Three-dimensional crystallographic orientation measurement of polycrystalline alumina by Raman-microprobe polarization

Abstract

A method for determining crystallographic orientation in alumina grains was developed using a polarized Raman spectroscopy. The experimental setup is similar to the typical Raman microprobe system, but it is capable of rotating the sample and equipped with a pinhole plate to achieving high resolution along the surface. In order to determine the Al2O3 crystallite orientation, intensities of Raman scattering in the modes of Eg and A1g were measured as a function of rotational angle. The measured intensities of polarized scattering lines in the Eg and A1g modes were fitted with a theoretical function to determine the three-dimensional c-ax- is orientation of the grains. Suitable Raman scattering lines of alumina appeared at 378 and 645 cm-1, which correspond to the Eg and A1g modes, respectively. In order to calculate theoretical intensities from Raman tensors, the Raman intensities were measured in a sapphire crystal, in which the crystallographic orientation was known. The present method was successfully applied to small crystal grains appearing on the surface of polycrystalline alumina.