Comparison of X-ray patterns and Raman spectra of n= 2 and 3 Aurivillius phases by principal component analysis

Abstract

Eight series of n= 2 and 3 Aurivillius phases with structures derived from the original Bi₂A_n–1B_nO_3n+3 structure by fractional substitution in the (Bi₂O₂)²⁺ sheets as well as in the perovskite-type blocks (A_n–1B_nO_3n+1)^2– have been prepared by solid-state reaction. Raman spectra of all 45 samples are shown and the origin of the vibrational modes discussed. Plots of the first two principal components of principal component analysis (PCA) of the X-ray data and Raman data for all the samples as well as within the n= 2 and 3 subsets are presented. The structural and compositional information contained in the Raman spectra and in the X-ray patterns is preserved in the PCA. Differences between the PCA results of the X-ray data and the Raman data are caused by the different sensitivities of the two techniques towards the various properties changed by the fractional substitutions. The availability of fast data acquisition and the quality of the PCA results suggest that a Raman microscope system in connection with a multivariate data analysis technique based on PCA can be a powerful tool for in situ quality control of devices based on these materials.