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Selenium is an essential nutrient for humans, animals and microorganisms, but it becomes toxic at concentrations slightly above the nutritional levels. This naturally occurring trace element can be released to the environment from various anthropogenic sources such as mining, agricultural, petrochemical and industrial processes and its toxicity is developed along a complex cycle involving adsorption by soil components and subsequent accumulation by plants. In the environment, selenium can occur in several oxidation states ranging from selenide (Se = ) to elemental selenium (Se 0 ), selenite (Se 4+ ) and selenate (Se 6+ ). Selenium contents above 900 ppm were recently assigned in mine wastes from the sulphur factory at the São Domingos exhausted pyrite mine exploited in the Iberian Pyrite Belt (south Portugal) since Roman times until 1966. Aiming at a sustainable remediation of this mining site, an X-ray absorption spectroscopy study using synchrotron radiation, combined with X-ray diffraction, was undertaken to clarify the speciation state of selenium and the nature of Se-carrier phase(s). The results show that selenium does not significantly replace sulphur under the form of selenate in the dominant sulphate phases and occasionally remains as a substituting selenide anion in debris of the original sulphides present in the mine waste materials.
Maria-Ondina Figueiredo; Teresa P. Silva; João Pedro Veiga; Maria-Joao Batista; Eduardo Salas Colera; Daniel P. De Oliveira. Selenium Speciation in Waste Materials From an Exhausted Iberian Pyrite Belt Mine. Journal of Materials Science Research 2014, 3, p22 .
AMA StyleMaria-Ondina Figueiredo, Teresa P. Silva, João Pedro Veiga, Maria-Joao Batista, Eduardo Salas Colera, Daniel P. De Oliveira. Selenium Speciation in Waste Materials From an Exhausted Iberian Pyrite Belt Mine. Journal of Materials Science Research. 2014; 3 (4):p22.
Chicago/Turabian StyleMaria-Ondina Figueiredo; Teresa P. Silva; João Pedro Veiga; Maria-Joao Batista; Eduardo Salas Colera; Daniel P. De Oliveira. 2014. "Selenium Speciation in Waste Materials From an Exhausted Iberian Pyrite Belt Mine." Journal of Materials Science Research 3, no. 4: p22.
Teresa P. Silva; Maria-Ondina Figueiredo; M. Alexandra Barreiros; M. Isabel Prudêncio. Diagnosis of pathologies in ancient (seventeenth-eighteenth centuries) decorative blue-and-white ceramic tiles: Green stains in the glazes of a panel depicting Lisbon prior to the 1755 earthquake. Studies in Conservation 2014, 59, 63 -68.
AMA StyleTeresa P. Silva, Maria-Ondina Figueiredo, M. Alexandra Barreiros, M. Isabel Prudêncio. Diagnosis of pathologies in ancient (seventeenth-eighteenth centuries) decorative blue-and-white ceramic tiles: Green stains in the glazes of a panel depicting Lisbon prior to the 1755 earthquake. Studies in Conservation. 2014; 59 (2):63-68.
Chicago/Turabian StyleTeresa P. Silva; Maria-Ondina Figueiredo; M. Alexandra Barreiros; M. Isabel Prudêncio. 2014. "Diagnosis of pathologies in ancient (seventeenth-eighteenth centuries) decorative blue-and-white ceramic tiles: Green stains in the glazes of a panel depicting Lisbon prior to the 1755 earthquake." Studies in Conservation 59, no. 2: 63-68.
Rhenium is a very scarce element, occurring in the Earth's crust mainly carried by molybdenite (MoS2). Due to a very low availability comparative to actual industrial demand, rhenium is nowadays one of the most expensive mineral commodities and an increased interest is focused on ex- ploring residues resulting from a long-term mining, particularly of sulphide ore deposits. It is therefore noteworthy to assign the presence of rhenium (in a concentration up to 3 ppm) in the waste materials from the old sulphur factory at the abandoned mine of Sao Domingos (Iberian Pyrite Belt, Southeast Portugal), exploited since the Roman occupation of Iberia. Aiming at a potential sustainable recovery of rhenium as a by-product, X-ray near-edge absorption spectroscopy (XANES) was applied to clarify the Re-binding and mode of occurrence by comparing Re L3-edge XANES spectra obtained from mine waste samples (previously fully characterized by X-ray laboratory techniques) with similar spectra collected from Re-rich molybdenites (Mo1-xRexS2) and from Re-O model compounds configuring various valences and coordination environments of rhenium ions. Obtained results are commented, ruling out a possible Re-S binding and rather conforming with the binding of rhenium to oxygen in the analysed mine waste materials.
