Signature of Jahn–Teller distortion and oxygen stoichiometry in Raman spectra of epitaxial LaMnO3+δ thin films

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Epitaxial thin films of LaMnO3 were grown by pulsed laser deposition in identical deposition conditions but in situ annealed in different oxygen environments. All the films showed an insulator to metal transition. It also showed a magnetic order that correlates well with an insulator to metal behavior. The transition temperature critically depends on annealing oxygen pressure and increases with increasing oxygen content. It is observed that instead of strain, oxygen content plays a major role in deciding the transport properties. X-ray diffraction and Raman spectroscopy measurements revealed that the increasing oxygen content results in a decrease in unit cell volume along with a reduction in Jahn–Teller distortion. It is shown that the intensities of the two Jahn–Teller activated modes in Raman spectra are highly sensitive to the oxygen stoichiometry of the films and that the intensity ratio can be effectively used to characterize oxygen content in these films.