PNNL

Abstract

The interface between polar perovskite LaCrO3 (LCO) and non-polar SrTiO3(001) (STO), grown by molecular beam epitaxy, is examined using a combination of electron microscopy, spectroscopy, and Rutherford backscattering spectrometry. The LCO/STO(001) interface is insulating, a potential counter example for the claim that polar/nonpolar perovskite interfaces should be conductive by virtue of an electronic reconstruction to alleviate the polar discontinuity. The A-site cations of these ABO3 perovskites are found to diffuse across the interface to a greater extent than the B-site cations, based on high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), energy dispersive x-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS). The B-site cation valences are shown to be partially reduced near the interface by analysis of EELS near-edge structures. The location and direction of these electronic modifications do not intuitively compensate the charge imbalance imposed by uneven cation inter-diffusion, and yet both the film and interface are insulating. These results highlight the importance of both the physical and electronic structure of such complex interfaces in determining their characteristics. Furthermore, the extent of inter-diffusion is shown to increase with increasing LCO film thickness, suggesting a potential mechanism behind the critical thickness for interfacial conductivity in other polar/non-polar oxide systems, and a fundamental limitation on the formation of abrupt interfaces in LCO/STO(001).