Maria-Ondina Figueiredo; Teresa Pereira da Silva; João Pedro Veiga; Daniel de Oliveira; Maria Jo~Ao Batista. Towards the Recovery of By-Product Metals from Mine Wastes: An X-Ray Absorption Spectroscopy Study on the Binding State of Rhenium in Debris from a Centennial Iberian Pyrite Belt Mine. Journal of Minerals and Materials Characterization and Engineering 2014, 02, 135 -143.
AMA StyleMaria-Ondina Figueiredo, Teresa Pereira da Silva, João Pedro Veiga, Daniel de Oliveira, Maria Jo~Ao Batista. Towards the Recovery of By-Product Metals from Mine Wastes: An X-Ray Absorption Spectroscopy Study on the Binding State of Rhenium in Debris from a Centennial Iberian Pyrite Belt Mine. Journal of Minerals and Materials Characterization and Engineering. 2014; 02 (02):135-143.
Chicago/Turabian StyleMaria-Ondina Figueiredo; Teresa Pereira da Silva; João Pedro Veiga; Daniel de Oliveira; Maria Jo~Ao Batista. 2014. "Towards the Recovery of By-Product Metals from Mine Wastes: An X-Ray Absorption Spectroscopy Study on the Binding State of Rhenium in Debris from a Centennial Iberian Pyrite Belt Mine." Journal of Minerals and Materials Characterization and Engineering 02, no. 02: 135-143.
Teresa P. Silva; Maria Ondina Figueiredo; M. Isabel Prudêncio. Ascertaining the degradation state of ceramic tiles: A preliminary non-destructive step in view of conservation treatments. Applied Clay Science 2013, 82, 101 -105.
AMA StyleTeresa P. Silva, Maria Ondina Figueiredo, M. Isabel Prudêncio. Ascertaining the degradation state of ceramic tiles: A preliminary non-destructive step in view of conservation treatments. Applied Clay Science. 2013; 82 ():101-105.
Chicago/Turabian StyleTeresa P. Silva; Maria Ondina Figueiredo; M. Isabel Prudêncio. 2013. "Ascertaining the degradation state of ceramic tiles: A preliminary non-destructive step in view of conservation treatments." Applied Clay Science 82, no. : 101-105.
Decorated glazed ceramic tiles are used as an ornamental art, constituting an important cultural heritage whose preservation is mandatory. Environmental conditions are responsible for the degradation of exposed ancient tile panels originating various pathologies, related to the development of microorganisms. This is the case of a valuable 18th century blue-and-white Portuguese tile panel called “Cura do Cego,” belonging to the collection of the National Tile Museum (MNAz), where green stains are nowadays observable in the glaze. A prospective diagnosis of this green tarnishing was the aim of the present work. Small tile fragments were directly irradiated using nondestructive techniques: X-ray fluorescence spectrometry with a wavelength-dispersive system (WDXRF) for chemical characterization of the tile glaze and X-ray powder diffraction (XRD) to assess the phase constitution of both the glaze and the ceramic body. A destructive technique (scanning electron microscopy with energy-dispersive system (SEM/EDS)) was applied to tentatively infer the chemical changes induced in the glaze by the green staining and also to characterize the morphology of the microorganisms associated to this staining. The obtained results are reported and discussed, as a preliminary step for testing an innovative nondestructive decontamination technique applying gamma radiation, particularly suitable for overcoming such tile pathologies.
