Ti diffusion in La-doped SrTiO3 single crystals

Abstract

Titanium tracer diffusivities were determined in donor doped SrTiO₃ at temperatures between 1573 and 1673 K in synthetic air. La-doped SrTiO₃ single crystals cut in the three crystal orientations (100), (110), and (111), were used. After annealing, the well known formation of SrO islands is observed. Their number and size increase with the La content supporting the model that under oxidizing conditions the dopant is compensated by Sr vacancies. Tracer sources of ⁴⁹Ti or ⁵⁰Ti were applied by ion implantation. The resulting depth profiles were measured by secondary ion mass spectrometry (SIMS). The bulk Ti tracer diffusivity is found to be several orders of magnitude lower than the O diffusivity and also the La and Nd diffusivities reported recently. In contrast to La, the Ti tracer profile broadening shows largely ideal behaviour. As even long term annealing (several weeks) of weakly doped SrTiO₃ does not lead to significant tracer migration, the Ti diffusion seems to be enhanced by the presence of the donor induced Sr vacancies. Although microscopic investigations undertaken on the same samples show strong differences in the surface reconstruction depending on the crystal orientation, no orientation dependence of the Ti diffusivity is observed.