Self-diffusion of constituent elements in nominally undoped LaAlO3 single crystals

The interface between the insulators LaAlO₃ and SrTiO₃ has very interesting electronic properties. The production of such heterointerfaces comprises high temperature steps. Therefore knowledge of the mobilities of the constituent elements in the two partner oxides is required. As the majority of the published oxygen mobility data is based on electrical conductivity measurements with a rather large scatter, a check with a direct method was required, i. e. ¹⁸O₂ exchange in combination with SIMS depth profiling. Our present results are in agreement with recently published ¹⁸O₂/SIMS data. For the two native cations no data at all were available in the literature. Using the rare stable isotope ¹³⁸La and the pseudo-stable radionuclide ²⁶Al in combination with SIMS depth profiling, for the first time upper limits of the tracer diffusivities could be determined at one temperature (1500 °C) for the very slow host cations in nominally undoped (100) oriented LaAlO₃ single crystals. The experimental observations of this work for LaAlO₃ are very similar to the situation in SrTiO₃ concerning the cation tracer diffusivities in nominally undoped single crystals. Both the experimental findings in LaAlO₃ and in SrTiO₃ are in plausible qualitative agreement with the results of calculated activation energies for native ion migration in various perovskite oxides.