Teresa P. Silva; Maria-Ondina Figueiredo; Maria-Alexandra Barreiros; M. Isabel Prudêncio; Prudê Maria-Isabel Ncio. Decorative 18th Century Blue-and-White Portuguese Tile Panels: A Type-Case of Environmental Degradation. Journal of Materials 2013, 2013, 1 -6.
AMA StyleTeresa P. Silva, Maria-Ondina Figueiredo, Maria-Alexandra Barreiros, M. Isabel Prudêncio, Prudê, Maria-Isabel Ncio. Decorative 18th Century Blue-and-White Portuguese Tile Panels: A Type-Case of Environmental Degradation. Journal of Materials. 2013; 2013 (1):1-6.
Chicago/Turabian StyleTeresa P. Silva; Maria-Ondina Figueiredo; Maria-Alexandra Barreiros; M. Isabel Prudêncio; Prudê Maria-Isabel Ncio. 2013. "Decorative 18th Century Blue-and-White Portuguese Tile Panels: A Type-Case of Environmental Degradation." Journal of Materials 2013, no. 1: 1-6.
Ferrihydrite is natural ferric oxyhydroxide occurring exclusively nanocrystalline. With ideal formula 5 Fe2 O3 . 9 H2 O, ferrihydrite is quite abundant in sediments, weathering crusts and mine wastes, being characteristic of red pre-soils formed by loose weathered rock plus mineral debris (regoliths) and commonly designated as “2-line” or “6-line” on the basis of the broadened maxima observed in the X-ray diffraction pattern. Synthetic nanocrystalline “6-line” ferrihydrite was recently studied through methods based on atomic-pair distribution functions disclosing the possible occurrence of icosahedral clusters formed by twelve octahedra centred by an inner tetrahedron, all filled by Fe 3+ ions. However, Mössbauer studies were inconclusive about the existence of 4-coordinated iron, thus suggesting that the tetrahedral cation may well be Si4+. In view of such structural uncertainty, a XANES study at the Fe K-edge was undertaken on ferrihydrite from a regolith to ascertain the occurrence of tetrahedral iron. Comparison with data collected from well crystallized iron oxide and hydroxide minerals where Fe 3+/2+ ions occur in octahedral and tetrahedral coordination is described and the results so far obtained are discussed, showing that supplementary study is needed on the elusive structure of ferrihydrite.
Maria Ondina Figueiredo; Teresa P. Silva; João Pedro Veiga. Natural Nanomaterials: Reappraising the Elusive Structure of the Nano-Sized Mineral Ferrihydrite through X-Ray Absorption Spectroscopy at the Iron K-Edge. Materials Science Forum 2012, 730-732, 931 -935.
AMA StyleMaria Ondina Figueiredo, Teresa P. Silva, João Pedro Veiga. Natural Nanomaterials: Reappraising the Elusive Structure of the Nano-Sized Mineral Ferrihydrite through X-Ray Absorption Spectroscopy at the Iron K-Edge. Materials Science Forum. 2012; 730-732 ():931-935.
Chicago/Turabian StyleMaria Ondina Figueiredo; Teresa P. Silva; João Pedro Veiga. 2012. "Natural Nanomaterials: Reappraising the Elusive Structure of the Nano-Sized Mineral Ferrihydrite through X-Ray Absorption Spectroscopy at the Iron K-Edge." Materials Science Forum 730-732, no. : 931-935.
The composition of cobalt blue pigments used in ancient blue-and-white Chinese glazes is known to have changed between the 14th and the 17th century and ratios of some main chemical components plus trace elements are relevant guide-lines to establish the porcelain manufacture period. Once archaeological findings of Chinese porcelains can contribute to set up dating processes, a study of blue-and-white porcelain shards recovered during recent excavations in Lisbon Old-City was carried out by non-destructive laboratory X-ray fluorescence spectrometry for chemical characterization, combined with X-ray absorption spectroscopy (XAS) using synchrotron radiation to ascertain the formal valence and coordination of pigmenting cobalt ions. Following a preliminary extended X-ray absorption fine-structure study that revealed a coordination of divalent cobalt ions slightly above four, a detailed analysis of the near-edge region of Co 1s X-ray absorption spectra (XANES) was carried out on the blue-and-white glazes from those archaeological Chinese porcelain fragments. Pre-edge features and edge details are discussed in comparison with XANES spectra obtained from model compounds with well known crystal structure – Co3O4, CoAl2O4 and Co2SiO4, plus a cobalt-based blue pigment (cerulean). Present chemical data validate the manufacture period of studied Chinese porcelains advanced by Art Historians on the single basis of stylistic features (late 16th and medium 17th century). Spectroscopic results confirm a coordination environment of pigmenting Co2+ ions close to tetrahedral and substantiate the dual role of cobalt as network former plus modifier in the glaze of ancient Chinese porcelains.
