Aluminium and oxygen tracer diffusion in doped alpha-Al2O3

α - al2o3是一种重要的高温材料，具有多种技术应用：例如，作为原位生长的自修复保护层，作为单晶或多晶块状材料用于非常不同的任务，或作为复合材料中的增强纤维。模拟正在进行的高温过程（蠕变、烧结、水垢生长）需要氧和铝的整体扩散数据。与低价或高价外来元素的掺杂能够有针对性地控制氧和铝的传输，因此是影响高温过程动力学的主要概念。由于方法上的困难，关于铝自扩散的资料很少，这意味着掺杂剂对铝扩散的影响尚不清楚。由于（所研究的）晶体的背景杂质不同，实验方法也不同，比较迄今为止发表的不同实验组的掺杂α - al2o3单晶的氧扩散数据（即为了定量评估掺杂剂浓度对氧扩散的影响）非常困难。与已发表的研究的实验方案相反，本项目将是第一个利用独特的可能性来测量氧示踪剂扩散和铝示踪剂扩散在同一材料上分别作为低价掺杂剂（Mg）和高价掺杂剂（Ti）浓度的函数，以及温度的函数。从这个联合数据集产生的相关性将首次为研究晶体中可操作的点缺陷提供可靠的证据。此外，该数据将能够评估由不同理论团体发表的缺陷形成能和迁移能。

Alpha-Al2O3 is an important high temperature material with multiple technological applications: e. g. as an in-situ growing self-healing protective scale, as a single-crystalline or polycrystalline bulk material for very different tasks or as a reinforcement fibre in composite materials. Modelling the ongoing high temperature processes (creep, sintering, scale growth) requires data on the bulk diffusion of oxygen and aluminium. Doping with lower-valent or higher-valent foreign elements enables a targeted control of the oxygen and aluminium transport and is, therefore, a prime concept to influence high temperature process kinetics. Because of severe methodological difficulties there is only very little information available on aluminium self-diffusion, which means that the influence of dopants on the aluminium diffusion is unknown as yet. Comparing the oxygen diffusion data of different experimental groups published to date for doped alpha-Al2O3 single crystals (i. e. in order to quantitatively asses the influence of dopant concentrations on oxygen diffusion) is extremely hindered because of different background impurities (of the crystals studied) and different experimental methods applied.Contrary to the experimental programmes of the published studies the present project will be the first to make consequently use of the unique possibility to measure both oxygen tracer diffusion and aluminium tracer diffusion on the same material as a function of the concentration of a lower-valent dopant (Mg) and a higher-valent dopant (Ti), respectively, as well as a function of temperature. The correlations originating from this joint data set will, for the first time, supply robust evidence on the point defects, which are operational in the studied crystals. Further, this data will enable to asses the defect formation energies and the migration energies, which have been published by different theoretical groups.