title: Thortveitite-type Tm2Si2O7.
abstract: Single crystals of dithulium disilicate, Tm2Si2O7, were obtained in flux synthesis experiments in the system SiO2-Tm2O3-LiF at ambient pressure. The compound belongs to the group of sorosilicates, i.e. it is based on [Si2O7]-units and crystallizes in the thortveitite (Sc2Si2O7) structure type. The Tm(3+) cation (site symmetry .2.) occupies a distorted octa-hedral site, with Tm-O bond lengths in the range 2.217 (4)-2.289 (4) Å. Each of the octa-hedra shares three of its edges with adjacent [TmO6] groups, resulting in the formation of layers parallel to (001). The individual [SiO4] tetra-hedra are more regular, i.e. the differences between the bond lengths between Si and the bridging and non-bridging O atoms are not very pronounced. The layers containing the octa-hedra and the sheets containing the [Si2O7] groups (point group symmetry 2/m) form an alternating sequence. Linkage is provided by sharing common oxygen vertices.
authors.affiliation: University of Innsbruck, Institute of Mineralogy & Petrography, Innrain 52, A-6020 Innsbruck, Austria.
authors.forename: Volker
authors.initials: V
authors.lastname: Kahlenberg
authors.affiliation: University of Innsbruck, Institute of Mineralogy & Petrography, Innrain 52, A-6020 Innsbruck, Austria.
authors.forename: Paul
authors.initials: P
authors.lastname: Aichholzer