title: High-temperature Fe oxidation coupled with redistribution of framework cations in lobanovite, K2Na(Fe2+4Mg2Na)Ti2(Si4O12)2O2(OH)4 - The first titanosilicate case
metadata.name: dc.date.accessioned
metadata.value: 2020-09-09T07:37:05Z
metadata.lang: -
metadata.name: dc.date.available
metadata.value: 2020-09-09T07:37:05Z
metadata.lang: -
metadata.name: dc.date.issued
metadata.value: 2019
metadata.lang: -
metadata.name: dc.identifier.uri
metadata.value: http://hdl.handle.net/11701/19314
metadata.lang: -
metadata.name: dc.description.abstract
metadata.value: The high-temperature (HT) behaviour of lobanovite, K2Na(Fe2+
  4Mg2Na)Ti2-
  (Si4O12)2O2(OH)4, was studied using in situ powder X-ray diffraction in the
  temperature range 25–1000 C and ex situ single-crystal X-ray diffraction of 17
  crystals quenched from different temperatures. HT iron oxidation associated
  with dehydroxylation starts at 450 C, similar to other ferrous-hydroxy-rich
  heterophyllosilicates such as astrophyllite and bafertisite. A prominent feature
  of lobanovite HT crystal chemistry is the redistribution of Fe and Mg+Mn
  cations over the M(2), M(3), M(4) sites of the octahedral (O) layer that
  accompanies iron oxidation and dehydroxylation. This HT redistribution of
  cations has not been observed in titanosilicates until now, and seems to be
  triggered by the need to maintain bond strengths at the apical oxygen atom of
  the TiO5 pyramid in the heteropolyhedral (H) layer during oxidation–
  dehydroxylation. Comparison of the HT behaviour of lobanovite with fivecoordinated
  Ti and astrophyllite with six-coordinated Ti shows that the
  geometry of the Ti polyhedron plays a key role in the HT behaviour of
  heterophyllosilicates. The thermal expansion, geometrical changes and redistribution
  of site occupancies which occur in lobanovite under increasing
  temperature are reported. A brief discussion is given of minerals in which the
  cation ordering (usually for Fe and Mg) occurs together with iron oxidation–
  dehydroxylation at elevated temperatures: micas, amphiboles and tourmalines.
  Now this list is expanded by the inclusion of titanosilicate minerals.
metadata.lang: en_GB
metadata.name: dc.title
metadata.value: High-temperature Fe oxidation coupled with redistribution of framework cations in lobanovite, K2Na(Fe2+4Mg2Na)Ti2(Si4O12)2O2(OH)4 - The first titanosilicate case
metadata.lang: en_GB
resources.filename: 12.pdf
resources.url: https://dspace.spbu.ru/bitstream/11701/19314/1/12.pdf
resources.format: Adobe PDF
resources.size: 1,49 MB