer for the ESS, which will be built in Lund by the end of the current decade. This diffractometer will aim to specialise in the data collection and analysis of hydrogenous materials using a combination of Diffraction and inelastic techniques.
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Hydrogenous materials using Powder Neutron Diffraction : full structural determination of adsorbed water molecules in a zeolite
Chemical communications (Cambridge England), 2008Co-Authors: Paul F. Henry, Mark T. Weller, Chick C. WilsonAbstract:A full structural description, including the adsorbed water molecules, of the zeolite goosecreekite CaAl(2)Si(6)O(16).5H(2)O, has been obtained from Powder Neutron Diffraction data in one hour, illustrating the potential of modern instrumentation for characterization of hydrogenous materials without deuteration.
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Rapid structure determination of the hydrogen-containing compound Cs2C2O4.H2O by joint single-crystal X-ray and Powder Neutron Diffraction.
Acta Crystallographica Section B Structural Science, 2007Co-Authors: Mark T. Weller, Paul F. Henry, Mark E. LightAbstract:The structure determination of caesium oxalate monohydrate using single-crystal X-ray Diffraction, Powder Neutron Diffraction data and a combination of both has been undertaken. Results show that even for hydrogen-containing materials data collected rapidly on a high-flux Neutron diffractometer improve the refinement such that accurate positional and thermal displacement parameters can be extracted for all atom types. This contrasts with structural models extracted from either data set alone that demonstrate the inherent limitations of the individual Diffraction methods. The rapidity with which useful Neutron Diffraction data has been collected from hydrogen-containing compounds, 10 min in this study, indicates that the technique should be widely applicable allowing the facile and accurate extraction of hydrogen positions for many compounds.
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Determination of the cation distribution in Fe2Ni(PO4)2 using isotopic substitution and Powder Neutron Diffraction
Journal of Applied Crystallography, 2003Co-Authors: Paul F. Henry, Mark T. Weller, Chick C. WilsonAbstract:The distribution of divalent iron and nickel over the two metal sites with differing coordination geometry in Fe2Ni(PO4)2, sarcopside, has been investigated using time-of-flight Powder Neutron Diffraction of nickel isotopically substituted materials. Data from four separate samples were collected using HRPD at ISIS, containing natNi, 58Ni, 60Ni and 62Ni, under identical conditions. The occupancy of iron on the M(1) site was found to be 0.290 (1) from a combined-data-set Rietveld refinement of the three isotopically substituted samples, compared with 0.26 (4) and 0.26 (15) respectively from this and a previous time-of-flight Powder Neutron Diffraction study using natural-abundance nickel, and 0.366 (6) and 0.376 (3) using anomalous X-ray scattering techniques. A critical comparison of isotope substitution Neutron Diffraction and anomalous X-ray scattering methods for distinguishing nickel and iron from Powder data is presented.
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Structural investigation of TS-1: determination of the true nonrandom titanium framework substitution and silicon vacancy distribution from Powder Neutron Diffraction studies using isotopes
The Journal of Physical Chemistry B, 2001Co-Authors: Paul F. Henry, Mark T. Weller, Chick C. WilsonAbstract:The first complete investigation of the structure of the selective oxidation catalyst TS-1 is presented. Constant wavelength Powder Neutron Diffraction data collected on isotopically substituted titanium silicalite (TS-1) samples, with a Si:Ti molar ratio of 39:1, have been studied using a combination of single and multiple data set Rietveld analysis exploiting the scattering length contrast between the different titanium isotopes and silicon. This has allowed both the silicon vacancy and titanium site substitution distributions to be determined, which has not been possible previously. Both distributions are found to be nonrandom with the titanium preferentially substituting on 3 of the 12 crystallographically independent framework sitesT8, T10 and T3 (in order of decreasing titanium content)and silicon vacancies on 2 framework sitesT1 and T5. This study illustrates the power of isotopic substitution in Powder Neutron Diffraction experiments to yield enhanced structural information in complex systems.
Chick C. Wilson - One of the best experts on this subject based on the ideXlab platform.
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Hydrogenous materials using Powder Neutron Diffraction : full structural determination of adsorbed water molecules in a zeolite
Chemical communications (Cambridge England), 2008Co-Authors: Paul F. Henry, Mark T. Weller, Chick C. WilsonAbstract:A full structural description, including the adsorbed water molecules, of the zeolite goosecreekite CaAl(2)Si(6)O(16).5H(2)O, has been obtained from Powder Neutron Diffraction data in one hour, illustrating the potential of modern instrumentation for characterization of hydrogenous materials without deuteration.
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Determination of the cation distribution in Fe2Ni(PO4)2 using isotopic substitution and Powder Neutron Diffraction
Journal of Applied Crystallography, 2003Co-Authors: Paul F. Henry, Mark T. Weller, Chick C. WilsonAbstract:The distribution of divalent iron and nickel over the two metal sites with differing coordination geometry in Fe2Ni(PO4)2, sarcopside, has been investigated using time-of-flight Powder Neutron Diffraction of nickel isotopically substituted materials. Data from four separate samples were collected using HRPD at ISIS, containing natNi, 58Ni, 60Ni and 62Ni, under identical conditions. The occupancy of iron on the M(1) site was found to be 0.290 (1) from a combined-data-set Rietveld refinement of the three isotopically substituted samples, compared with 0.26 (4) and 0.26 (15) respectively from this and a previous time-of-flight Powder Neutron Diffraction study using natural-abundance nickel, and 0.366 (6) and 0.376 (3) using anomalous X-ray scattering techniques. A critical comparison of isotope substitution Neutron Diffraction and anomalous X-ray scattering methods for distinguishing nickel and iron from Powder data is presented.
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Structural investigation of TS-1: determination of the true nonrandom titanium framework substitution and silicon vacancy distribution from Powder Neutron Diffraction studies using isotopes
The Journal of Physical Chemistry B, 2001Co-Authors: Paul F. Henry, Mark T. Weller, Chick C. WilsonAbstract:The first complete investigation of the structure of the selective oxidation catalyst TS-1 is presented. Constant wavelength Powder Neutron Diffraction data collected on isotopically substituted titanium silicalite (TS-1) samples, with a Si:Ti molar ratio of 39:1, have been studied using a combination of single and multiple data set Rietveld analysis exploiting the scattering length contrast between the different titanium isotopes and silicon. This has allowed both the silicon vacancy and titanium site substitution distributions to be determined, which has not been possible previously. Both distributions are found to be nonrandom with the titanium preferentially substituting on 3 of the 12 crystallographically independent framework sitesT8, T10 and T3 (in order of decreasing titanium content)and silicon vacancies on 2 framework sitesT1 and T5. This study illustrates the power of isotopic substitution in Powder Neutron Diffraction experiments to yield enhanced structural information in complex systems.