Mechanical doping of strontium titanate

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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.