Si- and Ge-mullite single crystals doped with foreign cations

近几十年来，对莫来石性能的研究主要集中在莫来石粉体和多晶莫来石陶瓷上。关于莫来石单晶的合成和表征的研究很少。没有关于掺杂有稀土（RE）元素的莫来石单晶的信息，尽管这些材料显示出如在相应粉末材料上所示的有趣的发光性质。本课题的第一个目的是研究稀土元素（Eu、Tb、Gd等）在陶瓷中的掺入机理。莫来石结构，并确定其光致发光性能与潜在的应用。为此目的，RE掺杂的莫来石单晶（2：1莫来石，2Al2O3 . SiO2）的厘米级尺寸将通过直拉法合成。将通过微量化学、光谱和晶体化学方法对其进行表征。该项目的第二个目标是对莫来石的锗类似物“锗莫来石”（3 Al 2 O3）中结合RE元素与“孤对元素”（Pb、Bi）的基础晶体化学研究。2GeO 2）。合成将在一系列的稀土掺杂锗莫来石的铅或铋的高温熔体的助熔剂实验。这项基础研究的目的是阐明建议的复杂和新的掺入机制的外来阳离子与孤电子对莫来石晶体结构。为此，首次合成了大尺寸的稀土掺杂硅莫来石晶体和掺杂锗莫来石单晶，并对其进行了基本表征。最后，就一般意义上的莫来石而言，这些贡献可能对莫来石材料的发展具有重要意义。

Intensive research on the properties of mullite was mainly performed on mullite powders and polycrystalline mullite ceramics within the last decades. Little work was documented on synthesis and characterization of mullite single crystals. There is no information on single crystals of mullites doped with rare-earth (RE) elements, although these materials display interesting luminescence properties as shown on corresponding powder materials. The first aim of this project is to study the incorporation mechanism of RE elements (Eu, Tb, Gd etc.) into the mullite structure and to determine their photo-luminescent properties with potential applications. For this aim RE-doped mullite single crystals (2:1 mullite, 2Al2O3 . SiO2) of centimeter size will be synthesized by the Czochralski method. They will be characterized by microchemical, spectroscopic and crystal-chemical methods. A second aim of the project focusses on the basic crystal-chemical study of the incorporation of RE elements combined with "lone-pair-elements" (Pb, Bi) in the germanium analog of mullite, 'germanium-mullite' (3 Al2O3 . 2GeO2). The synthesis will be performed in a series of flux experiments of RE-doped germanium mullites out of Pb- or Bi-containing high-temperature melts. This basic research study intends to shed light on the suggested complex and novel incorporation mechanism of foreign cations with lone electron pairs in the mullite crystal structure. For this purpose, for the first time large RE-doped Si-mullite crystals and doped single crystals of Ge-mullite are synthesized and fundamentally characterized. Finally, with respect to mullite in a general sense, the contributions may be of great importance for the development of mullite materials.