Detection of temperature- and stress-induced modifications of LaCoO3 by micro-Raman spectroscopy

Micro-Raman spectroscopy of LaCoO3-based perovskites was performed to characterize the vibrational properties of these Raman active rhombohedral perovskites and their temperature and stress induced changes. The cobaltite spectra were found to consist of four Raman active phonon modes at 162, 448, 557, and 673cm-1 in the case where the laser power had been 2.5mW. The two vibrational modes at 557 and 673cm-1 disappear at the semiconductor/metal transition at 500K driven by laser overheating during a collection of the Raman signal at higher laser power. Significant stress-induced changes in the Raman spectrum of LaCoO3 after indentation were also observed. An increase of the intensities of two 557 and 670cm-1 bands at the center of an indentation correlated with evidence of a tensile stress created by a deformation of perovskite during indentation. The tensile stress stabilizes the state with longer mean Co-O bond length. The 448cm-1 band was found to be stress sensitive, therefore it was used for mapping of the residual stresses induced in the material by indentation. A qualitative estimate of the sign of the residual stress distribution after the indentation in LaCoO3 perovskite is presented. © 2005 The American Physical Society.