Mechanical doping of strontium titanate

这一建议的目的在于科学地阐明位错对钛酸锶(SrTiO_3)电导率的影响。众所周知，这种材料中的位错核具有非常高的氧空位密度，因此是带正电荷的。位错周围的补偿电荷区带负电荷。因此，位错强烈地改变了样品中的缺陷平衡。在室温和中温条件下，通过塑性变形将位错引入到钛酸锶块体中。然后，电学性质将通过阻抗光谱在全局以及局部确定明确的位错结构来确定。在塑性变形之前，可以通过掺杂受主、掺杂施主或在还原气氛中回火来改变起始缺陷浓度。同样，通过温度和电场处理可以改变塑性变形后的位错结构。氧的传输要用二次质谱学来量化。与丹麦的DTU合作，在ESRF的光束线上，设想使用暗场X射线显微镜对位错网络及其动力学进行高分辨率的多尺度表征。这为成像奇异位错及其在机械载荷、电场和温度下的转变提供了基础。将使用商品化的钛酸锶单晶以及专门制造的低位错密度的钛酸锶单晶。后者具有通过塑性变形对位错密度有较大影响的优点。初步的工作提供了钛酸锶单晶的塑性变形，以及通过摇摆曲线量化和确定腐蚀坑来确定位错密度。

The goal of this proposal lies in a scientific elucidation of the influence of dislocations on the electrical conductivity of strontium titanate (SrTiO3). It is known, that dislocation cores in this material have a very high density of oxygen vacancies and are therefore positively charged. A compensating charge zone around the dislocations is negatively charged. The dislocations thereby strongly alter the defect equilibrium in the sample. Dislocations are to be introduced in blocks of SrTiO3 at room temperature and intermediate temperature by plastic deformation. Then the electrical properties are to be determined by impedance spectroscopy globally as well as locally at well-defined dislocation structures. Before plastic deformation the starting defect concentration can be modified by either acceptor-doping, donor-doping or tempering in reduced atmosphere. Similarly, the dislocation structure can be modified after plastic deformation by temperature and electric field treatment. Oxygen transport is to be quantified by secondary mass spectroscopy. A high resolution multi-scale characterization of the dislocation network and its dynamics is envisaged using dark-field X-ray microscopy in collaboration with the DTU in Denmark at a beamline at the ESRF. This affords imaging singular dislocations and their transformation under mechanical load, electric field and temperature. Commercial SrTiO3 single crystals as well as specially manufactured SrTiO3 single crystals with low dislocation density will be utilized. The latter provides the advantage to have a large effect of dislocation density through plastic deformation. Preliminary work provided plastic deformation of SrTiO3 single crystals as well as determination of the density of dislocations by rocking curve quantification and by determining etch pits.