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<OAI-PMH schemaLocation=http://www.openarchives.org/OAI/2.0/ http://www.openarchives.org/OAI/2.0/OAI-PMH.xsd> <responseDate>2018-01-15T18:18:58Z</responseDate> <request identifier=oai:HAL:hal-01467402v1 verb=GetRecord metadataPrefix=oai_dc>http://api.archives-ouvertes.fr/oai/hal/</request> <GetRecord> <record> <header> <identifier>oai:HAL:hal-01467402v1</identifier> <datestamp>2018-01-11</datestamp> <setSpec>type:ART</setSpec> <setSpec>subject:sdu</setSpec> <setSpec>collection:CNRS</setSpec> <setSpec>collection:UNIV-AG</setSpec> <setSpec>collection:GM</setSpec> <setSpec>collection:AGROPOLIS</setSpec> <setSpec>collection:GIP-BE</setSpec> <setSpec>collection:INSU</setSpec> <setSpec>collection:B3ESTE</setSpec> <setSpec>collection:UNIV-MONTPELLIER</setSpec> </header> <metadata><dc> <publisher>HAL CCSD</publisher> <title lang=en>Hydrogen diffusion in Ti-doped forsterite and the preservation of metastable point defects</title> <creator>Jollands, Michael c.</creator> <creator>PADRON NAVARTA, Jose Alberto</creator> <creator>Hermann, Jorg</creator> <creator>O'neill, Hugh st c.</creator> <contributor>Australian National University (ANU)</contributor> <contributor>Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS)</contributor> <contributor>Manteau et Interfaces ; Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) - Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS)</contributor> <description>International audience</description> <source>ISSN: 0003-004X</source> <source>American Mineralogist</source> <publisher>Mineralogical Society of America</publisher> <identifier>hal-01467402</identifier> <identifier>https://hal.archives-ouvertes.fr/hal-01467402</identifier> <source>https://hal.archives-ouvertes.fr/hal-01467402</source> <source>American Mineralogist, Mineralogical Society of America, 2016, 101 (7-8), pp.1571-1583. 〈10.2138/am-2016-55681571〉</source> <identifier>DOI : 10.2138/am-2016-55681571</identifier> <relation>info:eu-repo/semantics/altIdentifier/doi/10.2138/am-2016-55681571</relation> <language>en</language> <subject lang=en>Diffusion</subject> <subject lang=en>point defects</subject> <subject lang=en>nominally anhydrous minerals</subject> <subject lang=en>FTIR spectroscopy</subject> <subject>[SDU.STU.MI] Sciences of the Universe [physics]/Earth Sciences/Mineralogy</subject> <type>info:eu-repo/semantics/article</type> <type>Journal articles</type> <description lang=en>The effect of trace concentrations of Ti on the rate and mechanism of hydrogen diffusion in pure forsterite was investigated experimentally. Forsterite doped with 350–400 ppm Ti (predominantly octahedral Ti3+, minor tetrahedral Ti4+) was prepared by diffusing Ti into pure synthetic forsterite at high temperature (1500 °C), very low oxygen fugacity (~QFM-5) at atmospheric pressure. The Ti-doped forsterite was then diffusively hydroxylated in a piston-cylinder apparatus at much lower temperatures (650–1000 °C) and higher oxygen fugacities, at 1.5–2.5 GPa, with chemical activities buffered by forsterite-enstatite or forsterite-periclase and partial pressure of H2O equal to total pressure. This produced hydrogen concentration-distance profiles of several hundred micrometers in length. Diffusion of hydrogen through the Ti-doped forsterite, even at very high Embedded Image , does not lead to redox re-equilibration of the high Ti3+/ΣTi ratio set during the synthesis of the starting material at extremely reducing conditions—the metastable point defects are partially preserved.Three main hydroxylated point defects are observed; hydroxyl is associated with Ti4+ (titano-clinohumite point defects), Ti3+ (and possibly other trivalent cations), and M-site vacancies. Concentration-distance profiles represent an interplay between diffusion and reaction (i.e., site rearrangement) to form the observed point defects. In all experiments, the concentration-distance profiles of the hydroxylated Ti defects coincide with the concentration-distance profiles of the M-site vacancy substitution, with the same crystallographic anisotropy. This suggests that the macroscopic movement of hydrogen through the crystal is due to one diffusion mechanism (the diffusion of hydroxylated M-site vacancies). The net H diffusion coefficient [logD(ΣH)], between 650–1000 °C, is Embedded Image where the values of logD0(ΣH) parallel to [100] and [001] directions are −3.0 ± 0.4 and −2.2 ± 0.4, respectively; diffusion is therefore around one order of magnitude faster along the c axis than along the a axis. The diffusion of hydrogen is slightly faster in Ti-doped forsterite than in pure forsterite. There is no effect of chemical activity or oxygen fugacity on the rate of diffusion. Hydrogen diffusion profiles represent a complex interplay between the movement of H through the crystal lattice and point-defect reactions to maintain charge balance.</description> <date>2016</date> </dc> </metadata> </record> </GetRecord> </OAI-PMH>