M.O. Figueiredo; T.P. Silva; J.P. Veiga. A XANES study of cobalt speciation state in blue-and-white glazes from 16th to 17th century Chinese porcelains. Journal of Electron Spectroscopy and Related Phenomena 2012, 185, 97 -102.
AMA StyleM.O. Figueiredo, T.P. Silva, J.P. Veiga. A XANES study of cobalt speciation state in blue-and-white glazes from 16th to 17th century Chinese porcelains. Journal of Electron Spectroscopy and Related Phenomena. 2012; 185 (3-4):97-102.
Chicago/Turabian StyleM.O. Figueiredo; T.P. Silva; J.P. Veiga. 2012. "A XANES study of cobalt speciation state in blue-and-white glazes from 16th to 17th century Chinese porcelains." Journal of Electron Spectroscopy and Related Phenomena 185, no. 3-4: 97-102.
D. P. S. De Oliveira; João Xavier Matos; Carlos Rosa; Diogo Rosa; Maria Ondina Figueiredo; T. P. Silva; F. Guimaraes; João Ricardo Silva Carvalho; A. M. M. Pinto; Jorge Relvas; F. K. M. Reiser. The Lagoa Salgada Orebody, Iberian Pyrite Belt, Portugal. Economic Geology 2011, 106, 1111 -1128.
AMA StyleD. P. S. De Oliveira, João Xavier Matos, Carlos Rosa, Diogo Rosa, Maria Ondina Figueiredo, T. P. Silva, F. Guimaraes, João Ricardo Silva Carvalho, A. M. M. Pinto, Jorge Relvas, F. K. M. Reiser. The Lagoa Salgada Orebody, Iberian Pyrite Belt, Portugal. Economic Geology. 2011; 106 (7):1111-1128.
Chicago/Turabian StyleD. P. S. De Oliveira; João Xavier Matos; Carlos Rosa; Diogo Rosa; Maria Ondina Figueiredo; T. P. Silva; F. Guimaraes; João Ricardo Silva Carvalho; A. M. M. Pinto; Jorge Relvas; F. K. M. Reiser. 2011. "The Lagoa Salgada Orebody, Iberian Pyrite Belt, Portugal." Economic Geology 106, no. 7: 1111-1128.
Maria Ondina Figueiredo; T.P. Silva; M.J. Batista; J. Leote; M.L. Ferreira; V. Limpo. Uranium in surface soils: An easy-and-quick assay combining X-ray diffraction and X-ray fluorescence qualitative data. Journal of Geochemical Exploration 2011, 109, 134 -138.
AMA StyleMaria Ondina Figueiredo, T.P. Silva, M.J. Batista, J. Leote, M.L. Ferreira, V. Limpo. Uranium in surface soils: An easy-and-quick assay combining X-ray diffraction and X-ray fluorescence qualitative data. Journal of Geochemical Exploration. 2011; 109 (1-3):134-138.
Chicago/Turabian StyleMaria Ondina Figueiredo; T.P. Silva; M.J. Batista; J. Leote; M.L. Ferreira; V. Limpo. 2011. "Uranium in surface soils: An easy-and-quick assay combining X-ray diffraction and X-ray fluorescence qualitative data." Journal of Geochemical Exploration 109, no. 1-3: 134-138.
