Wisniewski Wolfgang, Seyring Martin, Patzig Christian, Höche Thomas, Keshavarzi Ashkan, Rüssel Christian
Otto-Schott-Institut, Jena University, Fraunhoferstr. 6, 07743 Jena, Germany.
Fraunhofer Institute for Mechanics of Materials IWM, Walter-Huelse-Straße 1, 06108 Halle (Saale), Germany.
Sci Rep. 2016 Jan 27;6:19645. doi: 10.1038/srep19645.
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.
一种摩尔百分比组成为17Y₂O₃·33Al₂O₃·40SiO₂·2AlF₃·3Na₂O·2CeF₃·3B₂O₃的玻璃在1000°C下热处理6至24小时。这导致了YAG在表面的形核和生长。此外，在块体中还观察到了星形氧化铝的形核和生长，随后是单斜β-Y₂Si₂O₇和正交δ-Y₂Si₂O₇的形核和生长。通过电子背散射衍射（EBSD）以及透射电镜分析进行相鉴定和定位。在块体中观察到的单斜β-Y₂Si₂O₇以尺寸范围为50至120μm的大晶体团聚体形式出现。单个晶体沿c轴排列，c轴是生长最快的轴。在极图中观察到十个概率最大值，说明了围绕c轴的取向旋转，表明具有五重对称性。这种对称性是由多重孪晶引起的，多重孪晶导致与围绕c轴约36°、约108°（也称为五边形角）和约144°的旋转角具有特定取向关系的高概率。所有这些旋转角都接近理想五重对称性所需的36°倍数。这是关于由阻碍晶体生长的障碍引发五重对称性的首次报道。
