title: Bulk Crystallization in a SiO2/Al2O3/Y2O3/AlF3/B2O3/Na2O Glass: Fivefold Pseudo Symmetry due to Monoclinic Growth in a Glassy Matrix Containing Growth Barriers.
abstract: A glass with the mol% composition 17 Y2O3·33 Al2O3·40 SiO2·2 AlF3·3 Na2O·2 CeF3·3 B2O3 is heat treated at 1000 °C for 6-24 h. This results in the surface nucleation and growth of YAG. Nucleation and growth of star-shaped alumina and later of monoclinic β-Y2Si2O7 and orthorhombic δ-Y2Si2O7 are additionally observed in the bulk. Phase identification and localization are performed by electron backscatter diffraction (EBSD) as well as TEM analysis. The monoclinic β-Y2Si2O7 observed in the bulk occurs in the form of large, crystal agglomerates which range from 50 to 120 μm in size. The individual crystals are aligned along the c-axis which is the fastest growing axis. Ten probability maxima are observed in the pole-figures illustrating the rotation of orientations around the c-axes indicating a fivefold symmetry. This symmetry is caused by multiple twinning which results in a high probability of specific orientation relationships with rotation angles of ~36°, ~108° (also referred to as the pentagon angle) and ~144° around the c-axis. All these rotation angles are close to the multiples of 36° which are required for an ideal fivefold symmetry. This is the first report of a fivefold symmetry triggered by the presence of barriers hindering crystal growth.
authors.affiliation: Otto-Schott-Institut, Jena University, Fraunhoferstr. 6, 07743 Jena, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wisniewski
authors.affiliation: Otto-Schott-Institut, Jena University, Fraunhoferstr. 6, 07743 Jena, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Seyring
authors.affiliation: Fraunhofer Institute for Mechanics of Materials IWM, Walter-Huelse-Straße 1, 06108 Halle (Saale), Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Patzig
authors.affiliation: Fraunhofer Institute for Mechanics of Materials IWM, Walter-Huelse-Straße 1, 06108 Halle (Saale), Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Höche
authors.affiliation: Otto-Schott-Institut, Jena University, Fraunhoferstr. 6, 07743 Jena, Germany.
authors.forename: Ashkan
authors.initials: A
authors.lastname: Keshavarzi
authors.affiliation: Otto-Schott-Institut, Jena University, Fraunhoferstr. 6, 07743 Jena, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Rüssel
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