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首页> 美国卫生研究院文献>Scientific Reports >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
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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

机译：SiO2 / Al2O3 / Y2O3 / AlF3 / B2O3 / Na2O玻璃中的本体结晶：由于单斜晶生长在含有生长壁垒的玻璃基质中的五重伪对称性

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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.
机译：摩尔百分比为17 Y2O3·33 Al2O3·40 SiO2·2 AlF3·3 Na2O·2 CeF3·3 B2O3的玻璃在1000 C下热处理6-24 6h。这导致YAG的表面成核和生长。在本体中还观察到星形氧化铝的形核和生长，以及后来的单斜晶形的β-Y2Si2O7和斜方晶系的δ-Y2Si2O7。通过电子背散射衍射（EBSD）以及TEM分析来执行相识别和定位。在大块中观察到的单斜晶β-Y 2 Si 2 O 7 7 以大的晶体聚集体形式存在，其范围为50至120尺寸为μm。单个晶体沿c轴排列，这是增长最快的轴。在极图中观察到十个概率最大值，说明围绕c轴的方向旋转，表明对称性为5倍。这种对称性是由多重孪生引起的，该多重孪生导致特定取向关系的可能性很高，围绕c轴的旋转角度分别为〜36°，〜108°（也称为五边形角）和〜144°。所有这些旋转角度都接近理想的五重对称所需的36°的倍数。这是有关阻碍晶体生长的势垒引起的五重对称的首次报道。

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