Raman spectra of vanadates MV2O6 (M=

Abstract

We report the first Raman spectra for the vanadates with chemical formula M V 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 M V 2 O 6 , was obtained by synthesis at high temperature and pressure from precursor powder samples in either P 1 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 Xray 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 M Nb 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 wavenumberω 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.

PbV2O6 under compression: near zero-linear compressibility and pressure-induced change in vanadium coordination

“…These modes involve significant stretching movements of the V-O bonds. 4,16,36 Therefore, it is not surprising that they will be affected by changes the coordination polyhedron of V that we determined based on XRD experiments and DFT calculations. This observation is discussed in detail in section III.B.…”

“…The family of metavanadate compounds (MV 2 O 6 , where M is a divalent atom) exhibits a rich polymorphism, even for each individual M element. 1 The structures that have been most extensively studied are the brannerite-type (space group C2/ m), [1][2][3] the columbite-type (space group Pbcn) 4,5 and the NiV 2 O 6 -type (space group P1 ˉ). 2,6 It is worth noting that for larger cations, such as Sr, Ba, Hg, or Pb, the metavanadates have orthorhombic structures that differ from those above mentioned.…”