Jarosite, KFe3(SO4)2(OH)6, is a secondary iron sulphate often found in acid mine drainage (AMD) environments, particularly in mining wastes from polymetallic sulphide ore deposits. Despite the negative environmental connotation usually ascribed to secondary sulphate minerals due to the release of hazardous elements to aquifers and soils, jarosite acts as an efficient remover and immobilizer of such metals, particularly lead. The mineral chemistry of jarosite is reviewed and the results of a Fe K-edge XANES (X-Ray Absorption Near-Edge Structure) study of K-, Na- and Pb-jarosite are described and discussed within the context of the abandoned old mines of São Domingos and Aljustrel located in southern Portugal, in the Iberian Pyrite Belt (IPB).
Maria-Ondina Figueiredo; Teresa Pereira Da Silva. The Positive Environmental Contribution of Jarosite by Retaining Lead in Acid Mine Drainage Areas. International Journal of Environmental Research and Public Health 2011, 8, 1575 -1582.
AMA StyleMaria-Ondina Figueiredo, Teresa Pereira Da Silva. The Positive Environmental Contribution of Jarosite by Retaining Lead in Acid Mine Drainage Areas. International Journal of Environmental Research and Public Health. 2011; 8 (5):1575-1582.
Chicago/Turabian StyleMaria-Ondina Figueiredo; Teresa Pereira Da Silva. 2011. "The Positive Environmental Contribution of Jarosite by Retaining Lead in Acid Mine Drainage Areas." International Journal of Environmental Research and Public Health 8, no. 5: 1575-1582.
Iron is a powerful chromophore element whose pigmenting properties were the first to be recognized among transition metals. The interest in blue iron minerals as pigments for painting was enhanced with the use of vivianite—a natural hydrated ferrous phosphate, Fe3(PO4)2⋅8H2O—which in medieval Europe became an alternative to the expensive lapis lazuli, (Na, Ca)4(AlSiO4)3(SO4, Cl, S), a member of the ultramarines whose appreciated blue tone is due to the presence of sulfur polyanions. Conversely, vivianite coloring is attributed to the intervalence charge transfer (IVCT) Fe2+–Fe3+ that in later decades was studied by optical techniques and Mössbauer spectroscopy. However, the aging of blue vivianite pigments in old paintings has become a serious concern for conservators, but the aging process still awaits a satisfactory explanation. As an input to this problem, an X-ray absorption near-edge structure (XANES) study at the Fe K-edge of vivianite with different colors and origins was undertaken at the European Synchrotron Radiation Facility using the instrumental facilities of beamline ID-21. The analysis of pre-edge features corroborates previous data on the origin of vivianite color and emphasizes the need for a precautious assessment of iron speciation on the exclusive basis of XANES data. Actual results are discussed and further work is outlined.
Maria Ondina Figueiredo; T. P. Silva; João Pedro Veiga. The blue of iron in mineral pigments: a Fe K-edge XANES study of vivianite. Applied Physics A 2010, 99, 357 -361.
AMA StyleMaria Ondina Figueiredo, T. P. Silva, João Pedro Veiga. The blue of iron in mineral pigments: a Fe K-edge XANES study of vivianite. Applied Physics A. 2010; 99 (2):357-361.
Chicago/Turabian StyleMaria Ondina Figueiredo; T. P. Silva; João Pedro Veiga. 2010. "The blue of iron in mineral pigments: a Fe K-edge XANES study of vivianite." Applied Physics A 99, no. 2: 357-361.
Maria Ondina Figueiredo; Teresa Ondinada Silva; Pereira. Effect of oxygen sharing on the white line of S K-edge XANES spectra of sulphate minerals. European Journal of Mineralogy 2009, 21, 79 -83.
AMA StyleMaria Ondina Figueiredo, Teresa Ondinada Silva, Pereira. Effect of oxygen sharing on the white line of S K-edge XANES spectra of sulphate minerals. European Journal of Mineralogy. 2009; 21 (1):79-83.
Chicago/Turabian StyleMaria Ondina Figueiredo; Teresa Ondinada Silva; Pereira. 2009. "Effect of oxygen sharing on the white line of S K-edge XANES spectra of sulphate minerals." European Journal of Mineralogy 21, no. 1: 79-83.
