Raman diagnostics of LACOO3 based perovskites

Micro-Raman spectroscopy of the LaCoO3 based perovskites was performed to characterize vibrational properties of these rhombohedral perovskites. The cobaltites have been found to be Raman active materials and, therefore, Raman spectroscopy was used to characterize temperature and stress induced changes. It was found that the cobaltite spectra are characterized by three E-g and one A(1g) phonon modes. The semiconductor/metal transition along with a decrease in rhombohedral distortion of the LaCoO3 was discovered. The transition could be driven by laser overheating during a collection of the Raman signal. Significant stress-induced changes in the Raman spectrum of LaCoO3 after indentation were also observed. An increase of the intensities of two 557 and 670 cm(-1) bands could be possibly explained by the reversible semiconductor-metal-semiconductor transition upon loading and further unloading of the perovskite during indentation.