Molecular vibrations of the layered-perovskite cobalt oxides characterized by infrared and Raman spectroscopies coupled with crystal structure refinement

Molecular vibrations of the polycrystalline Nd2−xSrxCoO4 are systematically characterized by powdered x-ray diffraction, Raman scattering and infrared spectra at different dopings as well as at different temperatures. Structural refinements reveal that all the specimens crystallize in the K2NiF4 structure with space group I4/mmmI4/mmm as is also confirmed by the phonon bands of Raman scattering and infrared transmittance. The frequency shifts of the phonon bands are found to be very well consistent with the elongation and/or contraction of the bond lengths. Moreover, for Nd0.75Sr1.25CoO4, the phonon bands of the Raman active modes seem to retrace the evolutions of magnetic and structural temperature.