João Pedro Veiga; Maria Ondina Figueiredo. A XANES study on the structural role of zinc in ancient tile glazes of Portuguese origin. X-Ray Spectrometry 2008, 37, 458 -461.
AMA StyleJoão Pedro Veiga, Maria Ondina Figueiredo. A XANES study on the structural role of zinc in ancient tile glazes of Portuguese origin. X-Ray Spectrometry. 2008; 37 (4):458-461.
Chicago/Turabian StyleJoão Pedro Veiga; Maria Ondina Figueiredo. 2008. "A XANES study on the structural role of zinc in ancient tile glazes of Portuguese origin." X-Ray Spectrometry 37, no. 4: 458-461.
Ceramic tiles used to manufacture artistic panels during the XVI to the XVIII centuries were decorated with high-lead soda-lime glazes, incorporating a diversity of chromophore cations, as ascertained by SRXRF (synchrotron radiation X-ray fluorescence). Previous X-ray absorption spectroscopy (XAS) studies have shown that sodium and lead are hosted by the glassy matrix in those glazes. However, the possible role of calcium as a modifier of the tetrahedral silica network is not fully clarified, despite being recognized that calcium cations alter some fundamental properties of glazes, namely transparency. An X-ray absorption fine structure (XAFS) study of glazes with varied colorings was therefore undertaken at Ca K- and L-edges. Well crystallized oxide minerals were used to model distinct coordination environments by oxygen atoms – close to octahedral geometry in calcite and dodecahedral in gypsum – while fluorite was chosen to mimic ideal cubic coordination. A first XAS approach suggested a minor variation in the energy separation between L2–L3 absorption edges when comparing blue and yellow glazes, irrespective of the period of manufacture. A further study on the X-ray absorption near-edge structure (XANES) carried out at the K-edge corroborated this difference and, along with the theoretical spectra modeling performed with the FEFF code, allowed interpreting of the Ca 1s absorption spectra of glazes as arising from a non-regular high-coordination environment within the silica matrix.
João Pedro Veiga; Maria Ondina Figueiredo. Calcium in ancient glazes and glasses: a XAFS study. Applied Physics A 2008, 92, 229 -233.
AMA StyleJoão Pedro Veiga, Maria Ondina Figueiredo. Calcium in ancient glazes and glasses: a XAFS study. Applied Physics A. 2008; 92 (1):229-233.
Chicago/Turabian StyleJoão Pedro Veiga; Maria Ondina Figueiredo. 2008. "Calcium in ancient glazes and glasses: a XAFS study." Applied Physics A 92, no. 1: 229-233.
A review is presented on constructive techniques plus materials and the processes involved in degradation phenomena observed in two historical monuments: the Zambujeiro dolmen (Portugal) and the Roman Aqueduct of Carthage (Tunisia). Dolmens are particularly impressive megalithic constructions for the dimensions of granite blocks. At Zambujeiro, the upright stones have undergone a catastrophic evolution after the archaeological exploitation due to accelerated weathering through a process apparently distinct from natural granite decay in nearby outcrops. The biological attack of granite minerals by lichen exudates has emphasized the hazardous character of bromine and more has been learnt about construction techniques, namely, the insertion in the mound of an impermeable clay stratum that hinders water penetration into the dolmen chamber. The characterization of original Roman ashlar blocks, including masonry and the diagnosis of Byzantine and medieval reconstruction testimonies in the Aqueduct of Carthage were the object of a detailed study by X-ray diffraction and synchrotron radiation X-ray fluorescence. Traditional constructive techniques and local construction materials were studied and successive historical, modern and recent rehabilitations were reappraised.
M.O. Figueiredo; T.P. Silva; João Pedro Veiga. Analysis of degradation phenomena in ancient, traditional and improved building materials of historical monuments. Applied Physics A 2008, 92, 151 -154.
AMA StyleM.O. Figueiredo, T.P. Silva, João Pedro Veiga. Analysis of degradation phenomena in ancient, traditional and improved building materials of historical monuments. Applied Physics A. 2008; 92 (1):151-154.
