Microstructure analysis of electrospun La0.8Sr0.2MnO3 nanowires using electron microscopy and electron backscatter diffraction (EBSD)

Abstract

The perovskite compound La1-xSrxMnO3 (LSMO) is known for the high spin-polarized currents, which makes it a material of great interest in spintronics [1]. The magnetoresistance (MR) observed was found to depend strongly on the microstructure, i.e., the grain boundaries (GBs) and the interfaces between the grains. By means of electrospinning, one can prepare long (up to 100 µm), free-standing LSMO nanowires. The diameter of the nanowires is in the 200 nm-range, and the individual nanowires are polycrystalline with a grain size of about 15-20 nm, which corresponds to the dimensions obtained via transmission electron microscopy (TEM). The microstructural properties of electrospun La0.8Sr0.2MnO3 (LSMO) nanowires were investigated using SEM, TEM and electron backscatter diffraction (EBSD). By means of EBSD, it is possible to measure the crystallographic orientation of the LSMO grains within an individual nanowire. As the LSMO grains within the nanowires are in the 10-nm range, we employ here parts of the recently developed transmission-EBSD or transmission Kikuchi diffraction technique [2,3] in order to enhance the Kikuchi pattern quality to enable an automated mapping of the crystallographic data. The diffraction results demonstrate that the grain orientation is not random, but there is a texture induced by the shape of the polymer nanowire formed after the electrospinning step. Within an individual nanowire section, the dominating GBs are high-angle grain boundaries, which play an important role in the current flow through the sample (low- and high field magnetoresistance). The data obtained allow further an analysis of the grain shape aspect ratio, and elucidate the grain and grain boundary arrangement within electrospun LSMO nanowires. This work is supported by DFG-project Ko2323-8.