Pianassola Matheus, Alexander Marlena, Chakoumakos Bryan, Koschan Merry, Melcher Charles, Zhuravleva Mariya
Scintillation Materials Research Center, University of Tennessee, Knoxville, TN 37996, USA.
Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Acta Crystallogr B Struct Sci Cryst Eng Mater. 2022 Jun 1;78(Pt 3 Pt 2):476-484. doi: 10.1107/S2052520622002967. Epub 2022 Apr 30.
The effects of composition on the phase formation of multicomponent garnet crystals grown via directional solidification by the micro-pulling-down method are studied. A relatively wide range of rare-earth (RE) average ionic radii (AIR) is explored by formulating ten compositions from the system (Lu,Y,Ho,Dy,Tb,Gd)AlO. Crystals were grown at either 0.05 or 0.20 mm min. The hypothesis is that multicomponent compounds with large AIR will form secondary phases as the single-RE aluminum garnets formed by larger Tb or Gd; this will result in crystals of poor optical quality. Crystals with large AIR have a central opaque region in optical microscopy images, which is responsible for their reduced transparency compared to crystals with small AIR. Slow pulling rates suppress the formation of the opaque region in crystals with intermediate AIR. Powder and single-crystal X-ray diffraction and electron probe microanalysis results indicate that the opaque region is a perovskite phase. Scanning electron microscopy and energy dispersive spectroscopy measurements reveal eutectic inclusions at the outer surface of the crystals. The concentration of the eutectic inclusions increases with increasing AIR.
研究了成分对通过微下拉法定向凝固生长的多组分石榴石晶体相形成的影响。通过配制系统（Lu、Y、Ho、Dy、Tb、Gd）AlO中的十种成分，探索了相对较宽范围的稀土（RE）平均离子半径（AIR）。晶体以0.05或0.20 mm min的速度生长。假设是，具有大AIR的多组分化合物将形成次生相，就像由较大的Tb或Gd形成的单稀土铝石榴石那样；这将导致光学质量较差的晶体。在光学显微镜图像中，具有大AIR的晶体有一个中心不透明区域，这导致它们与具有小AIR的晶体相比透明度降低。缓慢的提拉速率抑制了具有中等AIR的晶体中不透明区域的形成。粉末和单晶X射线衍射以及电子探针微分析结果表明，不透明区域是钙钛矿相。扫描电子显微镜和能量色散光谱测量揭示了晶体外表面的共晶夹杂物。共晶夹杂物的浓度随着AIR的增加而增加。