Chicago/Turabian StyleM.O. Figueiredo; T.P. Silva; João Pedro Veiga. 2008. "Analysis of degradation phenomena in ancient, traditional and improved building materials of historical monuments." Applied Physics A 92, no. 1: 151-154.
The colours of natural and synthetic beryl (ideally Be3Al2Si6O18) have been attributed either tothe presence of chromophore ions partially replacing Al and/or Be (Cr3+, Fe2+/3+, Mn2+) or to the occurrence of colour centres related to the presence of multi-atomic groups. However, no full explanation has been proposed for the blue colour in natural beryl gemstones (aquamarine) despite it being well established that bluish-green synthetic aquamarines containing Fe turn blue when heated for 1 h at 400°C.A X-ray absorption near-edge spectroscopy (XANES) study at the Fe K-edge was performed on blue beryl crystals from Licungo pegmatite (Mozambique) to ascertain the speciation state of this colouring element, reported in blue sapphire (ideally Al2O3) as a mixture of Fe2+ and Fe3+ in octahedral coordination. The general trend of the spectra is the same when synchrotron radiation (SR) impinges along the c axis of the hexagonal crystal, as well as along the a axis with c vertical. Conversely, a shoulder in the absorption edge is noticed when the incident beam is perpendicular to c, with this axis horizontal in the polarization plane of the SR beam, a reverse in the relative intensities of the two post-edge features is simultaneously observed. Pre-edge features accounting for Fe speciation (valence plus coordination) are identical in all three situations. Considering previous approaches which account for polarization, an explanation is suggested for the special effects observed on the Fe K-edge XANES spectra of analysed blue beryl crystals. Ideas on the origin of the blue colour of this mineral are also presented.
Maria Ondina Figueiredo; T. Pereira Da Silva; João Pedro Veiga; Carlos Leal Gomes; V. De Andrade. The blue colouring of beryls from Licungo, Mozambique: an X-ray absorption spectroscopy study at the iron K-edge. Mineralogical Magazine 2008, 72, 175 -178.
AMA StyleMaria Ondina Figueiredo, T. Pereira Da Silva, João Pedro Veiga, Carlos Leal Gomes, V. De Andrade. The blue colouring of beryls from Licungo, Mozambique: an X-ray absorption spectroscopy study at the iron K-edge. Mineralogical Magazine. 2008; 72 (1):175-178.
Chicago/Turabian StyleMaria Ondina Figueiredo; T. Pereira Da Silva; João Pedro Veiga; Carlos Leal Gomes; V. De Andrade. 2008. "The blue colouring of beryls from Licungo, Mozambique: an X-ray absorption spectroscopy study at the iron K-edge." Mineralogical Magazine 72, no. 1: 175-178.
M. O. Figueiredo. Simulating extended structures: a powerful crystallographic tool when interpreting X-ray absorption spectroscopy data. Acta Crystallographica Section A Foundations of Crystallography 2007, 63, 1 .
AMA StyleM. O. Figueiredo. Simulating extended structures: a powerful crystallographic tool when interpreting X-ray absorption spectroscopy data. Acta Crystallographica Section A Foundations of Crystallography. 2007; 63 (a1):1.
Chicago/Turabian StyleM. O. Figueiredo. 2007. "Simulating extended structures: a powerful crystallographic tool when interpreting X-ray absorption spectroscopy data." Acta Crystallographica Section A Foundations of Crystallography 63, no. a1: 1.
The convergence between extended structure provided by X‐ray diffraction and local structure of antimony extracted from spectroscopic data is reached through an alternative crystallographic description for a Sb‐pyrochlore arrangement within the same space group symmetry of pyrochlore structure‐type. A full account on this description is presented, along with a calculated diffraction pattern matching experimental data and conforming to Sb 1s XANES data.
Maria Ondina Figueiredo. Extended vs. Local Structure in Sb-Pyrochlores: An Illustration of the Valuable Interplay between Crystallography and XAFS. AIP Conference Proceedings 2007, 882, 205 -207.
