Raman spectra of vanadates MV2O6 (M= Mn, Co, Ni, Zn) crystallized in the non-usual columbite-type structure
Résumé
We report the first Raman spectra for the vanadates with chemical formula MV 2 O 6 (M = Mn, Co, Ni, Zn) crystallized in a columbite-type structure (Pbcn space group). The columbite-type structure, which is quite unusual for the compounds MV 2 O 6 , was obtained by synthesis at high temperature and pressure from precursor powder samples in either P1 or C2/m structures. The cell parameters, interatomic distances, and distortion indexes of the octahedra in the Pbcn structure, were obtained from the Rietveld refinement of powder X-ray diffraction patterns measured at room temperature for each sample. The Raman modes were obtained from high quality spectra recorded in the range of wavenumbers between 50 and 1170 cm − 1 ; these were assigned by comparison with the known spectra of the isostructural niobates MNb 2 O 6. Common sequences of peaks can be identified in the Raman spectra of all the studied samples, but the position of those peaks in wavenumber ω does not follow the behavior that is expected from looking only at the interatomic distances between the atoms involved in the vibration. The influence of the electronegativity of the atoms M in the force constants of the V-O bonds is proven in the evolution of the A g Raman mode observed at the highest wavenumber.
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