AMA StyleMaria Ondina Figueiredo. Extended vs. Local Structure in Sb-Pyrochlores: An Illustration of the Valuable Interplay between Crystallography and XAFS. AIP Conference Proceedings. 2007; 882 (1):205-207.
Chicago/Turabian StyleMaria Ondina Figueiredo. 2007. "Extended vs. Local Structure in Sb-Pyrochlores: An Illustration of the Valuable Interplay between Crystallography and XAFS." AIP Conference Proceedings 882, no. 1: 205-207.
The origin of a red colour in ancient soda-lime glasses has been attributed either to the presence of both copper clusters and cuprous oxide or to copper alone. As a contribution to this question, a non-destructive X-ray absorption study at the [ Cu]K-edge was undertaken on the red layer from a singular “rosette”-type archaeological glass bead dated as pre-XVII century. On comparing with data collected from metallic copper and the mineral cuprite, cubic Cu2O, XANES spectra of the red glass are identical to the first. Theoretical modelling of Cu 1s XANES spectra was undertaken using the FEFF code based on a multiple scattering formalism. A hypothetical tetragonal structure was simulated for Cu2O in order to remove the constraints arising from linear O–Cu–O bonds, unstable within the silica glass matrix, and an ideal body-centred array was considered on the basis of real metallic Cu–Cu distances in the metal. Calculations were performed for atom clusters of variable size within real and hypothetical structures. A spherical cluster of about 5 Å radius, capped by 24 copper atoms already provides a calculated Cu 1s XANES spectrum that compares well with data collected from the red glass. Post-edge details are noted in relation to the oxide, considering ionic states and effective valences of copper. The possibility of estimating the size of copper clusters through simulated structures is discussed.
M.O. Figueiredo; João Pedro Veiga; Jose Mirao. Modelling the size of red-colouring copper nanoclusters in archaeological glass beads. Applied Physics A 2006, 83, 499 -502.
AMA StyleM.O. Figueiredo, João Pedro Veiga, Jose Mirao. Modelling the size of red-colouring copper nanoclusters in archaeological glass beads. Applied Physics A. 2006; 83 (4):499-502.
Chicago/Turabian StyleM.O. Figueiredo; João Pedro Veiga; Jose Mirao. 2006. "Modelling the size of red-colouring copper nanoclusters in archaeological glass beads." Applied Physics A 83, no. 4: 499-502.
The blue colour in ancient soda-lime glasses has been attributed to the presence of copper and/or cobalt but the origin of different shades is not yet fully interpreted. As a contribution to this question, a non-destructive X-ray absorption study at [ Cu]K-edge was undertaken on the blue (turquoise) layer from a “Nueva Cadiz” type tubular glass bead dated pre-XVII century where copper is the unique colouring agent. Minerals configuring two distinct blue tonalities due to Cu (2+) in similar square coordination were selected as basic model compounds: azurite, which is a classical navy-blue pigment used in ancient wall paintings over plaster, and chalcanthite, displaying exactly the same turquoise-blue tonality of tubular glass beads manufactured since the Egyptian Antiquity. Theoretical modelling of the XAFS spectra was undertaken using the FEFF code. The IFEFFIT software package was used for fitting the calculated spectra to experimental data. EXAFS results are discussed in view of the crystal structures of copper minerals chosen to model the speciation state and structural situation of that element prevailing in the turquoise-blue archaeological glass. Special attention is focused on the difficulties in theoretical modelling [ Cu]K-XANES spectra of ancient glasses with different colourings.
João Pedro Veiga; Maria Ondina Figueiredo. Copper blue in an ancient glass bead: a XANES study. Applied Physics A 2006, 83, 547 -550.
AMA StyleJoão Pedro Veiga, Maria Ondina Figueiredo. Copper blue in an ancient glass bead: a XANES study. Applied Physics A. 2006; 83 (4):547-550.
Chicago/Turabian StyleJoão Pedro Veiga; Maria Ondina Figueiredo. 2006. "Copper blue in an ancient glass bead: a XANES study." Applied Physics A 83, no. 4: 547-550.